Thermal Modeling of Tissue Ablation During Pulsed CO2 Laser Gingivectomy for Gum Reshaping and Reduction
Bender, Ryan; Gross, Michael; Luo, Wenjie; Tess, Emily
Gingivectomy, a surgical gum treatment used to remove gum tissue, is applied for a variety of reasons, including the removal of diseased gum tissue and gum contouring for aesthetic purposes. While a scalpel has been previously used in this procedure, laser gingivectomy is now becoming common due to its decreased invasiveness, minimal bleeding, and quicker healing time. However, an entirely new set of considerations must be addressed with the introduction of lasers to the procedure. Since laser gingivectomy is essentially heat treatment, the heat from the laser can damage surrounding tissue and teeth. Therefore, the intensity of the laser beam must be carefully selected to prevent significant damage of teeth or non-targeted gum tissue above the incision line. A feature that helps preserve healthy tissue is the pulsed application of the laser, which prevents the exposure of the tissue to heat flux over an extended amount of time. Therefore, our goal was to model a laser gingivectomy process that may be used to identify the ideal laser power and pulse rate for gingivectomy that minimizes collateral tissue damage. To accomplish this, we created a 2D cross-sectional model in COMSOL of the middle of a maxillary incisor with an overextending gum. The COMSOL computer software allowed us to simulate the effects of laser contouring on the gum-tooth complex. Gum geometry was simplified to a slab of constant thickness across the top of the incisor, meeting the tooth at a rounded edge. Tooth geometry was simplified to a series of rectangular slabs exhibiting constant thickness consistent with parameters gleaned from literature. Preliminary results showed little heat penetration to the extremes of our computational domain, which supports the simplification of not including the entire length of the tooth in our geometry. Material properties, such as the thermal conductivity, density, and heat capacity of gum and tooth were taken from existing literature. We considered targeted gum to be vaporized at a temperature of 100˚C, consistent with surface soft tissue heat treatment characteristics. Ideally, tooth and preserved gum should stay below 60˚C. The tooth temperature profile is considered in an optimization equation that aims to minimize unnecessary tissue damage. This temperature profile is used to determine which regions are suffering protein denaturation and experiencing vaporization. By comparing our results with previously conducted procedures involving laser treatment of gum, we found that our results were consistent with the outcomes of these processes, which used the same type of laser as the one we modeled. Noting that the simplifications and conjectures on boundary and initial conditions limit the validity of our model, our results indicated that the ideal laser peak power for a gingivectomy process using a CO2 laser is 25 Watts. Our model could also be used to test the use of gingivectomy to dispose of diseased tissue, which likely exhibits different material properties than the healthy gum tissue we modeled. Therefore, our model can provide laser manufacturers and product trainers with crucial information that can be used to develop parameter settings for a more controlled gingivectomy. In this study, we model the ablation of the gum tissue and find the optimal power of the laser and pulse conditions in order to successfully ablate the tissue without causing unnecessary heat damage to the healthy tissue or the enamel of the tooth.
gingivectomy; thermal modeling