LASERS IN DENTISTRY Introduction Laser is an acronym, which stands for light amplification by stimulated emission of radiation. Several decades ago, the laser was a death ray, the ultimate weapon of destruction, something you would only find in a science fiction story. Then lasers were developed and actually used, among other places, in light shows. The beam sparkled, it showed pure, vibrant and intense colors. Today the laser is used in the scanners at the grocery store, in compact disc players, and as a pointer for lecturer and above all in medical and dental field. The image of the laser has changed significantly over the past several years. With dentistry in the high tech era, we are fortunate to have many technological innovations to enhance treatment, including intraoral video cameras, CAD-CAM units, RVGs and air-abrasive units. However, no instrument is more representative of the term high-tech than, the laser. Dental procedures performed today with the laser are so effective that they should set a new standard of care. This presentation intends to discuss the role of lasers in dentistry.
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History of Lasers • Approximately, the history of lasers begins similarly to much of modern physics, with Einstein. In 1917, his paper in Physikialische Zeil, “Zur Quantern Theorie der Strahlung”, was the first discussion of stimulated emission. • In 1954 Townes and Gordon built the first microwave laser or better known as ‘MASER’ which is the acronym for ‘Microwave Amplification by stimulated Emission of Radiation’ • In 1958, Townes, working with Schawlow at Bell Laboratories, published the first theoretic calculations for a visible light maser – or what was then called a LASER. • In May 1960, Theodore Maimen at Hughes Aircraft company made the first laser. He used a ruby as the laser medium. • One of the first reports of laser light interacting with tissue was from Zaret; he measured the damage caused by lasers incident upon rabbit retina and iris. • The first gas laser was developed by Javan et al in 1961. This was the first continuous laser and used helium – neon.
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• The Nobel Prize for the development of the laser was awarded to Townes, Basor and Prokhovov in 1964. • The neodymium – doped (Nd): glass laser was developed in 1961 by Snitzer. • In 1964 Nd: YAG was developed by Geusic. • The CO2 laser was invented by Patel et al in 1965. • In 1968 Polanyi developed articulating arms to deliver CO 2 laser to remote areas. • Polanyi in 1970 applied CO2 laser clinically. • In 1990 Ball suggested opthalmologic application of ruby laser.
Laser Physics Laser is a device that converts electrical or chemical energy into light energy. In contrast to ordinary light that is emitted spontaneously by excited atoms or molecules, the light emitted by laser occurs when an atom or molecule retains excess energy until it is stimulated to emit it.
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The radiation emitted by lasers including both visible and invisible light is more generally termed as electromagnetic radiation. The concept of stimulated emission of light was first proposed in 1917 by Albert Einstein. He described three processes: 1. Absorption 2. Spontaneous emission 3. Stimulated emission. Einstein considered the model of a basic atom to describe the production of laser. An atom consists of centrally placed nucleus which contains +vely charged particles known as protons, around which the negatively charged particles. i.e. electrons are revolving. When an atom is struck by a photon, there is an energy transfer causing increase in energy of the atom. This process is termed as absorption. The photon then ceases to exist, and an electron within the atom pumps to a higher energy level. This atom is thus pumped up to an excited state from the ground state. In the excited state, the atom is unstable and will soon spontaneously decay back to the ground state, releasing the stored
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energy in the form of an emitted photon. This process is called spontaneous emission. If an atom in the excited state is struck by a photon of identical energy as the photon to be emitted, the emission could be stimulated to occur earlier than would occur spontaneously. This stimulated interaction causes two photons that are identical in frequency and wavelength to leave the atom. This is a process of stimulated emission. If a collection of atoms includes, more that are pumped into the excited state that remain in the resting state, a population inversion exists. This is necessary condition for lasing. Now, the spontaneous emission of a photon by one atom will stimulate the release of a second photon in a second atom, and these two photon will trigger the release of two more photons. These four than yield eight, eight yield sixteen and so on. In a small space at the speed of light, this photon chain reaction produces a brief intense flash of monochromatic and coherent light which is termed as ‘laser’.
