The effect of DLC-coating deposition method on the reliability and mechanical properties of abutment’s screws Dent. Mater. (IF 4.07) Pub Date : 2018-04-10 Dimorvan Bordin, Paulo G. Coelho, Edmara T.P. Bergamo, Estevam A. Bonfante, Lukasz Witek, Altair A. Del Bel Cury
Objective To characterize the mechanical properties of different coating methods of DLC (diamond-like carbon) onto dental implant abutment screws, and their effect on the probability of survival (reliability). Methods Seventy-five abutment screws were allocated into three groups according to the coating method: control (no coating); UMS – DLC applied through unbalanced magnetron sputtering; RFPA-DLC applied through radio frequency plasma-activated (n = 25/group). Twelve screws (n = 4) were used to determine the hardness and Young’s modulus (YM). A 3D finite element model composed of titanium substrate, DLC-layer and a counterpart were constructed. The deformation (μm) and shear stress (MPa) were calculated. The remaining screws of each group were torqued into external hexagon abutments and subjected to step-stress accelerated life-testing (SSALT) (n = 21/group). The probability Weibull curves and reliability (probability survival) were calculated considering the mission of 100, 150 and 200 N at 50,000 and 100,000 cycles. Results DLC-coated experimental groups evidenced higher hardness than control (p < 0.05). In silico analysis depicted that the higher the surface Young’s modulus, the higher the shear stress. Control and RFPA showed β < 1, indicating that failures were attributed to materials strength; UMS showed β > 1 indicating that fatigue contributed to failure. High reliability was depicted at a mission of 100 N. At 200 N a significant decrease in reliability was detected for all groups (ranging from 39% to 66%). No significant difference was observed among groups regardless of mission. Screw fracture was the chief failure mode. Significance DLC-coating have been used to improve titanium’s mechanical properties and increase the reliability of dental implant-supported restorations.
Numerical fatigue analysis of premolars restored by CAD/CAM ceramic crowns Dent. Mater. (IF 4.07) Pub Date : 2018-04-10 Ehsan Homaei, Xiao-Zhuang Jin, Edmond Ho Nang Pow, Jukka Pekka Matinlinna, James Kit-Hon Tsoi, Khalil Farhangdoost
Objectives The purpose of this study was to estimate the fatigue life of premolars restored with two dental ceramics, lithium disilicate (LD) and polymer infiltrated ceramic (PIC) using the numerical method and compare it with the published in vitro data. Methods A premolar restored with full-coverage crown was digitized. The volumetric shape of tooth tissues and crowns were created in Mimics®. They were transferred to IA-FEMesh for mesh generation and the model was analyzed with Abaqus. By combining the stress distribution results with fatigue stress–life (S–N) approach, the lifetime of restored premolars was predicted. Results The predicted lifetime was 1,231,318 cycles for LD with fatigue load of 1400 N, while the one for PIC was 475,063 cycles with the load of 870 N. The peak value of maximum principal stress occurred at the contact area (LD: 172 MPa and PIC: 96 MPa) and central fossa (LD: 100 MPa and PIC: 64 MPa) for both ceramics which were the most seen failure areas in the experiment. In the adhesive layer, the maximum shear stress was observed at the shoulder area (LD: 53.6 MPa and PIC: 29 MPa). Significance The fatigue life and failure modes of all-ceramic crown determined by the numerical method seem to correlate well with the previous experimental study.
Thermo-setting glass ionomer cements promote variable biological responses of human dental pulp stem cells Dent. Mater. (IF 4.07) Pub Date : 2018-04-09 Mar Collado-González, Miguel R. Pecci-Lloret, Christopher J. Tomás-Catalá, David García-Bernal, Ricardo E. Oñate-Sánchez, Carmen Llena, Leopoldo Forner, Vinicius Rosa, Francisco J. Rodríguez-Lozano
ObjectiveTo evaluate the in vitro cytotoxicity of Equia Forte (GC, Tokyo, Japan) and Ionostar Molar (Voco, Cuxhaven, Germany) on human dental pulp stem cells (hDPSCs).MethodshDPSCs isolated from third molars were exposed to several dilutions of Equia Forte and Ionostar Molar eluates (1/1, 1/2 and 1/4). These eluates were obtained by storing material samples in respective cell culture medium for 24 h (n = 40). hDPSCs in basal growth culture medium were the control. Cell viability and cell migration assays were performed using the MTT and wound-healing assays, respectively. Also, induction of apoptosis and changes in cell phenotype were evaluated by flow cytometry. Changes in cell morphology were analysed by immunocytofluorescence staining. To evaluate cell attachment to the different materials, hDPSCs were directly seeded onto the material surfaces and analyzed by scanning electron microscopy (SEM). The chemical composition of the materials was determined by energy dispersive X-ray (EDX) and eluates were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). Statistical analysis was performed with analysis of variance (ANOVA) and Student’s t-test (α < 0.05).ResultsUndiluted Equia Forte extracts led to a similar cell proliferation rates than the control group from 72 h onwards. There were no significance differences between Equia Forte and Ionostar Molar in terms of cell apoptosis and phenotype. However, in presence of Equia extracts the migration capacity of hDPSCs was higher than in presence of Ionostar Molar (p < 0.05). Also, SEM studies showed a higher degree of cell attachment when Equia Forte extracts were used. Finally, EDX analysis pointed to different weight percentages of C, O and Ca ions in glass ionomer cements, while other elements such as La, Al, Si, W, Mo and F were also detected.SignificanceIn summary, Equia Forte promoted better biological responses in hDPSCs than Ionostar Molar.
Clinical evaluation of the bulk fill composite QuiXfil in molar class I and II cavities: 10-year results of a RCT Dent. Mater. (IF 4.07) Pub Date : 2018-04-07 Katrin Heck, Juergen Manhart, Reinhard Hickel, Christian Diegritz
ObjectiveThe objective of this RCT was to compare the 10-year clinical performance of QuiXfil with that of Tetric Ceram in posterior single- or multi-surface cavities.Methods46 QuiXfil (Xeno III) and 50 Tetric Ceram (Syntac classic) composite restorations were placed in 14 stress bearing class I and 82 class II cavities in first or second molars. Clinical evaluation was performed at baseline and after up to 10 years by using modified US Public Health Service criteria. At the last recall period, 26 QuiXfil and 30 Tetric Ceram restorations in 11 stress bearing class I and 45 class II cavities, were assessed.ResultsTen failed restorations were observed during the follow-up period, four Tetric Ceram restorations failed due to secondary caries (2), tooth fracture (1) and bulk fracture combined with secondary caries (1) whereas six QuiXfil restorations failed due to secondary caries (1), tooth fracture (2), secondary caries combined with restoration fracture (1), restoration fracture (1) and postoperative sensitivity (1). Fisher’s exact test yielded no significant difference between both materials (p = 0.487).SignificanceBoth materials, bulk fill QuiXfil restorations and Tetric Ceram restorations, showed highly clinical effectiveness during the 10-year follow-up.
In-vitro and in-vivo design and validation of an injectable polysaccharide-hydroxyapatite composite material for sinus floor augmentation Dent. Mater. (IF 4.07) Pub Date : 2018-04-07 J.C. Fricain, R. Aid, S. Lanouar, D.B. Maurel, D. Le Nihouannen, S. Delmond, D. Letourneur, J. Amedee Vilamitjana, S. Catros
ObjectivePolysaccharide-based composite matrices consisting of natural polysaccharides, pullulan and dextran supplemented with hydroxyapatite (Matrix-HA) have recently been developed. The principal objective of this study was to evaluate the capacities of this composite material to promote new bone formation in a sinus lift model in the sheep. Secondary objectives were to evaluate in vitro properties of the material regarding cell adhesion and proliferation.MethodsIn this report, once such composite matrix was prepared as injectable beads after dispersion in a physiological buffer, and evaluated using a large animal model (sheep) for a sinus lift procedure.ResultsIn vitro studies revealed that these microbeads (250–550 μm in diameter) allow vascular cell adhesion and proliferation of Endothelial Cells (EC) after 1 and 7 days of culture. In vivo studies were performed in 12 adult sheep, and newly formed tissue was analyzed by Cone Beam Computed Tomography (CBCT scanning electron microscopy (SEM) and by histology 3 and 6 months post-implantation. CBCT analyses at the implantation time revealed the radiolucent properties of these matrices. Quantitative analysis showed an increase of a dense mineralized tissue in the Matrix-HA group up to 3 months of implantation. The mineralized volume over total volume after 6 months reached comparable values to those obtained for Bio-Oss® used as positive control. Histological examination confirmed that the Matrix-HA did not induce any long term inflammatory events, and promoted direct contact between the osteoid tissue and lamellar bone structures and beads. After 6 months, we observed a dense network of osteocytes surrounding both biomaterials as well as a newly vascularized formed tissue in close contact to the biomaterials.SignificanceIn conclusion, the absence of animal components in Matrix-HA, the osteoconductive property of Matrix-HA in sheep, resulting in a dense bone and vascularized tissue, and the initial radiolucent property to follow graft integration offer great promises of this composite material for clinical use.
Wear measurement of dental tissues and materials in clinical studies: A systematic review Dent. Mater. (IF 4.07) Pub Date : 2018-04-04 C. Wulfman, V. Koenig, A.K. Mainjot
Objectives This study aims to systematically review the different methods used for wear measurement of dental tissues and materials in clinical studies, their relevance and reliability in terms of accuracy and precision, and the performance of the different steps of the workflow taken independently. Methods An exhaustive search of clinical studies related to wear of dental tissues and materials reporting a quantitative measurement method was conducted. MedLine, Embase, Scopus, Cochrane Library and Web of Science databases were used. Prospective studies, pilot studies and case series (>10 patients), as long as they contained a description of wear measurement methodology. Only studies published after 1995 were considered. Results After duplicates’ removal, 495 studies were identified, and 41 remained for quantitative analysis. Thirty-four described wear-measurement protocols, using digital profilometry and superimposition, whereas 7 used alternative protocols. A specific form was designed to analyze the risk of bias. The methods were described in terms of material analyzed; study design; device used for surface acquisition; matching software details and settings; type of analysis (vertical height-loss measurement vs volume loss measurement); type of area investigated (entire occlusal area or selective areas); and results. Sinificance There is a need of standardization of clinical wear measurement. Current methods exhibit accuracy, which is not sufficient to monitor wear of restorative materials and tooth tissues. Their performance could be improved, notably limiting the use of replicas, using standardized calibration procedures and positive controls, optimizing the settings of scanners and matching softwares, and taking into account unusable data.
Influence of Class V preparation on in vivo temperature rise in anesthetized human pulp during exposure to a Polywave® LED light curing unit Dent. Mater. (IF 4.07) Pub Date : 2018-03-29 Driellen Christine Zarpellon, Patrício Runnacles, Cristiane Maucoski, Dayane Jaqueline Gross, Ulisses Coelho, Frederick Allen Rueggeberg, Cesar Augusto Galvão Arrais
Objective This in vivo study evaluated pulp temperature (PT) rise in human premolars having deep Class V preparations during exposure to a light curing unit (LCU) using selected exposure modes (EMs). Methods After local Ethics Committee approval, intact first premolars (n = 8) requiring extraction for orthodontic reasons, from 8 volunteers, received infiltrative and intraligamental anesthesia and were isolated using rubber dam. A minute pulp exposure was attained and sterile probe from a wireless, NIST-traceable, temperature acquisition system was inserted into the coronal pulp chamber to continuously monitor PT (°C). A deep buccal Class V preparation was prepared using a high speed diamond bur under air-water spray cooling. The surface was exposed to a Polywave® LED LCU (Bluephase 20i, Ivoclar Vivadent) using selected EMs, allowing 7-min span between each exposure: 10-s in low (10-s/L), 10-s (10-s/H), 30-s (30-s/H), or 60-s (60-s/H) in high mode; and 5-s-Turbo (5-s/T). Peak PT values and PT increases over physiologic baseline levels (ΔT) were subjected to 1-way, repeated measures ANOVAs, and Bonferroni’s post-hoc tests (α = 0.05). Linear regression analysis was performed to establish the relationship between applied radiant exposure and ΔT. Results All EMs produced higher peak PT than the baseline temperature (p < 0.001). Only 60-s/H mode generated an average ΔT of 5.5 °C (p < 0.001). A significant, positive relationship was noted between applied radiant exposure and ΔT (r2 = 0.8962; p < 0.001). Significance In vivo exposure of deep Class V preparation to Polywave® LED LCU increases PT to values considered safe for the pulp, for most EMs. Only the longest evaluated EM caused higher PT increase than the critical ΔT, thought to be associated with pulpal necrosis.
