Purpose: The purpose of this study was to determine the relationship between polymerization contraction stress and leakage in Class V composites.
Methods: A microfill (Heliomolar) and two minifill hybrid composites (Herculite, Z100) were tested. Maximum contraction stress (n = 5) for the composites was evaluated in a MTS machine at a C-factor of 3 (ratio of bonded to non-bonded surface area). Composite was placed in the gap between the surfaces of glass stubs that had been air abraded, silane treated and coated with a layer of resin adhesive. Specimens were light-cured through the top glass stub for 60 seconds and maximum force was recorded during the first 10 minutes. Leakage (n = 10) was evaluated by cutting cylindrical cavity preparations with all enamel margins (C-factor = 3) in bovine incisors. The cavities were treated with two layers of Scotchbond MP adhesive. Composites were applied in one increment, light-cured at the same intensity used in the stress tests, and immediately finished on SiC paper. After 1 day in water, the restorations were placed in silver nitrate, developed and evaluated as a single cross-section (2-D) and multiple cross-sections (3-D) for leakage: 0 (none), 1 (minimal leakage), 2 (to the DEJ), 3 (to line angle), 4 (along the pulpal wall).
Results: The maximum stresses (MPa) recorded were lowest for Heliomolar (7.0 +/- 0.4), intermediate for Herculite (10.5 +/- 0.6) and greatest for Z100 (11.6 +/- 1.3). 3-D leakage was as follows: Heliomolar--two specimens scored 1, seven scored 2 and one scored 3; Herculite--six scored 2 and four scored 3; Z100--eight scored 3 and two scored 4. The Kruskal-Wallis test showed a significant difference in leakage for the three composites (P < 0.05), and leakage was greater when evaluated in 3-D. The leakage results correlated with the stress values, i.e. composites with higher contraction stress showed more extensive marginal leakage.