title: Effects of particle size of silica filler on polymerization conversion in a light-curing resin composite.
abstract: OBJECTIVE
  The effect of visible light passing through a resin composite with different particle sizes of spherical silica filler on the curing depth and Knoop hardness of the resin composite was examined. The null hypotheses tested were that the particle size of silica filler has no effect on (1) the transmitted amount of visible light passing through the resin composite, (2) the curing depth of the resin composite, and (3) the ratio of the Knoop hardness of the hardened resin composite.
  
  
  METHODS
  A series of different experimental resin composite pastes with different particle sizes of silica filler were prepared. The amount of visible light passing through each of the experimental resin pastes during the hardening process was determined. The curing depth and Knoop hardness of the resin composites were measured. Further, to characterize the polymerization conversion, the ratio of the Knoop hardness of the bottom surface against the irradiated surface of the hardened resin composites was determined.
  
  
  RESULTS
  Increases in the particle size of the silica filler resulted in decreases in the transmitted amount of visible light, curing depth, and ratio of the Knoop hardness of the resin composite. The rate of polymerization conversion of the resin composite occurring deep within the cavity was found to be less than the rate of polymerization conversion occurring at the upper surface.
  
  
  CONCLUSIONS
  To increase the rate of polymerization conversion deep within the resin composite, it is important to reduce the particle size of the silica filler.
authors.affiliation: Department of Dental Caries Control and Aesthetic Dentistry, Nihon University School of Dentistry at Matsudo, 870-1 Sakaecho, Nishi 2, Matsudo, Chiba 271-8587, Japan. fujita.kou@nihon-u.ac.jp
authors.forename: Kou
authors.initials: K
authors.lastname: Fujita
authors.forename: Takuji
authors.initials: T
authors.lastname: Ikemi
authors.forename: Norihiro
authors.initials: N
authors.lastname: Nishiyama
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D006244:Hardness; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D010316:Particle Size; D011092:Polyethylene Glycols / Q000737:chemistry; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D012031:Refractometry; D012822:Silicon Dioxide
chemical_list: D003188:Composite Resins; D008689:Methacrylates; D011109:Polymethacrylic Acids; D011140:Polyurethanes; C029824:urethane dimethacrylate luting resin; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D012822:Silicon Dioxide