Sonic Activation of a Desensitizing Gel Prior to In-Office Bleaching
This double-blind, randomized, and controlled clinical trial evaluated the effect of sonic activation during the application of a desensitizing agent (DA) containing 5% potassium nitrate and 2% sodium fluoride on the occurrence of tooth sensitivity (TS) associated with in-office dental bleaching. Treatment with or without sonic activation of the DA was randomly assigned to one-half of the maxillary teeth of 34 patients in a split-mouth design. On the side without sonic activation (noSA), the DA was applied and maintained in contact with the teeth for 10 minutes. On the sonic activation side (SA), the DA was activated 30 seconds per tooth. The DA application was followed by application of 35% hydrogen peroxide in two bleaching sessions separated by a one-week interval. The primary outcome was the absolute risk of TS, recorded using a numeric rating scale and a visual analog scale. Color was evaluated with a digital spectrophotometer and a value-oriented shade guide. No significant difference between treatments was observed in the absolute risk of TS, which occurred in 93% (p=1.00) of both noSA and SA groups. The TS intensity was higher in the 24-hour interval after sessions, for both treatments, without differences between them. There was no difference in the color change for the treatments, with the average change in number of shade guide units of the Vita Classical scale of 6.35 for both (p=0.87). Sonic activation of DA containing 5% potassium nitrate and 2% sodium fluoride did not reduce the absolute risk and intensity of TS associated with in-office bleaching.SUMMARY
INTRODUCTION
The demand for cosmetic solutions to treat tooth discoloration and improve smile esthetics is increasing. Dental bleaching techniques are attractive since they are the most conservative treatment and relatively simple to perform.1 Hydrogen peroxide, in varying concentrations, is the primary component used in the bleaching process, with a 35% concentration most commonly used for in-office whitening techniques.2 The safety in the use of hydrogen peroxide has been well-established,2–4 however, tooth sensitivity is a common adverse effect,3 particularly in patients with certain predisposing factors such as gingival recession or preexisting tooth sensitivity.5,6 In addition, cracks in the enamel are common and difficult to detect and may alter the diffusion intensity of the peroxide toward the pulp, with some increase in sensitivity.7,8
The use of a desensitizing agent associated with in-office bleaching may be an effective alternative to reduce sensitivity.9–11 Potassium nitrate is one such agent. Its exact mechanism of action is not known, but potassium nitrate is believed to reduce dentinal sensory nerve activity via chemical depolarization induced by the presence of potassium ions outside the nerve membrane.9,10 The level of potassium nitrate penetration is influenced by concentration and may also be partly affected by the viscosity of the material as well as other constituents of proprietary preparations.11 This may explain the controversial results in the literature regarding potassium nitrate as a desensitizing agent prior to in-office bleaching; three studies showed positive results,7,12,13 but three others did not.4,8,14 Although these results are promising, the application of desensitizing agents needs to be more effective.
Based on some positive results with dentin bonding agents,15–19 a possible alternative to improve the penetration of desensitizing agents could be the sonic activation of desensitizer agents. For dentin bonding agents, the sonic activation increased the adhesive infiltration into the dentin and enamel, thus enhancing its effectiveness.15–19 It could be assumed that the sonic activation of the desensitizing agent could increase its efficacy in a similar fashion. However, to the best of our knowledge, no study evaluated the effect of sonic activation of a desensitizing agent on tooth sensitivity associated with dental bleaching. Therefore, the objective of this clinical trial was to evaluate the tooth sensitivity in adult patients after in-office dental bleaching, using a sonically activated desensitizing agent (5% potassium nitrate and 2% sodium fluoride). We adopted two null hypotheses: 1) sonic activation of the desensitizing gel does not reduce tooth sensitivity associated with the bleaching procedure, and 2) sonic activation of the desensitizing agent does not alter the effectiveness of the bleaching.
METHODS AND MATERIALS
Protocol Registration
This clinical trial followed the standards of the Consolidated Standards of Reporting Trials20 and was approved by the Ethics Committee on Human Research of the local university (CAAE 49123715.1.0000.5020).
