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  • 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.

    更新日期:2018-01-18
  • 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

    ObjectiveThe aim of this laboratory study was to analyze the influence of titanium dioxide (TiO2) content and antagonistic material on the wear of polyetherketoneketones (PEKKs).MethodsTwenty-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).ResultsAfter 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).SignificanceThe inclusion of TiO2 particles influences the wear behavior of PEKK materials.

    更新日期:2018-01-17
  • 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

    ObjectiveTo assess the influence of alumina sandblasting on four highly translucent dental zirconia grades.MethodsFully 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.ResultsThe 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.SignificanceAl2O3-sandblasting did not affect the surface roughness of the three highly translucent Y-PSZ zirconia grades, but it changed its phase composition.

    更新日期:2018-01-08
  • 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.

    更新日期:2018-01-06
  • 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

    ObjectiveVarious 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.MethodsBilayer 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.ResultsBiodegradable 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.SignificanceThe 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.

    更新日期:2018-01-05
  • 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

    ObjectiveThis 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).MethodsHGF 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.ResultsGenerally, 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.SignificanceIn 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.

    更新日期:2018-01-03
  • 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

    ObjectivesTo 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.MethodsConditioner-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.ResultsSandblasting 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.SignificanceSurface conditioner application does not affect the biaxial flexural strength and phase stability of Y-TZP and can be considered practical for clinical use.

    更新日期:2018-01-01
  • 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

    ObjectiveThe 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.MethodsNon-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.ResultsA 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).SignificanceBecause 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.

    更新日期:2018-01-01
  • 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.

    更新日期:2017-12-27
  • 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
    更新日期:2017-12-27
  • 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.

    更新日期:2017-12-21
  • 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.

    更新日期:2017-12-21
  • 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.

    更新日期:2017-12-21
  • 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.

    更新日期:2017-12-21
  • 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
    更新日期:2017-12-18
  • 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.

    更新日期:2017-12-18
  • 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.

    更新日期:2017-12-14
  • 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.

    更新日期:2017-12-14
  • 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.

    更新日期:2017-12-14
  • 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.

    更新日期:2017-12-14
  • 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.

    更新日期:2017-12-14
  • Practical and theoretical considerations on the fracture toughness testing of dental restorative materials
    Dent. Mater. (IF 4.07) Pub Date : 2017-12-06
    Renan Belli, Michael Wendler, José I. Zorzin, Ulrich Lohbauer

    Background An important tool in materials research, development and characterization regarding mechanical performance is the testing of fracture toughness. A high level of accuracy in executing this sort of test is necessary, with strict requirements given in extensive testing standard documents. Proficiency in quality specimen fabrication and test requires practice and a solid theoretical background, oftentimes overlooked in the dental community. Aims: In this review we go through some fundamentals of the fracture mechanics concepts that are relevant to the understanding of fracture toughness testing, and draw attention to critical aspects of practical nature that must be fulfilled for validity and accuracy in results. We describe our experience with some testing methodologies for CAD/CAM materials and discuss advantages and shortcomings of different tests in terms of errors in testing the applicability of the concept of fracture toughness as a single-value material-specific property.

    更新日期:2017-12-14
  • Photopolymerization of cell-laden gelatin methacryloyl hydrogels using a dental curing light for regenerative dentistry
    Dent. Mater. (IF 4.07) Pub Date : 2017-12-06
    Nelson Monteiro, Greeshma Thrivikraman, Avathamsa Athirasala, Anthony Tahayeri, Cristiane M. França, Jack L. Ferracane, Luiz E. Bertassoni

