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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.
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