Special Section on Hard-Tissue Optics and Related Methods

High-speed scanning ablation of dental hard tissues with a ${\bm \lambda}$λ = 9.3 ${\bm \mu}$μm CO2 laser: adhesion, mechanical strength, heat accumulation, and peripheral thermal damage

[+] Author Affiliations
Daniel Nguyen, Kwang Chang, Saba Hedayatollahnajafi, Michal Staninec, Kenneth Chan, Robert Lee, Daniel Fried

University of California, San Francisco, San Francisco, California 94143-0758

J. Biomed. Opt. 16(7), 071410 (July 27, 2011). doi:10.1117/1.3603996
History: Received April 11, 2011; Revised May 30, 2011; Accepted June 06, 2011; Published July 27, 2011; Online July 27, 2011
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CO2 lasers can be operated at high laser pulse repetition rates for the rapid and precise removal of dental decay. Excessive heat accumulation and peripheral thermal damage is a concern when using high pulse repetition rates. 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. The interpulpal temperature rise was recorded using microthermocouples situated at the roof of the pulp chamber on teeth that were occlusally ablated using a rapidly-scanned CO2 laser operating at 9.3 μm with a pulse duration of 10 to 15 μs and repetition rate of 300 Hz over a 2 min time course. The adhesion strength of laser treated enamel and dentin surfaces was measured for various laser scanning parameters with and without post-ablation acid etching using the single-plane shear test. The mechanical strength of laser-ablated dentin surfaces were determined via the four-point bend test and compared to control samples prepared with 320 grit wet sand paper to simulate conventional preparations. Thermocouple measurements indicated that the temperature remained below ambient temperature if water-cooling was used. There was no discoloration of either dentin or enamel laser treated surfaces, the surfaces were uniformly ablated, and there were no cracks visible. Four-point 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 approaching 30 MPa for both enamel and dentin under certain irradiation conditions. These values were slightly lower than nonirradiated acid-etched control samples. Additional studies are needed to determine if the slightly lower bond strength than the acid-etched control samples is clinically significant. These measurements demonstrate that enamel and dentin surfaces can be rapidly ablated by CO2 lasers with minimal peripheral thermal and mechanical damage and without excessive heat accumulation.

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© 2011 Society of Photo-Optical Instrumentation Engineers (SPIE)

Citation

Daniel Nguyen ; Kwang Chang ; Saba Hedayatollahnajafi ; Michal Staninec ; Kenneth Chan, et al.
"High-speed scanning ablation of dental hard tissues with a ${\bm \lambda}$λ = 9.3 ${\bm \mu}$μm CO2 laser: adhesion, mechanical strength, heat accumulation, and peripheral thermal damage", J. Biomed. Opt. 16(7), 071410 (July 27, 2011). ; http://dx.doi.org/10.1117/1.3603996


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