title: Hardness of celluloid strip-finished or polished composite surfaces with time.
abstract: BACKGROUND
  An in-vitro study revealed that a celluloid strip-finished composite surface discolored more than the polished composite surface. Thus, the celluloid strip-finished composite surface may not cure enough compared with the polished composite surface.
  
  
  OBJECTIVE
  This study tested the hypothesis that the celluloid strip-finished composite surface did not cure enough compared with the polished composite surface.
  
  
  METHODS
  The composite was placed in a 1.5-mm thick aluminum mold and the upper surface was covered with a celluloid strip. Composite was light cured for 60 seconds, then a layer of approximately 200 microm thick was ground away from the lower surface and polished. The hardness of the upper composite surface that was polymerized under a celluloid strip and the polished lower surface were measured with Vickers hardness measuring instrument 15 minutes, 6 hours, and 6 days after light curing. The hardnesses of polished and celluloid strip-finished surfaces were compared using a paired t test. One-way ANOVA and Tukey was used for tests for the significant differences in hardnesses between 15 minutes, 6 hours, and 6 days after light curing for a given surface.
  
  
  RESULTS
  Microhardness of the celluloid strip-finished composite surface was 380.6 N/mm(2) at 15 minutes, 442.5 N/mm(2) at 6 hours, and 519.2 N/mm(2) at 6 days after light curing. Microhardnesses of the polished composite surface was 476.6 N/mm(2) at 15 minutes, 511.7 N/mm(2) at 6 hours, and 535.0 N/mm(2) at 6 days after light curing. The hardness of the celluloid strip-opposed composite surface was significantly lower than that of the polished surface 15 minutes and 6 hours after light curing (P <. 001). There was no difference in hardness between the celluloid strip-opposed surface and the polished surface on the sixth day.
  
  
  CONCLUSIONS
  The hardness of the celluloid strip-opposed composite surface was lower than that of the polished surface at 15 minutes and at 6 hours after light curing. However, there was no difference in microhardness in 6 days.
authors.affiliation: Yonsei University, Seoul, Korea. sunghopark@yumc.yonsei.ac.kr
authors.forename: S H
authors.initials: SH
authors.lastname: Park
authors.forename: I
authors.initials: I
authors.lastname: Krejci
authors.forename: F
authors.initials: F
authors.lastname: Lutz
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins; D003775:Dental Polishing / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D006244:Hardness; D006245:Hardness Tests / Q000379:methods; D008027:Light; D013499:Surface Properties; D013997:Time Factors
chemical_list: D003188:Composite Resins; C121818:Tetric ceram