Evaluation and comparison of effect of different irradiation patterns and new suggested light exposure pattern on microleakage of composite resin restorations

Introduction:
There is a significant relationship between polymerization rate and polymerization shrinkage stress in restoration. The more the polymerization rate is, the shorter viscoplastic phase of the composite would be, leaving no time for the composite to flow and consequently sudden hardening of the composite occurs. This leads into severe shrinkage stresses followed by composite detachment from cavity walls resulting in microleakage within restoration and tooth.
The aim of this study was to suggest a new method of light exposure pattern for composite curing and evaluation of its effect on enamel and dentinal microleakage in respect to some other light exposure patterns.
Materials & Methods:
In this exprimental invitro study, flat tooth sections, 40 dentinal and 40 enamel samples were etched and Dentin Bonding Agent (DBA) (Excite®) was applied according to the manufacturer’s instruction. While placed on the samples, one bulk Tetric ceram® A3 composite was inserted in to a 2×2 mm polyethylene cylindrical mould. Samples were divided into dentinal and enamel groups of ten and light cured with  Astralis 7 light exposure patterns including HIP (High Intensity Program), LOP (Low Intensity Program), PUL (Pulse Program) and SUP (Suggested Progressive Program) for 80 seconds. After curing, thermocycling, dye penetration and medial sectioning, samples were observed under a scaled reflective microscope for microleakage measurement. The data were analysed statistically using One-Way and Two-Way ANOVA and Duncan test through SPSS software.
Results:
There was a significant defference in microleakage between enamel samples. The microleakage rate was the highest in HIP group while no microleakage was detected in the other groups. The degree of microleakage in dentin samples was significantly less in SUP group than the others but there was no significant difference between the other groups.
Conclusion:

The least dentinal microleakage occurred with application of suggested progressive program (SUP) compared to other testing groups.
Like LOP and PUL light exposure patterns, no enamel microleakage occurred with SUP application.
Enamel microleakage was detected in HIP group which had higher light intensity.