The caries-preventive effects of full- and half-strength topical acidulated phosphate fluoride.

Due to concerns about the potential for acute toxicity following professional application of topical fluoride, this clinical trial was undertaken to determine if half-strength acidulated phosphate fluoride (APF) would be as clinically effective in reducing caries as the currently used 1.23% APF. Three hundred and sixteen junior high school students, 11-15 years of age, living in a nonfluoridated area were assigned randomly to 1 of 3 groups: a 1.23% APF thixotropic gel group, a 0.6% APF thixotropic gel group, or a placebo gel control group. Visual and tactile dental examinations, toothbrush and floss prophylaxis, and topical application of assigned gel were performed twice annually for each child. After 24 months, both the 1.23% APF group and the 0.6% APF group experienced statistically significant (p < .05) caries increment reductions when compared to the contro! group. Although the 2 fluoride-treated groups experienced caries increment reductions that were not statistically different from each other, there was a tendency for the half-strength fluoride (0.6% APF) to be less effective, especially in reducing pit and fissure caries. Thus, while a half-strength fluoride gel may be effective in reducing caries in selected cases where acute fluoride toxicity is of special concern, these findings suggest hat some effectiveness in pit and fissure caries prevention may be sacrificed. Therefore, this clinical trial does not support widespread reduction of fluoride content to 0.6% Fin twice-annual, professionally applied topical fluoride formulations. The results of previous clinical trials have shown that the use of acidulated phosphate fluoride (APF) gels containing 1.23% fluoride (F-) on a twice-annual basis is effective in preventing dental caries. ~-3 However, recent studies have shown that a considerable amount of fluoride may be ingested during the course of a standard professional topical fluoride application 4,5 and that plasma fluoride levels achieved after such an application may reach potentially toxic levels. 6-8 Acute fluoride toxicity is of particular concern when administering a topical fluoride treatment to the small child patient because of the exposure to a relatively higher fluoride dose per body weight than in the case of an adult receiving the same treatment. Since most currently used gels are both flavored and acidulated, salivation is stimulated and swallowing of this excess saliva-fluoride mixture generally occurs during gel application. The amount ingested by a young child may be increased if the child is unable to use a saliva ejector effectively. This potential for toxicity would be diminished if the fluoride concentration of the currently used 1.23% APF gels could be reduced without compromising clinical effectiveness. Due to differences in conditions under which clinical studies are conducted, the clinical effect of variations in fluoride concentration cannot be determined by comparing the results obtained in independent trials. As a result, the lowest fluoride concentration that achieves optimum clinical effectiveness when applied twice annually has not been established. Evidence exists, however, to support the idea that a lower concentration than the current standard 1.23% APF gel may be effective. All the current theories of mechanism of action of topical fluorides including remineralization, reduction of enamel solubility and antibacterial action, propose that lower concentrations of fluoride would suffice for these effects. 9-12 Fluoride gels of different concentrations ranging from 0.25 to 1.25% Fhave been tested in the rat model and all were found to be significantly effective in inhibiting caries. 13 In a previously reported clinical trial PEDIATRIC DENTISTRY: September 1985/Vol. 7 No. 3 185 in which a high-release 1.23% fluoride solution was compared with a gel that released only half as much fluoride, both agents were found to be equally effective in reducing caries when the agents were applied twice annually. 