Selective Removal of Dental Caries With a Diode-pumped Er:YAG Laser

Objectives: Conventional flash-lamp pumped Er:YAG lasers are poorly suited for the selective removal of dental caries, due to their low pulse repetition rates. This study aims to compare the ablation rates of sound and demineralized enamel and dentin using a new 30-W diode-pumped Er:YAG laser with a pulse duration of 20-150-µs operating at pulse repetition rates of up to 500-Hz to evaluate its potential for the selective removal of natural occlusal lesions on extracted teeth.
Methods: Microradiography was used to determine the mineral content of enamel and dentin sections of 300-µm thickness with natural carious lesions prior to laser ablation. One group (n=8) was used to calculate ablation rates for varying mineral content. A second group (n=8) used near-IR cross-polarized reflectance measurements at 1500-1700-nm to guide the laser for selective ablation of demineralized enamel and dentinal lesions. 3D digital microscopy was used to compare ablation rates. Finally, cross-polarized near-IR reflectance was used to guide the laser for selective ablation of natural occlusal carious lesions on extracted teeth (n=5). Optical coherence tomography pre- and post-ablation scans were used to assess ablation selectivity.
Results: Demineralized enamel was ablated at significantly higher rates (p<0.05) than sound enamel which is desirable for selective ablation. Sound and demineralized dentin were ablated at high-pulse repetition rates (500-Hz) without peripheral thermal damage using 20-30-µs pulses. Laser ablation of sound enamel increased the reflectivity at near-IR wavelengths of 1500-1700-nm which poses a challenge for serial near-IR reflectance imaging during image-guided ablation.
Conclusions: The diode-pumped solid state Er:YAG laser has a high repetition rate and small spot size. Combined with its selectivity for demineralized enamel, this laser holds great potential for highly selective removal of dental caries.