An in vitro assessment and a pilot clinical study of electrical resistanceof demineralized enamel

Electrical resistance measurement was evaluated in vitro and in vivo as a m ethod for comparing the remineralizing performance of toothpastes. In the i n vitro, study, areas of sound enamel on 12 unrestored, mature, extracted h uman molars and bicuspids, with electrical resistance readings greater than 99.99 M Omega, were demineralized to an electrical resistance of 1 to 4 M Omega. The teeth were divided into three groups. The change in electrical r esistance was measured following a 15 cycle regimen of treatment, demineral ization and salivary soaking. Treatments were live-minute exposures to eith er a 1:2 slurry in saliva of Enamelon(R) (E), a remineralizing fluoride-too thpaste also containing soluble calcium and phosphate ions, a 1:2 slurry in saliva of Crest(R) (C), a conventional fluoride toothpaste (P), or to sali va alone. Demineralization was performed with a 30-minute exposure to 0.1 M lactic acid 50% saturated with calcium hydroxyapatite. The salivary soakin g was 1 hour in duration. The mean electrical resistance of the E, C and th e saliva treated sites was 63.9 +/- 4.3. 37.6 +/- 9.5 and 2.1 +/- 0.7 M Ome ga, respectively The final resistance was statistically different for each group (p < 0.05). A pilot clinical study was then conducted to assess the e lectrical resistance technology in vivo. Eighteen adult subjects with at le ast one site of early enamel caries with an electrical resistance between 1 .0 M Omega and 20.00 M Omega were randomly assigned to either Enamelon, Cre st, or a non-fluoride placebo toothpaste and asked to brush twice daily. Af ter three months, the mean resistance of the test sites was 23.57 M Omega f or E. 9.61 M Omega for C and 13.24 M Omega for P. However, the mean resista nce changes did not proceed consistently over time. At the end of the study , the electrical resistance measurements on four sites out of twelve in Gro up E were suggestive of remineralization, whereas measurements on one site out of ten were suggestive of remineralization in Group C and two or three sites out of twelve were suggestive of remineralization in Group P. Progres sion of demineralization was possibly indicated in only one site, which was in Group C. There were insufficient subjects for statistical significance in the pilot clinical study. There were apparent problems with the variabil ity of some measurements between visits in the in vivo study. Overall, howe ver, the results of both studies indicate that with modifications to the eq uipment, electrical resistance measurements may be a means of comparing the remineralization performance of toothpastes.