Aging resistance, mechanical properties and translucency of different yttria-stabilized zirconia ceramics for monolithic dental crown applications Dent. Mater. (IF 4.07) Pub Date : 2018-03-26 E. Camposilvan, R. Leone, L. Gremillard, R. Sorrentino, F. Zarone, M. Ferrari, J. Chevalier
Objectives The dental market moves towards high-translucency monolithic zirconia dental crowns, which are usually placed either with – or without – a thin glaze layer. The microstructural features and the mechanical performances of these materials are still controversial, as well as their susceptibility to aging. This paper aims at studying these aspects in the current generation of zirconia dental crowns showing different degrees of translucency. Methods Four different commercial zirconia materials were investigated, including one standard ‘full-strength’ 3Y-TZP and three grades with improved translucency. The microstructural features (phase composition and assemblage, grain size) were carefully studied, as well as mechanical properties (biaxial bending strength and indentation toughness), translucency and aging behavior (in autoclave at 134 °C). Aging was conducted on crowns with and without glaze to better represent clinical uses. Results Important differences are found in terms of microstructures among the materials in terms of cubic phase content and yttria in the tetragonal phase, leading to different optical, mechanical and aging resistance properties. We show that higher cubic phase content leads to better translucency and stability in water steam, but at the expense of strength and toughness. A compromise is always inevitable between translucency and aging resistance on one side and mechanical properties on the other side. Significance - Even so called ‘high translucent’ zirconia ceramics tested in this work should be considered as medium translucency materials. - Aging occurs in standard state-of-the-art dental zirconia and glazing does not fully avoid this issue. However, aging did not compromise strength even after prolonged duration. - Aging is null in the ‘highly translucent’ zirconia grades but at the expense of strength, which is then comparable to glass-ceramics.
Fatigue failure load of two resin-bonded zirconia-reinforced lithium silicate glass-ceramics: Effect of ceramic thickness Dent. Mater. (IF 4.07) Pub Date : 2018-03-24 Jaiane Bandoli Monteiro, Hilton Riquieri, Catina Prochnow, Luís Felipe Guilardi, Gabriel Kalil Rocha Pereira, Alexandre Luiz Souto Borges, Renata Marques de Melo, Luiz Felipe Valandro
Objectives To evaluate the effect of ceramic thickness on the fatigue failure load of two zirconia-reinforced lithium silicate (ZLS) glass-ceramics, adhesively cemented to a dentin analogue material. Methods Disc-shaped specimens were allocated into 8 groups (n = 25) considering two study factors: ZLS ceramic type (Vita Suprinity — VS; and Celtra Duo — CD), and ceramic thickness (1.0; 1.5; 2.0; and 2.5 mm). A trilayer assembly (ϕ = 10 mm; thickness = 3.5 mm) was designed to mimic a bonded monolithic restoration. The ceramic discs were etched, silanized and luted (Variolink N) into a dentin analogue material. Fatigue failure load was determined using the Staircase method (100,000 cycles at 20 Hz; initial fatigue load ∼60% of the mean monotonic load-to-failure; step size ∼5% of the initial fatigue load). A stainless-steel piston (ϕ = 40 mm) applied the load into the center of the specimens submerged in water. Fractographic analysis and Finite Element Analysis (FEA) were also performed. Results The ceramic thickness influenced the fatigue failure load for both ZLS materials: Suprinity (716 N up to 1119 N); Celtra (404 N up to 1126 N). FEA showed that decreasing ceramic thickness led to higher stress concentration on the cementing interface. Significance Different ZLS glass-ceramic thicknesses influenced the fatigue failure load of the bonded system (i.e. the thicker the glass ceramic is, the higher the fatigue failure load will be). Different microstructures of the ZLS glass-ceramics might affect the fatigue behavior. FEA showed that the thicker the glass ceramic is, the lower the stress concentration at the tensile surface will be.
Improvement of the mechanical, tribological and antibacterial properties of glass ionomer cements by fluorinated graphene Dent. Mater. (IF 4.07) Pub Date : 2018-03-19 Li Sun, Zhuanjun Yan, Youxin Duan, Junyan Zhang, Bin Liu
Objective The aim of this study was to improve the mechanical properties, wear resistance and antibacterial properties of conventional glass ionomer cements (GICs) by fluorinated graphene (FG), under the premise of not influencing their solubility and fluoride ion releasing property. Materials and methods FG with bright white color was prepared using graphene oxide by a hydrothermal reaction. Experimental modified GICs was prepared by adding FG to the traditional GICs powder with four different weight ratios (0.5 wt%, 1 wt%, 2 wt% and 4 wt%) using mechanical blending. Compressive and flexural strength of each experimental and control group materials were investigated using a universal testing machine. The Vickers microhardness of all the specimens was measured by a Vicker microhardness tester. For tribological properties of the composites, specimens of each group were investigated by high-speed reciprocating friction tester. Fluoride ion releasing was measured by fluoride ion selective electrode methods. The antibacterial effect of GICs/FG composites on selected bacteria (Staphylococci aureus and Streptococcus mutans) was tested with pellicle sticking method. Results The prepared GICs/FG composites with white color were successfully fabricated. Increase of Vickers microhardness and compressive strength and decrease of friction coefficient of the GICs/FG composites were achieved compared to unreinforced materials. The colony count against S. aureus and S. mutans decreased with the increase of the content of FG. And the antibacterial rate of S. mutans can be up to 85.27% when the FG content was 4 wt%. Additionally, fluoride ion releasing property and solubility did not show significant differences between unreinforced and FG reinforced GICs. Significance Adding FG to traditional GICs could not only improve mechanical and tribological properties of the composites, but also improve their antibacterial properties. In addition, the GICs/FG composites had no negative effect on the color, solubility and fluoride ion releasing properties, which will open up new roads for the application of dental materials.
Cellular differentiation, bioactive and mechanical properties of experimental light-curing pulp protection materials Dent. Mater. (IF 4.07) Pub Date : 2018-03-16 Salvatore Sauro, Ashvin Babbar, Borzo Gharibi, Victor Pinheiro Feitosa, Ricardo Marins Carvalho, Lidiany Karla Azevedo Rodrigues, Avijit Banerjee, Timothy Watson
Shining a light on high volume photocurable materials Dent. Mater. (IF 4.07) Pub Date : 2018-03-14 William M. Palin, Julian G. Leprince, Mohammed A. Hadis
Spatial and temporal control is a key advantage for placement and rapid setting of light-activated resin composites. Conventionally, placement of multiple thin layers (<2 mm) reduces the effect of light attenuation through highly filled and pigmented materials to increase polymerisation at the base of the restoration. However, and although light curing greater than 2 mm thick layers is not an entirely new phenomenon, the desire amongst dental practitioners for even more rapid processing in deep cavities has led to the growing acceptance of so-called “bulk fill” (4–6 mm thick) resin composites that are irradiated for 10–20 s in daily clinical practice. The change in light transmission and attenuation during photopolymerisation are complex and related to path length, absorption properties of the photoinitiator and pigment, optical properties of the resin and filler and filler morphology. Understanding how light is transmitted through depth is therefore critical for ensuring optimal material properties at the base of thick increments. This article will briefly highlight the advent of current commercial materials that rationalise bulk filling techniques in dentistry, the relationship between light transmission and polymerisation and how optimal curing depths might be achieved.
Secondary caries formation with a two-species biofilm artificial mouth Dent. Mater. (IF 4.07) Pub Date : 2018-03-12 Stefanie Amend, Roland Frankenberger, Susanne Lücker, Eugen Domann, Norbert Krämer
Objectives The present study aimed to establish Lactobacillus casei in a completely automated Streptococcus mutans-based artificial mouth model and to investigate secondary caries inhibiting properties of glass ionomer cements / resin composite groups in vitro. Methods Sixty extracted, caries-free human third molars were used for preparation of standardized class-V-cavities. Specimens were restored with a resin-modified (Photac Fil; PF) as well as a conventional glass ionomer cement (Ketac Molar; KM) and one resin composite bonded with and without conduction of etch-and-rinse technique (Prime&Bond NT, Ceram X mono; C+ERT, C). Following an incubation in distilled water for 28 d at 37 °C, specimens were exposed to 10,000 thermocycles (+5 °C/+55 °C). A completely automated S. mutans-based (DSM No.: 20523) artificial mouth model was extended by establishment of L. casei (DSM No.: 20021). During microbiological loading, demineralization (4 h/d) was caused by acid production resulting from bacterial glycolysis and artificial saliva was used for remineralization (20 h/d). For quantitative margin analysis under am SEM, epoxy replicas were produced from impressions taken after thermocycling and after microbiological loading. Specimens were cut in half perpendicularly to restoration surfaces and demineralization depths at restoration margins and in 500 μm distance from margins were evaluated by means of a fluorescence microscope (FITC filter). Results After microbiological loading, overall demineralization depths in enamel at restoration margin (EM) and in 500 μm distance (ED) as well as in cementum/dentin at restoration margin (DM) and in 500 μm distance (DD) were measured as follows (μm ± SD): PF: EM 42 ± 15, ED 60 ± 17, DM 83 ± 18; DD 127 ± 16; KM: EM 46 ± 22, ED 62 ± 17, DM 104 ± 21, DD 143 ± 28; C+ERT: EM 67 ± 19, ED 61 ± 17, DM 165 ± 31, DD 176 ± 35; C: EM 65 ± 23, ED 64 ± 17, DM 161 ± 27, DD 166 ± 33. For the glass ionomer cements, the overall demineralization depths at restoration margins were significantly lower than in 500 μm distance from margins (T-test, p < 0.05). Especially at restoration margins in cementum/dentin, the resin composite groups showed significantly larger overall demineralizations than the glass ionomer cements (ANOVA, mod. LSD, p < 0.05). Decreases of marginal quality were detected in all groups after microbiological loading (Friedman-test, p < 0.05). Significance The refined experimental setup was suitable for production of artificial secondary caries-like lesions. Glass ionomer cements as fluoride-releasing materials may show an inhibition of secondary caries formation to a certain extent.
Freshly-mixed and setting calcium-silicate cements stimulate human dental pulp cells Dent. Mater. (IF 4.07) Pub Date : 2018-03-07 Mariano S. Pedano, Xin Li, Shuchen Li, Zeyi Sun, Stevan M. Cokic, Eveline Putzeys, Kumiko Yoshihara, Yashuhiro Yoshida, Zhi Chen, Kirsten Van Landuyt, Bart Van Meerbeek
Acidic pH weakens the bonding effectiveness of silane contained in universal adhesives Dent. Mater. (IF 4.07) Pub Date : 2018-03-07 Chenmin Yao, Jian Yu, Yake Wang, Chuliang Tang, Cui Huang
The effect of ultraviolet induced fluorescence on visually perceived tooth color under normal light conditions Dent. Mater. (IF 4.07) Pub Date : 2018-03-07 Sascha Hein, Jaap J. ten Bosch
Objective Restorative and prosthetic materials should provide an appearance similar to natural teeth under all light conditions, including UV-rich environments and daylight. Various studies claim that UV-induced fluorescence makes teeth whiter and brighter in daylight. The aim of this paper is to determine experimentally the significance of tooth fluorescence in natural sunlight on perceived tooth color. Methods A total of 35 extracted, hydrated teeth without restorations or endodontic treatments were evaluated in an experimental setup. A UV/VIS spectrometer using a reflectance/backscattering probe was used to collect the reflected spectrum. Unfiltered and filtered sunlight was used for irradiation of the samples so as to use the combined ultraviolet and visible spectrum (UV/VIS) and the visible spectrum (VIS) exclusively. Color coordinates for each group were measured using the CIE L*a*b* 1976 system, averaged, and compared. Results The average color difference between both groups (UV/VIS and UV) was ΔE* 0.527. The average tooth color for the VIS group was L*VIS 72.21, a*VIS −2.42, and b*VIS 22.35, and for the UV/VIS group was L*UV/VIS 72.00, a*UV/VIS −2.47, and b*UV/VIS 22.44. Significance UV induced fluorescence from sunlight does not make teeth whiter and brighter.
