title: Light-polymerized compomers: coefficient of thermal expansion and microhardness.
abstract: BACKGROUND
  The relationship between the filler content, coefficient of thermal expansion, and microhardness of commercial light-polymerized compomers has not been fully investigated.
  
  
  OBJECTIVE
  This study evaluated the effect of filler content on the coefficient of thermal expansion and microhardness of 3 commercially available light-polymerized compomers.
  
  
  METHODS
  Five specimens each from 3 commercially available compomers (Compoglass F, Elan and F2000) were evaluated. Linear thermal expansion (microm/ degrees C) was measured with a thermomechanical analyzer in the temperature range 20 degrees to 80 degrees C with increments of 10 degrees C. Standardized specimens were prepared in a metal die (1.5 x 2 x 12 mm) and polymerized for 40 seconds at 700 mW/cm(2) light intensity. The microhardness of 5 specimens from each of 3 compomers were measured with a Vickers hardness tester under a 15-second dwell time and 200-g load conditions. The specimens were polymerized at 700 mW/cm(2) intensity for 40 seconds after placing the compomers into a round aluminum mold. Differences in thermal expansion and microhardness among the compomers evaluated were statistically analyzed by use of one-way analysis of variance at P<.01 significance level, with differences assessed by use of Duncan's multiple range post hoc test.
  
  
  RESULTS
  The coefficients of thermal expansion of Compoglass F (54.17 +/- 0.54 microm/ degrees C), Elan (40.94 +/- 0.78 microm/ degrees C) and F2000 (24.43 +/- 89 microm/ degrees C) were almost linear in the temperature range 25 degrees to 80 degrees C for all 3 compomers (r >.99). Inverse correlations between the %wt of filler and the coefficient of thermal expansion (r = -0.98, P<.0001), as well as between the microhardness and the coefficient of thermal expansion (r = -0.98, P<.0001) were observed. On the other hand, a linear correlation between the %wt of filler and microhardness of compomers was exhibited (r = -0.96, P<.0001). The microhardness values for Compoglass F, Elan, and F2000 were 43.82 +/- 1.62, 58.16 +/- 1.90, and 72.94 +/- 3.29, respectively.
  
  
  CONCLUSIONS
  Within the limitations of this study, an inverse correlation between percent weight of filler and coefficient of thermal expansion, and a linear correlation between percent weight of filler and microhardness was observed for the evaluated compomers.
authors.affiliation: College of Dentistry, Kyungpook National University, Taegu, Korea.
authors.forename: Yong Hoon
authors.initials: YH
authors.lastname: Kwon
authors.forename: Tae-Yub
authors.initials: TY
authors.lastname: Kwon
authors.forename: Joo L
authors.initials: JL
authors.lastname: Ong
authors.forename: Kyo-Han
authors.initials: KH
authors.lastname: Kim
mesh_terms: D000704:Analysis of Variance; D020770:Compomers / Q000737:chemistry*; D003188:Composite Resins / Q000737:chemistry; D003793:Dental Restoration, Permanent; D004055:Differential Thermal Analysis; D005899:Glass Ionomer Cements / Q000737:chemistry; D006244:Hardness; D006358:Hot Temperature; D008027:Light; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry; D018709:Statistics, Nonparametric
chemical_list: C105428:Compoglass; D020770:Compomers; D003188:Composite Resins; C472110:Elan (compomer); C118368:F2000 cement; D005899:Glass Ionomer Cements; D011108:Polymers