title: Effect of a multi-layer infection control barrier on the micro-hardness of a composite resin.
abstract: OBJECTIVE
  The aim of this study was to evaluate the effect of multiple layers of an infection control barrier on the micro-hardness of a composite resin.
  
  
  METHODS
  One, two, four, and eight layers of an infection control barrier were used to cover the light guides of a high-power light emitting diode (LeD) light curing unit (LCU) and a low-power halogen LCU. The composite specimens were photopolymerized with the LCUs and the barriers, and the micro-hardness of the upper and lower surfaces was measured (n=10). The hardness ratio was calculated by dividing the bottom surface hardness of the experimental groups by the irradiated surface hardness of the control groups. The data was analyzed by two-way ANOVA and Tukey's HSD test.
  
  
  RESULTS
  The micro-hardness of the composite specimens photopolymerized with the LED LCU decreased significantly in the four- and eight-layer groups of the upper surface and in the two-, four-, and eight-layer groups of the lower surface. The hardness ratio of the composite specimens was <80% in the eight-layer group. The micro-hardness of the composite specimens photopolymerized with the halogen LCU decreased significantly in the eight-layer group of the upper surface and in the two-, four-, and eight-layer groups of the lower surface. However, the hardness ratios of all the composite specimens photopolymerized with barriers were <80%.
  
  
  CONCLUSIONS
  The two-layer infection control barrier could be used on high-power LCUs without decreasing the surface hardness of the composite resin. However, when using an infection control barrier on the low-power LCUs, attention should be paid so as not to sacrifice the polymerization efficiency.
authors.affiliation: Department of Conservative Dentistry and Dental Science Research Institute, School of Dentistry, Chonnam National University, Gwangju, Korea.
authors.forename: In-Nam
authors.initials: IN
authors.lastname: Hwang
authors.forename: Sung-Ok
authors.initials: SO
authors.lastname: Hong
authors.forename: Bin-Na
authors.initials: BN
authors.lastname: Lee
authors.forename: Yun-Chan
authors.initials: YC
authors.lastname: Hwang
authors.forename: Won-Mann
authors.initials: WM
authors.lastname: Oh
authors.forename: Hoon-Sang
authors.initials: HS
authors.lastname: Chang
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D055117:Curing Lights, Dental; D006245:Hardness Tests; D006801:Humans; D019552:Infection Control, Dental / Q000379:methods*; D008422:Materials Testing; D058105:Polymerization; D013499:Surface Properties; D013997:Time Factors
chemical_list: D003188:Composite Resins