Surface coating and leakage of dentin-bonded resin composite restorations

Objectives: To compare the marginal leakage of dentin-bonded resin composite restorations in tooth sections coated with nail varnish and similarly restored sections coated with cyanoacrylate cement. Methods: MO and DO cavities were prepared with the gingival floor below the CEJ in 11 non-carious extracted human molars. Each cavity was restored with a dentin adhesive and resin composite. Sectioning yielded four specimens per tooth (N=44). One specimen from each restoration was coated with varnish. The other specimen was coated with cyanoacrylate cement. The coatings were applied to all surfaces except that a 1 mm window on either side of the interproximal gingival margin was left uncoated. Specimens were thermocycled and stained with silver nitrate. Silver penetration into the gingival margin of each section was measured with a measuring microscope. The predominant leakage path for each coating type was determined by scanning electron microscopy. Results: There was no significant difference between the leakage of the varnish-coated and cyanoacrylate-coated specimens. No marginal gaps were observed either by optical or by electron microscopy. However, the both optical and electron microscopy revealed leakage in nearly all specimens. This leakage was confined to either the dentin/hybrid layer interface or the adhesive resin/hybrid layer interface. Conclusions: The results suggest that these coating materials are not confounding factors in laboratory investigations of marginal leakage along dentin-bonded interfaces of resin composite restorations. Although marginal gaps were undetectable even at high magnification, leakage was observed along the gingival margin of almost all of these Class II resin composite restorations.