Study Design
This study was a randomized, double-blind (subjects and evaluator), controlled clinical trial with a split-mouth design. The study was registered at ClinicalTrials.gov (NCT03039270). Patients provided written informed consent and were submitted to two in-office bleaching sessions as detailed below. The trial was conducted at the clinic of the School of Dentistry of the local university from March 2016 to June 2016.
Eligibility Criteria
Patients included in this clinical trial were adults aged 18 years and older who sought dental bleaching treatment and were in good oral and general health. Participants were required to have six maxillary anterior teeth free of caries and restorations on the buccal face and at least one central incisor or canine showing A2 or darker coloration on a visual value-oriented color scale (Vita Classical, Vita Zahnfabrik, Bad Sackingen, Germany). Exclusion criteria were as follows: use of fixed orthodontic appliances, pregnant or lactating, severe intrinsic stains on the teeth (discoloration by tetracycline, fluorosis, and pulped teeth), use of any anti-inflammatory or antioxidant drugs, use of desensitizing toothpaste, and history of tooth sensitivity or associated pathology (eg, bruxism, gingival recession, and noncarious lesion with dentin exposure).
Sample Size Calculation
The primary outcome of this study was the absolute risk of tooth sensitivity. This risk was previously reported to be approximately 87%12,14 for in-office bleaching using 35% hydrogen peroxide. The present sample size was performed to test if there is equivalence between both treatments. Therefore, based on a power of 90% and alpha of 5%, a minus sample size of 25 patients per group was necessary to detect a difference of more than 33% between the groups, considering an equivalent limit of 31%. Considering a possible dropout rate of 35% of patients, the final sample size calculation was 34 patients per group.
Randomization
A randomized list was computer generated by an individual not involved in the intervention or evaluation. Participants were defined as blocks in the randomization process in which the sequence of treatment (sonic activation [SA] or no sonic activation [noSA] of the desensitizing agent) applied on their right and left (maxillary incisors and canine teeth) hemiarches was randomly set for each block by computer-generated tables (www.sealedenvelope.com). The sequence was inserted into sealed opaque envelopes and numbered sequentially. Once a participant was eligible for the procedure, the distribution of the allocation among the hemiarches was revealed when the assistant opened the envelope. The participant and the evaluator were blinded to the protocol.
Study Intervention
The operator applied a desensitizing gel containing 5% potassium nitrate and 2% sodium fluoride (Desensibilize KF2%, FGM, Joinville, Brazil) to the buccal surfaces of the maxillary anterior teeth (central incisor to canine) as described in Table 1. On the noSA side (control), the gel was left for 10 minutes, and after that, the desensitizing agent was rubbing with a rubber cup for 20 seconds and then removed from the teeth with cotton and water irrigation. On the SA side, immediately after the gel application, the disposable brush (Microbrush, KG Sorensen, Cotia, Brazil) was coupled to the sonic device (Smart Sonic Device, FGM, Joinville, Brazil), and sonic activation was performed for 30 seconds per tooth, and after that, the desensitizing agent was rubbing with a rubber cup for 20 seconds, and then removed from the teeth with cotton and water irrigation.
For patient blinding, the operator also applied vibration to sites in the contralateral hemiarch where the desensitizing gel was not applied (eg, marginal gingiva, premolars, lower teeth, and lips). The gel remained in contact with the teeth of the SA side for 2.75 minutes. The desensitizing agent was sonically activated at 15-second intervals for each tooth from the hemiarch. Each activation interval was intercalated by the 15-second activation of a gel-free site. Each tooth received 30 seconds of sonic activation of the gel.
After the sonic activation was applied to each of the three anterior teeth of the SA side, the desensitizing agent was removed from the teeth with cotton until the 10 minutes of treatment on the noSA side was completed, then the teeth were irrigated with water.
After removal of the desensitizing gel, the gingival tissues of the teeth to be bleached on both sides were isolated using a photoactivated resin barrier (Top Dam, FGM, Joinville, Brazil). For the bleaching of the two sides, a 35% hydrogen peroxide gel (Whiteness HP, FGM, Joinville, Brazil) was applied for 45 minutes. The gel was refreshed every 15 minutes during the 45-minute session. The operative sequence is summarized in Table 1. Participants were submitted to this protocol again after one week, for a total of two bleaching sessions.
