INTRODUCTION

In some cultures of the world, tooth color is one of the most important factors in the achievement of a smile that is aesthetically pleasing.¹ It also has a substantial impact on a person's aesthetic and psychosocial perceptions.² Thus, when a single tooth doesn't match the other teeth, the negative effects can be more pronounced because a situation more visible to social scrutiny exists.³ However, there is no information on the incidence of intracoronal color effects and maintenance on a patient's self-perception or on the psychosocial impact to the patient.⁴ Some authors⁵ have shown that alterations in aesthetic dentistry can cause psychosocial consequences that could have more impact on the person who has problems caused by dental caries lesions. Intracoronal whitening is a widely used, minimally invasive alternative treatment/technique to solve discoloration (dark teeth) of nonvital teeth. Although there are several reports in the literature about external combined with internal bleaching, the main effects are seen within the pulp chamber of a tooth that has been endodontically treated and well sealed.⁶

Possible etiologies of tooth discoloration include 1) history of dental trauma with intrapulpal hemorrhage and posterior pulpal tissue necrosis and 2) transfer of metal ions into the dentin substrate of a previous or combined restoration.⁷ The first condition occurs when hemolysis of red blood cells releases iron ions, subsequently forming ferric sulfate, which produces a dark color. The second clinical situation occurs when metal ions penetrate the dentin substrate, causing discoloration of the tooth stump preparation. The first condition has a more favorable prognosis for bleaching, whereas the second does not; thus, consideration of the patient's medical history is very relevant before internal bleaching is undertaken. The recurrence of internal bleaching is much more frequent and damaging and has rarely been studied.⁸

Prospective studies that objectively measure color stability and rebound after intracoronal bleaching and maintenance of the effect on the quality of a patient's life are not available in the literature.

The main objective of this study was to evaluate the following two parameters: 1) color rebound in patients who have undergone bleaching of nonvital teeth with 35% hydrogen peroxide or 37% carbamide peroxide gels using the walking bleaching technique and 2) the impact on aesthetic self-perception and psychosocial impact in this cohort of patients.

The null hypothesis of this article was that there are no differences in the rebound between nonvital bleached teeth treated with either 35% hydrogen peroxide or 37% carbamide peroxide. The second null hypothesis was that there is no impact on aesthetic self-perception and psychosocial impact at the one-year follow-up in patients who have undergone intracoronal bleaching.

METHODS AND MATERIALS

This randomized trial was approved by the ethics committee of the faculty of dentistry of the local university (2016/04) and was carried out according to the standards of consolidated reporting trials⁹ and the Declaration of Helsinki (2002) (1975, revised in 2000).

Entry Criteria

A total of 74 patients were examined in order to assess whether they met the criteria for study inclusion (Figure 1). Inclusion criteria consisted of several parameters: 1) patients >18 years; 2) patients having one or more discolored nonvital teeth; 3) patients whose restorations did not include vestibular surfaces; 4) patients with root canal treatment in good condition with no apical lesions; 5) patients with no previous tooth whitening; and 6) patients with a tooth tone of ≥A2 according to the Classic Vita Scale. Exclusion criteria consisted of several parameters: 1) pregnant or breastfeeding patients; 2) patients with enamel hypoplasia; 3) patients with teeth stained by tetracycline; 4) patients with fluorosis or previous metallic restorations related to tooth discoloration; 5) patients receiving fixed orthodontic devices; 6) patients with cancer; and 7) patients with periodontal pathologies. Patients with clinical or radiographic caries, periapical lesions, resorption of internal or external tooth structure, or those with periodontal disease were excluded. These patients were referred to specialized treatment clinics.

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Patients meeting the inclusion criteria were randomized into two groups of 25 each according to bleaching agent: Group 1 (G1) - teeth bleached with 35% hydrogen peroxide (Opalescence Endo, Ultradent, United States) and Group (G2) - teeth bleached with 37% carbamide peroxide (Whiteness Superendo, FGM, Joinville, SC, Brazil). Bleaching agents were applied according to the manufacturers' instructions in four weekly sessions using an ambulatory technique (walking bleach).

Preparation Session

The canal was prepared under absolute isolation, removing 3 mm of the endodontic filling from the cementoenamel junction in the apical direction. To protect the endodontic treatment, a 2 mm seal made with a resin-reinforced glass ionomer (Riva light cure, SDI, Australia) was applied and cured for 60 seconds at a distance of approximately 1 cm (1200-mW/cm², Cal Raddi, SDI, AU). Due to the distribution of s italic dentin tubules in the cervical area of the tooth, the coronal limit of the seal was 1 mm below the cementoenamel junction to guarantee whitening. To confirm the proper sealing of the endodontic treatment, a radiographic control was made.

