CO2 Laser Gingivectomy for Gum Reshaping and Reduction - Medical fiber

Keywords:medical fibers, laser fiber,  Time:19-02-2016

The introduction of lasers to soft tissue surgical procedures has dramatically enhanced gingivectomy for both the surgeon and the patient by eliminating the scalpel and thus allowing for a faster, cleaner, and more pain-free procedure [1]. Typically, a laser emitting a far-infrared wavelength of light (10.6   ) is used to cut soft tissue, such as the gingiva [2].

Many types of lasers have been developed for use in this type of oral surgery. Two common examples are the CO2 laser medical fibers and the diode laser. While the light emitted by CO2 lasers is absorbed primarily by water, diode laser light is absorbed by melanin and hemoglobin proteins [1]. Therefore, diode laser light targets only pigmented tissues, leading to rapid heating in the gingiva. [3].
 
These lasers fibers cut tissue with a phenomenon known as the photothermal effect: the light energy emitted by the optic fiber of the laser is transformed into heat in the soft tissue. As the tissue heats, chemical bonds between cells break down causing ablation of the tissue with simultaneous cauterization at the site where the cut was made [1]. This creates a clean cut with minimal bleeding and significantly reduced recovery time when compared to the traditional scalpel method. We have chosen to focus in particular on the CO2 laser, in which the wavelength is generated through the excitation of CO2 gas [3]. These lasers have grown in popularity due to their advantages in providing minimal post-operative discomfort, little bleeding, and easier accessibility to areas of mouth [4]. Many of these advantages relate to their short penetration depth that focuses thermal tissue damage only on the surface of the tissue [3].  These lasers allow for very accurate cutting and do not involve the complex considerations involved with light scattering in more deeply penetrating lasers, such as the diode laser.

Since the laser wavelength is primarily absorbed by water, it targets the moist soft tissue of the gingiva more directly than the enamel of the tooth. However, the heat transfer through the healthy gum tissue and into the tooth itself must be considered and minimized in order to minimize postsurgical complications. A pulsing laser is ideal since continuous laser delivery often yields.

To minimize injury to healthy gum tissue, the peak power of the laser and pulsation frequency can be adjusted to reduce the temperature of surrounding tissue.  We aimed to ablate all targeted gum tissue, achieved by reaching 100oC in all areas of this tissue, since 100oC is the point at which tissue vaporizes [5] (see Appendix B). We aimed to successfully model the ablation of all targeted tissue while minimizing thermal tissue injury, as proteins denature significantly past 60oC and tissues are considered damaged beyond this point.

In minimizing thermal tissue damage, we consider the temperature of the enamel, dentin and the untargeted gum tissue, which we defined as all gingival tissue above the incision line. Although a small amount of damage to untargeted tissue is inevitable due to the cauterizing effect of laser cutting, we want to minimize any additional potential loss of this healthy tissue. All gingival tissue below the incision line is removed during the procedure so we will not factor any thermal damage of this tissue into the optimization.

We created an objective function that calculated the area of the damaged tissue for different sets of parameters, giving higher weights to any enamel or dentin damaged. From this, we determined which combination of laser properties minimizes tissue damage.

Our work in this project does not aim to develop a new technique for gingivectomy. The surgery has already been used successfully for many years. However, it has been implemented using many slightly varying techniques. We aim to focus on creating a model of the procedure to determine the optimum parameters of pulse type and peak laser power in an attempt to inform the potential for device advancement and manufacturing goals for future iterations of dental lasers.

Since there is no existing model for laser gingivectomy of the maxillary incisor using a CO2 laser, our goal was to create a 2D simulation in COMSOL to model the laser ablation of this tissue.