# Tooth sensitivity and efficacy of in-office bleaching in restored teeth

## Tooth sensitivity and efficacy of in-office bleaching in restored teeth

Journal of Dentistry, 2013-04-01, Volume 41, Issue 4, Pages 363-369, Copyright © 2013 Elsevier Ltd

## Objectives

The aim of this clinical trial was to evaluate efficacy (BE) and tooth sensitivity (TS) of in-office bleaching with a 35% hydrogen peroxide (HP) in patients with aesthetic restorations.

## Methods

Hydrogen peroxide 35% was applied in two sessions, of three 15 min applications, in 15 patients with upper anterior sound teeth (S) and 15 with aesthetic restorations (R). The colour was recorded at baseline, one week and 6 months after treatment completion. Patients recorded TS on a 0–4 scale. The BE was evaluated by two-way ANOVA and Tukey’s tests ( α = 0.05). The percentage of patients with TS was evaluated by Fisher’s exact test and TS intensity of treatments was compared with Mann–Whitney U -test ( α = 0.05).

## Results

All participants experienced TS at least once during treatment. Higher TS intensity was observed in R (1.5 [1/1.75]) compared to S (0.5 [0/1.25]) during the bleaching ( p < 0.05). S and R demonstrated similar tooth colour enhancement compared to baseline ( p < 0.05) and both presented colour stability after 6 months of evaluation ( p > 0.05).

## Conclusions

The in-office bleaching with 35% HP was effective in patients with aesthetic restorations, however, a higher intensity of TS was observed during the bleaching protocol.

## Clinical relevance

In-office dental bleaching can be performed in patients with adhesive restorations promoting satisfactory results; however, it can promote higher intensity of sensitivity compared to patients with sound teeth.

## Introduction

Nowadays, vital tooth bleaching is one of the most requested cosmetic dental procedures asked by patients who want an aesthetically more pleasing smile. This procedure is performed by the application of carbamide or hydrogen peroxide gels on tooth surfaces and can be done at home, with or without the supervision of the dentist, or in-office by the clinician.

At-home bleaching is the most widely taught bleaching technique in the USA and the most accepted technique among patients. This is probably due to the high number of successful records of satisfactory results reported with this technique. However, there are still some people that do not want to use bleaching trays or who want faster results. In addition, some patients may not adapt well to the daily use of a bleaching tray, which increases the treatment time and costs. In these circumstances, in-office bleaching seems to be the most suitable treatment.

Although clinical studies have shown that in-office bleaching can achieve as satisfactory degree of whitening as at-home bleaching, as long as the materials are used for the appropriate period of time most of the data we have about tooth bleaching has been gathered from participants with sound teeth, because the clinical protocol of these studies did not usually include participants with restored teeth. Few studies have included participants with adhesive restorations on anterior maxillary teeth in clinical trials. However, in a clinical practice, vital tooth bleaching is often performed on teeth with adhesive restorations on a daily basis, and therefore, more knowledge about the bleaching efficacy (BE) and tooth sensitivity (TS) of in-office bleaching in relation to this common condition is required.

Laboratory studies have shown that higher amounts of hydrogen or carbamide peroxide can penetrate the pulp chamber of teeth with adhesive restorations, compared to sound teeth. Considering that TS has been reported as a common side effect, affecting more than 60% of the patients that undergo this cosmetic treatment, this situation may be even worse in patients with restored teeth. To the extent of the authors’ knowledge, no previous study has compared the BE, and most importantly, the TS experiences of patients with and without adhesive restorations. Therefore, the aim of this clinical trial was to compare the degree of whitening and the TS intensity of patients with and without adhesive restorations.

## Materials and methods

This clinical investigation was approved under protocol number 12/2011 by the scientific review committee and by the committee for the protection of human beings of the local university (UEPG). Based on pre-established criteria, 30 volunteers were selected for this study. Two weeks before the bleaching procedures, all the volunteers received dental screening and prophylaxis with pumice and water in a rubber cup. They also signed an informed consent form.

