The current status of laser applications in dentistry

Transcription

1 REVIEW Australian Dental Journal 2003;48:(3): The current status of laser applications in dentistry LJ Walsh* Abstract A range of lasers is now available for use in dentistry. This paper summarizes key current and emerging applications for lasers in clinical practice. A major diagnostic application of low power lasers is the detection of caries, using fluorescence elicited from hydroxyapatite or from bacterial by-products. Laser fluorescence is an effective method for detecting and quantifying incipient occlusal and cervical carious lesions, and with further refinement could be used in the same manner for proximal lesions. Photoactivated dye techniques have been developed which use low power lasers to elicit a photochemical reaction. Photoactivated dye techniques can be used to disinfect root canals, periodontal pockets, cavity preparations and sites of peri-implantitis. Using similar principles, more powerful lasers can be used for photodynamic therapy in the treatment of malignancies of the oral mucosa. Laser-driven photochemical reactions can also be used for tooth whitening. In combination with fluoride, laser irradiation can improve the resistance of tooth structure to demineralization, and this application is of particular benefit for susceptible sites in high caries risk patients. Laser technology for caries removal, cavity preparation and soft tissue surgery is at a high state of refinement, having had several decades of development up to the present time. Used in conjunction with or as a replacement for traditional methods, it is expected that specific laser technologies will become an essential component of contemporary dental practice over the next decade. Key words: Lasers, dental applications, débridement, photosensitization, resin curing. (Accepted for publication 6 February 2003.) INTRODUCTION The past decade has seen a veritable explosion of research into the clinical applications of lasers in dental practice, and the parallel emergence of organizations to support laser dentistry with an international focus. Once regarded as a complex technology with limited uses in clinical dentistry, there is a growing awareness *Professor of Dental Science, School of Dentistry, The University of Queensland. of the usefulness of lasers in the armamentarium of the modern dental practice, where they can be used as an adjunct or alternative to traditional approaches. Traditionally, lasers have been classified according to the physical construction of the laser (e.g., gas, liquid, solid state, or semiconductor diode), the type of medium which undergoes lasing (e.g., Erbium: Yttrium Aluminium Garnet (Er:YAG)) (Table 1), and the degree of hazard to the skin or eyes following inadvertent exposure (Table 2). Lasers have been available commercially for use in dental practice in Australia since 1990, and the currently available systems represent a high state of technical refinement in terms of both performance and user features. The purpose of this paper is to provide an overview of various laser applications which have been developed for dental practice, and to discuss in more detail several key clinical applications which are attracting a high level of interest. Diagnostic laser applications Low power laser energy has found numerous uses in diagnosis, both in clinical settings (Table 3) and in dental research (Table 4). By way of background, low power lasers operate typically at powers of 100 milliwatts or less, and may produce energy in the visible spectrum ( nm wavelength), or in the ultraviolet ( nm), or near infrared regions ( nm). At the present time, there are few purpose built low power lasers for the middle infrared ( nm) or far infrared regions ( nm). Rather, lasers operating in the middle and far-infrared regions are used in health care primarily for hard and soft tissue procedures. Laser fluorescence systems for detection of dental caries have been particularly popular in Australia. The original technique employed visible blue light from the argon laser, relying on the lack of fluorescence from carious enamel and dentine to demonstrate the presence of the lesion. Subsequent development of the technique allowed visible red laser light from a semiconductor diode laser to be used to elicit fluorescence from bacterial deposits, and from calculus. Combining a detection system with a therapeutic laser has allowed automated removal of subgingival calculus 146 Australian Dental Journal 2003;48:3.

