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PRINCIPLES OF LASER DENTISTRY

The word laser is an acronym for light amplification by stimulated emission of radiation . A brief description of these five terms helps explain the unique qualities of a laser instrument.
LIGHT : Is a form of electromagnetic energy that exists as a particle (photon) & that travels in waves at a constant velocity . the waves of photon travel can be defined by two basic properties :
1- amplification : vertical height of the wave from the zero axis to its peak as it moves around that axis.
2-wavelength : the horizontal distance between any two corresponding points on the wave . wavelength is measured in meter (m)
One billionth (10-9) of meter nanometer
One millionth (10-6) of meter micrometer

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As the waves travel, the rotate around the zero axis a certain number of times per second ; this is called oscillation. The number of oscillations per unit time is defined as frequency & measured in hertz . Frequency is inversely proportional to wavelength .
AMPLIFICATION :
Is the part of this process that occurs inside the laser . The center of the laser is called laser cavity & composed of
1-active medium
2-pumping mechanism
3-optical resonator
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The active medium is composed of chemical element , molecules or compounds .laser are generically named for the material of the active medium .
*a canister of carbon dioxide (co2) gas in CO2 laser .
*solid crystal such as a crystal of yttrium ,aluminum & garnet (YAG) in erbium (ER)YAG or neodymium (ND)YAG laser.
*solid-state semiconductor such as diode laser .
*liquid such as found in some medical laser devices

Surrounding this active medium an excitation source such as electrical circuit ,electrical coil that pumps energy into the active medium ,when this pumping mechanism pumps energy into the active medium the is absorbed by the electrons in the outer most shell of the active medium , s atoms . those electrons have absorbed a specific amount of energy to reach to the next shell farther from the nucleus , which is at a higher energy level .
A" population inversion" occurs when more of the electrons are in higher energy level shell than are in the ground state . The electrons in this excited state then spontaneously give off that energy in the form of a photons . This is called spontaneous emission .

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Completing the laser cavity are tow mirrors , one at the each end of the optical cavity , placed parallel to each other (or polished surface ) which act as resonators . these optical resonator reflecting the waves back & forth ,&help to collimate & amplify the developing beam.
A cooling system ,focusing lenses & other controlling mechanisms complete the mechanical component s.
STIMULATED EMISSION :
Is the process by which laser beam are produced inside the laser cavity .The theory of stimulated emission was postulated by Albert Enstien in 1916 . This energy is emitted or radiated as identical photons , traveling as coherent wave. These photons in turn are then able to energize more atoms in a geometric progression , which further causes the emission of additional photons ,resulting in an amplification of the light energy , thus producing a laser beam.
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RADIATION :The electromagnetic spectrum is the entire collection of wave energy ranging from Gamma rays to Radio waves. All available dental laser devices have emission wavelengths of approximately (500nm-10600nm)which places then in the visible or invisible nonionizing portion of electromagnetic spectrum
The following dental laser instrument emit visible light
*Argon laser :blue wavelength 488nm
*Argon laser :blue-green wavelength 514nm
*potassium titanyl phosphate (KTP)laser : green wavelength 532nm
*low level laser:red wavelength 635nm(for photobiomoulation),655nm(caries detection)
Other dental laser emit invisible laser light in the near, middle & far infrared portion of the electromagnetic spectrum
*diode laser :various wavelength between (800-1064)
*Erbium –chromium doped yttrium-scandium –gallium - garnet (Erb,Cr:YSGG)laser 2780nm
*Er:YAG laser 2940nm
*Co2 laser 10600nm

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EMISSION MODE:

Dental laser device can emit light energy in two modalities
1-constant on
2-pulsed on & off
The pulsed laser can be further divided into gated & free-running mode . Thus three different emission modes are described as fallows
*continuous –wave mode :meaning that the beam is emitted at only one power level for as long as the operator depresses the foot switch
*gated –pulse mode :meaning that there are periodic alteration of the laser energy , similar to a plinking light . this mode is achieved by the opening & closing of a mechanical shutter in front of the beam path of continuous-wave emission (advantage)
*free- running pulsed mode: this emission is unique in that large peak energies of laser light are emitted for usually microsecond followed by a relatively long time in which the laser is off .

