Patients’ Assessments of Tooth Sensitivity Increase One Day Following Different Whitening Treatments

Abstract

Objectives

The aim of this clinical study was to compare tooth sensitivity scores and color change values before and 1 day following whitening treatments using different concentrations of whitening agents for in-office and at-home procedures.

Materials and methods

A total of 60 participants divided into 3 groups were included in this study. A whitening procedure was carried out in groups using 40% hydrogen peroxide (HP) in in-office treatment, 16% and 10% carbamide peroxide (CP), respectively. Participants rated their tooth sensitivity at the baseline and 1 day following the treatment. The CIEl_ab values were recorded and color differences were calculated.

Results

Within each of the whitening treatments, the tooth sensitivity scores significantly increased following the procedure (p<0.05). The largest significant increase in scores was noted in 40% HP in-office whitening treatment, while the lowest increase was noted in 10% CP at-home whitening treatments (p<0.05). The highest color change 1 day following the procedure was found in the 40% HP in-office whitening treatment group (3.3) and it significantly differed from both 16% CP and 10% CP at-home whitening treatments whose color difference was both 2.0, respectively (p<0.05).

Conclusion

1 day following the procedure, a low concentrate CP agent for at-home whitening causes the least tooth sensitivity compared to higher concentrate CP for at-home and HP for in-office agents, with the same color change efficacy as higher concentrate CP agent. In case with slight tooth sensitivity reported at the baseline, a 10% CP whitening treatment should be recommended.

Introduction

Tooth color is one of the most important esthetic visual parameters in dental medicine (1). Patients’ demands for esthetic appearance have increased over the past decade, including correction of their tooth color (2, 3). Therefore, tooth whitening becomes an increasingly requested dental technique considered more conservative for improving tooth color, thus avoiding more no invasive procedures such as for crowns or veneers (4).

Today there are two types of dentist-supervised whitening techniques for vital teeth: at-home whitening and in-office whitening (5). Both procedures provide whitening agents containing hydrogen peroxide (HP) or carbamide peroxide (CP) over the vestibular tooth surface (6, 7). CP is a well-accepted agent for home whitening procedure where the patients apply the gel on the tooth surface using a customized tray. A 10% CP was considered as a golden standard material for home whitening but to increase the efficacy of the material, higher concentrations of CP are being used (8, 9). The main advantages of home whitening technique are reduced chair time, ease to use, less gingival irritation and lower tooth sensitivity (10). Manufacturers usually incorporate fluoride and desensitizing products in at-home whitening agents, such as potassium nitrate, that reduce tooth sensitivity (11). On the other hand, in-office tooth whitening technique uses much higher concentration of HP (15-40%), which produces faster tooth whitening results visible after only one visit (12). Despite the advantage of achieving faster results, the main disadvantages of this method are longer chair time, gingival irritation and higher risk of TS (13). A higher concentration of HP increases the activation of inflammatory receptors in the pulp chamber and causes tooth sensitivity (14). Some manufacturers have also incorporated fluoride or desensitizing products into the in-office gel formula to decrease sensitivity (4).

Many studies have already reported a certain degree of TS following different whitening procedures using various products containing different concentrations of HP or CP (15-20).

The aim of this randomized clinical study was to compare tooth sensitivity before and 1 day following in-office and at-home whitening treatments using different concentrations of HP and CPs in patients self-reporting mild sensitivity prior to the treatment. The null hypothesis tested was that the application of different concentrations of HP and CPs had no effect on both tooth sensitivity increase and whitening results.

Materials and methods

Sample

The study was performed upon the approval from the Ethics Committee of the School. All participants were provided with a patient information sheet and were required to sign informed consent forms.

