Effects of pre-operative air-powder polishing and rubber-cup prophylaxis on tooth bleaching : Randomized controlled split-mouth clinical study

45 Background : The aim the study to compare the effects of pre-operative air-powder polishing 46 and rubber-cup prophylaxis on tooth bleaching. 47 Methods : 23 subjects suffering from discoloration, were enrolled in a randomized controlled 48 split mouth experimental study. Before bleaching, air powder polishing (APP) and rubber-cup 49 polishing (RCP) techniques were applied on either side of the mouth. A 40% hydrogen peroxide 50 bleaching agent applied two 15-minute applications for in-office bleaching. The tooth bleaching 51 effects assessed immediately after and 1 week. 52 Results : There were no significant differences between prophylaxis groups with respect to all 53 color parameters ( ∆ L, ∆ a, ∆ b, ∆ SGU, ∆ Eab, ∆ E00) at immediate period (p>0,05). At 1 week 54 assessment period there were no significant differences between prophylaxis groups with 55 respect to all color parameters (p>0,05) except delta E00 (p<0,05). 56 Conclusions : Two prophylaxis techniques produced similar efficacy in bleaching treatment and 57 the APP technique produced higher levels of color changes. 58 Trial


Background
Vital bleaching treatment in dentistry are classified as in-office bleaching and at-home bleaching.Currently, in-office bleaching gels are the most commonly used agents and contain high hydrogen peroxide concentrations (typically 15-40%) while at-home bleaching products usually contain 3-10% of hydrogen peroxide [1].The in-office bleaching technique has some advantages such as avoiding soft tissue irritation, preventing the use of excess material and producing immediate esthetic results [2,3].
The agents used in bleaching treatment could penetrate enamel/dentin and oxidize the molecules of the substances that cause discoloration in the tissue.In the bleaching reaction, peroxides convert into peroxide radicals, which have singular and unpaired electrons with no electronic charge.These highly reactive radicals have a high affinity for double bonds.Peroxide radicals bond to and destroy the carbon-carbon double bonds of the chromophore and either convert them into single bonds or completely break down [4].The resulting molecules are colorless and make teeth look whiter.
Various factors are reported to effect tooth bleaching such as bleaching type, concentration, time and other factors (ie.plaque, pellicle on the tooth surface) [5].The success of bleaching is directly related to the diffusion capacity of peroxides to enamel and dentin.The penetration of hydrogen peroxide in the tooth structure is time-dependent [6].
Up to date various studies have been performed to increase the effectiveness of the bleaching procedure in a shorter period of treatment time.In-office 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 [7,8].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 inflammatory response in the pulp.Less application and sessions are recommended to minimize these side effects [9][10][11].Researchers investigated whether reduced contact time of the bleaching gels could yield less-adverse effects while still being effective [10,12,13].Several studies have shown that the substance released from bleaching gels is proportional to their contact time with enamel [14][15][16][17].However, some authors have shown that exposure of pulp cells to low HP concentrations encourages the differentiation of odontoblasts and the formation of mineralization [18,19].On the other hand, shortening the bleaching time may prevent it from achieving satisfactory results.The gel used in the in-office 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 (2X15 minutes) for one session as recommended by the manufacturer was performed in the current study.
The activation of bleaching agents is limited and decreases over time [20].Contact with plaque and external stains before tooth enamel during active time of agent might reduce its effectiveness.The superficial stains, plaque accumulation, and microorganisms formed on the outer surface of tooth enamel should be removed before starting bleaching treatment by polishing in order to make bleaching agent more effective.Dental bleaching manufacturers recommend dental prophylaxis before bleaching treatment in their instruction manuals.But there is no research about prophylaxis techniques before bleaching treatment.
The most common method of polishing is rotary rubber-cup prophylaxis with various types of pastes.These polishing pastes include flour of pumice, glycerine and fluoride.Air-powder polishing devices (APDs) are an alternative to rubber cup polishing.These devices use a slurry of water, abrasive powder and pressurized air to clean or polish tooth surface [21].Sodium bicarbonate is the first air-polishing powder used with these devices.There are many literature stating that air polishers are more effective and efficient in removing extrinsic stain and plaque from tooth surfaces than rubber cup polishers [22,23,24,25,26] In addition air polishing requires less time than traditional polishing methods [27].Polishing with a rubber cup and prophylaxis paste has been shown to remove the fluoride-rich enamel and rough the enamel [28,29].
Studies have generally found air polishing to be safe on enamel with no significant loss of enamel and less abrasive than rubber-cup polishing [30].However marked rise in aerosols with air polishing, additional health hazards may potentially exist for patients, or health care professionals present in the treatment room during or after a procedure [31].
The aim this study is to compare the effects of pre-operative air-powder polishing and rubbercup prophylaxis on tooth bleaching.
The null hypothesis was that there would be no difference in the change of color according to the type of prophylaxis on tooth bleaching.

