Laser is the acronym for Light Amplification by Stimulated Emission of Radiation.
INTRODUCTION TO LASERS
Lasers are devices capable of emitting a beam of coherent and monochromatic light, concentrated in a rectilinear and collimated beam having an extremely high luminance (brightness). Coherence, monochromaticity and high luminance are the basis of the vast number of possible applications that laser equipment has had in the past and continues to have in different fields: cutting, engraving and welding of metals; measuring distances, transmitting information through optical fibres covering very long distances; medical and surgical treatments, etc.
Characteristics of laser radiation
- Directionality and collimation: the laser beam propagates in one direction with a small divergence beam, called laser beam width.
- Monochromaticity: laser light is characterised by a single wavelength (peculiar to the type of generating device), unlike the emissions of natural electromagnetic waves which are constituted by a set of wavelengths: in practice, when natural electromagnetic waves (e.g. visible light) goes through an optical prism, they are decomposed into an iris of different wavelengths (in this case colours), whereas when the laser beam goes through an optical prism, a single wavelength is returned (the one that characterized the initial laser light).
- Luminance: in lasers, the energy output is incomparably higher compared to that of traditional sources.
- Coherence: the energy is transmitted in a single wavelength (monochromaticity), with perfect phase concordance, whereas in spontaneous emissions each photon is emitted randomly with respect to the others. In laser emissions the phase is maintained over time and space.
- Pulse: laser radiation can be constituted by a constant light beam or modulated in extremely short wave packets. Currently, pulses in the order of femtoseconds have been generated (the time required for an electron to move from one atom to another). In the medical field, all types of emissions are used: continuous, pulsed and super-pulsed.
Laser classification
Lasers are classified according to their power:
- Class 1 (<0.04 mW): completely harmless.
- Class 2 (<1 mW): these do not normally damage the eyesight (e.g. laser printers).
- Class 3a (<5 mW): these can damage the eyesight if viewed through optical devices capable of producing beam concentration (e.g. laser pointers).
- Class 3b (5–500 mW): these are always harmful to the unprotected eyes and can also be dangerous to the skin; the reflections are also dangerous.
- Class 4 (> 500 mW): exposure is dangerous, even when the beam is diffused (industrial lasers, medical lasers, etc.).
Laser use in medicine
Since 1962 the use of lasers has been proposed for the photocoagulation of retinopathies; a CO2 laser was later developed (J.A. Weichmann and F.M. Johnsonn). Research then continued and many types of lasers were conceived and widely used for medical purposes.
The wavelength (which often falls outside the range of visible light) determines the range of use of the laser device.
Fig. 1. Working frequencies of lasers used in medicine
The therapeutic response depends in a complex manner on the choice of the wavelength, on the duration of irradiation and on the power of the laser. Different combinations of these parameters are used to transform light energy into mechanical, thermal or chemical energy. In general, the mechanical effects are produced by the use of short pulses (in the order of nanoseconds) and high levels of energy.
Elements making up a laser system
1. Active material: a population of atoms at suitable energy levels, which can be in either a solid, gaseous, liquid or semiconductor state.
2. Pumping action: it serves to keep the atoms in an energy state in order to obtain the emission of photons.
3. Resonant cavity: contains the active medium and is constituted by two mirrors placed opposite one another so that the radiation goes repeatedly through the active medium, thereby amplifying the action of the latter.
4. Cooling system.
Various types of lasers for medical purposes are present on the market, based on the active material:
- Solid-state lasers - glass bars or pure single crystals doped with atoms of active elements. In these lasers, the pumping is obtained by means of broad-spectrum lamps. The power output may be very high, especially with the pulsed mode, but the yields rarely exceed 10%. The most common solid-state lasers are:
- Rubidium
- Neodymium - Yag
- Erbium - YAG
- ErCr - YSGG
- Liquid-state lasers - the support of the active elements is constituted by a liquid (water, alcohol, etc.) in which a dye (curarine, xanthene, etc.) is dissolved as the active medium. The pumping is of the optical type (lamp or laser). These are truly versatile lasers, because, by acting on the dilution of the active medium, it is possible to obtain a great variety of wavelengths; on the other hand, the efficiency of these devices does not reach 0.1%.
