Pulpal Temperature Rise During Light-activated Bleaching

Pulpal Temperature Rise During Light-Activated Bleaching Ayc¸e Unverdi Eldeniz,1 Aslihan Usumez,2 Serdar Usumez,3 Nilgun Ozturk

2

1

Department of Endodontics, School of Dentistry, Selcuk University, Konya, Turkey

2

Department of Prosthodontics, School of Dentistry, Selcuk University, Konya, Turkey

3

Department of Orthodontics, School of Dentistry, Marmara University, Istanbul, Turkey

Received 5 February 2004; revised 29 June 2004; accepted 2 July 2004 Published online 20 October 2004 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.b.30144

Abstract: The purpose of this study was to measure intrapulpal temperature rise induced by two kinds of bleaching gels when the tooth was exposed to a variety of light-curing units and a diode laser in vitro. The root portions of 80 extracted intact human maxillary central incisors were sectioned with a carborundum disk approximately 2 mm below the cementoenamel junction perpendicular to the long axis of the teeth. Two bleaching agents containing heatenhancing colorant was applied to the labial surface. Light-curing units used were a conventional halogen (40 s), a high-intensity halogen (30 s), a light-emitting diode unit (40 s), and a diode laser (15 s). The temperature rise was measured in the pulpal chamber with a J-type thermocouple wire that was connected to a data logger. Ten specimens were used for each system and bleaching-agent combination. Differences between the starting temperature and highest temperature reading were taken and the calculated temperature changes were averaged to determine the mean value in temperature rise. Temperature rise values were compared using two-way analysis of variance (ANOVA) at a preset ␣ of 0.05. Temperature rise varied significantly depending on curing unit and diode laser used. The diode laser induced significantly higher temperature increases than any other curing unit (11.7°C). The lightemitting diode unit produced the lowest temperature changes (6.0°C); however, there were no statistically significant differences among the curing units and there were no statistically significant differences between bleaching agents. Light activation of bleaching materials with diode laser caused higher temperature changes as compared to other curing units and the temperature rise detected was viewed as critical for pulpal health. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 72B: 254 –259, 2005

Keywords:

light-activated bleaching; temperature; dentin

INTRODUCTION Aesthetics, by definition, is the science of beauty, the particular detail of an animate or inanimate object that makes it appealing to the eye.1 Tooth discoloration is becoming a greater concern as more emphasis is placed on esthetics. With the growing awareness of esthetic options, there is greater demand for solutions to such unsightly problems as food staining, fluorosis, and tetracycline staining. Bleaching systems have been received by the public as a more conservative and economical method of improving the appearance of the dentition.2 Bleaching is one of the corrective measures used to treat discolored teeth. It can be performed internally on nonvital teeth or externally on vital teeth. Hydrogen peroxide,

Correspondence to: A. Usumez, Selcuk Universitesi, Dishekimligi Fakultesi, Protetik Dis Tedavisi Anabilim Dalı, Kampus, Konya, Turkey (e-mail: [email protected]) © 2004 Wiley Periodicals, Inc.

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sodium perborate, and carbamide peroxide are generally used for bleaching.3,4 These materials are found effective for bleaching teeth, but side effects are changes in tooth structure,5,6 microleakage of restorations,2 external root resorption, and pulpal irritation.7,8 The thermocatalytic, walking bleach and mouthguard are the most popular bleaching methods.9 In the thermocatalytic method, an external heat source is applied to activate the bleaching agent.3 The energy of the heat source is absorbed into all intermolecular and intramolecular bonds and reaches maximum vibrations.10 The hydrogen peroxide molecule falls apart into different, extremely reactive ionic fragments that swiftly combine with chromophilic structure of the organic molecules, altering them and producing simpler chemical chains.10 Cohen11 reported on the histological effects of hydrogen peroxide and heat for vital bleaching and concluded that vital bleaching utilizing this method is harmless to pulpal tissue. Bleaching systems have offered easy-to-use bleaching agents, essentially using highly concentrated hydrogen per-

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TEMPERATURE RISE DURING LIGHT-ACTIVATED BLEACHING TABLE I. Visible Light Curing Units Studied

