Int. J. Morphol.,27(2):441-446, 2009.

 

Morphological Alterations of the Surfaces of Enamel and Dentin of Deciduous Teeth Irradiated with Nd:YAG, C0₂and Diode Lasers

 

Alteraciones Morfológicas de las Superficies de Esmalte y Dentina de Dientes Deciduos Irradiados con Láseres de Nd:YAG, C0₂ y Diodo

 

Mónica Rodrigues de Souza; Ii-Sei Watanabe; Luciane H. Azevedo & Edgar Y. Tanji

Universidade de Sao Paulo, Sao Paulo, S.P., Brazil.

Correspondence to:

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SUMMARY: In this work, we studied the effects of C0₂, Nd:YAG and diode lasers on the enamel and dentin of deciduous human teeth. After the irradiations, the samples were duly prepared and set up on metallic bases, covered with gold and examined in the scanning electron microscope. The results showed that the irradiation with the C0₂ mode locked laser with 1.0 W power caused melting and irregularities with small cavities on the surface of the enamel. The irradiated area on the dentin surface appeared circular and well delimited, containing blocks of dentin and cracks. By using the pulsed Nd:YAG laser with 1.0 W mean power and 10 Hz frequency, the enamel surface presented granules of molten enamel, with a typical melting look. The irradiated dentin surface presented a cavity with a margin elevated with granules and holes, and its bottom presented dentinary tubules with globules of melted dentin. Irradiation with the mode locked of diode laser with 1.0 W mean power, showed the formation of a melted and evenly resolidified enamel surface, and the dentin surface presented a block of melted dentin with adjacent regions of normal dentin, evidently with a relatively smooth surface.

KEY WORDS: Deciduous tooth; Enamel; Dentin; C0₂ laser; Nd:YAG laser; Diode laser; Scanning electron microscope.

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RESUMEN: El estudio presenta algunos resultados del efecto del láser de C0₂, Nd:YAG y Diodo sobre el esmalte y dentina de dientes deciduos humanos. Después de las irradiaciones, se prepararon las muestras y se montaron sobre bases metálicas, cubiertas con oro y examinadas en el microscopio electrónico de barrido. Los resultados mostraron que la irradiación con el láser C0₂ en modo conmutado con 1,0 W de potencia, provoca fusión e irregularidades con pequeños cráteres en la superficie del esmalte. En la superficie de la dentina, el área irradiada se mostró circular y bien definido, con bloques de dentina y grietas. Con el uso del láser Nd: YAG en el modo pulsado con 1,0 W de potencia media y frecuencia de 10Hz, la superficie del esmalte presentó granulos de esmalte fundido, dándole el aspecto de "melting" (derretido). La superficie de dentina irradiada presentó un cráter con borde elevado con granulos y agujeros, y su fondo presentó túbulos dentinarios con glóbulos de dentina derretida. La irradiación del láser de Diodo en el modo conmutado con potencia media de 1,0 W, provocó la formación de una superficie de esmalte fusionada y resolidificada uniforme y la superficie de la dentina presentó un bloque de dentina fundida en la regiones adyacentes de dentina normal, mostrando una superficie bastante lisa.

PALABRAS CLAVE: Diente deciduo; Esmalte; Dentina; Láser C02; Láser Nd:YAG; Láser diodo; Microscopía electrónica de barrido.

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INTRODUCTION                                                                   

Several studies have shown the possible applications of different types of lasers in dentistry clinics, as for example, in the inhibition of carious lesions (Stern etal., 1966,1972; Yamada, 1996), as well as in their removal (White et al, 1993), in the oral mucous (Taylor et al, 1965), and in gum healing (Chomette et al, 1987), among others. The scanning electron microscope has shown the different morphological alterations in the enamel and dentin surfaces irradiated with the C0₂ laser (Takahashi et al. ,1998; Watanabe et al, 1986), the diode laser (Wetter, 2002), and the Nd: YAG laser (Lin et al, 2001). However, most of these studies were carried out on permanent teeth. In deciduous teeth, the effects of the C0₂, Nd:YAG and diode laser, were scarcely studied (Watanabe et al, 1990; Rode et al, 1994). Therefore, the obj ective of this work is to study the effects of the irradiation of these three kinds of lasers on the surface of enamel and dentin of deciduous human teeth with the scanning electron microscope.

