Dr.N. PADMAPRIYA PG Student Division of Orthodontia RMDCH

INTRODUCTION The theoretical concept of the laser was proposed by Einstein in 1917Lasers were developed in early 1960s and rapidly found a number of uses in medicine and surgery. Laser introduced into general dentistry in 1994 and they have been used in orthodontics for number of years.

The term laser is an acronym of light amplification by the stimulated emission of radiation, a process that can efficiently transmit energy through an electro optical device in the form of a concentrated beam of light. LASER

BASIC PRINCIPLE

When an atom of a substance in an excited state undergoes a spontaneous decay it emits a photon.In laser that photon interacts with another energized atom and stimulates the emission of another photon with precisely the same wave characteristics, further stimulates atoms and produce additional identical photons. Teruo Matsumoto Colour atlas laser surg, Ishiyaku Euro America, Inc Publ.,)

The light waves generated in the way are reflected back and forth repeatedly between mirrors set on either end of the laser chamber. The laser beam leaves, the chamber through a hole at center of the partially reflective mirror.

BASIC LASER PROPERTIESLaser light has 3 basic properties:It consists almost exclusively of one wave length advancing in the same direction (coherence)The light is traveling in a parallel plane with no divergence. (collimation) All laser energy intensifies at one wavelength and barely deviates (Monochromaticity).

CLASSIFICATION According to Physical Construction of the laser Gases Excimer (is that the laser are generated from gas mixture of halogens (F, Cl, Br) and rare gases. - Argon - Krypton, CO2 Solids - NaCl YAG - Ruby Liquid - Rhodamine dye - Teruo Matsumoto

The types of medium which undergoes lasing Eg: - Erbium - Yttrium - Aluminum - GarnetThe degree of hazard to the skin (or) eye following inadvertent exposure.

COMMON LASER TYPES USED IN DENTISTRY ArgonHeliumDiodeNd: YAGEr: Cr: YSGGEr: YAGCO2 ( L J Walsh, Australian dental journal 2003)

The main applications for lasers in orthodontics are for Laser scanning Holography Soft tissue lasersHard tissue lasers (Robert Harry, BJO1994)

LASER SCANNING This is a method of three dimensional image capture which has been described by Arridge et al (1985) and further developed by Moss et al (1988). A low power, Helium Neon, type II laser is fanned across subject face or body and the reflected beam is captured by a video camera.(Robert Harry, BJO1994)

The information is then analyzed by specially developed software and stored on a computer.The image can then be viewed on a computer screen and rotated in any direction so that all the individual features can be viewed. Super imposition of serial scans is now possible and therefore longitudinal assessment of facial growth or the results of facial surgery can be assessed.

Three dimensional dental cast analyzing system using laser scanning (Tajayuki Kuroda et al. Am.J.Ortho 1996, Br.J Ortho 1994)The three dimensional dental cast analyzing system with laser scanning Its preliminary clinical application is that the system is composed of a measuring device with a slit ray laser projector and two sets of coupled charged devised video cameras, an image processing unit. A 16 bit personal computer as a controller and an engineering workstation as a post processor.

The dental cast is projected and scanned with a slit ray beam, the coordinates of the target are determined with an image processor.Triangulation is applied to determine the location of each point.Generation of 3-D graphics of a dental cast takes 40 minute. The measurement error is less than 0.5 mm. Beside the conventional linear and angular measurement of the dental cast is able to demonstrate the size of the palatal surface area and the volume of the oral cavity.

The advantage of this system is that it facilitates the other wise complicated and time consuming mock surgery necessary for treatment planning in orthognathic surgery. In orthodontic treatment the information obtained from the dental cast is invaluable not only for the diagnosis, however it has been difficult to obtain quantitative information regarding probable changes in volume of the oral cavity of the treatment. It is the set of treatment goal.

HOLOGRAPHY Holographs can be used for three dimensional record collection and stress analysis in hard tissue subjected to various loading forces. This is also used for three dimensional facial image recording, their main application in terms of record collection is as a substitute for orthodontic study casts. (Robert Harry, BJO1994)

Holograms are about the same size as radiographs or photographs and are resistant to damage. A special camera is required which will take white laser light reflection holograms from study casts.

Disadvantage: Lack of familiarity with the hologram and the fact that some views of the teeth were poor, particularly in assessing overbite and actually measuring the over jet. Because of above disadvantage, an interesting development is, the use of reverse holography. (ie). A system might be developed that could take holograms directly of the patient teeth, without having to use study casts or dental impression at all.

