Effects of diverse laser parameters at 9.3 μm on soft tissue and bone

Abstract

These investigations were performed to determine thermal, histological and incisional effects in soft tissue of laser irradiation at 9.3um. Specifically, the consequences of varying pulse duration, interval and frequency, peak and average powers and energy densities were studied.In fresh pig's jaws, 6 standardised incisions, 3cm in length, were made per parameter using a template and motorised jig. Incisions were made at various standardised anatomical sites, and surface thennal events monitored using an IR camera. Laser parameters investigated: power: 1-11W, duty cycle: 10-90%, Pulse duration: 1-200ms, at gated continuous wave (Cw). Superpulse and OptiPuls& modes with 300us pulses were also investigated. Incision width and depth as well as collateral tissue effects were assessed statistically. They were directly related to the parameters used. Ease of incision and effects on underlying bone were also parameter-related. INTRODUCTIONOver the past 25 years, areas of routine CO' laser use in oro-facial surgery have progressed to include frenectomies, periodontal surgery, tumor resections and excision of lesions such as hyperplasias, papillomas, hemangiomas, lymphangiomas and mucoceles. Clinical and laboratory investigations have consistently confirmed the advantages of this tool: precision, minimal iniraoperative hemorrhage, sterilization of the surgical area and healing with minimal scarring, postoperative pain and swelling (1-5).The C02 laser emits light energy which is strongly absorbed by water, and therefore also by tissues with a high water content, such as the oral soft tissues. The absorbed energy causes vaporization of the intra-and exiracellular fluid and destruction of the cell membranes at the focal point (6,7), producing zones of incision or ablation. The energy applied to the target tissues will also affect, to a varying degree, adjacent or underlying tissue structures. The extent of collateral damage is related to the absorption characteristics of light in the tissues, and the laser parameters used. At a given wavelength, longer pulse durations will tend to result in higher levels of coagulation and necrosis in collateral structures, as they allow thermal energy to accumulate and penetrate to a greater extent than short, transient pulses. For clinical applications, the zone of thennal damage to adjacent structures should ideally be kept to a minimum, as it may impede wound healing, graft take, and reduce wound tensile strength, especially if it is extensive. Furthermore, laser-induced temperature increases can threaten the vitality of adjoining structures such as teeth, pulp or periodontium. Conversely, very short pulse durations may hinder haemostasis and reduce ease of incision or ablation; attempts at compensating for this phenomenon by increasing pulse frequency can result in an exacerbation of thermal effects.In the CO lasers traditionally available to clinical dentistry, light at lO.6u is delivered by means of an articulated arm or a hollow waveguide and a handpiece to the surgical site....