Effect of CO2 Laser on Class V Cavities of Human Molar Teeth
under a Scanning Electron Microscope
Ruberval Armando LOPES2
Américo Yuiti KATAYAMA3
Ana Eliza Castanho GARDINI3
1Departamento de Anatomia, ICB-USP, São Paulo,
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
| Introduction | Material
and Methods | Results and Discussion | Conclusions
| References |
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.
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.
- 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).
2 - Laser-treated area shows smooth dentin with cracks
and lines (375X).
3 - Higher magnification of Figure 2 showing concentric
lines (small arrow) and cracks in several directions (major arrow) (700X).
4 - SEM view showing concentric lines with melted
dentin and granulation on the surface (1,800X).
5 - Higher magnification of Figure 4 showing details
of the surface granules (5,000X).
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
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).
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.
Adrian JC: Pulp effect of neodymium laser. Oral Surg Oral Med Oral Pathol
44: 301-305, 1977
Dederich DN, Zakariasen KL, Tulip J: Scanning electron microscopic analysis
of canal wall dentin following Nd:YAG laser irradiation. J Endod 10: 428-431,
Fisher SE, Frame JW, Browne RM: A comparative histological study of
wound healing following CO2 laser and conventional surgical
excision of canine buccal mucosa. Arch Oral Biol 28: 287-291, 1983
Frentzen M, Koort HJ, Thiensiri I: Excimer lasers in dentistry: future
possibilities with advanced technology. Quintessence Int 23: 117-133, 1992
Goldman L, Gray JA, Goldman J, Goldman B, Meyer R: Effect of laser beam
impacts on teeth. J Am Dent Assoc 70: 601-606, 1965
Goodman BD, Kaufman HW, Gedali I: Effect of a CO2 laser on
fluoride uptake by extracted human teeth. J Jap Soc Laser Med 6: 231-234,
Kantola S: Laser-induced defects on the tooth structure: V-Electron
probe micro analysis and polarized light microscopy of dental enamel. Acta
Odont Scand 30: 475-484, 1972
Launay Y, Mordon S, Cornil A, Brunetaud J, Moschetto Y: Thermal effects
of lasers on dental tissues. Lasers Surg Med 7: 473-477, 1987
Melcer J: Latest treatment in dentistry by means of the CO2
laser beam. Lasers Surg Med 6: 396-398, 1986
Miller M, Truhe T: Lasers in dentistry: an overview. J Am Dent Assoc
124: 32-35, 1993
Miserendino L: The laser apicoectomy: endodontic application of the
CO2 laser in apical surgery. Oral Surg Oral Med Oral Pathol
66: 615-619, 1988
Peck S, Peck H: Laser radiation: some specific dental effects and evaluation
of its potential in dentistry. J Prosth Dent 17: 195-203, 1967
Pogrel MA: The carbon dioxide laser in soft tissue preprosthetic surgery.
J Prosthet Dent 61: 203-208, 1989
Stern RH, Sognnaes RF: Laser effects on dental hard tissues. A preliminary
report. J South Calif 33: 17-19, 1965
Stern RH, Sognnaes RF, Goodman F: Laser effect on in vitro enamel permeability
and solubility. J Am Dent Assoc 73: 838-843, 1966
Stern RH, Renger HL, Howell FV: Laser effects on vital dental pulps.
Br Dent J 127: 26-28, 1969
Stern RH, Vahl J, Sognnaes RF: Lased enamel: Ultrastructural observations
of pulsed carbon dioxide laser effects. J Dent Res 51: 455-460, 1972
Taylor R, Shilar G, Rocher F: The effect of laser radiation on teeth,
dental pulp, and oral mucosa of experimental animals. Oral Surg Oral Med
Oral Pathol 19: 786-795, 1965
Watanabe I, Liberti EA, Azeredo RA, Araujo MV, Nuti-Sobrinho A, Goldenberg
S: The effects of CO2 laser irradiation in human permanent molar.
A scanning electron microscopic study. Estomat Cult 16: 27-30, 1986
Watanabe I, Semprini M, Lopes RA, Morais JOR: Efeitos da irradiação
do laser CO2 no esmalte de dentes decíduos humanos. Estudo
ao microscópio eletrônico de varredura. Rev Bras Odont 47:
Correspondence: Ii-sei Watanabe, Departamento de Anatomia, ICB-USP,
05508-900 São Paulo, SP, Brasil.
Accepted January 17, 1996
Electronic publication: September, 1996
BACK TO CONTENTS