Comparative clinical study of the effectiveness of different dental bleaching methods - two year follow-up.
Journal: 2013/January - Journal of Applied Oral Science
ISSN: 1678-7765
PUBMED: 23032205
Abstract:
This study evaluated color change, stability, and tooth sensitivity in patients submitted to different bleaching techniques.
METHODS
In this study, 48 patients were divided into five groups. A half-mouth design was conducted to compare two in-office bleaching techniques (with and without light activation): G1: 35% hydrogen peroxide (HP) (Lase Peroxide - DMC Equipments, São Carlos, SP, Brazil) + hybrid light (HL) (LED/Diode Laser, Whitening Lase II DMC Equipments, São Carlos, SP, Brazil); G2: 35% HP; G3: 38% HP (X-traBoost - Ultradent, South Jordan UT, USA) + HL; G4: 38% HP; and G5: 15% carbamide peroxide (CP) (Opalescence PF - Ultradent, South Jordan UT, USA). For G1 and G3, HP was applied on the enamel surface for 3 consecutive applications activated by HL. Each application included 3x3' HL activations with 1' between each interval; for G2 and G4, HP was applied 3x15' with 15' between intervals; and for G5, 15% CP was applied for 120'/10 days at home. A spectrophotometer was used to measure color change before the treatment and after 24 h, 1 week, 1, 6, 12, 18 and 24 months. A VAS questionnaire was used to evaluate tooth sensitivity before the treatment, immediately following treatment, 24 h after and finally 1 week after.
RESULTS
Statistical analysis did not reveal any significant differences between in-office bleaching with or without HL activation related to effectiveness; nevertheless the time required was less with HL. Statistical differences were observed between the results after 24 h, 1 week and 1, 6, 12, 18 and 24 months (intergroup). Immediately, in-office bleaching increased tooth sensitivity. The groups activated with HL required less application time with gel.
CONCLUSIONS
All techniques and bleaching agents used were effective and demonstrated similar behaviors.
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Journal of Applied Oral Science. Dec/31/2011; 20(4): 435-443

Comparative clinical study of the effectiveness of different dentalbleaching methods - two year follow-up

Abstract

This study evaluated color change, stability, and tooth sensitivity in patientssubmitted to different bleaching techniques.

Material and methods

In this study, 48 patients were divided into five groups. A half-mouth design wasconducted to compare two in-office bleaching techniques (with and without lightactivation): G1: 35% hydrogen peroxide (HP) (Lase Peroxide - DMC Equipments, SãoCarlos, SP, Brazil) + hybrid light (HL) (LED/Diode Laser, Whitening Lase II DMCEquipments, São Carlos, SP, Brazil); G2: 35% HP; G3: 38% HP (X-traBoost -Ultradent, South Jordan UT, USA) + HL; G4: 38% HP; and G5: 15% carbamide peroxide(CP) (Opalescence PF - Ultradent, South Jordan UT, USA). For G1 and G3, HP wasapplied on the enamel surface for 3 consecutive applications activated by HL. Eachapplication included 3x3' HL activations with 1' between each interval; for G2 andG4, HP was applied 3x15' with 15' between intervals; and for G5, 15% CP wasapplied for 120'/10 days at home. A spectrophotometer was used to measure colorchange before the treatment and after 24 h, 1 week, 1, 6, 12, 18 and 24 months. AVAS questionnaire was used to evaluate tooth sensitivity before the treatment,immediately following treatment, 24 h after and finally 1 week after.

Results

Statistical analysis did not reveal any significant differences between in-officebleaching with or without HL activation related to effectiveness; nevertheless thetime required was less with HL. Statistical differences were observed between theresults after 24 h, 1 week and 1, 6, 12, 18 and 24 months (intergroup).Immediately, in-office bleaching increased tooth sensitivity. The groups activatedwith HL required less application time with gel.

Conclusion

All techniques and bleaching agents used were effective and demonstrated similarbehaviors.

INTRODUCTION

Tooth color is determined by a combination of the different optical properties ofenamel, dentin and pulp15. Toothdiscolorations vary in etiology, appearance, localization, severity and adherence totooth structure, and they are categorized as intrinsic or extrinsic. Although extrinsicdiscoloration can be removed with a prophylactic cleaning procedure, intrinsic stainingnecessitates chemical bleaching. Bleaching has been accepted as the least aggressivemethod for treating discolored teeth.

