RESUMO
BACKGROUND: Studies show that fluoride (F) and nano-hydroxyapatite (nano-HA) would result in remineralization of white spot lesions (WSLs), which are among the most prevalent consequences of fixed orthodontic treatment. The present study evaluates and compares the clinical effects of an Iranian toothpaste containing nano-HA with F-containing one on early enamel lesions. MATERIALS AND METHODS: In this randomized clinical trial study, 50 patients who had received fixed orthodontic treatment were recruited immediately after debonding. Three photographs, including frontal, lateral right and left views of occlusion, were obtained. Moreover, surfaces with WSLs were recorded using DIAGNOdent. Plaque index of each patient determined using disclosing agents. At first visit, each patient was asked to select one type of toothpaste (nano-HA containing vs. F containing named A or B), randomly and were instructed how to brush their teeth (25 patients in each group). Examination was done at 1, 3, and 6 months' intervals. Finally, photographs were analyzed by Digimizer (V5) software, and the lesion extent was recorded in pixels. SAS 9.4 was used to analyze data and was set at 0.05. RESULTS: According to data, lesion extent showed a significant decrease (P < 0.001). At baseline, the difference between the two groups regarding the lesion extent was 268 pixels while it dropped to 89 pixels after 6 months. DIAGNOdent results showed that at baseline, fluorescence difference was 0.3 while it reached the number of 0.8 after 6 months, indicating the outperformance of nano-HA containing toothpaste. CONCLUSION: The Iranian nano-HA containing toothpaste performed better than F-containing one in terms of the amount of remineralization and diminishing the lesion extent.
RESUMO
When a high voltage is applied between two beakers filled with deionized water, a floating bridge of water is formed in between exceeding the length of 2 cm when the beakers are pulled apart. Currently two theories regarding the stability of the floating water bridge exist, one suggesting that the tension caused by electric field in the dielectric medium is holding the bridge and the other suggesting surface tension to be responsible for the vertical equilibrium. We construct experiments in which the electric field and the geometry of the bridge are measured and compared with predictions of theories of the floating water bridge stability. We use a numerical simulation for estimation of the electric field. Our results indicate that the two forces of dielectric and surface tensions hold the bridge against gravity simultaneously and, having the same order of magnitude, neither of the two forces are negligible. In bridges with larger diameters, the effect of dielectric tension is slightly more in the vertical equilibrium than surface tension. Results show that the stability can be explained by macroscopic forces, regardless of the microscopic changes in the water structure.