Brand

Launch Year

Type of Unit

Applied Activation Time (s)

Laser Smile Optilux 501 Hilux Elipar Freelight II

2001 2001 1996 2003

Diode laser High-intensity halogen Conventional halogen LED

15 30 40 40

oxide mixed with thickening agents or additional buffering agents, catalysts, or heat-enhancing colorants.12 The energy source can be derived from halogen curing units, high-intensity curing units, and diode lasers.12 Laser devices have been used in dentistry for soft tissue surgery, root end sealing and sterilization, and for altering enamel and dentin surfaces to increase resistance to decay or to facilitate the bonding of composites and bleaching.13,14 Conventional halogen usually operates at light intensities between 400 and 800 mW/cm2. Halogen bulbs produce light when electric energy heats a small tungsten filament to high temperatures. Despite their common use in dentistry, halogen bulbs have several disadvantages. The basic principle of light conversion by this technique is claimed to be inefficient as the light power output is less than 1% of the consumed electrical power and as they have a limited effective lifetime of approximately 100 h due to degradation of bulb components by the high heat generated.15 A solid-state light-emitting diode (LED) technology was proposed in 1995 for the polymerization of light-cured dental materials to overcome the shortcomings of halogen visible light-curing units.16 LEDs use junctions of doped semiconductors to generate light, instead of the hot filaments used in halogen bulbs.17 LEDs have a lifetime of over 10,000 h and undergo little degradation of output over this time. LEDs require no filters to produce blue light, are resistant to shock and vibration, and take little power to operate.18 LEDs’ longer life span and more consistent light output compared with halogen bulb technology show promise for dental applications.19 Light curing with high-energy output causes significantly higher pulp chamber temperature changes as compared to conventional halogen curing light.20 The purpose of this in vitro study was to measure the temperature rise induced by selected curing units: conventional halogen (40 s), high-intensity halogen (30 s), LED unit (40 s), and diode laser (15 s) during activation of two different bleaching agents. The hypothesis tested assumed that there is no difference in temperature rise in pulpal chamber when bleaching material was activated with these three curing units and the diode laser.

MATERIALS AND METHODS The three curing units evaluated were Hilux 550 (First Medica, NC, USA); Optilux 501 (Kerr, Danbury, CT, USA);

Manufacturer Biolase, San Clemente, CA, USA Kerr, Danbury, CT, USA First Medica, NC, USA 3M Espe, St. Paul, MN, USA

Elipar FreeLight (3M Espe, St. Paul, MN, USA); and a diode laser (Lasersmile, Biolase, San Clemente, CA, USA). Manufacturers’ names and addresses, applied time and other pertinent information are listed in Table I. Preparation of Teeth

Eighty maxillary central incisor teeth, extracted for periodontal reasons, were selected. Each tooth was free of dental caries or restoration. The teeth were cleaned and stored in deionized water at room temperature immediately after extraction. The root portions of the teeth were sectioned with a slow-speed diamond saw (Isomet, Buehler Ltd., Lake Bluff, IL) approximately 2 mm below the cementoenamel junction perpendicular to the long axis of the teeth, and stored in deionized water until used. An opening was made into the pulpal chamber from the radicular portions of the teeth so that a thermocouple wire could be inserted. The pulpal chamber was cleaned of remnant pulpal tissues. The root stub was then secured to an acrylic plastic base with an autopolymerizing resin. A hole was drilled through the acrylic plastic base to provide entrance for thermocouple wire into the pulpal chamber. The labial surfaces of the teeth were thoroughly pumiced for 2 min, rinsed for 2 min in distilled water, and dried with clean, dry, compressed air. Each experimental group was treated with one of the following 35% hydrogen-peroxide– containing bleaching materials: Opalescence XTRA (Ultradent, South Jordan, UT, USA) or Quasar Brite (Spectrum Dental, Culver City, CA, USA). Quasar Brite was mixed according to the manufacturer’s instructions and both of the bleaching agents were applied with a brush to the tooth surface, in a layer approximately 1-mm thick. Light application time for conventional halogen light (light intensity, 450 mW/cm2) and LED (light intensity, 380 mW/cm2) unit was 40 s. Laser irradiation was 15 s (under bleaching mode, 10 W, continuous wave) and high-intensity halogen (light intensity, 850 mW/cm2) application time was 30 s (under bleaching mode). Temperature Measurement

