Clinical treatment applications of dental lasers fibers

Keywords:dental, laser, treatment,  Time:08-12-2015

Dental lasers function by producing waves of photons (quanta of light) that are specific to each laser wavelength.2 This photonic absorption within the target tissue results in an intracellular and/or intercellular change to produce the desired result. Dental lasers may be separated into three basic groups: soft tissue lasers, hard tissue lasers, and nonsurgical devices such as diagnostic/ composite and photodisinfection lasers. This article will provide details on each of these laser classification groups; however, it also is important to be familiar with the common terms related to dental lasers.

specific target tissue that serves as an attractant for a laser photon.3 This photonic absorption within a target tissue’s chromophore is the basis for a dental laser’s functional dynamic process, referred to as a laser/tissue interaction.1 Nearly all surgical dental medical fibers function via this wavelength-specific photonic absorption, which causes the temperature within the target tissue cells to increase very rapidly to an evaporative state. These dental lasers cut tissue by a functional process known as a photothermal interaction or photothermal ablation.2 A typical example is the clinical use of a diode, a laser that is utilized in dentistry to treat soft tissue only.3 The chromophore of diode lasers is pigmented (or colored) tissues, specifically melanin, hemoglobin (Hb), and oxyhemoglobin.3 The diode is efficient for treating a patient’s soft tissues because gingival tissues have a concentration of these chromophores; as a result, a diode photon has a high affinity for gingival tissues. Diode lasers are used in contact with a patient’s soft tissue to perform common dental procedures such as gingivectomies or soft tissue lesion (fibroma) removal.4 Dental lasers offer a number of clinical advantages (especially for soft tissues), including hemostasis (the sealing of local vasculature), the ability to seal nerve endings and
lymphatic vessels, reduced postoperative pain and swelling (thus reducing the need for postoperative analgesics/narcotics), reduced bacterial counts, and a minimized need for sutures in most surgical procedures.5 Although clinicians can control some of the factors that affect laser/ tissue interactions, two factors remain independent of the operator: the unique characteristics of the laser wavelength’s emissions and the qualities inherent within the specific target tissue. Among the factors that clinicians can control are the power setting of the laser (power density), the total power delivered over a given surface area (energy density or fluence), the rate and duration of exposure (continuous versus pulsed, and pulse duration and repetition), and the method by which energy is delivered to the target tissue (contact versus non-contact).6 In fact, clinicians will have precise control over the laser to achieve the desired tissue effect by adjusting any of four variables (power, spot size, total treatment time, and repetition rate).2 For example, when an area of inflammatory tissue and an equivalent volumetric area of fibrotic tissue are treated with a diode laser at the same power setting, two very different interactions will occur.

The laser will cut the fibrotic tissue at a far slower rate, as there is more collagen in the thicker dermal layer, which scatters the diode’s energy and prevents that energy from reaching the underlying blood vessels. Conversely, the laser will cut the inflammatory tissue much faster because of the higher concentration of Hb-rich red blood cells (RBCs). Using the same laser power setting and decreasing the diameter of the laser tip used (spot size) by 50% (for example, from 1.0 mm to 0.5 mm) will cause the power density exerted on the target to quadruple, due to the inverse square rule.2 Clinicians should understand that by using a smaller diameter laser tip (and increasing the power density to the target as a result), the rate of ablation will increase dramatically. The clinical technique will need to be adjusted accordingly by either defocusing the beam (moving the tip farther away from the target) or decreasing the laser’s power setting.

The dental laser wavelengths used most commonly are located within the near, mid, and far infrared portions of the electromagnetic spectrum (EMS).2 Within these specific areas of the EMS, the photons emitted by these lasers are an invisible, non-ionizing, non-mutagenic type of radiation.6 These laser wavelengths are clinically effective when they are used at proper power settings by trained hands. Dentists should always use the lowest possible power setting to achieve the intended treatment objective.2 Merely increasing a laser’s power settings will not necessarily cut tissue faster or more efficiently; in fact, it can cause an adverse result or even lead to treatment failure. Using too much power unnecessarily will increase the target tissue’s temperature too rapidly and by too much, resulting in collateral thermal damage.1 This effect can manifest as tissue necrosis and/or sloughing of tissue due to the wide zone of edema that has been created. These complications defeat the clinical advantage for using a dental laser: to achieve treatment goals in a more effective and conservative manner (due to the laser's specific ablative capacity) than conventional instrumentation would allow. Lasers are named according to the chemical elements or molecules that make up their core (also known as the active medium).2 The active medium serves to retain a specific laser’s dopant ions and may consist of a man-made crystal rod, a gas, or a semi-conductor.2 When reading a free-running pulsed laser wavelength’s specific name, the elements to the left of the colon refer to the dopant ions; the elements to the right of the colon are its active medium.2 For example, an Er:YAG laser includes a crystal rod active medium consisting of yttrium, aluminum, and garnet (YAG), which is doped (or externally coated) with a layer of erbium ions. Examples of other dopant ions used in lasers include chromium (Cr), neodynium (Nd), and holmium (Ho). The dopant ion within a free-running pulsed laser produces a specific wavelength. Diode lasers use a semiconductor containing aluminum (or indium), gallium, and arsenide as its active medium.6 Currently, the only gas laser used in dentistry is carbon dioxide (CO2), whose active medium is a tube filled with a mixture of CO2, nitrogen (N), helium (He), and neon (Ne) gases. This laser uses a beam of energy that lases soft tissue in a non-contact mode.2 In the past, CO2 laser models were superpulsed or millipulsed machines that measured pulses by 10-3 seconds. By contrast, the newer micropulsed CO2 lasers pulses are measured in 10-6 seconds, which is 1,000 times faster. The newer ultrafast, micropulsed CO2 lasers are capable of ablating soft tissue without charring.7 (Charring is defined as the carbonization of a patient’s tissues, which happens when they are heated to temperatures above 200°C.)

The newer CO2 lasers fibers can deliver more power to the intended target with shorter pulse intervals, making more efficient ablative effects with less potential for collateral thermal damage to adjacent tissues. The FDA has four different laser classes, based on the potential danger posed by the lasers within each class as a result of their inherent power. Most lasers used in dentistry are considered Class IV lasers.2 These lasers require eye protection (in the form of safety glasses) for the patient, the dentist, and the assisting staff—in short, anyone located with the Nominal Hazard Zone.2 These safety glasses must be wavelengthspecific and must have protective side shields and a specific optic density.2 Failure to use proper eye protection could cause severe and possibly irreversible eye damage.