title: Polymerization contraction stress in light-cured compomer restorative materials.
abstract: OBJECTIVE
  The magnitude and kinetics of polymerization contraction stress build-up may be potential predictors of bond failure of adhesive restorations. The present study determined these properties of seven commercial compomers (Dyract, Dyract AP, F2000 Rasant, Hytac, Compoglass F, Luxat, Glasiosite).
  
  
  METHODS
  Polymerization shrinkage was generated by 40 s light curing the test materials (800 mW/cm2). The contraction force induced was recorded for 300 s at room temperature (23-24 degrees C) by means of a Stress-Strain-Analyzer (C factor=0.33). Maximum contraction stress (MPa), coefficient of near linear fit of contraction force/time (gradient) and relative force rate (%/s) of each material were compared with that of two hybrid composites (Tetric Ceram, Prodigy). The statistical analysis was conducted by ANOVA (alpha=0.05) and post hoc Tukey's test.
  
  
  RESULTS
  No statistically significant differences in the maximum stress between Glasiosite (2.27+/-0.06 MPa), Hytac (2.31+/-0.07 MPa) and Tetric Ceram (2.21+/-0.11 MPa), and between Compoglass F (2.60+/-0.18 MPa) and Prodigy (2.70+/-0.06 MPa) were found. The contraction stress of F2000 Rasant (3.41+/-0.09 MPa) and Luxat (3.33+/-0.08 MPa) were significantly highest, whilst Dyract exhibited the significantly lowest shrinkage stress (1.27+/-0.08 MPa) among the tested materials.
  
  
  CONCLUSIONS
  High contraction stress, early start of stress build-up and rapid contraction force development may lead to failure of bond to tooth structure. This study suggested that the contraction stress and kinetic behavior of compomers are generally similar to those of hybrid composites in a dry condition. Dyract might be superior in maintaining the bond with cavity walls compared to conventional hybrid composites in view of its low shrinkage stress.
authors.affiliation: Department of Restorative Dentistry, Dental School of the Ludwig--Maximilians-University, Goethe Street 70, Munich 80336, Germany. hchen@dent.med.uni-muenchen.de
authors.forename: H Y
authors.initials: HY
authors.lastname: Chen
authors.forename: J
authors.initials: J
authors.lastname: Manhart
authors.forename: K-H
authors.initials: KH
authors.lastname: Kunzelmann
authors.forename: R
authors.initials: R
authors.lastname: Hickel
mesh_terms: D000704:Analysis of Variance; D020770:Compomers / Q000528:radiation effects*; D003188:Composite Resins / Q000528:radiation effects; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis; D007700:Kinetics; D008027:Light; D011108:Polymers / Q000737:chemistry; D013314:Stress, Mechanical
chemical_list: D020770:Compomers; D003188:Composite Resins; D011108:Polymers