Effect of dental monomers and initiators on Streptococcus mutans oral biofilms Dent. Mater. (IF 4.07) Pub Date : 2018-03-06 Nancy J. Lin, Courtney Keeler, Alison M. Kraigsley, Jing Ye, Sheng Lin-Gibson
Controlled release of chlorhexidine from a HEMA-UDMA resin using a magnetic field Dent. Mater. (IF 4.07) Pub Date : 2018-02-26 Dong Luo, Saroash Shahid, Samiul Md. Hasan, Robert Whiley, Gleb B. Sukhorukov, Michael J. Cattell
Objectives To functionalize novel chlorhexidine (CHX) particles with iron oxide (Fe3O4) nanoparticles and control their release kinetics in a dental resin using an external magnetic field. Methods Fe3O4 nanoparticles were synthesized and incorporated into spherical CHX particles and the powder was freeze dried. Resin disc specimens were produced using a UDMA-HEMA resin mixed with freeze dried spherical Fe3O4-CHX particles (5 wt.%), which were placed into a Teflon mould (10 mm diameter × 1 mm depth) and covered with a Mylar strip. A MACS magnet was left in contact for 0 min (Group 1), 5 min (Group 2) or 10 min (Group 3) and the resin discs subsequently light cured (Bluedent LED pen, Bulgaria) for 60 s per side. The resin discs were immersed in deionized water at various time points up to 650 h. UV–Vis absorbance was used to determine the CHX content. CHX released for each time point was determined. The functionalized CHX particles and resin discs were characterized using TEM, TGA, EDX and SEM. Results Fe3O4 nanoparticles (20 nm) incorporated into the spherical CHX particles led to a mean (SD) particle size reduction from 17.15 (1.99) μm to 10.39 (2.61) μm. The presence of Fe3O4 nanoparticles in the spherical CHX particles was confirmed with SEM, EDX, and TGA. SEM of Group 1 resin discs (no magnetic exposure) showed functionalized CHX spheres were homogeneously distributed within the resin discs. For resin discs which had magnetic exposure (5 or 10 min) the particles started to cluster nearer the surface (Group 2: 43.7%, Group 3: 57.3%), to a depth of 94 μm. UV–Vis absorbance revealed Group 1 resin discs had a cumulative CHX release of 4.4% compared to 5.9% for Group 2 and 7.4% for Group 3 resin discs, which had magnetic exposure (5, 10 min). Significance Fe3O4 nanoparticle functionalized CHX spheres demonstrated a magnetic field responsive property. A magnetic field responsive release of CHX may be useful in clinical situations where the drug can be directed to give a tailored release at the site of infection.
Saturation reduces in-vitro leakage of monomers from composites Dent. Mater. (IF 4.07) Pub Date : 2018-02-14 Stevan M. Cokic, Radu C. Duca, Jan De Munck, Peter Hoet, Bart Van Meerbeek, Mario Smet, Lode Godderis, Kirsten L. Van Landuyt
Objective Accurate knowledge of the quantity of released monomers from composites is important. To evaluate the elution of monomers, polymerized composites are typically immersed in an extraction solvent. The objective was to determine whether the volume of extraction solvent and the immersion time influences monomer leachability from dental composite materials. Methods Composite disks of two commercial composites, (Filtek Supreme XTE, 3M ESPE and G-aenial Universal Flo, GC) were prepared. The disks (n = 10) were placed in a glass vial with 1 ml, 2 ml or 3 ml of extraction solvent (100% ethanol with deuterated diethylphalate as internal standard). After either 7 or 30 days at 37 °C, the supernatant was collected and the amount of released monomers (BisEMA, BisGMA, UDMA, TEGDMA) and bisphenol A was measured with liquid chromatography mass spectroscopy. Results For both tested composites, the highest amount of released monomers was measured after sample incubation in 3 ml, while the lowest amount was measured in 1 ml of extraction solvent. Furthermore, 30 days did not result in much more monomer release compared to 7 days, and for most monomers, there was no statistically significant difference in release between 7 and 30 days. Significance Release kinetics in in-vitro experiments are also influenced by saturation of the extraction solvent with the leached monomers. This is important as it is unlikely that saturation can be reached in an in-vivo situation, where saliva (or pulpal fluid) is continuously refreshed. Saturation of the extraction solvent can be avoided in-vitro by refreshing the extraction medium after equal time intervals.
None Dent. Mater. (IF 4.07) Pub Date : 2018-02-03
Objective To estimate the fatigue resistance of a new translucent zirconia material in comparison to lithium disilicate for 3-unit fixed partial dentures (FPDs). Methods Eighteen 3-unit FPDs (replacement of first upper molar) with a connector size of 4 mm × 4 mm were dry milled with a five-axis milling machine (Zenotec Select, Wieland, Germany) using discs made of a new translucent zirconia material (IPS e.max ZirCAD MT, Ivoclar Vivadent). Another 9 FPDs with a reduced connector size (3 mm × 4 mm) were milled. The zirconia FPDs were sintered at 1500 °C. For a comparison, 9 FPDs were made of IPS e.max Press, using the same dimensions. These IPS e.max Press FPDs were ground from a wax disc (Wieland), invested and pressed at 920 °C. All FPDs were glazed twice. The FPDs were adhesively luted to PMMA dies with Multilink Automix. Dynamic cyclic loading was carried out on the molar pontic using Dyna-Mess testing machines (Stolberg, Germany) with 2 × 106 cycles at 2 Hz in water (37 °C). Two specimens per group and load were subjected to decreasing load levels (at least 4) until the two specimens no longer showed any failures. Another third specimen was subjected to this load to confirm the result. All the specimens were evaluated under a stereo microscope (20× magnification). The number of cycles reached before observing a failure, and their dependence on the load and on the material, were modeled, using a Weibull model. This made it possible to estimate the fatigue resistance as the maximum load for which one would observe less than 1% failure after 2 × 106 cycles. In addition to the experimental study, Finite Element Modeling (FEM) simulations were conducted to predict the force to failure for IPS e.max ZirCAD MT and IPS e.max Press with a reduced cross-section of the connectors. Results The failure mode of the zirconia FPDs was mostly the fracture of the distal connector, whereas the failure mode of the lithium disilicate FPDs observed to be the fracture of the connectors or multiple cracks of the pontic. The fatigue resistance with 1% fracture probability was estimated to be 488 N for the IPS e.max ZirCAD MT FPDs (453 N for repeated test), 365 N for IPS e.max ZirCAD MT FPDs with reduced connector size and 286 N for the e.max Press FPDs. All three IPS e.max ZirCAD groups statistically performed significantly better than IPS e.max Press (p < 0.001). On the other hand, no significant difference could be established between the two IPS e.max ZirCAD MT3 groups with a 4 mm × 4 mm connector size (p > 0.05). The allowable maximum principal stress (σmax) which did not lead to failure during fatigue testing for IPS e.max ZirCAD MT3 was calculated between 208 MPa and 223 MPa for FPDs with 4 mm × 4 mm connectors for 2 × 106 cycles. This value could also be verified for the FPDs of the same material with 3 mm × 4 mm connectors. On the other hand fatigue strength in terms of σmax at 2 × 106 cycles of IPS e.max Press was calculated to be between 78 and 90 MPa. Significance The fatigue resistance of the translucent zirconia 3-unit FPDs was about 60–70% higher than that of the lithium disilicate 3-unit FPDs, which may justify their use for molar replacements, provided that a minimal connector size of 4 mm × 4 mm is observed. Even with a limited number of specimens (n = 9) per group it was possible to statistically differentiate between the tested groups.
Effect of matrix metalloproteinase 8 inhibitor on resin–dentin bonds Dent. Mater. (IF 4.07) Pub Date : 2018-02-12 Qianmin Ou, Ya Hu, Siqi Yao, Yan Wang, Xuefeng Lin
Objectives This study investigated the effect of matrix metalloproteinase 8 (MMP-8) on resin–dentin bonds, assessed the mechanical properties of the interfaces over time, and discussed the potential application of MMP-8 inhibitor I (MMP8-I) as a specific MMP-8 inhibitor to be incorporated into dental adhesives. Methods The activation and inhibition of MMP-8 was detected by colorimetric assay. After 1 day, 6 months and 1 year of storage of Control, MMP8-I, and chlorhexidine (CHX) groups, the microtensile bond strengths (μTBS) were used to evaluate the bond strength and failure mode distributions, and nanoleakage analysis was used to evaluate the minor scattered silver particles. Results Colorimetric assay showed that the activated MMP-8 was enhanced by adhesive procedures, while it was inhibited by the additional treatment of MMP8-I or CHX. Compared with the Control and CHX groups, the MMP8-I group had significantly higher bond strength and the hybrid layer from the MMP8-I-treated dentin exhibited structural integrity of the collagen network and decreased silver nitrate penetration after 1 year of storage. Significance MMP-8 inhibition I protects against the degradation of resin–dentin bonds over time, which is better than broad-scale enzyme inhibitor CHX. It shows that MMP8-I may be used in dentistry for preventing collagen degradation within hybrid layers to extend the longevity of resin–dentin bonds.
Profiling cytokine levels in chlorhexidine and EGCG-treated odontoblast-like cells Dent. Mater. (IF 4.07) Pub Date : 2018-02-07 Alexander Terry Stavroullakis, Marcela Rocha Carrilho, Celine Marie Levesque, Anuradha Prakki
Objective To screen the effect of two compounds, chlorhexidine diacetate (CHX) and epigallocatechin-gallate (EGCG), on the levels of cytokines produced by odontoblast-like cells (MDPC-23). Methods Cells were seeded at 24 h and 48 h with serial dilution of the compounds to determine cell metabolic activity by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay (n = 3). Cells with no compound treatment were used as control (Ctr). For the highest equal non-cytotoxic compound dilution tested at 48 h cell treatment, total protein concentration was measured using a Pierce bicinchoninic acid (BCA) assay (n = 3), and expression of 23 cytokines was analyzed using the Bio-Plex cytokine assay (n = 2). Data were analyzed by one-way ANOVA and Tukey’s test (α = 5%). Results The MTT assay revealed that at 24 h and 48 h, CHX and EGCG did not reduce cell metabolic activity at concentrations of 2.5–20 μM (CHX) and 2.5–160 μM (EGCG), respectively (p > 0.05). At 48 h, total protein levels were consistent across all groups for 20 μM compound dilution (Ctr: 1.04 mg/mL; CHX: 0.98 mg/mL; and EGCG: 1.06 mg/mL). At 20 μM dilution, both CHX and EGCG significantly increased the secretion of IL-1β, IL-10, IL-12, KC, MIP-1α, IFN-γ and IL-6 (p < 0.05). Treatment with CHX significantly increased secretion of IL-4 and RANTES (p < 0.05). Treatment: with EGCG significantly increased Eotaxin secretion (p < 0.05). Both CHX and EGCG significantly decreased secretion of IL-17 (p < 0.05). GM-CSF and TNF-α did not present significant change in secretion after treatment with either CHX or EGCG (p > 0.05). Significance Both CHX and EGCG modulate secretion of various inflammatory and anti-inflammatory mediators in odontoblastic cells.
Early responses of human pulp to direct capping with resin adhesive systems and calcium hydroxide Dent. Mater. (IF 4.07) Pub Date : 2018-02-03 Anna Poimenova, Efthymia Kitraki, Afroditi Kakaboura, Christos Rahiotis
Objective Early responses of human pulp to Prime&Bond/phosphoric acid, Clearfil SE Bond, Clearfil S3 Bond and Dycal were investigated ex vivo. Materials and methods The three adhesives, Dycal or buffer (DPBS) were applied directly onto the pulp of human teeth slices that were placed in culture for 4 days. Cell viability was monitored by the MTT assay during the culture period. After 4 days, tissue integrity was examined by hematoxylin–eosin staining. Vimentin levels were assessed by Western blotting. TUNEL assay was applied for apoptotic cell detection at specific pulp areas. Results Profound reduction of cell viability and tissue integrity was observed in adhesive-treated groups, while the impact of Dycal was found to be less harmful. Extended apoptosis was caused mostly by the Clearfil SE and Prime&Bond. All adhesives reduced Vimentin levels. Significance The study provides evidence that early pulp responses to direct capping with different adhesive systems or calcium hydroxide may vary significantly and underline the need for further studies in relevant ex vivo systems.
