The Impact of a Customized Tray on In-Office Bleaching Tooth Sensitivity: A Randomized Clinical Trial
It was recently demonstrated that using a tray over a bleaching agent reduces its pulpal chamber penetration, which can reduce tooth sensitivity. This study evaluated the effect of the sealed technique on the presence and level of sensitivity reported by patients during and after the bleaching procedure performed in office. Forty-six patients underwent a bleaching procedure with 35% hydrogen peroxide used in a single application of 45 minutes for two sessions with an interval of seven days. A customized tray was maintained over the bleaching agent during the entire procedure in half of the patients. The sensitivity level was evaluated during and immediately after the bleaching using verbal and visual analogue scales. The shade alteration was evaluated with a bleach guide scale. The peak sensitivity after 24 hours and the presence/level at 24 hours were also evaluated using a verbal rating scale. Relative risks were calculated for all time assessments. Data on the sensitivity level for both scales were subjected to Friedman and Mann-Whitney tests (α=0.05). Data on the shades were analyzed by two-way repeated-measures analysis of variance and Tukey's test (α=0.05). The use of a customized tray increased the relative risks to the tooth measured 24 hours after each bleaching session. The sealed technique also increased the level of tooth sensitivity only at 24 hours after the first session. No difference was observed between the bleaching techniques regarding the shade evaluation. Using a tray over the bleaching agent can increase the level and risk of tooth sensitivity for the first 24 hours after in-office bleaching.SUMMARY
Objective
Methods
Results
Conclusion
INTRODUCTION
Tooth discoloration is frequently treated by in-office bleaching, a conservative procedure that presents a high level of success.1,2 In-office bleaching consists of the application of a high-concentration hydrogen peroxide–based agent over the buccal surface of the teeth presenting discoloration. The bleaching ability has been associated with the oxidative effect of free radicals, released by the breakdown of H2O2.3 The peroxide penetrates the enamel by diffusion to reach the dentin tissue, where it oxidizes the darker molecules, promoting a whitening effect.4 However, the peroxides and their products also reach the pulp tissue and can damage the cells of this tissue.5-7 Clinically, the effects of peroxide on pulp tissue are observed by tooth sensitivity reported by patients.8,9
Some clinical trials have reported that 60% to 100% of patients undergoing in-office bleaching report some tooth sensitivity during the procedure.10-12 The tooth sensitivity observed is commonly transitory and disappears by 48 hours after the procedure.11 However, this adverse effect caused by bleaching can lead the patient to interrupt the treatment, compromising the results. Several alterations to bleaching protocols have been proposed in an effort to reduce tooth sensitivity. Prior application of desensitizing agents was attempted.13-16 Another approach was the preemptive use of anti-inflammatory drugs; however, this protocol also did not alter the risk of tooth sensitivity.11,12
A recent in vitro study found that covering the bleaching agent with a tray reduced the penetration of peroxide into the pulp chamber.17 This protocol was evaluated in a previous clinical trial that demonstrated a reduction in the level of sensitivity during the in-office bleaching procedure when the bleaching agent was covered with a customized tray, although no alteration to the relative risk was observed.18 However, the effect of this technique on tooth sensitivity during the first 24 hours after tooth bleaching was not evaluated in this study, although sensitivity is commonly reported by patients during this period. Furthermore, a small sample size (10 patients per technique) was evaluated. Thus, the aim of this parallel, single-blind randomized clinical trial was to evaluate the absolute risk of tooth sensitivity during and until 24 hours (primary outcome) as well as the intensity of tooth sensitivity and the bleaching effect (secondary outcome) of the sealed protocol for in-office bleaching compared to a conventional technique. The hypothesis of this study was that the sealed protocol reduces tooth sensitivity without altering the bleaching effectiveness.
METHODS AND MATERIALS
The protocol of study was registered at clinicaltrials.gov under no. NCT02067715 and followed the CONSORT statements.19
Study Design
This study was a randomized, single-blind, controlled trial with a parallel group and an allocation rate of 1:1. The patients were allocated to receive tooth bleaching with the bleaching agents during the procedure covered by a customized tray (experimental treatment) or without a tray (control). The study was conducted at the clinic of the School of Dentistry of the Federal University of Sergipe (UFS) from March 2014 to September 2014.