2 Table 1. Common laser types used in dentistry Laser type Construction Wavelength(s) Delivery system(s) Argon Gas laser 488, 515nm Optical fibre KTP Solid state 532nm Optical fibre Helium-neon Gas laser 633nm Optical fibre Diode Semiconductor 635, 670, 810, Optical fibre 830, 980nm Nd:YAG Solid state 1064nm Optical fibre Er,Cr:YSGG Solid state 2780nm Optical fibre Er:YAG Solid state 2940nm Optical fibre, waveguide, articulated arm CO 2 Gas laser 9600, 10600nm Waveguide, articulated arm from teeth and dental implants, a point discussed in further detail below. For detection of dental caries in pits and fissures, laser fluorescence offers greater sensitivity than conventional visual and tactile methods. 1,2 The technique is also well suited to smooth surface lesions on cervical surfaces of teeth, 3,4 and to recognition of caries beneath clear fissure sealants. 5 Detection of proximal lesions is technically more difficult, and in this setting, argon laser-induced fluorescence offers a valuable adjunct to conventional methods. 6-9 The differential water content of early fissure caries and sound occlusal enamel has also led to the development of methods using the carbon dioxide laser to reveal such lesions, and to modify the fissure system to increase resistance to future carious attack. 11 Two key advantages of laser-based systems are their high sensitivity, and the lack of attendant risks of ionizing radiation. This has allowed their frequent use for monitoring lesions of dental caries and dental erosion Extension of the principles of laser fluorescence from the visible to the near infrared and terahertz portions of spectrum opens the possibility for more detailed analysis of the internal composition of the tooth. 17 Moreover, the use of dyes in conjunction with laser fluorescence holds promise for using the method for delineating cavitated from non-cavitated lesions in sites of poor clinical access, such as approximal surfaces. 18,19 Bacterial porphyrins in dental calculus give a strong fluorescence signal, 20 which can be used to control lasers used for scaling. The same principle could be applied to lesions of dental caries, where a targeting laser could induce fluorescence and provide feedback to Table 2. Laser classification according to potential hazards Class Risk Example I Fully enclosed system Nd:YAG laser welding system used in a dental laboratory II Visible low power laser Visible red aiming beam of a protected by the blink reflex surgical laser IIIa Visible laser above No dental examples 1 milliwatt IIIb Higher power laser unit Low power (50 milliwatt) (up to 0.5 watts) which diode laser used for may or may not be visible. biostimulation Direct viewing hazardous to the eyes IV Damage to eyes and skin All lasers used for oral surgery, possible. Direct or indirect whitening, and cavity viewing hazardous to preparation the eyes the user as to the presence of residual bacteria (i.e., the presence of infected carious dentine), and could also control the action of a pulsed laser to achieve automated caries removal. There are already data on the spectral changes which occur during infrared laser treatment of enamel and dentine 21,22 which could similarly be applied clinically when assessing the presence or absence of carious tooth structure during laser-based cavity preparation. Photoactivated dye disinfection using lasers Low power laser energy in itself is not particularly lethal to bacteria, but is useful for photochemical activation of oxygen-releasing dyes. Singlet oxygen released from the dyes causes membrane and DNA damage to micro-organisms. The photoactivated dye (PAD) technique can be undertaken with a range of visible red and near infrared lasers, and systems using low power (100 milliwatt) visible red semiconductor diode lasers and tolonium chloride (toluidine blue) dye are now available commercially (Fig 1). The initial work which demonstrated the PAD technique used helium-neon lasers. 23 However, such units have been surpassed with high efficiency diode lasers which operate at the same wavelength. The PAD technique has been shown to be effective for killing bacteria in complex biofilms, such as subgingival plaque, which are typically resistant to the action of antimicrobial agents It can be used effectively in carious lesions, since visible red light transmits well across dentine, 27 and can be made species-specific by tagging the dye with monoclonal Table 3. Diagnostic laser applications for clinical practice Argon Helium-neon Diode Diode CO 2 488nm 633nm 633nm 655nm 10600nm Laser fluorescence detection of dental caries Laser fluorescence detection of subgingival calculus Detection of fissure caries lesions by optical changes Laser doppler flowmetry to assess pulpal blood flow Scanning of phosphor plate digital radiographs Scanning of conventional radiographs for teleradiology Australian Dental Journal 2003;48:3. 147

