Efficacy of products for bleaching and whitening under orthodontic brackets

ABSTRACT Introduction: Many patients wearing orthodontic appliances request alterations in the shade of their teeth during orthodontic treatment. Objective: This study aimed to evaluate the efficacy of different products for bleaching and whitening under orthodontic brackets. Methods: Seventy bovine incisors were randomly divided into five groups (n = 14): C) non-whitening toothpaste (control); WTsi) hydrated silica whitening toothpaste; WThp) 2% hydrogen peroxide whitening toothpaste; OB) in-office bleaching; and HB) at-home bleaching. Two buccal surface areas were evaluated using the Easyshade spectrophotometer: under the metal bracket (experimental) and around the bracket (control). The paired t-test, ANOVA, and Tukey tests were applied for statistical analysis. Results: Intragroup comparisons showed that in groups C, WThp and HB, there were statistically significant differences in the enamel color changes (ΔEab) between under and around the bracket areas (C - under bracket = 7.97 ± 2.35, around bracket = 2.86 ± 0.81, p< 0.01; WThp - under bracket = 4.69 ± 2.98, around bracket = 2.05 ± 1.41, p< 0.01; HB - under bracket = 7.41 ± 2.89, around bracket: 9.86 ± 3.32, p= 0.02). Groups WTsi, OB and HB presented similar perception of tooth whiteness (ΔWID) between the tested areas. Intergroup comparisons demonstrated that under the bracket area, the color change (ΔEab) was similar for all groups, except WThp (C = 7.97 ± 2.35; WTsi = 8.54 ± 3.63; WThp = 4.69 ± 2.98; OB = 9.31 ± 4.32; HB = 7.41 ± 2.89; p< 0.01). Conclusions: The dental color changes were effective for the products tested in groups WTsi, OB and HB in the presence of metallic orthodontic brackets.


INTRODUCTION
Dental bleaching and alignment are the majority of complaints from patients who attend dental offices. [1][2][3] Besides the aesthetic benefits, dental color and position changes have also been correlated with individuals' social perception, including more positive judgments related to social competence and appeal, intellectual ability, and relationship satisfaction. 1,4 Many orthodontic patients request dental bleaching during orthodontic treatment, 5 to simultaneously achieve the desired dental color and position. Usually, dissatisfaction with the color of teeth increases when the crowding is solved. 2 Dental bleaching and whitening are different processes. Dental bleaching involves the application of gels containing hydrogen peroxide or carbamide peroxide on the tooth surface. The peroxide diffuses through the enamel and dentin, producing free radicals that react with the intrinsic pigments, making the teeth appear whiter. 6,7 A recent study suggested that hydrogen peroxide might whiten normal dentin by oxidizing the benzene ring of aromatic amino acids in dentin phosphoprotein, the main noncollagenous protein located in the organic-inorganic interface, responsible for the fluorescence and color of normal dentin. 8 On the other hand, dental whitening consists of the removal and control of extrinsic tooth stains. 7 Currently, many whitening products, with the promise of rapid and convenient color alteration, are available Pinzan-Vercelino CRM, Lima SNL, Pereira FFJV, Gurgel JA, Silva GR, Freitas KMS -Efficacy of products for bleaching and whitening under orthodontic brackets 5 on the market, including whitening toothpastes. 7,9,10 Whitening toothpastes have become popular due to low costs, unrestricted selling, ease of use, and high availability. 7,11 Most whitening products act in one of these mechanisms: chemical (the use of peroxides for tooth bleaching) or mechanical (removal of extrinsic stains through abrasive action). 7,12 Toothpastes that act using a mechanical mechanism contain abrasives that only remove the extrinsic stains, instead of changing the tooth color, as is observed in a real bleaching action. Some whitening toothpastes have included peroxide in their formulations; however, the efficacy of peroxide from toothpaste is questioned regarding the concentration and exposure time during toothbrushing. 13 Previous clinical 14,15 and laboratory 16-19 studies have shown color alteration under the bracket area using bleaching agents. However, even with the increasing presence of whitening toothpastes on the market, the authors are unaware of a study that has been conducted to test their efficacy on teeth with bonded brackets. Therefore, the present study aimed to evaluate different products' efficacy for bleaching and whitening under orthodontic brackets. The null hypothesis tested was that there would be no differences in color change when hydrated silica whitening toothpaste; 2% hydrogen peroxide whitening toothpaste; in-office dental bleaching using 35% hydrogen peroxide; and at-home bleaching using 22% carbamide peroxide procedures are applied on teeth with bonded brackets. Seventy experimental units were obtained from bovine incisors aged between 24 and 30 months, and were stored in a refrigerated 1% chloramine-T solution, ph7, for 30 days. The following criteria for tooth selection were used: intact buccal enamel, with no cracks, no abrasion, or any other crown defect, and similar size and shade (A3, determined by comparison with a value-oriented shade guide -Vita Toothguide 3D Master; VITA Zahnfabrik, Bad Säckingen, Bade-Württemberg, Germany). The morphological enamel conditions were evaluated by two researchers, using a simple magnifying glass. Only in cases of agreement, the teeth were selected. The researchers inspected 120 teeth and selected 70 from this set. The roots and pulp chamber of the teeth were removed. The pulp chamber was accessed and extended using a Pinzan-Vercelino CRM, Lima SNL, Pereira FFJV, Gurgel JA, Silva GR, Freitas KMS -Efficacy of products for bleaching and whitening under orthodontic brackets 7 conical diamond tip. The dental pulp and debris were removed using a dental curette and air/water jets. Afterward, the bovine incisors were stored for 7 days in distilled water.
One matrix was made for each tooth, using high-viscosity silicone, to standardize the color measurement area, and guide the bracket bonding. In the matrix, two vertically adjacent circular windows were located close to the center of the crown, on the buccal surface of the teeth (Fig 1): one experimental area (under the bracket) and one control area (around the bracket).
They were configured using a circular metal-cutting device measuring 6 mm in diameter (Biopsy Punch, Miltex; York, PA, USA), corresponding to the diameter of the spectrophotometer probe (Easyshade Advance 4.0; Vident, Brea, CA, USA). 14,15,21,22 A single calibrated operator performed the bonding procedure.
Before brackets bonding, the teeth received dental screening and dental prophylaxis, using pumice and a rubber cup with a low-speed handpiece. With the matrix installed on the buccal surface of the teeth, at the circular opening of the experimental area, 37% phosphoric acid gel was applied for 30s, followed by rinsing for 30s, and  The specimens were numbered and then equally (n=14) and randomly (Random.org Integer Generator; http://www.random.org) divided into five groups (Table 1)  The specimens were brushed twice a day for 15 days (500 cycles in each brushing), totalizing 15,000 cycles of circular mechanical brushing. After each brushing cycle, specimens were washed in running water and stored in distilled water at 37ºC.
In group OB, the bleaching agent used was 35% hydrogen peroxide for the in-office procedure. The gel was applied in three applications, each one lasting 15 min. Two bleaching sessions were performed, with a 1-week interval between them.
After the bleaching treatment, the teeth surfaces were abundantly washed with water. Between the sessions, the teeth were stored in distilled water at 37ºC, changed daily.
In group HB, the bleaching agent used was 22% carbamide peroxide for at-home bleaching, for 15 consecutive days, being 2 hours per day. The specimens were stored over cotton gauze soaked with distilled water throughout the bleaching procedure. After the bleaching treatment, the teeth surfaces were abundantly washed with water, and stored in distilled water at 37ºC, changed daily.
Bracket debonding pliers were used to debond the accessories.
Removal of resin remnants was performed using a 12-blade tungsten carbide bur on low-speed handpiece, at 20,000 rpm without water cooling.
One operator made the color evaluations, using the matrix to standardize the spectrophotometer probe placement during consecutive color evaluations. 14,15,21,22 The color measurements were recorded at baseline and one month after bracket removal, to give the teeth adequate time to rehydrate. 15,23 The color was measured using color coordinates established