Inclusion and Exclusion Criteria
Only patients older than 18 years with good general and oral health were included in this study. The participants were recruited by means of advertisements placed on the buildings of the university. Patients with any of the six maxillary anterior teeth presenting caries, restoration, severe internal tooth discoloration (eg, tetracycline stains), hypoplasia stains, gingival recession, dentin exposure, pulpitis, or endodontic treatment were excluded. Participants who reported the continuous use of drugs with anti-inflammatory activities were also excluded from the study. The participants were required to have all six maxillary anterior teeth with shade 2.5M2 or darker, as judged by comparison with the scale of the Vita Bleach guide (Vita-Zahnfabrik, Bad Säckingen, Germany). One previously calibrated evaluator conducted the initial shade evaluation for eligibility assessment for the study.
Sample Size Calculation
The primary outcome of this study was the absolute risk of tooth sensitivity measured during the 24 hours after the bleaching procedure. The sample size was calculated using the absolute risk of tooth sensitivity (100%) found in a previous study using a single 45-min application of the same bleaching agent of this study (Whiteness HP Maxx, FGM, Joinville, SC, Brazil).11 The calculation was performed for a superiority trial, binary outcome, considering a power test of 80%, a significance level of 5%, and a decrease of 25% for the experimental treatment compared to the control. Thus, 48 patients were required, and 50 patients were included in the randomization to address the possibility of dropout during the follow-up.
Randomization
The participants were randomly allocated to a conventional protocol of in-office bleaching (control) or an experimental protocol of sealed bleaching. A blocked randomization (block sizes of 2 and 4) with an equal allocation ratio was used to produce a random list for the two comparison groups (www.sealedenvelope.com). A randomized list was computer generated by a person not involved in the study. Sealed opaque envelopes containing the treatment for each patient were numbered following the generated list and were opened by the operator only at the moment of the intervention. The patients were numbered according to the sequence of enrollment.
Baseline Measurements
The tooth sensitivity and shades of the six maxillary anterior teeth were evaluated prior to the bleaching procedures. Dental prophylaxis with pumice and water was performed using a rubber cup. The tooth sensitivity was evaluated using a visual analogue scale (VAS) and a verbal rating scale. The VAS consisted of a 10-cm color scale from green (no pain) to red (worst pain), where the patient set his or her pain level by pointing with a pen to the scale. The distance between the marking and the border of the scale was measured and recorded as the level of sensitivity. The tooth sensitivity was also evaluated using a 5-point verbal rating scale (VRS), where 0 = none, 1 = mild, 2 = moderate, 3 = considerable, and 4 = severe. For the initial evaluation, a slight airstream was applied over the buccal surfaces of the upper maxillary teeth. The patients were excluded if the scores were different from 0 in either scale.
Before starting the study, two evaluators were calibrated to use the Vita Bleach Guide scale. For this purpose, the shade of the maxillary anterior teeth from six volunteers (not included in the study) was recorded. This procedure was repeated to obtain a kappa coefficient higher than 0.85 for inter- and intraevaluator agreement. The shade evaluation was made by comparing the shade tabs with the middle third of the teeth. During the study, in the case of disagreement on evaluation, the evaluators discussed the matter to obtain a consensus. A third evaluator was used in the absence of consensus. The 15 shade tables in the guide were numbered from 1 (highest value—0M1) to 15 (lowest value—5M3) for data analysis.
Intervention
Alginate impressions of both dental arches of all patients included in the study were performed, and stone molds were prepared. Customized bleaching trays were made with acetate. The bleaching procedures were performed by two operators. A light-polymerized resin dam (Top Dam, FGM, Joinville, SC, Brazil) was applied over the gingival tissue corresponding to the teeth to be bleached. A 35% hydrogen peroxide gel (Whiteness HP Maxx) was applied over the buccal surfaces of the teeth and remained in position for 45 minutes, according to the procedure in a previous study.11 The bleaching tray was carefully positioned over the bleaching agent in the patients allocated to the sealed bleaching protocol. Two bleaching sessions were performed with a one-week interval between them.
