Material and methods: One hundred twenty Class II cavities were prepared at the mesial and the distal side of human extracted premolars. The teeth were randomly divided into four groups (n=15). In each tooth the mesial Class II cavities were restored with the micro-hybrid resin composite Filtek Z250 (3M ESPE) and the distal Class II cavities were restored with the nano-filled resin composite Filtek Supreme (3M ESPE) The light curing unit used in this study was a conventional quartz tungsten halogen (QTH) curing light, the QHL 75 (Dentsply) modified by adding a regulating electronic device, controlled by a special software that gives 4 different modes of polymerization as follows:

Group A: Standard polymerization: Exposure for 20 seconds at 700 mW/cm², this group was used as control.
Group B: Modified pulse-delay polymerization: Exposure for 2 seconds at 700 mW/cm², 5 seconds at 0 mW/cm², then 20 seconds at 700mW/cm².
Group C: Modified ramp polymerization: Exposure for 20 seconds with a slow rise of the intensity to reach the 700 mW/cm² then 20 seconds at 700 mW/cm2.
Group D: Slow and Gradual polymerization: Exposure for 4 minutes with a slow rise of the intensity to reach 700 mW/cm².

The teeth were stored in water at 37°C for 48 hours, then finished and subjected to thermocycling (3000 cycles between 5°C and 55°C). All the teeth were immersed in 2% methylene blue solution for 12 hours at 37°C, sectioned, and evaluated at the gingival margins. Data were statistically analyzed by two-way analysis of variance followed by Tukey HSD multiple comparisons.
Results: The main effect for the type of composites (p= 0.682), and the interaction effect (p=0.678) did not reach statistical significance. There was a statistically significant main effect for the type of polymerization used (p=0.014). Post-hoc comparisons using the Tukey HSD test indicated that the mean score for the Group A (M=2.40, SD= 1.102) was significantly different from the group D (M= 1.30, SD= 1.393, p= 0.010). The group D did not differ significantly from group B (M= 1.63, SD= 1.351, p=0.767), and group C (M= 1.60, SD= 1.404, p=0.819). There was a difference between the group A (M=2.40, SD= 1.102), group B (M= 1.63, SD= 1.351) and group C (M= 1.60, SD= 1.404). However, when the Tukey HSD was used, no statistically significant differences between Group A, B and C were found (p=0.122 and p =0.098).
Conclusions: There was a statistically significant difference in micro leakage between the “slow and gradual polymerization” and the standard polymerization, however no significant differences were found when using the nano-filled or the micro-hybrid composite materials cured with different polymerization regimens.

" lang="fr" xml:lang="fr" /> Material and methods: One hundred twenty Class II cavities were prepared at the mesial and the distal side of human extracted premolars. The teeth were randomly divided into four groups (n=15). In each tooth the mesial Class II cavities were restored with the micro-hybrid resin composite Filtek Z250 (3M ESPE) and the distal Class II cavities were restored with the nano-filled resin composite Filtek Supreme (3M ESPE) The light curing unit used in this study was a conventional quartz tungsten halogen (QTH) curing light, the QHL 75 (Dentsply) modified by adding a regulating electronic device, controlled by a special software that gives 4 different modes of polymerization as follows:

Group A: Standard polymerization: Exposure for 20 seconds at 700 mW/cm², this group was used as control.
Group B: Modified pulse-delay polymerization: Exposure for 2 seconds at 700 mW/cm², 5 seconds at 0 mW/cm², then 20 seconds at 700mW/cm².
Group C: Modified ramp polymerization: Exposure for 20 seconds with a slow rise of the intensity to reach the 700 mW/cm² then 20 seconds at 700 mW/cm2.
Group D: Slow and Gradual polymerization: Exposure for 4 minutes with a slow rise of the intensity to reach 700 mW/cm².