Review on Orthodontic Lasers

Light amplification and stimulated emission of radiation techniques have been introduced in both medicine and science. Currently many lasers are available which are very efficient for dental soft and hard tissues. To achieve the desirable results, knowledge of laser technology such as power of particular type of lasers, its wavelength, and the time for which the particular laser is used. Lasers are mainly preferred because it prevents bleeding, is pain free and there is no need of intervention and saves valuable time of both patients and specialist, lasers are currently being used for alteration in conventional enamel etching and dentine bonding procedures during composite restorations, laser technology has made an advancement in orthodontics it has known to accelerate the movement of teeth to be moved, lasers are also used for removing the brackets and other bonding procedures, many researchers claim that this technology can also be used for implant procedures like it will increase the stability and strength of implant, reduction in demineralisation of enamel during various procedures. Lasers are mainly used in field of orthodontics which has resulted in better patient co-operation due to reduced pain and discomfort and is also convenient for the operator. Along with the advantages that lasers offer they are associated with few disadvantages. Lasers are relatively higher in prices than conventional equipments, for treating the patients with this modern technology the operator must be specially trained. If not used properly it can cause deleterious effects on tissues. This review article is about various dental lasers, effects of lasers on tissues and clinical and nonclinical applications and laser safety. Review Article Waghmare et al.; JPRI, 33(60B): 2745-2752, 2021; Article no.JPRI.79684 2746


INTRODUCTION
One innovative technology in the light has made significant advances into a variety of fields of dentistry. Because of the unique properties of lasers, therapy modalities such as ablation of soft tissues, haemostasis, alleviation of pain, and dental hard tissue procedures are now possible [1].
LASER refers for Light Activation by Stimulated Emission Radiation. It is a term that explains how amplification of light occurs by stimulated emission. Lasers are made up of three primary components: one energy source, one active medium, and a group of 2 or more lasers [2]. A laser beam differs from a standard source of white light in various ways, like collimation, coherence (phase correlation), and monochromaticity (single wavelength) [3].
Light is often transmitted to the target tissue in dental laser systems via optical fibre cable, a hollow waveguide, or an articulated arm [4]. There are many of lasers available that can produce visible light, infra-red, and UV wavelengths. Lasers used in dentistry have wavelengths ranging from 488 nm to 10,600 nm. The principal lasers used in dentistry today are the argon, carbon dioxide (CO 2 ), diode, neodymium-doped yttrium aluminium garnet (Nd: YAG), and erbium lasers, erbium-doped yttrium aluminium garnet (Er: YAG), and erbium, chromium: yttrium scandium gallium garnet (Er, Cr: YSGG) [5]. The specific wavelength, output current, time of application, and total energy given to the tissue all influence the laser's effect on the tissues it's aimed at during a dental treatment [6] .
The most frequent dental operations are the excision of labial and lingual midline frenectomies, crown lengthening procedures, curing composites, and the management of gingivitis. Caries identification and elimination, bleeding problems, pain relief and hypersensitivity treatments. Gingivectomy, gingivoplasty, soft-tissue defects, and other procedure, every type of aphthous ulcers can be adequately treated by using lasers for dentistry [7] .

HISTORY
Gordon Gould was the first to introduce the LASER in 1957, based on Albert Einstein's light propagation theory and stimulated emission idea. In 1960, Theodore Maiman employed laser for the first time at Hughes Aircraft Company, USA, utilising a Ruby lasing medium to generate light with a high energy density. In the same year, Kumar Patel pioneered the use of CO 2 LASER. Leon Goldman was the first to demonstrate the clinical use of LASER on dental tissues in 1969. Paghidiwala first described the use of Er: YAG in year 1985, and then employed it for hard tissue in the year 1997 and on the soft tissue the following year [8].

Laser's Interaction at Molecular
Level that can Occur are: [13] 3.

Absorption
Photons are elementary particles that are absorbed by certain molecules called chromophores. The beginnings of light energy are transformed into different energy types.

Reflection
Without interfering with or penetrating the surface, the laser beam bounces off it.

Transmission
Initially, energy passes through the surface tissues before it interacts with the deeper tissues. It can be viewed using diode and Nd: YAG lasers.

