Effects of Pre-Operative Air-Powder Polishing and Rubber-Cup Prophylaxis on Tooth Bleaching Outcomes: Randomized Controlled Split-Mouth Clinical Study

Background: The aim the study to compare the effects of pre-operative air-powder polishing and rubber-cup prophylaxis on tooth bleaching outcomes. Methods: 23 subjects suffering from discoloration, were enrolled in a randomized controlled split mouth experimental study. Before bleaching, air powder polishing and rubber-cup polishing techniques were applied on either side of the mouth and the tooth bleaching effects assessed immediately after and 7 days. Results: No statistically signicant difference was found in for DL, Da, Db, DE and DSGU values between air-powder polishing and rubber-cup groups at immediate and 1 week. The difference between immediate and 1 week measurements is statistically signicant in both air-powder polishing and rubber-cup groups, except DL for rubber-cup group, and Da, Db for air-powder polishing group. Conclusions: Within the limitations of the study, it can be concluded that there was no lasting difference in tooth bleaching effects between rubber-cup and air-polishing techniques at immediately after and 1-week post treatment.

The aim this study is to compare the effects of pre-operative air-powder polishing and rubber-cup prophylaxis on tooth bleaching outcomes.

Methods
This study used randomized, controlled split-mouth experimental design to compare the effects of pre-operative APD application (test side) and rubber-cup prophylaxis with paste (control side) on teeth bleaching. The ow chart of study design was given in Figure 1. The sample size analysis for paired-sample t-test was done by G-Power package program. The sample size calculation was based on a previous study [9]. The expected mean difference of for the color change parameter between groups was 2,2 units with a standard deviation of 3,3 -3,7 (the speci ed power of 80% and the Type I error rate of 5%). The calculated sample size was 21 patients while 23 patients (10% more) were included in the study to compensate possible dropouts.

Study protocol Clinical parameters
Tooth color was measured using spectrophotometer VITA Easyshade V (Vita Zahnfabrik, Germany). The spectrophotometer was calibrated before use in each participant and the device tip was placed on middle thirds of the labial surface of teeth as suggested by the manufacturer's manual.
The tooth color was measured before initial prophylaxis (baseline), immediately after bleaching and after one week. The digital spectrophotometer used in the current study measures the shade of teeth based on the CIE L*a*b* color space system [10]. This system expresses color as three values: L* for the lightness from black (0) to white (100), a* from green (−) to red (+), and b* from blue (−) to yellow (+). The following values were recorded in the units of CIE L*a*b* color space.
-Data of lightness (L*) and a* and b*axis -DE: calculated as: DE = [(DL *) 2 + (Da *) 2 + (Db *)2] 1/2 While making Shade guide units (SGU) measurements, the bleached index is set according to the VITA Bleached guide 3D-MASTER at spectrophotometer for the measured shade. The measured bleached index after treatment was subtracted from the baseline value. The difference corresponded to the change of the SGU (D SGU) achieved immediately and 1 week after the bleaching treatment.

Randomization
The patients had bleaching treatment on the maxillary anterior area including right and left canines. The registration of the patients has been done by Department of Oral Diagnosis and randomly allocated by ZGBK. The right and left sides of the patients were randomized by toss of a coin to receive polishing with rubber cup prophylaxis or air powder polishing system before bleaching.

Clinical procedures
The rubber cup prophylaxis was applied with low-speed handpieces. A rubber cup was attached to the prophy-angle. The handpiece used at a steady slow pace of 2500-3000 rpm. The rubber cup contacted (Pro-Cup, Light Blue, Soft, KerrHawe S.A., Bioggio, Switzerland) each tooth surface for an average of 5 seconds together with polishing paste consisting of our of pumice, glycerin and uoride (Cleanic, KerrHawe S.A., Bioggio, Switzerland).
The air polishing treatment was performed by AIRFLOW ® Master device (EMS, Nyon, Switzerland) with a six LED power setting (2.2 bars dynamic pressure inside powder chamber) and an 11 LED (35 mL/min) water setting for 30 seconds (powder consumption was 1.1 g). Sodium bicarbonate air-powder polishing powder (AIR-FLOW ® Plus, EMS Electro Medical Systems, Nyon, Switzerland) was used. The nozzle was held 3-4 mm from the tooth surface and the tip was angulated diagonally. The spray was delivered for an average of 5 seconds using a constant circular motion for each tooth. The spray was directed towards the middle one-thirds of the exposed tooth [11].
The bleaching agent (Opalescence Xtra Boost/ Ultradent, South Jordan, UT, USA) was prepared and used following the manufacturer's instructions. Opal Dam (Ultradent, South Jordan, UT, USA) was used for protection of the gingiva. The bleaching gel was then applied to form 1-2 mm thickness on the buccal surfaces of the teeth of both arches. The gel remained on teeth for 15 minutes and was then suctioned from teeth using a surgical suction tip. This application was repeated a second time in the same session.

Statistical Analysis
The assumption of normal distribution of difference scores were examined prior to conducting the analysis. The assumption was considered satis ed for many differences of color scores, some of them not satis ed which were indicated with asterisk (*) in Table 1.
The proper reporting for non-normal distributed (skewed) data were summarized by using median (minimum and maximum) value instead of mean and standard deviation. Because of a consistent illustration in the Table 1 for parametric and nonparametric tests the both descriptive statistics mean ± SD, and Median (min, max) noted across all treatment levels.
The differences of color scores of the teeth were assessed for normality assumption by Shapiro-Wilks test (p>0.05) and homogeneity of variances were assessed by Levene's Test for Equality of variances (p>0.05).
The paired t-test were used if the normality assumptions were valid, otherwise the Wilcoxon-signed rank test were used to compare the rubber-cup and air-powder polishing treatments, and for the differences of 1 week and immediate values.