Properties of Laser 1. Coherent: Coherence of light means that all waves are in certain phase relationship to each other both in space and time
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2. Mono- chromatic: Characterized by radiation in which all waves are of same frequency and wavelength. 3. Collimated: That means all the emitted waves are parallel and the beam divergence is very low. This property is important for good transmission through delivery systems. 4. Excellent concentration of energy: When a calcified tissue for eg. dentin is exposed to the laser of high energy density, the beam is concentrated at a particular point without damaging the adjacent tissues even though a lot of temperature is produced ie 800-900oC. 5. Zero entropy.
Laser Design The laser consist of following components. 1. A laser medium or active medium: This can be a solid, liquid or gas. This lasing medium determines the wavelength of the light emitted from the laser and the laser is named after the medium. 2. Housing tube or optical cavity: • Made up of metal, ceramic or both. 6
• This structure encapsulates the laser medium. • Consists of two mirrors, one fully reflective and the other partially transmittive, which are located at either end of the optical cavity. 3. Some form of an external power source: This external power source excites or “pumps” the atom in the laser medium to their higher energy levels. A population inversion happens when there are more atoms in the excited state rather than a non-excited state. Atoms in the excited state spontaneously emit photons of light which bounce back and forth between the two mirrors in the laser tube, they strike other atoms, stimulating more spontaneous emission. Photons of energy of the same wavelength and frequency escape through the transmittive mirror as the laser beam. An extremely small intense beam of energy that has the ability to vaporize, coagulate, and cut can be obtained if a lens is placed in front of the beam. This lens concentrates the emitted energy and allows for focussing to a small spot size.
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Laser Light Delivery Light can be delivered by a numbered of different mechanisms. Several years ago a hand held laser meant holding a larger, several hundred pound laser usually the size of desk above a patient. Although the idea was comical at the time, it is becoming more feasible as laser technology is producing smaller and lighter weight lasers. In the more future it is probable that hand held lasers will be used routinly in dentistry. 1. Articulated arms Laser light can be delivered by articulated arms, which are very simple but elegant. Mirrors are placed at 45 o angles to tubes carrying the laser light. The tubes can rotate about the normal axis of the mirrors. This results in a tremendous amount of flexibility in the arm and in delivery of the laser light. This is typically used with CO 2 laser. The arm does have some disadvantages that include the arm counter weight and the limited ability to move in straight line. 2. Optical Fiber Laser light can be delivered by an optical fiber, which is frequently used with near infrared and visible lasers. The light is trapped 8
in the glass and propagates down through the fiber in a process called total internal reflection. Optical fibers can be very small. They can be either tenths of micros or greater than hundreds of microns in diameter. Advantages of optical fiber is that they provide easy access and transmit high intensities of light with almost no loss but have two disadvantages, one the beam is no longer collimated and coherent when emitted from the fiber which limits the focal spot size and second disadvantage is that the light is no longer coherent.
Patient to laser Another method of delivering laser light to the patient is actually to bring the patient up to the laser. Eg: Slit lamp used in the ophthalmologist gist has been doing this for quite some time. The ophthalmic laser microscope is simply a slit lamp with a laser built into it. The doctor simply images what he wants on the cornea or retina and then pushes the foot pedal to deliver laser beam to the target. Once the laser is produced, its output power may be delivered in the following modes.
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1. Continuous wave: When laser machine is set in a continuous wave mode the amplitude of the output beam is expressed in terms of watts. In this mode the laser emits radiation continuously at a constant power levels of 10 to 100 w. Eg: CO2 laser 2. Gated: The output of a continuous wave can be interrupted by a shutter that “chops� the beam into trains of short pulses. The speed of the shutter is 100 to 500ms. 3. Pulsed: Lasers can be gated or pulsed electronically. This type of gating permits the duration of the pulses to be compressed producing a corresponding increase in peak power, that is much higher than in commonly available continuous wave mode. 4. Super pulsed: The duration of pulse is one hundredth of microseconds. 5. Ultra pulsed: This mode produces an output pulse of high peak power that is maintained for a longer time and delivers more energy. 6. Q-scotched: Even shorter and more intense pulse can be obtained with this mode.