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 flow chart of study design was given in Figure 1.

Sample size calculation
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 [32].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 specified 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.

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
Dental prophylaxis was made by a single operator (MO).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 flour of pumice, glycerin and fluoride (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 5 seconds for each tooth (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 [33].
In-office 40% HP 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.

Clinical parameters
Tooth color was measured using spectrophotometer VITA Easyshade V (Vita Zahnfabrik, Germany).All measurements were made by a single operator under same light source between 1-3 pm.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), after prophylaxis, immediately after bleaching and after 1 week.The digital spectrophotometer used in the current study measures the shade of teeth based on the CIE L*a*b* color space system [34].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.
-∆Eab calculated as: [(∆L) 2 + (∆a Where ΔE00 is the change in color; RT is a hue rotation term; ΔL, ΔC, and ΔH are the compensation differences for neutral colors (primed values; L,C,H); SL is the compensation for lightness; SC is the compensation for chroma; SH is the compensation for hue; and kL, kC, and kH are constants and usually unity.

∆SGU:
The other bleaching scale shade guide (SGU) unit also used to monitör tooth whitting prpcess.While making 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.

Statistical Analysis
The assumption of normal distribution of difference scores were examined prior to conducting the analysis.The assumption was considered satisfied for many differences of color scores, some of them not satisfied 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 non-parametric 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 Wilcoxonsigned rank test were used to compare the rubber-cup and air-powder polishing treatments, and for the differences of 1 week and immediate values.The mean change of ∆E00 (2,22±2,11) was significant from immediate to 1-week assessment periods in APP group, (p <0.001) and also in rubber-cup group the mean change of ∆E00 (1,0±1,2) was statistically significant (p=0.012).
The mean change of ∆SGU (3.14±2.83)value was significant from immediate to 1-week treatment period in rubber-cup group, p<0.001, and also in the air-powder polishing group the mean change of SGU (2.80±1.89)was statistically significant, p<0.001.

