Comparison of polymerization contraction stresses between self- and light-curing composites.
OBJECTIVE
The objective of this study was to examine the distributions and the magnitudes of the internal stresses in self- and a light-curing composite restorations resulting from polymerization shrinkage.


METHODS
Butt-joint box-shaped cavities (5.0 x 2.0 mm2, 2.0 mm in depth) prepared in composite molds were filled with either a self- or light-curing transparent resin composite. The restorations were cross-sectioned perpendicular to the longitudinal axes of the cavities and observed using polarizing microscopes. The principal stresses in the restorations, normal and shear stresses at the cavity wall were evaluated by photoelastic analysis.


RESULTS
The distributions of the principal stresses and the stresses generated at the cavity wall in both the self- and the light-curing composite restorations were similar. The maximum stress generated at the cavity wall in the light-curing composite restorations was twice as large as that seen in the self-curing restorations.


CONCLUSIONS
The results of this study indicated that the difference in the magnitude of the internal stresses between self- and light-curing composites was not related to the distribution of the stresses. The velocity of polymerization appeared to be the most important factor contributing to the magnitude of the internal stresses generated in the composite restorations in this study.
Kinomoto
Y
Y
Department of Conservative Dentistry, Osaka University Faculty of Dentistry, Japan. kinomoto@dent.osaka-u.ac.jp
Torii
M
M
Takeshige
F
F
Ebisu
S
S
D001718:Birefringence; D003188:Composite Resins / Q000737:chemistry*; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D004548:Elasticity; D008027:Light; D008422:Materials Testing; D008859:Microscopy, Polarization; D011108:Polymers / Q000737:chemistry; D013314:Stress, Mechanical; D013997:Time Factors
D003188:Composite Resins; D011108:Polymers; C074539:Palfique Light