## Inclusion and exclusion criteria

Participants included in this clinical trial were between 18 and 35 years old. A total of 64 participants were examined in a dental chair to check if they meet the inclusion and exclusion criteria ( Fig. 1 ). The participants were required to have central incisors of shade A2 or darker, as judged by comparison with a value-oriented shade guide (Vita Lumin, Vita Zahnfabrik, Bad Säckingen, Germany). The following were excluded from the study, since they would not be suitable for a cosmetic study such as bleaching: people who had undergone tooth-whitening procedures, smokers, pregnant/lactating women, people with severe internal tooth discoloration or endodontic treatment in anterior teeth, people taking any kind of medicine, with bruxism habits, recession, dentine exposure, or active carious lesions. Participants who reported to have spontaneous TS or sensitivity to hold and cold drinks were also excluded from the study.

Flow diagram of the clinical trial.

## Sample size calculation

With a 90% confidence interval, the number of subjects required to detect an absolute risk of TS was around 80% for both groups with a total width of the confidence interval of 0.35, being 14 participants per group. A total of 15 participants were selected for each group in order to compensate for likely dropouts.

## Study groups

Participants who met the inclusion criteria were examined in a dental chair to see whether they had anterior teeth with adhesive restorations. Those participants who did not have any restoration in the facial surface of the eight upper maxillary teeth were assigned to the control group, while participants with at least one restoration in the central incisor and a maximum of four in other anterior teeth were assigned to the restored group. These restorations were not to involve more than 25% of the facial surface of the anterior teeth and were to be judged as satisfactory (Alfa and Bravo for marginal adaptation and discoloration, and lack of caries lesions adjacent to the restorations) with no need of repair according to FDI criteria.

## Study intervention

The gingival tissue of the teeth to be bleached was isolated using a light-cured resin dam (Top Dam, FGM, Joinville, SC, Brazil). Hydrogen peroxide (HP) gel, 35% (Whiteness HP Maxx, FGM) was used in three 15-min applications for both groups according to the manufacturer’s directions. The in-office bleaching agent was refreshed every 15 min during the 45-min application period. Two sessions with a one week interval were performed.

## Tooth sensitivity evaluation

The participants recorded their perception of TS during the bleaching on a daily basis up to 7 days following each bleaching session. The patients were asked to report any tingling or shooting pain without provoking stimuli. A five-point verbal rating scale [0 = none, 1 = mild, 2 = moderate, 3 = considerable and 4 = severe] was employed in this study. The median score value obtained in both bleaching sessions for each time assessment was considered for statistical purposes. The values were arranged into two categories: percentage of patients that reported TS at least once during treatment (absolute risk of TS), and overall TS intensity during and up to 24 h after each bleaching session. The participants were also instructed to identify the painful teeth every time they experienced TS.

Shade evaluation was recorded using two methods: a subjective evaluation using a shade guide (Vita Lumin, Vita Zahnfabrik, Bad Säckingen, Germany) and an objective evaluation using the spectrophotometer (Easyshade, Vident, Brea, CA, USA). Colour was evaluated with teeth in a complete hydrated condition at baseline, 1 week and 6 months after the bleaching protocol. Colour was not evaluated soon after each bleaching session in order to avoid the influence of tooth dehydration and demineralization that occurs simultaneously with the whitening effect on the final colour outcome.

For the subjective examination, the shade guide’s 16 tabs were arranged from the highest (B1) to the lowest (C4) value, making the colour A2 number 5, for example, in order to allow calculation of the variation of the shade guide units (ΔSGU). Although this scale is not linear in the truest sense, we treated the changes as representing a continuous and approximately linear ranking for the purpose of analysis. The measurement area of interest for shade matching was the middle third of the facial surface of the anterior central incisor. For calibration purposes, five patients whom we did not include in the sample because they were used in the pilot study participated in the training phase of this study. The two examiners, scheduled the patients for bleaching after evaluating their teeth against the shade guide. The two examiners were required to have an agreement of at least 85 (weighted Kappa statistic) before beginning the study evaluation. If disagreements arose during evaluation they were encouraged to reach a consensus.