Scattering
The energy emitted spreads in all directions as it hits the tissue. They are unappealing and have no clinical utility.

BIOLOGICAL EFFECTS OF LASER
Laser has a total of five distinct effects.: [13]

The Photothermal Effect
When the light energy strikes a tissue of interest, it is converted to heat, causing the cells to vaporise. When chromophores receive laser energy and release heat as a result, this phenomenon is produced. Work like incising tissue or coagulating blood is done with this heat. When CO 2 laser is utilised on teeth, photothermal ablation is at work as hard tissue is vaporised during removal, whereas photothermal interaction is predominant in soft tissue treatments. Because these operations generate heat, more caution is essential to minimise thermal harm to the target tissues.

Flourescence
When a visible wavelength 655nm is used on a carious tooth during diagnostic operations, this event may occur. The degree of fluorescence is proportional to the lesion's size.

Photodisruptive Effects
Short pulsed bursts of extremely high intensity laser light contact water molecules in the tissue, causing the water molecule to expand thermally. This generates a thermomechanical sonic shock capable of effectively shattering tooth and bone. Because of this kind of shock waves a unique popping sound was detected during Erbium LASER operation. Thermal injury is extremely improbable when there is no remnant heat.

Photochemical
A chemical reaction occurs within the tissue as a result of the photon produced.

Photobiomodulation
It is LASER's capacity to accelerate healing, improve circulation, and lessen discomfort. Biostimulation causes histological changes such as enhanced collagen production, fibroblast proliferation, and osteogenesis. The majority of these reactions are caused by LASER's interactions with the mitochondria and cellular matrix. In dentistry, biostimulation (Low Level Laser therapy) is used to alleviate postoperative pain.

EFFECTS ON ENAMEL, DENTINE AND PULP [13]
Protein denaturation at 45-60 degrees, necrosis and coagulation at temperatures above 60 degrees, and vaporisation of water in tissue (temperatures more than 100 degrees) are some of the effects of LASER on tissues.

Enamel
Microcracks emerge as a result of the water vaporising process. Lasers increases acid resistance of enamel it occurs because of organic matrix decomposition. Laser treatment increases the acid resistance capacity of the enamel, which is very useful in patients with rampant caries, poor oral hygiene. Lasers have been proved to prevent caries. Different types of lasers specifically used for increasing acid resistance of enamel surface are CO 2 , Er: YAG, Er Cr: YSGG and Nd: YAG.

Dentine
Although there are no visible fissures, the damage is primarily necrosis and carbonisation. Laser treatment changes the morphology of the dentine. It changes the structure of the intertubular and peritubular structure of dentine. Lasers have also known to reduce the most common problem like dentin hypersensitivity. Lasers have bactericidal effects on dentin and has potential usefulness in root canal disinfection. Irradiation with erbium laser improves adhesive and bonding properties of dentine.

Pulp
The teeth which are treated with lasers show excellent haemostasis. Lasers are also effective in stimulating the healing of the pulp. Rise of a few degrees creates irreparable pulpitis, but a rise of one degree causes pulp necrosis.

Advantages
Lasers are light, handy and most of the time wireless. They are easy blood-free environment [13]. 4. Diode Lasers: after using this type of lasers there is less post operative swelling, patient experiences less pain, diode lasers can be used near implants due to their low power generation. It does not cause any harm to the dental hard tissues and are safe for dental pulp.
5. Erbium Lasers: this type of lasers has ability to cut dental hard tissues like enamel, dentin and cementum along with oral soft tissue. It reduces vibrations during cutting hard tissues and is less fear full to the patient.

Disadvantages
LASER has a few drawbacks, including a higher cost, less tactile sense as compared to traditional procedures, and the need for the specialist training to use it [13].
1. Argon lasers: Preparation of argon lasers are difficult. Efficacy of this type of laser is very less usually less than 1%. High voltage power supply is needed.
2. Nd:YAG Lasers: It has low absorption as well as low efficacy in thicker tissues. Sometimes the process becomes slower.
The molecular structure of this type of laser is very complex.
3. CO 2 Lasers: CO 2 lasers are very costly. sometimes not affordable to the patient.

