Residual shrinkage stress distributions in molars after composite restoration.
OBJECTIVE
Experimental measurements on various restoration configurations have shown that restored teeth deform under the influence of polymerization shrinkage, but actual residual stresses could not be determined. The purpose of this study was to calculate and validate shrinkage stresses associated with the reported tooth deformations.


METHODS
Three different restoration configurations were applied in a finite element model of a molar. The composite properties were based on experimentally determined composite behavior during polymerization. The occlusal deformation pattern and the residual stress states of the tooth, restoration, and tooth-restoration interface were calculated using a polymerization model based on the post-gel shrinkage concept. Reported strain gauge measurements and occlusal deformation patterns were used for validation.


RESULTS
The shrinkage stresses depended on the configuration and size of the restorations. The tooth's resistance against polymerization shrinkage diminished with loss of dental hard tissue. Larger restorations resulted in lower stress levels in the restoration and tooth-restoration interface, but increased stresses in the tooth. The maximum stress values found for different configurations were not decisively different.


CONCLUSIONS
The validated model indicated that shrinkage stress cannot be based on composite properties or restoration configuration alone, but has to be approached as a distributed pattern that depends on the location and on the properties of tooth and restoration, geometry, constraints, and restoration procedures. Tooth deformation was indicative of stresses in the tooth rather than in the restoration or across the tooth-restoration interface.
Versluis
Antheunis
A
Department of Oral Science, Minnesota Dental Research Center for Biomaterials and Biomechanics, University of Minnesota, 16-212 Moos Tower, 515 Delaware Street SE, Minneapolis 55455, USA. antheun@umn.edu
Tantbirojn
Daranee
D
Pintado
Maria R
MR
DeLong
Ralph
R
Douglas
William H
WH
D003188:Composite Resins / Q000528:radiation effects*; D003737:Dental Cavity Preparation; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent / Q000009:adverse effects*; D003799:Dental Stress Analysis; D004548:Elasticity; D020342:Finite Element Analysis; D006244:Hardness; D006801:Humans; D008027:Light; D008956:Models, Chemical; D008963:Molar; D015394:Molecular Structure; D044367:Phase Transition; D012822:Silicon Dioxide; D019228:Tooth Crown / Q000473:pathology*; D015040:Zirconium
D003188:Composite Resins; C083568:Z100 composite resin; D012822:Silicon Dioxide; D015040:Zirconium