Evaluation of an autopolymerizing fissure sealant as a vehicle for slow release of fluoride.

The purpose of this study was to investigate the rate of fluoride release from an autopolymerizing fissure sealant containing various proportions of sodium fluoride. In the first phase, cured resin discs containing 0.00%, 0.1%, 0.25%, 1.0%, and 2.5% sodium fluoride were evaluated over a 180-day period. The second phase studied the release from the fissure sealant containing 2.5% sodium fluoride when bonded to the occlusal surfaces of noncarious premolars and molars. Determinations were made at the end of 7 and 30 days. The pattern of fluoride release was similar for all experimental groups with considerable fluoride being leached during the first day but decreasing rapidly thereafter. The surge of fluoride released after one day apparently was due to sodium fluoride on the surface of the cured sealant resin which quickly went into solution. The fluoride released from samples containing 2.5% sodium fluoride was significantly greater than that released from the other test specimens from days 31 to 90. However, there was no significant difference in fluoride release from the resins containing 1.0% and 2.5% sodium fluoride during the 91 to 180-day test period. Over 96% of the total incorporated fluoride remained bound at the end of the test period. In conclusion, a bis-GMA fissure sealant would not appear to be an appropriate vehicle for delivering fluoride to the oral cavity. The cariostatic effects of fluoride are well known. However, these benefits are limited primarily to the smooth surfaces of teeth. Approximately 80% of the dental caries experienced by children are of the pit and fissure variety. 1 Several methods have been proposed to provide protection to these areas by using sealants. Investigations by Buonocore and others led to the development of the first effective and clinically practical occlusal fissure sealant which was an ultraviolet light-cured reaction product of bisphenol A and glycidyl methacrylate (bis-GMA). 2,3 The protective effects of fluoride are enhanced if its clearance from the oral cavity is prolonged. Systems have been developed for providing ambient fluoride, e.g., varnishes containing--or used with-fluoride compour~ds, fissure sealants containing fluoride, or fluoride-releasing devices. Varnishes containing fluoride have provided marked protection to the tooth even though the varnish layer lasts only a few days. 4"6 A device that would provide a slow, continual release of fluoride should provide even greater benefit. 7 However, they are not yet available for general use. It would be useful if an existing sealant could be modified in order to provide protracted low levels of fluoride. Attempts to combine the benefits of extended topical fluoride application with occlusion of caries-susceptible fissures have been made in the past. 8,9 Recently, E1-Mehdawi et al. presented data which suggested that a hard, nonflexible, ultraviolet light-cured, bis-GMA fissure sealant ~ could be used as a vehicle for extended fluoride release. They reported that fluoride ion release increased over the duration of the in vitro study and with the level of sodium fluoride in the resin. 1° The present study investigated the rate of fluoride release from mixtures containing various proportions of sodium fluoride in an autopolymerizing fissure sealant, b Methods and Materials The stock for these mixtures was formed by adding sodium fluoride powder to bottles of universal sealant resin, b These mixtures when added to a catalyst b (1:1) formed a plastic containing various concentrations of fluoride. Five experimental groups were prepared: Nuva Seal; L.D. Caulk Co., Milford, DE. Delton Pit and Fissure Sealant (Batch #2M402); Johnson & Johnson Products, Inc., East Windsor, NJ. PEDIATRIC DENTISTRY: September 1984/Vol. 6 No. 3 145 Group A (control) --0.00% sodium fluoride Group B --0.1% sodium fluoride Group C --0.25% sodium fluoride GroUp D --1.0% sodium fluoride Group E --2.5% sodium fluoride The study was divided into two phases. In the first phase, six resin discs, or specimens, were made for each of the five groups. Each specimen was transferred to a plastic tube containing 5 ml of distilled water which was replaced after each extraction period. The extraction, periods were 0-1, 2-7, 8-30, 3190, and 91-180 days. A 1 ml aliquot of each extract was mixed with an equal volume of total ionic strength adjustor (TISAB IIc). Fluoride levels of the resultant mixtures were measured using a fluoride-specific ion electrode and meter, c The electrode was allowed to equilibrate for one minute in each sample before recording the results. Data from each time period were analyzed with a one-way ANOVA. Mean differences were tested using Tukey’s method. 1~ In the second phase of the study four extracted noncarious mandibular permanent molars and four maxillary premolars were selected and washed with a toothbrush and distilled water. The autopoIymerizing fissure sealant containing 2.5% sodium fluoride was placed on the ocdusal surface of the teeth according to the manufacturer’s instructions. Each tooth was placed in an individual plastic test tube along with 5 ml of distilled water. Fluoride release was determined at the end of days 7 and 30 using the same methods described earlier.