| It has been widely acknowledged that Fluoride plays an important role in the prevention of caries prevalent worldwide. It is generally accepted that the preventive effect of fluoride is mainly topical: the continuous presence of low fluoride concentrations in the fluid phase surrounding the teeth is now considered essential to have an optimal cariostatic effect. However, because of their drawbacks such as short-term fluoride retention on tooth surface and in dental plaque, requirement of high frequently repeated intakes of agents containing low concentrations of fluoride ion, possible danger of toxicity when using concentrated fluoride administration, etc, topical fluoride agents are not yet ideal. Therefore, it is rather inviting to develop new pharmaceutical forms that can sustained release fluoride or control the release of it.Microspheres as drug carries have the advantages of sustained or controlled release, passive or active drug targeting to specific tissues and so on, which will notably reduce the side effects of drug and improve their bioavailability as well as patient compliance. Therefore, microspheres as drug delivery system have drawn much attention in pharmaceutical field and have been successfully applied in some clinical cases.In order to improve the therapeutical efficiency and retention of fluoride in oral cavity, and to explore the possibility of preparing targeted fluoride delivery devices, this study-5-aimed at developing a new kind of fluoride-releasing system梥odium fluoride gelatin microspheres (NaF-GMS). We applied gelatin to encapsulate sodium fluoride, the most useful fluoride salts, by emulsification chemical-crosslinking method. The biological characteristics and fluoride releasing profile of NaF-GMS were investigated. Their cariostatic ability was tested in artificial dental plaque in vitro.This study is divided into 3 parts: 1. Preparation and quality examinations of the sustained-release NaF-GMS. 2. Investigation of fluoride releasing characters in vitro and in vivo. 3. Experimental study on the cariostatic properties in vitro.1. Preparation and quality examinations of the sustained-release NaF-GMS.On the basis of gelatin's self-crosslinking and its solidification by aldehyde, NaF-GMS were prepared using emulsification chemical-crosslinking method. Optimal preparation parameters were obtained by the orthogonal design. The drug content and micro-encapsulation efficiency were evaluated using fluoride ion selected electrode (ISE). The morphology and particle size of NaF-GMS were determined by observing the samples on a scanning electron microscope (SEM). The results show that the microspheres were spherical in shape and easily dispersible in character, with an average diameter of about (11.33?.56)um. The drug content and encapsulation efficiency were 8.80% and 76.73%, respectively. They were stable when stored in common conditions such as in refrigerator or at room temperature.2. Investigation of fluoride releasing characters in vitro and in vivo.The in vitro fluoride releasing profiles of NaF-GMS in saline and artificial saliva (pH4.5, pH6.8 respectively) were analyzed with dynamic dialysis method simulating the temperature in vivo. Rabbits' salivary fluoride concentrations before and after topical administration of NaF-GMS were tested using a fluoride electrode at different times. The-6-study showed that fluoride-releasing kinetics in vitro fitted to first-order and Higuchi equations. In saline, the equation was ln(l-P)= -0.014t-0.166, T1/2was 38.80min, while theT(1/2 of NaF solution was 5.05min. It could be concluded from this point that the NaF-GMS had a sustained release property. Moreover, data in artificial saliva of pH4.5 and pH6.8 following the equations of ln(l-P)= -0.015t-0.497 T1/2=13.05min and P=0.253+0.040t1/2 (T1/2=39.06min respectively, indicated that fluoride release rate was increased in pH4.5 artificial saliva. This might have important clinical meanings. Experiments conducted in rabbits' oral cavity...
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