The effect of tooth cleaning procedures on fluoride uptake in enamel.

Premolars were cleaned in different ways prior to application of a toph:al fluoride gel The teeth were extracted one week later and the fluorine concentrations in the surface enamel were determined by proton activation analysis. The facial and distal surfaces were analyzed. The results showed that a toothbrush and floss cleaning resulted in higher fluorine concentration than did a rubber cup prophylaxis using either a fluoridated or nonfluoridated prophylaxis paste. The results of numerous clinical trials have shown that the topical appheation of acidulated phosphate fluoride, (APF) solutions or gels on regular basis is effective in reducing the occurrence of dental caries in test populations, especially in areas that lack optimum fluoride concentrations in the water supply. ~ While evidence for this caries preventive effect is abundant, the exact mechanism by which it occurs remains unclear. When the fluoride is applied at relatively infrequent intervals (three to six months), resistance to dental caries appears to be associated, at least in part, with the amount of fluoride that is deposited in surface enamel as a result of the treatmentY-4 On the basis of these findings, it seems desirable to use topical application methods that result in the greatest possible fluoride uptake and retention by the surface enamel. Various treatment regimens have been described for the topical application of APF agents? A dental prophylaxis using an abrasive paste prior to the topical treatment is a common procedure. In the absence of extrinsic tooth stains, the rationale for use of an abrasive paste has been questioned.6The addi tion of sodium fluoride, stannous fluoride or APF solutions to these pastes has not been shown to be an effective vehicle for topical fluoride. 7 The purpose of tlhis project was to examine the effect of various toothcleaning procedures on fluoride uptake by enamel of human permanent teeth. Methods and Materials The procedures were completed on 24 informed and consenting patients who were scheduled to have four premolar teeth removed as part of their orthodontic treatment. The premolars were fully erupted and in contact on the distal surface with the adjacent tooth. A history of the subjects’ exposure to fluoridated water and topical fluorides was taken. Three treatment procedures and one control procedure was assigned to the four test teeth. Because of possible differences in chronology of crown development and fluoride exposure between maxillary and mandibular teeth, the upper and lower teeth of a patient were considered as separate blocks. Thus, there were a total of 48 blocks. Because there were only two teeth per block and four treatments, a balanced incomplete block design was used. Treatments were assigned to teeth at random subject to the constraints of this design. Any patients having calculus or stain present on the four test teeth were excluded from the study. The following procedures were assigned and completed on one of the four teeth: Treatment I: One tooth was thoroughly cleaned with a soft-bristled toothbrush using no dentifrice or prophylaxis paste. Interproximal surfaces were cleaned with unwaxed dental floss. Treatment II: A prophylaxis was completed on one test tooth with a rubber cup in a slow-speed handpiece using a commercially available prophylaxis paste containing fluoride in the form of APF and a fine-grit pumice and silicon dioxide abrasive." Usual clinical pressures were used during the prophylaxis procedure. The tooth was then rinsed and the interproximal surfaces were cleaned a Nupro, Janar Corporation, East Windsor, NJ. 228 TOOTHCLEANING D FLUORIDE UPTAKE: Steele, Waltner, and Bawden with unwaxed dental floss. The duration of prophylaxis on each tooth was approximately 10 seconds. Treatment III: A similar dental prophylaxis procedure was completed on another test tooth using a rubber cup in a slow-speed handpiece with the same commercially available prophylaxis paste but without fluoride. The tooth was then rinsed and the interproximal surfaces were cleaned with unwaxed dental floss. Control: No toothcleaning procedure or topical fluoride treatment was completed on the control tooth. The tooth was covered with orthodontic wax {including the interproximal areas} which was kept in place for 30 minutes following the fluoride treatment to minimize contact with residual APF gel. The treatment procedures were followed by a fourminute topical fluoride application with an APF gel containing 1.23% fluoride and 0.1M orthophosphoric acid at a pH of 4.5b in disposable polystyrene trays c. In the arch in which the wax-covered control tooth was located, the tray was divided in half and that part of the