Four Tooth Whitening Sessions

Application of the whitening agent was conducted according to the manufacturers' instructions. The correct amount of whitening gel was placed in the cavity pulp chamber in the presence of mild moisture (walking bleach technique). The cavity closure was made with temporary cement (Fermín, Detax, Germany) until the next session, which occurred seven days later. This procedure was repeated in each of the sessions for up to four weeks. The same amount of gel was used at each session.

Final Session

After washing the cavity access with abundant water, a temporary restoration was inserted for seven days and then the final restoration with composite resin was done. Patients were warned not to eat or drink any foods, including coffee, tea, or wine, that might stain their teeth during the study period. Patients were given instructions in writing and provided with contact information if they had any questions or experienced any adverse events.

RESULTS

Participants' characteristics are shown in Table 1. Tooth distribution (G1=12 upper central incisors; four upper lateral incisors, and one lower central incisor; G2=13 upper central incisors and four upper lateral incisors) at one-year follow-up. There were no statistically significant differences between the characteristics of participants in the groups (Mann-Whitney test, p>0.05.) ΔE is shown in Table 2. Efficacy was similar at all times except at immediate subsequent measurement (p<0.05). These two groups showed high efficiency, with an average ΔE of >13 units. A slight rebound was similar to one-month follow-up values.

Table 1 Participants' Baseline Characteristics

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Table 2 Values of ΔE Expressed as Mean and Standard Deviation

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Results for ΔSGU differed over time, as shown in Tables 3 and 4. More effective efficiency was noted in G1. However, values were not significantly different (p>0.05). Results of the color comparison of the bleached teeth vs homologous teeth are shown in Tables 5 and 6.

Table 3 Comparison of ΔSGU Values at Different Timepoints Using the Vita Classic Scale [Median (Minimum:Maximum)]

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Table 4 Comparison of ΔSGU Values at Different Timepoints Using the Vita Bleach Guide [Median (Minimum:Maximum)]

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Table 5 Comparison of SGU Values at Different Timepoints Using the Vita Classic Scale [Median (Minimum;Maximum)]

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Table 6 Comparison of SGU Values at Different Timepoints Using the Vita Bleach Guide [Median (Minimum:Maximum)]

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Dental Aesthetics Psychosocial Impact (PIDAQ)

The PIDAQ score was significantly different at the start of the study in comparison with one year later for all factor scores except aesthetic concern in G2. When comparing groups (Table 7), no statistical differences were observed between them (p>0.05).

Table 7 PIDAQ. Values of Factors Expressed as Median (Minimum/Maximum) at Different Timepoints^†

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Table 7 Extended

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Oral Health Impact Profile (OHIP-Aesthetics)

There were statistically significant differences in G2 (p<0.05) for total score, functional limitations, and psychological disabilities. G1 was not statistically different when compared with baseline. There were no statistically significant differences between groups at the one-year follow-up (Table 8).

Table 8 OHIP. Values of Factors and Sum Expressed at Median (Minimum/Maximum) at Different Timepoints^†

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Table 8 Extended

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DISCUSSION

This randomized trial showed that the effectiveness of two bleaching agents (35% hydrogen peroxide and 37% carbamide peroxide) can be measured objectively and subjectively, and both agents can be applied for intracoronal nonvital teeth using the walking bleach technique. Both products showed high efficiency with very low rebound at the one-year follow-up period. The results showed that the treatment had a positive influence on a patient's psychosocial aspects one year after showing improvement in the tooth color in the majority of participants. Therefore, the first null hypothesis was accepted, as the two gels are widely effective according to objective and subjective measurements at the one-year follow-up. The second hypothesis was partially accepted, but the psychosocial impact was maintained, and the aesthetic perception showed a partial regression to baseline values.

Our results showed that after four sessions with the walking bleach technique at one-year follow-up after the treatment, there was a ΔE of 15.11 ± 5.59 for G1 and of 13.17 ± 5.13 for G2. In terms of the final results, no differences between agents (p>0.05) were observed, although there was a tendency for the color to recur after one month of treatment. Subjective evaluation of the color changes also indicated that treatment was very effective.

