Polymerization composite shrinkage evaluation with 3D deformation analysis from μCT images
Received 18 June 2009; received in revised form 7 August 2009; accepted 20 September 2009.
Abstract
Objectives
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 1.5wt% 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 (μCT). Image segmentation was performed to extract the glass beads from the acquired 3D μCT 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 (46.8μm/10.0μm) was significantly higher (p<0.01) than unbonded group (31.3μm/8.5μm), and the histogram curve was flatter (skew/kurtosis: 0.10/−0.56) as compared to the unbonded group (skew/kurtosis: 0.03/−0.26).
Significance
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.
aDepartment of Restorative Dentistry and Periodontology, Dental School of the Ludwig-Maximilians-University, Goethestr. 70, D-80336 Munich, Germany
bFaculty of Computer Science, University of Applied Sciences, Augsburg, Germany
cSchool of Dentistry and Graduate Institute of Clinical Dentistry, National Taiwan University and National Taiwan University Hospital, No. 1, Chang-Te Street, Taipei 10016, Taiwan
ABSTRACT