The effect of resin shades on microhardness, polymerization shrinkage, and color change of dental composite resins

Abstract

The present study sought to evaluate the effect of resin shades on the degree of the polymerization. To this end, response variables affected by the degree of polymerization were examined in this study -namely, microhardness, polymerization shrinkage, and color change. Two commercial composite resins of four different shades were employed in this study: shades A3, A3.5, B3, and C3 of Z250 (Z2) and shades A3, A3.5, B3, and B4 of Solitaire 2 (S2). After light curing, the reflectance/absorbance, microhardness, polymerization shrinkage, and color change of the specimens were measured. On reflectance and absorbance, Z2 and S2 showed similar distribution curves regardless of the resin shade, with shade A3.5 of Z2 and shade A3 of S2 exhibiting the lowest/highest distributions. Similarly for attenuation coefficient and microhardness, the lowest/highest values were exhibited by shade A3.5 of Z2 and shade A3 of S2. On polymerization shrinkage, no statistically significant differences were observed among the different shades of Z2. Similarly for color change, Z2 specimens exhibited only a slight (ΔE*=0.5-0.9) color change after immersion in distilled water for 10 days, except for shades A3 and A3.5. Taken together, results of the present study suggested that the degree of polymerization of the tested composite resins was minimally affected by resin shade.

The Effect of Different Curing Time Regimens on Immediate Postpolymerization Color Changes of Resin Composites

“…2 As previously mentioned, after initiation of polymerization, camphorquinone would lose its yellowness. 1 Nevertheless, interesting changes occurred by the midway during polymerization. All CIE color components were increased during 10 to 20s followed by a considerable reduction at 30s.…”

“…This is explained by retarding effect of dental composite stabilizer reaction with free radicals. 1 A probable answer to the unique pattern of color changes may be related to reaction of such stabilizers with initiators and free radicals at first when transient gel matrix is been formed. This final color change is not influenced by the shade of resin composite and initial 'b' quantity.…”

“…During polymerization, double carbon-carbon bonds would be changed into the single-bonded spatial structure which permits elongation and polymerization of the resin composite. 1 It is postulated that the color of resin composites would be changed by the progression of polymerization. 2 Photoinitiator, camphorquinone, would be eventually invisible; hence the yellowness of resin composite would be diminished along with an increased blue chroma.…”

“…2,3 Even after the completion of polymerization, resin composites undergo further changes in mouth by hydrophilic volumetric changes, Hydrolysis, stains and alteration of surface smoothness. 1,4,5 Overly, determination of color changes may be accomplished with either visual method applying a color shade or quantitavely with a device (e.g. colorimetric or spectrophotometric method).…”

Effect of Dental Restorative Material Type and Shade on Characteristics of Two-Layer Dental Composite Systems

“…Another consideration is that in the layered specimens, the indentation test was performed on a section of restoration layers which was perpendicular to the light-cured surface. The degree of polymerization is changed by the distance from the light-cure device, unless the light curing is performed carefully according to an optimum procedure which is usually the same as manufacturer instruction (Jeong et al, 2009, Lodhi, 2006, Shortall, 2005. In this study, all specimens were light-cured according to their manufacturer's instructions.…”