Polymerization composite shrinkage evaluation with 3D deformation analysis from microCT images.
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.
Chiang
Yu-Chih
YC
Department of Restorative Dentistry and Periodontology, Dental School of the Ludwig-Maximilians-University, Goethestr. 70, D-80336 Munich, Germany.
Rösch
Peter
P
Dabanoglu
Alp
A
Lin
Chun-Pin
CP
Hickel
Reinhard
R
Kunzelmann
Karl-Heinz
KH
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
D003188:Composite Resins; D017220:Dentin-Bonding Agents; C408584:Prompt L-Pop; D019279:Resin Cements; C452226:tetric flow composite resin