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Focussing Lasers can be used in either a focussed mode or in a defocused mode. A focussed mode is when the laser beam hits the tissue at its focal points or smallest diameter. This diameter is dependent on the size of lens used. This mode can also be referred as cut mode. Eg. While performing biopsies. The other method is the defocused mode. By defocusing the laser beam or moving the focal spot away from the tissue plane, this beam size that hits the tissue has a greater diameter, thus causing a wider area of tissue to be vaporized. However, laser intensity / power density is reduced. This method is also known as ablation mode. Eg. In Frenectomies. In removal of inflammatory papillary hyperplasias.
Contact and Non contact modes In contact mode, the fiber tip is placed in contact with the tissue. The charred tissue formed on the fiber tip or on the tissue outline increases the absorption of laser energy and resultant tissue effects. Char can be eliminated with a water spray and then slightly more energy will be required to provide time efficient results. Advantage is that there is control feed back for the operator.
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Non contact mode: Fiber tip is placed away from the target tissue. The clinician operates with visual control with the aid of an aiming beam or by observing the tissue effect being created. So generally laser can be classified as Dental Lasers Those work in both Solely in the non contacted
Contact & focussed
contact mode
Non &
defocused Eg: CO2
Eg: Agon, HO : YAG,
Nd:YAG
Laser Types I. Based on wavelength. 1. Soft lasers 2. Hard lasers II.
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Based on the type of active / lasing medium used 1. ArF excimer 2. KrF excimer 3. XeCl excimer 4. Argon ion 5. KTP 6. Ruby 7. Nd: YAG 8. HO: YAG 9. YSGG 10. Er: YAG 11. CO2
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I. 1. Soft Lasers: With a wave length around 632mm Soft lasers are lower power lasers. Eg: He Ne, Gallium arsenide laser. These are employed to relieve pain and promote healing eg. In Apthous ulcers. 2. Hard lasers: Lasers with well known laser systems for possible surgical application are called as hard lasers. Eg: CO2, Nd: YAG, Argon, Er:YAG etc.
CO2 Lasers The CO2 laser first developed by Palet et al in 1964 is a gas laser and has a wavelength of 10,600 nanometers or 10.6 ¾ deep in the infrared range of the electromagnetic opectrum. • CO2 lasers have an affinity for wet tissues regardless of tissue color.
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• The laser energy weakens rapidly in most tissues because it is absorbed by water. Because of the water absorption, the CO 2 laser generates a lot of heat, which readily carbonizes tissues. Since this carbonized or charred layer acts as a biological dressing, it should not be removed. • They are highly absorbed in oral mucosa, which is more than 90% water, although their penetration depth is only about 0.2 to 0.1mm. There is no scattering, reflection, or transmission in oral mucosa. Hence, what you see is what you get. • CO2 lasers reflect off mirrors, allowing access to difficult areas. Unfortunately, they also reflect off dental instruments, making accidental reflection to non-target tissue a concern. • CO2 lasers cannot be delivered fiber optically Advances in articulated arms and hollow wave guide technologies, now provide easy access to all areas of the mouth.
•
Regardless of the delivery method used, all CO 2 lasers work in a non-contact mode.
• Of all the lasers for oral use, CO2 is the fastest in removing tissue.
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• As CO2 lasers are invisible, an aiming helium – neon (He Ne) beam must be used in conjunction with this laser. Nd: YAG Laser: Here a crystal of Yttrium – aluminum – garnet is doped with neodymium. Nd: YAG laser, has wavelength of 1,064 nm (0.106 µ) placing it in the near infrared range of the magnetic spectrum. • It is not well absorbed by water but are attracted to pigmented tissue. Eg: hemoglobin and melanin. Therefore various degrees of optical scattering and penetration to the tissue, minimal absorption and no reflection. • Nd: YAG lasers work either by a contact or non-contact mode. When working on tissue, however, the contact mode in highly recommended. • The Nd: YAG wavelength is delivered fiber optically and many sizes of contact fibers are available. Carbonized tissue remains often build of on the tip of the contact fiber, creating a ‘hot tip’. This increased temperature enhances the effect of the Nd:YAG laser, and it is not necessary to rinse the build up away. Special tips, the coated sapphire tip, can be used to limit lateral thermal damage. A heliumneon-aiming beam is generally used with Nd: YAG wavelength.
