Effects of sintering time and hydrothermal aging on the mechanical properties of monolithic zirconia ceramic systems

doi:10.1016/j.prosdent.2020.09.006

The Journal of Prosthetic Dentistry

Volume 126, Issue 5, November 2021, Pages 688-691

https://doi.org/10.1016/j.prosdent.2020.09.006 Get rights and content

Abstract

Statement of problem

The flexural strength of zirconia restorations is partially dependent on the sintering process. Changes in sintering protocols as well as hydrothermal aging may affect the flexural strength of zirconia materials.

Purpose

The purpose of this in vitro study was to investigate how changes in sintering parameters and hydrothermal aging affect the biaxial flexural strength of monolithic zirconia.

Material and methods

Specimens were produced from 2 translucent monolithic zirconia ceramics (Zircon X ST, Upcera YZ HT). After coloring, specimens of both ceramics were distributed into groups and subjected to 1 of 6 different sintering protocols. Half were subjected to biaxial flexural strength tests directly after sintering, and the remaining specimens were subjected to hydrothermal aging and then to biaxial flexural strength testing. Biaxial flexural strength data were analyzed by using a statistical software program. Normality of distribution was determined by the Shapiro-Wilk test. Biaxial flexural strength data were compared among groups by using 1-way ANOVA and Tukey post hoc tests, and intragroup data were compared by using paired specimens t tests (α=.05).

Results

The highest overall biaxial flexural strength value was obtained in UW-II. The highest biaxial flexural strength for Zircon X was obtained in ZX-VI and ZX-HTA-VI, whereas the highest biaxial flexural strength for Upcera was obtained in UW-II before hydrothermal aging and in UW-HTA-V after aging (P<.05).

Conclusions

The biaxial flexural strength of Zircon X increased with longer sintering times. Upcera specimens were more fracture-resistant than Zircon X both before and after hydrothermal aging. Based on these findings, longer sintering times are recommended to increase the strength of monolithic zirconia.

Section snippets

Material and methods

A total of 240 disk-shaped specimens were prepared from presintered blocks of 2 different translucent monolithic zirconia ceramics (Zircon X ST; President Dental GmbH, Upcera YZ HT; Shenzhen Upcera Dental Technology) (n=120) by using CAD-CAM technology. Material details are provided in Table 1. Specimens were prepared approximately 20% larger³² than the target size to compensate for sintering shrinkage.

After coloring with an A2 color solution (Tanaka ZirColor; Tanaka Dental), all specimens were

Results

The mean BFS values (MPa), standard deviations, and statistical findings for each group are presented in Table 3. For the Zircon X ceramic specimens not subjected to hydrothermal aging, the group with the longest sintering time had the highest BFS value (ZX-VI, 776.2 MPa), whereas a group with a relatively short sintering time had the lowest BFS value (ZX-II, 578.5 MPa). When the Zircon X ceramic specimens were subjected to hydrothermal aging, the highest BFS value was again observed in

Discussion

This study found the BFS of CAD-CAM fabricated monolithic zirconia specimens was significantly affected by changes in sintering conditions. When the BFS of Zircon X ceramic specimens was examined, among those specimens not subjected to hydrothermal aging, higher BFS values were observed with longer sintering times (ZX-IV, V, and VI) as compared with shorter sintering times (ZX-I, II, and III). Therefore, the null hypothesis that sintering time would not affect the BFS of monolithic zirconia was

Conclusions

Based on the findings of this in vitro study, the following conclusions were drawn:

1.
The BFS of Zircon X ceramic increased with longer sintering times.
2.
Hydrothermal aging did not affect the BFS of Zirconia X ceramic subjected to shorter sintering times (ZX-I and II).
3.
The BFS of Upcera ceramic decreased with hydrothermal aging.
4.
The BFS values of Upcera ceramic were higher than those of Zircon X before and after hydrothermal aging.
5.
Longer sintering times are recommended to increase the strength and

CRediT authorship contribution statement

Perihan Oyar: Investigation, Methodology, Writing - original draft, Supervision, Writing - review & editing. Rukiye Durkan: Investigation, Methodology, Data curation, Writing - original draft. Gonca Deste: Investigation, Conceptualization.

