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The theoretical basis of lasers truly came into context with the work of Albert Einstein in the early 20th century. Einstein's work in 1917 in the Theory of Wavelength, concluded that it was possible to realise amplified stimulated radiation, i.e laser light. (Parker 2007c)
Theodore Maiman eventually invented the first laser at the Hughes Airccraft Company USA, in 1960. The laser Maiman invented used the active medium of solid ruby, which was energised by an electrical source. (Parker 2007c)
The use of lasers in dentistry came about much later, in 1989 with the manufacture of the American Dental Laser using an active medium of Nd:YAG. (Parker 2007c)
Fundamentals of laser physics
The word LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. Below, I will explain briefly how these words can be related to laser function.
Dental laser light is monochromatic and exhibits three other characteristics. The first is collimation in which the light rays are parallel. This ensures that there is a constant size and shape of the beam emitted from the laser cavity.(Coluzzi 2004) Next is coherency, the light waves produced are in phase with each other.(Coluzzi 2004) Lastly, efficiency, which is clinically effective as a large amount of heat is produced as a by-product of the laser light. (Coluzzi 2004)(Myers 1991)
The optical cavity lies at the centre of the mechanism. It contains the active medium from which the laser is named after. The active medium can be a gas, a crystal with layers of metal or a solid-state semiconductor. (Coluzzi 2004) The process of amplification is when the two mirrors at the end of the active medium reflect photons back and forth allowing further stimulated emission, and successively elevating the power of the photon beam. (Fig 1) (Coluzzi 2004)
Stimulated emission is a quantum mechanical phenomenon whereby photon emission from one atom will stimulate the release of a second photon from a second atom in phase with the original photon. (Sulieman 2005a)
Figure 1. "The basic components of a laser. The excitation source provides energy so that stimulated emission will occur within the active medium. The photons are then amplified by the mirrors and emerge as laser light." (Diagram and caption from (Coluzzi 2004) )
There are four main ways in which lasers can interact with tissues, depending on the optical properties of that tissue. (Coluzzi 2004)
The first most desired is absorption. Chormophores in tissues preferentially absorb certain wavelengths and therefore cause a transference of energy to the tissue.(Coluzzi 2004, Sulieman 2005a) (Frank F., 1989)
Another interaction is transmission, of which the laser energy is transmitted directly through the target tissue, unchanged.(Sulieman 2005a) For example, tissue fluids absorb the erbium family and CO2 superficially so there is little energy transmitted to surrounding tissues. (Coluzzi 2004)
Next is reflection, in which the laser beam redirects itself off of the surface, having no penetration or interaction on the target tissue. Reflection can be dangerous because the energy can be directed to an unintentional target, such as the eyes. (Coluzzi 2004)
Lastly, scattering some of the laser light produced may penetrate the tissue and be scattered without producing a profound biological reaction within the tissues.(Sulieman 2005a) Conversely, scattering of the laser beam could conduct heat to the adjacent tissues to the surgical site, causing damage. (Coluzzi 2004)
Lasers in periodontology
Periodontal disease refers to both gingivitis and periodontitis (Kinane DF 2000 2001) (Schwarz, Becker 2005) Gingivitis can be defined as the inflammation of the gingival tissue without loss of tooth attachment. It can be caused by a number of pre-disposing and modifying factors. Periodontitis is the inflammation of the periodontal tissues with loss of connective tissue of the tooth involved such as the periodontal ligament and ultimately loss of alveolar bone. (Schwarz, Becker 2005) (Kinane DF 2000 2001)
The ultimate goal of periodontal treatment is the regeneration of the abovementioned lost tissues and its attachments. (Crespi, Barone et al. 2003) (Rechmann, Hennig 2001)