Until recently, the most commonly used method for vital teeth was home bleaching,originally proposed by Haywood and Heymann14 (1989), in which an individual tray that contained 10% carbamideperoxide was used by the patient during the night for approximately 2 to 5 weeks. Thistechnique presents a number of advantages such as easy application, less peroxideconcentration, lower cost and less time in the dental office2,13. However, italso presents some disadvantages, especially because of the professional's lack ofcontrol over monitoring the use of the bleaching agents and trays by the patients. Inaddition, some patients did not adjust to the trays, a weekly visit is necessary toobserve any initial bleaching results, and 2 to 5 weeks are required to obtain thedesired results.

With the hope of obtaining more control, color stability, and effectiveness, as well asto save time, in-office bleaching was proposed. This technique utilizes highconcentrations of hydrogen peroxide (between 15% and 38%) that can be activated by lightsources or heat. The equipment can use different light sources, such as halogen, Plasmaarc, light emitting diode (LED), ultraviolet lamp, laser (Argon, Diode, Neodymium-YAG orCO2) and hybrid light3,18,20,22,24,25,30.

Tooth discoloration and bleaching assessments/measurements can range from subjectivecomparison methods to the use of objective instrumentation. There are limitations to theuse of subjective measurement methods using porcelain or acrylic resin shade guides;these include the effectiveness of variables such as light conditions, experiences, age,fatigue of the human eye, and conditions such as color blindness28.

This CIELAB system was defined in 1967 by the International Commission onIllumination9. This is athree-dimensional uniform color space with equal distances corresponding to equallyperceived color differences. This system has three axes: the L* axis representslightness and extends from 0 (black) to 100 (white); and a* and b* represent theredness-greenness and yellowness-blueness axis, respectively. When a* and b* coordinatesapproach zero, the colors become neutral. A color difference (ΔE) between two objectscan be calculated within the CIELAB color system. The spectrophotometer was consideredmore reliable by Matis, et al.19(2002) because this method is more objective and sensible than a visual scale andphotos. Many authors have used this evaluation system as it allows for a bettercomparison of the results obtained3,17,18,22,26,29.

Tooth sensitivity during the bleaching period, at home or in office, is described as thebiggest problem for some authors, but sensitivity can disappear before bleachingends2,3,13,20,21,24. Other effects, such as small changes inthe enamel structure after bleaching treatments, have also raised concerns for someresearchers. These alterations can be easily restored by polishing, and enamel contactwith calcium and phosphate present in the saliva1, as well as the application of fluoride4. Changes in the micro-hardness, morphology, roughness,and wear are considered insignificant to many authors6,13,21.

Many studies have evaluated the effectiveness and security of some new products andtechniques. However, there is no consensus in relation to the effectiveness of at-homeor in-office bleaching, nor about their effects on the dental tissues2,25. The activation of a bleaching agent by the thermocatalytic techniquehas been questioned due to its deleterious effects on the structure. The objective ofthis randomized clinical study was to evaluate tooth sensitivity, the degree of thecolor alteration (ΔE) and bleaching maintenance after 2 years, and to compare theeffectiveness of the at-home and in-office bleaching techniques, with and without theuse of hybrid light source for gel activation.

MATERIAL AND METHODS

Patient inclusion and exclusion criteria

This research was approved by the Ethics Committee in Research of the Bauru School ofDentistry, University of São Paulo (process: 29/2006). Forty-eight patients wereselected using the following inclusion criteria: needed to have all anterior teeth(superior and inferior) without restorations or caries; to agree to sign the consentform; 18 to 30 years old; in good health; color A3 in at least four teeth; and toagree to return for scheduled visits and follow-up examinations. The exclusioncriteria were: any disease that can interfere in the research; gingivitis orperiodontitis; those who smoke; any reaction to peroxides; any family history ofneoplasia in the oropharinge and adjacency; use of any bleaching agents within thelast year; tooth sensitivity of less than 1 on the VAS questioner scale; pregnant orlactating women; and tetracycline stained teeth.

