INTRODUCTION

Color is central to the appearance of teeth; the discoloration of teeth understandably is a cause of great concern to a large number of subjects¹ who seek dental treatment to improve the appearance of their teeth. The cause of discoloration is multifactorial,^2,3 and an appropriately prescribed tooth whitening regimen offers a safe, non invasive, and predictable approach to improving appearance.⁴ Methods for achieving chemical whitening of teeth can be divided into four categories as follows:

1. Home whitening: This is undertaken by the patient at home with the use of custom-made trays under the direction of a dentist.

2. Assisted whitening: Hydrogen/carbamide peroxide is applied in trays in-office.

3. Power whitening: This practice-only treatment requires gingival protection because of the high concentrations of hydrogen peroxide used; it may or may not be used in conjunction with a light or heat source.

4. Over-the-counter products: These may include toothpastes or whitening strips.⁵

Tooth sensitivity is the most common side effect of vital tooth whitening⁶; its prevalence has been reported to lie between 11% and 93%.^7-10 This huge variation in reported levels of sensitivity can be explained by the subjective nature of sensitivity, but also by the variation in concentrations of whitening agents used in these studies. Although sensitivity is very common, robust research investigating the severity of sensitivity associated with different whitening regimens is lacking.

Both at-home and in-office whitening techniques have been shown to produce favorable changes in tooth color,^11-18 and several manufacturers have attempted to combine the two techniques to develop a more efficacious procedure. Available research suggests that this combination technique produces significantly greater tooth whitening when compared with in-office whitening alone.¹² However, the effect of combined whitening vs that of home whitening alone has not been studied to date. Similarly, no study to date has examined the sensitivity associated with concentrations of carbamide peroxide used in assisted whitening, which are up to 22%. Tooth sensitivity studies related to the use of carbamide peroxide in at-home systems, however, report a higher level of sensitivity associated with higher concentrations as opposed to lower concentrations.¹³

Over-the-counter whitening treatments have been extensively evaluated in contrast to power whitening or office whitening, which has not.⁴ Although it is accepted that over-the-counter whitening products are effective, the outcome is short-lived.⁴ Regression of whitening in the period immediately following whitening, however, is recognized as a problem for all whitening agents, but this is a particular problem with over-the-counter products.⁵ Because of the paucity of good quality evidence, it is difficult to comment further on the effectiveness of power or in-office whitening.

This randomized clinical study, therefore, aimed to assess the efficacy of color change and production of sensitivity after home whitening alone, and after two different regimens of in-office assisted whitening. Color change was assessed by visual comparison with a modified shade guide, which is a widely accepted technique for studies of this type,^19-23 whereas sensitivity was evaluated with a visual analog scale (VAS).

METHODS AND MATERIALS

This randomized clinical study assessed efficacy in terms of color change and production of sensitivity after home whitening alone and home whitening supplemented with in-office bleaching.

Methods

This study was reviewed by Leeds Dental Institute Ethics Committee; all subjects were provided with a patient information sheet and were required to sign informed consent forms before they were enrolled into the study.

Once subjects were enrolled into the study, upper and lower alginate impressions were made to allow custom whitening trays to be made, and tooth shades were assessed. Before active treatment was begun, the following baseline measurements were recorded at this appointment (“Baseline visit”): tooth shade (upper six anterior teeth), sensitivity, full intraoral examination, and digital color images of the upper anterior teeth.

All tooth shades were assessed visually by one examiner and the examiner's dental nurse independently with reference to a value-ordered shade guide—the Vitapan Classical Shade Guide (Vita Zahnfabrik, Bad Säckingen, Germany)—and for shades lighter than Vita B1, a “bleaching” shade guide was used (Ivoclar Vivadent, Leicester, UK) (Figure 1). Following independent assessment, an agreed tooth shade was recorded. According to the scale shown in Figure 1, each shade was then assigned a numeric value.

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Sensitivity was self-assessed with the use of a VAS, with 1 correlating to no sensitivity and 10 correlating to unbearable sensitivity.

Different treatment regimens were randomly allocated, as explained in the following paragraphs.

RESULTS

Table 1 shows the mean tooth shade by treatment group at various time points. All 36 subjects evaluated at baseline returned for all planned visits. At baseline, no significant differences between groups in terms of tooth shade were noted (X²_[2] = 2.05; p=0.36).

Table 1:  Mean (Standard Deviation) Shading by Group and Time Point

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All groups showed a significant change in tooth color when baseline shades were compared with those at final recall (Table 1). Home whitening, which was used in all treatment groups, resulted in an improvement in tooth color of the order of eight shade tabs when measured immediately after the home whitening stage of treatment (Table 2). The additional use of in-office assisted whitening resulted in a statistically significant shade change immediately post treatment (ie, post office bleach visit) (9% hydrogen peroxide, p=0.002; 27% hydrogen peroxide, p=0.002). However, clinically, this was insignificant because the mean difference was less than one shade tab. Also, no statistically significant difference was noted in shade change immediately post treatment (ie, at post office bleach visit) when 9% hydrogen peroxide was used in comparison with 27% hydrogen peroxide (p=0.25). In all groups, the shade change was found to have regressed somewhat when assessed at final recall (ie, one week follow-up visit); this regression occurred to such a degree that no significant difference in shade change was observed between any of the treatment groups (X²_[2] = 2.05; p=0.359).