The temperature rise was measured in the pulp. The distance between the emitting tip of the light source and the tooth surface was set at 10 mm. A silicone heat-transfer compound

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ELDENIZ ET AL.

tion of bleaching material and curing unit or diode laser and difference between start and highest temperature reading was taken. Then 10 calculated temperature changes were averaged to determine the mean value in temperature rise. The results of testing were entered into an Excel (Microsoft威, Seattle, WA, USA) spreadsheet for calculation of descriptive statistics. Statistical analysis was performed using two-way analysis of variance (ANOVA) and then Tukey HSD tests (SPSS/PC, Vers.10.0, SPSS, Chicago, IL, USA) for comparisons among groups at the 0.05 level of significance. RESULTS Figure 1. Schematic drawing of experimental set up showing the temperature measurement during activation of bleaching material.

(ILC P/N 213414, Wakefield Engineering, MA, USA) was applied in the pulp chamber. This compound facilitated the transfer of heat from the wall of the dentin to the thermocouple wire. A J-type thermocouple wire with 0.36-inch diameter (Omega Engineering, Stamford, CT, USA) was connected to data logger (XR440-M Pocket Logger, Pace Scientific, NC, USA) during application of curing units and diode laser (Figure 1). The sampling rate of the data logger was set to one sample every 2 s for a recording period starting with light curing for approximately 60 –90 s until the temperature started to decrease. The collected data which was available in both tabular and graphic form was monitored in real time and transferred to a computer. Measurements were made for each combina-

Temperature rise values of the bleaching agents with the three light units and diode laser tested are given in Figures 2 and 3 and Table II. Temperature rise values with the same light source was pooled as no statistically significant effect of bleaching agent on temperature rise values was detected with ANOVA (p ⫽ 0.647). Pooled temperature rise values with three light units and diode laser are given in Table III. Temperature rise varied significantly depending on the curing unit (conventional halogen, high-intensity halogen, LED) and diode laser used (ANOVA, p ⬍ 0.001; Table IV). The diode laser (11.7°C ⫾ 2.1°C) induced a significantly higher temperature increase than any other curing unit (Tukey, p ⬍ 0.001). The LED unit produced the lowest temperature increase (6.04°C ⫾ 1.0°C), however there were no statistically significant differences among the curing units tested (Tukey, p ⬍ 0.05).

Figure 2. Temperature versus time graphs of diode laser, high-intensity halogen, conventional halogen, and LED during activation of Opalescence-Xtra.

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TEMPERATURE RISE DURING LIGHT-ACTIVATED BLEACHING

Figure 3. Temperature versus time graphs of diode laser, high-intensity halogen, conventional halogen, and LED during activation of Quasar-Brite.

DISCUSSION This in vitro study measured the temperature changes caused by the heat generated by three commercially available curing units and a diode laser. Under the conditions of the present study, the highest temperature rise was recorded using the diode laser for 10 s. The temperature rise during activation of bleaching material was lower with the LED unit than the conventional halogen, high-intensity halogen, and the diode laser. This result is in accordance with the previous studies21,22 which concluded that LED unit produces the least thermal insult during polymerization process. Aqueous hydrogen peroxide has been used clinically at 30% to 35% levels to lighten teeth for many years, but the process has required multiple visits. Heat and light have been used empirically in attempts to catalyze hydrogen peroxide decomposition and speed tooth lightening.12 The current study was planned to determine comparative thermal risk to the pulp induced by these three light units and diode laser.

TABLE II. Intrapulpal Temperature Rise Values (⌬T, °C) with Various Light Sources

Light Source

Quasar Brite

Opalescence Xtra

Diode laser High-intensity halogen Conventional halogen LED

11.5 ⫾ 2.2 7.2 ⫾ 1.9 6.3 ⫾ 1.4 5.9 ⫾ 1.0

12.0 ⫾ 2.0 8.5 ⫾ 1.6 6.4 ⫾ 2.2 6.0 ⫾ 1.0

[Mean ⫾ standard deviation (n ⫽ 10)].