Study design

The 48 patients selected were randomly divided into 5 groups (n=16), and allbleaching gels were used according to the manufacturer's instructions and aredescribed in Figure 1. For a directcomparison between bleaching protocols employed, a split-mouth design was used, wherethe same patients were submitted to two bleaching treatments, one on the rightsuperior and inferior arcs and the other in the left superior and inferior arcs (G1and G2; G3 and G4). The hybrid light (HL), Whitening Laser II (LED/therapeutic diodelaser) - (DMC Equipments, São Carlos, SP, Brazil), was used and employed 6 LEDs eachwith a wavelength of 470 nm and irradiance of 350 mW/cm2, and 3 infrareddiode laser points each with a wavelength of 810 nm and 200 mW/cm2.

Figure 1
Bleaching gels used
Comercial brandsBleaching gelsManufacturerClinical use
Opalescence PF(CP 15%)Carbamine Peroxide15%UltradentProducts Inc.Home bleaching
OpalescenceXtra Boost (HP 38%)Hydrogen Peroxide38%UltradentProducts Inc.In office with chemical and/or physical activation
Laser Peroxide(HP 35%)Hydrogen Peroxide35%DMC EquipamentsLtdaIn office with chemicaland/or physical activation

For Groups 1, 2, 3 and 4, the clinical steps were done in office, with and withoutlight activation:

Supra-gingival prophylaxis using pumice stone and a "Robson" brush was performed,followed by color measurement (canines, central and lateral incisors, superior andinferior arcs) with a spectrophotometer and the initial photo using a digital camera(D-70, Nikon) (Figure 2).

Figure 2
(A) Initial photo and (B) spectrophotometer color measurement

Application in the superior and inferior arcs of a gingival barrier (Lase-Protect,DMC Equipments, São Carlos, SP, Brazil) in Groups 1 and 2 and an OpalDam (UltradentProducts Inc., South Jordan UT, USA) in Groups 3 and 4 was followed byphotoactivation.

In Group 1, the superior and inferior teeth on the right side received an applicationof a 1 mm thick bleaching gel composed of 35% HP (Figure 3A), and the left side was protected with gauze. Next, thebleaching gel was activated with HL for 3' in both arcs simultaneously (Figure 3B), followed by a 1' wait to allow thetemperature to fall. This step was performed twice more consecutively. After theremoval of the gel and teeth cleansing, the procedure was repeated two more times inthe same appointment for a total 33' of gel action. After the completion of the rightside arcs, the bleaching gel (HP 35%) without HL activation (Group 2) was applied tothe left side arcs for 3 consecutive 15' periods, with 15' intervalsbetween each application, totaling 45' of gel action. In Groups 3 and 4, thebleaching gel (HP 38%) was applied and followed the same activation protocols asGroups 1 and 2 (right side activated with HL and left side without),respectively.

Figure 3
Clinical bleaching procedure in groups 1 and 2: A- bleaching gel application inthe right side arcs; B- activation of the gel with hibrid light (HL) in theright side arcs and protection of the left side arcs

Polishing of the teeth in the vestibular faces was performed on all groups with afelt disc impregnated with abrasives (Laser Peroxide, DMC Equipments, São Carlos, SP,Brazil) to reestablish the enamel smoothness. After polishing, a desensitizing gel(Lase Sensy, DMC Equipments, São Carlos, SP, Brazil) composed of 2% sodium fluorideand 5% potassium nitrate was applied for 4'. For the groups activated with HL, lasertherapy was performed (25 J for 30") on all patients, regardless of toothsensitivity, in order to avoid and control postoperative sensitivity.

For Group 5 (home bleaching), after initial photos were taken and color measurementswere done, the individual trays for the superior and inferior arcs were given to eachpatient, as well as four gel-filled syringes (CP 15%) and instructions for use. Thegel was to be used 2 hours per day over a period of 10 days. Duringthis period, patients were not to use any products that could compromise thebleaching.

In the present study, Group 5 (home bleaching) was employed only to compare with theresults of in-office bleaching, with and without light activation. It is important toknow that in all groups, the control was obtained in the baseline color measurementof each tooth that was evaluated from each patient.