In order to determine the sample size, the Univariate Analysis of Variance was performed as a pilot on 10 subjects who had undergone whitening procedures using 40% HP, 16% CP and 10% CP, respectively. Color differences (ΔE) were calculated with p value set to <=01. With the effect size produced of 0.55 in this sample size, there was 99% chance to detect the difference in dE values (between different concentrations of whitening agents). Upon these results, we have decided to double the sample size aiming to achieve a total of 60 participants in the study. Participants were recruited from the group of postgraduate students of School of Dental Medicine. After pre investigation and post investigation, the exclusion criteria were determined and the final number of participants was set of on 60, and it was partially randomized in the group which reported higher pain threshold. Finally, 41 women and 19 men (mean 27.5 and 34.5 years; respectively), using the inclusion and exclusion criteria and tooth sensitivity self-assessment as described in Table 1 and Figure 1 (5 excluded upon the criteria and 2 upon tooth sensitivity self-assessment) were selected.

Table 1. Criteria used in this study.

Inclusion criteria	Exclusion criteria
adult (18-70 years)	currently undergoing treatment for caries, gingivitis, or periodontitis, or having undergone or currently undergoing orthodontic treatment
minimum of 20 natural teeth, including incisors and canines in both arches	structural alteration of tooth structure, or alternation of oral mucosa
willing to sign consent form	medical condition that the investigator believed might compromise the study or the individual's safety
willing to change the color of their teeth for cosmetic reasons	existing dental restorations in teeth to be whitened
willing to return for post whitening evaluation	use of tobacco products during previous 30 days
good oral hygiene	pregnant or breast-feeding women
no caries on teeth to be whitened	tetracycline-stained teeth or fluorosis

Figure 1.

Clinical study design flow chart.

Dropouts (2 participants were excluded due to the failures during the at-home whitening procedure) were replaced with new participants to achieve desired power of the statistical analysis. All the participants wanted to change the color of their teeth for cosmetic reasons. In 50% of the participants the initial color was A1, and in 50% A2 or even darker.

Participants’ randomization upon tooth sensitivity assessment

After the exclusion of additional 5 participants from the initial group who did not meet the inclusion criteria, the participants were asked to self-assess any noticeable, short-term, transient and sporadic tooth sensitivity experienced in the past year on a Numerical Rating Scale (NRC) circling the number between 0 and 10, wherein 0 represented no pain and 10 represented the worst pain ever possible (21). Further two participants did not report any pain, and were therefore excluded from the further studies (Figure 1).

Based on the obtained results, 20 patients with the lowest scores were included in 40% HP in-office whitening treatment group. The rest of them were randomly distributed to one of two at-home whitening treatment groups (16% and 10% CP)(Figure 1).

One day following whitening treatment, the participants were asked to score possible occurrence of the previously described pain using the same NRC scale.

Positioning jig

The teeth of the participants were professionally cleaned (Proxyt RDA 36; Ivoclar Vivadent, Schaan, Liechtenstein). One alginate (Hydrogum® 5, Zhermack, Badia Polesine (RO), Italy) impression of the maxillary arch was made, and a stone model (Fuji rock EP Classic line; GC, Tokyo, Japan) was produced to fabricate a modified form of whitening tray, 1-mm-thick thermoplastic tray material and thermoforming unit (Erkodent, Pfalzgrafenweiler, Germany), to make a positioning jig to ensure the placement of the tip of the spectrophotometer in the same position at every color measurement (at baseline, and 7 days following the treatment). An impression of the tip of the probe of the device was made and a cast was fabricated. The spectrophotometer probe cast was used as a stamp guide to mark the whitening tray. The facial middle-third of the maxillary teeth was marked with the spectrophotometer tip cast. The facial marks were cut, leaving an opening for the placement of the s probe. Prior to color measurement, the custom jig was positioned in the patient's mouth, and the probe was positioned into the jig opening. The subjects were asked to brush their teeth at least twice a day in order to maintain high level of oral hygiene.

In-office whitening treatment

Twenty participants chosen for in-office whitening treatment in this study were chairside treated with 40% HP (Opalescence Boost: PF 40, Ultradent, USA). Prior to treatment, protective lip cream, and a light-cured resin barrier Opal Dam (Ultradent, South Jordan, UT, USA) for gingival protection were applied (included in the kit). To prevent saliva from flowing through embrasures of anterior teeth, a saliva ejector and cotton rolls were used in the sublingual region. An expanded lip retractor was used to protect the lips. An Ultradent IsoBlock (Ultradent, South Jordan, UT, USA) was used to keep the tongue in a safe position. For Opalescence Boost PF, the activator was mixed into the whitening agent using an adequate syringe. The mixture was then applied, 1–2 mm thick, to buccal surfaces of the teeth (canine to canine) of the maxillary arch. It remained there for twenty minutes. There were three applications. No heat or special lamps were used to complete the process. The agent was removed using suction and gauze only for a new application. After the third, last, application, the teeth were rinsed with water and the gingival isolation and lip retractor were removed. Both the participants and the dentist wore protective glasses during the treatment.