MATERIAL AND METHOD

Thirty-two exfoliated human upper and lower deciduous teeth (incisor, canine, molar) were used, which were fractured with the help of a screw clamp lengthwise. To guide the fractures, orientation grooves were made with a high rotative diamond bur. The teeth were subsequently stored in 5% sodium hypochlorite for 3 to 5 days, to remove the remaining soft tissue in the dental cavity. The teeth were then washed in distilled water, dehydrated in an increasing series of alcohol beginning with 60% up to the absolute, and left on filtered paper for 24 hours to dry. The samples were set up on a wooden base for the treatment with the lasers. Irradiation on the enamel surfaces were made on the buccal surface of the teeth, whereas irradiation on the dentin surfaces was made laterally to the pulpar cavity, always in a concentrated manner. After being irradiated, the samples were set up on metallic bases, covered with gold and examined on the JEOL 6100 scanning electron microscope. The parameters used were: C0₂ laser: with LOW power for 6 seconds, and 84.9 J/ cm³ energy density in the locked method; Nd:YAG laser: 1.0 W mean power for 6 seconds, energy density of 84.9 J/ cm³ and frequency of 10Hz, in the pulsed method; diode laser: LOW power for 6 seconds, 84.9 J/ cm³ energy density in the locked method. The C0₂ Laser System apparatus, UM-L-30 model, of the Union Medical Engineering Co., the Nd:YAG Pulse Master apparatus, of the American Dental Technologies and the L808 diode laser model apparatus, were used at LELO-USP (Special Laboratory of Laser in Odontology in University of Sao Paulo).

RESULTS

The normal enamel surface of deciduous teeth presents characteristic depressions and enamel prisms (Fig. 1). The surface of the normal fractured dentin shows numerous parallel dentinary tubules (Fig. 2). Irregular areas with rugosities were formed on the surface of the enamel irradiated with C0₂ laser. These can be noticed in their entire extension, with insertion of smooth enamel surfaces and presence of some cavities with variable sizes (Fig. 3). On the other hand, irradiation on the dentin surface showed the formation of a well-delimited circular surface, with blocks of fractured dentin and numerous fissures (Fig. 4).

Fig. 1. SEM image of normal enamel surface of deciduos teeth showing the enamelm prism (arrow). Bar 10 ¡am.

Fig. 2. SEM image of normal dentin surface showing numerous parallel dentinary tubules. Bar 10 ¡am.

Fig. 3. SEM image of enamel surface irradiated with C0₂ laser showing irregular areas with rugosites (large arrow) and smooth enamel surface (small arrow). Bar 100 ¡am.

Fig. 4. Surface of dentin irradiated with C0₂. Shows blocks of fractured dentin (arrows) and fissures. Bar lOOjam.

Fig. 5. Surface of enamel irradiated with Nd:YAG laser. Shows the «melting» with the presence of enamel granules and holes (arrows).

Bar 10 ¡am.

Fig. 6. Surface of dentine irradiated with Nd:YAG laser revealing a very deep and dehmited cavity with elevated margins. Bar 100 ¡am.

 

The enamel surface irradiated with the Nd: YAG laser showed melting, with the presence of enamel granules and holes (Fig. 5). When the dentin surface was irradiated with the Nd:YAG laser, a very deep and delimited cavity was formed, with elevated margins (Fig. 6). The presence of granules and holes in the cavity margin became very evident due to the increased melting of the dentin surface (Fig. 7). In the bottom of the cavity, dentinary tubules, melted dentin globules and small holes and cracks were present (Fig. 8).

Fig. 7. Surface dentine irradiated with Nd:YAG laser. Note the presence of granules nad holes in the cavity margin with the melting of dentine surface (arrows). Bar 10 urn.

Fig. 8. The botton of the cavity irrdiated with Nd: YAG laser, showing dentinary tubules, melted dentin globules and holes (arrows). Bar 10 urn.

Fig. 9. Surface of enamel irradiated with diode laser shows the aspect of fusion in some areas (white arrow) and enamel prisms (black

arrow). Bar 100 urn.

Fig. 10. Surface of dentin irradiated with diode laser shows the delimitation block of relatively smooth melted dentin (arrow). Bar 100 urn.

The aspect of fusion was noticed in some areas of the enamel surface irradiated with the diode laser (Fig. 9). On the other hand, the dentin surface revealed the delimitation of the region irradiated, forming a block of relatively smooth melted dentin, with adjacent regions of normal dentin (Fig. 10).

