Journal of Dental Medicine

Indirect esthetic restorations have recently gained popularity, and choosing suitable cement is an important concern in this regard. A wide variety of resin cements with different curing models:(chemical, light, dual), have been introduced to the profession, and among them the dual systems are claimed to be able to continue polymerization after stopping the light. In order to study and compare the polymerization process of different curing systems, this research was performed.The present study measured the degree of conversion (DC) of three types of resin cements: a self cured,a light cured and a dual cured cement. The samples were prepared as follows:1-The self cured samples were made according to the manufacturer.2-The light cured samples were exposed to the curing light for 60 seconds, through a 2 mm thick wafer
of porcelain.3- The dual cured samples were divided into 2 groups. The first was lighted similar to the light cured samples, and the second did not receive any light.The degree of polymerization was measured by FTIR at time levels of 5, 10,20,30,45,60 minutes and 24 hours post mixing. The infrared spectrum of the samples were recorded and degree of conversion were determined. The results demonstrated an increase in mean DC of all groups at post mixing time, but this was significant only in the lighted dual cured cement (PO.05). The light cure resin showed high DC at the base line time (5min). At the end of 60 minutes, the self cure resin had the most DC. The unlighted dual cement had a very low DC and didn't improve in polymerization during the post mixing controls.The lighted dual cement had a significant improve in curing at post mixing times, and it was significantly different from unlighted dual cement. So the dual cure cement needs to receive sufficient light energy to initiate the curing process and the chemical component of this cement could not improve the DC completely.After 24 hours migration of unpolymerized monomers, seams to decrease the DC at the surfaces and removing the most superficial layer, showed that the underlying parts, had improved DC. It seems that in order to be sure of what happens at the restoration-tooth interface, it is appropriate to use self cure cements with improved flow and film thickness.

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.