Color Evaluation
Prior to the bleaching procedure, the participants received anamnesis, intraoral examination, and dental prophylaxis with pumice and water. An examination was also performed to verify the presence of cracks in enamel. For this, we used a curing light with an adapted diagnostic tip (Radii Plus, SDI Brazil, São Paulo, Brazil), positioned on the palatal face of the teeth so that the emitted white light crossed the teeth indirectly, showing cracks if present.
The color evaluation was performed in a room under artificial lighting without interference from outside light. To standardize the lighting conditions during shade determination, a 500° Kelvin handheld lamp was used (Color-I-dent, Waldmann, Germany). It was evaluated in the first bleaching session and 7, 14, and 30 days after the first bleaching session. Two methods were used: objective evaluation using the Easyshade spectrophotometer (Vident, Brea, CA, USA) and subjective evaluation using two value-oriented shade guides—Vita Classical (Vita Zahnfabrik) and Vita Bleachedguide 3D-MASTER (Vita Zahnfabrik). For both methods, color was checked at the middle third of the teeth. For subjective evaluation, the 16 color guides of the Vita Classical scale were organized from the highest value (B1) to the lowest (C4). Although the scale is not linear, it was organized by value to allow ranking for analysis purposes. The Vita Bleachedguide 3D-MASTER scale already features 15 linearly organized guides of the highest value (OM1) to the lowest (5M3).
For calibration, the color assessments of 10 patients were conducted three times with an interval of three days between assessments to verify the intra- and interobserver agreement. The operator was considered calibrated only when he was able to achieve a weighted kappa of 80% in two consecutive readings of the same teeth in 10 different patients. Agreement between color evaluators was verified to obtain a minimum agreement percentage of 85%.
For the objective shade evaluation, an impression of the maxillary arch with high-putty silicone paste (Clonage, Nova DFL, Rio de Janeiro, Brazil) was taken, and a window on the labial surface of the silicone guide was created by using a metal device with a 6 mm radius to standardize the area for color evaluation with the spectrophotometer. Color was determined using the parameters of the digital spectrophotometer, on which the following values were indicated: L*, a*, and b*, where L* represented luminosity (a value from 0 [black] to 100 [white]), a* represented the color along the red-green axis, and b* the color along the yellow-blue axis.
The difference between baseline and each recall period (ΔE*) was calculated using the following formula: ΔE* = [(ΔL*)2 + (Δa*)2 + (Δb*)2 ]1/2. For the subjective evaluation, the 16 tabs of the shade guide (VITA Classical, VITA Zahnfabrik,) were arranged from lightest to darkest as follows: B1, A1, B2, D2, A2, C1, C2, D4, A3, D3, B3, A3.5, B4, C3, A4, and C4. Color changes were calculated from the beginning of the active phase through to the individual recall times by calculating the change in the number of shade guide units (ΔSGUs), which occurred toward the lighter end of the value-oriented list of shade tabs.
Two examiners, blinded to the allocation assignment, scheduled these patients for bleaching and evaluated their teeth against the shade guide at each assessment. In the event of disagreements between the examiners during shade evaluation, a consensus was reached.
Tooth Sensitivity Evaluation
The patients recorded the occurrence of tooth sensitivity in a diary, registering if they experienced tooth sensitivity during the treatment and within 48 hours of bleaching. Intensity was assessed with two scales: the Numerical Rating Scale (NRS) and the Visual Analogue Scale (VAS).
The NRS scale comprises scores to denote the intensity of pain (0 = none, 1 = mild, 2 = moderate, 3 = considerable, and 4 = intense). The VAS scale is a horizontal 10 cm line in which patients indicated a vertical line corresponding to the intensity of their sensitivity, according to their proximity to the scores at the end of the line (0 = none and 10 = severe). After that, the value was measured using a millimeter ruler. As two bleaching sessions were performed, the worst scores or numerical values obtained were considered for statistical purposes. The values were organized into two categories: percentage of patients who reported tooth sensitivity at some time of treatment (absolute risk of sensitivity) and intensity of pain.