 

DISCUSSION

The results of this work revealed the effects of the action of 3 types of laser (the C0₂, Nd: YAG and the diode) on the enamel and dentin surfaces of deciduous human teeth, through the scanning electron microscope. With regard to the C0₂ laser action on the enamel surface of deciduous human teeth, our results showed the aspect of fusion and melting of the samples, similar to those related by McCormack et al. (1995) and Kantorowitz et al. (1996). Furthermore, we noticed the presence of extensive rugosities in all the area irradiated with laser, confirming the findings of Takahashi et al. Around the rugosities, we noticed the formation of some cavities with variable sizes in the area of the enamel irradiated with the C0₂ laser, clearly showing fissures as had Ferreira et al. (1989).

Besides the cavities, Miserindo et al. (1989) also revealed the presence of major deep destruction when the energy parameters were increased. Cavities with smooth and vitrified walls were observed by Takahashi et al. when the number of pulses was increased. In our data we confirmed the presence of smooth walls between the rugosities. This is probably due to the use of different energy density and power applied in the different experiments. Other authors, such as Lobene et al. (1968), on the contrary, state that there was no formation of cavities when they irradiated the teeth fissures with the C0₂ laser. They further identified the melted and whitish aspect of the surfaces.

With regard to the surface of the human deciduous teeth dentin irradiated with the C0₂ laser, our findings revealed the presence of a fairly circular and well-delimited area, containing dentin blocks between fissures and cracks. These characteristics were also noticed by Watanabe et al. (1997) in permanent human teeth, identifying the presence of small holes in the interior of the dentin blocks, whereas Lan et al. (2000) observed the presence of fissures and cracks on the dentinary surface irradiated with smear layer. On the dentinary surface irradiated without the presence of smear layer, there was a flat cavity with melted masses. The margin was irregular and well defined.

The use of the Nd:YAG laser in this work revealed melting and resolidification of the enamel surface of the deciduous human teeth irradiated, based on the three-dimensional images by the scanning electron microscope, agreeing with the findings of Rode et al. According to some authors (Shirazuka et al., 1991; Pelino et al., 1999), the morphological alterations on the irradiated enamel surfaces make it more resistant with regard to demineralization. Laser irradiation associated to the fluor, is also efficient in the increase of the enamel resistance (Twasi et al. ,1991), and in the increase of the fluor incorporation (Tagomori & Morioka, 1989), being able to play an important role in the prevention or removal of dental caries (White et al).

In our results, we noticed the typical melting appearance of the irradiated enamel surface, forming enamel granules of variable sizes, with small shallow cavities around some of them, in agreement with the findings of Myaki et al. (1998) and Hess (1990). Furthermore, Rauhamaa-Mákinen etal (1991) did not notice the presence of cavities when only the Nd:YAG laser was irradiated on the surface of the enamel and the dentin of the extracted teeth.

The dentin surface irradiated with the Nd: YAG laser in the deciduous teeth, our findings revealed the formation of well-delimited cavities with elevated margins containing granules of melted dentin and holes, in agreement with the findings of Watanabe etal (1997), who defined the irradiated area as circular or elongated. The presence of these cavities was also observed by Lan et al Furthermore, in the interior

of the cavity, there were globules of melted dentin, clearly showing holes and formation of some cracks. Lin et al. also noticed the existence of globules, not only in the interior, but also outside the cavity with the increase of the pulse, forming a deeper cavity and with cracks. Myaki et al. clearly revealed the morphological aspect of melting and vitrification of the dentin surface of the deciduous human teeth.

There are hardly any studies with regard to the effects of the diode laser in the dental structures. The literature consulted did not show any work commenting its effects on the dentin surface, but only on the enamel surface. Our results revealed that the enamel surface of the deciduous teeth suffered melting and resolidification, agreeing with the findings of Wetter, who observed the effects of the diode laser with the scanning electron microscope. These alterations suggest a resistance increase of the dental enamel versus the acids, thus possibly playing an important role in the prevention of dental caries.

We can conclude that the three types of lasers induced different aspects of morphological alteration, both on the enamel and the dentin surfaces of all the deciduous teeth irradiated. These evident alterations on the surface of the enamel and the dentin of the deciduous teeth irradiated with the C0₂, Nd: YAG and diode lasers, in the future can suggest extrapolation for certain dental clinical procedures.

ACKNOWLEGEMENTS

The authors express immense thanks to Mr. Sebastiao Boleta and Mr.Gerson Batista (in memorian) for their technical assistance, and to the LELO-USP (Special Laboratory of Laser in Odontology in University of Sao Paulo).

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Dra. Mónica Rodrigues de Souza
Universidade de Sao Paulo
Sao Paulo, S.P
BRASIL

Email: Prof. Dr. Ii-Sei Watanabe watanabe@icb.usp.br

Received: 27-07-2008
Accepted: 22-01-2009