Laser wavelengths used in soft tissue application dentistry
One of the laser wavelengths used in periodontal treatment has the active medium of argon gas. Its emission wavelengths are 488nm and 514nm.(Coluzzi 2004) Argon has a very good haemostatic ability as it absorbs the pigment contained in haemoglobin and melanin. It is often used in acute inflammatory periodontal diseases and highly vascularised lesions. (Coluzzi 2004) (Finkbeiner RL. 1995) There is minimal interaction with enamel and dentine and is therefore beneficial when you want to avoid damage to sound tooth structure. (Coluzzi 2004)
Another active medium used is a semiconductor diode with wavelengths of 810-830nm and 980nm. (Sulieman 2005b) It is similar to argon as it is poorly absorbed by tooth structure and achieves relatively good haemostasis. (Coluzzi 2004, Sulieman 2005b) Indications for its use are sulcular debridement and gingival cutting. (Coluzzi 2004), (Moritz A et al.1997, Coluzzi DJ. 2002)
The main preference for this laser is that it is small and portable.(Coluzzi 2004)
Besides that, an active medium of neodymium with yttrium, garnet and aluminium can be used. Its emission wavelength is 1064nm.(Sulieman 2005b) Its indications of use are for cutting and coagulating of dental soft tissues and sulcular debridement.(Coluzzi 2004)
There are two different active mediums containing erbium; solid crystal of yttrium scandium gallium garnet that is doped with erbium and garnet(YSGG 2780nm) and solid crystal of yttrium aluminium garnet that is doped with erbium. (YAG, 2940nm). (Coluzzi 2004). Both absorb water and have poor haemostatic abilities. (Sulieman 2005b) The uses include removal of pulpal tissue and dentine for root canal treatment and hard tissue cutting. (Coluzzi 2004, Sulieman 2005b)
Lastly, CO2 is used as a gas active medium with the wavelength of 10600nm and absorbs water. (Coluzzi 2004) Its properties include very good haemostatic ability and ability to cut soft tissue and fibrous tissue. (Coluzzi 2004) Care must be taken when using CO2 because it has a high absorption in mineralised tooth structure.(Coluzzi 2004)
Clinical uses of lasers in periodontology
Effects on bacteria
Periodontal disease is caused by colonisation and maturation of bacteria.(Convissar 2004) These bacteria, which include Actinobacillus actinomycetemcomitans have been proven to be difficult to be removed effectively by conventional methods of mechanical debridement such as scaling and root planing. (Mavrogiannis, Thomason et al. 2004) (Goene RJ, et al. 1990, Renvert S et al. 1990) (Crespi, Barone et al. 2003)
Consequently, the use of antibiotics such as doxycycline and metronidazole to eliminate these bacterial infections has been warranted. (Convissar 2004) Currently though, it has been recommended that limitations be placed on prescription of antibiotics as they pose a potential risk of developing antibiotic-resistance strains of bacteria. (Ishikawa, Aoki et al. )
The use of lasers as a bactericidal instrument is therefore beneficial. The Nd:YAG and semiconductor laser has demonstrated to be effective in decontamination. (Convissar 2004) According to Ishikawa et al., Er:YAG laser also 'exhibits a high bactericidal effect against periodontopathic bacteria at a low energy level and has the potential to remove toxins diffused into the root cementum, such as bacterial lipopolysaccharides'. (Ishikawa, Aoki et al. ) (Ando Y et al. 1996, Folwaczny M, et al.2002, Yamaguchi H et al. 1997)
Several studies(Trylovich DJ et al. 1992; Spencer P et al.1992, Thomas D et al. 1994; Tewfik HM et al.1994, Ito K et al.1993) however deduced that the Nd:YAG and semiconductor laser cannot always replace mechanical debridement. Instead, they should be used as an adjunct.(Convissar 2004) This is because laser light is deemed inefficient in removing bacteria from root surfaces as it will damage it if it is used directly onto the root surface. (Convissar 2004)
Effect on root surfaces
Loss of attachment causing true pockets cause root surfaces to act as infectious reservoirs for bacteria and play an important role in the advancement of periodontal disease. (Mavrogiannis, Thomason et al. 2004) ( Ruben MP et al. 1978)