Light-activated, heat-enhancing colorant may increase intrapulpal temperature values.23 Two different bleaching agents that contain 35% hydrogen peroxide with different colorants [Quasar Brite (pink) and Opalescence Xtra (dark red)] were selected for the current study. Temperature rise in the latter was higher but there were no statistically significant differences between groups. When using high-energy lasers in biological vital tissues, the adverse effects must be considered. Histological reactions after laser treatment were investigated. Adrian24 found a localized pulpal response in the region that, through dentinal tubules, had indirect contact with the irradiation spot of an Nd:YAG laser in dentin. The rest of the pulp was unaffected.24 This finding was confirmed by Stelzel and colleagues,25 who found pulpal response when irradiating deep dentin layers. The current study focused on the intrapulpal temperature changes and no information is given about histological evaluation. Pulpal changes caused by bleaching agents have been investigated by several authors. Seale and colleagues8

TABLE III. Pooled Intrapulpal Temperature Rise Values with Light Sources

Diode laser High-intensity halogen Conventional halogen LED

Mean ⫾ SD

Tukey Grouping*

11.75 ⫾ 2.07 7.84 ⫾ 1.93 6.35 ⫾ 1.80 6.04 ⫾ 1.03

A B B B

Mean ⫾ standard deviation. *Groups with different letters are statistically significantly different.

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TABLE IV. Two-Way Analyses of Variance

Mode

DF

MS

F

P

Bleaching material Light source Bleaching material† Light source

1 3 3

6.14 133.08 1.72

1.95 42.29 .55

.16 .00 .65

intensity halogen, conventional halogen, and LED curing units. The maximal temperature increases determined were viewed as critical for the pulpal health for any of the three types of curing units and diode laser tested. The authors would like to thank Ultradent for supplying “Opalescence” and Mr. Enver Atali for supplying Lasersmile unit.

REFERENCES found that histological damage to dog teeth from hydrogen peroxide used alone or with heat is reversible after 60 days. They reported histological evidence of disappearance of the odontoblastic layer under the treated area and a dense inflammatory infiltrate and area of scalloped dentin with isolation. Robertson and Melfi7 indicated that these pulpal alterations appear to be reversible. According to the results of the current study, temperature rise values are critical for pulp tissue. Reversibility in alterations in calcified structures and pulp tissue needs to be evaluated further on human teeth. Zach and Cohen26 reported irreversible pulpal damage in 15% of rhesus monkeys for temperature elevations of 5.6°C, 60% for temperature elevations of 11°C, and 100% for temperature elevations of 16.6°C. Even though their experimental setting was different from this study, their results can be suggested as a baseline for potential histopathological changes in pulpal tissues when the temperature rise exceeds 5.6°C. The total duration of temperature rise and storage of harmful heat is important. Eriksson and colleagues27 stated that 42°C was a critical temperature when maintained 1 min. However, Reingewirtz and colleagues28 showed that energy dissipation is rather rapid and happens within 10 s. Kreisler and colleagues29 stated that diode laser irradiation of root surfaces may jeopardize pulp vitality and recommended that a power output of 1.0 W and exposure time of 10 s must not be exceeded to ensure a safe clinical application. In the current study a power output of 10 W and exposure time of 15 s were applied according to the manufacturer’s instructions and diode laser caused a temperature rise of 11.7°C, whereas an increase of 7.8°C for high-intensity halogen, 6.35°C for conventional halogen, and 6.0°C for LED was recorded. Considering these values, the maximal temperature increase detected for all curing unit and diode laser tested in this study were viewed as critical. However, the temperature values measured in this study cannot be directly applied to temperature changes in vivo. The reason is that the experimental set up of this study did not consider heat conduction within the tooth during in situ bleaching material activation due to the effect of blood circulation in the pulp chamber.30

CONCLUSION Measurements of temperature rise during activation of bleaching material in vitro indicated that during light activation of selected bleaching materials, diode laser caused significantly higher temperature increases as compared to high-

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