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• Penetration depth is ~ 2 to 4m, and can be varied by upto 0.5-4mm in oral tissues by various methods. • A black enhancer can be used to speed the action. • Most dental Nd: YAG lasers work in a pulsed mode. At higher powers and pulsing, a super heated gas called a plasma can form on the tissue surface. It is the plasma that can be responsible for the effects of either coagulation, vaporization or cutting. If not cooled (e.g. by running a water stream down the fiber) the plasma can cause damage to the surrounding tissues. • Suffer from dragability • The Nd:YAG beam is readily absorbed by amalgam, titanium and non-precious metals, requiring careful operation in the presence of these dental materials.
Argon Lasers • Argon lasers are those lasers in the blue-green visible spectrum. • They operate at 488nm or 514.5nm, are gas like CO 2 lasers and are easily delivered fiber optically like Nd:YAG.
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• Argon lasers have an affinity for darker colored tissues and also a high affinity for hemoglobin, making them excellent coagulators. It is not absorbed well by hard tissue, and no particular care is needed to protect the teeth during surgery. • In oral tissues there is no reflection, some absorption and some scattering and transmission. • Argon lasers work both in the contact and non contact mode • Like, Nd: YAG lasers, at low powers argon lasers suffer from ‘dragability’
and need sweeping motion to avoid tissue from
accumulating on the tip. • Enhances are not needed with Argon lasers. • Argon lasers also have the ability to cure composite resin, a feature shared by none of the other lasers. • The blue wavelength of 488 nm is used mainly for composite curing, while the green wavelength of 510nm is mainly for soft tissue procedures and coagulation.
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Er: YAG laser • Have a wavelength of 2.94 µm. • A number of researchers have demonstrated the Er: YAG lasers ability to cut, or ablate, dental hard tissue effectively and efficiently. The Er: YAG laser is absorbed by water and hydroxyapatite, which particularly accounts for its efficiency in cutting enamel and dentin. • Pulpal response to cavity preparation with an Er: YAG laser was minimal, reversible and comparable with pulpal response created by a high-speed drill.
Ho: YAG laser [Holmium YAG lasers] • Has a wavelength of 2,100 nm and is a crystal • Delivered through a fiber optic carrier. • A He-Ne laser is used as an aiming light • Dragability is less compared to Nd: YAG and argon lasers • Like Nd: YAG, can be used in both the contact and non-contact modes and are pulsed lasers.
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• Ho: YAG laser has an affinity for white tissue and has ability to pass through water and acts as a good coagulator.
Laser interaction with biologic tissues Light can interact with tissues in four different mechanisms 1. Reflected 2. Scattered 3. Absorbed 4. Transmitted Reflection:
Reflected light bounces off the tissue surface and is
directed outward. Energy dissipates after reflection, so that there is little danger of damage to other parts of mouth and it limits the amount of energy that enters the tissue. Scattering: occurs when the light energy bounces from molecule to molecule within the tissue. It distributes the energy over a larger volume of tissue, dissipating the thermal effects. Absorption: occurs after a characteristic amount of scattering and is responsible for the thermal effects within the tissue. It converts light energy to heat energy The absorption properties of tissue and cells
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depends on the type and amount of absorbing pigments or chromophores. Eg. Hemoglobin, water, Melanin, Cytochromes etc. Transmission: Light can also travel beyond a given tissue boundary. This is called transmission. Transmission irradiates the surrounding tissue and must be quantified. Its effects should be considered before laser treatment can be justified.
Tissue effects on laser irradiation When radiant energy is absorbed by tissue 4 basic types of interactions occurs.
Laser effects on Dental Hard Tissues The absorption and transmission of laser light in human teeth is mainly dependent on the wavelength of the laser light. For eg. – Ultraviolet laser light is well absorbed by teeth. In water and in hydroxyapatite, there is a very low absorption at a wavelength of 2µm in comparison to high absorption of laser energy at 3µm and 10µm. The laser effects can be grouped as:
1. Thermal effects: 21
The best known laser effect in dentistry is the thermal vaporization of tissue by absorbing laser light i.e. the laser energy is converted into thermal energy or heat that destroys the tissues. From 45o – 60 o
denaturation occurs
>60 o
coagulation and necrosis
At 100 o C
water inside tissue vaporizes
>300 o C
carbonization and later phyrolysis
with
vaporization of bulky
tissues.
