In Vitro Dentinal Surface Reaction of 9.5% Buffered Hydrofluoric Acid in Repair of Ceramic Restorations: a Scanning Electron Microscopic Investigation

Statement Of Problem: Fracture of porcelain is a relatively common clinical misfortune. Recent research has indicated that strong bonds can be formed between composite and dental porcelain. Porcelain surfaces are etched with hydrofluoric acid and treated with silane coupling agents before composite application. The question is how exposed dentin may react to etching with hydrofluoric acid.

Purpose: This investigation examined the effect of 9.5% buffered hydrofluoric acid, of 36% o-phosphoric acid alone and in combination on the surface structure of cut human dentin.

Material And Methods: Human molar teeth were sectioned in approximately 0.8-mm thick slices and treated with different acids or their combinations. Application periods were 10, 60, and 180 seconds. Specimens were processed for SEM and for energy-dispersive x-ray (EDX) microanalysis.

Results: The smear layer on the surface of sectioned dentin was not completely removed by hydrofluoric acid alone and that a dense amorphous precipitate was formed on the peritubular zone. Starlike structures in dentinal tubules were visible. EDX analysis revealed different fluoride content on the treated surface, dependent on the etchant used.

Conclusion: Topical application of hydrofluoric acid appeared to provide a dentinal surface with an amorphous precipitate of fluoride. This layer may be important both for resistance of dental caries in dentin and for bonding reactions.