Effect of posts and materials on flared teeth's mechanical behavior

Objectives: Assess the effect of different post systems and restorative techniques on stress-strain behavior and fracture resistance of flared roots.

Methods: The coronary portion was removed from 105 bovine incisors, leaving a 15.0 mm root. After endodontic treatment samples were embedded in polystyrene resin and the periodontal ligament was simulated. The specimens were divided into 7 groups (n=15) and the roots of two reference groups were restored with cast post and core (CPC – G1) and fiber-glass post (FGP – G2). In the other groups, root canal were flared and restored with CPC (G3); FGP (G4); FGP and accessories FGP (G5); and FGP directly (G6) or indirectly (G7) rebased with accessories FGP and composite resin. All teeth were restored with all-metal crowns. Samples were submitted to mechanical fatigue (3x10⁵ cycles of 50N). Strain-gauges were attached to the roots and strain values (µS) were obtained under a 100N load. Fracture resistance (N) was tested with a oblique load at a 0.5 mm/min cross-head speed. Data were analyzed with one-way ANOVA and Tukey HSD test (p<0.05). Failure mode was classified in accordance to the degree of dental structure destruction. Bi-dimensional finite element analysis was performed with representative models of each group, based on von Mises stress distribution criteria.

Results: The results (N) were: G6- (867.9±198.1)a; G1- (859.9±199,2)a; G7- (847±112.2)a; G5- (842.7±174)a; G2- (627.1±119,8)b; G4- (625.3±164,3)b; G3- (620.2±164.2)b. There was no significant difference in the strains measured among groups, however, CPC increase catastrophic failures. Finite element analyses revealed higher stress concentration in CPC than in FGP, irrespective of restorative technique.

Conclusion: Fiber-glass posts associated with composite resin or with accessory fiber-glass posts seem to be more indicated as alternative to cast post and core in flared roots, because of the lower risk of catastrophic failures and better stress distribution.