Low Level Laser Therapy for Non-Invasive Dental applications: A Review

Laser therapy has an excellent track record in medical applications, and it has made its unmatched position by treating several dental problems. Laser devices has successfully improved healthcare in medical field by providing non-invasive and painless ways of treatment. In this paper the systematic review has been conducted for the comparative study of Laser technology using Low Level Laser Therapy in dental applications. For this the database is looked through utilizing Pubmed, IEEE, Science Direct utilizing foreordained inquiry term Low Level Laser Therapy and Laser treatment in dental treatment for the most part centered around laser diode dental treatment. Our clinical comparative study shows that Laser therapy is a painless treatment which may help fast healing in less time as compare to traditional treatment. Keywords—LLLT, Dental, Laser application, Laser Parameters, soft tissue laser.


INTRODUCTION
Word "laser" is an abbreviation for Light Amplification by the Stimulated Emission of Radiation. The primary low-level remedial laser was created in 1962. Before the finish of the 1960's, Endre Mester in Hungary was announcing an improved recuperating of wounds through low-level laser radiation. From that point forward, researchers and specialists around the globe have been utilizing laser light to treat conditions which can influence all age gatherings [1,2]. Low Level Laser therapy is the use of coherent beams of laser light is used to diagnose or treat medical conditions. Lasers have four main parts: the active medium, the excitation mechanism, the feedback mechanism, which is usually a reflective mirror, and the output coupler. Laser light is created by controlled emissions which allows a doctor to target a specific tissue, as the light is focused and can be turned on and off easily. Lasers are treated in two ways, contact and noncontact mode. Contact lasers work by sending a light through a fiber tip or sapphire tip. The tip absorbs energy and becomes hot. When the hot tip touches any live tissue in the body, the target cells are vaporized, which is the removal of tissue through the conversion of a solid to a gas. Noncontact lasers do not touch the tissue [3]. They operate by transferring laser light as radiant energy in a single beam to the tissue. Heat is generated after the laser's radiant energy is absorbed by the targeted tissue. The light vitality created by a laser can have four distinct communications with an objective tissue: Reflection, Transmission, Scattering, and Absorption. At the point when a laser is retained, it lifts the temperature and produces photochemical impacts relying upon the water substance of the tissues. At the point when a temperature of 100°C is reached, vaporization of the water inside the tissue happens, a procedure called removal. At temperatures underneath 100°C, yet above around 60°C, proteins start to denature, without vaporization of the hidden tissue. On the other hand, at temperatures above 200°C, the tissue is got dried out and afterward consumed, bringing about an unfortunate impact called carbonization. Low Level Laser Therapy (LLLT) is an application of light over the injuries or lesions to improve the healing and it can regenerate damage cell tissue or it can destroy unwanted cells like a cancerous cell. At the point when the right force and treatment times are utilized, laser light can lessen oxidative pressure and builds the Adenosine Tri-Phosphate which improves cell's digestion and expands its wellbeing [6]. LLLT gadgets incorporate the gallium arsenide (GaAs), gallium aluminum arsenide infrared semiconductor (GaAlAs), and helium neon (HeNe) lasers. Our focus is on Diode laser because of its wavelength spectrum (810-1064 nm) is very much consumed by melanin, hemoglobin, and different chromophores that are normally present in periodontal tissues [7,8]. In diode laser the laser energy can be transmitted through a fiber as small as 600μ, 400µ and 200µ Diameter Size so that it can undoubtedly infiltrate profound periodontal pockets to convey its restorative impacts [8]. Along with these features, it also has the added advantages such as portability, convenience and cost efficiency. Hence it can be easily incorporated into the dental practice [8]. Diodes dynamic vehicle of aluminum, gallium and arsenide, strong semiconductor working at 810-980 nm. frequencies ingest exceptionally pigmented tissues containing hemoglobin, melanin and collagen chromospheres. This clarifies particular activity of diode lasers on the delicate tissue tasks, for example, cut, vaporization, blood coagulation, curettage and hemostasis than dental hard tissues [9]. Currently most commonly used wavelengths for dental treatment are 810 and 980nm [10]. Where 810 nm frequency is explicit for hemoglobin retention; the 940nm frequency gives a decent proportion between the light illuminated into the tissue and the assimilation by hemoglobin and water; the 980nm frequency is with the end goal that it is explicit for hemoglobin and water. [11,12]. The laser technology for LLLT treatment are mostly used with proper setting of parameters and may be used for the treatment of wound healing, soft tissue injury and relief of pain. Study shows that there may be strong results and weak results of treatment, generally weak results are because of incorrect parameters setting and strong results shows treatment efficacy on healing.
