Effect of ferrule, post and crown on anterior-teeth biomechanical behavior

Objectives: to evaluate the influence of post type, the ferrule presence and crown type on strain, resistance and fracture pattern of endodontically treated teeth.

Methods: 180 bovine incisor roots were selected, endodontically treated, and embedded in polystyrene resin simulating periodontal ligament. Roots were divided into 2 groups prepared with 2.0mm ferrule (Fe) and no ferule (NFe). Each group was divided into 3 subgroups and teeth were reconstructed with: (Cpc) NiCr-cast-post and core; (Gfp)glass-fiber-post and composite resin core; (GfpRc)glass-fiber-post associated with fiber-glass coronal portion. Half of the samples (n=15) of each subgroup was restored with metallic crowns (Cm) and the other half restored with all-ceramic crowns (Cc). For strain-gauge test the 100N loading was applied. Strain was measured on the proximal root surfaces. The fracture resistance was assessed by compressive loading in universal test machine. Fracture modes were analized. Data were analyzed using 3way-ANOVA and Tukey test (p<0.05). Results: The fracture resistance values (N) were: Cpc: Fe/Cc:910.1±237.8^a; Fe/Mc:902.9±252.5^a; Nfe/Cc:796.3±181.0^b; NFe/Mc:656.7±239.8^d; Gfp: Fe/Cc:919.9±285.1^a; Fe/Mc:910.4±272.8^a; NFe/Cc:712.7±165.0^ab; NFe/Mc:570.0±147.8^b; GfpRc: Fe/Cc:945.6±224.8^a; Fe/Mc:919.3±273.8^a; NFe/Cc:719.5±207.4^ab; NFe/Mc:572.0±117.1^b. Strain values (μS) were: Cpc: Fe/Cc:52.2±27.2^a; NFeCc:70.7±35.1^b; Fe/Mc:80.0±49.0^c; NFe/Mc:90.8±51.2^d; Gfp: Fe/Cc:59.2±19.8^a; NFe/Cc:72.9±19.2^b; Fe/Mc:80.9±43.3^c; NFe/Mc:113.2±53.7^d; GfpRc: Fe/Cc:51.2±19.9^a; Fe/Mc:69.2±19.8^b; NFe/Cc:88.8±50.3^c; NFe/Mc:130.2±57.1^d. When ferrule was present, strain and fracture resistance values were no influenced by any factor tested. The ferrule presence or use of Cpc resulted in better biomechanical performance for Mc-groups. The presence or absence of ferrule no influenced the fracture resistance and strain for Cc groups irrespective of the post system. Fracture-modes of Gfp and GfpRc groups were less catastrophics then of Cpc-groups. Mc resulted in more catastrophic fractures then Cc.

Conclusion: Biomimetic reproduction of the human tissue by association of Gfp or GfpRc, which are mechanically similar to dentin, associated with Cc, which is mechanically similar to enamel, produced the best mechanical behavior in all conditions tested.