To allow for subsequent reattachment of periodontal tissues, a clean root surface is needed as this decreases the microbial challenge. (Mavrogiannis, Thomason et al. 2004). Among the reasons lasers are thought enhance reattachment are that it sterilizes the root surface microbes, curettes the periodontal pocket epithelium, removes the smear layer and facilitates calculus removal. (Mavrogiannis, Thomason et al. 2004) (Myers TD. 1991)
Despite the advantages, it was found that the residual charring produced by a CO2 laser has been shown to impede periodontal tissue reattachment and carbonize root cementum. (Ishikawa, Aoki et al. ) (Gopin BW et al. 1997) When semiconductor diode was used on blood coated root surfaces, severe damage was displayed, depending on the irradiating conditions. (Ishikawa, Aoki et al. ) (Kreisler M et al. 2002) Conditions provided by the Er:YAG laser, allow better in vitro adherence of fibroblasts compared to using physical debridement solely. (Ishikawa, Aoki et al. ) (Belal MH et al. 2007, Feist IS et al. 2003, Schwarz F 2003)
It has also been reported that there is a significant rise in intra-pulpal and root surface temperature during root surface irradiation that may cause thermal damage to the tooth and its periodontal attachment. (Mavrogiannis, Thomason et al. 2004) (Wilder-Smith P et al. 1995)
Effect on calculus
Calculus can be defined as plaque containing inorganic salts, organic material, bacteria and water that has been calcified. (Parker 2007a) Periodontal tissues may be damaged during the irradiation of calculus due to the close proximity of calculus to the periodontal tissues. (Parker 2007a) Some of the wavelengths that are recommended are the frequency-doubled alexandrite (FDA, 377 nm) and the Er:YAG lasers. (Parker 2007a) One benefit of using the FDA, 377nm laser is that it is able to ablate calculus selectively without affecting cementum , enamel and dentine. (Ishikawa, Aoki et al., Parker 2007a) (Rechmann P. 2004, ix.Pilgrim C et al. 2000)
However, to date this laser is not available for general clinical use. (Ishikawa, Aoki et al. )
Effects on soft tissues
A large number of soft tissue procedures are carried out by lasers including gingivectomy, frenectomy, biopsies, and the removal of benign tumours and lesions. (Convissar 2004, Mavrogiannis, Thomason et al. 2004). (Mavrogiannis, Thomason et al. 2004) states that ideally, the laser effects on soft tissue 'should be minimal with atraumatic cuts, homogeneous removal of the tissue, coagulation of the wound surface, good healing process, minimal or no post-operative discomfort and patients' acceptance.'
For example, gingival hyperplasia which can be caused by iatrogenic trauma, drug induced, induced by an orthodontic appliance or because of poor margins on a restoration. (Roshkind 2008) Laser treatment is preferred in the treatment of gingival hyperplasia because of the decreased bleeding, less postoperative pain and the elimination of perio-packing, dressing or sutures and the bactericidal effect.(Roshkind 2008) As gingival hyperplasia is a side effect of calcium channel blockers, which are often taken alongside blood thinners such as warfarin, the decreased bleeding is a desired effect. (Convissar 2004)
The mediums that can be used for soft tissue laser treatment include the semiconductor diode, argon and Er:YAG. The figures below demonstrates hyperplastic tissue(Fig. 2) and its subsequent healing 2 weeks after treatment with a diode laser (Fig. 3) (Roshkind 2008)
Fig. 2 Preoperative view of gingival hyperplasia. (Courtesy Dr. Philip Hudson, Spokane, WA.)
(Roshkind 2008, Roshkind 2008)
Figure 3. Two-week postoperative view of the patient seen in Figure 2. (Courtesy Dr. Philip Hudson, Spokane, WA.) (Roshkind 2008)
Effect on Osseous surgery
Anatomy of the alveolar bone needs to be recontoured and reshaped to allow periodontal tissue attachment after surgery. (Ishikawa, Aoki et al. ) The reshaping of the bone is said to be more precise with the use of Er:YAG laser compared to mechanical rotary instruments, using burs and hand instruments. (Ishikawa, Aoki et al. )
On the next page is a table showing various clinical studies of laser application on bone tissue compiled by Ishikawa et al.