Results
All included patients completed the study protocol without any adverse events. The mean age of patients was 34.1±8.9. The results of the study are summarized in Table 1. The baseline measurements of teeth colors and the color changes (ΔL, Δa, Δb, ΔE, ΔSGU) immediately after bleaching and at week 1 are shown in Table 1.
The baseline measurements of teeth colors and the color changes (ΔL, Δa, Δb, Δe, ΔSGU) immediately after bleaching and at week 1 are shown in Table 1. There was no signi cant difference at the baseline CIE L*, a*, b* value between the groups (p > 0,05). At immediate and 1 week recall, both treatment groups remained signi cantly lighter than the baseline, as for the color parameters: lightness improvement (ΔL) (p < 0.001), reduction of redness (Δa) (p = 0,003), reduction of yellowness (Δb) (p < 0.001).
No statistically signi cant differences were found for ΔL, Δa, Δb, ΔE and ΔSGU values between air-powder polishing and rubbercup groups at immediate and 1 week results.
The difference between immediate and 1-week measurements is statistically signi cant for both air-powder polishing and rubbercup groups, except for ΔL (p = 0.354) for rubber-cup group, and for Δa (p = 0,181), Δb (p = 0,484) for air-powder polishing group. ΔSGU value was signi cantly changed during immediate and 1-week treatment period in rubber-cup group the mean change of SGU = 3.14 ± 2.83, p < 0.001, and also in the air-powder polishing group the mean change of SGU = 2.80 ± 1.89, p < 0.001 was statistically signi cant.

Discussion
The null hypothesis was not rejected. The results of the study have shown that while effective bleaching was achieved [12] (as determined by a change in E of over 6 units immediately after and over 9 in rst week), there were no signi cant changes between prior APD and rubber-cup prophylaxis.
Previous literatures have shown that whitening from bleaching agents is manifested mainly by an increase in lightness (higher L) and reduction in yellowness (lower b) and redness (lower a) [13,14]. There were increase in the L value and decrease in a and b values immediately after the bleaching treatment. After 1 week, statistically different developments continued according to baseline measurements in all these three values. There are signi cant differences in and values in the rubber-cup group and in ow group between immediate and 1-week measurements. Some studies found that the variance in b and L values had major in uence on color change [15,16]. In the judgement of whiteness of tooth none of a, b or L value distinctly evaluated, hence all off them equally valuable for the calculation of E value. Therefore, in this study, we also included SGU in the comparison.
To our knowledge, there are no studies comparing the effects of prior APD and rubber cup prophylaxis on the bleaching effectiveness which makes the interpretation of the results impossible. Results of previous studies comparing the effectiveness of air-polishing to the rubber cup polishing for bacterial plaque and stain removal demonstrate that both methods are equally effective with similar gingival trauma [17]. While some studies report APDs to be more effective for plaque and stain removal in a b L pits and ssures [18] and complete cleaning, down to the tooth microstructure [19] ; others indicate that polishing with rubber cup was more effective for the crown and root surface smoothening and debris removal [20]. The main disadvantage of rubber-cup prohylaxis is that the polishing pastes abrade, atten, and deposit debris into the microcavities voids on the enamel surface [19] which may theoretically decrease bleaching effectiveness. In addition, Nakamura et al. [21] reported that tooth polishing with a polishing agent and a brush caused a decrease in lightness and reduction of yellowness. The polishing with rubber cup and prophylaxis paste is highly operator-sensitive as rotation speed, abrasiveness of paste, pressure applied with hand piece and duration in uence affect the e cacy of the procedure [22]. On the other hand, the aerosols generated by air polishing may present an infection control hazard hence, preprocedural rinse is always recommended along with aerosol reduction devices [23].
Up to date various studies have been performed to increase the effectiveness of the bleaching procedure in a shorter period of treatment time. O ce-bleaching usually requires long application period and sometimes additional visits to obtain optimum results. Prolonging bleaching treatment may result in several side-effects such as tooth sensitivity, gingival irritation and alteration of enamel surface [24,25]. Low molecular weight of HP diffuses through permeable enamel and dentin substrates, then reaches the pulp chamber via the dentinal tubules. Exposure to high HP concentrations, may cause in ammatory response in the pulp. Less application and sessions are recommended to minimize these side effects [26][27][28]. Researchers investigated whether reduced contact time of the bleaching gels could yield less-adverse effects while still being effective [27,29,30]. Several studies have shown that the substance released from bleaching gels is proportional to their contact time with enamel [31][32][33][34].
However, some authors have shown that exposure of pulp cells to low HP concentrations encourages the differentiation of odontoblasts and the formation of mineralization [35,36]. On the other hand, shortening the bleaching time may prevent it from achieving satisfactory results. The gel used in the in-o ce technique is exposed to the environment and seemingly loses water faster. This is the argument used by manufacturers to recommend applications of 15 minutes. The shortest time of application (2 × 15 minutes) for one session as recommended by the manufacturer was performed in the current study.
The split-mouth design used in this study allows different experimental groups within the same patient. Thus, each patient served as his or her own control. This eliminates patient dependent variables on the results. In order to be more precise and objective, the spectrophotometer measurement was preferred over the visual evaluation [37]. Besides this, a positioning guide with ori ces in the center of the middle third of teeth was fabricated [38]. This was because the middle area of teeth is generally atter and provides a stable platform for the spectrophotometer sensor [39], and this area is the most representative tooth-color region as it re ects the light from the dentin with little in uence from the enamel [38][39][40].

Conclusions
The results of the study show that both rubber cup prophylaxis and APD devices can be used before bleaching treatment as there were no statistical differences in color change.