    Photopolymerized hydrogels, such as gelatin methacryloyl (GelMA), have desirable biological and mechanical characteristics for a range of tissue engineering applications. Objective This study aimed to optimize a new method to photopolymerize GelMA using a dental curing light (DL). Methods Lithium acylphosphinate photo-initiator (LAP, 0.05, 0.067, 0.1% w/v) was evaluated for its ability to polymerize GelMA hydrogel precursors (10% w/v) encapsulated with odontoblast-like cells (OD21). Different irradiances (1650, 2300 and 3700 mW/cm2) and photo-curing times (5–20 s) were tested, and compared against the parameters typically used in UV light photopolymerization (45 mW/cm2, 0.1% w/v Irgacure 2959 as photoinitiator). Physical and mechanical properties of the photopolymerized GelMA hydrogels were determined. Cell viability was assessed using a live and dead assay kit. Results Comparing DL and UV polymerization methods, the DL method photopolymerized GelMA precursor faster and presented larger pore size than the UV polymerization method. The live and dead assay showed more than 80% of cells were viable when hydrogels were photopolymerized with the different DL irradiances. However, the cell viability decreased when the exposure time was increased to 20 s using the 1650 mW/cm2 intensity, and when the LAP concentration was increased from 0.05 to 0.1%. Both DL and UV photocrosslinked hydrogels supported a high percentage of cell viability and enabled fabrication of micropatterns using a photolithography microfabrication technique. Significance The proposed method to photopolymerize GelMA cell-laden hydrogels using a dental curing light is effective and represents an important step towards the establishment of chair-side procedures in regenerative dentistry.

    更新日期:2017-12-14
  • Characterization, mechanistic analysis and improving the properties of denture adhesives
    Dent. Mater. (IF 4.07) Pub Date : 2017-12-06
    Afsoon Fallahi, Nona Khadivi, Nima Roohpour, Andrew M. Middleton, Mehdi Kazemzadeh-Narbat, Nasim Annabi, Ali Khademhosseini, Ali Tamayol

    Objective Denture adhesives are widely used to avoid the detachment and sliding of dentures. However, the adhesion properties can be affected by variation in mouth conditions such as the level of salivation. The objective of this study was to understand the effect of environmental conditions on the adhesion properties of a commercially available denture adhesive named as Poligrip® Free manufactured by GlaxoSmithKline Ltd., UK and to identify the reasons for the observed variation in its adhesion strength. Methods The failure mechanisms of denture adhesive have been assessed through using different physical, mechanical and thermal characterization experiments. All methods were used in different pH, temperatures, and salivation conditions and at the end, a strategy was proposed to overcome the failure of the paste in hyposalivation as well. Results In vitro models mimicking the denture gingival interface were designed to evaluate the adhesion properties of the investigated adhesive. Changes in the adhesion strength in response to three major factors related to the oral conditions including level of salivation, pH, and temperature were measured. The results of lap shear, tensile test, and internal interactions suggested a cohesion failure, where the lowest adhesion strength was due to hyposalivation. Fourier transform infrared spectroscopy (FTIR) and rheological analysis confirmed the importance of hydrogen bonds and hydration in the adhesion strength of the paste. Significance The investigated scenarios are widely observed in patient using denture adhesives and the clinical reports have indicated the inconsistency in adhesion strength of the commercial products. After identifying the potential reasons for such behavior, methods such as the addition of tripropylene glycol methyl ether (TPME) to enhance internal hydrogen bonds between the polymers are proposed to improve adhesion in the hyposalivation scenario.

    更新日期:2017-12-14
  • Induction of DNA double-strand breaks in human gingival fibroblasts by eluates from titanium dioxide modified glass ionomer cements
    Dent. Mater. (IF 4.07) Pub Date : 2017-11-27
    Arunee Laiteerapong, Franz-Xaver Reichl, Yang Yang, Reinhard Hickel, Christof HÖgg