Diode Lasers:
The main disadvantage is high cost. Thicker tissues require more time to cut. The practitioner must be well trained for operating such devices. Some users may think that it is slower than conventional equipments.
5. Erbium Lasers: Erbium lasers are not cost effective. The practitioner must be trained properly to use this laser. It is considered more aggressive and ablative than other lasers.

Laser Etching
When laser energy is applied to enamel, it induces localised ablation and melting, and hence loss of enamel structure. [14] Enamel removal (etching) is mostly caused by micro explosions. There may also be a buildup of entrapped water in the enamel. Some hydroxylapatite crystals have melted. Temperature induced alterations on the enamel are caused by laser irradiation in particular. Based on the laser and the amount of energy delivered to the surface. Surfaces are roughened and irregularities are generated to a depth of 10-20 nm as if acid etching had been performed [15]. If 0.60kg/mm bond strength is considered the minimum acceptable value for clinical application, the study's findings imply that to achieve consistent surface conditioning, laser enamel etching should be conducted at the complete power output of the 'American Dental Nd: YAG laser' [16].

De-bonding Technique with a Laser
With promising results, lasers are employed in enamel acid etching and bracket de-bonding. This method has been demonstrated to be effective in order to de-bond, leading to a lower adhesive residual relatively and index minor increase in pulp temperature. The use CO 2 and Nd: YAG lasers, in particular, has yielded satisfactory results with minimal side effects from increased pulp temperature [16]. The effectiveness of 'CO 2 and Nd: YAG' lasers in removing ceramic brackets from the enamel surface when compared to traditional debonding approaches, laser assisted debonding was found to significantly minimise residual debonding force, the danger of enamel damage, and the rate of failure. As a result, this approach has the capability of being less stressful (less unpleasant) and more secure for the patient (reduced danger of enamel damage) [17].

Lasers for Light Curing
Light-cured adhesives provide a longer installation time, allowing for more precise bracket positioning. Curing light takes 20-40 seconds to set each brackets which is the main drawback of this technique. Although light-cured adhesives have the same shear bond strength as chemically activated adhesives, the bond strength improves significantly between five min and 24 hours of application, with the bond strength at 5 minutes being only 60 to 70 percent of the strength properties at 24 hours. The capacity of an argon laser to accomplish photopolymerization of composite resins has been the subject of recent research. To commence polymerization, dental resins with photo-activation employ a reducing agent, like a tertiary amine, and a dike tone initiator, camphoroquinone. With a peak of activity centred at 480 nm, this system of photoinitiators is extremely light sensitive in the visible spectrum's blue region. The argon laser is monochrome and emits the light in a wavelength of 457.9-514.5 nm in the blue and green spectra, making it ideal for polymerisation of composites [16]. If irradiation of enamel with an argon laser can be utilised to bind orthodontic brackets and found that argon lasers can achieve bonding power comparable to those achieved with traditional resins with a light cure. [18]

Using Lasers to Regulate Orthodontic Treatment and Improve Aesthetics
Patients seeking orthodontic treatment are looking for more than simply "straight teeth." They value properly-aligned, white teeth, functional and occlusal stability, gingival aesthetics, well-proportioned features as well as stunning grins. In addition, patients want this to be completed in a reasonable length of time. The soft-tissue laser, recently acquired popularity as an effective tool for managing treatment and improving aesthetic results [16].

Pain Relief
The effect of a single dose of low-level laser therapy on elastomeric separator-induced pain in a single-blind trial. The LASER used in the investigation was a GaAlAs Diode LASER operating at 200 mW in constant mode with a wavelength of 940 nm [19]. The laser provide effective pain relieved by improving blood circulation, which eliminates pain mediators and boosts cellular activity (BioStimulation).

