Laser ablation as a function of the primary absorber in dentin

Area of Science:

• Biomedical Engineering
• Laser-Tissue Interaction
• Dental Materials Science

Background:

• Dentin's infrared transmission spectra exhibit a broad absorption band (6.0-7.0 microns) due to water, collagen, and carbonated hydroxyapatite.
• Nearly constant absorption and distinct peaks allow investigation of ablation based on primary absorbers.

Purpose of the Study:

• To investigate laser ablation of dentin as a function of optical fluence and wavelength.
• To determine the influence of primary absorbers on ablation efficiency and threshold.

Main Methods:

• Laser ablation experiments conducted on dentin using a Free-Electron Laser (FEL) between 6.0 and 7.5 microns.
• Ablation crater depth and volume measured using silicon replica and confocal laser topometry.
• Scanning Electron Microscopy (SEM) used for surface analysis; an ablation model developed.

Main Results:

• Ablation depth increased linearly with fluence above a threshold at all tested wavelengths.
• Higher absorption at 6.0-7.0 microns resulted in lower ablation thresholds compared to 7.5 microns.
• Ablation model showed good agreement with experimental data using mean absorption coefficient; no thermal cracking observed.

Conclusions:

• Ablation efficiency and threshold are primarily governed by mean absorption, irrespective of the specific chemical identity of the absorber in dentin.
• Thermal equalization via heat conduction during laser pulses minimizes dependence on the primary absorber.
• Surface roughness varied with wavelength, with 7.5 microns showing greater roughness.