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PURPOSE: 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 x 2.0 mm x 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 lo clinic application, and can give more theoretical and experimental evidence for clinic use. [ABSTRACT FROM AUTHOR]

PURPOSE: To evaluate the clinical application of digital photography in special color teeth, and to explore the role and the problems s of digital photos to improve cosmetic effect. METHODS: Digital photography combined visual color- matching was applied in 50 cases with special color teeth in ceramic restorations selected randomly. Then the satisfactory degree of the patients and dentists was evaluated and the value of L*a*b* between prosthesis and its neighbors was collected by self-developed software Dental ImgShop. Chroma (Cab)and hue (hab°) were calculated according to the value of a and b. The data was analyzed with paired t test using SAS6.12 software package, so as chromatic aberration (ΔE). RESULTS: The satisfactory degree of the patients was 98%, and the satisfaction degree of the dentists was 94%. The range of L, a ,b Cab, hab ° of special color teeth was 54.50-92.29, -0.97-8.12,-0.73-20.85,0.85-21.34,29.73-89.20, respectively. There was no significant difference between the prosthesis and their neighbors statistically (P>0.05). The mean value of chromatic aberration (ΔE) was 0.948 (0.136-3.45), and only 3 cases were unacceptable (ΔE≥52). CONCLUSIONS: Digital photography could record and transmit the color information of special color teeth more exactly, and could improve the patients satisfaction and the cosmetic effect in color measuring. Supported by Research Fund of Natural Science for Young Scholars of Minhang Central Hospital. [ABSTRACT FROM AUTHOR]