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Proceedings Paper

High-speed scanning ablation of dental hard tissues with a lambda=9.3-µm CO[sub]2[/sub] laser: heat accumulation and peripheral thermal damage
Author(s): Daniel Nguyen; Michal Staninec; Chulsung Lee; Daniel Fried
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Paper Abstract

A mechanically scanned CO2 laser operated at high laser pulse repetition rates can be used to rapidly and precisely remove dental decay. This study aims to determine whether these laser systems can safely ablate enamel and dentin without excessive heat accumulation and peripheral thermal damage. Peripheral thermal damage can adversely impact the mechanical strength of the irradiated tissue, particularly for dentin, and reduce the adhesion characteristics of the modified surfaces. Samples were derived from noncarious extracted molars. Pulpal temperatures were recorded using microthermocouples situated at the pulp chamber roof of samples (n=12), which were occlusally ablated using a rapid-scanning, water-cooled 300 Hz CO2 laser over a two minute time course. The mechanical strength of facially ablated dentin (n=10) was determined via four-point bend test and compared to control samples (n=10) prepared with 320 grit wet sand paper to simulate conventional preparations. Composite-to-enamel bond strength was measured via single-plane shear test for ablated/non-etched (n=10) and ablated/acid-etched (n=8) samples and compared to control samples (n=9) prepared by 320 grit wet sanding. Thermocouple measurements indicated that the temperature remained below ambient temperature at 19.0°C (s.d.=0.9) if water-cooling was used. There was no discoloration of either dentin and enamel, the treated surfaces were uniformly ablated and there were no cracks observable on the laser treated surfaces. Fourpoint bend tests yielded mean mechanical strengths of 18.2 N (s.d.=4.6) for ablated dentin and 18.1 N (s.d.=2.7) for control (p>0.05). Shear tests yielded mean bond strengths of 31.2 MPa (s.d.=2.5, p<0.01) for ablated/acid-etched samples, 5.2 MPa (s.d.=2.4, p<0.001) for ablated/non-etched samples, and 37.0 MPa (s.d.=3.6) for control. The results indicate that a rapid-scanning 300 Hz CO2 laser can effectively ablate dentin and enamel without excessive heat accumulation and with minimal thermal damage. It is not clear whether the small (16%) but statistically significant reduction in the shear bond strength to enamel is clinically significant since the mean shear bond strength exceeded 30 MPa.

Paper Details

Date Published: 5 March 2010
PDF: 8 pages
Proc. SPIE 7549, Lasers in Dentistry XVI, 754907 (5 March 2010); doi: 10.1117/12.849334
Show Author Affiliations
Daniel Nguyen, Univ. of California, San Francisco (United States)
Michal Staninec, Univ. of California, San Francisco (United States)
Chulsung Lee, Univ. of California, San Francisco (United States)
Daniel Fried, Univ. of California, San Francisco (United States)

Published in SPIE Proceedings Vol. 7549:
Lasers in Dentistry XVI
Peter Rechmann D.D.S.; Daniel Fried, Editor(s)

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