All patients received instructions to avoid any substance that could stain teeth inthe first 48 hours following the treatment, e.g., coffee, black tea, cola, mustard,ketchup, red wine, soy sauce, chocolate, red fruits, tomato sauce, beets, etc. Beyondthese, patients were instructed to avoid other substances that could stain teeth suchas red lipstick, consumption of tobacco products, and food and beverages with acidicpH levels. For patients who experienced exacerbated tooth sensitivity (Groups 1, 2, 3and 4), an anti-inflammatory (Nimesulida 100 mg EMS, Eurofarma, Medley, Novartis) wasprescribed for one or two days.

Instrumental method for color measurement

Digital photos were taken and instrumental color monitoring was performed beforebleaching and 24 hours, 1 week, 1 month, 6 months, 12 months, 18 months and 24 monthsafter (Figure 4), using a contact-typeintra-oral spectrophotometer (Vita Easyshade, Vita-Zanhnfabrik, Bad Säckingen,Germany). Color differences were calculated using the following equation:ΔE=[(ΔL*)2+(Δa*)2+(Δb*)2]1/2 9.

Figure 4
Control after: (A) 24 hours; (B) 1 month; (C) 12 months; (D) 24 months

The measurements to obtain tooth color were done using a spectrophotometer followingthe manufacturer's instructions and in agreement with Kim-Pusateri, et al.16 (2009); these measurements were takenfrom the same area of each tooth (middle of the tooth) two times consecutively. Whenthese values were equal, they were registered. When the values were not equal,additional measurements were taken until equal measurements were obtained, and onlyone measurement for each tooth was recorded.

Tooth sensitivity assessment

Before bleaching, the patients were submitted to the VAS questionnaire to measuretooth sensitivity (baseline), as well as immediately after bleaching, 24 hours and 1week. This evaluation determined the differences between the evaluation periods andthe bleaching gels tested. The patient was to indicate any tooth or oral sensitivityby marking the level of sensitivity on the horizontal line, which ranges from 0 to10, with 10 being the most sensitive.

Range of sensitivity scores used:

0-1: No pain

2-3: Mild pain

4-6: Moderate pain

7-8: Severe pain

9-10: Intolerable pain

Statistical analysis

All groups were submitted to histogram and Kolmogerov-Smirnov tests, and all datapresented normal distribution criteria. As a result of this normal distribution, theresults were submitted to ANOVA tests to identify any differences between groups(p≤0.05%) and Tukey tests for individual comparisons between all groups with a levelof significance of p≤0.05%.

RESULTS

The number of subjects who returned for each evaluation period for all groups evaluated(n=16) can be observed in Figure 5.

Figure 5
Distribution of the number of subjects that returned for each evaluation periodfor all groups evaluated (n=16)
GroupsInitial24 hours1 week1 month6 months12 months18 months24 months
11616151615141111
21616151615141111
31616161514141110
41616161514141110
516161313121298

The values of the degree of change and color maintenance (ΔE) in the in-office andat-home bleaching techniques over 24 months were submitted to ANOVA testing by three-wayANOVA (bleaching agents, photoactivation and time), and Group 5 was submitted to two-wayANOVA (time and bleaching gel). No statistically significant differences were observedbetween in-office bleaching treatments (G1, G2, G3, and G4). The home bleaching group(G5) presented statistically higher values of ΔE in comparison to the other twobleaching agents used in office with or without HL (G1, G2, G3 and G4) (Table 1; Figure6).