Discussion
This study evaluated the influence of dental prophylaxis technique prior tooth bleaching in the change of color.Our results suggest that the dental prophylaxis technique before bleaching treatment affects the bleaching color results, thus rejecting the null hypothesis.
CIELab and CIEDE2000 have been developed to identify the color differences of objects.
Studies have revealed that the ΔE2000 reflects small color differences better with the way human observers perceive [35,36].
∆Eab acceptability threshold (AT) in the literature ranges from 2.0 to 4.0, as much as half of the literature refers to its value as being 3,3 or 3,7 [37].After dental prophylaxis, in the APP group ∆Eab and ∆E00 were 3.177 ± 1.756 and 1.878 ± 0.957, respectively.In RCP group, ∆Eab and ∆E00 were 2.699 ± 1.462 and 1.569 ± 0.765, respectively.Values in both groups were below ∆Eab acceptability threshold.The ΔE00 acceptability threshold value was considered to be 1.8 [38].With reference to ΔE00, the APP group was above the acceptability threshold value.
There was no statistical difference between techniques in the color change of teeth after prophylaxis (p>0,05).Pereira et al. reported that tooth color change below the threshold values after prophylaxis with a nylon brush with prophylaxis paste [39].This finding is similar to our results.
To our knowledge, there are no studies comparing the effects of prior APP and rubber cup prophylaxis on the bleaching effectiveness which makes the interpretation of the results impossible.Results of previous study 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 [40].While a study report APDs to be more effective for plaque and stain removal in pits and fissures [41] and complete cleaning, down to the tooth microstructure [42] ; another indicates that polishing with rubber cup was more effective for the crown and root surface smoothening and debris removal [23].The main disadvantage of rubber-cup prohylaxis is that the polishing pastes abrade, flatten, and deposit debris into the microcavities voids on the enamel surface [42] which may theoretically decrease bleaching effectiveness.This may be the reason why the APP is more effective than RCP on bleaching in our study.In addition, Nakamura et al. [44] 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 influence affect the efficacy of the procedure [45].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 [46].
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) [47,48].There were increase in the L value and decrease in a and b values immediately after the bleaching treatment in both groups.
After 1 week, statistically significant developments obtained according to baseline measurements in all these three values.There are significant differences in ∆a and ∆b values in the rubber-cup group and ∆L in air-flow group from immediate to 1-week measurements.Some studies found that the variance in b and L values had major influence on color change [49,50].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.At 1 week period there was no difference between the groups between ∆Eab and ∆SGU while ∆E00 was statistically significant differences.This is due to the difference in the ∆E00 calculation technique.There are few studies on color changes after bleaching using this CIEDE2000 formula [51].This may be because the regression lines of ∆Eab on ∆E00 change from linear to curvilinear shapes when the values increases in color space.Hence in significant test we can reach different conclusion for ∆Eab and ∆E00 [52].
It was reported that the bleaching activity peaked on the 7th day, therefore in our study the observations were measureed at one week after treatments [53].ADP might benefit bleach results and patient and might be considered as the best choice for dental prophylaxis before bleaching treatment.
The split-mouth design used in this study allows different experimental groups within the same patient [54].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 [55].Besides this, a positioning guide with orifices in the center of the middle third of teeth was fabricated [56].This was because the middle area of teeth is generally flatter and provides a stable platform for the spectrophotometer sensor [57], and this area is the most representative tooth-color region as it reflects the light from the dentin with little influence from the enamel [56][57][58].
The limitations of this study are structural differences between teeth.The amount of bleaching agent that penetrates the tooth structure is affected by the thickness of enamel and dentin [59].
The CIEDE 20000 formulation is the most modern method and better reflects visual differences between colors.The use of the CIEDE 2000 formulation is recommended for future bleaching color evaluation studies.The ow chart of study design.

Supplementary Files
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Figure 1 b
Figure 1 Among the patients who applied to the Cukurova University, Dental Faculty, Department of Oral Diagnosis for whitening treatment and volunteered to participate in the study and redirected to Department of Restorative Dentistry.The inclusion criteria were: -being at least 18 years of age -having minimum of 20 natural teeth (including incisors, canines, and premolars in both arches) -having good oral hygiene (Plaque index <1, Gingival index <1) The exclusion criteria were: -having restorations or active caries on the anterior teeth of either arch -presence of tetracycline staining or fluorosis -general hypersensitivity -gingival recession or periodontal disease -smokers -pregnant or lactating women -history of prior bleaching treatment

Figure 1 .
Figure 1.The flow chart of study design.

Figures Figure 1
Figures

Table 1 :
Descriptive analysis before dental prophylaxis

Table 2 :
Color change after dental prophylaxis

Table 4 :
Mean±standart deviations and change from baseline to 1 week for ∆L, ∆a, ∆b, ∆Eab, ∆E00 and ∆SGU Asterisk indicates the p values belong to Wilcoxon signed rank test statistics, the other p values belong to paired t-test statistics.

Table 5 :
The mean differences of color changes from immediate to 1 week period for ∆L, ∆a, ∆b, ∆Eab, ∆E00 and ∆SGU (*) Asterisk indicates the p values belong to Wilcoxon signed rank test statistics, the other p values belong to paired t-test statistics.