The effects of dentin bonding agent formulas on their polymerization quality, and together with tooth tissues on their microleakage and shear bond strength: an explorative 3-step experiment

PURPOSE: Bonding agents (BA) are the crucial weak link of composite restorations. Since the commercial materials' compositions are not disclosed, studies to formulize the optimum ratios of different components are of value. The aim of this study was to find a proper formula of BAs. MATERIALS AND METHODS: This explorative experimental in vitro study was composed of 4 different sets of extensive experiments. A commercial BA and 7 experimental formulas were compared in terms of degree of conversion (5 experimental formulas), shear bond strength, mode of failure, and microleakage (3 experimental formulas). Statistical analyses were performed (alpha=.05). The DC of selected formula was tested one year later. RESULTS: The two-way ANOVA indicated a significant difference between the shear bond strength (SBS) of two tissues (dentin vs. enamel, P=.0001) in a way that dentinal bonds were weaker. However, there was no difference between the four materials (P=.283). The adhesive mode of failure was predominant in all groups. No differences between the microleakage of the four materials at occlusal (P=.788) or gingival (P=.508) sites were detected (Kruskal-Wallis). The Mann-Whitney U test showed a significant difference between the microleakage of all materials (3 experimental formulas and a commercial material) together at the occlusal site versus the gingival site (P=.041). CONCLUSION: A formula with 62% bisphenol A-glycidyl methacrylate (Bis-GMA), 37% hydroxy ethyl methacrylate (HEMA), 0.3% camphorquinone (CQ), and 0.7% dimethyl-para-toluidine (DMPT) seems a proper formula for mass production. The microleakage and SBS might be respectively higher and lower on dentin compared to enamel.

Polymerization behavior and thermal characteristics of two new composites at five temperatures: refrigeration to preheating

PURPOSE: Heat of composite polymerization (HP) indicates setting efficacy and temperature increase of composite in clinical procedures. The purpose of this in vitro experimental study was to evaluate the effects of 5 temperatures on HP of two new composites. MATERIALS AND METHODS: From each material (Core Max II [CM] and King Dental [KD]), 5 groups of 5 specimens each were prepared and their total HPs (J/gr) were measured and recorded, at one of the constant temperatures 0degrees C, 15degrees C, 23degrees C, 37degrees C and 60degrees C (2 x 5 x 5 specimens) using a differential scanning calorimetry (DSC) analyzer. The data were analyzed using a two-way ANOVA, a Tukey's test, an independent-samples t-test, and a linear regression analysis (alpha=0.05). RESULTS: No polymerization reactions occurred at 0degrees C; then this temperature was excluded from statistical analyses. The mean HP of the remaining 20 KD specimens was 20.5 +/- 14.9 J/gr, while it was 40.7 +/- 12.9 J/gr for CM. The independent-samples t-test showed that there were significant differences between the HP of the two materials at the temperatures 15degrees C (P=.0001), 23degrees C (P=.0163), 37degrees C (P=.0039), and 60degrees C (P=.0106). Linear regression analysis showed statistically significant correlations between environment temperatures and HP of CM (R2=0.777). CONCLUSION: Using CM is advantageous over conventional composite because of its better polymerization capacity. However due to its high HP, further studies should assess its temperature increase in vivo. Preheating KD is recommended. Refrigerating composites can negatively affect their polymerization potential.