[Use of digital image correlation method to measure polymerization shrinkage dynamics of light cured composite resin].
OBJECTIVE
To evaluate the role of digital image correlation method in measuring the initiation and propagation of polymerization shrinkage of light cured composite resin.


METHODS
Six freshly extracted complete molars were collected and divided into 2 groups randomly. The proximal surface was sliced to plane and proximal-occlusal cavity were prepared with 2.0 mm×2.0 mm×2.0 mm in size, then the tissue surface was treated with etch and bond. The cavity samples in the first group were filled with 3M Z350, and the samples in the second group were filled with material 3M Valux Plus, the proximal surfaces were dealt with random speckle, then fixed to micro tensile framework. As light curing proceeded for 40 seconds, all the speckled images were collected by digital camera in real-time simultaneously. The digital image correlation analysis software was used to deal these images and achieve the displacement and strains in both horizontal and vertical direction on all pixel points, at last the linear shrinkage ratios were counted and the displacement at free surface of the two materials at the 20th second were analyzed with SPSS 12.01 software package for Student's t test.


RESULTS
The results showed displacement and strain distribution were accurately achieved and their correlation ratios (R) were bigger than 0.98. The shrinkage represented anisotropy with different direction and unequal value in 40 seconds. The linear shrinkage values of the two materials were 0.439%-0.75%, 0.526%-0.834% in horizontal direction and 0.253%-1.34%, 0.355%-1.51% in vertical direction,respectively. Considering the displacement at the 20th second, shrinkage of Z350 was lower than V. P's both in horizontal and vertical directions (P<0.05).


CONCLUSIONS
This study indicates that digital image correlation method can be used to study the polymerization shrinkage of light-cured composites kinematically and effectively, and calculate displacement and strain continually in full fields. Also this method is much closer to clinic application, and can give more theoretical and experimental evidence for clinic use.
Department of Stomatology, Minhang Central Hospital, Shanghai 201199, China. ruandanping1978@163.com
Dan-ping
DP
Ruan
Chun-yun
CY
Wu
Ding-hua
DH
Zhang
D003188:Composite Resins; D055117:Curing Lights, Dental; D006801:Humans; D008422:Materials Testing; D008963:Molar; D058105:Polymerization; D011897:Random Allocation
D003188:Composite Resins; C067319:valux