Table 2:  Shade Changes at Start and End of Home Whitening Phase

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No significant differences in sensitivity were observed between the three groups at baseline according to ANOVA (p=0.23) (Table 3). In general, sensitivity increased during the course of the study; the maximum increase was noted immediately after the home whitening stage (ie, post home bleach visit). These findings were statistically significant according to the t-test (group A, p=0.003; group B, p=0.016; group C, p=0.008).

Table 3:  Mean (Standard Deviation) Sensitivity by Group by Visit

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For subjects treated with in-office assisted whitening, an additional increase in sensitivity was recorded, although this was not statistically significant (p>0.05). At the completion of the study, all sensitivity levels had returned to baseline levels. This sensitivity increase may be regarded as transient, in that comparison of sensitivities at baseline and at final recall revealed no significant differences between the three groups (p=0.47), or when final levels of sensitivity were compared with baseline scores of each group (group A, p=0.46; group B, p=0.67; group C, p=0.75).

DISCUSSION

This study showed that significant improvement in tooth color, in terms of whitening, occurs when 16% carbamide peroxide is used in a nightguard vital bleaching procedure; this is consistent with the findings of previous research.^7,11,15-17 Supplemental use of in-office whitening with 9% and 27% hydrogen peroxide was shown to result in a further degree of whitening, which is thought to be due to higher levels of oxygen within the tooth immediately after the supplemental use of in-office whitening agents.^11,17 However, no statistical difference was observed in the degree of additional whitening produced with 9% and 27% hydrogen peroxide. The whitening effect seen in all groups regressed somewhat, such that comparison of whitening from baseline to final recall showed no significant differences between the three groups. This regression is well recognized,^10,18 and it is thought that oxygen within the tooth from the oxidative process initially alters the optical properties of the tooth. Oxygen then dissipates over the following week(s), and the tooth takes on the actual lightened shade.⁵

Tooth sensitivity is a recognized complication of tooth whitening with peroxide,^5-7,10,11,19 and so its occurrence in this study was to be expected. The greatest increase in sensitivity levels was reported immediately after the home whitening phase (ie, at the post home bleach visit). Subjects receiving supplemental in-office whitening reported a further increase in sensitivity immediately after the application of in-office hydrogen peroxide. However, this was not significant, and overall, changes in sensitivity from baseline to final recall for all groups were found to be not significant.

Several modes of measuring tooth shade are available in dentistry, including shade guides, colorimeters, and spectrophotometers, to name a few. For this study, the Vitapan Classical Shade Guide (Vita Zahnfabrik) and the four-tab “bleaching” shade guide (Ivoclar Vivadent) were used. They are familiar to practicing dentists and are practical and economical; the Vitapan guide is often used in research studies.^20-22 Furthermore, when the Vita guide is arranged in value order, this has been shown to make shade selection easier and more predictable when used for whitening teeth.²³ In addition, in this study, shade was measured independently and was subsequently agreed upon by two independent examiners before the shade was recorded. However, a greater degree of standardization could have been achieved (ie, shades taken under the same lighting conditions, at the same time of day, etc.), and this may have enhanced the accuracy of results. It is important to note though that the “random” nature of result collection mirrors the situation encountered in day-to-day practice.

There is always a potential problem when statistical analyses are translated into the clinical situation. For instance, in this present study, the additional use of in-office whitening resulted in a statistically significant shade change immediately post treatment (9% hydrogen peroxide; 27% hydrogen peroxide); clinically, though, this was insignificant, because the mean difference was less than one shade tab. Measurement of sensitivity is also subjective. To reduce this subjectivity (although it could not be eliminated), the study focused on changes in sensitivity within the same subjects.

To more fully assess the combination of home whitening and assisted whitening, further research could investigate the effect of using in-office whitening before home whitening. This would assess the impact of high-strength hydrogen peroxide in-office treatments on subsequent home whitening, rather than the converse. Future research could also investigate the effect of increasing the frequency of in-office hydrogen peroxide application, and its effect on tooth whitening and/or sensitivity. However, it would appear from the results of this study that there is likely to be no statistically significant difference in whitening outcomes or clinical indications to support combining home whitening and assisted whitening, because the results are not significantly different from those produced by home whitening alone.

CONCLUSION

Within the limitations of the study, it was concluded that home whitening with 16% carbamide peroxide produces changes in mean tooth shade that result in significant tooth whitening. The addition of a supplemental in-office whitening phase (9% and 27% hydrogen peroxide) produces no significant change (p>0.05) in tooth color when compared with home whitening alone (at the final recall). No significant difference (p>0.05) in changes in sensitivity was noted for any of the three groups; any change in sensitivity from baseline to final recall was deemed to be not statistically significant.