Application Technique Determines Marginal Seal of Class II Composite Restorations

Objectives: To evaluate the influence of cavity depth, polymerization shrinkage and application technique on marginal seal and margin quality of class II resin-based composite restorations.

Methods: Standardized MOD class II cavities were prepared in extracted human molars. Occlusal boxes were 3.5mm wide and either 3mm or 4.5mm deep. Standardized interproximal boxes (box size: 3.5x4.5mm, bevel size 5.5x5.5mm) were prepared using sonic shape preparation instruments (SonicSys Approx Size 3) and reciprocating files (Bevelshape B15C). After application of a 3-step etch&rinse adhesive (Optibond FL), the cavities were restored using a resin-based composite of high (Tetric Ceram, 2.8%) or low polymerization shrinkage (Grandio, 1.6%). Interproximal boxes were restored using either a centripetal [CP] or a horizontal [Hor] layering technique. After water storage (30 days, 37°C) and thermocycling (2500x 5-55°C), margin quality was evaluated in the SEM using the replica technique. Marginal seal was studied using dye penetration (AgNO₃ 50%, 2h, 37°C). For each combination of parameters six specimens were prepared. Results were analyzed using 3-way ANOVA.

Results: All data: means ± SD

Cavity size	small				deep
Shrinkage	high		low		high		low
Layering technique	CP	Hor	CP	Hor	CP	Hor	CP	Hor
Penetration depth1 [mm]	0.09 ±0.13	0.7 6±0.4	0.23 ±0.22	0.44 ±0.27	0.27 ±0.34	0.68 ±0.33	0.43 ±0.58	0.36 ±0.32
Margin gap1 [%]	19.6 ±26.7	88.0 ±12.8	50.1 ±26.4	47.9 ±13.4	15.6 ±12.1	66.4 ±18.9	58.8 ±31.6	72.9 ±19.9

¹at cervical margins

The centripetal layering technique produced less dye penetration (P<0.01) and margin gaps (P<0.001) than the horizontal layering technique. This difference was more pronounced for the high shrinkage composite (interaction: P<0.05 / P<0.001). In deep cavities, more margin gaps were observed for the low shrinkage composite, whereas both composites were equivalent in small cavities (interaction: P<0.01).

Conclusions: The centripetal layering technique may improve marginal seal, at least for high shrinkage resin-based composites.