Optical properties of composite restorations influenced by dissimilar dentin restoratives Dent. Mater. (IF 4.07) Pub Date : 2018-02-03 Jovana Marjanovic, Djordje N. Veljovic, Jovana N. Stasic, Tatjana Savic-Stankovic, Branka Trifkovic, Vesna Miletic
Objectives To evaluate optical properties (color and translucency) of ‘sandwich’ restorations of resin-based composites and esthetically unfavorable dentin restoratives. Methods Cylindrical ‘dentin’ specimens (8 mm in diameter and 2 mm thick, N = 5/group) were prepared using EverX Posterior (GC), Biodentine (Septodont), experimental hydroxyapatite (HAP) or conventional composites (Gradia Direct Posterior, GC; Filtek Z250 and Filtek Z500, 3M ESPE). Capping ‘enamel’ layers were prepared using composites (Gradia Direct Posterior, Filtek Z250 or Z550) of A1 or A3 shade and the following thickness: 0.6, 1 or 2 mm. Color (ΔE) and translucency parameter (TP) were determined using a spectrophotometer (VITA Easyshade Advance 4.0, VITA Zahnfabrik). Data were statistically analyzed using analysis of variance with Tukey’s post-hoc tests (α = 0.05). Results TP was greatly affected by layer thickness, whilst ΔE depended on shade and layer thickness of the capping composite. HAP and Biodentine showed significantly lower TP and higher ΔE (deviation from ‘ideal white’) than composites (p < 0.05). Greater TP was seen in EverX_composite groups than in corresponding control groups of the same shade and thickness. TP of composites combined with Biodentine or HAP was below 2, lower than the corresponding control groups (p < 0.05). Within-group differences of ΔE were greatest in HAP_composite groups. EverX_Gradia and EverX_FiltekZ250 combinations showed the most comparable ΔE with the control groups. Significance A 2 mm thick layer of composite covering dentin restoratives with unfavorable esthetics is recommended for a final ‘sandwich’ restoration that is esthetically comparable to a conventional, mono-composite control restoration.
Long-term dentin remineralization by poly(amido amine) and rechargeable calcium phosphate nanocomposite after fluid challenges Dent. Mater. (IF 4.07) Pub Date : 2018-02-03 Kunneng Liang, Shimeng Xiao, Junling Wu, Jiyao Li, Michael D. Weir, Lei Cheng, Mark A. Reynolds, Xuedong Zhou, Hockin H.K. Xu
Objective Previous studies investigated short-term dentin remineralization; studies on long-term dentin remineralization after fluid challenges mimicking fluids in oral environment are lacking. The objective of this study was to develop a long-term remineralization method to via poly(amido amine) (PAMAM) and rechargeable composite containing nanoparticles of amorphous calcium phosphate (NACP) after fluid challenges for the first time. Methods NACP composite was immersed at pH 4 to exhaust its calcium (Ca) and phosphate (P) ions, and then recharged with Ca and P ions, to test the remineralization of the exhausted and recharged NACP composite. Dentin was acid-etched with 37% phosphoric acid. Four groups were prepared: (1) dentin control, (2) dentin with PAMAM, (3) dentin with the recharged NACP composite, and (4) dentin with PAMAM plus recharged NACP composite. PAMAM-coated dentin was immersed in phosphate-buffered saline with shaking for 72 days, because there is fluid flow in the mouth which could potentially detach the PAMAM from dentin. Specimens were treated with a cyclic artificial saliva/lactic acid regimen for 35 days. Results After 72 days of immersion plus shaking, the PAMAM still successfully fulfilled its mineralization nucleation. The recharged NACP composite still provided acid-neutralization and ion re-release, which did not decrease with increasing the number of recharge cycles. The immersed-PAMAM plus NACP achieved complete dentin remineralization and restored the hardness to that of healthy dentin. Signifiance In conclusion, superior long-term remineralization of the PAMAM plus NACP method was demonstrated for the first time. The immersed-PAMAM plus recharged NACP completely remineralized the pre-demineralized dentin, even after prolonged fluid-challenge similar to that in oral environment. The novel PAMAM plus NACP composite method is promising to provide long-term tooth protection and caries inhibition.
Nano-graphene oxide incorporated into PMMA resin to prevent microbial adhesion Dent. Mater. (IF 4.07) Pub Date : 2018-02-03 Jung-Hwan Lee, Jeong-Ki Jo, Dong-Ae Kim, Kapil Dev Patel, Hae-Won Kim, Hae-Hyoung Lee
The two sides of the C-factor Dent. Mater. (IF 4.07) Pub Date : 2018-02-02 Alex S.L. Fok, Wondwosen A. Aregawi
Objective The aim of this paper is to investigate the effects on shrinkage strain/stress development of the lateral constraints at the bonded surfaces of resin composite specimens used in laboratory measurement. Methods Using three-dimensional (3D) Hooke’s law, a recently developed shrinkage stress theory is extended to 3D to include the additional out-of-plane strain/stress induced by the lateral constraints at the bonded surfaces through the Poisson’s ratio effect. The model contains a parameter that defines the relative thickness of the boundary layers, adjacent to the bonded surfaces, that are under such multiaxial stresses. The resulting differential equation is solved for the shrinkage stress under different boundary conditions. The accuracy of the model is assessed by comparing the numerical solutions with a wide range of experimental data, which include those from both shrinkage strain and shrinkage stress measurements. Results There is good agreement between theory and experiments. The model correctly predicts the different instrument-dependent effects that a specimen’s configuration factor (C-factor) has on shrinkage stress. That is, for noncompliant stress-measuring instruments, shrinkage stress increases with the C-factor of the cylindrical specimen; while the opposite is true for compliant instruments. The model also provides a correction factor, which is a function of the C-factor, Poisson’s ratio and boundary layer thickness of the specimen, for shrinkage strain measured using the bonded-disc method. For the resin composite examined, the boundary layers have a combined thickness that is ∼11.5% of the specimen’s diameter. Significance The theory provides a physical and mechanical basis for the C-factor using principles of engineering mechanics. The correction factor it provides allows the linear shrinkage strain of a resin composite to be obtained more accurately from the bonded-disc method.
8DSS peptide induced effective dentinal tubule occlusion in vitro Dent. Mater. (IF 4.07) Pub Date : 2018-02-01 Kunneng Liang, Shimeng Xiao, Hongling Liu, Wenyuan Shi, Jianshu Li, Yuan Gao, Libang He, Xuedong Zhou, Jiyao Li
Objective Eight repetitive nucleotide sequences of aspartate–serine–serine (8DSS) derived from dentin phosphoprotein (DPP) has been proved to be a good remineralization agency. In this study, 8DSS peptide was employed to induce dentinal tubule occlusion. Methods Dentin samples were acid-etched, and then the samples were coated with 8DSS solution. The binding capacity of 8DSS to acid-etched dentin was tested by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Subsequently, the 8DSS-treated dentin samples were immersed in artificial saliva for 1, 2 and 4 weeks. After 4 weeks, the remineralized dentin was treated with 6 wt% citric acid (pH 1.5) solution for 1 min. Dentin permeability measurement and scanning electron microscopy (SEM) were carried out after different periods. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were used to identify the mineral phase of the regenerated minerals. Results The results showed that 8DSS had a good binding capacity to the acid-etched dentin, and significantly reduced the dentin permeability by inducing minerals deposited within the dentinal tubules. After 4 weeks, all the dentinal tubules were occluded by large bulk of regenerated minerals, which largely decreased the diameters of the tubules. The regenerated minerals deposited with a deep depth within the dentinal tubules, ensuring an effective occlusion even after an acid challenge. The results of XRD and EDS confirmed that the regenerated minerals were mainly hydroxyapatite (HA). Significance 8DSS peptide induced strong dentinal tubule occlusion. 8DSS have a great potential to be used in the treatment of dentin hypersensitivity in the future.
Zirconia toughened mica glass ceramics for dental restorations Dent. Mater. (IF 4.07) Pub Date : 2018-02-01 Sivaranjani Gali, Ravikumar K., B.V.S. Murthy, Bikramjit Basu
Objective The objective of the present study is to understand the role of yttria stabilized zirconia (YSZ) in achieving the desired spectrum of clinically relevant mechanical properties (hardness, elastic modulus, fracture toughness and brittleness index) and chemical solubility of mica glass ceramics. Methods The glass–zirconia mixtures with varying amounts of YSZ (0, 5, 10, 15 and 20 wt.%) were ball milled, compacted and sintered to obtain pellets of glass ceramic-YSZ composites. Phase analysis was carried out using X-ray diffraction and microstructural characterization with SEM revealed the crystal morphology of the composites. Mechanical properties such as Vickers hardness, elastic modulus, indentation fracture toughness and chemical solubility were assessed. Results Phase analysis of sintered pellets of glass ceramic-YSZ composites revealed the characteristic peaks of fluorophlogopite (FPP) and tetragonal zirconia. Microstructural investigation showed plate and lath-like interlocking mica crystals with embedded zirconia. Vickers hardness of 9.2 GPa, elastic modulus of 125 GPa, indentation toughness of 3.6 MPa·m1/2, and chemical solubility of 30 μg/cm2 (well below the permissible limit) were recorded with mica glass ceramics containing 20 wt.% YSZ. Significance An increase in hardness and toughness of the glass ceramic-YSZ composites with no compromise on their brittleness index and chemical solubility has been observed. Such spectrum of properties can be utilised for developing a machinable ceramic for low stress bearing inlays, onlays and veneers.
Influence of thread shape and inclination on the biomechanical behaviour of plateau implant systems Dent. Mater. (IF 4.07) Pub Date : 2018-02-01 Michele Calì, Elisabetta Maria Zanetti, Salvatore Massimo Oliveri, Riccardo Asero, Stefano Ciaramella, Massimo Martorelli, Cristina Bignardi
Objective To assess the influence of implant thread shape and inclination on the mechanical behaviour of bone-implant systems. The study assesses which factors influence the initial and full osseointegration stages. Methods Point clouds of the original implant were created using a non-contact reverse engineering technique. A 3D tessellated surface was created using Geomagic Studio® software. From cross-section curves, generated by intersecting the tessellated model and cutting-planes, a 3D parametric CAD model was created using SolidWorks® 2017. By the permutation of three thread shapes (rectangular, 30° trapezoidal, 45° trapezoidal) and three thread inclinations (0°, 3° or 6°), nine geometric configurations were obtained. Two different osseointegration stages were analysed: the initial osseointegration and a full osseointegration. In total, 18 different FE models were analysed and two load conditions were applied to each model. The mechanical behaviour of the models was analysed by Finite Element (FE) Analysis using ANSYS® v. 17.0. Static linear analyses were also carried out. Results ANOVA was used to assess the influence of each factor. Models with a rectangular thread and 6° inclination provided the best results and reduced displacement in the initial osseointegration stages up to 4.58%. This configuration also reduced equivalent VM stress peaks up to 54%. The same effect was confirmed for the full osseointegration stage, where 6° inclination reduced stress peaks by up to 62%. Significance The FE analysis confirmed the beneficial effect of thread inclination, reducing the displacement in immediate post-operative conditions and equivalent VM stress peaks. Thread shape does not significantly influence the mechanical behaviour of bone-implant systems but contributes to reducing stress peaks in the trabecular bone in both the initial and full osseointegration stages.
Application of radiopaque micro-particle fillers for 3-D imaging of periodontal pocket analogues using cone beam CT Dent. Mater. (IF 4.07) Pub Date : 2018-02-01 M. Elashiry, M.M. Meghil, S. Kalathingal, A. Buchanan, R. Elrefai, S. Looney, M. Rajendran, M. Ochieng, N. Young, A. Elawady, R.M. Arce, K.H. Sandhage, C.W Cutler
Background Periodontitis is an infectious/inflammatory disease most often diagnosed by deepening of the gingival sulcus, which leads to periodontal pockets (PPs) conventional manual periodontal probing does not provide detailed information on the three-dimensional (3-D) nature of PPs. Objectives To determine whether accurate 3-D analyses of the depths and volumes of calibrated PP analogues (PPAs) can be obtained by conventional cone beam computed tomography (CBCT) coupled with novel radiopaque micro-particle fillers (described in the companion paper) injected into the PPAs. Methods Two PPA models were employed: (1) a human skull model with artificial gingiva applied to teeth with alveolar bone loss and calibrated PPAs, and (2) a pig jaw model with alveolar bone loss and surgically-induced PPAs The PPAs were filled with controlled amounts of radiopaque micro-particle filler using volumetric pipetting Inter-method and intra-method agreement tests were then used to compare the PPA depths and volumes obtained from CBCT images with values obtained by masked examiners using calibrated manual methods. Results Significant inter-method agreement (0.938–0.991) and intra-method agreement (0.94–0.99) were obtained when comparing analog manual data to digital CBCT measurements enabled by the radiopaque filler. Significance CBCT imaging with radiopaque micro-particle fillers is a plausible means of visualizing and digitally assessing the depths, volumes, and 3-D shapes of PPs This approach could transform the diagnosis and treatment planning of periodontal disease, with particular initial utility in complex cases Efforts to confirm the clinical practicality of these fillers are currently in progress.