    Objectives (1) To investigate the genotoxicity of a glass ionomer cement (GIC) and GIC incorporated with titanium dioxide nanopoarticle (TiO2NPs) and with microparticle (TiO2MPs) on DNA double-strand breaks of human gingival fibroblast cells (HGFs). (2) To compare the genotoxic differences between GIC and two modified cements. Methods TiO2NPsGIC and TiO2MPsGIC were prepared by adding 10% w/w of TiO2NPs and TiO2MPs to the GIC powder and hand-mixed followed the manufacturer instruction. Dulbecco’s Minimum Essential Medium (DMEM) was used as a culture medium for HGFs and eluate preparation. Eluates from all groups were collected for XTT cell viability assay to obtain EC50 values. γ-H2AX immunofluorescence assay was performed to detect DNA double-strand breaks (DSBs) of HGFs. Results EC50 values were from 38% to 60% and eluate concentrations at 20% and 5% were selected for γ-H2AX immunofluorescence assay. At both concentrations, HGFs exposed to eluates from all cements groups had fewer mean foci per cell and higher percentage of free foci cells than H2O2 (p < 0.05). At 20% concentration, cells exposed to eluates from both TiO2NPsGIC and TiO2MPsGIC groups had fewer mean foci per cell and higher percentage of free foci cell than GIC and culture medium (p < 0.05). Significance Neither GIC nor 10% TiO2-modified GICs had a genotoxic effect on HGFs. Both TiO2NPsGIC and TiO2MPsGIC demonstrated less genotoxic effect than GIC. When comparing between the two modified cements, there was no genotoxic difference between the modified cements from different particle sizes (nanoparticle and micro-particle) of TiO2.

    更新日期:2017-12-14
  • The effect of chewing simulation on surface roughness of resin composite when opposed by zirconia ceramic and lithium disilicate ceramic
    Dent. Mater. (IF 4.07) Pub Date : 2017-11-27
    Ting Khee Ho, Julian D. Satterthwaite, Nikolaos Silikas

    Objective To assess the change in surface roughness of nanohybrid resin composite (Tetric EvoCeram) after antagonist wear against monolithic zirconia and lithium disilicate ceramics through a simulated chewing test using a three-dimensional (3D) profilometer. Methods A total of 40 Tetric EvoCeram™ resin composite specimens against either a Lava™ Plus zirconia antagonist (n = 20) or IPS e.max Press lithium disilicate antagonist (n = 20) were prepared for the study. The surface roughness profiles of each resin composite before and after an in-vitro simulated chewing test were analysed using a 3D profilometer and Talymap software. After the simulated chewing, the surface profiles of representative Tetric EvoCeram specimens from each group were analysed using scanning electron microscopy. Independent t-test and paired t-test were used for statistical analysis. Results For both lithium disilicate and zirconia groups, all surface roughness parameters (Ra, Rt, Sa, Sq,) of Tetric EvoCeram were significantly higher post-chewing compared to pre-chewing (p < 0.05); the post-chewing surface roughness parameters of Tetric EvoCeram for the lithium disilicate group were significantly higher (p < 0.05) than in the zirconia group. Significance This chewing simulation test showed that Tetric EvoCeram composites exhibited a rougher surface when opposing lithium disilicate ceramic compared to opposing zirconia ceramic.

    更新日期:2017-12-14
  • Effects of different sterilization methods on surface characteristics and biofilm formation on zirconia in vitro
    Dent. Mater. (IF 4.07) Pub Date : 2017-11-26
    Aifang Han, James K.H. Tsoi, Jukka P. Matinlinna, Yu Zhang, Zhuofan Chen

    Objective The current laboratory study was to investigate the effect of different sterilization treatments on surface characteristics of zirconia, and biofilm formation on zirconia surface after exposure to these sterilization treatments. Methods Commercially available zirconia discs (Cerconbase, Degu-Dent, Hanau, Germany) were prepared and polished to the same value of surface roughness. The discs were treated with one of the following sterilization methods steam autoclave sterilization, dry heat sterilization, ultraviolet C (UVC) irradiation, and gamma (γ) ray irradiation. The characteristics of zirconia surfaces were evaluated by scanning electron microscopy (SEM), surface roughness, surface free energy (SFE), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) measurements. Then, Staphylococcus aureus (S.a.) and Porphyromonas gingivalis (P.g.) bacteria were used and cultured on the respective sterilized zirconia surfaces. The amount of biofilm formation on zirconia surface was quantified by colony forming unit (CFU) counts. Results Significant modifications were detected on the colour and SFE of zirconia. The colour of zirconia samples after UVC irradiation became light yellow whilst dark brown colour was observed after gamma ray irradiation. Moreover, UVC and gamma ray irradiation increased the hydrophilicity of zirconia surface. Overall, dry heat sterilized samples showed the significantly lowest amount of bacteria growth on zirconia, while UVC and gamma ray irradiation resulted in the highest. Significance It is evident that various sterilization methods could change the surface which contribute to different biofilm formation and colour on zirconia.

