Volume of the internal gap formed under composite restorations in vitro.

Objectives: The gap that develops at the interface of dentin composite restoration during the polymerization of the resin can be subsequently filled by fluid filtrating from the pulp via the dentinal tubules. This in vitro study was designed to determine the volume of such a gap, at the occlusal floor of class I restoration and as a result of different dentin treatments and restoration procedures.
Methods: Fifty-six human third molars had their pulp chambers first sealed and connected to a hydraulic apparatus permitting microlitre fluid shift recordings. The teeth then received class I cavities of uniform dimensions and were sampled into nine groups for three dentin treatments (bonding with a dentin bonding agent, lining with a resin modified light-cured glass ionomer, lining with a zinc phosphate cement) and three restoration procedures (Bulk placement of the composite material, Multilayer, Indirect inlay). Fluid displacements were recorded during the filling procedures and stopped 30 min after the completion of the restorations.
Results: Dentin bonding agent treated cavities consistently presented the smallest gap volumes, followed by the GI and the ZnPO4 lined specimen. Multilayer and Indirect restoration techniques reduced the formation of gaps.
Conclusions: None of the materials or techniques tested assured a gap-free interface and more effort should be directed at increasing the adhesive and sealing properties of restorative materials to be placed on the dentin.