Biomechanical analysis of the restorative procedure of endodontically treated anterior-teeth

Objectives: To investigate in vitro the effects of different post systems and lengths on stress distribution, strain and fracture resistance of endodontically treated teeth.

Methods: 135 bovine incisors were sectioned 15mm from apex and have root filled, embedded in polystyrene resin simulating periodontal ligament. Roots were divided into 3 groups (n=45): fiber-glass-post (Fgp); prefabricated-steel-post (Psp); cast-post and core (Cpc). Each group was divided into 3 subgroups (n=15) according to post length: L5- 5.0 mm; L7.5- 7.5 mm; L10- 10.0 mm. All teeth were restored with metal crowns. For strain-gauge test, 2 strain-gauges per sample were used. The fracture resistance was assessed by compressive loading in universal test machine. Data were analyzed with 2-way ANOVA and Tukey HSD test (p<0.05). Finite element analysis was realized by 2D-models and the stress distribution was analyzed by von Mises criterious. Results: Fracture resistance values (N) were: Fgp- L10:618.5±177.5^Aa, L7.5:615.5±127.7^Aa, L5:607.2±139.7^Aa; Cpc- L10:769.9±68.5^Aa, L7.5:540.0±86.2^Bab, L5:399.2±90.0^Cb; Psp- L10:698.8±96.8^Aab, L7.5:502.8±134.7^Bb, Pl5:390.2±94.6^Cb. Strain values (μS) were: Fgp- L10: 78±22^Aa, L7.5:80±15^Aa, L5: 80±15^Aa; Cpc- L10: 90±25^Aab, L7.5: 130±44^Bb, L5: 200±93^Cb, Psp- L10:106±44^Ab, L7.5:138±44^Bb, L5: 216±57^Cb (Capital letters represent analysis among length post for each post system and lower case letter represent analysis among post systems for each length). Strain values were lowers in Fgp groups than Cpc and Psp groups. Fracture modes of Cpc and Psp groups were no reparable and all fracture modes of Fgp were reparable. Stress distribution of Cpc and Psp concentrated into root dentin- post interface. Fgp showed homogeneous stress distribution.

Conclusions: The cast post and core with 10.0 mm showed the highest fracture resistance; however the fiber-glass-post was effective with the three post lengths, showing higher fracture resistance than metal posts when the length was 5.0 mm with lower strain levels and the best stress distribution.