- Gas-state lasers - the active medium may be a single gas or a mixture and the pumping action is obtained by means of electrical discharges. Gas lasers may operate in continuity for long periods of time. The most common gas lasers are:
- He-Ne (Helium-Neon with wavelengths of 3,390, 1,152 and 632.8 nm)
- CO2–Ar (Carbon dioxide - Argon)
- CO2
- Nitrogen-Helium
- Semiconductor or diode lasers - the active medium is made up of layers of semiconductor materials of different types; the most used are those in gallium arsenide doped with aluminium. These lasers have high yields (up to 65%) and are compact. However, they do not produce high powers; the latter feature excludes them from industrial use, but not from the medical use, for which the power output is more than enough.
The purchase cost, the compactness of the equipment, the versatility and relative user-friendliness point in favour of the use of diode lasers over other models. Therefore, also the discussion that follows will refer mainly to this type of equipment.
The laser beams used in odontostomatology are invisible, due to their frequency, so it is necessary to have a light-pointing signal. The peculiarity of the beam produced by the diodes is that it is absorbed by dark substances (pigmented) and therefore, within the animal, by haemoglobin and melanin, thus enabling a good haemostatic effect. The handpieces can vary according to the different applications: surgery and therapy (biostimulation). The transformation of light energy produced by the laser into thermal power is at the base of the effects of the interaction between laser beam and biological tissue. The greater the increase in temperature, the quicker the vaporisation effect. The energy absorbed is dependent on the energy emitted, and therefore in part on the wavelength of the operating laser.
It is important to clarify that the laser should not entirely replace or radically change the work method but must instead be used alongside and in support of traditional instruments.
Schematically, there are four main interactions with organic matter:
1. Absorption: this is the predominant effect; the beam propagates through the tissue and interacts with atoms and molecules. According to the energy output the laser beam can cut, vaporise or coagulate tissue.
2. Reflection: part of the laser light is always reflected after impact with the tissue, though with negligible intensity. In all cases appropriate protective goggles must be worn.
3. Transmission: part of the transmitted energy is absorbed by the underlying tissues.
4. Dissemination: a small part of the absorbed energy is spread in new directions, through the tissue, generating a therapeutic and decontaminating effect.
Four kinds of interactions exist between laser light and tissue:
1. Photochemical,
2. Photothermal,
3. Photomechanical
4. Photoablation.
- In the medical field the most relevant kind is the photothermal interaction; during absorption heat develops, with different consequences based on the temperatures reached:
- T = 42°-60° C - denaturation of proteins
- T = 50°-60° C - coagulation and vacuolation
- T = 100° C - evaporation
- T => 100° C - carbonisation
Laser light conduction systems
Once the laser radiation has been generated, it must then be conveyed to its point of use through a conduction system:
- Articulated arms with prisms and/or mirrors
- Hollow fibres
- Optical fibres (diode and Nd-YAG laser)
The optical fibres used in laser diodes have diameters between 200 and 600 μm; the thinner the fibre, the greater the energy per surface unit (fluence), but at the same time the fibre becomes more fragile.
- The most commonly used diameters are:200 μm - endodontics, periodontics and, rarely, small surgeries.
- 300-400 μm - surgery of the oral cavity, parenchyma, etc.
- 600 μm - (low-emission of energy) biostimulation, guided polymerisation of composite resins, teeth whitening.
Practical use of a diode laser
The desired results can be obtained only by closely following a set of practical rules:
- Control of the spot - the guiding light (red or green LEDs) makes it possible to control the uniformity and circular shape of the spot; when these characteristics are met, the tip of the fibre is not dispersing energy by sending it into unwanted directions. When the spot is not regular, a small portion of the fibre is to be cut (one millimetre or less) using the appropriate tools (scissors with ceramic inserts and dedicated cutters with wire strippers). Once the fibre has been cut, it is considered as non-activated.
- Activation - optical fibres are activated by making them work for a second or more on a surface congruent with the working wavelength (e.g. on a thin blue or black cardboard). As already mentioned, the deactivation of the fibre is obtained by cutting the end portion of the fibre itself with the appropriate instruments.
- Cleaning – with use, the end portion of the optical fibre can become dirty and hence cleaning with a sterile gauze soaked in saline solution or H2O2 becomes necessary.
- Control of instruments - in addition to exercising extreme care in order to avoid stressing the optical fibre (stretching, bending at acute angles, etc.), it is also advisable to check the cleanliness of the laser beam output terminal from the instrument panel and that of the optical fibre.
Safety regulations
Lasers for medical use are equipped with the following safety systems:
- Activation key - this allows the turning on of the device and must be safely kept by specialised staff.
- Emergency stop push button - usually red; when pressed, it stops the laser radiation emission.