Statistical Analysis
Data analysis followed the intent-to-treat protocol and involved all randomly allocated participants. The data were first analyzed using the Kolmogorov-Smirnov test to assess whether the data followed a normal distribution, as well as the Bartlett test for equality of variances to determine if the assumption of equal variances was valid. Based on that, the primary outcome (absolute risk of tooth sensitivity) was compared using the McNemar test (α=5%). Regarding the evaluation of intensity of tooth sensitivity, a group comparison for each pain scale, a comparison of the two groups was performed using the Wilcoxon paired test (α=5%).
For color evaluation, mean values and standard deviations were calculated from the change in the number of ΔSGU that occurred toward the lighter end of the scales. These ΔSGU and color difference (ΔE) values for the two groups were compared using the Student t-test (α=5%).
RESULTS
A total of 44 participants aged between 20 and 32 years were examined to select 34 participants who met the inclusion criteria (Figure 1). Three participants did not attend the return visits and were excluded from the study. There was a high level of agreement between the evaluators (93%). The mean color of the incisors in the SA and noSA groups was 9.3 ± 3.5 and 9.4 ± 2.9, respectively. The means and standard deviations of color change are described in Table 2. No significant difference between the groups regarding efficacy of bleaching was observed, with mean values of ΔE of 8.3 and 11.5 for the noSA and SA groups, respectively (p=0.53). Both treatments were effective, with mean values of ΔSGU for the Vita Classical scale of 6.4 and 6.3 in the SA and noSA groups, respectively (p=0.87).
Citation: Operative Dentistry 46, 2; 10.2341/19-283-C
No significant difference between treatments was observed in the absolute risk of tooth sensitivity (Table 3). In both groups including both bleaching sessions, 93% of patients experienced tooth sensitivity in the first 48 hours after bleaching (p=1.0).
Concerning the intensity of tooth sensitivity, the highest mean scores were found 1–24 hours after the bleaching sessions (Table 4; p=0.001), with no significant differences between the noSA and SA groups in the VAS scale (3.8 and 3.9, respectively; Table 4; p>0.05). For the NRS scale, the mean scores were 2 for both groups in the same time period (Table 4; p>0.05). There was no statistical difference between the intensity of sensitivity scores in either scale immediately after to one hour after bleaching compared with those recorded 1–24 hours after bleaching (Table 4; p>0.05). However, for both scales, the interval from 24 to 48 hours after bleaching was statistically different from the other intervals, showing the lowest mean scores (Table 4; p=0.001).
DISCUSSION
Based on promising results observed in previous studies,15–19 this clinical trial aimed to evaluate the effect of sonically activating a desensitizing agent prior to bleaching. The assumption was that sonic activation would enhance the desensitizing agent effect. However, we observed no significant difference in the occurrence of tooth sensitivity between the SA and noSA groups.
Considering that a desensitizing agent was applied in both groups, the higher occurrence of absolute risk and intensity of tooth sensitivity in both groups was unexpected. Although some contradictory results were published in the literature regarding the use of a containing-potassium nitrate gel as a desensitizer agent in the in-office bleaching,4,7,8,12–14 several clinical studies7,12,13 showed that the use of a desensitizing gel, based on 5% potassium nitrate, before in-office bleaching with higher concentrated hydrogen peroxide reduced the bleaching-induced tooth sensitivity.
A possible explanation for this high prevalence could be the presence of a predisposing factor such as enamel cracks. Although the mechanisms involved in tooth sensitivity have not been fully elucidated, it is presumably related to the permeability of dental tissues,4 which facilitates the passage of the peroxide molecules to the pulp, where it may induce a pain-causing inflammatory reaction.21 In the present trial, more than 70% of participants’ teeth showed cracks, and a high occurrence of tooth sensitivity was found, regardless of treatment group.