Strength and fracture toughness of zirconia dental ceramics Dent. Mater. (IF 4.07) Pub Date : 2018-02-01 Miquel Turon-Vinas, Marc Anglada
Objective The aim of the paper is to determine and discuss the correlation between the fracture toughness and the fracture stress in zirconia transforming ceramics with a small artificial crack. As an R-curve behaviour is usually present in transforming ceramics for both small and long cracks, predictions of the fracture stress can only be done with an accurate knowledge of the R-curve and crack dimensions. Methods First, basic concepts of fracture mechanics, strength and testing of ceramic materials are introduced. This is followed by a very brief introduction to zirconia dental ceramics and to strength degradation by hydrothermal ageing of 3Y-TZP. Fracture toughness of 3Y-TZP and 12Ce-TZP are then determined for a short (∼50 μm) sharp edge crack produced by ultra short pulsed laser ablation on prismatic bending bars in four point bending. The crack size is small but large enough for controlling fracture and for applying elastic fracture mechanics. Results In both materials the determined fracture toughness is similar, in spite of their difference R-curves. The results of fracture toughness and fracture stress are analysed by using a simple function to represent the R-curve, but which contains the main ingredients of experimental R-curves extracted from the literature either for short or long cracks in 12Ce-TZP. Significance It is concluded that the high R-curves reported in the literature for long and short cracks in 12Ce-TZP and 3Y-TZP might have only a marginal influence on the fracture resistance with cracks of the size studied. This effect is of more significance in 12Ce-TZP. The use of an ideal and simple model of R-curve is presented as a useful guide to predict whether the fracture stress will be enhanced by an existent R-curve.
Development of a novel dental resin cement incorporating FGF-2-loaded polymer particles with the ability to promote tissue regeneration Dent. Mater. (IF 4.07) Pub Date : 2018-02-01 Ririko Tsuboi, Jun-Ichi Sasaki, Haruaki Kitagawa, Itsumi Yoshimoto, Fumio Takeshige, Satoshi Imazato
Objective Aiming to achieve bioactive dental resins that promote healing of surrounding tissues, we developed novel poly(2-hydroxyethyl methacrylate/trimethylolpropane trimethacrylate) (polyHEMA/TMPT) particles. These particles have been reported to be useful as a non-biodegradable carrier for fibroblast growth factor-2 (FGF-2) in vitro. The aim of this study was to evaluate the ability of an adhesive resin incorporating FGF-2-loaded polymer particles to promote tissue regeneration in vitro and in vivo. Methods Experimental adhesive resins were prepared by incorporating FGF-2-loaded polyHEMA/TMPT particles into a 4-META/MMA-based adhesive resin, and the release profiles of FGF-2 were evaluated. The proliferation of osteoblast-like cells in the eluate from cured experimental resin was assessed. When the experimental resin was implanted into rat calvaria defects, bone regeneration was evaluated by microcomputed tomography and histological observations. Results Sustained release of FGF-2 from the experimental resin was observed for 14 days. Eluate from the cured experimental resin significantly promoted the proliferation of osteoblast-like cells. Significantly greater bone regeneration was observed using the experimental resin compared with the control resin without FGF-2. Significance 4-META/MMA-based adhesive resin incorporating FGF-2-loaded polymer particles is useful to promote tissue regeneration, suggesting that its application would be beneficial for root-end filling or the repair of fractured roots in cases with severely damaged periodontal tissue.
Multitechnique characterization of conventional and experimental Ag-based brazing alloys for orthodontic applications Dent. Mater. (IF 4.07) Pub Date : 2018-02-01 Argyro Ntasi, Youssef S. Al Jabbari, Nick Silikas, Theodore Eliades, Spiros Zinelis
Objectives To characterize the microstructure, mechanical properties, ionic release and tarnish resistance of conventional and experimental Ag-based soldering alloys for orthodontic applications. Methods Disk shaped specimens were prepared from four commercial Ag based soldering alloys [Dentaurum Universal Silver Solder (DEN), Orthodontic Solders (LEO), Ortho Dental Universal Solder (NOB), and Silver Solder (ORT)] and four experimental alloys Ag12Ga, Ag10Ga5Sn, Ag20In and Ag7Sn. The elemental composition and microstructure was determined by SEM/EDX and XRD analysis, while the mechanical properties were determined by Instrumented Indentation Testing. Ionic release of Ag, Cu, Zn, Ga, In and Sn was determined by ICP-EAS in 0.9% NaCl and Ringer’s solutions after 28, 49 and 70 days. Tarnish resistance was also tested and colorimetry was applied to quantify the differences in color (DE) before and after immersion in testing media. DSC was used to determine the melting range of the experimental alloys. Mechanical properties, ionic release and DE were statistically compared by ANOVA and Holm-Sidak multiple comparison test (a = 0.05). Results All commercially alloys belong to the Ag–Zn–Cu ternary system and consist a Ag rich face centered cubic (FCC) and Cu (FCC) phase. The former is the predominant phase also in experimental alloys. Conventional alloys demonstrated higherhardness, less ductility and lower melting rangers compared to experimental alloys. Immersion testing revealed the release of Cu and Zn ions from the commercially alloys and Ga ions from AgGa and AgGaSn while no ionic release was identified for AgIn and AgSn. All alloys failed tarnish testing according to ISO 10271 showing DE values much higher than the clinical acceptable limit (3.7). Significance The conventional Ag based soldering alloys showed substantial differences in their microstructure, mechanical properties and ionic release, and thus different clinical performance is anticipated. Ga, Sn and In might be employed as alloying addition to modify the properties of Ag brazing alloys.
The effect of hydrofluoric acid concentration on the fatigue failure load of adhesively cemented feldspathic ceramic discs Dent. Mater. (IF 4.07) Pub Date : 2018-02-01 Andressa B. Venturini, Catina Prochnow, Gabriel K.R. Pereira, Arie Werner, Cornelis J. Kleverlaan, Luiz Felipe Valandro
Objective This study investigated the influence of hydrofluoric acid (HF) etching at different concentrations on the fatigue failure load of adhesively cemented feldspathic ceramic discs (Vita Mark II). Besides, their effect on the micromorphology of ceramic surface was investigated. Methods Eighty ceramic discs (ϕ = 10 mm; thickness = 1.5 mm) were cemented to epoxy supporting discs (ϕ = 10 mm; thickness = 2.0 mm) using different surface conditioning methods (n = 20): nonetched control (CTRL), or etched for 60 s with different HF concentrations: 1% (HF1), 5% (HF5), or 10% (HF10). All the ceramic discs received a silane application (Monobond Plus). The epoxy discs were etched with 10% HF for 60 s and received a primer coating (Multilink Primer A + B). Adhesively cementation was performed (Multilink Automix), and the assemblies (ceramic discs/epoxy discs) were subjected to cyclic loads in water by a staircase approach (500,000 cycles; 20 Hz; initial load = 290 N; step size = 30 N). Fatigue failure load data were analyzed using 1-way ANOVA and post-hoc Tukey’s tests (α = .05). Results Mean failure load of the HF5 group (255.0 ± 23.0 N) was significantly lower; HF1 group (301.7 ± 71.0 N) presented intermediate values, and the highest values were achieved in CTRL (351.7 ± 13.4 N) and HF10 (341.7 ± 20.6 N) groups. All the failures were radial cracks starting from the bonding surface. Significance In terms of fatigue failure load, etching with 1% and 5% HF had a deleterious effect on the fatigue behavior of an adhesively cemented feldspathic ceramic, while 10% HF had no negative influence.
In-vitro wear of natural tooth surface opposed with zirconia reinforced lithium silicate glass ceramic after accelerated ageing Dent. Mater. (IF 4.07) Pub Date : 2018-02-01 Salma M. Fathy, Michael V. Swain
Objective To evaluate the effect of different pH media on zirconia-reinforced lithium silicate glass ceramic and how they interact with opposing dentition after being aged in different pH cycling and high temperature conditions. Methods Twenty-five rectangular shaped specimens were prepared from lithium silicate reinforced with zirconia blanks (Suprinity, Vita Zahnfabrick) and stored in different pH media (3 & 7.2) for different periods (24 h & 7 days) at temperature (55 °C). After their surface roughness (Ra) evaluation, aged ceramic specimens were subjected to cyclic abrasive wear with opposing natural teeth enamel for 150,000 cycles using a chewing simulator. Weight loss and Scanning Electron Microscope (SEM) images were used to evaluate the cyclic wear results. Results After different pH storage, ceramic group stored at 3 pH for 1-W (1 week) gave significantly higher mean Ra value (0.618 μm ± 0.117) than control lowest mean value (0.357 μm ± 0.054) before cyclic wear. On the other hand, it caused the least significant weight loss value (0.004 gm ± 0.001) to opposing tooth enamel. There was significant tooth enamel weight loss (0.043 gm ± 0.004) when opposed with ceramic group stored in 3 pH media for 24 h (24-H). Their SEM images showed a prominent wear scar on enamel cusp tip. There was a significant increase in surface roughness Ra of ceramic material after abrasive cyclic wear. Significance Great attention should be paid to Ra of this type of glass ceramic even if it is considered as minimal values. It can induce a significant amount of enamel tooth wear after a period equivalent to one year of intra-oral function rather than the significantly higher surface Ra of such ceramic type can do.
Mechanical properties and fracture behavior of flowable fiber reinforced composite restorations Dent. Mater. (IF 4.07) Pub Date : 2018-01-20 Lippo Lassila, Filip Keulemans, Eija Säilynoja, Pekka K. Vallittu, Sufyan Garoushi
Objective The aim was to evaluate the effect of short glass-fiber/filler particles proportion on fracture toughness (FT) and flexural strength (FS) of an experimental flowable fiber-reinforced composite (Exp-SFRC) with two methacrylate resin formulations. In addition, we wanted to investigate how the fracture-behavior of composite restorations affected by FT values of SFRC-substructure. Methods Exp-SFRC was prepared by mixing 50 wt% of dimethacrylate based resin matrix (bisGMA or UDMA based) to 50 wt% of various weight fractions of glass-fiber/particulate filler (0:50, 10:40, 20:30, 30:20, 40:10, 50:0 wt%, respectively). FT and FS were determined for each experimental material following standards. Specimens (n = 8) were dry stored (37 °C for 2 days) before they were tested. Four groups of posterior composite crowns (n = 6) composed of different Exp-SFRCs as substructure and surface layer of commercial particulate filler composite were fabricated. Crowns were statically loaded until fracture. Failure modes were visually examined. The results were statistically analysed using ANOVA followed by post hoc Tukey’s test. Results ANOVA revealed that ratio of glass-fiber/particulate filler had significant effect (p < 0.05) on tested mechanical properties of the Exp-SFRC with both monomer systems. Exp-SFRC (50 wt%) had significantly higher FT (2.6 MPam1/2) and FS (175.5 MPa) (p < 0.05) compared to non-reinforced material (1.3 MPam1/2, 123 MPa). Failure mode analysis of crown restorations revealed that FT value of the substructure directly influenced the failure mode. Significance This study shows that short glass-fibers can significantly reinforce flowable composite resin and the FT value of SFRC-substructure has prior importance, as it influences the crack arresting mechanism.
Optimization of large MOD restorations: Composite resin inlays vs. short fiber-reinforced direct restorations Dent. Mater. (IF 4.07) Pub Date : 2018-01-20 Luciana Mara Soares, Mehrdad Razaghy, Pascal Magne
Objective To compare mechanical performance and enamel-crack propensity of direct, semi-direct, and CAD/CAM approaches for large MOD composite-resin restorations. Methods 45 extracted maxillary molars underwent standardized slot-type preparation (5-mm depth and bucco-palatal width) including immediate dentin sealing (Optibond FL) for the inlays (30 teeth). Short-fiber reinforced composite-resin (EverX Posterior covered by Gradia Direct Posterior) was used for the direct approach, Gradia Direct Posterior for the semi-direct, and Cerasmart composite resin blocks for CAD/CAM inlays. All inlays were adhesively luted with light-curing composite-resin (preheated Gradia Direct Posterior). Shrinkage-induced enamel cracks were tracked by transillumination photography. Cyclic axial isometric chewing (5-Hz) was simulated, starting with a load of 200 N (5000 cycles), followed by stages of 400, 600, 800, 1000, 1200, and 1400 N (maximum 30,000 cycles each) until fracture or to a maximum of 185,000 cycles. Survived specimens were subjected to cyclic-load-to-failure test at 30-degree angle on the palatal cusp. Results Only small shrinkage-induced cracks were found in 47% of the direct restorations compared to 7% and 13% of semi-direct and CAD/CAM inlays, respectively. Survival to accelerated fatigue was similar for all three groups (Kaplan–Meier p > .05) and ranged between 87% (direct) and 93% (semi-direct and CAD/CAM). Cyclic-load-to-failure tests did not yield significant differences either (Life Table analysis, p > .05) with median values of 1675 N for CAD/CAM inlays, 1775 N for fiber-reinforced direct restorations and 1900 N for semi-direct inlays. Significance All three restorative techniques yielded excellent mechanical performance above physiological masticatory loads. Direct restorations performed as good as inlays when a short-fiber reinforced composite-resin base was used.