    更新日期:2017-12-14
  • Effect of titania content and biomimetic coating on the mechanical properties of the Y-TZP/TiO2 composite
    Dent. Mater. (IF 4.07) Pub Date : 2017-11-26
    Ranulfo Benedito de Paula Miranda, Walter Gomes Miranda Junior, Dolores Ribeiro Ricci Lazar, Valter Ussui, Juliana Marchi, Paulo Francisco Cesar

    Objective To investigate the effect of titania addition (0, 10 and 30 mol%) on the microstructure, relative density, Young’s modulus (E), Poisson’s ratio (υ), mechanical properties (flexural strength, σf, and Weibull modulus, m) of a Y-TZP/TiO2 composite. The effect of the presence of a biomimetic coating on the microstructure and mechanical properties was also evaluated. Methods Y-TZP (3 mol% of yttria) and Y-TZP/TiO2 composite (10 or 30 mol% of titania) were synthesized by co-precipitation. The powders were pressed and sintered at 1400°C/2 h. The surfaces, with and without biomimetic coating, were characterized by X-ray diffraction analysis and scanning electron microscopy. The relative density was measured by the Archimedes’ principle. E and υ were measured by ultrasonic pulse-echo method. For the mechanical properties the specimens (n = 30 for each group) were tested in a universal testing machine. Results Titania addition increased the grain size of the composite and caused a significant decrease in the flexural strength (in MPa, control 815.4a; T10 455.7b and T30 336.0c), E (in GPa, control 213.4a; T10 155.8b and T30 134.0c) and relative density (control 99.0%a; T10 94.4%c and T30 96.3%b) of the Y-TZP/TiO2 composite. The presence of 30% titania caused substantial increase in m and υ. Biomimetic coating did not affect the mechanical properties of the composite. Significance The Y-TZP/TiO2 composite coated with a layer of CaP has great potential to be used as implant material. Although addition of titania affected the properties of the composite, the application of a biomimetic coating did not jeopardize its reliability.

    更新日期:2017-12-14
  • Effect of tribochemical treatments and silane reactivity on resin bonding to zirconia
    Dent. Mater. (IF 4.07) Pub Date : 2017-11-26
    Raphael Pilo, Maria Dimitriadi, Anna Palaghia, George Eliades

    Objective The aim of the study was to assess the roughness, structure and bond strength with zirconia of four grit-blasting treatments combined with three silane types, the reactivity of which was evaluated, as well. Methods The grit-blasted treatments performed on zirconia (Lava) were alumina (ALU), CoJet (COJ), SilJet (SLJ) and SilJet Plus (SJP, with silica-encapsulated silane). The other two silanes selected were the S-Bond (SB, prehydrolyzed) and Clearfil Ceramic Primer Plus (CP, prehydrolyzed with 10-MDP). The activity of the silanols in the silanes was evaluated by FTIR spectroscopy. Optical profilometry and Raman microspectroscopy were used for the assessment of roughness (Sa, Sz, Sdr parameters) and structure (monoclinic volume-Vm) of zirconia, before (REF) and after grit-blasting, and a shear bond strength (SBS) with a flowable resin composite, for the investigation of the bonding capacity of the treatments. Results Only SB demonstrated reactive silanols. CP and the SJP silanes were mostly in a polymerized siloxane state. Roughness was increased after grit-blasting as follows: ALU > SLJ,SJP > COJ > REF (Sa,Sz) and ALU > SLJ,COJ,SJP > REF (Sdr). ALU demonstrated the highest Vm (7.52%) from all other treatments (4.16–4.81%) and the REF (0%). COJ and SLJ showed the highest SBS (14–15.94 MPa) regardless of the silane type used. SJP showed no significant differences from SLJ-SB and COJ-SB. Weibull analysis showed a reliability (β) ranking of COJ, SJP, SLJ, ALU-CP > ALU-SB > REF and a characteristic life (η) ranking of COJ, SLJ, ≥SLJ-SB, SJP, ALU ≥ ALU-SB,REF-CP > REF-SB. Significance The reactivity of the silanes used showed great variations to support a predictable effect in all treatments. CP with deactivated silanols demonstrated a) the most reliable and strongest treatment with a silica-rich powder (COJ), despite the lowest Sa,Sz substrate values and b) high strength with a low-silica powder (SLJ) with higher Sa,Sz substrate values. Therefore, it may be concluded that 10-MDP greatly contributes to the bonding mechanism of the silane containing primers.