References (36)

C. Piconi et al.
Zirconia as a ceramic biomaterial
Biomaterials
(1999)
J. Chevalier
What future for zirconia as a biomaterial?
Biomaterials
(2006)
I.L. Denry et al.
State of the art of zirconia for dental applications
Dent Mater
(2008)
M.J. Tholey et al.
Thermal gradients and residual stresses in veneered Y-TZP frameworks
Dent Mater
(2011)
P. Benetti et al.
Analysis of thermal distributions in veneered zirconia and metal restorations during firing
Dent Mater
(2013)
T.A. Sulaiman et al.
Effect of different treatments on the flexural strength of fully versus partially stabilized monolithic zirconia
J Prosthet Dent
(2017)
Y. Zhang et al.
Edge chipping and flexural resistance of monolithic ceramics
Dent Mater
(2013)
A.A. Almazdi et al.
Applying microwave technology to sintering dental zirconia
J Prosthet Dent
(2012)
J. Hjerppe et al.
Effect of sintering time on biaxial strength of zirconium dioxide
Dent Mater
(2009)
M.R. Kaizer et al.
Speed sintering translucent zirconia for chairside one-visit dental restorations: optical, mechanical, and wear characteristics
Ceram Int
(2017)

M.J. Heffernan et al.

Relative translucency of six all-ceramic systems. Part I: core materials

J Prosthet Dent

(2002)

J.R. Kelly

Future of dental biomaterials: gazing into Bob’s crystal ball

J Prosthet Dent

(2021)

D.R. Lazar et al.

Y-TZP ceramic processing from coprecipitated powders: a comparative study with three commercial dental ceramics

Dent Mater

(2008)

J.U. Jansen et al.

Impact of high-speed sintering on translucency, phase content, grain sizes, and flexural strength of 3Y-TZP and 4Y-TZP zirconia materials

J Prosthet Dent

(2019)

N. Lümkemann et al.

Impact of hydrothermal aging on the light transmittance and flexural strength of colored yttria-stabilized zirconia materials of different formulations

J Prosthet Dent

(2021)

M. Inokoshi et al.

Influence of sintering conditions on low-temperature degradation of dental zirconia

Dent Mater

(2014)

S. Tekeli et al.

A quantitative assessment of cavities in 3 mol% yttria-stabilized tetragonal zirconia specimens containing various grain size

Ceram Int

(2002)

G.J. Chistensen

Choosing an all-ceramic restorative material: porcelain fused-to metal or zirconia based?

J Am Dent Assoc

(2007)

Cited by (5)

