Comparison of four monolithic zirconia materials with conventional ones: Contrast ratio, grain size, four-point flexural strength and two-body wear

Abstract

OBJECTIVES: To test the mechanical and optical properties of monolithic zirconia in comparison to conventional zirconia. MATERIALS AND METHODS: Specimens were prepared from: monolithic zirconia: Zenostar (ZS), DD Bio ZX2 hochtransluzent (DD), Ceramill Zolid (CZ), InCoris TZI (IC) and a conventional zirconia Ceramill ZI (CZI). Contrast ratio (N=75/n=15) was measured according to ISO 2471ISO :2008. Grain sizes (N=75/n=15) were investigated with scanning electron microscope. Fourpoint flexural strength (N=225/n=15/zirconia and aging regime) was measured initially, after aging in autoclave or chewing simulator (ISO 13356:2008). Two-body wear of polished and glazed/veneered specimens (N=108/n=12) was analyzed in a chewing simulator using human teeth as antagonists. Data were analyzed using 2-/1-way ANOVA with post-hoc Scheffé, Kruskal-Wallis-H, Mann-Whitney-U, SpearmanRho, Weibull statistics and linear mixed models (p<0.05). RESULTS: The lowest contrast ratio values were found for ZS and IC and CZ. IC showed the largest grain size followed by DD and CZI. The smallest grain size was observed for ZS followed by CZ. There was no correlation between grain size and contrast ratio. The aging regime showed no impact on flexural strength. All non-aged and autoclave-aged specimens showed lower flexural strengths than the control group CZI. Within groups aged in chewing simulator, ZS showed significantly lower flexural strength than CZI. CZI showed higher material and antagonist wear than monolithic polished and glazed groups. Glazed specimens showed higher material and antagonist loss compared to polished ones. There was no correlation between roughness and wear. CONCLUSIONS: Monolithic zirconia showed higher optical, but lower mechanical properties than conventional zirconia. (ISO 13356:2008). Two-body wear of polished and glazed/veneered specimens (N=108/n=12) was analyzed in a chewing simulator using human teeth as antagonists. Data were analyzed using 2-/1-way ANOVA with post-hoc Scheffé, Kruskal-Wallis-H, Mann-Whitney-U, Spearman-Rho, Weibull statistics, and linear mixed models (p<0.05).Results. The lowest contrast ratio values were found for ZS and IC and CZ. IC showed the largest grain size followed by DD and CZI. The smallest grain size was observed for ZS followed by CZ. There was no correlation between grain size and contrast ratio. The aging regime showed no impact on flexural strength. All non-aged and autoclave-aged specimens showed lower flexural strengths than the control group CZI. Within groups aged in chewing simulator, ZS showed significantly lower 3 flexural strength than CZI. CZI showed higher material and antagonist wear than monolithic polished and glazed groups. Glazed specimens showed higher material and antagonist loss compared to polished ones. There was no correlation between roughness and wear.Conclusions. Monolithic zirconia showed higher optical, but lower mechanical properties than conventional zirconia.

Effect of ceramic thickness, grinding, and aging on the mechanical behavior of a polycrystalline zirconia

“…39 Thus, the increased resistance to hydrothermal degradation after grinding is possibly related to the existence of this very thin layer of tetragonal recrystallized nano-grains (10-20 nm) that are smaller than the critical size for transformation in humid environment, in addition to the presence of residual compressive stress on the surface of Y-TZP ceramics. 39,40 Although the tested Y-TZP ceramic consists of a new translucent material, and therefore alterations on microstructure and composition (that are not clearly stated by the manufacturer) may be expected in comparison to conventional Y-TZP ceramics 4 , our data support a similar performance of the tested ceramic to the ones that have been evaluated by previous studies. 15,16,17,18,19 Finally, we showed that the protocols for grinding and aging used by this study do not promote a deleterious effect on the mechanical properties of Y-TZP ceramic, regardless of the ceramic thickness.…”

“…3,4 The major advantage of monolithic restorations is that they allow a substantial reduction of ceramic thickness by eliminating Rodrigo Diniz PRADO (a) Gabriel Kalil Rocha PEREIRA (b) Marco Antonio BOTTINO (a) Renata Marques de MELO (a) Luiz Felipe VALANDRO (b) the veneer layer without compromising the final strength of the system. Thus, this assembly results in a more conservative tooth preparation and decreased removal of tooth structure.…”

Dental ceramics: a review of new materials and processing methods

“…Considering the thickness of 0.5 mm, traditional Y-TZP shows contrast ratio (CR) values that are higher (0.77) than those of monolithic Y-TZPs (0.57 to 0.62). 13 In addition to the mechanical and optical properties, another important characteristic for the long-term success of a restoration is the wear of the antagonist enamel and the marginal adaptation. Fortunately, laboratory studies have shown that monolithic zirconia usually causes a rather comparable wear of the antagonists in comparison to other restorative ceramics, and this wear rate is within the physiological range reported in the literature.…”

“…Some of these studies compared different surface finishing techniques for monolithic zirconia restorations, such as polishing versus glazing, and found that polished surfaces resulted in less enamel wear of the antagonist. 13,14,15,16 It is needless to say that the high surface hardness of zirconia has a major influence on the antagonist wear and a perfect polish of any monolithic zirconia restoration is therefore very important. A clinical study evaluated the occlusal surface wear of monolithic zirconia crowns placed in premolars and molars.…”

Efeito da coloração nas propriedades mecânicas e ópticas de cerâmicas odontológicas à base de zircônia

“…Por outro lado, uma pressão excessiva pode introduzir defeitos na microestrutura do material e também induzir uma não uniformidade da densidade ao longo do bloco. Existem evidências na literatura mostrando que defeitos originados durante a prensagem são frequentemente a origem da fratura de estruturas de Y-TZP para uso dentário (31)(32)(33)(34)(35)(36).…”