[62] published a work about the use of electrical resistance strain gauges. Many adaptations using the strain gauges were applied latter [63�C65]. In 1993, de Gee et al. [66] published a paper describing the linometer, which evaluates the linear displacement of a thin plate positioned on the resin-composite surface during the polymerization pathway signaling process. More recently, complex methods using video images [67, 68], laser speckle contrast analysis [69, 70], and mathematical and computational models [53, 71�C73] have also been developed for research applications. Lately, new powerful and promising techniques, such as the X-ray microtomography, have been employed to investigate polymerization shrinkage [74]. Kakaboura et al.

used the X-ray Inhibitors,Modulators,Libraries microtomography to evaluate the 3D-marginal adaptation to dentine versus shrinkage strain Inhibitors,Modulators,Libraries of two light-cured microhybrid resin composites [8]. The authors used sequential sections of restorations to calculate the interfacial microvoid volume fraction and compared the results with the bonded-disc Inhibitors,Modulators,Libraries method. As result, the authors found a strong correlation between the microvoid volume fractions with the data from the bonded-disc apparatus. 4.2. Shrinkage Stress Methods used to evaluate shrinkage strain are important to understand the material’s behavior. However, it is important to remember that shrinkage stress, that is not a material property, is a consequence of multiple factors and specific methods have to be used for evaluation.

Such methods are described in the literature: ring slitting method [75, 76], photoelastic analysis [77�C79], finite element analysis [42, 80�C83], mathematical models [84], crack propagation [85], and force transducers [2, 40, 41, 46, 86, 87]. The ��ring-slitting method�� is a simple and inexpensive way to evaluate residual stress in ring-shape resin composite specimens [75, 76]. In Inhibitors,Modulators,Libraries this method, the resin composite is cured and the gap distance previously created in the ring is measured before and after the polymerization process. Photoelastic or finite element analyses (FEAs) are interesting methods to observe the spatial distribution and concentration areas of stress. While photoelastic analysis determines stress distribution through optical fringes created in specific resins [77�C79], FEA evaluates stress distributions by computer models.

This method requires not only an anatomically accurate geometry but other input data, Inhibitors,Modulators,Libraries especially elastic moduli, Poisson’s ratios, and shrinkage strain. Although the previous methods brought important contributions for the current knowledge, it has to be stated that force transducers are the most widely used and versatile Batimastat methods for analyses of stress development. The wide application of such equipment relies on the fact that it is possible to analyze the influence of important factors, like C-factor and mass of material, by simple variations in cylinder/disk size and aspect ratio.