SOFT & HARD TISSUE APPLICATION CO2 lasers have been used in oral techniques for operating on both hard and soft tissue (Shoji et al 1985). Drawback - due to the wave length of the emitted light (10.6 microns), the guiding system has to consists of a number of joined arms with mirrors to reflect the beam

This makes this type of unit extremely unyielding and because this wavelength is largely absorbed by water molecules.It will cut many tissue, both hard and soft and has to be used with caution.

Nd:YAG (Neodymium: Yttrium Aluminium Garnet) laser. It was developed by Ceusic in 1964 A wave length of 1.06 microns and can be transmitted via a fibre optic cable to handpieces which resemble conventional dental instrument in size and shape. It is possible to cut soft tissues relatively painlessly.

Unlike the Co2 laser, Nd:YAG laser beam because of its near infrared range can be delivered through a pure optical fiber. The laser beam is delivered through a silica fiber 320 m in diameter. Nd: YAG laser uses a helium - neon (red) laser for aiming the beam, it can be delivered either contact or non contact system.

The soft tissue surgery can be performed without the need for local anesthetic which may be useful for removing opercula from partly erupted teeth. This type of laser cannot be used on bone because it will destroy bone cells at a considerable depth, producing necrosis. Eg: not suitable for mucoperiosteal flaps, fraenectomies.

It can be used for exposure of teeth where no flap is raised The use of soft, non-cutting laser has been suggested for various dental applications including the desensitization of hypersensitive dentine, to aid the healing of dry sockets promote healing and reduce the discomfort associated with aphthous ulcer.

Disadvantage: One of the early problems associated with the application of laser technology to dental hard tissue was that laser irradiation of teeth generate too much heat. A temp rise of 6 C may result in an invisible pulpal reaction which can lead to pulpal necrosis.

TISSUE REACTION Each tissue type has a specific energy absorption pattern. Laser absorbed by tissues and laser are strictly frequency and tissue dependent. Because of the limitations of laser physics & tissue biophysics, one laser cannot be applied to all the various tissue types with complete efficacy.

When laser light interacts with oral tissue, it is either absorbed, partially transmitted, scattered, or back scattered. Only the absorbed laser light has an effect on tissues. Tissue absorption is low with Nd:YAG lasers; has optical scattering with deeper and uniform penetration within tissue. CO2 lasers have the most absorption, with basically negligible scattering followed by the argon laser.

HARD TISSUE APPLICATIONSNd: YAG laser cannot be used on bone because of the resultant necrosis, it has been used for a variety of other dental procedures. These include cavity preparation,(removal of soft caries) endodontics (to access the extremely fine root canals) and as a substitute for acid etching of teeth.

Laser tooth whitening: The whitening effect with the use of argon laser is achieved by a chemical oxidation process. once the laser energy is applied, the hydrogen peroxide (H2O2) breaks down to water (H2O) and a free oxygen radical, which combines with and thus removes the stains molecule.

Laser etching of enamel for direct bonding and with an Er: YAG and Er, Cr; YSGG, hydrokinetic laser system (Bor-Shiunn Lee et al. AO 2003, AJO 2002) Irradiation of enamel with laser energy changes the physical and chemical characteristics of the enamel surface and these alteration hold for the conditioning enamel for bonding procedure , Normal minimum time etching - (orthophosphoric acid) - 15 seconds, followed by 15 30 seconds, washing (30-45 sec) 5 10 sec for drying Laser etching and drying 20 25 seconds Allowing immediate placement of bracket saving 10 to 50 seconds per tooth.

Curing with laser Curing with lasers is possible and comparable to the conventional curing lights.Wavelengths required for light curing ranges from400-800Nm. Photo sensitivity of camphoroquinone, the photo activator in almost all the composite resin restorative materials can be activated by laser light .Thus the laser beam can activate, the polymerization like visible light curing sources.

LASER CURINGThe wavelengths produced by argon lasers include a 488 segment, that is an exact match with photo sensitivity of camphoroquinone, the photo activator in almost all the composite resin restorative materials.The laser beam activates the polymerization much faster than a visible curing source. (Laser in pediatrics and adolescent dentistry)

Within 10 sec for filled resins and 5 sec for unfilled resins there is significant time savings especially with layered resin placement the physical properties are also improved with the laser curing, dimetral strength, surface hardness readings, and bond strengths all are enhanced. Shrinkage is similar but occurs more quickly.