3 Table 4. Diagnostic laser applications used as research tools Nd:YAG Er:YAG Argon Helium-neon Diode 1064nm 2940nm 488 and 515nm 633nm 633 and 670nm Raman spectroscopic analysis of tooth structure Terahertz imaging of internal tooth structure Breakdown spectroscopic analysis of tooth structure Confocal microscopic imaging of soft and hard tissues Flow cytometric analysis of cells and cell sorting Profiling of tooth surfaces and dental restorations antibodies. 28 Photoactivated dye can be applied effectively for killing Gram-positive bacteria (including MRSA), Gram-negative bacteria, fungi and viruses. 29,30 Major clinical applications of PAD include disinfection of root canals, periodontal pockets, deep carious lesions, and sites of peri-implantitis. 31,32 In such locations, PAD does not give rise to deleterious thermal effects, 33 and adjacent tissues are not subjected to bystander thermal injury. Photoactivated dye treatment does not cause sensitization and killing of adjacent human cells such as fibroblasts and keratinocytes. 34 Neither the dye nor the reactive oxygen species produced from it are toxic to the patient. Tolonium chloride is used in high concentrations for screening patients for malignancies of the oral mucosa and oropharynx, 35,36 and does not exert toxic effects at the low concentrations used in the PAD technique. Moreover, residual reactive oxygen species are rapidly dealt with by the enzyme catalase, which is present in all tissues and in the peripheral circulation, 37 and by lactoperoxidase, which is a normal component of saliva. Photodynamic therapy A more powerful laser-initiated photochemical reaction is photodynamic therapy (PDT), which has been employed in the treatment of malignancies of the oral mucosa, particularly multi-focal squamous cell carcinoma. As in PAD, laser-activation of a sensitizing dye in PDT generates reactive oxygen species. These in turn directly damage cells and the associated blood vascular network, triggering both necrosis and apoptosis. 38 Of interest, while direct effects of PDT destroy the bulk of tumour cells, there is accumulating evidence that PDT activates the host immune response, and promotes anti-tumour immunity through the activation of macrophages and T lymphocytes. 37 For example, there is direct experimental evidence for photodynamic activation of the production of tumour necrosis factoralpha, 39 a key cytokine in host anti-tumour immune responses. Clinical studies have reported positive results for PDT treatment of carcinoma-in-situ and squamous cell carcinoma in the oral cavity, with response rates approximating 90 per cent. 40,41 The treated sites characteristically show erythema and oedema, followed by necrosis and frank ulceration. The ulcerated lesions typically take up to eight weeks to heal fully, and supportive analgesia is required in the first few weeks. Other than short-term photosensitivity, the treatment is tolerated well. 39 Other photochemical laser effects The argon laser produces high intensity visible blue light (488nm) which is able to initiate photopolymerization of light-cured dental restorative materials which use camphoroquinone as the photoinitiator The temperature increase at the level of the dental pulp is much less with argon laser curing than when conventional quartz tungsten halogen lamp units are used. 45,46 Argon laser radiation is also able to alter the surface chemistry of both enamel and root surface dentine, 47,48 which reduces the probability of recurrent caries. This clinical benefit is arguably more important than the reduced curing time and improved depth of cure achieved with the argon laser. A further photochemical effect produced by high intensity green laser light is photochemical bleaching (Table 5). This effect relies upon specific absorption of a narrow spectral range of green light ( nm) into chelate compounds formed between apatites, Table 5. Laser-enhanced tooth whitening Fig 1. Laser system for photo-activated dye therapy, which uses a diode laser (635nm) and tolonium chloride dye (SaveDent, Asclepion Meditec, Fife, UK). Argon KTP Diode CO 2 515nm 532nm nm 10600nm Photochemical bleaching Photothermal bleaching 148 Australian Dental Journal 2003;48:3.

4 laser (532nm) can both be used for photochemical bleaching, since their wavelengths approximate the absorption maxima of these chelate compounds ( nm). 50 Argon and KTP lasers can achieve a positive result in cases which are completely unresponsive to conventional photothermal power bleaching (Fig 2). Laser applications in the dental laboratory There is a range of laboratory-based laser applications (Table 6). Laser holographic imaging is a well established method for storing topographic information, such as crown preparations, occlusal tables, and facial forms. The use of two laser beams allows more complex surface detail to be mapped using interferometry, 51,52 while conventional diffraction gratings and interference patterns are used to generate holograms and contour profiles Laser scanning of casts can be linked to computerized milling equipment for fabrication of restorations from porcelain and other materials. An alternative fabrication strategy is to sinter ceramic materials, to create a solid restoration from a powder of alumina or hydroxyapatite. 