title: [Effect of thermal cycling on surface microstructure of different light-curing composite resins].
abstract: OBJECTIVE
  To evaluate the effect of thermal cycling on surface microstructure of different light-curing composite resins.
  
  
  METHODS
  A nanofilled composite (Z350) and 4 microhybrid composites (P60, Z250, Spectrum, and AP-X) were fabricated from lateral to center to form cubic specimens. The lateral surfaces were abrased and polished before water storage and 40 000 thermal cycles (5/55 degrees celsius;). The mean surface roughness (Ra) were measured and compared before and after thermal cycling, and the changes of microstructure were observed under scanning electron microscope (SEM).
  
  
  RESULTS
  Significant decreases of Ra were observed in the composites, especially in Spectrum (from 0.164±0.024 µm to 0.140±0.017 µm, P<0.001) and Z250 (from 0.169±0.035 µm to 0.144±0.033 µm, P<0.001), whose Ra approximated that of P60 (0.121±0.028 µm) with smoothly polished surface. SEM revealed scratches and shallower pits on the surface of all the 5 resins, and fissures occurred on Z350 following the thermal cycling.
  
  
  CONCLUSIONS
  Water storage and thermal cycling may produce polishing effect on composite resins and cause fissures on nanofilled composite resins.
authors.affiliation: Department of Stomatology, Peking University Shenzhen Hospital, Shenzhen 518036, China. E-mail: kkdplvda@139.com.
authors.forename: Da
authors.initials: D
authors.lastname: Lv
authors.forename: Kai-Lei
authors.initials: KL
authors.lastname: Liu
authors.forename: Yao
authors.initials: Y
authors.lastname: Yao
authors.forename: Wei-Sheng
authors.initials: WS
authors.lastname: Zhang
authors.forename: Chu-Hong
authors.initials: CH
authors.lastname: Liao
authors.forename: Hong
authors.initials: H
authors.lastname: Jiang
mesh_terms: D003188:Composite Resins; D003775:Dental Polishing; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D013499:Surface Properties; D013696:Temperature
chemical_list: D003188:Composite Resins