Conclusions that can be made from this table:
The Er:YAG laser is deemed to be the most effective laser in vivo and clinically for osseous surgery.
The time of healing for surgery conducted by the Er:YAG seemed to be inconclusive whereby there were studies that had delayed, normal and quick healing.
Little to no charring was seen when the Er: YAG laser was used
The time take for laser osseous surgery seems to be longer than the time taken when using conventional burs.
CO2 is not recommended for osseous surgery as most studies concluded that thermal damage and a char layer is produced.
Table 1: In vitro, in vivo and clinical studies of laser application on bone tissue
(Entire table compiled by Ishikawa et al.)
Table 1 (continued): In vitro, in vivo and clinical studies of laser application on bone tissue
(Entire table compiled by Ishikawa et al.)
Lasers in Endodontics
Endodontics is the clinical discipline which deals with the prevention, diagnosis, management and treatment of endodontic disease within teeth and of the dental pulp. The aim of endodontic treatment is to remove the soft, necrotic , infected tissue from the root canal system and the pulp chamber and to obdurate and create an apical and coronal seal. Research has also been conducted for the use of lasers in direct pulp capping, pulpectomy and pulpotomy procedures but for the purposes of this discussion, I will be focusing solely on root canal treatment.
Preparation removes debris and prevents formation of smear layer on root canal walls
Cleaning and shaping the root canal system to remove bacteria and necrotic tissue and create tapered shape is vital for the success of endodontic treatment. (Inamoto, Horiba et al. 2009) Conventionally this is done with either hand or rotary instruments using the Stepback or Crowndown technique. One disadvantage of these mechanical shaping techniques is that a smear layer is produced on the walls of the root canal.(Inamoto, Horiba et al. 2009) Besides that, the shape, curvature or complexity of the root canal may affect the ability to successful create the desired tapered shape and to remove all infected tissue even though various disinfectant chemicals are used.(Inamoto, Horiba et al. 2009) (Aktener BO et al. 1993; Guerisoli DM et al. 2002)
One possible type of laser that could be used for preparation of the root canal system is the Er:YAG laser.(Inamoto, Horiba et al. 2009) It has the ability to ablate dental hard tissue efficiently thus able to shape and create a taper in the root canal system. (Inamoto, Horiba et al. 2009) (Shoji S et al. 2000, Matsuoka E et al. 2000, Kesler G et al. 2002)
It has been proven that ablation of dentine by Er:YAG does not form a smear layer and decreases the number of bacteria in the canal.(Inamoto, Horiba et al. 2009) (Schoop U et al. 2002; Shoji S et al. 2000, Matsuoka E et al. 2000, Kesler G et al. 2002)
According to (Inamoto, Horiba et al. 2009), the smear layer must be removed completely as it 'harbours bacteria and prevents irrigants, medicaments, and filling materials from penetrating into the dentinal tubules'.(Inamoto, Horiba et al. 2009) However, some studies believe that leaving the smear layer is beneficial as it blocks the pulpal aspect of the dentinal tubules, thus limiting the bacterial penetration. (Drake DR et al. 1994)
Further research has to be conducted in order to determine the efficacy of the root canal preparation by Er:YAG before it is used clinically. (Inamoto, Horiba et al. 2009)
When preparing the root canal system, it is essential that water cooling be implemented with the laser action as without it, there will be a rise in temperature in the root canal system. (Parker 2007b)The risks of these are the dentine walls may crack. (Parker 2007b)
Irrigation, cleaning and disinfection of the root canal system
Pulpal and periapical lesions often develop due to bacterial infiltration of the root canal system.(Stabholz, Sahar-Helft et al. 2008) (Kakehashi S et al. 1965; Bergenholz G. 1974; MoÂ¨ ller AJ, Fabricius L et al. 1981)