It would be expected that, with a higher number of cracks in the evaluated teeth, an increase in the diffusion rate of the peroxide gel into the dentin and consequently the pulp4,5 would cause a higher absolute risk of tooth sensitivity.6,7 This seems to explain the high percentage of patients with tooth sensitivity, even in the noSA group (control). It is worth mentioning that although the occurrence of cracks is very common in adult patients,22,23 it has not been reported or addressed in numerous previously published clinical trials.7,12–14,24–29 Therefore, future studies should be conducted to evaluate the effect of desensitizing agents in the occurrence of tooth sensitivity associated with in-office dental bleaching in patients with and without presence of enamel craze lines.
It is worth mentioning that, in the present study, in the SA group, the application of the desensitizing gel for 10 minutes was followed according to the manufacturer’s recommendation and the previously published literature.4,7,8,12–14 However, the time of desensitizing gel application was significantly shorter in the SA group (2.75 min) than for the noSA group (10 min).
In our point of view, for the SA procedure to be clinically relevant and applicable, the sonic activation should be employed during a period shorter than the regular application of 10 minutes. If the clinician would have to wait the same 10 minutes during the sonic activation, there would not be a rationale to add this step. Besides, if the same duration of gel application was used for both groups, it would not be clear if any possible outcome was truly due to the sonic activation or the effect of the desensitizing itself.
However, it is important to mention that the shorter application time of desensitizing gel in the SA group would be partially responsible for the high occurrence of tooth sensitivity in this group. Thus, future clinical studies should be conducted to evaluate the effect of different application time of desensitizing agents associated with the sonic activation device.
The average color change observed in this study for both groups was 6.35 SGU, which is within the 5–9 SGU range of color change reported for 35% hydrogen peroxide bleaching.30,31 A previous clinical trial12 assessed the effectiveness of bleaching with 35% hydrogen peroxide after the application of a desensitizing gel containing 5% potassium nitrate and 2% sodium fluoride, and we found that the desensitizing agent did not decrease bleaching effectiveness, which still exhibited a mean color variation of 6.2 SGUs, similar to that found in the present study.
No difference was found in color change between the groups and confirmed that sonic activation of the desensitizing gel did not interfere with bleaching effectiveness. Actually, as previously observed for several clinical trials,4,7,8,12–14 potassium nitrate does not react with hydrogen peroxide or compete with the same sites for binding in the dental structure.32
CONCLUSION
After two sessions of 35% hydrogen peroxide bleaching, sonic activation of the desensitizing agent for a shorter application time did not reduce the absolute risk or intensity of tooth sensitivity. The use of a desensitizing agent with sonic activation did not reduce the effectiveness of dental bleaching.
Flow diagram of study design phases, including enrollment and allocation criteria.
Contributor Notes
Clinical Relevance
The use of a desensitizing agent with sonic activation for a shorter application time did not reduce the absolute risk of tooth sensitivity associated with in-office bleaching.
Verônica P. Lima, DDS, MS, PhD candidate, Graduate Program in Dentistry, Federal University of Pelotas, Brazil
Luciana M. Silva, DDS, MS, PhD, adjunct professor, School of Dentistry, Federal University of Amazonas, Manaus, AM, Brazil
Alejandra Nuñez, DDS, MS, PhD student, School of Dentistry, Department of Restorative Dentistry, State University of Ponta Grossa, Ponta Grossa, PR, Brazil; professor, Department of Restorative Dentistry, San Francisco de Quito University (USFQ), Quito, Ecuador.
Ana Armas-Vega, DDS, MS, PhD, adjunct professor, Facultad Ciencias de la Salud, Eugenio Espejo, Universidad UTE, Quito, Ecuador.
* Alessandro D. Loguercio, DDS, MS, PhD, associate professor, School of Dentistry, Department of Restorative Dentistry, State University of Ponta Grossa, Ponta Grossa, PR, Brazil; visiting professor, Facultad Ciencias de la Salud, Eugenio Espejo, Universidad UTE, Quito, Ecuador.
Leandro M. Martins, DDS, MS, PhD, associate professor, School of Dentistry, Federal University of Amazonas, Manaus, AM, Brazil.