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Diode laser-activated bleaching SI-3

Diode Laser-Activated Bleaching

Tatjana DOSTALOVA1

Helena JELINKOVA2

Devana HOUSOVA3

Jan SULC2

Michal NEMEC2

Mitsunobu MIYAGI4

Aldo BRUGNERA JUNIOR5

Fatima ZANIN6

1Charles University, 1st Medical Faculty, Department of Prosthodontics, GFH, Prague, Czech Republic2Czech Technical University, FNSPE, Prague, Czech Republic

3Institute of Dental Research, Prague, Czech Republic4Tohoku University, Graduate School of Engineering, Department of Electrical Communications, Sendai, Japan

5Biomedical Laser Center at IPD-UNIVAP, Sao Jose dos Campos, SP, Brazil6Camilo Castelo Branco University, São Paulo, SP, Brazil

This study describes a preclinical investigation with laser-activated bleaching agent for discolored teeth. Bleaching techniques involvea broad-spectrum approach utilizing hydrogen peroxide (3-38%) with or without heat or laser, carbamide peroxide (10-30%), or amixture of sodium perborate and hydrogen peroxide. Extracted human maxillary central incisors were selected. In the bleachingexperiment, 38% hydrogen peroxide was used. Two different laser systems and light emission diodes for activation of the bleachingagent were used: diode laser, wavelength 970 nm, and infra-red diode laser, wavelength 790 nm, with eight blue light emission diodes,wavelength 467 nm. The enamel surface was evaluated with the scanning electron microscope. The method of chemical oxidationresulted in a 2-3 shade change in one treatment (15 min). Shorter time (5 min) was not effective. The diode laser, wavelength 970 nm,and the bleaching agent produced the same effect but with a shorter time of bleaching process (5 min – 1 W, 2.5 min – 2 W). Infra-reddiode laser, wavelength 790 nm with eight blue light emission diodes, wavelength 467 nm, and the bleaching agent reached the desiredcolor shade also after a shorter time (5 min – 40 mW). Slight surface modification after the bleaching process was detected with scanningelectron microscopy. Currently, the laser has been proven the most valuable energy source for power bleaching with simple and shortapplication in the dental office.

Key Words: dentistry, laser, bleaching.

Correspondence: Prof. Tatjana Dostalova, MD, Charles University, 1st Medical Faculty, GFH; Katerinska 32; 128 01 Prague 2, Czech Republic.Tel/Fax: +420-2-2491-6573. e-mail: t.dostalova@quick.cz

ISSN 0103-6440

INTRODUCTION

The desire to have whiter teeth and the bleachingtechnique have been documented since the mid-nine-teenth century. Patients’ awareness of options availablefor changing the color of natural dentition has createdan increase in public demand. Bleaching corrects orimproves the color of teeth, and is also the least expen-sive esthetic treatment option. The indications are ac-quired superficial stains, penetration and absorbed stains,age-related stains, patients who desire conservative

treatment to improve appearance, color change relatedto pulp trauma and necrosis, and interproximal discol-orations (1,2).

The current techniques involve a broad-spec-trum approach utilizing hydrogen peroxide (3-38%)with or without heat or laser, carbamide peroxide (10-30%), or a mixture of sodium perborate and hydrogenperoxide (3). The methods can be used in-office or athome. Severely discolored teeth or difficult bleachingcases are treated initially in the office, followed bybleaching at home.

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Some patients cannot complete the home bleach-ing process for various reasons, such as the time re-quired, discomfort or irritation from wearing the trays,or the unpleasant taste, and gingival or stomach irrita-tion from the bleaching gel. For such patients, powerbleaching or in-office bleaching produces the whiten-ing results quickly, without the long-term commitmentof wearing trays. To have this procedure performed, thepatient visits the dentist only once.

The history of power bleaching goes back toAbbots' use of high-intensity light to raise the tempera-ture of hydrogen peroxide, accelerating the chemicalprocess of bleaching. Since the early 1980's, the heatlamp and heated spatula have been used as a heat sourceto accelerate the bleaching process of concentratedhydrogen peroxide. This has been shown to be effec-tive, but it also causes pulp irritation. The process ofcontrolling the caustic 35% hydrogen peroxide liquidhas been challenging (4).

