title: Polishing mechanism of light-initiated dental composite: Geometric optics approach.
abstract: OBJECTIVE
  For light-initiated dental hybrid composites, reinforcing particles are much stiffer than the matrix, which makes the surface rugged after inadequate polish and favors bacterial adhesion and biofilm redevelopment. The aim of the study was to investigate the polishing mechanism via the geometric optics approach.
  
  
  METHODS
  We defined the polishing abilities of six instruments using the obtained gloss values through the geometric optics approach (micro-Tri-gloss with 20°, 60°, and 85° measurement angles). The surface texture was validated using a field emission scanning electron microscope (FE-SEM). Based on the gloss values, we sorted polishing tools into three abrasive levels, and proposed polishing sequences to test the hypothesis that similar abrasive levels would leave equivalent gloss levels on dental composites.
  
  
  RESULTS
  The three proposed, tested polishing sequences included: S1, Sof-Lex XT coarse disc, Sof-Lex XT fine disc, and OccluBrush; S2, Sof-Lex XT coarse disc, Prisma Gloss polishing paste, and OccluBrush; and S3, Sof-Lex XT coarse disc, Enhance finishing cups, and OccluBrush. S1 demonstrated significantly higher surface gloss than the other procedures (p < 0.05). The surface textures (FE-SEM micrographs) correlated well with the obtained gloss values.
  
  
  CONCLUSIONS
  Nominally similar abrasive abilities did not result in equivalent polish levels, indicating that the polishing tools must be evaluated and cannot be judged based on their compositions or abrasive sizes. The geometric optic approach is an efficient and nondestructive method to characterize the polished surface of dental composites.
authors.affiliation: School of Dentistry and Graduate Institute of Clinical Dentistry, National Taiwan University and National Taiwan University Hospital, Taipei, Taiwan; Department of Operative Dentistry and Periodontology, Dental School of Ludwig-Maximilians-University Munich, Munich, Germany. Electronic address: munichiang@ntu.edu.tw.
authors.forename: Yu-Chih
authors.initials: YC
authors.lastname: Chiang
authors.affiliation: School of Dentistry and Graduate Institute of Clinical Dentistry, National Taiwan University and National Taiwan University Hospital, Taipei, Taiwan; Department of Dentistry, National Taiwan University Hospital, Hsin-Chu Branch, Hsin-Chu, Taiwan.
authors.forename: Eddie Hsiang-Hua
authors.initials: EH
authors.lastname: Lai
authors.affiliation: Department of Operative Dentistry and Periodontology, Dental School of Ludwig-Maximilians-University Munich, Munich, Germany.
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Kunzelmann
mesh_terms: D003188:Composite Resins / Q000032:analysis*; D003775:Dental Polishing / Q000379:methods*; D006801:Humans; D008422:Materials Testing / Q000379:methods; D008855:Microscopy, Electron, Scanning; D055620:Optical Phenomena; D055095:Optics and Photonics / Q000379:methods*; D013499:Surface Properties
chemical_list: D003188:Composite Resins
keywords: FE-SEM; geometric optics; hybrid dental composites; nondestructive testing; polish