In This paper the Literature is divided into five section in first section brief introduction has been explained with background of topic. In next section detailed review has conducted from good publications such as Pubmed, Springer, IEEE searched on google search engine. A comparison of clinical study table is designed of Laser diode and its parameters effect on clinical outcomes. Section three shows the applications of laser treatment used for dental treatment. Section four describe various laser diode parameters and their mathematical calculation formulas followed by the conclusion. II. LITERATURE REVIEW Study of literature review has been conducted from some scientific research articles and journals available on web science PubMed, Springer, science direct and IEEE. 250 Articles are searched out of which some latest research articles are selected for comparison mainly focused on LLLT using GaAlAs Laser Diode. Figure-1 shows a flow study of review started from search or identification then screening is done on the basis of applications and type of laser used after that full articles are shortlisted for full paper study and only those articles are included in which clinical study is done and results are analyzed with hypothesis testing and compared. Table-2 shows the methods of clinical trials with laser parameters are compared and results shows with proper setting of parameters LLLT provides better results in reducing pain and analgesic effects. This review study shows that Low Level Laser therapy is a wide field of study; many research works has been done on different applications areas with the help of different parameters and wavelengths and much more study needs to be done for different parameter setting at different wavelengths.  LLLT has a scope of dental, clinical, physiotherapy applications. Low-level laser applications in dentistry remember the advancement of twisted recuperating for a scope of tissues. They are processed in two formats one is for Soft tissue based and others for hard tissue applications. In dental lasers, the laser light is conveyed from the laser to the objective tissue by means of a fiber-optic link, empty waveguide, or explained arm, centering focal points, a cooling framework, and different controls total the framework. The frequency and different properties of the laser are resolved principally by the organization of a functioning medium, which can be a gas, a gem, or a strong state semiconductor.  [29] investigated that Laser therapy was performed in combination with radiotherapy and chemotherapy twice a week using a diode laser (660 nm, power 30 mW., spot size 2 mm, energy 2 J per point) on 36 patient of laser group with head and neck cancer concluded that laser therapy is effective in mucositis of patient under the treatment of cancer. Shoheir Shehata et. al. [30] investigated that 3B Laser device produces pulsed infrared GaAs laser with wavelength of 904 nm, peak power of 25 W, pulse duration of 200 ns, and energy density of 1 J/cm2. Laser therapy was applied on each point for 1 minute with energy density of 3 J/cm2 and treated 80 Patients 6 days/week results concluded Improvement on mucositis for Chemotherapy-induced oral Mucositis (COM). f) Paresthesia: Paresthesia is a Symptoms of abnormal sensation like pin and needles tingling or burning, prickling sensation in the body. In dentistry paresthesia is one of the complexities of careful treatment, most ordinarily observed after the careful extraction of third molars. Reneta et. al. [31] Investigated that low power laser of wavelength 808nm. Effect the recovery of nerve sensitivity after oral surgery. Icaro Girao et. al. [32] Investigated that laser of wavelength 660nm. visible red light with parameters 100mW. Power, 140 J/cm2 Energy density, 4 J of energy application per point 0.028 cm2 of spot area used for the treatment of paresthesia into inferior alveolar nerve in first session then 810nm wavelength laser applied concluded that it helps patient in pain with 9 visual analog score. g) Periodontitis: Periodontitis is a gum disease that may causes damaging of soft tissues and it can also damage the bone of teeth if not treated on time. Tanya M. L. et. al. [33] Investigated that a laser diode of wavelength 940nm. unit (having a maximum power output of 7 W) was used with a 7 mm long, 300-micron diameter, and disposable fiber-optic tip for energy delivery system is applied on 30 patients having chronic to severe periodontitis and concluded that it can help in tissue healing and shows improvement in gingival inflammation. Lohar Nilam Baburao et. al. [34] Investigated that diode laser of wavelength 980nm power 2W with treatment time per session of 30 sec. in non-contact mode for the treatment of scaling and root planning in periodontitis concluded that root surface slightly altered in the form of cracks.

B. Hard tissue applications
Dentinal hypersensitivity is a tooth sensitivity when sharp pain arises from exposed of dentine surface in response to thermal, chemical, electrical, osmotic, chemical evaporative stimuli. Marwan el Mobadder et. al. [35] conducted a clinical study to investigate dentinal hypersensitivity using 980nm laser diode of 1W Power in continuous mode. Graphite is applied on dentine before treatment and total irradiation time depends on removal of this graphite concluded that dentine hypersensitivity reduces safely in a long-term effectiveness.