Layering management is recommended. Because the filler particles in composite resins block the penetration of curing lights, both laser and visible light curing, the recommended 2-mm depth of curing holds for both methods.

Mark Kurchak et al in 1997 (JCO) study shows region laser produce wavelength of 457-514 Nm and in a peak of 488 Nm, can be used as curing light. Argon laser have been found to cause no damage to pulp or enamel levels of 1.6 to 6 watts.

Sergio J. Weisberger et al in 1997 (A.O) study shows there is no difference noted in bonded system between laser and light cured brackets. The laser cured specimens exhibited a significantly higher incidence of cohesive failure. Chemically cured bonding system may be superior to laser or light cured bonding system because of then decreased risk of enamel damage.

Travis Q Talbot et al., (2000) compared the effect of argon laser energy level on curing visible light cure orthodontic adhesive system and concluded that there was no apparent effect with increasing energy level from 200 mw to 300 mw and 10 seconds. Argon laser bonding produced bond strength comparable to 40 seconds conventional visible light curing. AJO DO 2000 .

Lalani. N et al., (2000) conducted a study to determine the efficiency of an argon laser in polymerizing a light-cure orthodontic adhesive and concluded that a 5-second cure using an argon laser produced bond failure loads comparable to those obtained after 40 seconds of conventional light cure, with less than half the frequency of enamel fracture at debond. Angle Orthod 2000

LASER DE-BONDING OF CERAMIC BRACKETS (Ezz Azzeh & Paul J. Feldon et al. AO 2003 AJO 1992, 1997)

Laser energy degrades the adhesive resin used to bond brackets consequently, lower forces can be used than when mechanical debonding is performed, reducing the risk of enamel damage.The heat produced by some laser can damage vital pulp, selecting the appropriate laser, resin and bracket combination can minimize risks and make debonding more efficient.

Mechanism of laser debonding (According to Tocchio et al.AJO 2003 Laser energy can degrade the adhesive resin by 3 methods Thermal softening Thermal ablation Photo ablations Thermal softening - occur when the laser heats the bonding agents until it softens.

Thermal ablation - occurs when heating is fast enough raise the temp of the resin into its vaporization range before debonding by thermal softening occur.Photo ablations - occur when high energy laser light interacts with the adhesive material and the energy level of the bonds b/w the adhesive resin atom rapidly rises above their dissociation energy levels resulting in decomposition of material. {CO2 YAG lasers}

Time span for debonding in the laser less than 4 second (2.9 0.9 seconds) Debonding force is reduced in laser. Risk of enamel damage and bracket fracture is reduced.No pulpal injuring occur when the max intra pulpal temp rise stayed below 2C.The effect of lasting time on intrapulpal temp increased and tensile debonding force with a 18 watt carbondioxide laser.Ceramic bracket can also be debonded by laser debonding pliers.

Surface roughness of orthodontic arch wire via laser specular reflectance (Robert P.Kusy et al EJO. & AJO 1998) The surface roughness of orthodontic archwires is an essential factor that determines the effectiveness of arch guided tooth movementUsing the non-destructive technique of atomic force microscopy (AFM), laser specular reflectance and profilometry, the roughness of wire is measured.

In orthodontic, surface roughness of archwires additionally may affect the aesthetics of the appliance and the performance of sliding mechanics but its influence on the co-efficient of frictionGuiding a tooth along the archwire results in tipping and rotating of the tooth and in a contact between the bracket and the guiding wire.

Consequently frictional forces may reduce the orthodontic force by 50% or more The loss due to friction depends on a larger number of mechanical parameters of the combination of arch wire and brackets being used Above all the material parameters of the guiding archwire are dominant factors

EFFECT OF LOW POWER LASER IRRADIATION ON BONE REGENERATION IN MID PALATAL SUTURE DURING EXPANSION IN RATS(Shiro Saito and Noriyoshi Shimizu. AJO, 1997)The low power laser irradiation can accelerate bone regeneration, in mid palatal suture during rapid palatal expansion and that this effect is dependent not only on the total laser irradiation dosage but also on the timing and frequency of irradiation.

Laser therapy may be of therapeutic benefit in inhibiting relapse and shortening the retention period through acceleration of bone regeneration in the mid palatal suture. Low power laser source, gallium- aluminium arsenide diode laser device was used.

