Effect of Thickness Ratio on Load‐Bearing Capacity of Bilayered Dental Ceramics

Abstract

The residual thermal stresses in the core layer have slightly beneficial effects on the strength of the beams. The first strength theory can be used to explain the mechanism of failure, which can be described as the failure is interpreted by tensile stress and ultimate strength of the material. Based on the relationship between the thickness ratio and load-bearing capacity, the core/veneer thickness ratio of the connector of a fixed partial denture could be relatively small to about 1:2 to obtain a good appearance.

Influence of Core‐Veneer Thickness Ratio on the Fracture Load and Failure Mode of Zirconia Crowns

“…The effect of the CTE mismatch and thermal behavior on the performance of bilayered all‐ceramic systems has been frequently discussed in the dental literature . In an effort to generate acceptable levels of residual stresses within the veneering ceramic, dental manufacturers have developed ceramic cores and low‐fusing ceramics with similar CTEs .…”

“…Studies have emphasized the importance of design and thickness of the cores and of the veneering ceramics on the mechanical strength of restorations and stress distribution. The core‐veneer thickness ratio and the core design are reported as influencing the reliability of all‐ceramic restorations, particularly Y‐TZP restorations . The recommended approach to prevent chipping and residual thermal stresses between core and veneer is to ensure optimal support to veneering ceramic by providing a thicker core, yet avoiding excessive thickness …”

“…Aside from material thickness, cooling rate is another factor that could strongly affect the clinical longevity of restorations, and that plays an important role in stress accumulation in the structure . Alternatives have been studied for reducing residual thermal stresses in Y‐TZP restorations by managing the cooling rates.…”

“…In years past, cores have often been generically milled to arbitrary thicknesses, and have sometimes considered only a patient's anatomic needs . It has been suggested that a 1 to 1 (1:1) ratio of core to veneering ceramic thickness may provide reasonable strength, esthetics, and fabrication tolerance . However, the importance of adequate core thickness may be paramount, since a higher ratio between core and veneer thickness (1:3) may be required to obtain a desired esthetic outcome of the restoration.…”

“…Moreover, the core‐veneer thickness ratio and the properties of the veneering material affect the strength of bilayered restorations, as well as the ideal core proportion for sufficient support of the veneering material is difficult to determine . Several studies addresses an increase in the strength of bilayered systems as core‐veneer thickness increases, although others have found that strength has not being dependent on relative layer thicknesses . These contradictory findings suggests the need for more investigation to optimize the core‐veneer thickness ratio required for different all‐ceramic restorations.…”