3 However, the vehicles were not the same and that variable may have been a factor. Although such supporting evidence exists, no clinical trials directly comparing the caries reducing effects of twice-annual, professionally applied topical gels of varying fluaride concentrations have been reported. This controlled clinical trial was designed to compare directly the caries-preventive effects of an APF topical gel containing the standard 1.23% Fwith those of a gel containing a reduced fluoride concentration (0.6% F-) when the agents were applied twice annually in a child population. Methods and Materials The initial study sample consisted of 428 seventh grade students in nonfluoridated ( < 0.2 ppm F-) areas of Guilford County, North Carolina. Students undergoing fixed orthodontic appliance therapy were excluded from the study since the presence of banded appliances would not allow adequate examination and would interfere with the direct contact between enamel and fluoride. Students who returned a permission slip were assigned randomly to 1 of 3 groups of equal size: those to be treated with a 1.23% APF gel (Group A); those to be treated with a 0.6% APF gel (Group B); and those to receive a placebo gel containing no fluoride (Group C). At the beginning of the study in March, 1981, each child received a dental prophylaxis, a dental examination, and an application of his assigned gel. These procedures were repeated every 6 months (_+ 3 weeks) for 2 years. To obtain subject demographic data and ascertain the extent of the child’s dental care and past fluoride exposure, a questionnaire was mailed to the parents of each participant. Prior to examina~tion and gel application, each subject’s teeth were stained with a disclosing solution. "~ The stained plaque was removed with a soft bristle brushb and unwaxed dental floss b by dental hygiene students or dental assistants who were familiar with the study protocol. No prophylaxis paste or dentifrice was used in the prophylaxis procedure. A single examiner (PH) performed all dental examinations. Portable dental chairs and lights were set up in the schools for the procedures. The teeth were dried with compressed air prior to the examinations. Front surface mirrors and sharp #23 explorers were Trace Dental Disclosing Solution -Lorvic Corp: St. Louis, MO. Oral B 40 Toothbrushes and Oral B Unwaxed Dental Floss -Coopercare, Inc: Fairfield, NJ. used to perform the visual and tactile examinations. Radiographs were not taken. The DMFS index was used as the measurement of caries experience. The examiner adhered to the DMFS criteria set forth by the Caries Measurement Task Group~a as modified by the NIDR for the National Dental Caries Prevalence Survey. ~s Only erupted, permanent teeth were included in the study. Third molars were excluded from the data. The data for each child were recorded by trained individuals on separate forms designed for ease of recording as well as for facilitating subsequent data entry into a computer. Results from prior examinations were not available to the examiner during the course of the study. All data were edited before, during, and after entry into the computer by means of logical checks by a dentist (PH). The edited data then were processed using a Statistical Analysis System (SAS) package. ~6 Following plaque removal and examination, the subjects received a 4-min topical application of their assigned gel. Approximately 2.5 ml of the appropriate gel was placed into the trough of disposable styrofoam trays~ by trained dental personnel. The study followed the classic double-blind protocol in that the examiner, subjects, and dental auxiliaries were unaware of which agent was applied in each subject. All gels were packaged in plain containers labeled only with an identifying code letter. The code was broken only after data collection was completed. Group A received an application of a 1.23% FAPF thixotropic gel; d Group B received an application of a 0.6% Fo APF thixotropic gel; a and Group C received an application of a placebo thixotropic gel. d To minimize potential bias, the placebo gel was similar to the fluoride gels in color, odor, and physical appearance but contained no fluoride or acid. Prior to placing the fluoride trays firmly onto the dental arches, the teeth were dried with compressed air or cotton gauze. A saliva ejector was placed sublingually to remove excess saliva and fluoride. Participants were allowed to expectorate into a disposable bowl after the trays were removed and each child then was instructed not to eat or drink for 30 min. Students were observed for at least 15 min following gel applications for any signs of acute toxicity such as nausea or vomiting. The data collected were evaluated statistically to determine the significance of DMFS increment difCentrays -Pacemaker Corp: (Coopercare, lnc). All gels were manufactured for this study by Pacemaker Corp: (Coopercare, |nc). The manufacturer of the gels used in this study had no regulatory or administrative role in the planning or implementation of the study or in the analysis of results. After receipt from the manufacturer, fluoride release from the gels was measured according to the flow dialysis method of Congleton et al. ~7 186 PREVENTIVE FFECTS OF TOPICAL FLUORIDE: Hagan et al. ferences using analysis of variance (ANOVA). TM Differences were regarded as significant at the 95% confidence level. Only data from subjects who finished the 2-year study were included in the data analysis.