Table 1
Mean and standart deviation of ΔE for bleaching groups evaluated during 24months
Groups24 hours1 week1 month6 month12 months18 months24 months
(mean±SD)(mean±SD)(mean±SD)(mean±SD)(mean±SD)(mean±SD)(mean±SD)
G1:7.80+1.42Ba6.45+1.40Bb5.64+1.45Bc4.49+1.45Bd2.99+1.45Be2.87+0,67Bf2.23+0.61Bg
HP 35% + HL
G2:7.49+1.45Ba6.54+1.37Bb5.43+1.47Bc4.33+1.39Bd2.85+1.41Be2.94+0.68Bf2.09+0.69Bg
HP 35%
G3:7.83+1.39Ba6.77+1.32Bb5.78+1.37Bc4.64+1.26Bd2.75+1.15Be2.77+0.60Bf1.85+0.56Bg
HP 38% + HL
G4:7.76+1.50Ba6.67+1.56Bb5.64+1.38Bc4.42+1.47Bd2.75+1.26Be2.63+0.64Bf1.87+0.60Bg
HP 38%
G5:9.80+1.75Aa8.70+1.64Ab7.67+1.57Ac6.52+1.62Ad5.07+1.63Ae4.27+0.98Bf3.29+0.78Bg
CP 15% + HL
* Lower case letters: analysis between columns in the same line* Capital letters: analysis between lines in the same columnHL= hibrid light
Figure 6
Graph of mean (ΔE) for bleaching groups evaluated during 24 months

The observation time (intra-groups) presented statistically significant differences inthe five periods for all groups evaluated (Tukey test, p≤0.05).

The differences in degree of sensitivity were determined using two-way ANOVA testing(bleaching agent and time evaluation) and the Tukey test for individual comparisons(Table 2). Statistical differences wereobserved only in the period immediately after the bleaching between PH 35% and PC 15%.After 24 hours, there were no differences between in-office bleaching gels, and after 1week, the sensitivity levels returned to normal.

Table 2
Description of the sensitivity results based on the bleaching gel used
Bleaching gelsBaselineImmediately after bleaching24 hours7 days
(mean±SD)(mean±SD)(mean±SD)(mean±SD)
HP 35%0.45+0.88A5.47+3.13B0.93+0.90D0.42+0.87E
HP 38%0.71+0.83A3.95+1.78BC1.89+2.33D0.69+0.82E
CP 15%0.65+0.73A2.54+1.91C-0.72+0.68E
*Capital letters: analysis between lines in the same column

DISCUSSION

The purpose of this in vivo study about vital tooth bleaching was tocompare the effectiveness and stability in-office (with or without photoactivation) andat-home bleaching techniques in relation to color change (ΔE) and tooth sensitivity, for24 months after the treatments. CP 15% gel was used at home and in office, two bleachingagents with high concentrations (HP 35 and 38%) were used for chemical and physicalactivation.

Tooth color alteration can be determined by means of a visual evaluation using a colorshade, which is a subjective method, very functional, easy and fast to use25. Objective methods that can be employedare the use of a spectrophotometer, colorimeters and software images15. The instrumental evaluation has beenpreferred over the visual evaluation because it makes the process more practical andstatistically more reliable19. ForGroups 1, 2, 3 and 4 (in-office bleaching), six teeth were evaluated from each patient,and for Group 5, twelve teeth; this allowed measurements from each patient to becomemore precise in obtaining the color alteration (ΔE) in numeric values (CIELAB System)and provided normal distribution results. This is another advantage of this method(spectrophotometer) in comparison to a visual scale evaluation by operators. In a studydone by Kim-Pusateri, et al.16 (2009),using the same methods, they confirmed that this method gives more confidence andstandard results, with 96% accuracy.

Tooth bleaching is directly related to tooth structure and permeability25. The enamel behaves like asemi-permeable membrane that possibly transmits water and other substances with smallmolecular size, such as oxygen ions (O-) present in the HP. These characteristics allowoxygen diffusion (oxygen reaction) over the organic structure of teeth and permitreaction to the stained molecules, and this promotes the bleaching13. A light source was used with theobjective to accelerate the reaction and become more effective1,7,20,22,26,30. The theoretical advantage of the light source is the increase inthe hydrogen peroxide temperature, thus accelerating the reaction and forming hydroxyland oxygen free radicals1,26,30. A temperature rise of 10ºC increases the speed of hydrogen peroxidedecomposition by 2.2 times12. Toincrease the interaction of visible light with the bleaching gel, manufacturersincorporate coloring agents or pigments into their products, which have colors capableof promoting maximum absorption of this light and subsequent conversion into heat.

For the present study, one hybrid light source composed of a LED and a therapeutic diodelaser were used to activate the bleaching gel in the in office techniques. In accordancewith Camargo, et al.7 (2009), the useof a LED or Nd:Yag laser for activation of the HP 35% permitted a higher degree ofpenetration in the direction of the chamber pulp (20 minutes after the gel application),in comparison to the groups without photo activation.