At-home whitening treatment

In participants chosen for one of two at-home whitening treatments in this study (40 of them) maxillary and mandibular alginate impressions were made (Aroma fine plus fast set, GC, Tokyo, Japan), and stone casts were poured (Fuji rock EP Classic line, GC, Tokyo, Japan). The custom whitening trays were then made by using a 1-mm-thick thermoplastic tray material and thermoforming unit (Erkodent, Pfalzgrafenweiler, Germany). All excess was trimmed just short of the gingival margin. The participants were than randomly divided in two groups of 20 and each group was delivered with different concentration of CP (Opalescence PF 16% and 10%, Ultradent, South Jordan, UT, USA). They were instructed to use their custom trays with the whitening gel for 14 consecutive nights, for at least six hours per night.

Instrumental color measurement

Instrumental color measurement was performed on six maxillary anterior teeth before whitening (baseline—t₀) and 1 day following whitening treatment (t₁). The VITA Easyshade Advance 4.0^® (VITA Zahnfabrik, Bad Sackingen, Germany) spectrophotometer was used and calibrated according to the manufacturer's instructions, with the operating mode set to single shade measurement. To provide accurate repositioning of the spectrophotometer probe and measurement of the middle third of the labial tooth surface over time, a custom positioning jig was made for each participant, as described in the previous chapter. The spectrophotometer measured the tooth shades based on the CIE L*a*b* color notation system. CIE L*a*b* (ΔE_ab) color differences were calculated using formula:

Repeatability, accuracy and reliability of this device has already been tested (23, 24).

Statistical analysis

Data were statistically analyzed using statistical program SPSS 19.0 (SPSS, Chicago, IL, USA).

Normality of distribution was evaluated using the Saphiro-Wilk test and by inspection of data distribution graphs. Data were not normally distributed for variables about tooth sensitivity (P<0.05) with the exception of the tooth sensitivity variable assessed 1 day after the whitening treatment using 40% HP (P>0.05), and they were normal for color measurements (P>0.05).

Marginal homogeneity was performed to test the difference between patients’ assessments of tooth sensitivity within each whitening treatment before and 1 day after it. The Kruskal-Wallis test was used to determine whether there were any differences in patients’ tooth sensitivity assessments between three different whitening treatments before and 1 day after it, and the Mann Whitney tests for post hoc corrections to conduct paired comparison between these three whitening treatment groups.

One-way ANOVA was used to test the differences between three different mean ΔE values and Bonferroni corrected post hoc tests (paired t tests) were used to find the differences within three different ΔE values.

The level of significance was set to 0.05 (5%).

Results

The distribution of patients’ assessment of tooth sensitivity before and 1 day following three different whitening treatment was found not to be normal in majority of the variables (P<0.05)(Figure 2; Table 1). Both Skewness and Kurtosis values in patients’ estimated scores indicated of a mild asymmetry from the bell curve, with a slight shift towards left (lower scores) and the lower peeks compared to normal distribution (Figure 2). The only variable with normal distribution was the patients’ assessment of tooth sensitivity 1 day after the whitening treatment using 40% HP (P>0.05)(Figure 2; Table 1). Therefore, non-parametric statistical tests were conducted in the further analysis.

Figure 2.

Histograms

The results of the marginal homogeneity tests revealed a statistically significant difference within scores related to sensitivity of their teeth given by patients before and 1 day following whitening treatments using 40% HP, 16% CP and 10% CP (P=0.000, 0.000 and 0.008, respectively)(Figure 3). The patients’ scores 1 day following each of the treatments were significantly higher compared to baseline scores (Figure 3)(P<0.05). Mean values at the baseline and 1 day after the whitening treatment using 40% HP were 1.4 and 6.2, using 16% CP 1.9 and 3.0, and after 10% CP 1.7 and 2.2, respectively (Figure 3; Table 2)(P<0.05).

