Fracture resistance of re-attached coronal fragments – influence of different adhesive materials and bevel preparation

Abstract – The purpose of this study was to investigate the fracture resistance of re‐attached coronal fragments of teeth using different materials and tooth preparations. Seventy‐two recently extracted bovine incisors were selected. Eight incisors were maintained without any preparation as a control group. The incisal third of the other teeth was sectioned using a diamond saw. In one group (n = 32), a 2‐mm bevel was prepared, whereas in the second group no preparation was made (n = 32). The specimens (beveled and non‐beveled) were divided in four groups (n = 8) and re‐attached with the following materials: a dual‐cured resin cement RelyX ARC (RX); a chemically cured composite Bisfil 2B (B2); a light‐cured composite Z250 (Z2); and a one‐bottle adhesive Single Bond (SB). The bevel region was restored with adhesive and composite. All materials were used according to manufacturer's directions. A light‐curing unit was used to polymerize the materials. Specimens were stored in saline solution for 72 h. De‐bonding procedures were performed in a testing machine with cross‐head speed of 0.6 mm min^?1. The load was applied in the incisal third. The resistance to fracture for control group was 70 (7) kg. The fracture resistance for non‐beveled and beveled specimens were: SB, 3.3 (2.4) and 17.0 (4.1); RX, 11.5 (3.0) and 16.3 (3.1); Z2, 14.4 (4.2) and 20.5 (1.7); and B2, 19.5 (3.5) and 32.5 (7.4) kg. Analysis of variance (anova ) and Fisher's protected least significant difference (PLSD) test disclosed significant influence for materials and cavity designs (P = 0.001). The highest failure loads were obtained with the B2 group and then with the Z2 with either bevel or non‐bevel. RX produced lower failure loads than the restorative composites. The lowest failure load was obtained with SB in the non‐beveled group. No technique studied was able to attain the fracture resistance of the control group and both materials and tooth preparation influenced the fracture resistance.