Effect of different sintering protocols on the fracture strength of 3-unit monolithic gradient zirconia fixed partial dentures: An in vitro study
2023, Journal of Prosthetic Dentistry
Strength-gradient zirconia combining 3 zirconia formulations with different flexural strengths has been reported to have outstanding mechanical properties. However, data concerning the effect of different sintering protocols on the fracture strength of 3-unit monolithic gradient zirconia fixed partial dentures (FPDs) are sparse.
The purpose of this in vitro study was to test the effect of different sintering protocols on the fracture strength of 3-unit monolithic gradient zirconia FPDs.
Two custom-made stainless-steel master dies were designed to replicate a mandibular right second premolar and second molar prepared to receive a 3-unit monolithic zirconia FPD. Thirty monolithic zirconia FPDs were milled from gradient zirconia blanks and allocated to 3 groups (n=10) according to the sintering protocols: high-speed sintering, speed sintering, and conventional sintering. The FPDs were cemented onto the corresponding dies with traditional glass ionomer cement. All FPDs were cyclic loaded (600 000 cycles/49 N/1.7 Hz) in a mastication simulator. Fracture load measurements for each FPD were determined by using a universal testing machine. Scanning electron microscopy (SEM) at ×80 magnification was used to examine a fractured FPD from each group. A representative specimen from each group was examined with SEM at ×30 000 magnification to determine the grain size. One-way ANOVA, pair-wise Tukey honestly significant difference (HSD), and Pearson correlation tests were used for statistical analysis of the data (α=.05).
The high-speed sintered FPDs recorded the highest statistically significant fracture load mean ±standard deviation value (2526 ±300 N), followed by the speed sintered FPDs (2136 ±127 N), while the lowest statistically significant fracture load mean value was recorded with the conventionally sintered FPDs (1361 ±181 N) (P<.001). In addition, the mean ±standard deviation grain size values were 488 ±272 nm for the high-speed sintered specimen, 578 ±409 nm for the speed sintered specimen, and 832 ±551 nm for the conventionally sintered specimen (P<.001). A significant negative correlation was found between fracture strength and grain size among the 3 groups.
The fracture strength of 3-unit monolithic gradient zirconia FPDs sintered by using a high-speed protocol was significantly higher than that of speed and conventionally sintered FPDs (P<.001). The high-speed sintering protocol reduced the mean grain size of gradient zirconia FPDs compared with that of both speed and conventional sintering protocols.
Crystal structure and morphology of CeO<inf>2</inf> doped stabilized zirconia ceramics under high-frequency microwave field sintering
2022, Ceramics International
Citation Excerpt :
To avoid this issue, the application of CeO2 as a stabilizer has attached attention, since CeO2 stabilized zirconia ceramics have excellent low-temperature aging resistance between 100 °C and 300 °C [42]. In addition, the tetragonal solid solution band formed by CeO2 and zirconia has a wide range of compositions, which significantly reduces the phase transformation temperature for phase transformation toughening [43,44]. For the preparation of CeO2 doped stabilized zirconia ceramic, a heating process, usually a traditional arc heating method, is required to complete doping.
Under high-frequency microwave irradiation, zirconia ceramics were prepared by sintering nano-CeO₂ (Ce = 7 mol%) doped zirconia powder. The different effects of temperature environment on the phase structure transformation, surface functional groups, microstructure, growth process, and density of doped zirconia were analyzed, and the optimized microwave sintering process for zirconia was determined. The experimental results reveal that the tetragonal phase of zirconia is positively correlated with the temperature when the temperature reaches about 1100 °C in the studied range. The reason is that the grain grows with the increase of sintering temperature, and the surface energy of grain decreases, which leads to the fluctuation of tetragonal phase content. The density of zirconia reaches 98.03% at 1300 °C, and the growth activation energy is 27.40 kJ/mol. There is no abnormal growth of zirconia particles, and the phase transition temperature decreases, which is attributed to the efficient heating of microwave and the incorporation of nano-ceria stabilizer.
Effect of sintering programs and surface treatments on monolithic zirconia
2024, Journal of Advanced Prosthodontics
The effects of heating rate and sintering time on the biaxial flexural strength of monolithic zirconia ceramics
2023, Biomedizinische Technik
Laboratory, Clinical-Related Processing and Time-Related Factors’ Effect on Properties of High Translucent Zirconium Dioxide Ceramics Intended for Monolithic Restorations a Systematic Review
2023, Ceramics

View full text

Research and EducationEffects of sintering time and hydrothermal aging on the mechanical properties of monolithic zirconia ceramic systems

Abstract

Statement of problem

Purpose

Material and methods

Results

Conclusions

Section snippets

Material and methods

Results

Discussion

Conclusions

CRediT authorship contribution statement

Biomaterials

Biomaterials

Dent Mater

Dent Mater

Dent Mater

J Prosthet Dent

Dent Mater

J Prosthet Dent

Dent Mater

Ceram Int

J Prosthet Dent

J Prosthet Dent

Dent Mater

J Prosthet Dent

J Prosthet Dent

Dent Mater

Ceram Int

Choosing an all-ceramic restorative material: porcelain fused-to metal or zirconia based?

J Am Dent Assoc

Research and Education
Effects of sintering time and hydrothermal aging on the mechanical properties of monolithic zirconia ceramic systems