    更新日期:2017-12-14
  • Using glass-graded zirconia to increase delamination growth resistance in porcelain/zirconia dental structures
    Dent. Mater. (IF 4.07) Pub Date : 2017-11-26
    Herzl Chai, Adam J. Mieleszko, Stephen J. Chu, Yu Zhang

    Objective Porcelain fused to zirconia (PFZ) restorations are widely used in prosthetic dentistry. However, their tendency to delaminate along the P/Z interface remains a practical problem so that assessing and improving the interfacial strength are important design aspects. This work examines the effect of modifying the zirconia veneering surface with an in-house felspathic glass on the interfacial fracture resistance of fused P/Z. Methods Three material systems are studied: porcelain fused to zirconia (control) and porcelain fused to glass-graded zirconia with and without the presence of a glass interlayer. The specimens were loaded in a four-point-bend fixture with the porcelain veneer in tension. The evolution of damage is followed with the aid of a video camera. The interfacial fracture energy GC was determined with the aid of a FEA, taking into account the stress shielding effects due to the presence of adjacent channel cracks. Results Similarly to a previous study on PFZ specimens, the fracture sequence consisted of unstable growth of channel cracks in the veneer followed by stable cracking along the P/Z interface. However, the value of GC for the graded zirconia was approximately 3 times that of the control zirconia, which is due to the good adhesion between porcelain and the glass network structure on the zirconia surface. Significance Combined with its improved bonding to resin-based cements, increased resistance to surface damage and good esthetic quality, graded zirconia emerges as a viable material concept for dental restorations.

    更新日期:2017-12-14
  • Dentin bonding systems: From dentin collagen structure to bond preservation and clinical applications
    Dent. Mater. (IF 4.07) Pub Date : 2017-11-26
    Lorenzo Breschi, Tatjana Maravic, Sandra Ribeiro Cunha, Allegra Comba, Milena Cadenaro, Leo Tjäderhane, David H. Pashley, Franklin R. Tay, Annalisa Mazzoni

    Objectives Efforts towards achieving durable resin–dentin bonds have been made for decades, including the understanding of the mechanisms underlying hybrid layer (HL) degradation, manufacturing of improved adhesive systems, as well as developing strategies for the preservation of the HL. Methods This study critically discusses the available peer-reviewed research concerning the formation and preservation of the HL, the mechanisms that lead to the degradation of the HL as well as the strategies to prevent it. Results The degradation of the HL occurs through two main mechanisms: the enzymatic degradation of its collagen fibrils, and the leaching of the resin from the HL. They are enabled by residual unbound water between the denuded collagen fibrils, trapped at the bottom of the HL. Consequently, endogenous dentinal enzymes, such as the matrix metalloproteinases (MMPs) and cysteine cathepsins are activated and can degrade the denuded collagen matrix. Strategies for the preservation of the HL over time have been developed, and they entail the removal of the unbound water from the gaps between the collagen fibrils as well as different modes of silencing endogenous enzymatic activity. Significance Although there are many more hurdles to be crossed in the field of adhesive dentistry, impressive progress has been achieved so far, and the vast amount of available research on the topic is an indicator of the importance of this matter and of the great efforts of researchers and dental material companies to reach a new level in the quality and longevity of resin–dentin bonds.