The smear layer consists of inorganic and organic substances, for example, microorganisms and necrotic tissue.(Stabholz, Sahar-Helft et al. 2008) (Torabinejad M et al. 2002) It's thickness on the root canal wall is about 1-2mm and up to 40mm in the dentinal tubules.(Stabholz, Sahar-Helft et al. 2008) (Mader CL et al. 1984)
An Nd:YAG laser was used in a study by Bergmans et al. to determine its function as a disinfection tool for the root canal system. (Stabholz, Sahar-Helft et al. 2008) (Bergmans L et al. 2006) The conclusion was that Nd:YAG should be used as a supplement to current disinfection methods such as with NaOCl and not an alternative. (Stabholz, Sahar-Helft et al. 2008) The laser light that is emitted also does not necessarily shine into lateral canals therefore making it nearly impossible to get constant, symmetrical disinfection of all surfaces in the root canal system.(Stabholz, Sahar-Helft et al. 2008) (Goodis HE et al. 2002; Stabholz A et al. 2003) Thermal damage also could occur to the surrounding periapical and periodontal tissues.(Stabholz, Sahar-Helft et al. 2008) (Stabholz A et al. 2003) Besides that, the laser light may travel through the apical foramen and affect the surrounding tissues especially in teeth around the are of the mental nerve and the mandibular nerve. (Stabholz A et al. 2003; Matsumoto K. 2000)
Sealing with or removal of gutta percha obturation material
The use of lasers to soften and provide flowable gutta percha for the obturation of the root canal has been researched. (Parker 2007b) (Anjo T et al. 2004; Viducic D et al. 2003; Carvalho C A et al. 2002; Maden M et al. 2002; Kimura Y et al. 2001)
However, the development of heat-softened or solvent softened gutta percha has deemed the use of lasers for these purposes time consuming and expensive. (Parker 2007b) (Anic I et al. 1996)
Clinical usage of lasers
Risks and precautions of using lasers in the dental surgery
Caution should be taken when using lasers. Inadvertent irradiation to any exposed areas of the patient and dental staff should be avoided. (Ishikawa, Aoki et al. ) Precautions such as eye and throat protection for the patient and dental staff should be adequately taken.(Ishikawa, Aoki et al.) (AAP. The Research, Science and Therapy Committee of the American Academy of Periodontology, Cohen RE et al. 2002)
Among the risks being taken while using a dental laser is the risk of thermal injury when dealing with these tissues.(Ishikawa, Aoki et al. ) Sufficient understanding of the physics and clinical guidelines of laser use and penetration by the operator will avoid this from happening as well as frequent and effective use of water spray. (Ishikawa, Aoki et al. )
Also, there is the risk of over preparing the tissues and destruction of mineralised tooth structures such as enamel and dentine while irradiation of periodontal tissues. (Ishikawa, Aoki et al.) This again may be overcome with adequate knowledge of the laser equipment from the operator.
Lasers vs. scalpels and conventional drills
The main difference between lasers and scalpels is the reduced bleeding effect by lasers and its ability to provide complete haemostasis at times. (Sulieman 2005b) Less bleeding therefore provides better quality vision for the operator to incise. (Sulieman 2005b) Generally, scalpels can cut into soft tissue faster than lasers.(Sulieman 2005b)
These are the main advantages and disadvantages of the use of lasers in periodontology and endodontics.
The advantages include the fact that lasers are bactericidal, able to get into places that may be hard to manoeuvre a scalpel or an endodontic file.
The disadvantages of laser therapy include the fact that they are expensive pieces of equipment. Besides that, the operator requires a sound education on the physics and biology of the tissue cutting before they attempt to use this equipment.
In conclusion, the use of lasers should be restricted to usage as an adjunct to conventional periodontal and endodontic therapies. This is because there is no significant, long-term and conclusive data to support the usage of lasers as the main treatment.
I would like to say thank you to Dr Abigail Tucker for answering my queries and providing her support throughout the duration of the project.