Post-bleaching sensitivity differs from dentin hypersensitivity because it is relateddirectly to the penetration of the sub-products of the bleaching gels in the dentin andpulp tissue, through the enamel, causing reversible pulpit and consequent teeth thermalsensitivity, but not causing permanent damage to the pulp23. These responses are correlated with the peroxideconcentration, time, frequency of gel application and pulp temperature rise with lightactivation2,13,19,24. Carrasco, Carrasco-Guerisoli andFröner8 (2008), in an invitro study, found low indexes of temperature increases consideredcompatible with pulp vitality maintenance, when applying an LED source or HL to the gel(35% HP). Coutinho, et al.10 (2008)evaluated the rise of pulp-chamber temperature induced by different light sources inin-office bleaching with HP 35%, and they concluded that the specific combination ofcolor agent + light color determines good dental bleaching with a smaller temperatureincrease and, consequently, less sensitivity. In the present study, the lowest dentalsensitive index was observed in the G5 (home bleaching) in the function of low gelconcentration (CP 15%). Groups 1-4 used high concentrations of the bleaching gel (HP 35and 38%), and all experienced higher levels of sensitivity. After 24 hours, the degreeof sensitivity had lowered considerably and returned to normal levels after one week forall groups evaluated. Although the groups in office were completed in the sameappointment, to each patient (right and left side), it was not possible to determinewhether the teeth with or without HL activation presented higher or lower degrees ofsensitivity. As a result, sensitivity analysis was determined just by the bleachingagent (Table 2). Marson, et al.18 (2008), in an in vivostudy, found high levels of sensitivity (92% of patients) in in-office bleaching usingHP 35% with and without any light source, but in all cases, this sensitivity disappeared24 hours after the treatment.

The use of HL in one in vitro study of rats found a less inflammatoryresponse in the coronal pulp independent of the bleaching gel concentration used (HP15%, 25% and 35%), when compared to the in-office bleaching without HL activation. Thisindicated that the diode laser present in the HL equipment has a therapeutic effect inthe process11. The initial results(after 1 month) presented by Rosa and Mondelli24 (2009), in a clinical research study comparing the level ofsensitivity in in office bleaching (HP 35%) with and without light activation (HL), wereobtained by performing the procedure at different times (7 days apart) to the samepatient. The group without HL activation (3x15') presented, immediately after thebleaching, a significant increase in sensitivity compared to the groups with HL(3x7'30"). These results (Table 2) suggest thatthe light activation system (LED/therapeutic laser), with half of the gel action time,produces the same level of color change, but with less pulp inflammation and,consequently, lower sensitivity degree, in agreement with Frigo, et al.11 (2009). In the present study, allmanufacturers' instructions were followed; it is possible that the diode laserdiminished the effects of sensitivity, though it was impossible for all patients toidentify differences between the right and left side arches. As a result of thisobservation, tooth sensitivity was compared between bleaching gels rather than bleachingprotocols.

Micro-structure alterations, such as microhardness and roughness, which revertednaturally after 7 to 15 days after bleaching due to the effect of the calcium andphosphate ions present in the saliva15,19,21,26, as well as to fluorideapplications4, are notconsidered significant. One in vitro study done by Mondelli, etal.21 (2009) evaluated roughnessand wear, before and after brushing, of bovine enamel submitted to different bleachingprotocols (CP 16%; HP 35%+HL; HP 35%+halogen light). There were no significantdifferences among the groups comparing initial and post-bleaching roughness. Afterbrushing, there were differences between the control group and experimental groups. Thehome bleaching group (CP 16%) showed a significant increase in roughness values comparedto group HP 35%+HL. Wear was significantly less for the control group compared to theother groups. Bleaching techniques promoted increased bovine enamel surface roughnessand wear when submitted to simulated brushing.