    更新日期:2017-12-14
  • Bisphenol A release from an orthodontic resin composite: A GC/MS and LC/MS study
    Dent. Mater. (IF 4.07) Pub Date : 2017-11-26
    Marc Deviot, Isabelle Lachaise, Christof Högg, Jürgen Durner, Franz-Xaver Reichl, Jean-Pierre Attal, Elisabeth Dursun

    Objectives First, to analyse the in vitro release of BPA and Bis-GMA from an orthodontic resin composite (Transbond XT, 3M Unitek), stored in various conditions, by gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS); then to extrapolate the data to the clinical situation. Secondly, to explore the thermal stability of Bis-GMA. Methods Cylinders of resin composite were prepared and stored according to 3 different protocols: (1) they were light-cured 20 s, then placed in artificial saliva; (2) they were light-cured 2 s, then placed in acetonitrile; (3) they were light-cured 2 s, then placed in methanol. For each group, BPA and Bis-GMA release were determined with GC/MS and/or LC/MS at least after one week. Besides, 120 brackets (10 of each type) were bonded over metal teeth, then debonded, and the weight and the surface of resin composite residues were measured. BPA and Bis-GMA release of adhesive residues were extrapolated from the data obtained with the cylinders. Besides, BPA release from a heated Bis-GMA solution was measured. Results With GC/MC, BPA was detected in all samples. With LC/MS, BPA was detected only from samples immersed in MeOH; Bis-GMA was detected, in varying amount according to the extraction media and the light-curing time. BPA was found after heating of the Bis-GMA solution. Significance Contamination risk and the heat applied in GC/MS may overestimate the BPA release from resin composite. Based on the LC/MS results, the risk of BPA release after orthodontic bonding would be more than 42 000 times lower than the TDI for a 30-kg child.

    更新日期:2017-12-14
  • Mechanism of bioactive molecular extraction from mineralized dentin by calcium hydroxide and tricalcium silicate cement
    Dent. Mater. (IF 4.07) Pub Date : 2017-11-24
    Xue-qing Huang, John Camba, Li-sha Gu, Brian E. Bergeron, Domenico Ricucci, David H. Pashley, Franklin R. Tay, Li-na Niu

    Objectives The objective of the present study was to elucidate the mechanism of bioactive molecule extraction from mineralized dentin by calcium hydroxide (Ca(OH)2) and tricalcium silicate cements (TSC). Methods and results Transmission electron microscopy was used to provide evidence for collagen degradation in dentin surfaces covered with Ca(OH)2 or a set, hydrated TSC for 1–3 months. A one micron thick collagen degradation zone was observed on the dentin surface. Fourier transform-infrared spectroscopy was used to identify increases in apatite/collagen ratio in dentin exposed to Ca(OH)2. Using three-point bending, dentin exposed to Ca(OH)2 exhibited significant reduction in flexural strength. Using size exclusion chromatography, it was found that the small size of the hydroxyl ions derived from Ca(OH)2 enabled those ions to infiltrate the intrafibrillar compartment of mineralized collagen and degrade the collagen fibrils without affecting the apatite minerals. Using ELISA, TGF-β1 was found to be extracted from dentin covered with Ca(OH)2 for 3 months. Unlike acids that dissolve the mineral component of dentin to release bioactive molecules, alkaline materials such as Ca(OH)2 or TSC released growth factors such as TGF-β1 via collagen degradation. Significance The bioactive molecule extraction capacities of Ca(OH)2 and TSC render these dental materials excellent for pulp capping and endodontic regeneration. These highly desirable properties, however, appear to be intertwined with the untoward effect of degradation of the collagen matrix within mineralized dentin, resulting in reduced flexural strength.

    更新日期:2017-12-14
  • An interproximal model to determine the erosion-protective effect of calcium silicate, sodium phosphate, fluoride formulations
    Dent. Mater. (IF 4.07) Pub Date : 2017-11-24
    Natalie J. Wood, Siân Bodfel Jones, Nick Chapman, Andrew Joiner, Carole J. Philpotts, Nicola X. West

