Study On Fluoride Release And The Effect Of Caries Prevention Of Fluoride-Containing Pit And Fissure Sealants In Vitro

Background:Pit and fissure sealant (PFS) is recognized as the most effective way to prevent pit and fissure caries, and the success or failure of the technology is closely related to the performance of sealant. Traditional sealants form a protective barrier after seal the surface of tooth to prevent bacteria and food debris to enter the pit and fissure, while the original bacteria in the pit and fissure die gradually because of no nutrition. Thus, the occurrence of pit and fissure caries is prevented. It can also stop the development of early caries. But there is no preventive effect on smooth surface caries because it only seal the pit and fissure of teeth, and traditional sealants can not prevent secondary caries caused by microleakage of the sealant.Recently, caries-preventive effect of fluoride has been confirmed by a lot of reseach and a variety of agents have been widely used. Fluoride-containing pit and fissure sealant as the 4th generation material, it combines effects of fluoride and sealant. It not only has the role of protective barriers of traditional sealant, but also through the slow release of fluoride ion to the oral environment, it can prevent caries of the tooth surface adjacent to the sealant potentially. With the development of materials, the performance of glass ionomer cement (GIC) has been greatly improved, and it can release fluoride ion.So recently,many scholars classify glass ionomer cement into the area of fluoride-containing pit and fissure sealant.There are very little studies on fluoride-containing pit and fissure sealant in China. Basic researches on its caries-preventive mechanism are rare. Whether fluoride-containing sealant is better than traditional sealant, what's the mechanism of fluoride release and caries prevention, as well as whether the glass ionomer cement can used as pit and fissure sealant in clinic? These issues need to further explore.So it is necessary to investigate systematically the fluoride-containing pit and fissure sealant in depth.Objective:Based on some domestic and abroad studies,the objections of this study are to observe and compare the state of fluoride release from two different types of fluoride-containing pit and fissure sealants in artificial saliva, and the effect of fluoride-releasing resin sealant and glass ionomer sealant on inhibition of enamel demineralization in vitro,and marginal microleakage.Through this study,we evaluate the ability of fluoride release and the effect of of two different types of fluoride-containing sealants,and provide basic research datas for in-depth study on mechanism of caries prevention of fluorine-containing pit and fissure sealant, meanwhile, provide theoretical evidence for clinical wide use of fluorine-containing sealant, in particular glass ionomer sealant to some extent.Material & Methods:1.Study on fluoride release from two different types of fluoride- containing pit and fissure sealants in vitro. Five disc-shaped specimens (6mm×1.5mm)of each sealant were prepared.Each specimen was immersed in 12ml artificial saliva at a temperature of 37℃.Fluoride ion concentrations were measured at 1,2,3,7,14,21,28 and 35 days after immersion with a fluoride-specific ion electrode and a acidometer meter.2.Study on inhibition of enamel demineralization by fluoride- containing resin sealant and glass ionomer sealant in vitro. 30 noncarious extracted human third molars were randomly divided into three groups with 10 samples in each group.Cavity preparations was placed on the buccal surfaces of the molars. Then the specimens were filled with fluoride-releasing resin sealant(ClinproTMSealant), glass ionomer sealant (FujiⅨGP) and nonfluoride-releasing resin sealant(Concise),respectively. After thermocycling for 300 cycles, measure the surface microhardness of 1mm rim of sound enamel surrounding the sealant-filled cavities in each group.Then the specimens were placed in an artificial demineralizing solution for a week.The surface microhardness of specimens for each group was detected again after demineralization.3. Study on microleakage between fluoride-containing resin sealant and glass ionomer sealant in vitro. 30 noncarious extracted human third molars were randomly divided into three groups with 10 samples in each group. The occlusional surfaces of the specimens were sealed with ClinproTMSealant, FujiⅨGP and Concise,respectively.After thermo- cycling for 120 cycles, all specimens were immersed in 1% solution of methylene blue dye for 48 hours, then the microleakage of each specimen was measured under a stereomicroscope.Results:1.The highest fluoride release from two types of sealants was observed in first day after immersion.The level of fluoride ion released from the sealants decreased rapidly in a week,and invariable release of fluoride was observed between 14 to 35 days.Fluoride released from glass ionomer sealant was higher than that from fluoride-containing resin sealant in each period of time(P<0.01).2. The mean reduction of surface microhardness were(87.30±23.84)HV for ClinproTMSealant group(,76.90±27.75)HV for FujiⅨGP group and(147.67±46.42)HV for Concise.There was a significant difference (P<0.01) among the fluoride-releasing materials versus the nonfluoride- releasing material.There was no significant difference between ClinproTMSealant group and FujiⅨGP group(P>0.05). 3. The result of dye penetration revealed there was no significant difference in microleakage among two test groups versus the control group(P> 0.05), and there was no significant difference between 2 test groups (P> 0.05),either.Conclusion:1.The study indicates that both the new type of fluoride-containing resin sealant and the glass ionomer sealant can release fluoride into liquid surrounding persistently and slowly as fluoride reservoirs during a period of time.Therefor, it could enhance the effect of caries prevention of pit and fissure sealants potentially.2.This study showed that both the fluoride-releasing resin sealant and glass ionomer sealant could effectively reduce the amount of enamel demineralization adjacent to the materials.Fluoride ion released from the sealants afforded protection to the adjacent enamel against in vitro demineraIization to some extent.3. All of the three types of pit and fissure sealants showed lower microleakage, while the adaptation of glass ionomer material(FujiⅨGP) was comparatively similar to resin sealants,the sealing ability was satisfactory.4. Fluoride-containing pit and fissure sealant has some value and broad prospects of clinical application, it is worth further study.