title: Analysis of local shrinkage patterns of self-adhering and flowable composites using 3D digital image correlation.
abstract: OBJECTIVE
  To analyze local shrinkage patterns in terms of surface shrinkage strains and z-axis displacements in a novel self-adhering composite and a conventional flowable composite using three-dimensional digital image correlation.
  
  
  METHODS
  Seven samples of each material were prepared in cylindrical Teflon molds 5 mm in diameter and 2 mm thick. The surface of the composites facing the cameras was sprayed with a fine layer of black paint. The unsprayed surface of each sample, opposite the one facing the cameras, was light cured for 40 seconds using a light-emitting diode unit. Digital images were taken immediately before and after light curing. Shrinkage was calculated as von Mises strains, and z-axis displacements were measured in microns. The data were statistically analyzed using two-way ANOVA at a = .05.
  
  
  RESULTS
  No significant difference in strain was observed between the two materials (P > .05). Strain distribution was nonhomogenous--the outer segments showed significantly higher strains than central parts in each material (P < .05). The opposite was observed for z-axis displacements-significantly greater displacements were found in central parts compared to the outer segments (P < .05).
  
  
  CONCLUSIONS
  Different shrinkage vectors across the surface of the tested flowable composites showed predominant in-plane shrinkage of the outer surface segments and out-of-plane shrinkage of the inner segments. These complex local deformation patterns in composite materials indicate zones of different types of forces exerted on the tooth-restoration interface in situ.
authors: Department of Restorative Dentistry and Endodontics, School of Dentistry, University of Belgrade, Belgrade, Serbia. miletic@gmail.com
authors: Vesna
authors: V
authors: Miletic
authors: Dragica
authors: D
authors: Manojlovic
authors: Milos
authors: M
authors: Milosevic
authors: Nedad
authors: N
authors: Mitrovic
authors: Tatjana Savic
authors: TS
authors: Stankovic
authors: Tasko
authors: T
authors: Maneski
mesh_terms: D000465:Algorithms; D017609:Barium Compounds / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D055117:Curing Lights, Dental / Q000145:classification; D003764:Dental Materials / Q000737:chemistry*; D005994:Glycerophosphates / Q000737:chemistry; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D055115:Light-Curing of Dental Adhesives / Q000379:methods; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D023861:Photography, Dental / Q000379:methods; D058105:Polymerization; D012822:Silicon Dioxide / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D014783:Viscosity
chemical_list: D017609:Barium Compounds; D003188:Composite Resins; D003764:Dental Materials; D005994:Glycerophosphates; D008689:Methacrylates; C102735:Revolution (composite resin); C102738:barium glass filler; C111840:flowable hybrid composite; D012822:Silicon Dioxide