Analysis of peripheral thermal damage during the rapid ablation of dentin and bone using a λ= 9.3-μm TEA CO ₂ Laser

TEA CO ₂ lasers tuned to the strong mineral absorption of hydroxyapatite at λ=9-μm are ideally suited for the efficient ablation of dental hard tissues if the laser-pulse duration is stretched to greater than 10-μs to avoid plasma formation. CO ₂ lasers are capable of operating at high repetition rates for the rapid removal of dentin and bone. The purpose of this study was to test the hypothesis that stretched λ=9.3-μm TEA CO ₂ laser pulses can produce lateral incisions in dentin and bone for dental restorations and implants at repetition rates as high as 400-Hz without peripheral thermal damage. A high repetition rate, 0-500-Hz, λ=9.3-μm TEA CO ₂ laser with pulse durations of 10-20-μs was used to make incisions in human dentin and porcine alveolar bone with a computer controlled scanning stage and water spray at varying irradiation intensities. The single pulse ablation rates were determined for incident fluence ranging from 1-150-J/cm ². Lateral incisions 2-3-mm in length were produced in the 2-mm thick sections. Following irradiation, transverse cross-sections were examined using polarized light microscopy (PLM) and Fourier transform infrared spectro-microscopy (SR-FTIR) at the Advanced Light Source at Lawrence Berkeley National Laboratory. The single-pulse ablation rates approached 40-μm per pulse for the stretched TEA laser pulses in dentin and bone. All incisions with and without water spray yielded thermal damage zones of less than 22-μm. Thermal damage zones with water spray were less than 14-μm, even at repetition rates of 400-Hz and SR-FTIR showed no spectral changes around the periphery of the incisions. CO ₂ laser pulses at λ=9.3-μm of 10-20-μs duration are well suited for the precise removal of dentin and bone for dental restorations and implants at high repetition rates without peripheral thermal damage.