Effects of porcelain thickness on the flexural strength and crack propagation in a bilayered zirconia system

Abstract

Objective:This study evaluated the influence of porcelain (VM9, VITA Zahnfabrik, Germany) thickness on the flexural strength and crack propagation in bilayered zirconia systems (YZ, VITA Zahnfabrik, Germany).Material and Methods:Thirty zirconia bars (20.0x4.0x1.0 mm) and six zirconia blocks (12.0x7.5x1.2 mm) were prepared and veneered with porcelain with different thickness: 1 mm, 2 mm, or 3 mm. The bars of each experimental group (n=10) were subjected to four-point flexural strength testing. In each ceramic block, a Vickers indentation was created under a load of 10 kgf for 10 seconds, for the propagation of cracks.Results:The results of flexural strength were evaluated by One-way ANOVA and Tukey's test, with a significance level of 5%. The factor “thickness of the porcelain” was statistically significant (p=0.001) and the l-mm group presented the highest values of flexural strength. The cracks were predominant among the bending specimens with 1 and 2 mm of porcelain, and catastrophic failures were found in 50% of 3-mm-thick porcelain. After the indentation of blocks, the most severe defects were observed in blocks with 3-mm-thick porcelain.Conclusion:The smallest (1 mm) thickness of porcelain on the zirconia infrastructure presented higher values of flexural strength. Better resistance to defect propagation was observed near the porcelain/ zirconia interface for all groups. Higher flexural strength was found for a thinner porcelain layer in a bilayered zirconia system. The damage caused by a Vickers indentation near and far the interface with the zirconia shows that the stress profiles are different.

Biaxial Flexural Strength of High-Translucence Monolithic Ceramics upon Various Thicknesses

“…This study clearly indicated that when the thickness was varied, neither monolithic HTY-PSZ nor ZLS had any significant effect on flexural strength. The result of this study does not correspond with that of some other studies which reported an increase in flexural strength as the thickness of the ceramic increased [ 1 , 13 , 21 , 24 ]. This was probably due to the fact that the testing methodology of this study was different from the methodology adopted in the other studies.…”

“…e thickness of restorations may influence the durable ability to withstand the ceramic fracture [14][15][16][17][18][19]. Previous studies found that the thickness of ceramic strongly influenced the strength of ceramic restoration [13,20,21]. e thickness of 0.5-1 mm was recommended for the margin of all ceramic restorations with a slightly rounded internal angle to reduce the stress at the line angle that frequently initiated fracture [22,23].…”

Shear Bond Strength of Colored and Sandblasted Zirconia to Ceramic Veneers Fabricated by the Pressing and Layering Techniques: An In Vitro Study

“…Several parameters may affect the bond strength of zirconia to porcelain such as porcelain thickness [ 7 ], porcelain-veneering technique [ 8 ], and type of zirconia surface treatment (such as coloring [ 9 ] and sandblasting [ 10 ]). However, the results are controversial regarding the effect of sandblasting on bond strength of zirconia.…”

Influence of ceramic primers on microshear bond strength to zirconia

“…However, this zirconia polymorphic transformation can be prevented by adding oxides (3 to 6% of CaO, MgO, Y2O3, or CeO2), which restricts the volume increase by stabilizing the tetragonal phase. If a crack grows in the zirconia, the tetragonal crystals are transformed into the monoclinic phase, resulting in a volume expansion of 3% that induces compressive stress and interrupts crack propagation (Figueiredo et al 2017). This mechanism represents an increase in material strength, thus zirconia is known as a "smart" ceramic (Badami and Ahuja 2014).…”