Evaluation
The patients reported their level of tooth sensitivity using both the VAS and VRS during the bleaching procedure, and the highest values reported were recorded. The tooth sensitivity was also evaluated immediately (five minutes) after the bleaching procedures using the same scales. Twenty-four hours after the bleaching procedure, the patients were questioned about the level of sensitivity at that moment and the highest level felt until that moment, using only the VRS. The tooth sensitivity measurements were repeated during and after the second session. The shade evaluation of the six anterior maxillary teeth was performed one week after each bleaching session. All evaluations were performed by two evaluators blinded to the allocation assignment.
Statistical Analysis
Data on tooth sensitivity using the VRS were arranged into absolute risk of sensitivity (score 0 vs scores 1-4) and overall sensitivity intensity. The first measure represented the likelihood that sensitivity would occur, and the second was the level of intensity likely to occur. At each moment of evaluation, the percentages of presence of sensitivity between the techniques evaluated were compared using the Fisher exact test. The absolute and relative risk for each technique were calculated, followed by determination of the confidence interval (95%). The data on sensitivity intensity were subjected to the Mann-Whitney rank sum test (between two techniques at each assessment point) and the Friedman repeated measures analysis of variance on rank (between assessment points within each group). Multiple comparisons were performed using the Tukey test.
The absolute values measured (in cm) in the VAS were used in statistical analysis. The data did not show normality (Shapiro-Wilk test; p<0.05) and were subjected to the Mann-Whitney rank sum test and the Friedman repeated measures analysis of variance by ranks. The color evaluation data were analyzed by Mann-Whitney rank sum test (comparing the techniques at each assessment point) and the Friedman repeated measures analysis of variance by ranks (comparing assessment within each technique). Multiple comparisons were performed using the Tukey test. The significance level was set at α = 0.05 for all analyses.
RESULTS
The mean age (years) of the participants in this study was similar between the groups (conventional technique=22.5±2.0, and sealed technique=23.5±2.0 years; p=0.485; t-test). Four patients (two per technique) did not attend the second session of bleaching and were excluded from the study (Figure 1). Thus, 23 patients were analyzed for each bleaching technique, of whom 12 (52%) and nine (39%) were males for the conventional and sealed techniques, respectively (Fisher exact test; p=0.554).
Citation: Operative Dentistry 41, 1; 10.2341/15-029-C
Tooth Sensitivity
Regarding the absolute risk of tooth sensitivity, a significant difference was observed between the techniques only at 24 hours after the bleaching procedures (Table 1). Covering the bleaching agent with a customized tray significantly increased the risk of sensitivity 24 hours after the first (approximately 50%) and second (approximately 140%) sessions. However, the sealed bleaching presented the highest intensity of tooth sensitivity only at the evaluation performed during the first 24 hours (both peak and at the moment of reporting) after the first session (Table 2). For the conventional technique, comparison of the time assessments showed a significant difference only between the peak during the first 24 hours of the second session and the level measured immediately after this session. A tendency was observed toward increased sensitivity 24 hours after the two bleaching sessions for the sealed technique. The VAS did not show any difference between the techniques or time assessments (Table 3).
Color Evaluation
The results are displayed in Table 4. For both bleaching techniques, the highest shade scores were observed at the baseline, followed by measurement performed a week after the first session. The measurement performed a week after the second session showed the lowest shade scores. No difference between the techniques was found regardless of the time of assessment.
DISCUSSION
Despite the high success rate for in-office tooth bleaching, the tooth sensitivity reported by patients during and after this procedure remains a challenge for clinicians.8-12 Among the modifications in clinical procedures described in the dental literature, none of the protocols reported are effective in reducing the sensitivity compared to the control.11-13,15,16 Recently, an in vitro study demonstrated a reduction in peroxide penetration (main cause of sensitivity9) by the use of a tray over the bleaching agent.17 However, the outcomes of the present clinical trial did not demonstrate a reduction in the level or risk of tooth sensitivity when the sealed technique was used. On the contrary, the sealed technique increased the risk of tooth sensitivity 24 hours after the bleaching procedure. Furthermore, the level of sensitivity also increased during the first 24 hours after the first session. Thus, the hypothesis of the present study was rejected.