57 The same approach can be used to form complex shapes from dental wax and other materials which can be sintered, such that these can then be used in conventional lost wax casting. A variation on this theme is ultraviolet (helium-cadmium) laser-initiated polymerization of liquid resin in a chamber, to create surgical templates for implant surgery and major reconstructive oral surgery. These templates can be coupled with laser-based positioning systems for complex reconstructive and orthognathic surgical procedures. Fig 2. KTP laser photochemical bleaching. A. Initial clinical appearance of the dentition in a 9-year-old patient with intense discolouration of the incisor teeth caused by prolonged childhood illnesses and associated medications. B. The situation immediately after three 60-minute appointments of power bleaching using a conventional quartz tungsten halogen curing lamp and 35 per cent hydrogen peroxide gel. The incisal enamel shade has improved somewhat, but the areas of discolouration at the gingival third are unchanged. The arrow indicates a residue of the protective gingival dam. C. Clinical appearance immediately after one session of photochemical bleaching using the KTP laser and proprietary alkaline hydrogen peroxide (Smartbleach ) gel. The laser treatment was targeted to the gingival third. The patient and her parents were pleased with the immediate post-operative result and did not request any additional treatment. porphyrins, and tetracycline compounds. 49 The argon laser (515nm) and potassium titanyl phosphate (KTP) Laser procedures on dental hard tissues Cavity preparation using lasers has been an area of major research interest since lasers were initially developed in the early 1960s. At the present time, several laser types with similar wavelengths in the middle infrared region of the electromagnetic spectrum are used commonly for cavity preparation and caries removal. The Er:YAG, Er:YSGG and Er,Cr:YSGG lasers operate at wavelengths of 2940, 2790, and 2780nm, respectively. These wavelengths correspond to the peak absorption range of water in the infrared spectrum (Fig 3), although the absorption of the Er:YAG laser (13,000cm -1 ) is much higher than that of the Er:YSGG (7000cm -1 ) and Er,Cr:YSGG (4000cm -1 ) Since all three lasers rely on water-based absorption for cutting enamel and dentine, the efficiency of ablation (measured in terms of volume and mass loss of tooth structure for identical energy parameters) is greatest for the Er:YAG laser. 58,60 These laser systems can be used for effective caries removal and cavity preparation without significant thermal effects, collateral damage to tooth structure, or patient discomfort Normal dental enamel contains sufficient water (approximately 12 per cent by volume) that a water mist spray coupled to an Er-based laser Australian Dental Journal 2003;48:3. 149

5 Table 6. Laser applications in the dental laboratory Helium neon Diode Nd:YAG CO 2 Helium-Cadmium 633nm 635nm 1064nm 10600nm 300nm Scanning of models for orthodontics or holographic storage Scanning of crown preparations for CAD-CAM Welding of metals (Co:Cr, titanium) Sintering of ceramics CAD-sintering fabrication CAD-polymer fabrication of splints or surgical models Cutting of ceramics system can achieve effective ablation at temperatures well below the melting and vapourization temperatures of enamel. 61 Er-based dental lasers can also be used to remove resin composite resin and glass-ionomer cement restorations, and to etch tooth structure (Fig 4). A characteristic operating feature of Er-based laser systems is a popping sound when the laser is operating on dental hard tissues. Both the pitch and resonance of this sound relate to the propagation of an acoustic shock wave within the tooth, and vary according to the presence or absence of caries. This feature assists the user in determining that caries removal is complete. 66 In contrast to the popping sound during caries removal, one current generation Er,Cr:YSGG laser system creates a loud snapping sound even when not in contact with any structure in the mouth. This seeming paradox can be explained by an effect termed plasma de-coupling of the beam, in which incident laser energy heats the air and water directly in front of the laser handpiece. In the Er,Cr:YSGG laser, this is done intentionally in order to deliver energy onto the rear surface of atomized water molecules, with the aim of accelerating them to a higher speed (so-called HydroKinetic cutting ). 67 Detailed studies of the cutting mechanisms of Er:YAG and Er,Cr:YSGG lasers have revealed that the mechanism by which enamel is removed is basically the same for both laser systems, namely explosive subsurface expansion of interstitially trapped water. 