A novel approach to study in situ enamel erosion and abrasion lesions.

OBJECTIVES: This study investigated previous hypotheses that the tongue can abrade acid softened/eroded enamel surfaces. METHODS: Twelve upper removable appliances each retaining 2 anterior and 2 posterior human enamel specimens were constructed. Each specimen was exposed to acid on both surfaces, but only one surface was allowed contact with the tongue. Therefore, 96 surfaces were assessed. Appliances were worn from 9.30 to 17.00 Monday to Friday for 22days. Acid eroded lesions were created by immersing the specimens for 5min in 50ml orange juice three times daily. Enamel loss was measured using Quantitative light- induced fluorescence (QLF) and Non- contact profilometry (NCLP) and the differences (D) between tongue (Dt) and palate facing (DP) surfaces determined. RESULTS: %ΔFD(t-p) from the two anterior specimens were greater than from those placed posteriorly with mean values of 15.9% (±9.1) and 14.4% (±8.4), 5.6% (±8.7) and 4.5% (±6.6) respectively. Similarly, NCLP data showed anterior specimens had greater differences for mean step height (MSH) between tongue- facing and the palate- facing (control) surfaces than posterior specimens. MSHD(t-p) values were 59.4µm (±30.3) for anterior tongue facing surfaces and 55.5µm (±29.4) for posterior palate facing surfaces. For the posterior specimens MSH was 48.1µm (±26.1) and 51.7µm (±30.4) respectively (p<0.05). CONCLUSION: The greater enamel surface loss of the anterior specimens demonstrates that abrasion by the tongue on acid softened/eroded enamel in situ is likely.

The whitening effect of chlorine dioxide--an in vitro study.

OBJECTIVES: The aim of this study was to investigate the whitening properties and rate of bleaching action of chlorine dioxide and compare them with those of hydrogen peroxide of similar concentration. METHODS: Sixty bovine central incisor crowns were ground and polished until flat surfaces were obtained. The crowns were subjected to extensive staining cycles of artificial saliva, chlorehexidine and tea before being randomly assigned to three groups: chlorine dioxide (ClO2), hydrogen peroxide (H2O2) and deionised water (H2O). The crowns in each group were subjected to seven 2 min exposure cycles in addition to an extra 30 min cycle. CIE LAB spectrophotometric measurements were taken at baseline, after each 2 min, and each extended 30 min bleaching cycle. RESULTS: L* for ClO2 specimens was significantly higher only after the first 2 min cycle (p<0.001) while for H2O2 specimens, L* significantly increased after the first two cycles (p<0.001) and continued to increase, at a slower rate, until the end of the treatment cycles. ΔE was significantly greater within H2O2 than within ClO2 specimens (p<0.001). CONCLUSION: Chlorine dioxide whitens teeth at a faster rate than hydrogen peroxide. Specimens treated with chlorine dioxide were significantly lighter than those treated with hydrogen peroxide at the end of the first 2 min application cycle, however, extended exposures did not enhance color.