tray that would cover the tooth was discarded. This was to further prevent the fluoride gel from contacting the enamel surface of the control tooth. A sufficient amount of gel was placed in the trays to cover the test teeth, and suction was provided by a saliva ejector to eliminate unnecessary ingestion of excess gel. The patient was instructed to not eat or drink for 30 minutes following the fluoride treatment, at which time the wax on the control tooth was removed. All toothcleaning and topical fluoride procedures were completed seven days prio r to the extraction of the four teeth, which were always removed at a single appointment. No attempt was made to alter the patients’ fluoride exposure, diet, or oral hygiene measures during the time between the fluoride application and the extractions. The four test teeth were extracted using standard oral surgical techniques with the exception that a gauze pad was placed between the tooth surface and the beaks of the forceps. Contact between the forcep beaks and the tooth surface was made as close to the cementoenamel junction as possible. This was to avoid any mechanical abrasion of the enamel surface which was to be analyzed. After extraction, the teeth were stored in separate bottles containing gauze lightly moistened with 10% formalin until preparation for fluorine analysis. The method used for the analysis of elemental fluorine in the sample teeth utilized the application of the nuclear reaction 19F {p,a¥} 160. This method, b Luride, Hoyt Laboratories, Needham, MA. c Centrays, Cooper Laboratories, Fairfield, NJ. which has been referred to as charged particle or proton activation analysis, is a physical method for determining fluorine levels at various depths from the outer surface. The technique has the advantages of being nondestructive to the sample and producing good depth resolution. 81° After removing the root with a carbide bur in a high-speed handpiece, each tooth crown was bonded to a lead/antimony cube with a low-pressure adhesive and placed in a target chamber under vacuum. The cube could be rotated 90 degrees, allowing the proton beam to strike the facial and distal surfaces for analysis. All teeth were coated with a thin layer of gold to prevent artifacts due to charging. A 2 Mev Van de Graff accelerator was used to produce the proton beam. The beam was collimated to 1 x 1 1/2 mm2 at the tooth surface with a current of 80-120 nanoamperes. The beam was centered on a point midway between the cusp tip and the cementoenamel junction on the facial surface, and just below the contact point on the distal surface. A Ge(Li) detector was used to measure the gamma radiation being produced. The duration of gamma-ray detection was a function of the total proton beam charge which was 8 x 10-6 Coulombs. The resonance reaction occuring at 872 keV was used since it is the first strong reaction with a high sensitivity. 8 Resonance energies below 872 keV were considered as background radiation and corrections were made as the gamma-ray yield at these energies was low. The concentration of fluorine was determined by the yield of gamma radiation occurring at beam energies of 900, 1000, 1100, 1200, and 1300 keV. The increasing energies were necessary to achieve the 872 keV resonance reaction at successively greater depths from the surface. At the energies above 900, secondary resonances occur and corrections were made according to the method described by Kregar et al,9 using a hydroxyapatite pellet of known fluorine concentration as a standard. The specific depth at which the resonance reaction for fluorine occurred was a function of the beam energy and the stopping power (density) of the sample, in this case, hydroxyapatite.l°Thecorresponding872 keV resonance depths for the selected beam energies were as follows: 900 keV -.47 microns 1000 keV -2.34 microns 1100 keV -4.30 microns 1200 keV -6.36 microns 1300 keV -8.48 microns The estimated error of these depth measurements was +10%. Statistical analysis of the data was by a general linear model type of analysis." This was completed PEDIATRIC DENTISTRY: Volume 4, Number 3 229 on both the distal and facial surfaces at the five depths. Thus, there was a total of 10 dependent variables to be analyzed. The first analysis was to determine if the two blocks, maxillary and mandibular teeth, could be reduced to one block and so reduce the model to a total of 24 blocks instead of 48 blocks. Second, the data was tested for any overall differences between the treatments with an a -.05. If it was determined that an overall difference was present, the six individual treatment differences were examined. Because there were multiple comparisons on the same set of data, a result was considered significant at a p-value of _< .01.