title: Polymerization composite shrinkage evaluation with 3D deformation analysis from microCT images.
abstract: OBJECTIVE
  The aim of this study was to develop a method to experimentally determine and visualize the direction and amount of polymerization shrinkage.
  
  
  METHODS
  We modified a composite to include 1.5 wt% traceable glass beads. A cylindrical cavity (6mm diameter, 3mm height) was restored with this traceable composite, with and without dentin adhesive, and digitized with high-resolution micro-computed tomography (microCT). Image segmentation was performed to extract the glass beads from the acquired 3D microCT images (uncured and cured). Afterwards, each glass bead was subjected to local rigid registration. The resulting displacement vectors were used to examine and calculate the changes.
  
  
  RESULTS
  In unbonded restorations, the displacement vectors were oriented inwards to the center of mass, although not perfectly. Bonded restorations exhibited two contraction patterns: either toward one side of the cavity or toward the top-surface of the restoration. The displacement vector length values (mean/SD) for the bonded group (46.8 microm/10.0 microm) was significantly higher (p<0.01) than unbonded group (31.3 microm/8.5 microm), and the histogram curve was flatter (skew/kurtosis: 0.10/-0.56) as compared to the unbonded group (skew/kurtosis: 0.03/-0.26).
  
  
  CONCLUSIONS
  The proposed method can visualize real 3D displacement vectors generated by polymerization shrinkage. The bonding quality and cavity geometry are critical for the direction of polymerization contraction. This method has the potential to validate current models concerning the amount and orientation of shrinkage vectors.
authors.affiliation: Department of Restorative Dentistry and Periodontology, Dental School of the Ludwig-Maximilians-University, Goethestr. 70, D-80336 Munich, Germany.
authors.forename: Yu-Chih
authors.initials: YC
authors.lastname: Chiang
authors.forename: Peter
authors.initials: P
authors.lastname: Rösch
authors.forename: Alp
authors.initials: A
authors.lastname: Dabanoglu
authors.forename: Chun-Pin
authors.initials: CP
authors.lastname: Lin
authors.forename: Reinhard
authors.initials: R
authors.lastname: Hickel
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Kunzelmann
mesh_terms: D003188:Composite Resins / Q000737:chemistry; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis / Q000379:methods*; D017220:Dentin-Bonding Agents; D005898:Glass; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008863:Microspheres; D019279:Resin Cements; D055114:X-Ray Microtomography
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; C408584:Prompt L-Pop; D019279:Resin Cements; C452226:tetric flow composite resin