Favorable residual stress induction by resin-cementation on dental porcelain.

OBJECTIVES: Despite developments in polycrystalline ceramics, glassy dental-ceramic materials provide the optimum cosmetic option in most clinical situations to mimic the natural dentition. The clinical success of glassy dental-ceramic materials is often attributed to resin-adhesive bonding techniques. In this study we explore whether shrinkage stresses generated on photo-polymerisation of the resin-cement are sufficient to induce ceramic surface defect stabilization, and we quantify the transient nature of the induced stresses. METHODS: Stress-induced changes in a feldspathic ceramic over a range of thicknesses (0.5-2.0mm: n=20 per thickness) were measured using a profilometric technique at baseline for each disc-shaped specimen (mean of the maximum deflection (delta(baseline))) and again following polymerisation of a controlled resin-cement thickness on the contra-lateral surface. Measurements were repeated at 30, 60, 90 and 1440min following photo-polymerization (delta(30), delta(60), delta(90) and delta(1440), respectively) before bi-axial flexure strength (BFS) determination at 24h. RESULTS: A repeated measures ANOVA and post-hoc Bonferroni tests determined that delta(1440) was significantly different from delta(baseline) (p=0.02), delta(30) (p<0.01) and delta(60) (p<0.01) but not delta(90) (p=0.61). Data exploration revealed that there were differences in directionality of the independent variable (mean of the maximum deflection (delta)) with a proportion of specimens increasing in deflection and others reducing. The directionality of the effect strongly correlated with the BFS values. Where delta(1440)-delta(baseline) was low and/or negative, BFS values were also low. High BFS values were observed when delta(1440)-delta(baseline) was large and positive (indirectly inferring high shrinkage-stress-induced-deformation). SIGNIFICANCE: A link between shrinkage stresses associated with the photo-polymerization of dental resin-based cements and the reinforcement of dental porcelain has clearly been established.