- Danger sign - to be displayed outside the laser room. The sign must state the laser class, laser type and the rule requiring that everyone wear personal protective equipment. (Legend: danger; visible and/or invisible laser radiation; avoid eye or skin exposure to direct or scattered radiation; laser protective eyewear required; diode laser; class IV laser product; lock the door during use)
- Interlock – This is a socket to be connected to the opening of the door of the room in which the laser is used: when the door is opened, the laser radiation emission stops.
- Protective eyewear - all the people in the room in which a class 3a, 3b or 4 laser is used must wear protective goggles. No other pets should be present, and the patient's eyes must be closed with patches or shielded. There are different types of protective goggles:
- Designed for the main operator (surgeon); they are more expensive and heavier, but they permit a clear view as they allow the contemporary use of eyeglasses.
- Designed for secondary operators (assistants, anaesthesiologists, etc.); they are less expensive and lighter; vision is affected by the colour of the lens and they also allow the contemporary use of eyeglasses.
- These goggles do not allow the contemporary use of eyeglasses.
Biological effects obtainable with a diode laser
- Coagulation
- Antibacterial activity
- Stimulation of fibroblast activity
- Accelerated elimination of intermediate metabolites
- Stimulation of cellular and phagocytic activity
- Increased production of mitochondrial ATP
- Increase in the rate of absorption of interstitial fluidsIncreased production of endogenous cortisol
- Acceleration of tissue replacement
The advantages in terms of quality, comfort and efficiency of laser-assisted treatments can be summarized as follows:
Clinical bebenefits of the laser for patients
- Reduction or absence of anaesthetics
- Haemostasis
- Absence of swelling
- Major decontamination
- Reduced healing time
- Reduction or absence of post-operative drugs
Professional benefits of using a laser
- Superior quality of the intervention
- Cutting precision (better view of the cut)
- Wider range of treatments
- Easy and safe to use
- Professionalism of the veterinarian
- Satisfaction of the pet owner
USE OF LASER IN VETERINARY ODONTOSTOMATOLOGY
In veterinary odontostomatology the diode laser is suitable for numerous procedures, among which:
- Periodontitis
- Treatment of gingival pockets
- Adjuvant in the treatment of chronic stomatitis
- Gum grafting: for gum incision (gingivectomy and gingivoplasty)
- Frenulectomy and papillectomy
- Creating flaps
- Biopsies
- Haemostasis
- Surgery of the oral cavity
- Surgery for cancer of the oral cavity
- Incision and drainage of abscesses
- Sterilization of draining tracts
- Root canal decontamination
- Direct capping of dental pulp
- Teeth whitening
Other applications of lasers in medicine
- Cancer surgery
- Surgery performed in orifices (nose, ear, throat, etc.)
- Treatment of viral papillomatosis
- Surgery of the parenchyma
- Endoscopy
- Adjuvant in the treatment of perineal fistulae
Treatment of gingival pockets
After a thorough subgingival curettage and irrigation with iodopovidone, a line grid pattern is then performed using a 200 or 320 μm fibre, depending on the pocket width, at a power output of 2.5 Watts in pulsed mode (10 ms on / 10 ms off), for a period of time of about one second per mm of periodontal pocket. An accurate cleaning of the optical fibre is necessary after the treatment of each pocket.
Treatment of chronic stomatitis
Feline chronic gingivostomatitis (FCGS) is often resistant to systemic medical treatments (administration of corticosteroids, antibiotics, thalidomide, etc.), to local treatments (application of chlorhexidine or other products) and to surgical interventions (targeted dental extractions, dental root extractions, etc.). Good results have been achieved in a certain number of subjects with three laser biostimulation treatments performed at a distance of 15 days from one another, with a 600 μm defocused contact fibre, with a slow circular movement, with a power output of 2 Watts applied for 30-90 seconds to an area of 1 cm2. At the end of these cycles the subjects experienced increased appetite, weight gain and less manifest pain. However, the small number of trials and the lack of an appropriate experimental protocol does not allow a definitive judgement of this application.
Creation of flaps
The creation of flaps is facilitated by a laser-assisted procedure due to minimal or absent bleeding and to the limited intraoperative and postoperative pain. A mixed technique can also be used, first making a scalpel blade incision in the more superficial tissues and then continuing with a laser incision in the deeper tissues.
