Can adhesive cementation improve the strength of glass-ceramics by filling surface defects?

The susceptibility of glass-ceramics to surface defects can weaken their mechanical performance.

The aim of the present study was to investigate the effect of cementation on the load-to-failure of 2 glass-ceramic materials in the presence and absence of an induced surface defect.

Bars of lithium disilicate - LD (Initial LiSi Block; GC Dental) and feldspathic - F (VITA Mark II; VITA Zahnfabrik H. Rauter) ceramics, as well as a dentin analog, were prepared for cementation. The ceramic specimens were assigned to 5 groups: untreated (no cementation); indented (I); cemented (C); indented and cemented with defect filling (CI); and indented and cemented without defect filling (CIN). Flexural strength was measured for the non-cemented specimens, whereas the load-to-failure was evaluated for all cemented groups, using the ball-in-hole test on bar specimens (1 × 1 × 12 mm). Finite element analysis (FEA) was performed for the groups without induced defects. Data was analyzed using the one-way analysis of variance (ANOVA) and Tukey's post hoc test (α = 0.05).

One-way ANOVA revealed significant differences among the groups for both materials (p < 0.001). For LD, the load-to-failure values were: LDC (16.7 ±2.9 N)A > LD (14.6 ±2.6 N)B = LDCI (13.9 ±3.0 N)B > LDCIN (10.5 ±1.7 N)C > LDI (6.9 ±1.4 N)D. For F, the values were: FC (13.7 ±3.7 N)A = FCIN (13.1 ±3.3 N)A = FCI (11.8 ±3.3 N)A > F (8.1 ±1.3 N)B > FI (5.1 ±0.4 N)C. Indentation significantly reduced the flexural strength of the non-cemented ceramics (p < 0.001). Finite element analysis showed that cementation reduced the maximum principal tensile stress by 44% for LD and by 62% for F.

Filling surface defects with cement increased the load-to-failure of LD, but did not significantly affect F. Overall, the mechanical performance of both glass-ceramics was influenced by the cementation process, whereas the effect of defect filling was material dependent.