65 The same investigations also failed to show Er,Cr:YSGG laser cutting of a variety of materials which were free of water, which the authors stated was contradictory to the existence of the hydrokinetic phenomenon Er,Cr:YSGG An important theoretical extension to the principle of water-based laser ablation of tooth structure is the recently described effect of laser abrasion, in which Er:YAG laser energy is used to accelerate the movement of particles of sapphire micrometers in diameter in aqueous suspension. As in air abrasion, the impact of these particles causes brittle splitting, resulting in tooth substance removal. In the laser abrasion method, high speed photography has documented particle velocities in the range of metres per second, which enable a rate of enamel removal higher than that of high speed turbines with a very low volume of abrasive particles. 68 This technique could be employed with current generation lasers once a suitable dispensing system for the suspension of particles has been developed. As well as the potential of even more rapid cutting rates than conventional rotary instrumentation, laser abrasion offers the promise of laser-based cutting of structures which are not otherwise amenable to this, such as ceramic restorations. Intensive research over the past three decades on other non-erbium laser-based cavity preparation systems has yet to be translated to direct clinical application. To date, alternative laser systems, including super-pulsed CO2, Ho:YAG, Ho:YSGG, Nd:YAG, Nd:NLF, diode lasers and excimers, have not proven feasible for use for cavity preparation in general practice settings. Other than caries removal, this is a range of other well established laser hard tissue procedures include desensitization of cervical dentine (using Nd:YAG, Er:YAG, Er,Cr:YSGG CO2, KTP, and diode lasers), laser analgesia (using Nd:YAG, Er:YAG, and Er,Cr:YSGG lasers), laser-enhanced fluoride uptake (using Er:YAG, Er,Cr:YSGG, CO2, argon, and KTP lasers). Furthermore, there is a considerable range of periodontal procedures (Table 7), and endodontic procedures (Table 8) which can be undertaken with lasers as an alternative to conventional approaches Er:YAG Fig 3. The absorption curve of water in the middle infrared region. Data on the vertical axis are units of absorption, while the horizontal axis shows wavelength in micrometers. The plot shows the position of two laser wavelengths used for cavity preparation: Er,Cr:YSGG 2.78 micrometers, and Er:YAG 2.94 micrometers. The figure is based on data from reference 59. Soft tissue laser procedures There are numerous soft tissue procedures which can be performed with lasers Two key features of these are reduced bleeding intra-operatively and less pain post-operatively compared to conventional techniques such as electrosurgery. The degree of absorption in key tissue components dictates the type of effect gained by the laser on soft tissues, and in this regard the content of water and haemoglobin in oral tissues is important 150 Australian Dental Journal 2003;48:3.

6 Fig 4. Restorative procedures using the Er:YAG laser, in anxious dental patients, without local anesthesia. The Er:YAG laser was used with a non-contact handpiece. A. Pre-operative appearance of a 22-year-old male with salivary dysfunction, and associated cervical and approximal caries. B. Areas of caries and defective resin composite have been removed. The intense white appearance of the margins is typical of laser etching. C. The restored teeth immediately post-operatively. The etched appearance of the margins disappears once bonding resin has been placed. D. 30-year-old female patient with areas of hypoplastic enamel. E. The enamel surface has been peeled using a series of pulses from the laser. F. The two areas have been restored with resin composite. G. 65-year-old female patient undergoing anti-cancer chemotherapy, with recurrent caries at the margins of several restorations. H. Areas of caries and undermined resin composite have been removed. I. The cavity preparations have been restored. for the efficient absorption of many commonly used dental lasers. 72 Certain procedures in patients with bleeding disorders are better suited to lasers with greater haemostatic capabilities (Table 9). Examples of simple soft tissue procedures are presented in Fig 5. CONCLUSIONS Laser technology for caries detection, resin curing, cavity preparation and soft tissue surgery is at a high state of refinement, having had several decades of development up to the present time. This is not to say that further major improvements cannot occur. Indeed, as is in the case with laser abrasion, the fusion of concepts from differing technologies may open the door to novel techniques and treatments. The field of laser-based photochemical reactions holds great promise for additional applications, particularly for targeting specific cells, pathogens or molecules. A further area of future growth is expected to be the combination of diagnostic and therapeutic laser techniques in the one device, for example the detection and removal of dental caries or dental calculus. For Australian Dental Journal 2003;48:3. 151

