Full text
| |
| Author(s): |
Flávia Pires Rodrigues
Total Authors: 1
|
| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Faculdade de Odontologia (FO/SDO) |
| Defense date: | 2009-02-18 |
| Examining board members: |
Rafael Yague Ballester;
Leonardo Gonçalves Cunha;
Estevao Tomomitsu Kimpara;
Raul Gonzalez Lima;
Nikolaos Silikas
|
| Advisor: | Rafael Yague Ballester |
| Abstract | |
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 \'glue\' contact 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 volume\' of 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 volume\' of 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. (AU) | |
| FAPESP's process: | 06/00186-3 - Interfering factors in the mechanical requirement of adhesive restoration interfaces and solutions to reduce them |
| Grantee: | Flávia Pires Rodrigues |
| Support Opportunities: | Scholarships in Brazil - Doctorate |