2. Mechanical effects: High energetic and short pulsed laser light can lead to a fast heating of the dental tissues in a very small area. The energy dissipates explosively in a volume expansion that may be accompanied by fast shock waves. These shock waves lead to mechanical damage of the irradiated tissue.
3. Chemical effects: Here molecules can be associated directly with laser light of high photon energies.
Histologic Results: 22
With continuous wave and pulsed CO2 lasers. When continuous wave and pulsed CO2 lasers were used, structural changes and damage in dental hard tissue were reported. Microcracks and zones of necrosis and carbonization are unavoidable. Because of drying effects, the microhardnes of dentin increases. The crystalline structure of hydroxyapatite changes and a transformation of apatite to tricalcium phosphate takes place.
Nd: YAG Lasers: The Nd: YAG laser shows low absorption in water as well as in hydroxyapatite. Therefore the laser power diffuses deeply through the enamel and dentin and finally heats the pulp. In dentin, at the laser impact, zones of debris and carbonization are surrounded by an area of necrosis can be seen. Microcracks appear when energies above a threshold of 100mj / pulse are used. But the appearance and the extent of the side effects are not predictable.
Er: YAG Laser: In dentin, shallow cavities were surrounded by a zone of necrosis of 1-3Âľm thickness when water-cooling systems were used. In deeper
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cavities areas of carbonization and microcracks were observed. Ablating enamel always cracked and deep zones of debris appeared.
Excimer Lasers: No pathologic changes in the tissue layers adjacent to the dissected areas were found after the ablation. The ablation effects of dental hard tissues are predictable. Compared to conventional diamond and burs, however, the effectiveness is low. Thermal side effects increase as photon energies of excimer lasers decrease.
Laser Effects On Dental Pulp: Recent histologic evidence suggests that a normal odontoblasts layer, stroma and viable epithelial root sheath can be retained following laser radiation provided damage threshold energy densities are not exceeded. If pulp temperatures are raised beyond the 5째C level, research has shown that the odontoblasts layer may not be present. Characteristics
of
the
dentinogenesis
process
related
to
root
development, predentin and reparative dentin formation, dentinal bridge presence, typically reflect the overall trauma that has been induced in the odontoblasts. 24
Application of Lasers in Dentistry: Application
Possible Laser Types
Basic research Laser tissue interaction
All types
Technical development of applications
All types
of lasers in dentistry Measurement and diagnosis Holography
He Ne, diodes
Laser Doppler fowmetry
He Ne, diodes
Spectroscopy (caries diagnosis)
Various types
Oral and Maxillofacial Surgery Cutting and Coagulation
CO2, Nd: YAG, Ar, dye
Photodynamic therapy
Dye, Au-Cu vapour
Conservative dentistry Preventive dentistry (fissure sealing)
CO2, Nd:YAG, ruby
Caries treatment
CO2, Nd:YAG, Er: YAG, Excimer
Composite resin light Curing
Ar, dye, HeCd
Tooth surface conditioning
Excimer, CO2, Nd:YAG, Er:YAG
Endodontics Root canal treatment
Nd: YAG, CO2, Excimer
Apicoectomy
CO2, Nd:YAG
Periodontics
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Laser sealing of affected root surfaces
CO2, excimer
Excision of gingival soft tissues
CO2
Analgesic effect and bio-stimulation Stimulation of wound healing
He Ne, diodes
Low power laser radiation with analgesic
Nd: YAG
Effects
Other applications: Laser processing of dental materials • Welding of dental alloys Cobalt – chrome – molybdinum Nickel – chrome – aluminum Silver Palladium Titanium alloys • Welding of ceramic materials Still under investigation
Advantages of laser welding: 1. High bond strength and corrosion resistance since laser welding is a form of sweating that does not use solders of different materials. 2. Reduced oxidation when argon gas is used for welding.
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3. Decreased thermal influence and greater precision in processing than with soldering or other techniques.
