Temperature Rise Beneath Etched Dentin Discs During Composite Polymerization

Methods: Forty dentin discs (diameter 5 mm, height 0.5 mm or 1 mm) were prepared from extracted permanent third molars. These dentin discs were etched by 37% orthophosphoric acid or erbium: yttrium aluminium garnet (Er: YAG) laser (Fidelis plus III, Fotona) and were placed on apparatus developed to measure temperature rise. The composite resin (Quadrant Universal LC, Cavex) was polymerized with high intensity quartz tungsten halogen (HQTH, Monitex, 800 mW/cm2) and light emitting diode unit (LED, Kerr, 1100 mW/cm2). The temperature rise was measured under the dentin disc with a J-type thermocouple wire that was connected to a data logger. Five measurements were carried out for each dentin disc, curing unit and etching system combination. Differences between initial and highest temperature readings were taken and the five calculated temperature changes were averaged to determine the value in temperature rise. Statistical analysis was performed with 3 way ANOVA and Tukey HSD tests at a 0.05 level of significance. Further SEM examinations were performed.

Results: Temperature rise values varied significantly depending on etching systems (p<0.05), dentin thickness (p<0.05) and curing units (p<0.05). Temperature rise measured beneath laser etched discs were significantly higher than acid etched dentin discs (p<0.05). HQTH unit induced significantly higher temperature increases than LED unit (p<0.05). The LED unit induced the lowest temperature change (5.2°C) at 1mm acid etched dentin group. The HQTH unit induced the highest temperature change (10.4°C) at 0.5mm laser etched dentin group.

Conclusion: The risk for heat induced pulpal damage should be taken into consideration during polymerization of composite resin after laser etching when dentin thickness is less than 0.5 mm.