Influence of resin cements on cuspal deflection and fracture load of endodontically-Treated teeth restored with composite inlays

Objectives. To evaluate the influence of resin cements on cuspal deflection, fracture load and failure mode of endodontically-Treated teeth restored with composite resin inlays. Materials and methods. Forty maxillary premolars were randomly divided into four groups: G1 (sound teeth, control), G2 (RelyX ARC), G3 (RelyX Unicem) and G4 (Maxcem Elite). The teeth from groups 2, 3 and 4 received mesial-occlusal-distal preparations and endodontic treatments. Impressions were taken with vinyl polysiloxane and poured using type IV die stone. Inlays with Z250 composite resin were built over each cast and luted with the resin cements. A 200-N load was applied on the occlusal surface and the cuspal deflection was measured using a micrometer. The specimens were then subjected to an axial load until failure occurred. The resulting failure mode was analyzed. Results. The means for cuspal deflection (μm) and fracture load (N) followed by the same letter represent no statistically significant difference based on ANOVA and Tukey's test (p < 0.05). Cuspal deflection: G1 = 4.7 (±1.7)^a, G2 = 12.0 (±8.9)^a, G3 = 39.0 (±27.0)^b and G4 = 56.8 (±18.2)^b. Fracture load: G1 = 1982 (±893)^a, G2 = 690.9 (±225.5) ^b, G3 = 679 (±193.6)^b and G4 = 465.5 (±121.6)^b. G1 presented cusp fractures only at the cement-enamel junction (CEJ). There was a high frequency of cusp fractures below the CEJ in G2, G3 and G4. Conclusions. Composite resin inlays luted with resin cements do not recover the strength of sound teeth. However, teeth restored with composite resin inlays and luted with RelyX ARC can withstand mechanical fatigue longer before failure occurs than those luted with RelyX Unicem and Maxcem Elite.