Finite element analysis of bonded model Class I 'restorations' after shrinkage.
OBJECTIVE
The C-Factor has been used widely to rationalize the changes in shrinkage stress occurring at the tooth/resin-composite interfaces. Experimentally, such stresses have been measured in a uniaxial direction between opposed parallel walls. The situation of adjoining cavity walls has been neglected. The aim was to investigate the hypothesis that: within stylized model rectangular cavities of constant volume and wall thickness, the interfacial shrinkage-stress at the adjoining cavity walls increases steadily as the C-Factor increases.


METHODS
Eight 3D-FEM restored Class I 'rectangular cavity' models were created by MSC.PATRAN/MSC.Marc, r2-2005 and subjected to 1% of shrinkage, while maintaining constant both the volume (20 mm(3)) and the wall thickness (2 mm), but varying the C-Factor (1.9-13.5). An adhesive contact between the composite and the teeth was incorporated. Polymerization shrinkage was simulated by analogy with thermal contraction. Principal stresses and strains were calculated. Peak values of maximum principal (MP) and maximum shear (MS) stresses from the different walls were displayed graphically as a function of C-Factor. The stress-peak association with C-Factor was evaluated by the Pearson correlation between the stress peak and the C-Factor.


RESULTS
The hypothesis was rejected: there was no clear increase of stress-peaks with C-Factor. The stress-peaks particularly expressed as MP and MS varied only slightly with increasing C-Factor. Lower stress-peaks were present at the pulpal floor in comparison to the stress at the axial walls. In general, MP and MS were similar when the axial wall dimensions were similar. The Pearson coefficient only expressed associations for the maximum principal stress at the ZX wall and the Z axis.


CONCLUSIONS
Increase of the C-Factor did not lead to increase of the calculated stress-peaks in model rectangular Class I cavity walls.
Biomaterials Research Group, School of Denstistry, Anhanguera-Bandeirante University of São Paulo, São Paulo, Brazil. flapiro@gmail.com
Flávia P
FP
Rodrigues
Nick
N
Silikas
David C
DC
Watts
Rafael Y
RY
Ballester
D001696:Biomechanical Phenomena; D003188:Composite Resins / Q000737:chemistry*; D003198:Computer Simulation; D001840:Dental Bonding; D003737:Dental Cavity Preparation / Q000145:classification; D003743:Dental Enamel / Q000473:pathology; D003764:Dental Materials / Q000737:chemistry*; D003782:Dental Pulp / Q000473:pathology; D003793:Dental Restoration, Permanent / Q000145:classification*; D003804:Dentin / Q000473:pathology; D055119:Elastic Modulus; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008422:Materials Testing; D008954:Models, Biological; D058105:Polymerization; D013314:Stress, Mechanical; D013499:Surface Properties; D013816:Thermodynamics
D003188:Composite Resins; D003764:Dental Materials