7 Table 7. Periodontal laser procedures Er:YAG Er,Cr:YSGG KTP Argon 488 Diode Nd:YAG Helium-neon Diode 635, CO nm 2780nm 532nm and 515nm nm 1064nm 633nm 670 or 830nm 10600nm Calculus removal Periodontal pocket disinfection Photoactivated dye disinfection of pockets De-epithelialization to assist regeneration Table 8. Endodontic laser procedures CO 2 Erbium:YAG Er,Cr:YSGG KTP Argon 488 Diode Nd:YAG Helium-neon Diode 635, 10600nm 2940nm 2780nm 532nm and 515nm nm 1064nm 633nm 670, or 830nm Direct pulp capping Drying of the root canal Removal of smear layer Root canal disinfection Photoactivated dye disinfection of pockets example, an autopilot system for subgingival débridement has been developed (for detailed review, see ref 73), and the potential exists to extend this concept further. There is a large research effort internationally focused on developing new laser applications for dental practice, and each year several large meetings are held which bring together this research. Examples include the International Society for Lasers in Dentistry (ISLD), the European Society for Oral Laser Applications (ESOLA), and the Academy of Laser Dentistry (ALD). With the further development of laser dentistry as an area of clinical pursuit, there will be considerable opportunity for clinicians to become involved in these research meetings and in specific research projects. The Australasian region has played a substantial role in the development of hard tissue laser applications, 74,75 and this level of involvement is expected to continue in the future, as various research groups examine uses for lasers in conjunction with or as a replacement for traditional methods. There is little argument that over recent years the use of lasers in dentistry in Australia has moved beyond academic centres and specialist units into the mainstream of general practice. Looking to the future, it is expected that specific laser technologies will become an essential component of contemporary dental practice over the next decade. ACKNOWLEDGMENTS I thank the dental practitioners who have referred patients to the Laser Clinic over the past 12 years, and the numerous staff and students who have contributed to the dental laser research programme at the University of Queensland. REFERENCES 1. Shi XQ, Welander U, Angmar-Månsson B. Occlusal caries detection with KaVo DIAGNOdent and radiography: an in vitro comparison. Caries Res 2000;34: Lussi A, Megert B, Longbottom C, Reich E, Francescut P. Clinical performance of a laser fluorescence device for detection of occlusal caries lesions. Eur J Oral Sci 2001;109: Shi XQ, Tranaeus S, Angmar-Månsson B. Validation of DIAGNOdent for quantification of smooth-surface caries: an in vitro study. Acta Odontol Scand 2001;59: Shi XQ, Tranaeus S, Angmar-Månsson B. Comparison of QLF and DIAGNOdent for quantification of smooth surface caries. Caries Res 2001;35: Table 9. Surgical laser applications Er:YAG 2940nm Er,Cr:YSGG CO 2 KTP Diode Argon 488 Nd:YAG 1064nm (least haemostasis) 2780nm 10600nm 532nm nm and 515nm (most haemostatis) Minor soft tissue surgery Major soft tissue surgery Surgical treatment of large vascular lesions Bone cutting Implant exposure with bone removal 152 Australian Dental Journal 2003;48:3.

8 Fig 5. Soft tissue procedures using middle and far infrared lasers. A. Pre-operative clinical appearance of a 22-year-old female with marked gingival overgrowth from nifedipine and cyclosporin. The patient has received a kidney transplant, is immuno-suppressed, and has a bleeding tendency. B. the immediate post-operative appearance following gingivoplasty with the carbon dioxide laser. Complete haemostasis is maintained during the procedure. C. Initial clinical appearance of a 16-year-old female patient with marked gingival overgrowth, which has obscured the orthodontic brackets and caused the cessation of fixed orthodontic treatment. D. Immediate post-operative view of quadrant 1 following gingival recontouring with the carbon dioxide laser. E. Immediate post-operative view of quadrant 2 following recontouring with the Er:YAG laser in contact mode. Note the different appearance of the tissues compared to quadrant 1. Both segments were treated at the same appointment. F and G. Clinical appearance of the two sites two weeks following surgery. The tissue contours are identical to those determined at the time of surgery. 5. Takamori K, Hokari N, Okumura Y, Watanabe S. Detection of occlusal caries under sealants by use of a laser fluorescence system. J Clin Laser Med Surg 2001;19: Bjelkhagen H, Sundström F, Angmar-Månsson B, Ryden H. Early detection of enamel caries by the luminescence excited by visible laser light. Swed Dent J 1982;6: Angmar-Månsson B, ten Bosch JJ. Optical methods for the detection and quantification of caries. Adv Dent Res 1987;1: Hafström-Bjorkman U, Sundström F, Angmar-Månsson B. Initial caries diagnosis in rat molars, using laser fluorescence. Acta Odontol Scand 1991;49: Hafström-Bjorkman U, Sundström F, de Josselin de Jong E, Oliveby A, Angmar-Månsson B. Comparison of laser fluorescence and longitudinal microradiography for quantitative assessment of in vitro enamel caries. Caries Res 1992;26: Longbottom C, Pitts NB. CO 2 laser and the diagnosis of occlusal caries: in vitro study. J Dent 1993;21: Australian Dental Journal 2003;48:3. 153

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