EFFECTS OF TISSUEON LASER:

Depending on the optical properties of the tissue, the light energy from a laser may have four different interaction with the target tissue.
*reflection :is simply the beam being redirecting off the surface , with no effect on the target tissue.
*transmission :is the transmission of the laser energy directly through the tissue with no effect on the target tissue .This effect is highly depended on the wavelength of the laser light
*scattering :scattering of the laser light ,which weaken the intended energy. Scattering of the laser beam could also cause heat transfer to the tissue adjacent to the surgical site .scattering would be useful in curing of composite resin .
*absorption: absorption of the laser energy by the intended target tissue is the usual desirable effect . The amount of energy absorbed by the tissue depend on the tissue characteristic ,such as pigmentation &water content &on the laser wavelength

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The primary &beneficial geol of laser energy is therefore absorption of the laser light by the intended biological tissue .

PHOTOBIOLOGICAL EFFECTS WHEN USING A DENTAL LASER :

*photo thermal:
Which mean the laser energy is transformed into heat. The three primary photo thermal laser –tissue effect 1-incision / excision 2-ablation / vaporization 3-hemostasis /coagulation
By varying the various laser parameters of beam size ,energy & time laser can be made to perform any of the three photothermal interactions
*photo chemical:
This effects occur when the laser is used to simulate chemical reaction , such as the curing of composite resin . The breaking of chemical bonds such as using photosensitive compounds exposed to laser energy ,can produce a single oxygen radical for disinfection of periodontal pockets & endodontic canals .
*fluorescence:
which can be used for caries detection .
* biostimulation :
It can be used in nonsurgical mode for more rapid wound healing ,pain relief , increase collagen growth & general anti-inflammatory effect .

TISSUE TEMPERATURE:

The thermal effect of laser energy on tissue primarily involves the water content of tissue & the temperature rise of the tissue
*60o
Protein begin to denature without any vaporization of the underlying tissue .This is useful in surgically removing diseased granulomatous tissue without affecting the healthy tissue
*70o -80o
Soft tissue edges can be welded back together without sutures
*100o
Vaporization of the water within the tissue occur s .This process is called ablation ,excision /incision of soft tissue commences at this temperature
*200o
Dehydrated &then burned & carbon is the end product .The heat conduction will then causes extensive collateral thermal trauma, referred to as tissue charring

Time is important factor in producing a thermal interaction if the laser is used in a pulsed mode ,the target tissue may have time to cool before the next pulse of laser energy is emitted .Longer intervals between pulses can also help avoiding the transfer of heat to the surrounding tissue
Gentle air stream or an air current from the high volume suction aids in keeping the area cooler .When using hard tissue laser a water spry helps in preventing micro fracturing of the crystalline structure & reduce the possibility of carbonization .

DUTY CYCLE (emission cycle):

Is the term used to describe the amount of on &off time . A duty cycle of 10% mean that the laser is on for 10% & off for 90% of the time . Thin , friable tissue should be treated with small duty cycle , where as thicker tissue may be treated with larger duty cycle .
LASER SAFETY :
*protective eye wear must be worn by the patient & surgical team .
*the surgical environment must have a warning sign posted , with limited access to the treatment room .
*high –volume suction must be used to evacuate plume formed by tissue ablation.
*mask must be of appropriate filtering capacity to prevent inhalation of laser plume.

ADVANTAGE OF LASER :

*ability to interacted selectively & precisely with diseased tissues .
*laser allow the clinician to reduce the amount of bacteria & other pathogens in surgical field .
*achieve good haemostasis with reduced need for sutures.
*reduce the postoperative oedema & less postoperative discomfort
*the hard tissue laser device can selectively removes diseased tooth structure because the carious lesion has much higher water content .
DISADVANTAGE OF LASER:
*high cost
*required training
*embolism caused by excessive pressure of air & water spry during laser procedures .
*inability to remove metallic restorations.
*no single wavelength will optimally treat all dental diseases .
LOW LEVEL LASER IN DENTISTRY :
The wavelength of surgical laser (Nd :YAG,Co2,erbium, diode)effect tissue not only through ablation ,coagulation & vaporization but also through stimulation of natural healing process in the cells .Other laser ,at much lower power than the surgical laser , act more as biostimulater .The instrument are generally referred to as therapeutic lasers .