For the objective evaluation we followed the method employed by Marson et al. A preliminary impression of the maxillary arch was made using dense silicone Adsil (Vigodent S/A Indústria e Comércio, Rio de Janeiro, RJ, Brazil), that served as a standard colour measurement guide for the spectrophotometer. A window was created on the labial surface of the silicone guide for the central incisor to be evaluated. It window was made using a metallic device with well-formed borders, 3 mm in radius. The measurement was carried out on all 30 patients using Vita Easyshade (Easyshade, Vident, Brea, CA, USA) at the same time assessment used in the subjective evaluation. In the restored teeth, care was taken to perform the measurements only on the tooth surface. The shade was determined using the parameters of the Easyshade device where it indicated the following values: L *, a * and b *, in which L * represents the value from 0 (black) to 100 (white) and a * and b * represent the shade, where a * is the measurement along the red-green axis and b * is the measurement along the yellow-blue axis. The colour comparison before and after treatment is given by the differences between the two colours (Δ E ), which is calculated using the formula :

ΔE=[(ΔL)2+(Δa)2+(Δb)2]1/2. $\Delta E={\left[{\left(\Delta {L}^{}\right)}^{2}+{\left(\Delta {a}^{}\right)}^{2}+{\left(\Delta {b}^{}\right)}^{2}\right]}^{1/2}\text{.}$

## Statistical analysis

The analysis followed the intention-to-treat protocol and involved all participants who were randomly assigned. The statistician was blinded to the study groups.

The primary outcome, absolute risk of TS, was compared by using the Fisher’s exact test. Statistical analyses of TS intensity, comparing the two groups in each assessment points, were performed using the Mann–Whitney U -test. As two bleaching sessions were performed, the median score at each assessment point was considered for statistical analysis. Comparisons between times within each group were performed using the Wilcoxon Signed Rank test. The proportion of patients from both groups that reported TS at least once in the central incisors, lateral incisors, canines and premolars were calculated and compared by chi-square test. The proportion of painful restored teeth was compared with the proportion of sound restored teeth in the restored group by chi-square test.

For the subjective evaluation of colour, the mean and standard deviations of shade guide units at baseline, one week after and 6 months after bleaching were compared with two-way repeated measures ANOVA (Groups vs. Assessment time) and Tukey’s test. The data from ΔSGU and Δ E of both groups were submitted to two-way repeated measures ANOVA. A post hoc analysis (Tukey’s test) was used to make pairwise comparisons. In all statistical tests, the significance level was set at α = 0.05.

## Results

A total of 64 participants with age ranging from 18 to 35 years old were evaluated to select 30 participants that met the inclusion criteria. Reasons for exclusion of participants were the following: shade lighter than A2 ( n = 17), presence of spontaneous TS ( n = 10), anterior incisors with endodontic treatment ( n = 5) and other reasons ( n = 2). The mean age (years) of the participants in this study was similar between the groups (control: 24.4 ± 3.7 and restored: 25.3 ± 5.4). Sixty percent of the participants were females, 10 in the control group and 8 in the restored group.

All participants in this study reported TS at least once during treatment and thus the absolute risk of TS was 100% (95% CI: 80–100%) for both groups (Fisher’s exact test, p = 1.0). In regard to the intensity of TS ( Table 1 ), participants from the restored group reported a higher intensity during bleaching than those from the sound group (Mann–Whitney U -test, p = 0.0362). Most participants of both groups reported tooth pain up to 6 h post-bleaching (83.3%, 95% CI: 66.4–92.7%), with some experiencing pain up to 24 h (16.7%, 95% CI: 7.3–33.6%) and no statistical difference was observed between groups at this assessment time (Wilcoxon Signed Rank test, p = 0.3507).