IV. LASER DIODE AND ITS PARAMETERS
LLLT right now being followed in all the fortes including orthodontics, wherein it has brought about a superior and patient fulfillment work on, including diminished treatment timings and better outcomes alongside torment decrease methods. It helps in drawing, molding of the delicate tissue, relieving, laser holography and laser welding hemoglobin and it is used in soft tissue applications. Research has shown that the diode laser wavelength (800-980 nm) is ideally suited for numerous soft tissue procedures due to their high absorption in hemoglobin. This fact gives diode laser the ability to precisely and efficiently cut, coagulate, ablate or vaporize the target tissues. The emitted laser energy is scattered in the target tissues and later converted to heat. Conversely, the energy is poorly absorbed by the hydroxyapatite and by water present in the enamel. Specific procedures appropriate to their use include aesthetic gingival re-contouring, soft tissue crown lengthening, and removal of inflamed and hypertrophic tissue.
Wavelength: Frequency is the most significant determinant in how light influences tissue. It is the separation between two progressive peaks of the wave. Each sort of laser has a specific frequency (or frequencies) as indicated by the idea of the dynamic medium. Laser frequencies are ordinarily estimated in units of length: nanometers (nm) or micrometers (μm), contingent upon whether they are in UV, noticeable or IR scope of the electromagnetic range. Essentially expressed, the frequency decides the quality or kind of cooperation between the laser and the tissue. Frequency is a property of photon vitality which is communicated in electron volts (eV). Red photon has ~2eV vitality and blue photon has ~3eV vitality.
Mode: Laser may be applying in CW (continuous wave) mode or in Pulse mode. The CW mode is commonly the quickest method to remove tissues however warmth can develop and make blow-back the objective and neighboring tissues. In Pulse mode beat width is estimated in a given period and the quantity of heartbeats every second, this identifies with the pace of discharge of laser light with time and the prime advantage of a beat mode will be the limit of the objective tissue to cool between progressive heartbeats. Heartbeat wave mode is reliant on the current force setting and Duty Cycle setting.
Pulse duration: Pulse duration is a one of the basic boundaries of laser radiation on tissue or living cells. Heartbeat span is estimated in units of time (milliseconds, microseconds, nanoseconds, picoseconds or femtoseconds). When beat mode is utilized the normal force conveyed will diminish relative to the beat recurrence that is chosen. Setting the beat recurrence decide the quantity of laser beats conveyed every second during a beat LLLT treatment. Heartbeat recurrence is estimated in Hertz (Hz). At the point when a low heartbeat recurrence is chosen the interruption between laser beats is more noteworthy so less force is conveyed. At the point when high heartbeat frequencies are chosen there is to a lesser degree a respite between laser beats for example it is nearer to constant yield. The term normal (or mean) power is utilized to depict the net force conveyed in the wake of calculating for both the on and off time of the shaft.Power and power density: Radiant power is the amount of radiant energy. The average power of the laser is equal to the output energy over the exposure time as shown in equation (1): In Pulsed Laser: Average power of the pulsed laser or mean power of the chopped laser is equal to the energy of the pulse multiplied by the repetition rate.
For a CW laser the power density is the average output power in watts divided by the irradiated area in square centimeters: Peak power of the pulsed laser divided by the irradiated area gives the power density of the pulsed laser: Irradiance: Irradiance is the radiometry term for the power per unit area of electromagnetic radiation incident on a surface. It is radiant energy flux (or power) incident on an element of the surface, divided by the area of the surface.
The power P that irradiates a surface area A is called the Irradiance E: W/cm 2 (5) Coherence: Coherence length depends on spectral Bandwidth and coherent light produces speckle are two types of coherence of laser light longitudinal and transverse. The longitudinal type of coherence represents time coherence along the longitudinal beam, whereas transverse coherence refers to coherence across the laser beam. Polarization: Laser light can be linearly polarized or circularly polarized Energy and Energy Density: Energy Density is a dose applied for the treatment and it is measured in J/cm 2 . Laser Energy Density is defined as the energy which is delivered per region or active area in J/cm 2 : Spot Size or Irradiation Area: spot size of a laser delivery system implies its littlest measurement at the central plane when centered by a focal point or width and spot diameter across is the diameter of irradiation on the objective surface. The spot distance across is viewed as equivalent to the bar breadth when the focal points are not be utilized. The units of the spot distance across are as a rule in centimeters.
Illumination time: it is the time of exposure to the target tissue.

IV. CONCLUSIONS
Lasers are unquestionably the future for dentistry as it makes it exceptionally simple to expel the rot. It is useful when arriving at regions that were difficult to treat with customary medicines. There is generally safe of contaminations in and around the treatment region. Low level laser therapy is safe, effective and painless treatment. Many wavelengths of laser diode have been analyzed in Continuous wave mode and in pulse wave mode with irradiation time on dental applications.