Figure 3.

Mean values of the tooth sensitivity scores at the baseline and 1 day following whitening treatments using different concentration of HP and CP.

Table 2. Patients' assessment of tooth sensitivity before and 1 day following three different whitening treatments and P values (p<0.05 indicating not normal distribution).

		Median/Medijan	Skewness	Kurtosis	P
40% HP	before / prije	1.5	-0,081	-1,043	0.011
	1 day following the treatment / 1 dan nakon zahvata	6.0	-0,642	0,407	0.203 NS
16% CP	before / prije	2.0	0,257	-1,043	0.001
	1 day following the treatment / 1 dan nakon zahvata	3.0	0,098	-1,518	0.001
10% CP	before / prije	2.0	-0,214	-0,595	0.023
	1 day following the treatment / 1 dan nakon zahvata	2.0	0,036	-0,589	0.014

At the same time, baseline scores in all three different whitening treatment groups did not differ and the Kruskal-Wallis test revealed only small differences in mean ranks between them (Table 3; P>0.05). On the other hand, scores assessed 1 day following treatments significantly differed, with highest mean ranks for 40% HP in-office whitening treatment and lowest mean ranks for 10% CP at-home whitening treatment (Table 3; P<0.05). Using the Mann-Whitney test for post hoc correction with the significance set to P=0.016 (P= 0.05/n of groups), this difference was confirmed to be significant only between scores for 40% HP and 10% CP whitening treatments.

Table 3. Significance of the differences in patients' assessment of tooth sensitivity using different concentrations of HP and CP before and 1 day following the treatment.

		rank	X2	df/ss	P
before / prije	40% HP	25.88	2.550	2	0.259
	16% CP	33.95
	10% CP	31.65
1 day following the treatment / 1 dan nakon zahvata	40% HP	48.38	35.193	2	0.000
	16% CP	25.88
	10% CP	17.25

df – degree of freedom

ss – stupnjevi slobode

The distribution of mean ΔE_ab values in three different whitening treatment groups was normal (Table 4)(P>0.05). One-way ANOVA test confirmed the presence of statistically significant differences between mean ΔE_ab values. In 40% HP in-office whitening treatment, the mean color change was 3.3 and in both 16% CP as well as 10% CP at-home it was the same, 2.0, respectively. The Bonferroni corrected post hoc test revealed the difference was significant between in-office and each of at-home whitening treatment groups (P=0.026 and P=0.03, respectively), and no significant difference between two at-home whitening treatment groups (P>0.05) was found.

Table 4. Significance of the differences in tooth color changes (ΔEab) using different concentrations of HP and CP.

	mean value/ srednja vrijednost	SD	F	df/ss	P
40% HP	3.3	1.88	4.853	2	0.011
16% CP	2.0	1.46
10% CP	2.0	0.87

df – degree of freedom

ss – stupnjevi slobode

Discussion

The null hypothesis was rejected as the application of different concentrations of HP and CPs using different techniques had significant effect on both tooth sensitivity increase and whitening results. The patients’ scores of tooth sensitivity significantly increased following each of the treatments (Figures 2 and 3;Table 2)(P<0.05). At the baseline, all of them reported a very low level of initial tooth sensitivity and there was no statistically significant difference between them (Table 3)(p>0.05). The highest increase in tooth sensitivity following the whitening treatment was recorded in in-office procedure using the highest concentration of HP agent (40% HP; Table 3)(P<0.05). In this particular group, the participants reported their initial tooth sensitivity on NRC scale as slight pain (mean value was 1.4), but 1 day after the treatment it was moderate (mean value was 6.1). This was the only group whose final score shifted the threshold of mild sensitivity to moderate, which was expected since it had already been proven that higher concentrations of HP caused higher tooth sensitivity (25). In order to avoid the onset of severe pain and patients’ suffering during the research, we have decided to assign to this group those participants who initially (at the baseline) reported the lowest level of the sensitivity (Figure 1). A significant increase in sensitivity in these two groups of at-home whitening treatments after the procedure was recorded too, but it was smaller and it remained within the range of (Figures 2 and 3)(P<0.05). These results are in agreement with other studies confirming tooth sensitivity after et-home whitening to be mild (15, 16) and after in-office whitening to be moderate (17, 18,) but in some cases even severe to that level that patients decided to abandon the procedure (19). Jorgensen et al. reported mild tooth sensitivity to be expected in about one-half of patients who undertake at-home whitening treatment using 16% CP, 10% of patients to experience moderate sensitivity, and 4% to experience severe sensitivity for one to two weeks (26). Kihn et al. reported no significant difference in sensitivity of the teeth in the 10% CP and 15% CP groups at the end of the study period and the same was confirmed in our study too (27).

