Fracture strength of restored premolars

To evaluate the fracture resistance (axial compressive strength) of premolars restored with different dental materials under two axial loads.

Fracture strength was performed using two metal spheres with 3 mm and 9 mm diameter. Five restorative techniques were chosen for MOD cavity preparations (n = 10): (1) direct resin composite restorations (Z-250); (2) indirect resin composite restorations (Z-250 and RelyX); (3) ceramic inlays (Vitadur Alpha); (4) conventional amalgam restorations (GS-80); (5) bonded amalgam restorations. The restored teeth were compared to human caries-free premolars (Group 6/control). Enforce resin cement was used for ceramic and amalgam adhesive restorative techniques, according to the manufacturers' instructions. Whenever required, the teeth were conditioned by the total etch technique.

The ANOVA analysis pointed out a significant difference among the groups (P < 0.01) and the "site" factor (P < 0.1). The ceramic restorations presented the highest values for fracture strength and were similar to the control group. The statistical results of direct and indirect resin composite restorations were similar but inferior to the control group. The amalgam restorations (conventional and bonded) presented the lowest values, with no difference between them. All amalgam groups displayed lower strengths when the load was applied on the central fossa (3 mm 0 sphere) compared to load applied on cusps (9 mm 0 sphere).