Fluoride Release And Recharge Capability In Vitro Of Several Fluoride-releasing Materials

Using restorative materials with fluoride release and fluoride recharge capability torestore teeth defecst can increase the resistance of enamel structure around the restorationto demineralization and consequently can prevent or delay the formation of secondarycaries around the restoration. Therefore, testing and evaluating the fluoride release andfluoride recharge capability of restorative materials containing fluoride compound are veryimportant for studing fluoride-releasing materials.AIM：In this study, we aimed to compare the fluoride release and fluoride rechargecapability of several types of dental restorative materials available in market and anexperimental fluoride release composite resin. Moreover, we also evaluated the effects of film-forming materials of fluoride varnishes on the early caries prevention of enamelstructure in vitro.METHODS：1. Testing of the fluoride release and recharge capability of restorative materials in vitroDiscs specimens of eight restorative materials, two conventional GICs (Fuji IX andFuji VII), one VLC GIC(Fuji II LC), two compomers (Compoglass and Beautifi), twocomposite resin (Z350and Charisma) and an experimental fluoride-releasing compositeresin, were made and then immersed in5.0ml deionized water respectively. The fluoriderelease in each day for each discs was tested using a fluoride-specific ion electrode. On the28thday, all discses were exposed to1.23%fluoride foam for four minute to rechargefluorid, followed by immersing in water again and fluoride released to the water wastested daily. The surface microstructure of the discs before and after immersion wereobserved under SEM.2. The surface micro-morphology and fluoride element distribution of restorative materialsThe surface micro-morphology and fluoride element distribution of each specimenwere observed and tested after immersion in distilled water for0day,1day,28days andafter fluoride recharge in fluoride foam for four minutes under SEM and EDAX.3. Comparative study of the inhibition of enamel demineralization of fluoride filmfluorescence strength and microhardness90bovine enamel blocks were divided into6groups and the labial surface of eachblock was treated with a fluoride varnish containing one of the following film-formingmaterial: copal resin(Copal), osmotic acrylic resin(OAR), ethyl methacrylate copolymerresins(PMME), polymerized rosin(Rosin), polyvinyl butyral(PB), or a commerciallyavailable fluoride varnish, Duraphat, respectively. After removal of the varnish, all enamelblocks were subjected to pH cycling for7days, and then the percent loss of surfacefluorescence and surface hardness of each enamel block were tested.4. Effects of the film-forming materials of fluoride varnishes on the inhibition of enameldemineralizationAll the enamel blocks were longitudinally cut through the center and embedded in acrylic resin so that the sectioned enamel block could be exposed and polished. Thedemineralization depth of each enamel block was measured using polarizing microscope.RESULTS：1. Fluoride-releasing materials showed different capability in fluoride-releasing andrecharging. GIC demonstrated an initial “burst” of fluoride release within48h and then arapid decrease, but it remained a higher fluoride release after28dayes comparing to othermaterials. Compomer and composite resin had no burst release of fluoride and presented alow level of fluoride release.. For all materials, fluoride releases increased substantiallyafter being immersing in fluoride foam for four minutes but declined rapidly to theprevious level after3~4days.2. After immersing in the deionized water for28days, all materials s showed variousdegree of erosion on the surface, with giomer being eroded mainly in glass particles.Therefore it can be inferred that the fluoride release is mainly from the dissolving ofglassy phase in GIC or compomer.3. All fluoride varnishes significantly reduced the percent loss of surface fluorescenceand surface hardness of the enamel blocks, and fluoride varnish containing OAR presentedthe least percent loss of surface fluorescence and surface hardness and leastdemineralization depth.4. We identified normal enamel showed negative birefringence by polarizingmicroscope. The experimental areas showed the main characteristics of demineralizationafter demineralization, presenting negative birefringence in surface and positivebirefringence under the surface. The fluoride varnish containing OAR as film-formingmaterial presented a significantly less depth in demineralization than other film-formingmaterials.CONCLUSION:(1).Characteristics of fluoride release is closely related to the type of the material.Glass ionomer cement releases more fluoride than other materials.(2). Characteristics of fluoride recharge depend on the matrices, fillers contained, aswell as porosity and densityof the material. (3). The fluoride release is mainly from the the dissolving of glassy phase in GIC orcompomer.(4).The film-forming material of a fluoride varnish affects its ability to preventenamel early caries in vitro significantly, and osmotic acrylic resin is a promisingfilm-forming material for fluoride varnish.