Cadenaro, et al.6 (2008), demonstratedin an in vivo study with HP and CP in high concentrations, aftermultiple applications, no occurrence of roughness alterations in the enamel superficies.All bleaching gels evaluated in this study possessed one important characteristic, aneutral pH level, because gels with acidic pH can promote higher alterations in thetopography of the enamel15 and havethe potential to induce collateral effects, such as tooth sensitivity and gingivalirritation13.

The difference in the action time of the bleaching gels (contact with teeth) evaluatedin this study explain the statistical differences in initial ΔE value G5 in relation tothe other groups. These differences disappear after 18 and 24 months of control inrelation to other in-office groups (Table 1).For G1 and G3 (9' HL activation), the total time of gel action was 33', divided into 3consecutive applications; for G2 and G4, (without light activation), the total time ofgel action was 45', divided into 3 consecutive applications of 15' each with 15' betweeneach applications; and for G5, the total time of tray use (15% CP) was 1,200'. The risein the number of in-office bleaching treatments without HL or the possibility ofapplying and activating, with HL, the bleaching gel up to five times in the samesession20 will determine thebest results (higher ΔE), in order to compensate for differences in gel actiontime20,24.

A new in-office protocol activated with HL (the same light used in this study),decreased the action time of the gel to 7'30" (30"+2'HL+30"+2'HL+30"+2'HL), possibly toobtain teeth bleaching in only one session, justifying the use of HL in the in officebleaching20,24. This protocol enables the bleaching to be obtained inonly one session by performing 5x gel applications. This finding is in agreement withthose of other authors, who observed that the light equipment can be used to shorten thegel application time, and this accelerates the bleaching process17,20,22,24.

The efficiency of these lights presented some conflicting results3,15,18. Marson, et al.18 (2008) discovered no differences in theactivation or note with a light source (halogen, LED, and LED/Diode laser) in in-officebleaching, but the authors did not follow the protocols recommended by the manufacturersand did not state the gel activation time. This information was obtained in the originalPhD thesis, where the activation time for all light sources was only 20" pertooth in each of two bleaching appointments. On another clinical study,Bernadon, et al.3 (2010), compared theefficiency of at-home bleaching versus in-office bleaching activated with HL (WhiteningLase, DMC Equipments, São Carlos, SP, Brazil); in-office bleaching with and without HLactivation; and at-home bleaching, versus a combination of at-home and in-officebleaching activated with HL. The authors did not observe differences in the bleachingresults, sensitivity and durability in the 6 months between the techniques, and theyconcluded that light activation is not recommended. The authors did not follow theprotocol recommended by the manufacturer of the HL, and instead, they performed twosessions with three gel applications of 15' each and light activation of 4'.

In the present study, independent of the technique, bleaching gel concentration andactivation with or without HL, all protocols employed were effective in promoting teethbleaching. This finding confirms that the results obtained with the bleaching are notdependent on the technique employed (home bleaching, in-office bleaching with or withoutlight activation). The color change (color rebound) in the bleaching treatments duringthe time evaluated (24 months) was similar among all groups evaluated withoutstatistically significant differences, a finding that supports the results of a two-yearstudy by Swift, May and Wilderider27(1999). Similar results were found in in vivo studies by Bizhang, etal.5 (2009), Marson, et.al.18 (2009) and Bernadon, etal.3 (2010). Bizhang, etal.5 (2009) utilized acolorimeter and concluded that at-home bleaching (CP 10%) and in office bleaching (HP15%) are equally efficient and patients retained the lightness for 3 months.

Given the results of this study and the literature presented, light activation with HLcan produce effective results with less time for gel action, when compared with at-homebleaching and in-office bleaching without light activation, and this knowledge can beuseful in many clinical situations.

CONCLUSIONS

Due to the results observed during the evaluated times, we can conclude:

In-office bleaching presented highest sensitivity initially in comparison to at-homehome bleaching;

All techniques and bleaching gels used were effective in teeth bleaching;

The in-office bleaching techniques utilizing two bleaching gels, with or without lightactivation (HL), presented similar results; and

The color change (ΔE) recorded in the bleaching treatments during the time evaluated wassimilar among all groups evaluated.

Acknowledgments

ACKNOWLEDGEMENTS

State of São Paulo Research Foundation/FAPESP (2006/02540-9) and Cordination ofHigher Education and Graduate Training - Capes.

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