Tetracycline demineralization of dentin: the effects of concentration and application time

The current investigation was initiated to study the effect concentration and application time has on the rate of tetracycline demineralization of dentin. Buccal and lingual surfaces of extracted bovine molars were ground to a smooth flat dentin surface using wetted silicon carbide discs. Standardized depressions were made in the dentin surface with a #909-055 diamond round wheel. Fresh tetracycline HCl (TTC-HCl) (Flavine Int. Inc.) solutions, i.e., 0, 25, 50, 75, 100, 125 and 150 mg/ml were prepared. A 30% citric acid solution was used as a positive control. The pH of each solution was recorded. 7 microl of each solution were pipetted into a depression and remained undisturbed for 1, 3, or 5 min. At the end of each application time period a fresh #3 cotton pellet was placed in the depression, once every 20 s for 1 min, to soak up the solution. The 3 pellets were placed in a 2.00 ml of 18 M omega H2O sample. As a measure of the rate of demineralization, the parts per million calcium (ppm Ca++) found in each sample were determined using atomic absorption spectrophotometry. Two-way analysis of variance was used to determine effects of TTC-HCI concentration and time on the rate of demineralization. No significant differences were found in the mean ppm Ca++ released at 1-, 3- and 5-min application times for 0, 25, or 50 mg/ml TTC. No significant differences were found in the mean ppm Ca++ released (i) between 3- and 5-min application times for 75, 100, 125 and 150 mg/ml TTC-HCl solutions and (ii) between 75, 100, 125 and 150 mg/ml TTC-HCl solutions within either the 3- or 5-min application times. The mean ppm Ca++ released at 3- and 5-min application times for 75, 100, 125 and 150 mg/ml TTC-HCI solutions were all significantly greater than the respective readings at the 1-min application time. The mean ppm Ca++ recorded for the 30% citric acid solution for all 3 application times were 3 to 5.5 x greater than the highest mean ppm Ca++ recording for TTC-HCl. The results of this study show that a 3-min application time of 75 mg/ml TTC-HCl solution is equally as effective at demineralizing dentin as is higher concentrations and/or longer application times, but was far less effective than a 30% citric acid solution.