Polymerization stress related to radiant exposure and its effect on microleakage of composite restorations

Objectives

Verify the influence of radiant exposure (dose) on polymerization stress and microleakage of composite restorations using two adhesive systems.

Methods

An experimental composite (1BisGMA:1TEGDMA, 75 wt.% filler) was subjected to 3, 6, 12 or 24 J/cm² under 500 mW/cm². Stress was measured in 1-mm height specimens placed between two glass rods (Ø = 5 mm) attached to a testing machine. Microleakage was assessed in cylindrical restorations (Ø = 5 mm, h = 2 mm) with enamel margins, using Adper Single Bond 2 (SB) or Adper Prompt (PR). After storage, specimens were subjected to dye penetration (50% AgNO₃) and sectioned twice, perpendicularly. Microleakage of the 8 tooth/composite interfaces was recorded in millimeters. KHN was measured at both surfaces of cylindrical specimens (Ø = 5 mm, 1 or 2 mm height). ANOVA/Tukey test were used (α = 0.05). KHN top and bottom were compared using paired t-tests.

Results

Stress increased significantly with dose (3 J/cm²: 1.4 ± 0.3^c; 6 J/cm²: 4.3 ± 0.5^b; 12 J/cm²: 9.3 ± 0.6^a; 24 J/cm²: 9.9 ± 0.7^a, in MPa). For both average and maximum microleakage, interactions were not statistically significant (p > 0.05). Tooth average microleakage was influenced by the adhesive system (SB < PR) and increased with dose (3 J/cm² < 6 J/cm² = 12 J/cm² = 24 J/cm²). Tooth maximum microleakage was influenced by dose only (3 J/cm² < 6 J/cm² = 12 J/cm² = 24 J/cm²). A direct association between stress and microleakage was suggested with SB, while with PR showed severe dye penetration at all doses evaluated. KHN showed significant differences among all groups, except at bottom of 2 mm specimens cured with 3 and 6 J/cm². Differences between top and bottom were found for 2 mm specimens cured with 3 and 6 J/cm².

Conclusions

Stress and microleakage increased significantly with the applied radiant exposure.