Genotoxic and mutagenic potential of camphorquinone in L5178/TK+/− mouse lymphoma cells Dent. Mater. (IF 4.07) Pub Date : 2018-01-17 J. Volk, C. Ziemann, G. Leyhausen, W. Geurtsen
Objectives Camphorquinone (CQ) is the most important photoinitiator used in dental composite resins. Sparse data indicate a mutagenic potential of CQ. Therefore, it was aim of this study to evaluate the cytotoxicity, genotoxicity, and mutagenicity of CQ in L5178Y TK+/− mouse lymphoma cells. Methods L5178Y/TK+/− cells were exposed to different concentrations of non-irradiated CQ (0.25–2.5 mM). Cytotoxicity was evaluated by propidium iodide assay, determination of suspension growth rate, relative total growth and the mitotic index. Intracellular levels of reactive oxygen/nitrogen species (ROS/RNS) were quantified by 2′,7′-dichlorofluoresceine diacetate (DCFH-DA). Early induction of DNA strand breaks and oxidative DNA base lesions was assessed using the 8-hydroxyguanine DNA-glycosylase 1 (hOGG1)-modified alkaline comet assay, whereas mutagenicity of CQ was determined in the mouse lymphoma TK assay (MLA), according to OECD Guideline No. 490. Results CQ (0.5–2.5 mM) induced concentration- and time-dependent inhibition of cell growth associated with increased ROS/RNS production, amounting to 2342% ± 1108% of controls after 90 min at 2.5 mM. Additionally, CQ concentration-dependently caused direct DNA-damage, i.e. formation of DNA strand breaks and 8-hydroxy-2′-deoxyguanosine. Whereas the MLA indicated lack of mutagenicity of CQ after a 4 h of treatment, CQ concentration-dependently increased total mutant frequency (MF) after 24 h (about 2-fold at 2.5 mM). But, based on the global evaluation factor concept, increase in MF did not reach biologically relevance. Significance CQ induced concentration-dependent, cytotoxic and genotoxic effects in L5178Y/TK+/− cells, most likely due to oxidative stress, but without mediating obvious biological relevant mutagenicity.
Wear of polyetherketoneketones — Influence of titanium dioxide content and antagonistic material Dent. Mater. (IF 4.07) Pub Date : 2018-01-17 Thomas Kewekordes, Sebastian Wille, Matthias Kern
Objective The aim of this laboratory study was to analyze the influence of titanium dioxide (TiO2) content and antagonistic material on the wear of polyetherketoneketones (PEKKs). Methods Twenty-four disk-shaped specimens of two PEKK materials containing either 10 wt% or 20 wt% TiO2 particles (P10 and P20) were dynamically loaded in a chewing simulator with 49 N and additional thermal cycling (5–55 °C). Subgroups of 8 specimens each were loaded with spherical antagonists made from either steatite ceramic (St), zirconia (Zr), or the same PEKK material (P10 or P20). After 120,000, 240,000, 480,000, 840,000, and 1,200,000 loading cycles the vertical substance loss and the volume loss of the loaded specimens were evaluated using a laser scanner. Data were checked considering the normal distribution (Shapiro–Wilk test) and were inspected for significant differences by means of single factor variance analyses and post hoc pair comparison (Games-Howell test). Results After 1,200,000 chewing cycles, statistical analyses revealed a significant influence of the antagonistic material. A significant difference was also found between the tested PEKKs if Zr was used as the antagonist. The volume loss ranged from between 0.073 mm3 (P20-P20) and 0.228 mm3 (P10-St), and the vertical substance loss ranged between 73.71 μm (P20-P20) and 115.268 μm (P10-Zr). Significance The inclusion of TiO2 particles influences the wear behavior of PEKK materials.
Crystallographic and morphological analysis of sandblasted highly translucent dental zirconia Dent. Mater. (IF 4.07) Pub Date : 2018-01-08 Masanao Inokoshi, Haruki Shimizu, Kosuke Nozaki, Tomohiro Takagaki, Kumiko Yoshihara, Noriyuki Nagaoka, Fei Zhang, Jozef Vleugels, Bart Van Meerbeek, Shunsuke Minakuchi
Objective To assess the influence of alumina sandblasting on four highly translucent dental zirconia grades. Methods Fully sintered zirconia disk-shaped specimens (15-mm diameter; 0.5-mm thickness) of four highly translucent yttria partially stabilized zirconia (Y-PSZ) grades (KATANA HT, KATANA STML, KATANA UTML, Kuraray Noritake; Zpex Smile, Tosoh) were sandblasted with 50-μm alumina (Al2O3) sand (Kulzer) or left ‘as-sintered’ (control) (n = 5). For each zirconia grade, the translucency was measured using a colorimeter. Surface roughness was assessed using 3D confocal laser microscopy, upon which the zirconia grades were statistically compared for surface roughness using a Kruskal–Wallis test (n = 10). X-ray diffraction (XRD) with Rietveld analysis was used to assess the zirconia-phase composition. Micro-Raman spectroscopy was used to assess the potentially induced residual stress. Results The translucency of KATANA UTML was the highest (36.7 ± 1.8), whereas that of KATANA HT was the lowest (29.5 ± 0.9). The ‘Al2O3-sandblasted’ and ‘as-sintered’ zirconia revealed comparable surface-roughness Sa values. Regarding zirconia-phase composition, XRD with Rietveld analysis revealed that the ‘as-sintered’ KATANA UTML contained the highest amount of cubic zirconia (c-ZrO2) phase (71 wt%), while KATANA HT had the lowest amount of c-ZrO2 phase (41 wt%). KATANA STML and Zpex Smile had a comparable zirconia-phase composition (60 wt% c-ZrO2 phase). After Al2O3-sandblasting, a significant amount (over 25 wt%) of rhombohedral zirconia (r-ZrO2) phase was detected for all highly translucent zirconia grades. Significance Al2O3-sandblasting did not affect the surface roughness of the three highly translucent Y-PSZ zirconia grades, but it changed its phase composition.
Precision of 655 nm Confocal Laser Profilometry for 3D surface texture characterisation of natural human enamel undergoing dietary acid mediated erosive wear Dent. Mater. (IF 4.07) Pub Date : 2018-01-06 F. Mullan, P. Mylonas, C. Parkinson, D. Bartlett, R.S. Austin
Objectives To assess the precision of optical profilometry for characterising the 3D surface roughness of natural and polished human enamel in order to reliably quantify acid mediated surface roughness changes in human enamel. Methods Forty-two enamel samples were prepared from extracted human molars and either polished flat or left unmodified. To investigate precision, the variability of thirty repeated measurements of five areas of one polished and one natural enamel sample was assessed using 655 nm Confocal Laser Profilometry. Remaining samples were subjected to forty-five minutes orange juice erosion and microstructural changes were analysed using Sa roughness change (μm) and qualitatively using surface/subsurface confocal microscopy. Results Enamel surface profilometry from the selected areas revealed maximal precision of 5 nm for polished enamel and 23 nm for natural enamel. After erosion, the polished enamel revealed a 48% increase in mean (SD) Sa roughness of 0.10 (0.07) μm (P < 0.05), whereas in contrast the natural enamel revealed a 45% decrease in mean (SD) roughness of −0.32 (0.42) μm (P < 0.05). These data were supported by qualitative confocal images of the surface/subsurface enamel. Significance This study demonstrates a method for precise surface texture measurement of natural human enamel. Measurement precision was superior for polished flat enamel in contrast to natural enamel however, natural enamel responds very differently to polished enamel when exposed to erosion challenges. Therefore, thus future studies characterising enamel surface changes following erosion on natural enamel may provide more clinically relevant responses in comparison to polished enamel.
Development of layered PLGA membranes for periodontal tissue regeneration Dent. Mater. (IF 4.07) Pub Date : 2018-01-05 Itsumi Yoshimoto, Jun-Ichi Sasaki, Ririko Tsuboi, Satoshi Yamaguchi, Haruaki Kitagawa, Satoshi Imazato
Objective Various commercial products are available for guided tissue regeneration (GTR) therapy; however, they do not combine biosafety with the ability to control cell function. The purpose of this study was to evaluate the physicochemical and biological characteristics of the novel bilayer biodegradable poly(lactic-co-glycolic acid) (PLGA) membrane, and to assess whether the bilayer PLGA membrane could be used for periodontal tissue regeneration. Methods Bilayer biodegradable membrane was fabricated thorough a two-step freezing and lyophilization process using PLGA solution. The characteristics of bilayer membranes were evaluated with respect to surface morphology, stability, mechanical strength, and operability for clinical use. Cell proliferation and osteogenic differentiation were investigated on the each surface of bilayer membrane. Then, these membranes were implanted to the rat calvaria bone defect models and evaluated their capability for tissue regeneration. Results Biodegradable membranes composed of the solid and porous layer were successfully prepared and the surface morphologies analyzed. Physicochemical analyses revealed that the membranes possessed enough stability and mechanical properties for clinical use. It was also confirmed that the solid layer inhibited cell proliferation and subsequent connective tissue invasion, while the inner layer promoted proliferation and osteogenic differentiation, thus resulting in bone regeneration in vivo. Significance The layering technology used to fabricate the bilayer polymer membrane could be applied in the developing of other novel biomaterials. The present study demonstrates that the bilayer biodegradable polymer membranes facilitate tissue regeneration in vivo, and therefore represent a prospective biomaterial for GTR therapy.
Modulation of gingival cell response towards dental composites Dent. Mater. (IF 4.07) Pub Date : 2018-01-03 A. Jerg, S.D. Schulz, P. Tomakidi, E. Hellwig, O. Polydorou
Objective This aim of this study was to investigate the cell behavioural response on clinically applied dental composites in exposition-relevant target cells, i.e. human gingival fibroblasts (HGF) and epithelial keratinocytes (HGK). Methods HGF and HGK were exposed to eluates of Ceram X™, Filtek™ Silorane, Filtek™ Supreme XTE, Fusio™ Liquid Dentin and Vertise™ Flow. Eluates were created by storing material samples in respective cell culture medium, for 24 h and 72 h (n = 17), according to ISO 10993-12:2012. Cell response was evaluated at eluate exposure periods of 24 h and 72 h by (i) impedance analysis-based real-time monitoring of adhesion and proliferation, (ii) semi-quantitative indirect immunofluorescence (sq-IIF) detection of tissue-specific biomarkers, and (iii) ELISA-detection of pro-inflammatory interleukin (IL)-6. Results Generally, cell behavioural response towards the eluates was gradual in HGK and HGF, the latter exhibiting a less pronounced modulation per se. In HGK, ERK 1/2 was mainly activated after 24 h by Fusio™ Liquid Dentin and Vertise™ Flow, while an increase in biomarker expression occurred time-delayed. A 72 h exposure of HGK to eluates of Filtek™ Supreme XTE, Fusio™ Liquid Dentin and Vertise™ Flow significantly decreased secreted IL-6 amounts. In HGK, the impedance analysis revealed less proliferation and/or adhesion in case of Fusio™ Liquid Dentin and Vertise™ Flow with matched other composites. Significance In detail, protein expression and secretion is modulated particularly in terms of signal transduction, differentiation and inflammation. On cell biological level, all tested materials modulated the analysed features of cell behaviour with emphasis on the self-adhering composites.