The latest development of power bleaching hasresulted in easy-to-use bleaching agents, essentiallyusing highly concentrated hydrogen peroxide mixedwith thickening agents or additional buffering agents,catalysts, or coloring agents. The energy source can bederived from blue-colored halogen curing lamps, infra-red CO2 lasers, and blue-colored plasma arc lamps aswell as the cool blue argon laser and 980-nm GaA1Aslasers (4,5). These studies showed that tissue ablationrequires a high-energy-density beam. This irradiationcondition could increase the temperature in the adja-cent tissue, which can cause thermal damage, i.e.,carbonization and the creation of fissures and cracks inthe surrounding tissues. Laser irradiation of dental hardtissue can cause morphological and chemical changes(6). The extent of these changes is affected by theabsorption characteristics of the tissues, so that thechanges can be varied according to the type of laser anddental tissues. Compositional changes were also con-firmed to decrease or increase the solubility of irradi-ated enamel or dentin (CO2, Nd:YAG laser) (7).

The goal of this study was to compare diodelaser systems, and chemical action agents to control thetime and quality of the bleaching process. The effect ofvarious laser techniques for bleaching teeth using in-office vital whitening was evaluated. The ultrastruc-tural changes in enamel caused by a laser-activatedbleaching agent for treating discolored teeth were alsodetermined.

MATERIAL AND METHODS

Tooth Material

For the study, twenty healthy human maxillarycentral and lateral incisors, extracted from adult malesand females for various reasons, were selected. Theteeth were kept hydrated in saline solution. For theexperiment, they were cleaned with pumice in thelaboratory, and tooth surface was divided into twosymmetrical parts in the sagittal (lengthwise) plane.The left control part was covered by wax before bleach-ing to protect the surface. The right part was used fortreatment.

Chemical Action Bleaching Techniques

In the experiment, 38% hydrogen peroxide(Ultradent Opalescence X Extra Boost; Ultradent Prod-ucts, South Jordan, UT, USA) was used. The agent wasprovided in a red gel form. The bleaching procedurehad the following steps:

1) preoperative photographic record;2) mechanical plaque removal – pumice, cleansing

with alcohol and drying;3) covering of control half of the incisor with wax;4) mixing the product;5) immediate application of 1-2 mm layer to uncov-

ered part of labial surface;6) time measurement of bleaching process;7) rinsing gel with water.

The chemical action process only was com-pleted in 15 minutes.

Laser Equipment

Two different diode laser systems for activationof the bleaching agent were used:

1) infra-red diode laser, wavelength 790 nm; power40 mW, and eight blue light emission diodes, wave-length 467 nm, P = 4000 milicandelas each (Kondortech,São Carlos, SP, Brazil; a set of blue LEDS with associ-ated therapeutic laser), 5 min.

2) infra-red diode laser, wavelength 790 nm; power40 mW, and eight light emission diodes, wavelength467 nm P = 4000 milicandelas each (Kondortech,) 10min.

3) diode laser, wavelength 970 nm (university proto-

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a stereomicroscope (Nikon SMZ 2T, Japan). The pre-and postoperative photographic records were made.The color shade was checked to compare both halves ofthe tooth. The enamel surface was analyzed with thescanning electron microscope (SEM) JSM 5500 LV(Jeol, Japan).

RESULTS

The results of laser-assisted bleaching in-officeprocedure are summarized in Table 1. The methodof chemical oxidation resulted in a 2-3 shadechange in one treatment (Figure 1). The time ofapplication had to be sufficient – the minimumwas 15 min for chemical activation only (Figure2). Slight surface modification after bleachingwas detected in SEM (Figures 3 and 4).

The blue light diode laser radiation, wave-length 970 nm and bleaching agent caused thesame effect and shorter time of bleaching process(5 min) (Figure 5). The power had a directinfluence on activation time (power 1 W – 5 min(Figure 7), 2 W – 2.5 min (Figure 6). No changesof enamel morphology were found (Figures 7 and8).

Infra-red diode laser, wavelength 790 nm(red light); power 40 mW, and eight light emis-sion diodes (blue light), wavelength 467 nm and

Table 1. Laser-assisted bleaching using hydrogen peroxide as the bleachingagent.