Laser in Restorative Dentistry and Endodontics Lasers find numerous applications in restorative dentistry and endodontics ranging from prevention of caries to antibacterial action in root canals.
1. Prevention of carries: •
Yamamoto and Oaya used as YAG laser at energy densities of 10 to 20 J/cm³ and demonstrated that the lased enamel
surface
was
more
resistant
to
in
vitro
demineralization than non lased enamel. •
Stern and Sognnaes demonstrated in vivo that enamel subjected to 10 to 15 J/cm² showed a greater resistance to dental caries than the controls.
•
Stern concluded that energy levels below 250 J/cm² did not permanently alter the pulp but necrosis could occur when energy level, reached 1800 J/cm² or higher.
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•
Lobene and Collogues in their experiment with CO2 laser, observed that CO2 irradiation to tooth enamel caused small amounts of hydroxyapatite to be converted to more insoluble calcium orthophosphate apatite. This paved the way for widespread use laser in prevention of caries.
•
Lasers can be used for removal of incipient caries, sealing pits and fissures. The CO2 and Nd:YAG lasers can remove the organic and inorganic debris found in pits and fissures. Following the
removal a synthetic
hydorxyapatite
compound is attached to enamel using the laser. Power densities used are low and it did not alter the health of pulp tissue. •
In 1985 Terry Myers used Nd:YAG laser for debrident of incipient caries.
•
When a topical fluoride treatment was performed after argon laser conditioning of enamel, an even more dramatic reduction in enamel acid demineralization was observed.
2. Diagnosis: Lasers can be used to detect incipient carious lesion which cannot be diagnosed clinically and radiographically.
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Transilliumination using lasers is used for this purpose. The lesion appears as a distinct dark red area easily differentiated from the rest of the sound tooth structure. Decalcified area appears as a dull, opaque, orange color. Also enamel fractures and recurrent decay around metallic and resin restoration can be diagnosed. 3. Laser Doppler Flowmetry: Pulpal blood flow can be assessed using laser doppler flowmentry. He Ne and diodes can be used.
Cavity preparation: The use of lasers for cavity preparation has been under scrutiny for 20yrs as many investigators found that pulpal necrosis would occur with use of lasers. The reasons for necrosis are: 1. The heat produced 2. Total power output (J/cm²) The search for laser that can be used to cut hard tissues begun in 1964 by Dr. Leo Goldman who used laser on his brother Bernard’s teeth. The subsequent search included many laser wavelengths such as
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CO2 but its disadvantages include cracking with flaking of enamel surface. Nd:YAG 10 J/cm² has shown to inhibit incipient carious lesions but at higher densities it causes irreversible pulpal damage. Other lasers such as Ho: YAG, ArF, Nd:YLF and Er: YAG have been investigated. Er: YAG at the wavelength of 2.94µm has shown most promising results. A number of researchers have demonstrated the Er:YAG laser’s ability to cut or ablate dental hard tissues effectively and efficiently. The Er:YAG laser is absorbed by water and hydroxyapatite, which partially accounts for its efficiency in cutting enamel and dentin. • It has generally been assumed that if pulpal temperature rises less than 5.5°C, the procedure would be safe and would not cause irreversible histologic damage to the pulpal tissues. Researchers who conducted in vivo animal studies reported that the pulpal response to cavity preparation with an Er:YAG laser was minimal, reversible and comparable with the pulpal response created by a high speed drill.
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• The temperature rise with these type of laser was less than 3°C. • Moreover, a water coolent can be used which not only cools the tooth during ablation but also increase the efficiency of ablation. • In a study by Timothy Smith, patients reported little or no pain during the treatment with dental laser. With many people reporting fear of pain as then chief reason for not seeking dental care, lasers may offer a more acceptable treatment technique.
Etching the Enamel: The laser absorbed by enamel causes the enamel surface to be heated to a high temperature, generating micro cracks in the surface and this aids in enhancing adhesion of composite to the tooth structure. The surfaces appear similar to acid etched surfaces. The Nd:YAG laser is not readily absorbed but absorption can be increased by using a dye on enamel surface.
