A MORPHOLOGICAL COMPARISON OF RADICULAR DENTIN FOLLOWING ROOT PLANING AND TREATMENT WITH CITRIC-ACID OR TETRACYCLINE HCL

The conditioning of root surfaces with saturated solutions of citric acid or tetracycline is unpredictable in facilitating new attachment, perhaps due to the low pH of these solutions which may be denaturing the organic matrix of the root as well as demineralizing the surface. The purpose of the present study was to compare the effects of a saturated solution of citric acid (pH = 1) with that of a 0.5% solution of tetracycline HCl (pH = 3.2) on radicular dentin with regard to the removal of the smear layer, exposure of dentinal tubule openings, and demineralization of the peritubular dentin. 10 bovine incisors were used in this study. The crowns and apical 1/3 of the root were resected and the resulting root segments were then frozen in icy freon. The cementum was fractured off of the root to produce a fracture-exposed, non-instrumented dentin surface. This fracture-exposed dentin surface was divided into 4 specimens, the 1st being a fracture-exposed, non-instrumented dentin control specimen (FE). After removal of the (FE) specimen from the root segment, the remainder of the fracture-exposed dentin surface was thoroughly root planed and then subdivided into the 3 remaining specimens. One of these specimens served as the root planed dentin surface (RP); another specimen (CA) was immersed in saturated citric acid (pH = 1) for 5 min and then washed in water for 5 min; the final specimen (T) was immersed in a 0.5 mg/ml solution of tetracycline HCl for 5 min and rinsed in water for 5 min. Using this technique, each of the 4 dentin specimens were derived from the same non-instrumented, fracture-exposed dentin surface. Dentin specimens were dehydrated in a series of graded ethanol solutions, critical point dried and sputter-coated with 20 nm of gold. Dentin surfaces were viewed and photographed in the SEM at magnifications of x 2000 and x 5000. Surfaces were examined for the presence of a smear layer, and the presence and morphology of dentinal tubule orifices. Morphometric analyses of the number of dentinal tubules openings per unit area, the percent of total surface area occupied by dentinal tubules and the diameter of dentinal tubule openings were performed using the photographs taken at x 2000 magnification with a digitizing tablet and morphometric analysis computer software. Instrumentation of these fracture-exposed dentin surfaces (RP) resulted in the formation of a surface smear layer. Treatment of the dentin surface with citric acid (CA) removed the smear layer and exposed and enlarged the dentinal tubule openings. The diameter of dentinal tubule openings on (CA) surfaces was significantly greater than that of tubules on (FE) surfaces suggesting a demineralization of the peritubular dentin. Treatment of dentin surfaces with tetracycline (T) did not routinely remove the surface smear layer, and tubule orifices were not significantly different in size from either CA or FE surfaces. These findings suggest that a 0.5% solution of tetracycline demineralizes the peritubular dentin to a lesser degree than does citric acid, and that higher concentrations of tetracycline HCl may be required to consistently remove the smear layer produced by instrumentation.