    Objectives Previous work has shown the effectiveness of a newly developed interproximal model to differentiate between the amount of remineralization caused by toothpastes used with or without a dual-phase gel treatment system containing calcium silicate, sodium phosphate salts and fluoride to repair acid-softened enamel. The aim of this study was to utilize the same interproximal model to identify how effective calcium silicate phosphate toothpastes are at reducing surface softening in the early stages of erosion. The model was also used to identify the effect of increasing the frequency of acid exposure on the reduction in surface hardness. Methods Human enamel specimens were prepared and mounted in an interproximal face-to-face arrangement and exposed to a cycling regime of whole human saliva, treatment, artificial saliva and 1% citric acid pH 3.75. Specimens were measured by surface microhardness at baseline and after three and seven days. The frequency of acid exposure was increased from 2 to 4 cycles a day for the second part of the study. Results The results showed that specimens treated with the calcium silicate phosphate toothpastes softened less than those treated with control fluoridated or non-fluoride toothpastes at each time point and following an increase in the frequency of acid exposure. Significance This work has demonstrated how an interproximal model can also be successfully used to determine differences in the erosion protection of various treatments as well as determining how they perform when the frequency of acid exposure is increased.

    更新日期:2017-12-14
  • Cross-linking effect on dentin bond strength and MMPs activity
    Dent. Mater. (IF 4.07) Pub Date : 2017-11-24
    Annalisa Mazzoni, Valeria Angeloni, Allegra Comba, Tatjana Maravic, Milena Cadenaro, Arzu Tezvergil-Mutluay, David H. Pashley, Franklin R. Tay, Lorenzo Breschi

    Objective The objectives of the study were to evaluate the ability of a 1-ethyl-3 (3-dimethylaminopropyl) carbodiimide (EDC)-containing primer to improve immediate bond strength of either self-etch or etch-and-rinse adhesive systems and to stabilize the adhesive interfaces over time. A further objective was to investigate the effect of EDC on the dentinal MMPs activity using zymographic analysis. Methods Freshly extracted molars (n = 80, 20 for each group) were selected to conduct microtensile bond strength tests. The following groups were tested, immediately or after 1-year aging in artificial saliva: G1: Clearfil SE (CSE) primer applied on unetched dentin, pretreated with 0.3 M EDC water-solution for 1 min and bonded with CSE Bond; G2: as G1 but without EDC pre-treatment; G3: acid-etched (35% phosphoric-acid for 15s) dentin pretreated with 0.3 M EDC, then bonded with XP Bond (XPB); Group 4 (G4): as G3 without EDC pre-treatment. Further, gelatinase activity in dentin powder treated with CSE and XPB with and without EDC pre-treatment, was analyzed using gelatin zymography. Results The use of 0.3 M EDC-containing conditioner did not affect the immediate bond strength of XPB or CSE adhesive systems (p > 0.05), while it improved the bond strength after 1 year of aging (p < 0.05). Pre-treatment with EDC followed by the application of CSE resulted in an incomplete MMPs inactivation, while EDC pretreatment followed by the application of XPB resulted in an almost complete inactivation of dentinal gelatinases. Significance The μTBS and zymography results support the efficacy of EDC over time and reveal that changes within the dentin matrix promoted by EDC are not adhesive-system-dependent.

    更新日期:2017-12-14
  • Hierarchical microcrack model for materials exemplified at enamel
    Dent. Mater. (IF 4.07) Pub Date : 2017-11-23
    H. Özcoban, E.D. Yilmaz, G.A. Schneider

    Objective This article investigates the mechanical properties of a material with hierarchically arranged microcracks. Methods Hierarchically structured biomaterials such as enamel exhibit superior mechanical properties as being stiff and damage tolerant at the same time. The common mechanical explanation for this behavior is based on the hierarchically structured arrangement of hard minerals and soft organics and their cooperative deformation mechanisms. In situ mechanical experiments with mm-sized bovine enamel bending bars an scanning electron microscope reveal that enamel is able to withstand mechanical loading even if it contains microcracks on different lengths scales. To clarify this issue an analytical hierarchical microcrack model of non-interacting cracks is presented. Results and Significance The model predicts a decrease of the elastic modulus and the fracture strength with increasing levels of hierarchy. The fracture strain on the other hand may decrease or increase with the number of hierarchical levels, depending on the microcrack density. This simple hierarchical microcrack model is able to explain already published experiments with focused ion beam prepared μm-sized enamel cantilevers on different hierarchical levels. In addition it is shown that microcracking during loading in hierarchical materials may lead to substantial pseudoplastic behavior.

    更新日期:2017-12-14
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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