Laser systems Power Time of Lightenedapplication teeth

2-3 shades

None - 5 min -None - 15 min +Diode laser, wavelength 790 nm; 40 mW 5 min +8 blue light emission diodes,wavelength 467 nmDiode laser, wavelength 790 nm; 40 mW 10 min +8 blue light emission diodes,wavelength 467 nmDiode laser, wavelength 970 nm 40 mW 5 min +Diode laser, wavelength 970 nm 1 W 5 min +Diode laser, wavelength 970 nm 2 W 2.5 min +

Figure 1. The method of bleaching results in a 2-3 shade changein one treatment.

Figure 2. Short time (5 min) had no effect on the process ofbleaching.

type) power 40 mW; 5 min.4) diode laser, wavelength 970 nm (university proto-

type) power 1 W; 5 min.5) diode laser, wavelength 970 nm (university proto-

type) power 2 W; 2.5 min.

Analyzing Methods

The wax was removed and bleaching gel wasrinsed with water. The teeth were viewed using

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Figure 3. SEM of enamel of left control part (magnification2000X).

Figure 4. Slight surface modification (right part of tooth) afterbleaching was detected in SEM (magnification 2000X).

Figure 5. The blue light diode laser radiation, wavelength 970 nmand bleaching agent activated process of bleaching for 5 min.

Figure 6. Results of bleaching process - diode laser radiation,wavelength 970 nm and bleaching agent, 2 W, 2.5 min.

Figure 7. SEM of enamel of left control part (magnification2000X).

Figure 8. No changes of enamel morphology after diode laserradiation, wavelength 970 nm and bleaching agent process ofbleaching activation 2 W, 2.5 min (magnification 2000X).

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Figure 9. Infra-red diode laser, wavelength 790 nm (red light);power 40 mW, and eight light emission diodes (blue light),wavelength 467 nm and bleaching agent helped to reach thedesired color shade after shorter time (5 min) (Fig. 9). Thesurface was smoother, and the relief of hydroxylapatite prismswas well formed (see Figs. 10,11).

Figure 10. SEM of enamel of left control part (magnification2000X).

Figure 11. The enamel surface was smoother, the relief ofhydroxyapatite prisms was well defined, the interprismatic matrixwas removed after diode laser, wavelength 790 nm (red light);power 40 mW, and eight light emission diodes (blue light),wavelength 467 nm and bleaching agent application(magnification 2000X).

DISCUSSION

The objective of laser bleaching is to achieve theultimate power bleaching process using the most effi-cient energy source, while avoiding any adverse effect.The following three dental laser wavelengths have beencleared by the FDA (Food and Drugs Administration)for tooth whitening: argon, CO2 and 980 nm GaAlAsdiode, but also other laser radiation systems have beentested for this purpose (4,6). In a previous investigation,it was confirmed that the Alexandrite (wavelength 750nm) and Er:YAG lasers (2940 nm) can activate theprocess of bleaching (8).

The goal of power bleaching is to whiten thetooth efficiently by obtaining controlled temperatureelevation (9,10), but with no morphological and chemi-cal changes of enamel (5). The heat element is favor-able for accelerating the rate of reaction but unfavor-able for maintaining pulp health. Zach and Cohen (11)showed that an intrapulpal temperature increase of10oF, 20oF, and 30oF caused a 15%, 60%, and 100%irreversible pulp damage in monkeys, respectively. Inanother study, Cohen (12) attempted to measure inci-dental discomfort relative to vital bleaching proceduresand to identify pulp changes that would explain thesensitivity and pain phenomenon. White et al. (6) foundthat since lasers and high intensity lamps produce highertemperatures than conventional lights the treatmenttime can be regulated to receive greater surface tem-perature increases than the pulp temperature increases.

Slight surface modification after the bleaching

bleaching agent helped to reach the desired color shadeafter a shorter time (5 min) (Figure 9), the surface wassmoother, the relief of hydroxylapatite prisms was wellformed (Figures 10 and 11).

It was found that selective laser radiation candecrease the time of bleaching without any surfacemodification.

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process (all used methods) was detected with SEM(13,14). In this study, it was found that selective diodelaser radiation can decrease the time of bleaching with-out surface modification. No differences betweenenamel surfaces were observed.

Dental lasers contribute to the field of toothbleaching. Currently, the laser has been proven to be themost valuable energy source for power bleaching withsimple and short application in the office.

ACKNOWLEDGMENTS

This research was supported by the Grant Agencyof the Ministry of Health of the Czech RepublicNo.6823-3, and Monbusho International Scientific Re-search program Joint Research No.09044122 of Japan.

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