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Curing of Composites and GIC: Currently, photoactivated dental resins employ a diketone, such as camphoroquinone, and a tertiary amine reducing agent to initiate polymerization. This photoinitiator system is sensitive to light in blue region of the visible spectrum with broad peak activity in the 480nm region. The argon laser’s monochromatic wavelengths of 488nm and 514.5nm have been shown to be effective in the initiation of polymerization of dental resins.
Advantages: • Enhanced physical properties like increased tensile strength
due
to
enhanced
or
more
thorough
polymerization. • Improved adhesion • Reduced microleakage • Reduced exposure time. Argon laser polymerization requires a 10sec cure cycle while visible light activation usually takes approximately 40sec.
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• The polymerization of light activated bases and or liners can also be accomplished with the argon laser. Advantages : A wide verity of fiber sizes provides access to all location of cavity preparation.
Pit and Fissure Sealant Therapy: Advantages are similar to those offered for curing composite resins.
Desensitization: Lasers are effective tool in the treatment of hypersensitivity. Mode of action is by blocking the dentinal tubules resulting in change in hydraulic conductance.
Bleaching: Lasers also find use in bleaching of vital and non-vital teeth.
Treatment of fractured teeth: Lasers have the potential to fuse the segments of fractured teeth.
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Pulpotomy: • Recent development
Removal of Old restoration: • Composites and cements can be ablated. • Gold crowns and cast fillings cannot be removal as laser beam is reflected. • Ceramics cannot be ablated.
In endodontics: • For root canal preparation. 1. For Root Canal Preparation: Based on the SEM investigation of prepared teeth, root canals appeared to be free of soft tissue and debris. There was no smear layer detectable and there were no cases of straightening or over instrumentation of the canals. The dentinal tubules appeared to be open. These were no detectable thermal or mechanical alteration to the root canal walls. There was a significant reduction in bacterial growth (disinfection). 2. For sterilization of Files & Reamers
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3. Apicoectomies: • for soft tissue procedures • for curing the retrograde filling materials.
Lasers in Surgical Systems: Lasers are an alternative to conventional surgical systems. Stated best by Apfelberg in 1987, lasers are a “new and different scalpel” (optical knife, light scalpel).
Advantages: • Easy access to the anatomic site • Possess inherent hemostatic properties. • Capable of ablation of lesions in proximity to normal structures, with minimal damage to normal structures. • Reduced pain during surgical procedures and less post operative pain. • Enhanced healing
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• Bactericidal and virucidal effects of laser result in decreased rates of wound infection.
Certain proven uses for dental soft tissue procedures using lasers are: 1. Frenectomy Maxillary midline Lingual (Tongue tie) 2. Incisional and exasional biopsies. 3. Removal of benign lesions
Fibrous Papillous Pyogenic granuloma Lichen Planus Erosive lichen planus Nicotinic stomatites Verruca vulgaris Inflammatory papillary hyperplasia
Epuli 4. Gingivoplasty
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5. Soft tissue tuberosity reduction. 6. Soft tissue distal wedge procedure. 7. Gingivectomy A. Removal of hyperplasias 1. Dilantin etc 2. Idopathic B. Crown trough. 8. Aphthous ulcer 9. Operculectomy 10. Removal of hyperkeratotic lesions 11. Removal of malignant lesions 12. Soft tissue crown lengthening 13. Coagulation. A. Graft donor sites. B. Seepage around crown preparation. 14. Vestibuloplasty 15. Removal of granulation tissue – periodontal clean out 16. Removal of vascular lesions A. Hemangioms B. Pyogenic granuloma
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17. Removal of lesion in patients with hemorrhagic disorders. A. Hemophelia etc. 18. Implants – Stage II – at the time of recovery. A. Soft tissue removal
Bio-stimulation and Photodynamic Therapy: Photodynamic therapy is an experimental cancer treatment that is based on a cytotoxic photochemical reaction. This reaction requires molecular oxygen, the photoactive drug dihematoporphyrin ether, a hematophorphyrin derivative and intense light, which is typically delivered by a laser. Dihematoporphyrin which is relatively retained in malignant tissue after several days, is given intravenously to a patient. Laser light at a wavelength corresponding to the absorption peak of the drug is used to activate the drug to an excited state. The drug then reacts with molecular oxygen to produce singlet oxygen, a highly reactive free radical which ultimately leads to tissue necrosis.