Accelerating Orthodontic Tooth Movement
Following LLLT, there was an increase in tooth mobility, which is related to an increase in collagen of synthesis, new capillaries formation, formation of bone. The release of interleukin 1 beta is enhanced, and the activity is more pronounced in the maxilla than other parts of the jaw. The laser used had a wavelength between 600-1000 nm and was made of GaAlAs and HeNe. For 80s for 2 days, the laser was used on the buccal as well as palatal aspects. For 5 seconds, the laser was positioned on the neck of tooth on the labial and lingual side. The retraction was examined after 4 weeks and 8 weeks and at the end of retraction. [20]

Use of Lasers on Soft Tissue in Orthodontic Treatment
Recontouring of the gingiva, unerupted teeth are exposed., enlarged tissues and inflammatory tissue removal, frenectomies, and aphthous lesions therapy are some of the applications for soft tissue connected to orthodontic intervention.
[21 Lasers are employed for contouring of gingiva for improving smile, teeth proportioning before the bracket implantation, crown elongation and crown asymmetry treatment, interdental and gingival margin contouring. [22] Soft-tissue procedures, including dental frenectomies, papillectomies, and gingival incisions, are commonly performed with Nd: YAG lasers. [2]

Laser Scanning
The laser only offers the surface map and cannot provide colour information for the texture map, the procedure for scanning needs the individual to remain motionless for a period ranging from seconds to minutes or longer as the scanner spins around the head of the patient. This information is provided via a laser scannerregistered colour camera. Orthodontic equipment for example splints, computerised wire bending, e-models, and surgical simulation models can be made by utilising three-dimensional digital data from a laser scanner using computer-aided manufacturing and stereolithography processes. The software can be used to combine photos obtained from various angles, removing undercuts. 3D computer-aided wire-frame schematics enable models to be cut, overlaid, and computed measurements, making studies using tooth casts a breeze. [16]

Laser Welding
Individual orthodontic appliances and efficient treatment processes typically necessitate metal framework connections. Laser welding is a new technology for combining metal frameworks. To emit laser beams, YAG crystals with additional neodymium are primarily used. Laser welding has several advantages, including the absence of solder, which prevents corrosion at the junction, a tiny focus, and an argon shielding gas, which prevents oxidation around the welding zone [16]

Laser Safety
According to the ANSI and the Occupational Safety and Health Administration, lasers are divided into 4 categories as per their possibility for harm: [23] Class I: This class consist of laser which have low-power that are safe to view.
Class II a: This class consist of visible lasers with a low power output. If one looks into the beam for more than 1s, chances of damage are there.
Class II: This class consist of visible lasers with a low output power. When viewed along the beam for more than 0.25 seconds, they become harmful.
Class IIIa: This class of lasers when viewed for less than 0.25 seconds, it consists of mediumpowered lasers that are not harmful.
Class III b: When these lasers are seen directly within the rays for any period of duration, that are hazardous.
Class IV: High-powered lasers can harm the skin and other organs like eyes. The beams that are reflected are also harmful. Appropriate safety precautions must be used. This category includes the majority of lasers used in medicine and dentistry.
The following are the various sorts of dangers that may be faced in the clinical practise of dentistry: [16]  Dangerous to the eyes  Tissue harm  Risks to the respiratory system  Explosions and fire  Electrocution  Dangers related to combustion  Dangers related to equipment.

MEDICO-LEGAL CONSIDERATIONS
Those lasers powerful enough to ablate tissue carry additional risk of damage through breach of duty of care and causation. Causationwould suggest that on the balance of probability either the need for reparative treatment or permanent damage was linked directly to the excessive laser power or inadequate technique. Conservative soft tissue surgery using a dental laser is considered standard dental practise and is normally covered by most professional liability insurance policies for dentists. Informed consent should be a standard procedure, and it is best handled as part of the general permission form that all patients must read and sign prior to starting dental treatment. Each practitioner is strongly advised to take a course from a recognised supplier. [24]

CONCLUSION
Laser means light amplification emission of radiation. LASER applications include pain reduction, an alternative to etched and bond procedures, increased in movement of tooth, removal of brackets, bracket number, increasing implant fixation, bracket design, a decreased in demineralization process, and surgery of oral tissue. Along with merits there are few demerits like lasers are costly for patients, costly for the dental practitioner, sometimes it increases the length of treatment and destructive for tissues.

DISCLAIMER
The products used for this research are commonly and predominantly use products in our area of research and country. There is absolutely no conflict of interest between the authors and producers of the products because we do not intend to use these products as an avenue for any litigation but for the advancement of knowledge. Also, the research was not funded by the producing company rather it was funded by personal efforts of the authors.

CONSENT
It is not applicable.

ETHICAL APPROVAL
It is not applicable.