Generally, when it comes to analyzing research in the field of dental whitening it is difficult to compare the results due to different concentrations of materials used, different protocols and techniques implemented and inconsistent monitoring periods in research. The same is true for our study. Usually, the researchers ask patients to assess tooth sensitivity following the whitening treatment considering it excluded upon exclusion criteria, but the authors of this study find it almost impossible for participants never to experience any type of clinically relatively irrelevant tooth sensitivity, even in those cases where participants have completely intact and healthy teeth and gums. In our exclusion/inclusion criteria (Table 1) we have eliminated those to whom a particular condition in the mouth can clinically cause any type of tooth sensitivity. Nonetheless, when asked, the participants at the baseline self-reported a very low but existing level of sensitivity (Figures 1 and 2). We believe our results can contribute to clinical work upon making decisions about material and techniques to be used in cases where patients self-report certain level of sensitivity despite the lack of clinical signs of sensitivity.

The results of our study confirmed a significant color change after 40% HP, 16% CP and 10% CP whitening treatments. The color change for in-office treatment significantly differed from both at-home treatments as it was expected and already confirmed in other studies (P<0.05). Again, it is difficult to compare the results due to differences in the assessment conducted immediately, one or two days, week or two following the treatment. Compared with the results of Matis et al. study, which compared several different whitening studies, the ΔE_ab for in-office treatment in our study matches theirs regarding a week after the procedure (28). However, our at-home whitening ΔE_ab for both CP concentrations was significantly lower than their ΔE_ab (28). One of the reasons probably lies in the fact that they evaluated 25 different whitening products in total, and we included in our research relatively younger participants with relatively lighter teeth at the baseline. Although somewhat lower, ΔE_ab values for in-office whitening treatment in our study were above both the 50:50% perceptibility threshold (PT) and 50:50% acceptability threshold (AT) (AT = 2.7, PT = 1.2), and ΔE_ab values for two different at-home whitening treatments were above the 50:50% perceptibility threshold (PT) in dentistry proving that the procedures were successful (29).

As already mentioned, higher concentrations of HP and CP have been strongly related to higher incidence of post treatment (28). Therefore, to get faster results with less tooth sensitivity, some authors proposed the combined whitening technique consisting of a single in-office whitening session using lower concentrations of HP, followed by at-home whitening. Some studies reported that a combination of techniques has reduced the risk of tooth sensitivity and gum irritation, thus achieving good results in tooth whitening (30-34). This technique is specially recommended within the EU countries because of the special EU Directive recommending the usage of lower concentrations of HP for in-office whitening treatments (35). It has to be mentioned that this study was conducted out of EU and it is not under their jurisdiction; therefore we were allowed to use high concentrations of HP to prove that such a concentration particularly causes the highest level of tooth sensitivity, is therefore not recommended for the patients reporting low level of tooth sensitivity before the treatment.

The limitation of this study is a relatively young sample with participants having lighter teeth. Our further study will expand the sample size and include those with darker teeth.

Conclusions

There was a significant increase in the level of tooth sensitivity 1 day following all three whitening treatments. The highest tooth sensitivity occurred after 40% HP whitening treatment, and lowest after 10% CP whitening treatment. In the range of color change, the 10% CP was as effective as 16% CP whitening treatment. Therefore, in case with slight tooth sensitivity reported at the baseline, the 10% CP whitening treatment should be recommended.