Laser Application in Operative Dentistry PDF

Lec.6 Laser applicationin operative dentistry The word ‘‘laser’’ is an acronym for Light Amplification by Stimulated Emission of Radiation. Is a device that emits very high intensity of light through a process of optical amplification based on the stimulated emission of electromagnetic radiation Las...

Lec.6 Laser applicationin operative dentistry The word ‘‘laser’’ is an acronym for Light Amplification by Stimulated Emission of Radiation. Is a device that emits very high intensity of light through a process of optical amplification based on the stimulated emission of electromagnetic radiation Laser basics: Dental lasers are named depending based on the active medium that is stimulated. The active medium can be: a gas (e.g. argon, carbon dioxide), a liquid (dyes) or a solid state crystal rod e.g. Neodymium yttrium aluminum garnet (Nd:YAG), Erbium yttrium aluminum garnet (Er: YAG) or a semiconductor ( diode lasers). The active mediums contain atoms whose electrons may be excited to a metastable energy level by an energy source. The active medium may be excited by excitation mechanisms that pump energy into the active medium by one or more of three basic methods; optical (e.g. xenon flash lamps, other lasers), electrical (e.g. gas discharge tubes, electric current in semi-conductors) or chemical. Laser light is unique in that: it is monochromatic (light at one specific wavelength), Directional (Low divergence) and coherent (all waves are in a certain phase relationship to each other). Dental laser wavelength The wavelength of a laser’s light dictates its interactions, indications, and specificity for use in treatment procedures and for which types of tissues. Softtissue lasers’ wavelengths range within the visible light spectrum from argon at 488 nm, argon at 515 nm, to potassium titanyl phosphate at 535 nm.11 On the electromagnetic spectrum, near-infrared soft-tissue lasers’ wavelengths consist of 810 nm, 940 nm, 980 nm, and 1064 nm.11 Mid-infrared region lasers-such as those used for hard-tissue procedures-include wavelengths of 2,780 nm and 2,940 nm, and far–infrared region at 10,600 nm Laser application in operative dentistry: Use of Laser in detection of caries: Laser fluorescence systems for detection of dental caries originally 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. For detection of dental caries in pits and fissures, laser fluorescence offers greater sensitivity than conventional visual and tactile methods. The technique is also well suited to smooth surface lesions on cervical surfaces of teeth and to recognition of caries beneath clear fissure sealants. Detection of proximal lesions is technically more difficult, and in this setting, argon laser-induced fluorescence offers a valuable adjunct to conventional methods. 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. 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. Cavity preparation The Er: YAG laser was tested for preparing dental hard tissues for the first time in 1988. It was successfully used to prepare holes in enamel and dentine with low ‘fluences’ (energy (mJ)/unit area (cm2)). Even without water-cooling, the prepared cavities showed no cracks and low or no charring while the mean temperature rise of the pulp cavity was about 4.3°C. it was concluded that dentine and enamel removal was very effective with no risk to the pulp and the ablation rates in enamel were stated to be in the range of 20-50 μm/pulse, and in dentine they were reported to be as high at lower fluences. Clinically, cavity preparation in enamel results in ablation craters with a white chalky appearance on the surface of the crater. In dentine, cavity margins are sharp and dentinal tubules remain open without a smear layer. Caries removal: Carious material contains a higher water content compared with surrounding healthy dental hard tissues. Consequently, the ablation efficiency of caries is greater than for healthy tissues. There is a possible selectivity in the removal of carious material using the Er: YAG laser because of the different energy requirement to ablate carious and sound tissues leaving those healthy tissues minimally affected. The ablation threshold of healthy dentine is two times higher than the corresponding threshold of carious dentine. Therefore, very small fluences (energy (Joules) / area (cm2)) of the Er: YAG laser energy are required to selectively ablate carious dentine. The laser removed infected and softened carious dentine to the same degree as the bur treatment. In addition, a lower degree of vibration was noted with the Er: YAG laser treatment. Restoration removal: The Er: YAG laser is capable of removing cement, composite resin and glass ionomer. The efficiency of ablation is comparable to that of enamel and dentine. Lasers should not be used to ablate amalgam restorations however, because of potential release of mercury vapor. The Er:YAG laser is incapable of removing gold crowns, cast restorations and ceramic materials because of the low absorption of these materials and reflection of the laser light. Etching: Laser etching has been evaluated as an alternative to acid etching of enamel and dentine. The Er: YAG laser produces micro-explosions during hard tissue ablation that result in microscopic and macroscopic irregularities. These microirregularities make the enamel surface microretentive and may offer a mechanism of adhesion without acid-etching. However, it has been shown that adhesion to dental hard tissues after Er: YAG laser etching is inferior to that obtained after conventional acid etching. These authors attributed the weaker bond strength of the composite to laser-etched enamel and dentine to the presence of subsurface fissuring after laser radiation. This fissuring is not seen in conventional etched surfaces. The subsurface fissuring contributed to the high prevalence of cohesive tooth fractures in bonding of both laser-etched enamel and dentine. The use of Laser in curing of resin restoration: 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. Argon laser radiation is also able to alter the surface chemistry of both enamel and root surface dentine which reduces the probability of recurrent caries. This clinical benefit is added to the reduced curing time and improved depth of cure achieved with the argon laser. Treatment of dentinal hypersensitivity: Dentinal hypersensitivity is one of the most common complaints in dental clinical practice. Various treatment modalities such as the application of concentrated fluoride to seal the exposed dentinal tubules have been tested to treat the condition. However, the success rate can be greatly improved by the ongoing evaluation of lasers in hard tissue applications. A comparison of the desensitizing effects of an Er: YAG laser with those of a conventional desensitizing system on cervically exposed hypersensitive dentine showed that desensitizing of hypersensitive dentine with an Er: YAG laser is effective, and the maintenance of a positive result is more prolonged than with other agents. Caries prevention: Several studies examined the possibility of using laser to prevent caries. It is believed that laser irradiation of dental hard tissues modifies the calcium to phosphate ratio, reduces the carbonate to phosphorous ratio, and leads to the formation of more stable and less acid soluble compounds, reducing susceptibility to acid attack and caries. Laboratory studies have indicated that enamel surfaces exposed to laser irradiation are more acid resistant than non-laser treated surfaces. Bleaching: The objective of laser bleaching is to achieve an effective power bleaching process using the most efficient energy source, while avoiding any adverse effects. Power bleaching has its origin in the use of high-intensity light to raise the temperature of hydrogen peroxide, accelerating the chemical process of bleaching. The FDA approved standards for tooth whitening has cleared three dental laser wavelengths: argon, CO2 and the most recent 980-nm gallium aluminum arsenide (GaAIAs) diode.