Residual heat deposition in dental enamel during IR laser ablation at 2.79, 2.94, 9.6, and 10.6 microm.
OBJECTIVE
The principal factor limiting the rate of laser ablation of dental hard tissue is the risk of excessive heat accumulation in the tooth. Excessive heat deposition or accumulation may result in unacceptable damage to the pulp. The objective of this study was to measure the residual heat deposition during the laser ablation of dental enamel at those IR laser wavelengths well suited for the removal of dental caries. Optimal laser ablation systems minimize the residual heat deposition in the tooth by efficiently transferring the deposited laser energy to kinetic and internal energy of ejected tissue components.


METHODS
The residual heat deposition in dental enamel was measured at laser wavelengths of 2.79, 2.94, 9.6, and 10.6 microm and pulse widths of 150 nsec -150 microsec using bovine block "calorimeters." Water droplets were applied to the surface before ablation with 150 microsec Er:YAG laser pulses to determine the influence of an optically thick water layer on reducing heat deposition.


RESULTS
The residual heat was at a minimum for fluences well above the ablation threshold where measured values ranged from 25-70% depending on pulse duration and wavelength for the systems investigated. The lowest values of the residual heat were measured for short (< 20 micros) CO(2) laser pulses at 9.6 microm and for Q-switched erbium laser pulses at 2.79 and 2.94 microm. Droplets of water applied to the surface before ablation significantly reduced the residual heat deposition during ablation with 150 microsec Er:YAG laser pulses.


CONCLUSIONS
Residual heat deposition can be markedly reduced by using CO(2) laser pulses of less than 20 microsec duration and shorter Q-switched Er:YAG and Er:YSGG laser pulses for enamel ablation.
Fried
D
D
Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, California 94143, USA. dfried@itsa.ucsf.edu
Ragadio
J
J
Champion
A
A
D000818:Animals; D002417:Cattle; D003731:Dental Caries / Q000601:surgery*; D003743:Dental Enamel / Q000528:radiation effects*; D004735:Energy Transfer; D006358:Hot Temperature / Q000009:adverse effects*; D007259:Infrared Rays / Q000009:adverse effects*; D053685:Laser Therapy / Q000009:adverse effects*; D023421:Models, Animal; D011874:Radiometry; D013997:Time Factors