Biopsies
The execution of laser biopsies, from both the oral cavity and from other sites, offers the following advantages:
- Minimal or absent bleeding,
- Negligible intraoperative pain
- Negligible postoperative pain
On the other hand, the execution is slower compared to the use of a scalpel blade and the biopsy is limited to the soft tissues; moreover, a wider margin than usual is indicated in order not to interfere with the pathologist's evaluation of the tissues (charred edges).
Laser-assisted surgery and cancer surgery of the oral cavity
Laser-assisted procedures cause limited or absent bleeding, as well as less intraoperative and postoperative pain. A mixed technique can also be adopted: a first scalpel blade incision in the more superficial tissues is then followed by a laser incision in the deeper soft tissues.
The hard tissues can be treated with the aid of piezoelectric surgery. The combination of laser-assisted and piezoelectric surgery allows for procedures that are virtually bloodless, extremely precise and with less intra- and postoperative pain.
Root canal decontamination
The decontamination of root canals in the process of devitalisation is always an unsatisfactory operation, as the complete removal of the biological material already contaminated by bacteria or that will be subsequently contaminated is highly unlikely. Laser-assisted decontamination performed with a 200 or 320 μm fibre, activated with a pulsed power output of 2.5 Watts in a hypochlorite environment for 5-15 seconds and manoeuvred in a circular motion, ensures the removal of nearly all the bacterial flora.
Direct capping of dental pulp
A useful conditioning of the dental pulp can be achieved with a 320 μm fibre placed at a distance of 1-2 mm from the vital pulp and with a continuous power output of 3-3.5 Watts. After this treatment, the usual techniques are carried out (e.g. stratification of Ca(OH)2 , glass ionomer and composite).
OTHER USES OF LASER IN MEDICINE
Cancer surgery
The benefits of limited bleeding and of less intra-and postoperative pain make the laser an ideal surgical aid; unfortunately, the limited power of the diode laser restricts the range of application.
Surgery performed in orifices (nose, ear, throat, etc.)
Spazi molto ristretti rendono complicate le manovre di taglio; in particolar modo, quando i tessuti sottoposti a chirurgia sanguinano e la visibilità viene a mancare, l’ausilio della tecnologia laser diventa impareggiabile.
Treatment of viral papillomatosis
In general, viral papillomatosis does not require surgical correction because it is self-limiting and disappears with time. Special conditions (risk of infection among puppies, difficulty in chewing, etc.) may however be an indication for their removal; in such cases a laser-assisted procedure guarantees therapeutic success.
Surgery of the parenchyma
The parenchyma of the liver, spleen and of others organs can be treated with laser technology, during which bleeding is noticeably reduced.
Endoscopy
The 200 or 320 μm optical fibres can slide into the working channels of most endoscopes, and can therefore be used during endoscopic procedures.
Aid in the treatment of perineal fistulae
In addition to the normal treatments for this disease, good results have been obtained in a certain number of subjects with three laser biostimulation treatments performed at a distance of 15 days from one another, with a 600 μm defocused contact fibre, with a slow circular movement, with a power output of 2 Watts applied for 30-90 seconds to an area of 1 cm2; at the end of these cycles, the subjects experienced less pain during defecation. However, at present, the small number of trials and the lack of an appropriate experimental protocol does not allow a definitive judgement of this application.
Suggested readings
- Benedicenti A, (1982) Manuale di laserterapia del cavo orale – Maggioli – Rimini
- Benedicenti A, (2005) Atlante di laser terapia 3a edizione – Teamwork media – Villa Caracina (BS)
- Carnovale F, Giardino L, Delle Fratte T, (1997) Il Laser in endodonzia, Minerva Stomatologia. 46:491-6
- Crippa R, Barone M, Benedicenti S, (2008) Laser a diodi in odontoiatria – edi-ermes Milano
- Eversole LR, (2006) Evidence-based practice of oral pathology and oral medicine, J Calif Dent Assoc, 34: 448-54
- Liboon J, Funkhousser W, Terris D, (1997) Comparison of mucosali incisions made by scalpel, CO2 laser, electrocautery and costant voltage electrocautery, Otolaryngol Head Neck Surg, 116: 379_85
- Martelli F, De Leo A, Zinno S, (2000) Laser in odontostomatologia – applicazioni cliniche – Masson – Milano
- Midda M, (1992) Lasers in periodontics, Periodontol Clin Invest, 14: 14-20
- Moritz A, (1998) Treatment of periodontal pockets with a diode laser, Lasers in surgery and medicine. 22:302-11
- Zingoni E, Tognazzi F, Zingoni A, (1998) Fisica bio–medica , Zanichelli – Bologna