Influence of a surface conditioner to pre-sintered zirconia on the biaxial flexural strength and phase transformation Dent. Mater. (IF 4.07) Pub Date : 2018-01-01 Tomofumi Sawada, Christine Schille, Judit Zöldföldi, Ernst Schweizer, Jürgen Geis-Gerstorfer, Sebastian Spintzyk
Objectives To assess the influence of a surface conditioner applied to pre-sintered yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) on the biaxial flexural strength and phase transformation. Methods Conditioner-coated specimens (12 mm diameter × 0.8 mm thickness) were prepared by application of a slurry conditioner using a brush on pre-sintered Y-TZP discs, followed by sandblasting with 50-μm Al2O3 after sintering (C-SB) or no further treatment (C-NT). The remaining conditioner-free specimens were subjected to sandblasting before sintering (NC-SB) or were maintained without treatment (NC-NT). Surface roughness measurements and scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray spectroscopy (SEM-EDX) were performed for surface characterizations. The phase transformation of Y-TZP was identified by X-ray diffraction (XRD), and the biaxial flexural strength was measured using the piston-on-three-ball test according to ISO 6872:2015. The data were analyzed using nonparametric Kruskal–Wallis tests and Weibull distributions with the maximum likelihood estimation. Results Sandblasting resulted in significantly rougher surfaces, irrespective of conditioner application. Conditioner layers were observed on surfaces in the C-NT and C-SB specimens. Monoclinic contents were present in a very small amount in the C-SB specimens. Both median biaxial flexural and characteristic strengths of all specimens exceeded ISO 6872:2015 requirements (Class 5: >800 MPa), except the NC-SB specimens which showed significantly the lowest strength (p < 0.001). Although no statistical difference was observed in Weibull modulus among the specimens (p = 0.598), the NC-SB specimens showed the highest. Significance Surface conditioner application does not affect the biaxial flexural strength and phase stability of Y-TZP and can be considered practical for clinical use.
Release of ICTP and CTX telopeptides from demineralized dentin matrices: Effect of time, mass and surface area Dent. Mater. (IF 4.07) Pub Date : 2018-01-01 Gianluca Turco, Milena Cadenaro, Tatjana Maravić, Andrea Frassetto, Eleonora Marsich, Annalisa Mazzoni, Roberto Di Lenarda, Franklin R. Tay, David H. Pashley, Lorenzo Breschi
Objective The present study evaluated the influence of time, mass and surface area of demineralized dentin collagen matrices on telopeptides release. The hypotheses tested were that the rates of ICTP and CTX release by matrix bound endogenous proteases are 1) not time-dependent, 2) unrelated to specimen mass, 3) unrelated to specimen surface area. Methods Non-carious human molars (N = 24) were collected and randomly assigned to three groups. Dentin slabs with three different thicknesses: 0.37 mm, 0.75 mm, and 1.50 mm were completely demineralized and stored in artificial saliva for one week. Collagen degradation was evaluated by sampling storage media for ICTP and CTX telopeptidases. Activity of MMPs in the aging medium was evaluated using fluorometric activity assay kit. Results A statistically significant (p < 0.05) decrease in the release of both ICTP and CTX fragments over time was observed irrespective of the specimen thickness. When data were normalized by the specimen mass, no significant differences were observed. Releases of ICTP and CTX were significantly related to the aging time as a function of surface area for the first 12 h. Total MMP activity, mainly related to MMP-2 and -9, decreased with time (p < 0.05). Significance Because the release of collagen fragments was influenced by specimen storage time and surface area, it is likely that cleaved collagen fragments closer to the specimen surface diffuse into the incubation medium; those further away from the exposed surface are still entrapped within the demineralized dentin matrix. Bound MMPs can only degrade the substrate within the limited zone of their molecular mobility.
Development of radiopaque, biocompatible, antimicrobial, micro-particle fillers for micro-CT imaging of simulated periodontal pockets Dent. Mater. (IF 4.07) Pub Date : 2017-12-26 M. Elashiry, M.M. Meghil, S. Kalathingal, A. Buchanan, M. Rajendran, R. Elrefai, M. Ochieng, A. Elawady, R.M. Arce, K.H. Sandhage, C.W. Cutler
Objectives Approximately 109 bacteria can be harbored within periodontal pockets (PP) along with inflammatory byproducts implicated in the pathophysiology of systemic diseases linked to periodontitis (PD). Calculation of this inflammatory burden has involved estimation of total pocket surface area using analog data from conventional periodontal probing which is unable to determine the three-dimensional (3-D) nature of PP. The goals of this study are to determine the radiopacity, biocompatibility, and antimicrobial activity of transient micro-particle fillers in vitro and demonstrate their capability for 3-D imaging of artificial PP (U.S. Patent publication number: 9814791 B2). Methods Relative radiopacity values of various metal oxide fillers were obtained from conventional radiography and micro-computed tomography (μCT) using in vitro models. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were used to measure the biocompatibility of calcium tungstate (CaWO4) particles by determination of viable keratinocytes percentage (%) after exposure. After introducing an antibacterial compound (K21) to the radiopaque agent, antimicrobial tests were conducted using Porphyromonas gingivalis (P. gingivalis) and Streptococcus gordonii (S. gordonii) strains and blood agar plates. Results CaWO4 micro-particle-bearing fillers exhibited an X-ray radiopacity distinct from tooth structures that enabled 3-D visualization of an artificial periodontal pocket created around a human tooth. MTT assays indicated that CaWO4 micro-particles are highly biocompatible (increasing the viability of exposed keratinocytes). Radiopaque micro-particle fillers combined with K21 showed significant antimicrobial activity for P. gingivalis and S. gordonii. Significance The plausibility of visualizing PP with 3-D radiographic imaging using new radiopaque, biocompatible, transient fillers was demonstrated in vitro. Antibacterial (or other) agents added to this formula could provide beneficial therapeutic features along with the diagnostic utility.
An evaluation of the biocompatibility and osseointegration of novel glass fiber reinforced composite implants: In vitro and in vivo studies Dent. Mater. (IF 4.07) Pub Date : 2017-12-26 Ya-Hui Chan, Wei-Zhen Lew, Emily Lu, Thomas Loretz, Luke Lu, Che-Tong Lin, Sheng-Wei Feng
Light irradiance through novel CAD–CAM block materials and degree of conversion of composite cements Dent. Mater. (IF 4.07) Pub Date : 2017-11-21 Diogo Pedrollo Lise, Annelies Van Ende, Jan De Munck, Kumiko Yoshihara, Noriyuki Nagaoka, Luiz Clovis Cardoso Vieira, Bart Van Meerbeek
Objective To assess light irradiance (LI) delivered by two light-curing units (LCU’s) and to measure the degree of conversion (DC) of three composite cements, when cured through different thicknesses of two novel CAD–CAM block materials. Methods 100-μm-thick films of a dual-curable composite cement (G-CEM LinkAce, GC), a light-curable flowable resin-based composite (RBC) (G-ænial Universal Flo, GC) and a micro-hybrid RBC (G-ænial Posterior, GC) were investigated as luting agents. Two ‘polymer–ceramic’ CAD–CAM blocks (Cerasmart, GC; Enamic, Vita Zahnfabrik) were sectioned in slabs with different thicknesses (1, 3 and 5 mm). LI at the bottom of the specimens was measured using a calibrated spectrometer, while being light-cured through the CAD–CAM block slabs for 40 s with a low- (±500 mW/cm2) or high- (±1,600 mW/cm2) irradiance LCU (n = 5). After light-curing, micro-Raman spectra of the composite films were acquired to determine DC at 5 min, 10 min, 1 h and 24 h. LI data were statistically analyzed by Kruskal–Wallis followed by post-hoc comparisons, while a linear mixed-effect model was applied for the DC analysis. In addition, the CAD–CAM blocks ultrastructure was characterized upon argon-ion slicing using scanning transmission electron microscopy (STEM). Finally, light transmission (LT) through each CAD–CAM block material was assessed using a spectrophotometer. Results Curing-light attenuation and DC were significantly influenced by thickness and type of the overlying material. LCU only had a significant effect on DC of the micro-hybrid RBC. DC significantly increased over time for all composite cements. CAD–CAM block structural analysis revealed a relatively small and homogenous filler configuration (mean filler size of 0.2–0.5 μm) for Cerasmart, while Enamic contained ceramic grains varying in shape and size (1–10 μm), which were interconnected by the polymer-based network. LT was much higher at a wavelength range of 300–800 nm for Cerasmart than for Enamic. Significance Light-curable composite cements can be cured through a restoration up to 2.7-mm thickness, depending on the kind of CAD–CAM material. A high-irradiance LCU only has a limited effect on the maximum thickness of the polymer–ceramic CAD–CAM material that can be cured through.
Influence of different smear layers on bond durability of self-etch adhesives Dent. Mater. (IF 4.07) Pub Date : 2017-11-13 Toshiki Takamizawa, Wayne W. Barkmeier, Keiichi Sai, Akimasa Tsujimoto, Arisa Imai, Robert L. Erickson, Mark A. Latta, Masashi Miyazaki
Objective The purpose of this study was to determine the influence of different smear layers on enamel and dentin bond durability of various types of self-etch adhesives. Methods Two universal adhesives, Scotchbond Universal (SU) and Prime & Bond elect (PE); a conventional single-step self-etch adhesive, G-ænial Bond (GB); and two two-step self-etch adhesives, Optibond XTR (OX) and Clearfil SE Bond (SE) were used in this study. Shear bond strengths (SBS) and shear fatigue strengths (SFS) to human enamel and dentin were determined with different smear layer conditions. The prepared specimens were divided into three groups. The bonding surfaces were prepared by grinding with either (1) #180, (2) #600, or (3) #4000-SiC papers before making the bonded assemblies. For each group, 15 specimens were prepared for the SBS and 30 specimens for the SFS. Results The two-step self-etch adhesives showed significantly higher SFS values than the single-step self-etch adhesives, regardless of the smear layer condition or substrate. Although most of the tested adhesives showed no significant differences in enamel SFS values among the smear layer groups, SU, GB, and SE showed significantly lower SFS values in the #180 in dentin groups than the #600 and #4000 groups. Conclusion The influence of different smear layer conditions on bond durability was adhesive dependent. Furthermore, the smear layers generated on different substrates also influenced the bond quality of the self-etch adhesives. Significance Smear layer conditions of enamel and dentin influence the bond durability of universal adhesives and conventional single and two-step self-etch adhesives.
Mapping the mechanical gradient of human dentin-enamel-junction at different intratooth locations Dent. Mater. (IF 4.07) Pub Date : 2017-11-12 Zhengzhi Wang, Kun Wang, Wanyin Xu, Xiaoyu Gong, Feiyu Zhang
Objectives The local structures and mechanical properties within tooth dentin-enamel-junction (DEJ) regions have been focused for numerous studies. The reported results, however, remain inconsistent particularly on the functional width and gradient architecture of the DEJ. The current study aims at systematically determining the mechanical gradient of the DEJ at different intratooth locations such that a clearer understanding on the tooth properties and the potential correlations with the tooth function could be obtained. Methods We re-examined how mechanical properties such as elastic modulus and hardness transitioned from those of dentin to those of enamel using combined static and dynamic nanoindentation mapping techniques. A new mapping method and associated image processing procedures were developed to improve the measurement accuracy and resolution. Results A thin, sigmoidally-transitioned interphase layer of the DEJ was identified with an accurate functional width of 2–3 μm. The DEJ width and gradient architecture were found intratooth location-dependent, with the DEJ at the occlusal sites being wider and transitioning smoother than that at the cervical sites. Such different widths and architectures of the interphase layer at sites subjected to different types and magnitudes of loadings during mastication could promote more efficient stress transferring between enamel and dentin without compromising the overall stiffness of the tooth. Significance The presented study not only adds our understanding in the local mechanical properties within tooth DEJ regions, it could also further advance the development of DEJ-mimetic, functional gradient interphase for strong and ultra-durable jointing between dissimilar materials.
Osseointegration of zirconia dental implants in animal investigations: A systematic review and meta-analysis Dent. Mater. (IF 4.07) Pub Date : 2017-11-06 Stefano Pieralli, Ralf-Joachim Kohal, Emilia Lopez Hernandez, Sam Doerken, Benedikt Christopher Spies
Objective To determine the osseointegration rate of zirconium dioxide (ZrO2) dental implants in preclinical investigations. Data Data on the osseointegration rate was extracted considering the bone to implant contact (BIC), removal torque analysis (RTQ) and push-in tests. Meta analyses were conducted using multilevel multivariable mixed-effects linear regression models. The Šidák method was used in case of multiple testing. Sources An electronic screening of the literature (MEDLINE/Pubmed, Cochrane Library and Embase) and a supplementary manual search were performed. Animal investigations with a minimum sample size of 3 units evaluating implants made of zirconia (ZrO2) or its composites (ZrO2 > 50 vol.%) were included. Study selection The search provided 4577 articles, and finally 54 investigations were included and analyzed. Fifty-two studies included implants made from zirconia, 4 zirconia composite implants and 37 titanium implants. In total, 3435 implants were installed in 954 animals. Conclusions No significant influence of the evaluated bulk materials on the outcomes of interest could be detected. When comparing different animal models, significant differences for the evaluated variables could be found. These results might be of interest for the design of further animal investigations.