INTRA ORAL LASER MICROWELDING OF ORTHODONTIC APPLICANCES(Leich E. Colby & Richard R. Bevis. AJO, 1978)

A common task for industrial lasers is the fusion of two metals without the aid of soldering agents. It was not surprising to find such an obviously practical process the center of more in dental research.Shifting the emphasis from intraoral use to laboratory procedures. It is clearly documented that laser welding is stronger than solder joints of comparable size.

This factor plus the low thermal distortion which accompanies the welding process makes the lab welding of prostheses very attractive. The work has been carried out safely. The rapid and repeatable action of the pulsed neodymium laser micro welder used in simulating intra oral welding strongly suggests that safe intra oral welding can be done with proper controls on a routine basis with no damage to hard tissue.

LASER FLUORESCENCE STUDY OF WHITE SPOT LESION IN ORTHODONTIC PATIENT (Susan Al-Khateeb et al. AJO, 1998)Enamel demineralization with white spot formation on buccal surface of teeth is a relatively common side effect from orthodontic treatment with fixed appliance.Enamel decalcification or formation of white spot lesion during orthodontic treatment presents of significant problem in orthodontic patients.

Fixed orthodontic appliances complicate the removal of food debris that result in the accumulation of plaque. There will be increase in number of streptococcus mutans and lactobacillus species in oral cavity after placement of fixed orthodontic appliances. Plaque bacteria produce organic acids that cause the dissolution of calcium and phosphate

ions from the enamel surface, this dissolution can cause white spots (or) carious lesions to form in 4 weeks. There is a evidence that suggests that, such small area of superficial enamel demineralization may remineralize. The QLF method (quantitative version of laser fluorescence) method is to monitor longitudinally small changes in incipient enamel lesions.

This method is useful for investigation of the effect of preventive and therapeutic measures in various cariogenic risk groups. When enamel demineralization take place, minerals will be replaced mainly by water, causing a decrease in the light path in the tooth substance.QLF test for assessment of mineral changes in artificial lesions during demineralization.

This will result in reduction of light absorption by enamel because fluorescence is a result of absorption, the intensity of fluorescence will decrease in demineralized region of the enamel which appear darker than the sound tooth structure.

The white spot lesions formed around the fixed orthodontic appliance recover partly over a relatively long period of time. To prevent (or) reduce enamel decalcification during orthodontic treatment.Including fluoride application, hygiene regimens, modified appliances designs, the use of Argon laser in dentistry has been proposed for polymerization of resin materials and bleaching of enamel.

ii. Photoactivated dye disinfection using lasersThis technique shown to be effective for killing bacteria in complex biofilms, such as subgingival plaque, which are resistant to the action of anti microbial agents. It can be used effectively in carious lesion, since visible red light transmits well across dentine and can be specific by tagging the dye with monoclonal antibodies.

This dye can be applied for killing gram positive and negative bacteria, fungi and viruses. Photodynamic therapy More powerful laser initiated photochemical reaction is photodynamic therapy, which has been employed in the treatment of malignancies of the oral mucous, particularly multi focal squamous cell carcinoma.

Laser procedures on dental hard tissue Er-based dental lasers can be also used to remove composite resin and glass-ionomer cement restorations and to etch tooth surface. These laser system can be used for effective caries removal and cavity preparation without significant thermal effects collateral damage to tooth structure (or) patient discomfort.

Soft tissue laser procedures Which can be performed with lasers by reducing bleeding in intra operatively and less pain post operatively compared it conventional techniques such as electro surgery.

LASER SAFETYEye protection is important for the operator, staff, and the patient. Different lasers require different safety glasses. CO2 laser protection can be afforded with clear safety glasses, such as those that are normally worn during dental procedures. Clear safety glasses are worn by the patient as well, and as a back up measure, wet gauze sponges are placed over the patient eyes.

For protection from Nd:YAG laser energy, both the doctor and staff need to wear green safety glasses. For the argon laser, orange safety glasses. Instruments that are highly reflective or that have mirrored surfaces should be avoided as there could be reflection of the laser beam.

Understanding the various uses of lasers ,is simply to accept, the cutting edge of present day orthodontics.From the daily bonding procedure including surface preparation, bonding, debonding, scalpel-less cutting,tooth bleaching Record maintenance ,cast analysis in 3-D, can be done using lasers.

CONCLUSION

With its numerous uses in dentistry and its ever growing uses in orthodontics,the safety precautions,and its disadvantages should also be kept in mind.Future of painless & faster dentistry, in an orthodontics practice, can all be achieved, to the one that understands the use of lasers in the field of orthodontics. To conclude, lasers are our tools of tomorrow, only if we are ready with the knowledge of it today !*