Few clinical studies have evaluated the effectiveness of nonvital whitening, and the most commonly used bleaching agent is sodium perborate.⁸ In an in vitro study by Lim and others,¹⁶ it was concluded that both 37% carbamide peroxide and 35% hydrogen peroxide were more effective than was sodium perborate. This study evaluated the color of each tooth using the Vita Lumin guide; after seven days, there was a change of 8 ΔSGU, and the color shifted by two additional units after 14 days.¹⁶ This study, however, is not considered to have provided a high level of evidence. In the present clinical trial, intracoronal whitening rebound was slight at the one-year follow-up period and was comparable to vital extracoronal whitening rebound results from another clinical trial¹² that was recently published. It is important to mention that the measurements were made on the middle sector of the vestibular face of the central incisors; since color recurrence in a nonvital tooth occurs from the cervical portion of the tooth, this finding could have been obviated by this difference in measurement location.¹⁷

The whitening agents that are most commonly used to whiten nonvital teeth are hydrogen peroxide, carbamide peroxide, and sodium perborate. Hydrogen peroxide is the active ingredient in the tooth whitening gels currently used. It can be applied directly or it can be produced by a chemical reaction of carbamide peroxide or sodium perborate.

High concentrations (35%) of hydrogen peroxide are caustic and can burn tissues on contact and cause free radical release. As a result of its low molecular weight, this substance can penetrate the dentin and release oxygen that breaks the double bonds of organic and inorganic compounds within the dentinal tubules. Carbamide peroxide [CO(NH₂)2H₂O₂] is an organic crystalline white compound formed by urea and hydrogen peroxide and is used in different concentrations. In a hydrophilic environment, it decomposes into approximately 30% hydrogen peroxide and 70% urea. Currently, the most popular commercial whitening preparations that contain carbamide peroxide also include different concentrations of glycerin because this makes it more chemically stable compared to hydrogen peroxide. Sodium perborate is an oxidizing agent available in powder form. It is stable when dry; however, in the presence of acid, hot air, or water, it decomposes to form sodium metaborate, hydrogen peroxide, and nascent oxygen. Sodium perborate is easier to control and safer than concentrated solutions of hydrogen peroxide.⁸

Visual assessment by colored guides is a complex process that involves individual and general parameters, such as age and experience of the examiner, fatigue of the human eye, external lighting, the color of the wall and the interior, and the angle of perception.¹⁸ The determination of the tooth color by visual means becomes less reliable as a result of the lack of guides of dental colors that are commercially manufactured. The concept of the threshold of perceptibility that varies among individuals is relevant, and despite being able to achieve good agreement rates between evaluators, the error of the subjective assessment is always greater.¹⁹ On the other hand, objective color instruments can measure color tones with greater precision and enable the communication of tone matches.²⁰ The reliability of the device used is important, as it ensures the reliability of these measurements using relatively simple and easy-to-replicate methodologies. Currently, the devices used are highly accurate and provide reliable measurements that correctly guide dentists with respect to the measured color.^20,21

The research team was not surprised at the high satisfaction levels of patients who underwent a whitening procedure in this trial and were then followed.²² For various reasons, we have been able to completely match neighboring tooth colors using our nonvital tooth whitening method. Results relative to the aesthetic perception and psychosocial impact were positive and significant with respect to whitening after one month. Whether this effect was maintained over time needs to be confirmed in patients undergoing positive vital tooth whitening² and then correlated with the maintenance of the bleaching procedure effectiveness at one year.

The OHIP-Aesthetic survey also showed positive effects on G2 patients' aesthetic perceptions. This result is supported by other studies,²³ whose authors evaluated the influence of extracoronal vital bleaching on patients' aesthetic perceptions. Our data confirmed that a patient's quality of life is complex, important, but poorly studied, and there are multiple factors that influence it. However, dental aesthetics appear to be important to a patient's quality of life, although its influence on patients' perceptions and psychological and social factors are unknown. The impact of psychological and social factor perceptions is unknown. No differences in OHIP-Aesthetic scores between the groups was observed, but there were differences in the changes in each group over time. This resulted in an effect that was more pronounced and positive for G2; however, there was a regression of values in G1, likely because the effect was not as durable and because patients were accustomed to the condition after one year. This finding must be further investigated to assess the correlation between perception and aesthetic color changes.

PIDAQ has been shown to decrease the negative impact of cosmetic dentistry for a patient and to decrease the values in social and psychological impact and aesthetic concerns. The psychosocial impact was similar in both groups (p>0.05). We found that a big impact was indicated by the PIDAQ data for all relevant factors, but minimal intervention in a tooth has a major effect in people who undergo intracoronal whitening.

CONCLUSION

Hydrogen peroxide (35%) and carbamide peroxide (37%) were highly effective for the nonvital tooth walking bleach technique and can achieve a high level of color matching with the counterpart teeth and color maintenance at the one-year follow-up, with a slight rebound. Each gel produced a positive impact on patients' psychosocial impact at the one-year follow-up.