The anti-caries effects of dental adhesive resin influenced by the position of functional groups in quaternary ammonium monomers Dent. Mater. (IF 4.07) Pub Date : 2017-12-18 Jingou Liang, Mingyun Li, Biao Ren, Tianmu Wu, Hockin H.K. Xu, Yong Liu, Xian Peng, Ge Yang, Michael D. Weir, Shiyong Zhang, Lei Cheng, Xuedong Zhou
Residual stress of porcelain-fused to zirconia 3-unit fixed dental prostheses measured by nanoindentation Dent. Mater. (IF 4.07) Pub Date : 2017-12-16 Vinicius P. Fardin, Estevam A. Bonfante, Paulo G. Coelho, Malvin N. Janal, Nick Tovar, Lukasz Witek, Dimorvan Bordin, Gerson Bonfante
Objective To evaluate the residual stress (nanoindentation based on hardness) of fatigued porcelain-fused to zirconia 3-unit fixed dental prostheses (FDP) with different framework designs. Methods Twenty maxillary 3-unit FDP replacing second-premolar (pontic) were fabricated with conventional framework-design (even-thickness of 0.5 mm and 9 mm2 connector area) and modified framework-design (thickness of 0.5 mm presenting lingual collar connected to proximal struts and 12 mm2 connector area). Connector marginal ridges were loaded and the fractured and suspended FDPs were divided (n = 3/each) into: (1) Fractured zirconia even-thickness (ZrEvenF); (2) Suspended zirconia even-thickness (ZrEvenS); (3) Fractured zirconia with modified framework (ZrModF); (4) Suspended zirconia with modified framework (ZrModS); (5) Non-fatigued FDP with conventional framework design (Control). The FDPs were nanoindented at 0.03 mm (Region of Interest (ROI) 1), 0.35 mm (ROI 2) and 1.05 mm (ROI 3) distances from porcelain veneer outer surface with peak load 4000 μN. The Linear Mixed Analysis of Variance (ANOVA) Model on ranks and Least Significant Difference Test on ranks (95%) were used. Results Highest rank hardness values were found for Control group and ZrModS, whereas the lowest values were found in ZrModF. Statistical differences (p = 0.000) were found among all groups except for comparison between ZrModS and Control group (p = 0.371). Hardness between ROIs were statistically significant different (p < 0.001) where ROI 1 presented the lowest values. Significance Framework-design modification did not influence the residual stress of porcelain-fused to zirconia fatigued 3-unit FDP. Whereas fractured FDPs showed the highest residual stress compared to suspended and control FDPs. Residual stress increased as nanoindented away from framework.
Smear layer-deproteinizing improves bonding of one-step self-etch adhesives to dentin Dent. Mater. (IF 4.07) Pub Date : 2017-12-09 Ornnicha Thanatvarakorn, Taweesak Prasansuttiporn, Suppason Thittaweerat, Richard M. Foxton, Shizuko Ichinose, Junji Tagami, Keiichi Hosaka, Masatoshi Nakajima
Objectives Smear layer deproteinizing was proved to reduce the organic phase of smear layer covered on dentin surface. It was shown to eliminate hybridized smear layer and nanoleakage expression in resin–dentin bonding interface of two-step self-etch adhesive. This study aimed to investigate those effects on various one-step self-etch adhesives. Methods Four different one-step self-etch adhesives were used in this study; SE One (SE), Scotchbond™ Universal (SU), BeautiBond Multi (BB), and Bond Force (BF). Flat human dentin surfaces with standardized smear layer were prepared. Smear layer deproteinizing was carried out by the application of 50 ppm hypochlorous acid (HOCl) on dentin surface for 15 s followed by Accel® (p-toluenesulfinic acid salt) for 5 s prior to adhesive application. No surface pretreatment was used as control. Microtensile bond strength (μTBS) and nanoleakage under TEM observation were investigated. The data were analyzed by two-way ANOVA and Tukey’s post-hoc test and t-test at the significant level of 0.05. Results Smear layer deproteinizing significantly improved μTBS of SE, SU, and BB (p < 0.001). Hybridized smear layer observed in control groups of SE, BB, and BF, and reticular nanoleakage presented throughout the hybridized complex in control groups of BB and BF were eliminated upon the smear layer deproteinizing. Significance Smear layer deproteinizing by HOCl and Accel® application could enhance the quality of dentin for bonding to one-step self-etch adhesives, resulting in the improving μTBS, eliminating hybridized smear layer and preventing reticular nanoleakage formation in resin–dentin bonding interface.
Effect of tetracalcium phosphate/monetite toothpaste on dentin remineralization and tubule occlusion in vitro Dent. Mater. (IF 4.07) Pub Date : 2017-12-09 L. Medvecky, R. Stulajterova, M. Giretova, J. Mincik, M. Vojtko, J. Balko, J. Briancin
Objectives To investigate the tubule occlusion and remineralization potential of a novel toothpaste with active tetracalcium phosphate/monetite mixtures under de/remineralization cycling. Methods Dentin de/remineralization cycling protocol consisted of demineralization in 1% citric acid at pH 4.6 with following remineralization with toothpastes and soaking in artificial saliva. Effectiveness of toothpastes to promote remineralization was evaluated by measurement of microhardness recovery, analysis of surface roughness, thickness of coating and scanning electron microscopy. Results The novel tetracalcium phosphate/monetite dentifrice had comparable remineralization potential as commercial calcium silicate/phosphate (SENSODYNE®) and magnesium aluminum silicate (Colgate®) toothpastes and significantly higher than control saliva (p < 0.02). Surface roughness was significantly lower after treatment with prepared and SENSODYNE® dentifirice (p < 0.05). The coatings on dentin surfaces was significantly thicker after applying toothpastes as compared to negative control (p < 0.001). Conclusions The new fluoride toothpaste formulation with bioactive tetracalcium phosphate/monetite calcium phosphate mixture effectively occluded dentin tubules and showed good dentin remineralization potential under de/remineralization cycling. It could replace professional powder preparation based on this mixture. It was demonstrated that prepared dentifrice had comparable properties with commercial fluoride calcium silicate/phosphate or magnesium aluminum silicate dentifrices.
Bonding strategies for MIH-affected enamel and dentin Dent. Mater. (IF 4.07) Pub Date : 2017-12-06 Norbert Krämer, Ngoc-Han Nana Bui Khac, Susanne Lücker, Vitus Stachniss, Roland Frankenberger
Objectives Aim of the present study was to evaluate resin composite adhesion to dental hard tissues affected by molar incisor hypomineralisation (MIH). Methods 94 freshly extracted human molars and incisors (53 suffering MIH) were used. 68 teeth (35 with MIH) were used for μ-TBS tests in enamel and dentin, 26 (18 with MIH) for qualitative evaluation. Specimens were bonded with Clearfil SE Bond, Scotchbond Universal, and OptiBond FL. For MIH affected enamel, additional OptiBond FL groups with NaOCl and NaOCl + Icon were investigated. Beside fractographic analysis, also qualitative evaluations were performed using SEM at different magnifications as well as histological sectioning. Results Highest μ-TBS values were recorded with dentin specimens (ANOVA, mod. LSD, p < 0.05). Results were independent of adhesive and dentin substrate (p > 0.05). Pre-test failures did not occur in dentin specimens. Sound enamel specimens exhibited significantly higher μ-TBS values than MIH enamel (p < 0.05). The two-step self-etch adhesive (Clearfil SE Bond) and the two-step etch-and-rinse adhesive (Scotchbond Universal) showed the lowest values in affected enamel specimens (p < 0.05) with most pre-test failures (p < 0.05). OptiBond FL on affected enamel showed better results than Clearfil SE Bond (p < 0.05). An additional pre-treatment of affected enamel with NaOCl or NaOCl and Icon did not enhance enamel bonding (p > 0.05), however, it caused less pre-test failures (p < 0.05). Micromorphological analyses revealed that conventional phosphoric acid etching produces a much less pronounced etching pattern in affected enamel and a porous structure as weak link for the resin-enamel bond was identified. Significance Bonding to porous hypomineralized MIH enamel is the limiting factor in adhesion to MIH teeth. MIH-affected dentin may be bonded conventionally.
Can pulpal floor debonding be detected from occlusal surface displacement in composite restorations? Dent. Mater. (IF 4.07) Pub Date : 2017-12-06 João Batista Novaes Jr, Elissa Talma, Estevam Barbosa Las Casas, Wondwosen Aregawi, Lauren Wickham Kolstad, Sue Mantell, Yan Wang, Alex Fok
Objectives Polymerization shrinkage of resin composite restorations can cause debonding at the tooth–restoration interface. Theory based on the mechanics of materials predicts that debonding at the pulpal floor would half the shrinkage displacement at the occlusal surface. The aim of this study is to test this theory and to examine the possibility of detecting subsurface resin composite restoration debonding by measuring the superficial shrinkage displacements. Methods A commercial dental resin composite with linear shrinkage strain of 0.8% was used to restore 2 groups of 5 model Class-II cavities (8-mm long, 4-mm wide and 4-mm deep) in aluminum blocks (8-mm thick, 10-mm wide and 14-mm tall). Group I had the restorations bonded to all cavity surfaces, while Group II had the restorations not bonded to the cavity floor to simulate debonding. One of the proximal surfaces of each specimen was sprayed with fine carbon powder to allow surface displacement measurement by Digital Image Correlation. Images of the speckled surface were taken before and after cure for displacement calculation. The experiment was simulated using finite element analysis (FEA) for comparison. Results Group I showed a maximum occlusal displacement of 34.7 ± 6.7 μm and a center of contraction (COC) near the pulpal floor. Group II had a COC coinciding with the geometric center and showed a maximum occlusal displacement of 17.4 ± 3.8 μm. The difference between the two groups was statistically significant (p-value = 0.0007). Similar results were obtained by FEA. The theoretical shrinkage displacement was 44.6 and 22.3 μm for Group I and II, respectively. The lower experimental displacements were probably caused by slumping of the resin composite before cure and deformation of the adhesive layer. Significance The results confirmed that the occlusal shrinkage displacement of a resin composite restoration was reduced significantly by pulpal floor debonding. Recent in vitro studies seem to indicate that this reduction in shrinkage displacement could be detected by using the most accurate intraoral scanners currently available. Thus, subject to clinical validation, the occlusal displacement of a resin composite restoration may be used to assess its interfacial integrity.
Long-term stability of dental adhesive incorporated by boron nitride nanotubes Dent. Mater. (IF 4.07) Pub Date : 2017-12-06 Felipe Weidenbach Degrazia, Vicente Castelo Branco Leitune, Fernanda Visioli, Susana Maria Werner Samuel, Fabrício Mezzomo Collares
Objective The aim of this study was to evaluate physicochemical properties, long-term microtensile bond strength and cytotoxicity of methacrylate-based adhesive containing boron nitride nanotubes (BNNTs) as fillers. Methods A dental adhesive was formulated using BisGMA/HEMA, 66/33 wt% (control). Inorganic BNNT fillers were incorporated into the adhesive at different concentrations (0.05, 0.075, 0.1 and 0.15 wt%). Analyses of degree of conversion (DC), polymerization rate [Rp.(s−1)], contact angle (CA) on dentin, after 24 h and 6 months microtensile bond strength (μTBS-24 h and 6 months) were assessed. Cytotoxicity was performed through viability of fibroblast cells (%) by sulforhodamine B (SRB) colorimetry. Results DC and max. polymerization rate increased (p < 0.05) after incorporating 0.075 and 0.1 wt% BNNT. The contact angle on dentin increased (p < 0.05) after incorporating 0.15 wt% BNNT. The μTBS-24 h showed no changes (p > 0.05) after incorporating up to 0.15 wt% BNNT comparing to control. After 6 months, μTBS decreased (p < 0.05) for control and 0.15 wt% BNNT and BNNT groups up to 0.15 wt% showed higher μTBS than control (p < 0.05). No difference of fibroblast growth was found among adhesives (p > 0.05) and up to 19% of cell viability was found comparing 0.05 wt% BNNT to positive control group (100%). Significance Incorporating boron nitride nanotubes up to 0.1 wt% into dental adhesive increased the long-term stability to dentin without decreasing viability of fibroblast cell growth. Thus, the use of BNNTs as filler may decrease failure rate of current dentinal adhesives.
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