Evaluation of Acid Resistance of Enamel Using Microdetermination of Phosphorus I. Correlation Between Agar Plate and Window Methods in Regard to the Amount of Phosphorus in Vitro System

• Published in: JOURNAL OF DENTAL HEALTH Vol. 22; no. 3; pp. 346 - 352
• Main Authors: TAKEUCHI, Mitsuharu, KAWASAKI, Tohru
• Format: Journal Article
• Language: English; Japanese
• Published: Japanese Society for Oral Health 1972
• ISSN: 0023-2831; 2189-7379
• DOI: 10.5834/jdh.22.346

TAKEUCHI proposed the epidemiological principles of dental caries attack introducing a mathematical formula in 1961. In this formula, the multiple factors involved in dental caries attack are classified and analyzed quantitatively: the rate of caries incidence could be expressed as functions of the factor (p) represented by the sugar consumption after eruption of the tooth, and of the factor (q) of susceptibility to caries by the morphological form of each kind of tooth, and of the factor (r) of the susceptibility to caries equally distributed among individuals. This study was conducted to established a useful method for evaluation of acid resistance of the surface enamel in order to elucidate one of the factors involved in the above mentioned formula. The agar plates used in this study were made of agar (0.5% weight/volume) and 0.1M lactic acid-sodium lactate buffer solution, pH 4.5, mixed together by heating in a water bath for 20 minutes and left standing for 24 hours to solidify in a glass vessel of 2mm in depth. Circular plates of 6.5mm in diameter were cut out and used for the experiments. Impacted third molars extracted at the clinic of oral surgery were collected and stored in 10% formalin. One hundred of teeth for the experiment were chosen from this stock samples. The surface of the enamel was polished with a slurry of pumice and glycerin and then washed several times with re-distilled water and dried at 50°C for 5 minutes. The agar plate was placed on the surface of the enamel for 5 minutes. After application of the agar plate, the phosphorus dissolved from the enamel was estimated by spectrophotometric determination with molybdate-safranin. Using the same teeth, a conventional window method was applied: 4×4 mm of enamel surface was exposed and the rest of surface was sealed with paraffin wax. The exposed surface of enamel was immersed in 10ml of 0.1M lactic acid-sodium lactate buffer solution, pH 4.5, agitated continuously at 37°C for 5 minutes or 30 minutes. The results showed that in the agar plate method, the values of mean and standard deviation were 1.00μg and 0.38μg, respectively. The distribution of phosphorus dissolved from the enamel revealed a fairly normal distribution pattern. In contrast, the window method pattern did not show a normal distribution, namely, the peak of distribution was biassed to low phosphorus dissolved in each case of 5-minute and 30-minute application. The amount of phosphorus extracted by the agar plate method was plotted against the amount of phosphorus dissolved in 5-minute and 30-minute application by the window method in order to examine the correlation between them. The result showed that there was a significant correlation between the amount of phosphorus of both methods (r=+0.570, r=+0.645). It was suggested that the agar plate method devised for this study could be useful for clinical testing.