Factors predicting the shrinkage stress for Class I bonded restorations interface / Fatores preditores da tensão de contração para interfaces de restaurações adesivas em cavidade de classe I

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

OBJECTIVES: The C-Factor is normally used to predict the shrinkage stress at composite-tooth interfaces. A study was outlined for clarifying the elements which allows providing the stress at bonded restorations interface. Theoretically, the stress varies as a function of the opposition to the shrinkage (substrate stiffness), the compliance, dimensions and mechanical properties of the composite. METHODS: Eight 3D non-linear stylized models of Class I cavities were obtained by the Finite Element Method (FEM), maintaining the volume (20 mm3) and wall thickness (2 mm) constant and varying the C-Factor (1.9 through 13.5). A gluecontact between the composite and teeth was simulated. A 1% polymerization shrinkage was simulated by using thermal analogy of the composite. Principal stresses and strains were analyzed. A method for calculating the local compliance by FEM was also idealized as well as its validity of comparing the obtained result with the analytical compliance value of a 1 mm dentin cube, with fixation at one of its faces. A method for calculating, for each cavity shape, the useful volumeof the composite, which is able to influence on the stress peak increase at the interface, was further idealized. And finally, using elements mentioned before, a compliance dependent value, so-called CA-Factor, was calculated for each cavity, at peak and useful volumeof the composite regions. The capability on predicting the stress peak by the correlation test (Pearson) between the stress peak and the CA-Factor as well as between the stress peak and the C-Factor was also evaluated. RESULTS: the stress peaks generated by the shrinkage on Class I cavities tend to decrease as a function of the C-Factor, though the Pearson only showed the significance for the maximum principal stress at the XZ wall and Z axis. The local compliance calculation obtained by FEM was 0.0652 m/N, which was very close to the analytical one (0.0666 m/N). The CA-Factor presented a positive and significant correlation with all three stresses obtained at the trihedral angle formed by two occlusal edges. (Von Mises, maximum principal and maximum shear stresses). CONCLUSION: the increase of the C-Factor does not lead to the increase of the stress peaks in Class I cavities. The method for calculating the compliance is valid for complex structures. The CA-Factor allows providing the stress peaks for bonded composites on Class I cavities.

ASSUNTO(S)

classe i restaurações adesivas tensão de contração class i elementos finitos bonded restorations interface finite elements shrinkage stress fator-c c-factor interface

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