Table 1
Median and interquartiles ranges of tooth sensitivity reported by patients at different assessment times for the two treatment groups. a
Sound Restored
During bleaching 0.5 (0/1.25) aA 1.5 (1/1.75) aB
Up to 24 h post-bleaching 2 (0.75/2.25) bA 2 (0/2) aA

a At each treatment, the two periods were compared with Wilcoxon Signed Rank ( α = 0.05) and differences are represented by different lowercase letters. For each period, the treatments were compared with Mann–Whitney U -test and the differences are represented by different uppercase letters.

The two-way ANOVA for the shade guide units (SGU) data showed that only the main factor assessment time was statistically significant ( p < 0.001). A higher degree of bleaching was obtained after two weeks of treatment and this result was stable after 6 months for both groups ( Table 2 ). The ΔSGU and Δ E values showed a similar trend. Neither the main factors nor the cross-product interaction were statistically significant (ANOVA test, p > 0.05). This means that a degree of bleaching of approximately 4 SGUs was detected for both groups and this was stable after 6 months ( Table 3 ).

Table 2
Means and standard deviations of shade guide units (Vita Classical shade guide) at different assessment points for the two treatment groups. a
Sound Restored
Baseline 5.7 ± 1.5 aA 5.9 ± 1.1 aA
1 week after bleaching 1.3 ± 0.5 aB 1.8 ± 0.7 aB
6 months after bleaching 1.5 ± 0.5 aB 1.9 ± 0.6 aB

a The same lowercase letters indicate statistically similar means within rows. The same uppercase letters indicate statistically similar means within columns (Tukey’s test, α = 0.05).

Table 3
Means and standard deviations (SD) of ΔSGU and Δ E at different assessment points for the two treatment groups. a
ΔSGU Δ E
Sound Restored Sound Restored
Baseline vs. 1 week 4.3 ± 1.3 a 4.1 ± 0.9 a 4.2 ± 0.9 a 4.7 ± 1.1 a
Baseline vs. 6 months 4.2 ± 1.4 a 4.0 ± 0.9 a 4.0 ± 0.7 a 4.1 ± 0.7a
a Means indicated by the same lowercase letters indicate statistically similar means for ΔSGU and means indicated by the same uppercase letters indicate statistically similar means for Δ E (Tukey’s test, α = 0.05).

For all patients included in this clinical trial, the teeth with most complaints of TS were the lateral incisors (76.7%) which were statistically different from the canines and premolars (chi-square test, p < 0.05) but similar to the central incisors ( Table 4 ). In relation to the participants of the restored group, 50% (95% CI: 32.0–68.0%) of their restored teeth and 31.3% (95% CI: 21.2–43.4%) of their sound anterior teeth were reported to be painful, respectively. These percentages were not statistically different (chi-square test, p = 0.16) to the participants in the control group, 34.4% (95% CI: 25.4–44.7%).

Table 4
Number of patients who reported tooth sensitivity at least once in the different tooth types.
Tooth type Number of patients of each group a Overall proportion (95% CI) **
Sound (a) Restored (b) Overall
Central incisors 9 8 17 53.3 (36.1–69.8) A
Lateral incisors 11 12 23 76.7 (59.0–88.2) A
Canines 5 4 9 30.0 (16.7–47.9) B
Premolars 0 0 0 0 (0–0.11) C

a Proportions indicated by the different lower case letters are statistically different (sound or restored; chi-square test, α = 0.05).

** Proportions indicated by the different upper case letters are statistically different (tooth types; chi-square test, α = 0.05)

## Discussion

Dental bleaching often promotes TS as an adverse effect. It probably occurs in response to the permeation of HP through enamel and dentin promoting the release of inflammatory mediators in the pulp and damage to the pulp cells. In accordance with previous studies, a high absolute risk of TS was observed in this study, regardless of the treatment group.

However, although the prevalence of TS among patients in the control and restored groups was similar, a higher TS intensity was observed in patients with adhesive restorations, especially during the application of the in-office bleaching gel. This means that all patients, regardless the presence or absence of restorations, can experience TS, but its intensity is likely to be higher in patients with restored teeth during the gel application.