RESULTS
The color coordinates evaluated (L*, a*, and b*) were similar at baseline, for all groups, between under the bracket area (experimental) and around the bracket area (control), demonstrating that the areas compared were compatible regarding color at baseline ( Table 2).   (Table 3).

DISCUSSION
Although previous studies [14][15][16][17][18][19] have evaluated the efficacy of different dental bleaching agents under orthodontic brackets, no study has evaluated the whitening toothpastes. Since many patients wearing orthodontic appliances perceive changes in the shade of their teeth, and whitening toothpaste is an easily accessible product, 12 its efficacy needed to be tested. The null hypothesis was Previous studies 26,27 observed that hydrated silica whitening toothpaste showed greater color changes than 2% hydrogen peroxide whitening toothpaste, corroborating with the present results. This finding suggested that the toothbrushing abrasion action was mainly responsible for the color changes. 26 The authors speculate that the low peroxide hydrogen concentration did not produce enough free radicals to oxidize dentin's organic component in the WThp group. 28,29 The in-office and at-home bleaching procedures showed statistically greater color changes and similarity around the bracket area, corroborating with previous studies. 18,19,21,22,25,30 The area under the bracket showed greater color alteration and tooth whiteness, when compared with the area around the bracket, for the non-whitening toothpaste, 2% hydrogen peroxide whitening toothpaste, and at-home bleaching procedure.
Previous studies 31-34 also observed enamel color changes after treatment with fixed orthodontic appliances, demonstrating an increase in the tooth color's lightness after bracket debonding.  and OB, and demonstrated clinical acceptability for HB, it is important to highlight that the use of these products in an abusive manner may result in enamel alterations and tooth sensitivity. 4,15,22,39 Bleaching is contraindicated in clinical conditions in which the tooth presents exposed dentin or other enamel tissue changes that presumably increase its permeability. 14 According to the results obtained in the present study, the in-office dental bleaching using 35% hydrogen peroxide, at-home bleaching using 22% carbamide peroxide, and the use of whitening toothpaste containing hydrated silica showed effectiveness in the presence of metallic orthodontic brackets.
Therefore, in cases where orthodontic patients request dental bleaching or whitening during orthodontic treatment, these products may be indicated.
Further studies comparing enamel roughness and possible physical and/or mechanical alterations in the orthodontic appliances (e.g. wires, brackets and ligatures) must be encouraged.

CONCLUSIONS
Considering the results obtained for the color changes (ΔE ab ) and the perception of tooth whiteness (WI D ), the dental color changes were effective, in the presence of metallic orthodontic brackets, for the use of whitening toothpaste containing hydrated silica and in-office dental bleaching with 35% hydrogen peroxide and at-home bleaching with 22% carbamide peroxide.