Journal of Dental Medicine

Discoloration of composite resins is considered to be a major factor in esthetic restoration failures. The aim of this study was to evaluate color stability of IDM composite (both light and self cure samples namely IL and IS), and to compare it with a self-cure composite (Degufill named DS) and a light cure ormocer composite (Definite, called DL in the Report). 60 disk shaped samples of each composite were prepared, according to ISO-7491. The samples were divided into 3 groups and aged as follows: A- (Control) 7 days in dark 37°c chamber B- Foil covered and kept in 100% humidity, and 37°c in xenotest chamber for 24 hours, then transferred to a dark 37°c chamber for 6 more days.C- Kept in 37°c, 100% humidity under the emission of xiiion lamp of xenotest chamber for 24 hours,and then transferred to 37°c dark chamber for 6 more days The lightness and chromaticity values of samples were measured both before and after aging using a spectrophotometer (Data Flash). The total color changes as well as changes in lightness and chromaticity values were measured in the CIE L * a * b * scale, and analyzed. Color change was recorded to be significant in all samples after aging. The maximum change belonged to IL, which was significantly
different from DL and DS. It seems, in order to have a durable esthetic restoration using IDM, more scientific and professional consideration is needed in the production process.

Statement of Problem: Composite reins have recently become popular for posterior teeth restorations. Gap formation and subsequent microleakage are of the complications resulting from such restorations. One of the techniques to overcome polymerization shrinkage of composite resins is sandwich technique (application of glass ionomer as a base beneath the composite resin). Since polymerization patterns in two types of composite resins (light cure and self cure) differ from each other, various effects on the bond strength between glass ionomer and dentin are expected.
Purpose: The aim of this in vitro study was to evaluate the effects of self- cure and light- cure composite resins in sandwich technique on the bond strength of light cure glass ionomer and dentin.
Materials and Methods: 40 extracted human premolars were selected and divided into four groups:Group 1: Light cure glass ionomer of 1mm thickness was placed on dentin.Group 2: 1mm thickness of light cure glass ionomer plus a mass of self cure composite resin of 2mm thickness were placed.Group 3: 1mm thickness of light cure glass ionomer plus light cure composite resin as two separate 1mm layer were placed.Group 4: 1mm thickness of light cure glass ionomer with 37% phosphoric acid etching followed by two separate layers of light cure composite resin of 1 mm thickness were placed.SEM was used to determine gap size ai Gl- dentin and Gi- composite interlaces. The findings were analyzed by ANOVA and t-student tests.

Results: Groups 1 and 2 showed no gap at Gl-dentm interface and also cracks were not observed in all these specimens. In group 3, there was gap between light cure GI and light cure composite resin and cracks were seen in GI, too. Group 4 showed gap at both interfaces and more cracks were seen in GI. Groups I and 2 showed the least gap formation and group 4 showed the most. Statistically significant difference was found between groups 3, 4 and group 1 (control), 2.
Conclusion: Base on this study, the application of self-cure composite resin on light cure GI showed no gap and crack formation on Gl-dentin and Gl-composite interfaces and GI itself. However, light cure composite resins and glass ionomer etching aggregated crack and gap formation.