TS results from the expression of inflammatory mediators such as substance-P and prostaglandins, which have a recognized role in triggering nociceptive impulses for the perception of pain. The amount of HP that reaches the pulp was shown to be 2–5 times higher in restored rather than in sound teeth. This is likely to be due to the fact that adhesive interfaces in the restored teeth may work as fast pathways of HP to pulp and that pulp cells may not be capable of producing enough peroxidades, catalases and oxygenases to protect the pulp from the immediate damage caused by HP. This might explain why during the application of the in-office bleaching gel, participants from the restored group showed TS with a high intensity than those from the control group.

However, as pointed out by Gökay et al. it is worth mentioning that several factors may affect the ability of HP to permeate the dental structures of restored teeth. The depth and size of the restorations, as well as the type of adhesive and restorative material, may also play a significant role. In the present study, only participants with composite resin restorations were evaluated. We were not aware of the brand of composite and adhesive system used. The impact of these factors on the amount of HP that reaches the pulp and the TS experienced by patients is not known and should be the focus of future studies.

In present study, the tooth that was reported to give most complaints of TS was the upper lateral incisor. In a review of the literature, Haywood reported that bleaching-induced TS usually affects the smaller teeth, such as the maxillary laterals and the mandibular incisors. These reports are in agreement with a recent histological study of pulp after in-office bleaching. In the latter study the authors observed notable damage to the pulp tissue of lower incisors but not in premolars. The thinner enamel and dentine layers of incisors compared to premolars may allow the fast passage of HP to the pulp, allowing less time for the production and release of protective enzymes against damage by HP.

At the present time, there are several recommendations for reducing post-bleaching sensitivity, such as the administration of analgesics a decrease in concentration and in application time of the bleaching gel and the application of desensitizing agents before each bleaching session. The most commonly used desensitizing agents include potassium nitrate, which prevents the transmission of nerve impulses. This could represent an alternative which might minimize TS in patients with restorations; however, this possibility must be clinically evaluated.

In regard to bleaching efficacy, the results of this present study indicated that both groups demonstrated similar and significant tooth colour enhancement as compared with baseline. Studies that employed 35% HP and reported their results in SGU have usually observed an overall colour change of 5–8 SGUs after two bleaching sessions. In our study, we found on average a variation of 4 SGUs which is in agreement with a previous study. These differences may be due to variations in the baseline colour shade of teeth included in the trial. Studies that usually report a higher variation in SGU include teeth with shade darker than C2. In the present study and in other recent research the investigation of teeth colour used a baseline of A2.

Visual colour determination by comparing teeth to a shade guide has been the most often used method in dentistry. Some authors concluded that the human eye is efficient in detecting even small differences, while other authors have commented that the human evaluation of tooth shade is not as accurate as digital evaluation. The digital method has been evaluated as being five times more likely to match the original shade colour compared to the visual method. Taking that into consideration, we opted to evaluate colour changes using a visual shade guide and a spectrophotometer. In the present study, both methods yielded similar results and were similar to the results shown in the study by Meireles et al. The standardization of lighting, the array used to support the spectrophotometer, and most importantly, the moment at which the objective evaluations were done (with teeth completely hydrated, avoiding bias in colour measurement), are probably responsible for such agreement between methods.

In regard to colour stability, 6 months after bleaching no significant differences among the groups were detected and there was also no significant colour rebound. These results are similar to those reported by other authors, but differ from the clinical study of Zekonis et al. and Matis et al. The findings of the latter two studies are controversial, probably due to differences in the total bleaching time, which was lower. In-office bleaching seems to achieve satisfactory results when more than one session is performed with no statistical rebound of colour, at least in periods ranging from 6 months to 2 year. Future studies should be conducted in order to evaluate the longevity of bleaching procedures after several years.

## Conclusions

Similar degrees of whitening could be observed in participants with restored teeth. However, a higher intensity of tooth sensitivity was reported by participants with restored teeth during the bleaching protocol.

## Acknowledgment

The authors would like to thank FGM Dental Products for the donation of the products used in this investigation.

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