Effect of tubule orientation in the cavity wall on the seal of dental filling materials: an in vitro study.

Dentinal tubules are oriented perpendicularly to the root canal walls but parallel to the lateral walls of class I occlusal preparation. It was hypothesized that the contact surface area of the material may depend on the tubule orientation in the cavity wall to which the material is applied, and that the difference in contact surface may affect the seal provided by the filling material. Standard central lumens, 2.6 mm in diameter and 3 mm high, were machined in human crown or root specimens. After removal of the smear layer with a conditioner, the specimens in each experimental group, consisting of 20 crown and 20 root specimens, were filled with amalgam, Fuji II glass ionomer (with or without varnish), or gutta-percha with Ketac-Endo root canal sealer. A modified fluid transport model was used to test the leakage along the fillings. Selected specimens were then split longitudinally and observed in a scanning electron microscope. The micrographs showed that all the test materials were pressed into the dentinal tubules. The contact surface of the material was calculated to be at least 45% larger in root specimens than in crown specimens, depending on the depth of the tubular penetration of the test material. The leakage results showed that all the test materials leaked less in root specimens than in crown specimens (P = 0.0000 for amalgam, P = 0.0374 for Fuji II with varnish, P = 0.0088 for Fuji II without varnish, P = 0.002 for gutta-percha with sealer). It was concluded that the tubule orientation in the cavity wall may influence the seal provided by certain dental filling materials.