Effect of bur cutting patterns and dentin bonding agents on dentin permeability in a fluid flow model

This study investigated the effects of bur cutting surface roughness and bonding systems on dentin permeability. A conventional straight edged bur, cross-cut serrated bur and an extensively serrated bur were utilized with two different bonding systems. Null hypothesis was that increased surface roughness does not decrease the permeability of dentin sealing after application of bonding agents. This study incorporated a fluid flow model for measuring dentin permeability. Seventy caries-free extracted molars were used and sectioned 2 mm apical to the cementoenamel junction (CEJ). The pulp tissue was removed and the chamber cleaned using 37% phosphoric acid followed by 1:1 sodium hypochlorite solution. The specimens were mounted to plexiglass plates using cyanoacrylate cement. A flow system was established through the pulp chamber and gravity pressurized phosphate buffered saline (PBS) was forced into the chamber and the "closed system" permeability measured. Burs were used to prepare flat surfaces in dentin, and after etching with phosphoric acid, the "open tubule" permeability was determined. After applying the dentin bonding agents, fluid flow from the pulp chamber into dentin was again measured. The percentage of reduction in permeability following bonding agent application was then calculated. A two-way ANOVA found a significant (p<0.05) decrease in bonded dentin permeability in specimens prepared using the cross-cut serrated and extensively serrated bur as compared to the conventional straight-edged bur. No significant differences were detected between bonding systems and no combination of surface topography or bonding agent completely sealed the surface.