The Experimental And Clinical Research On Fluoride Preconditioning Attenuates Sensitivity Induced By Tooth Bleaching

Background:With the increasing concern for esthetics, dentists are working hard to give their patient what is called the'perfect smile'. Another important feature that contributes to a pleasing appearance of teeth is color. A 1996 survey involving 215 subjects from the United Kingdom reported that 50 percent of the population perceived they had some kind of tooth discoloration, which indicated that patients commonly were dissatisfied with the color of their teeth. This finding helps to explain why the popularity of tooth bleaching hasincreased during the last few decades.Discoloration of anterior teeth is an esthetic problem, which requires effective treatment. Currently, many treatment modalities are available such as laminate veneers, jacket crowns, abrasion and bleaching. Among these, bleaching is the simplest, most common, least invasive and least expensive means for diminishing or eliminating stains in vital teeth.Over the last decade, home vital tooth bleaching has attracted the interest of patients and dentists due to its high success rates, ease of use and media publicity. This procedure utilizes low concentrations of hydrogen peroxide (3% to 7%) or carbamide peroxide (10% to 20%). Recently, new in-office bleaching products that utilize high concentrations of hydrogen peroxide or carbamide peroxide have been re-introduced. The latter procedure, which involves 30% to 35% carbamide peroxide or hydrogen peroxide, is totally under the dentist's control and has the potential for bleaching quickly in situations in which it is effective. Although the use of higher concentrations can shorten the treatment time, it have been reported to cause surface roughening of teeth and may induce in the patient an increased level of sensitivity, that clinicians cannot predict easily. Dentists have used several approaches to reduce tooth sensitivity. Reduction in wearing time and frequency of application, temporary interruption of whitening and use of an active ingredient such as potassium nitrate are methods commonly used by clinicians. To the extent of our knowledge, no study has been published addressing the sensitivity-preventive effect of fluoride when used concomitantly with a bleaching regimen.Objectives:The aim of our study was to evaluate whether the use of 2 percent sodium fluoride before bleaching regimen would decrease tooth sensitivity when compared with a placebo. to research the mechanisms of the sensitivity resistance, and to confirm the applicability and reliability of the fluoride in clinic.Materials and Methods:1. The study population consisted of twelve patients who required the extraction of first premolars for orthodontic reasons. Tooth A4,B4 and C4 were treated with BEYOND cold light bleaching and Tooth D4 was served as the control without treatment. Immediately after bleaching treatment, all teeth were extracted and prepared for scanning electron microscope.The SEM images were taken and the morphology changes was evaluated in surface of enamel and dentin.2. Selecting the 48 teeth of twelve patients who required the extraction of first premolars for orthodontic reasons. Twelve participants were divided into three groups: bleaching with NaF-treated group, bleaching-treated group and control group. Then bleaching agents were applied according to manufacturers' instructions. Immediately after bleaching treatment, all teeth were extracted and prepared for scanning electron microscope. Morphologic observations were carried out with SEM.3.60 rat were divided into three groups:bleaching with NaF-treated group, bleaching-treated group and control groug. Rat teeth of two treated group were bleached by 35 percent carbamide peroxide for 5 minute,10 minute and 15 minute.Every 5 rats were killed after bleaching immediately,3 days and 7days respectively.Then histopathologic examination of pulp tissue was taken with microscopy.4. Fifteen patients between 12 and 26 years of age with caries-free first premolars scheduled for orthodontic extraction were divided into three groups:bleaching with NaF- treated group, bleaching-treated group and untreated groug. Then bleaching agents were applied according to manufacturers' instructions. All teeth were extracted at the immediate, 3days later and 7 days later. Immediately after extraction,4 mm of the mostapical portion of the root was sectioned off and each specimen was placed in a vial containing 10% neutral buffered formalin. The samples were prepared for histological evaluation and pulp reactions were semi-quantitatively graded as none, slight, moderate and severe.5. The crowns of 36 caries and developmental defect free human maxillary incisors were stained internally with a standardised tea solution.12 specimens were power bleached with light activated 35% hydrogen peroxide and 12 were placed in water. Another 12 specimens bleached by same agents after using 2%NaF. Both exposure times were 30 min. Vita shade guide [SG] were employed prior to, after tea staining and after power bleaching/water treatments. Eighteen specimens each from three group were sectioned mesio-distally. An additional 18 specimens from the bleach and the control group were sectioned labio-palatally. The stain area for each specimen was measured using image analysis software.6. We divided 40 participants into two groups:one that received a placebo and another that was treated with fluoride. All patients used 35 percent carbamide peroxide for 30 minute. Before using of HP, the patients were treated by fluoride or placebo for ten minutes. Then we statistically analyzed the perception of the intensity of tooth sensitivity and the shade changes for both groups.Results:1. Mild demineralization was observed on the surface of enamel and collapse of collagen scaffold was also observed on the longitudinal section of dentine.The diameter of dentinal tubule was not uniform due to peritubular dentine being demineralized.2. In the bleaching-treated group, mild demineralization was observed on the surface of enamel and collapse of collagen scaffold was also observed on the longitudinal section of dentine.The diameter of dentinal tubule was not uniform due to peritubular dentine was demineralized. In the bleaching with NaF-treated group, the demineralization of enamel and dentin were reduced and some diameters of dentinal tubule were smaller than bleaching-treated group.3. No severe symptoms were observed for all teeth after bleaching with light activated 35% hydrogen peroxide. Vessel dilatation and exudation were found when bleaching time more then 5 min. Only slight histological changes were noticed following vital bleaching with 35% carbamide peroxide for up to 10 min in approximately one-third of the intact teeth. There no significant differences berween two treated groups.4. Slight pulpal changes were detected in 13 of the 44 bleached teeth. Neither moderate nor severe reactions were observed. The findings indicate that the slight histological changes sometimes observed after bleaching tend to resolve within two weeks post-treatment. Statistical differences existed only between the untreated control and the treatment groups.5. With tea staining, the mean changes in Vita shade guide units (SGU) ranged from 3.66 to 8.33. Samples bleached and sectioned mesio-distally showed stain coverage of 28.6-39.4%, while palatal sections showed stain coverage of 58-72%. Control samples, whether sectioned mesio-distally or labio-palatally, showed staining throughout the dentine (97-100% coverage).6. The use of fluoride gel did not affect the whitening efficacy of the CP. We observed no difference between the groups receiving the placebo and the fluoride treatment in terms of tooth sensitivity experience (P>0.05); however, patients who received the placebo had a higher-intensity tooth sensitivity than that of patients who received the fluoride (P<.001).Conclusion:1. Use of high concentrations of hydrogen peroxide or carbamide peroxide can immediately induce demineralization of dental enamel surface and changes'of dentin morphology.2. Fluoride can reduced the demineralization of enamel and dentine obviously, which may be applied as a therapeutic tool for sensitivity induced by tooth bleaching.3. The findings from this study demonstrated that vital bleaching procedures using 35% carbamide peroxide might cause initial mild, localized pulp reactions. However, the minor histologicalchanges observed did not affect the overall health of the pulp tissue and werereversible within weeks post-treatment. No significant change between the groups receiving the placebo and the fluoride treatment.4. A 35% hydrogen peroxide in-office bleaching gel demonstrated bleaching into dentine of uniform depth and no difference between the groups receiving the placebo and the fluoride treatment.5. The use of 2 percent sodium fluoride before each bleaching regimen does not affect the bleaching efficacy of HP. Also, the use of sodium fluoride gel reduces the intensity of tooth sensitivity.