Brazilian Dental Journal: Okamoto et al: Osseous Regeneration in the Presence of Fibrin Adhesive Material (Tissucol®) and Epsilon-Aminocaproic Acid (EACA)

Effect of CO₂ Laser on Class V Cavities of Human Molar Teeth under a Scanning Electron Microscope

Ii-sei WATANABE¹ Ruberval Armando LOPES² Aldo BRUGNERA³ Américo Yuiti KATAYAMA³ Ana Eliza Castanho GARDINI³ ¹Departamento de Anatomia, ICB-USP, São Paulo, SP, Brasil ²Departamento de Estomatologia, Faculdade de Odontologia de Ribeirão Preto, USP, Ribeirão Preto, SP, Brasil ³Centro de Estudo em Laser Aplicado à Odontologia, Faculdade de Odontologia, Universidade Camilo Castelo Branco, São Paulo, SP, Brasil

Braz Dent J (1996) 7(1): 27-31 ISSN 0103-6440

The purpose of this study was to evaluate the effects of CO₂ laser on dentin of class V cavities of extracted human molar teeth using a scanning electron microscope. SEM showed a smooth area with concentric lines formed by melting with subsequent recrystallization of dentin, areas of granulation, vitrified surface, numerous cracks, and irregular areas of descamative dentin. These data indicate that CO₂ laser (4 and 6 watts) produces dentin alterations and limit its clinical applications.

Key Words: CO₂ laser, dentin, molar teeth.

Introduction

Recent developments in laser dentistry have led to an increasing acceptance of this technology by both professionals and the general public. The potential hard-tissue applications are: vaporize carious lesions; desensitize exposed root surfaces; endodontically, vaporize organic tissue, glaze canal wall surfaces and fuse an apical plug with the potential to resist fluid leakage; roughen tooth surfaces, in lieu of acid etching, in preparations for bonding procedures; preventively, to treat enamel, arrest demineralization and promote remineralization; and debond ceramic orthodontic brackets (Miller and Truhe, 1993). However, the widespread use of laser technology in dentistry has been restricted (Stern et al., 1966) in part because of the inability of available lasers to effectively remove particles of enamel and because of the thermal changes produced in the dental pulp. The surface changes produced by ruby carbon dioxide (CO₂), neodymium:yttrium aluminum garnet (Nd:YAG), argon, and erbium:YAG (Er:Yag) lasers have been described with terms such as crazing, cratering and glazing. In contrast to other lasers, the 193-nm Argon-Fluorine excimer laser can prepare cavities in healthy dental hard tissues (see Frentsen et al., 1992). This study investigates the effects of CO₂ laser on the Class V cavity bottom of human upper molars using a scanning electron microscope.

Material and Methods

Four human upper molars from both sides were used. Class V cavities about 2 mm deep were performed with a diamond bur on a high-speed dental handpiece and water. The cavities were washed and irradiated by a continuous wave CO₂ laser Luxar (Lx-20) with the power reaching the tissue at 4 watts (final potency of 1.6 w/sec), for periods of 2 seconds, corresponding to energy density of 192 Joules/cm2. The laser produced 20 nsec pulses with a rest period to avoid over-heating in a proportion of 40/60. At 6 watts (final potency of 2.4 w/sec) the energy density was 288 Joules/cm2. The teeth were extracted, washed, and sectioned transversally (below the cemento-enamel junction), and longitudinally. The teeth were dehydrated in increasing series of ethanol and air dried. The samples were mounted on metallic stubs, coated with gold in an Ions Sputter Balzers SCD-040, and examined with a Jeol-JSM-T330 scanning electron microscope.

Results and Discussion

Irradiation of class V cavity bottoms with CO₂ laser caused a smooth area with concentric lines formed by melting with subsequent recrystallization of dentin (Figure 1). A larger smooth, vitrified surface was seen in the dentin, after 6 watts CO₂ irradiation (Figure 2). Cracks were seen to intersect the lines and vitrified areas in several directions (Figure 3); concentric lines with melted dentin and granulation were seen in several areas of the cavity (Figures 4 and 5). Low-power lasing (4 watts) caused the same kind of morphologic alterations in the specimens as observed with 6 watts, i.e., concentric lines, numerous cracks, descamative (Figure 6), vitrified areas (Figure 7), and irregular areas of descamative dentin (Figure 8), granules of melted dentin (Figure 9). Under melted dentine small dentinal tubules were seen (Figure 10). The CO₂ laser has been used in oral surgery for several years (Fisher et al., 1983). However, the laser has been used chiefly to reduce neoplasm or other abnormal structures with preservation of peripheral tissues only a secondary concern (Pogrel, 1989). Laser irradiation of oral calcified structures can cause pulpal inflammation using a pulsed ruby laser (Stern et al., 1969), a pulsed Nd glass laser (Adrian, 1977) or CW and pulsed CO₂, Nd:YAG and Argon lasers (Launay et al., 1987), because of the thermal changes produced. In this study, changes in dentin were observed, after CO₂ laser irradiation, which were morphologically similar to those reported by Stern et al. (1972), Goodman et al. (1986) and Watanabe et al. (1986,1990) using energy of 10 and 20 watts directed on the enamel and dentin. These alterations were also observed with ruby laser irradiation (Stern and Sognnaes, 1965; Goldman et al., 1965; Taylor et al., 1965; Peck and Peck, 1967). Kantola (1972) observed that dentin treated with a CO₂ laser closely resembles the crystalline structure of the enamel. Melcer (1986) has also reported that the same laser beam can convert the dentin into a crystalline structure. Miserendino (1988) directed a CO₂ laser on the apexes of freshly extracted human teeth and demonstrated recrystallization of the apical root dentin. Using a Nd:YAG laser to irradiate the root canal wall dentin, Dederich et al. (1984) observed melted, recrystallized, and glazed surfaces.

Figure 1 - SEM photomicrograph of 6 watt-CO₂ laser-treated class V cavity bottom. Note the smooth area with concentric lines (small arrow) and cracks (major arrow) (125X).
Figure 2 - Laser-treated area shows smooth dentin with cracks and lines (375X).
Figure 3 - Higher magnification of Figure 2 showing concentric lines (small arrow) and cracks in several directions (major arrow) (700X).
Figure 4 - SEM view showing concentric lines with melted dentin and granulation on the surface (1,800X).
Figure 5 - Higher magnification of Figure 4 showing details of the surface granules (5,000X).
Figure 6 - SEM view of 4 watt-CO₂ laser-treated dentin of class V cavity. Note the irregular surface with concentric lines (small arrow), areas of fractured dentine (*), and small cracks (major arrow) (250X).

Figure 7 - SEM view showing smooth areas (*) and descamative dentine (**) (500X).
Figure 8 - SEM view showing vitrified areas (*) and irregular dentin (**) (250X).
Figure 9 - Higher magnification of Figure 8 showing the vitrified dentin with concentric lines (arrow) and descamative dentine (*) (1,250X).
Figure 10 - SEM view showing vitrified dentine (*) and small dentinal tubules (arrow) (2,500X).

Conclusions

The cracks in the class V cavity bottom dentin observed after CO₂ lasing were probably caused by the thermal shock on tissue at the beam focus site. The thermal side effects of CO₂ laser limit its clinical applications and, obviously, the cracking of the dental hard tissues cannot be accepted in clinical work.

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Correspondence: Ii-sei Watanabe, Departamento de Anatomia, ICB-USP, 05508-900 São Paulo, SP, Brasil.

Accepted January 17, 1996
Electronic publication: September, 1996