It was expected that the use of a customized tray over the bleaching agent would reduce the tooth sensitivity reported during the procedure. Some studies have demonstrated that enamel porosity may increase during tooth bleaching.20,21 More porous enamel facilitates simple air currents reaching the dentinal tubules, where the sensory nerve fiber endings are located. Thus, an air current may induce fluid shifts in the dentinal tubules, and these fluid shifts trigger impulses in the nerve fiber to induce tooth sensitivity.9,22 Thus, covering the tooth surface during the beaching procedure can avoid the induction of sensitivity by a draft stimulus. Furthermore, it has been speculated that the sealed technique can reduce the dehydration of the bleaching agent and its penetration into the pulp chamber.17,23 However, in the present study, the same level of sensitivity and risk of sensitivity development were observed during the bleaching procedure compared to the control.
A previous clinical trial found a reduction in the level of sensitivity using the sealed technique, whereas a difference from the control technique was observed in the evaluation performed at 40 minutes during the bleaching procedure.18 In contrast to the present study, those authors used only the VAS to analyze the sensitivity caused by the in-office bleaching technique performed in a single session. The high variability of data from the VAS and the smaller number of evaluated patients (10 per experimental condition) increase the chance of bias occurrence.24 Thus, the sample size included in that study, lower than the sample used in the present study, can help explain the differences between the studies. In the present study, in contrast, the risk and level of tooth sensitivity increased during the first 24 hours after the bleaching procedure compared to the control. Thus, it can be speculated that covering the bleaching agent results in slower peroxide penetration, resulting in delayed sensitivity. In another study, Know and others17 found a reduction of peroxide penetration into the pulp chamber when a tray was used over the bleaching agent; however, these results were not confirmed by outcomes of the present clinical trial.
Regarding the color evaluation, both techniques used in this study were effective in reducing the scores for shade, and the second session of bleaching promoted an additional bleaching effect. No difference between the bleaching techniques was observed when the bleaching effectiveness was evaluated. One important observation is that the bleaching effectiveness was evaluated only one week after the bleaching procedures. It has been recognized that longer periods of follow-up are necessary to allow the color stabilization.25 A prior study using the same bleaching protocols,18 however, did not find alteration between the values of color alteration (delta E) measured at seven and 28 days after the bleaching procedures. Furthermore, this previous study also did not demonstrate a difference on bleaching effectiveness between the sealed and conventional techniques regardless of the time of evaluation.
Unfortunately, despite good results in a preliminary clinical study,18 this was not confirmed in the present study, mainly because the sealed technique increased the absolute risk and intensity of tooth sensitivity after 24 hours of bleaching. It is important to emphasize that a single 45-minute application of bleaching agent was used for both techniques in the present study. A single 45-minute application facilitates the use of the sealed technique, while replacements of bleaching agent are not necessary. However, a single 45-minute application may result in the highest intensity of tooth sensitivity when compared to three 15-minute applications.10 Moreover, the sealed bleaching technique has some disadvantages, such as the necessity of fabricating a customized bleaching tray (similar to the one used for at-home bleaching). Thus, this is more time consuming and makes the technique more difficult to implement. Thus, it is reasonable to affirm that using the bleaching agent without any covering remains the best option for in-office bleaching.
CONCLUSION
Using a customized tray over the bleaching agent in in-office bleaching did not affect the level of sensitivity reported by the patient during the procedures, whereas this technique may increase the absolute risk and intensity of tooth sensitivity for the first 24 hours after in-office bleaching.
Flow diagram of the clinical trial.
Contributor Notes
Ana C Correia, undergraduate student, Department of Dentistry, Federal University of Sergipe, Aracaju, Brazil