EFFECT OF RESIN-BASED MATERIALS ON FRACTURE RESISTANCE OF ENDODONTICALLY TREATED THIN-WALLED TEETH

Statement of problem. Composite resins are recommended for root reinforcement, but little information exists about self-adhesive resin cements that eliminate the acid etching and bonding steps. Purpose. The purpose of this study was to compare the fracture resistances of teeth restored with 2 different diameters of cast and fiber posts and to evaluate the effectiveness of increasing internal root thickness with 2 resin-based materials to reinforce thin-walled teeth. Material and methods. Ninety maxillary incisors were endodontically treated and divided into 9 groups. In the first 4 groups, teeth were restored with tapered end cast (C1.3 and C1.7) and fiber (F1.3 and F1.7) posts of 1.3 and 1.7 mm diameters. In the other 5 groups, the root canals were enlarged to simulate the thin-walled teeth and restored with low viscosity composite resin with fiber posts of 1.3 and 1.7 mm diameters (LF1.3 and LF1.7), self-adhesive resin cement with fiber posts of 1.3 and 1.7 mm diameters (SF1.3 and SF1.7), and cast posts of 4 mm diameter that fit in post spaces (C4). Teeth were loaded to fracture at a 135-degree angle to their long axis. Data were analyzed with 2-way ANOVA and the Tukey HSD test (alpha=.05). Results. Significant difference (P<.001) existed between the fracture resistances of the teeth restored with cast (C1.3, 588.4 +/-72.7 N) and fiber (F1.3, 375.3 +/-53.8 N) posts of 1.3 mm diameter; however, no significant difference was found between 1.3 and 1.7 mm post diameters. The teeth restored with the resin-based materials with fiber posts, groups SF1.3 (331.6 +/-135.2 N), SF1.7 (535.7 +/-134.4 N), LF1.3 (432.1 +/-120.3 N) and LF1.7 (563.8 +/-128.8 N), demonstrated fracture resistance values similar to or higher than those of the teeth restored with the fiber posts, groups F1.3 (375.3 +/-53.8 N) and F1.7 (461.8 +/-98.4 N). The parallel-sided cast posts C4 (799.8 +/-228.9 N) of 4 mm diameter demonstrated the highest fracture resistance of all groups (P<.001). Conclusions. The fracture resistance of the teeth increased as the elastic modulus of the posts increased but was not affected by small diameter variations of the posts. The resin-based materials were able to preserve and reinforce the remaining tooth structures.