Laser Hazards and Laser Safety: The subject of dental laser safety is broad in scope, including not only an awareness of the potential risks and hazards related to how
38
lasers are used, but also a recognition of existing standards of care and a thorough understanding of safety control measures. Laser Hazard Class for according to ANSI and OSHA Standards: Class I
- Low powered lasers that are safe to view
Class IIa
- Low powered visible lasers that are hazards only when viewed directly for longer than 1000 sec.
Class II
- Low powered visible lasers that are hazardous when viewed for longer than 0.25 sec.
Class IIIa
- Medium powered lasers or systems that are normally not hazardous if viewed for less than 0.25 sec without magnifying optics.
Class IIIb
- Medium powered lasers (0.5w max) that can be hazardous if viewed directly.
Class IV
- High powered lasers (>0.5W) that produce ocular, skin and fire hazards.
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The types of hazards can be grouped as follows: 1. Ocular injury 2. Tissue damage 3. Respiratory hazards 4. Fire and explosion 5. Electrical shock
1. Ocular Injury: Potential injury to the eye can occur either by direct emission from the laser or by reflection from a specular (mirror like) surface or high polished, convex curvatured instruments. Damage can manifested as injury to sclera, cornea, retina and aqueous humor and also as cataract formation. The use of carbonized and non-reflective instruments has been recommended.
2. Tissue Hazards: Laser induced damage to skin and others non target tissues can result from the thermal interaction of radiant energy with tissue proteins. Temperature elevation of 21째C above normal body temp (37째C) can produce cell destruction by denaturation of cellular enzymes and structural proteins. Tissue damage can also occur due to cumulative
40
effects of radiant exposure. Although there have been no reports of laser induced caroinogenesis to date, the potential for mutagenic changes, possibly by the direct alteration of cellular DNA through breathing of molecular bonds, has been questioned. The terms photodisruption and photoplasmolysis have been applied to describe these type of tissue damage.
3. Respiratory: Another class of hazards involves the potential inhalation of airborne biohazardous materials that may be released as a result of the surgical application of lasers. Toxic gases and chemical used in lasers are also responsible to some extent. During ablation or incision of oral soft tissue, cellular products are vaporized due to the rapid heating of the liquid component in the tissue. In the process, extremely small fragments of carbonized, partially carbonized, and relatively intact tissue elements are violently projected into the area, creating airborne contaminants that are observed clinically as smoke or what is commonly called the ‘laser plume’. Standard surgical masks are able to filter out particles down to 5Âľm in size.
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Particle from laser plume however may be as small as 0.3Âľm in diameters. Therefore, evacuation of laser plume is always indicated.
4. Fire and Explosion Flammable solids, liquids and gases used within the clinical setting can be easily ignited if exposed to the laser beam. The use of flame-resistant
materials
and
other
precautions
therefore
is
recommended. Flammable materials found in dental treatment areas.
Solids
Liquids
Gases
Clothing
Ethanol
Oxygen
Paper products
Nitrous oxide
Plastics Waxes and resins
Acetone
General anesthetics
Methylmethacrylate
Aromatic vapors
Solvents
5. Electrical Hazards: These can be: -
Electrical shock hazards
-
Electrical fire or explosion hazards
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Summary of laser safely control measures recommended by ANSI Engineering controls: -
Protective housing
-
Interlocks
-
Beam enclosures
-
Shutters
-
Service panels
-
Equipment tables
-
Warning systems
-
Key switch
Administrative controls: -
Laser safety officer
-
Standard operating procedures
-
Output limitations
-
Training and education
-
Medical surveillance
Personal protective equipment: -
Eye wear
-
Clothing
-
Screens and curtains
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Special controls: -
Fire and explosion
-
Repair and maintenance
Conclusion: Laser has become a ray of hope in dentistry. When used efficaciously and ethically, lasers are an exceptional modality of treatment for many clinical conditions that dentists treat on daily basis. But laser has never been the “magic wand� that many people have hoped for. It has got its own limitations. However, the futures of dental laser is bright with some of the newest ongoing researches.
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