THERAPEUTIC LASERS :

Therapeutic lasers are typically founded in the visible red to near visible infrared part of the electromagnetic spectrum (630-930)nm. Out put power typically range from (50-500)mill watts .The penetration depth vary ;laser in the red part of the spectrum are more superficially absorbed ,whereas (IR)lasers penetrate as much as (3-5)cm depending on wavelength & target tissue . Therapeutic lasers mainly affects cell in decreasing oxidation –reduction (redox) . A cell in low redox stage is acidic ,but after laser irradiation the cell becomes more alkaline & able to perform optimally .The most essential effect may be the increase of adenosine triphosphate .

DENTAL INDICATION :

Because LLLT can influence more than 30 condition .The most important are briefly described here .
*ANAESTHESIA
Applying LLLT to the mucosa before an injection result in a slight anaesthetic effect & improve healing of trauma which caused by the needle . Also LLLT shortened the effect of numbness .
*APHTHOUS ULCER
The healing time of the aphthous ulcer can be shortened & the immediate pain reduced by administrating (4-6)J over the lesion .
*EDEMA
The lymphatic system plays an important role in the inflammatory process & LLLT over the involved lymph node decrease edema .Start irradiation over the most distal node of the chain involved & work toward the focus of the swelling using (2-3)J per node . The permeability of the lymph vessels will be reduced & lumen size increased .

*EXTRACTION

LLLT after the extraction will reduce the inflammatory phase ,induce pain reduction ,stimulate the fibroblast in the wound periphery & stimulate osteoblast in the socket .

*HERPES SIMPLEX VIRUS

LLLT is the most efficient method of treating this infection if treated during the initial prodromal stage .The healing will only take a few days or may even disappear within hours . Large blisters can be opened with surgical laser ( erbium, Co2) to empty the fluid before LLLT is applied . patient with known recurrences can even be treated during the silent period . The actual effect is not known ,but research has confirmed that laser light enable the cell to resist viral attack for longer period providing time for immune system to react.
*INFLAMMATION
The body's inflammatory response is part of the healing process along with pain. LLLT will shorten the process . Lim et al conclude that (635nm) irradiation exiting Cox inhibiters inhibit expression of Cox & prostaglandin release .
Other study reported reduced TNF- alpha level in acute inflammation after LLLT . LLLT seems a good alternative to (NSAID) with similar results but without drug side effect .

*MUCOSAL LESION

The non malignant white lesion of the oral cavity can be treated with LLLT to reduce symptoms .
*MUCOSITIS
LLLT has a radio protective effect & should be used before therapy &then during the regimen until the wounds have disappeared . LLLT will reduce pain & xerostomia . Red laser (6-8)j/cm2 is recommended .
*PAIN
The effect of the therapeutic laser include reduction of the nerve conduction velocity , selective inhibition of A & C fibre .
*PARASTHESIA
LLLT has been shown to counteract the formation of parasthesia & even lessen the symptoms . Therefore recommended to irradiate any area where damage is suspected even intra operatively & during fallow up .
*DENTINAL HYPER SENSITIVTY
LLLT will produce an effect in the odontoblastic layer ,stimulate secondary dentin formation & reduce inflammation .
*T.M DISORDERS
TMD is multifactorial description of symptoms . In cases of arthritis the superficial head of the mandible is an easy target for any wavelength (2-3)J around the head of the condyle is sufficient but repeated irradiation is needed to reduce the inflammatory process .
(40-50) J may be needed to resolve a sever trismus . Muscles contain a large amount of haemoglobin ,the main absorber of the laser energy . the clinical effects are seen in the form of increased bite strength , range of motion & muscular relaxation .The occipital & neck muscles are often involved in the TMD syndrome &can be included in the laser treatment .
*SINUSITIS
LLLT at (3-4) J into the nostrils , or extra orally over the base of the nostril will reduce the edema & facilitate the breathing by opening the air ways.
*WOUND HEALING
In all wound LLLT is an excellent aid in reducing edema & accelerating healing . Red laser light is considered optimal for wound healing .

*ZOSTER & POSTHERPTIC NEURALGIA

Red laser is more effective in the initial phase with blister , where as IR light is preferred for post herptic neuralgia .The entire dermatome should be irradiated
In acute stage (3-4)J per point should be applied daily until improvement has been noted , then every second or third day . Treatment can stop when the vesicles have disappeared & pain is gone . In some patient the pain will remain , this is called PHN .In this patient IR laser is recommended (4-6)J per point over the involved area .



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