Pulpal Safety during Ablation of Tooth Occlusal Surfaces Using a CO2 Laser with a 9.3 Micrometer Wavelength

By: Michal Staninec, Cynthia L. Darling, Harold E. Goodis, Daniel Pierre, Darren P. Cox, Kenneth Fan, Michael Larson, and Daniel Fried (UCSF)

Overview

A new, conservative approach to restorative dentistry has emphasized the importance of early treatment of pits and fissures by means of micropreparation of such sites. When decay is highly localized, however, removing caries without damaging the surrounding healthy tissue can be difficult to accomplish.

Background

Although CO₂ lasers have been used for soft-tissue surgical procedures for three decades and today are the most common lasers found in clinics, early experimentation with CO₂ lasers operated at 10.6 µm for hard-tissue ablation resulted in cracking and charring of the surrounding enamel, dentin, and bone. However, recent studies using pulsed 9.3-9.6 µm CO₂ laser pulses of sub-millisecond duration have demonstrated efficient ablation of dental hard tissue with no excessive peripheral thermal and mechanical damage. The peak absorption of dental hard tissues occurs near 9.3 and 9.6 µm. At those wavelengths, the incident laser light is absorbed at a depth of less than 1-2 µm. For ablating enamel, dentin, and bone, pulse durations near 10-20 microseconds has been shown to be optimal.

Testing Methods

To evaluate the effect on tooth pulps of 9.3µm CO₂ laser irradiation of occlusal surfaces, a recent study irradiated third molar teeth scheduled for extraction using a 9.3 µm CO₂ laser.* Occlusal surfaces were irradiated for 1 minute at 50 Hz and 2 minutes at 25 Hz using an ablative fluence of 20 J/cm2 and 12-15 mJ per pulse. The same total number of laser pulses were delivered to each tooth for both repetition rates, namely 3,000 pulses for a total energy of approximately 36-45 J. After extraction, both short- and long-term (90-day) effects on the teeth were observed, and micro- thermocouple measurements were used to estimate the potential temperature rise in the pulp chamber of the extracted teeth. Results were compared to those for two control groups (one with no treatment and one with a small cut made with a conventional high-speed handpiece.)

Results

After 2 minutes of laser irradiation with water spray, the tooth temperatures rose by only 1.7°C (± 1.6°C). Their mean temperature was 7°C below the ambient temperature and well below the 5.5°C above ambient temperature at which pulpal inflammation has been shown to occur. Even without water cooling, the mean temperature rise above ambient temperature was only 3.3°C. None of the control or treatment groups showed any deleterious effects, and none of the 29 test subjects felt any pain or discomfort after the procedure.

Conclusion

The results indicate that this 9.3µm CO₂ laser can ablate enamel safely without harming the pulp.

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