Mechanical properties and color stability of provisional restoration resins

To evaluate the mechanical strength and color stability of provisional restoration materials.

For mechanical testing, four groups [Trim (PEMA), Alike (PMMA), Versatemp (bis-acrylic resin composite, BARC) and Perfectemp II (bis-acrylic fluoride enriched resin, BAFC)] of resin disks were prepared for fracture toughness and shear punch strength testing, respectively. Five samples were fabricated for each group; therefore, a total of 20 resin disks for each testing method was prepared. The load at fracture and shear punch values of each specimen were recorded after 24-hour storage in distilled water. The stress intensity factors (K(Ic)) were calculated by the formula reported by Atkinson et al. For shear strength, the following formula was used: Shear strength = Force (N)/section thickness (mm) x punch circumference (mm). Values of each group in both tests were analyzed using one-way-ANOVA and Tukey multiple comparison test. For color stability testing, provisional resin disk specimens of the above mentioned materials were fabricated. Five samples were prepared for each subgroup (with and without a surface coating agent - Permaseal) and three different solutions (distilled water, red wine and curry); a total of 120 disk specimens were fabricated. Color values of each group were measured using a spectrophotometer after 24 hours and 2 weeks of aging in the aforementioned solutions. The color differences (deltaE*ab) between before and after aging were calculated by CIE Lab color-difference formula. The interaction of deltaE*ab values were analyzed by two-way analysis of variance followed by Newman-Keuls Multiple comparison test.

The highest fracture toughness value [(MPa (m)1/2)] was obtained by PMMA (0.89) followed by BARC (0.67), PEMA (0.54) and BAFC (0.42). Significant differences were observed among all test groups (P < 0.05). The highest shear punch strength (MPa) was obtained by BARC (160), followed by PMMA (141) and PEMA (132). The lowest value was obtained by BAFC (106). BARC showed a significantly higher mean value than the other groups (P < 0.05). PEMA and PMMA demonstrated better color stability than the two bis-acrylic resin composites. Wine and curry showed higher stainability than water, recording higher deltaE*ab values than the clinically perceptible difference level of deltaE*ab 3.3. The surface coating agent groups demonstrated more staining than the non-coated groups. All groups, except for BARC, demonstrated significant differences dependent upon surface coating and solutions (P < 0.05).