Fatigue strength of bilayered ceramics under cyclic loading as a function of core veneer thickness ratios

Abstract

Statement of problem: Minimal evidence is available concerning the appropriate thickness of each layer in bilayered ceramic systems.

Purpose: The purpose of this in vitro study was to examine the effect of core-veneer thickness ratios on the fatigue strength of a bonded bilayered ceramic system.

Material and methods: Specimens of Ivoclar Porcelain System (IPS) e.max lithium disilicate were fabricated with core/veneer thicknesses of 0.5/1.0 mm, 0.75/0.75 mm, 1.0/0.5 mm, and 1.5/0.0 mm. All specimens were cemented to bases of a dentin-like material. Each specimen was cyclically loaded by a 2-mm-diameter G10 piston in water. Loads ranging from 10 N to the target load were applied at a frequency of 20 Hertz for 500,000 cycles. If cracked, the next specimen was cycled at a lower load; if not cracked, at a higher load (step size of 25 N).

Results: Mean and standard deviations of fatigue loads for the different core thicknesses were 0.5-mm core 610.94 N ±130.11; 0.75-mm core 600.0 N ±132.80; 1.0-mm core 537.50 N ±41.67; a Nd 1.5-mm core 501.14 N ±70.12. All veneered groups were significantly stronger than the full thickness group (ANOVA, P<.001; 95% post hoc). Cone cracking was observed only in the 2 thinner core groups (χ(2) test, P<.05), possibly indicating residual stresses.

Conclusions: Results indicate that the addition of veneering porcelain to lithium disilicate cores increases the fatigue strength of the biceramic system.