| Summary: | 碩士 === 國立臺灣大學 === 臨床牙醫學研究所 === 87 === Numerous studies reveal fluoride provides excellent effects for caries prevention. There are two forms of fluoride uptake gained from tooth enamel reacting with fluoride, namely, firmly bound fluoride and loosely bound fluoride. Each of them may provide cariostatic function. Most topical fluoride treatments can only deposit loosely bound fluoride, but a pretreatment by DCPD-forming solution may significantly increase the formation of firmly bound fluoride. The electrochemical properties of enamel may well affect the formation of caries. According to Brown's hypothesis, cation permselectivity of tooth enamel will benefit the ongoing of lesion progression, while anion permselectivity can inhibit the caries happening. The aim of this study is to investigate the amount and types of fluoride uptake gained from various topical fluoride treatment, as well the combining change of electrochemical behavior, and by which we may explore the cariostatic mechanism of fluoride and may help to develop more effective topical fluoride treatment.
21 slices of bovine enamel membrane which surfaces were grounded off about 200um and had a thickness of about 400um were used as specimens. They were divided into three groups by random. The first group receive 2% NaF treatment for 4 minutes; the second receive 1.23% APF for 4 minutes; the third got a 4-minute pretreatment of DCPD forming solution and then received 2% NaF treatment for 4 minutes. After that they were stored in distilled water, 3 weeks later KOH extraction was performed to remove loosely bound fluoride. Fluoride content and membrane potential of bovine enamel were measured before and right after fluoride treatment, and membrane potential were measured 1, 2, 3 weeks after fluoride treatment and fluoride content were measured before and after KOH extraction. In this study, scanning electron microscope was also utilized to observe the morphologic changes of enamel surface occurred at the different stages.
About the investigation of fluoride uptake, there were no difference of initial fluoride content between three groups, the mean was about 51 ppm. The APF group got the largest amount of fluoride uptake after fluoride treatment and the NaF-group got the least but still exceeding 1000 ppm. The amount decreased significantly 3 weeks later, less then 10% of the previous was remained. While after KOH extraction, the amount of the NaF-group was almost zero, and the DCPD/NaF group got 264.7, 279.9 ppm (the 1st , 2nd layer)of firmly bound fluoride, more than 104.2,126.3 of the APF group. While observing the electrochemical behavior of bovine enamel, we noticed the initial membrane potential of specimens did not express uniformity as fluoride content , the range varied from -8.2mV to 11mV. After fluoride treatment, the membrane potential of all specimens were increased, which indicated cation permselectivity improved. The NaF group had the biggest increase (10.44mV), the DCPD/NaF group had the least(3.74mV). Then the membrane potential all decreased , and 3 weeks later only the APF group got a small difference from its initial value(2.67mV). SEM observation showed lots of CaF2-like globules deposited after APF and DCPD/NaF treatments, but no such finding in the NaF group. The deposition diminished after storing the specimen in distilled water for 3 weeks and even less visible after KOH extraction.
In this study, we could not find the change of electrochemical property was useful to explain the caries inhibition mechanism of fluoride, because fluoride treatment did not make anion permselectivity increase. However, pretreatment of DCPD-forming solution was noticed to increase the formation of both firmly bound and loosely bound fluoride significantly. Therefore, pretreatment of DCPD-forming solution may be a beneficial adjunctive procedure while applying fluoride agents topically, but more in vivo and clinical studies are needed for proving.
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