title: [Influence of soft-start irradiation on polymerization shrinkage stress of universal hybrid composite resins].
abstract: OBJECTIVE
  To compare the difference between soft-start curing mode and standard curing mode in polymerization shrinkage stress of universal hybrid composite resins and to study effect of the soft-start curing mode on the decrease of shrinkage stress.
  
  
  METHODS
  Three universal hybrid resins (A: Charisma, B: TPH Spectrum, and C: Esthet-X) were respectively filled in cavities (4 mm in diameter) of epoxide resin disks, 16 specimens of each. Off them, eight of the specimens for each composite resin were exposed using soft-start mode and the other eight using standard mode. Polymerization contraction stress was calculated during 48 h after curing with photo-elastic stress analysis.
  
  
  RESULTS
  Three composite resins cured with soft-start mode showed the same trend of shrinkage stress changing as that with standard curing mode and values of polymerization shrinkage stress at 24 h after curing were (3.80 +/- 0.31) MPa, (3.21 +/- 0.40) MPa, and (2.84 +/- 0.22) MPa respectively for A, B and C composite resins. The corresponding figures for the composites with standard curing mode were (4.19 +/- 0.24) MPa, (3.69 +/- 0.33) MPa, and (3.14 +/- 0.28) MPa. Three composite resins cured with soft-start mode had significantly lower polymerization shrinkage stress compared with standard curing mode at 24 h after curing (P < 0.05).
  
  
  CONCLUSIONS
  Using soft-start curing mold can reduce, to some extent, the polymerization shrinkage stress of universal hybrid composite resins.
authors.affiliation: Department of Conservative Dentistry, School of Stomatology, Tongji University, Shanghai 200072, China.
authors.forename: Yan-qiang
authors.initials: YQ
authors.lastname: Kang
authors.forename: Shou-liang
authors.initials: SL
authors.lastname: Zhao
authors.forename: Fang
authors.initials: F
authors.lastname: Li
authors.forename: Chun-zhen
authors.initials: CZ
authors.lastname: Feng
mesh_terms: D003188:Composite Resins / Q000528:radiation effects*; D003799:Dental Stress Analysis; D008027:Light
chemical_list: D003188:Composite Resins