15. LASERS.pptx for lasers in conservative dentistry

Lasers used in endodontics and conservative dentistry

1. LASERS in endodontics Guided by : Presented By: Dr. Yogesh Sahu Patatri Mitra Dr. Praveen Mishra Dr. Abhishek Pal Dr. Shruti Sharma

2. Introduction landmarks in development of lasers laser physics laser delivering systems emission modes characteristics of laser light laser tissue interaction effects of laser on oral tissues classification of lasers diagnostic laser applications for detection of dental caries diagnostic laser applications used as research tools lasers in endodontics CONTENTS

3. Laser is one of the most significant contributions of the last century to science. The first successful demonstration of laser beam was done using rubycrystal by Theodore Mainman in the year 1960. With his contribution, we have lasers to help us progress in almost all scientific, technical, industrial, economic, social and medical fields. INTRODUCTION The development of Lasers has revolutionized every field of medical science, including endodontics. Laser is a device that transforms light of various frequencies into a chromatic radiation in the visible, infrared and ultraviolet regions with all the waves in a phase capable of mobilizing immense heat and power when focused at a close range. Laser is acronym for ‘Light amplification by stimulated emission of radiation’. The first laser was constructed by Theodore Harold Maiman in 1960 using synthetic Ruby.

4. Important Landmarks in the Development of Lasers

5. PRINCIPLE OF LASEr When electromagnetic wave containing photons passes through a cloud of ammonia gas , the gas molecules will be raised to a higher energy state as energy is absorbed Einstein predicted that if a photon of correct size struck a molecule already in an excited state, that molecule would fall back to lower energy level and would emit a photon of exactly the same size and moving in the same direction as the entering photon. Thus, in case of ammonia gas, the molecules can undergo two possible changes, i.e. either moving to a higher state or being pushed back to a lower one.

6. These two photons will strike two further molecules causing production of another two photons and the vicious reaction starts. Normally, the first process would predominate but if the majority of molecules are already in a higher energy state then the released photon will move in speed with the original photon These two photons will strike two further molecules causing production of another two photons and the vicious reaction starts. This process is called as LASER.

7. COMPONENTS OF LASER DEVICE LASER MEDIUM: Laser medium determines the wavelength of the light emitted from laser. The names of dental lasers are based on the active medium that is to be stimulated. The active medium can be a gas (argon, carbon dioxide), a liquid (dyes) or a solid state crystal rod [neodymium: yttriumaluminium -garnet ( Nd:YAG ), erbium-doped yttrium aluminium garnet ( Er : YAG) or a semiconductor (diode lasers)].

8. 2. OPTICAL CAVITY/LASER TUBE/OPTICAL SCREEN: It consists of two mirrors, one fully reflective and other partially transmissive; located on either end of the optical cavity. 3. POWER SOURCE: The power source excites or pumps the atoms of laser medium to their higher energy levels

9. Characteristics of laser light The significant feature of laser is the enormous difference between the character of its light and light from other sources The most striking features of lasers are their: Coherence Monochromatic Brightness and intensity Collimation Focusability

10. The solar system emits a wide spectrum of radiations; part of them (approximately 40 %) are within the visible spectrum of the light, and two limited bands extend to the ultraviolet and infrared spectrum that are not visible to human sight. Electromagnetic Spectrum of Light The solar system emits a wide spectrum of radiations; part of them (approximately 40 %) are within the visible spectrum of the light, and two limited bands extend to the ultraviolet and infrared spectrum that are not visible to human sight.

11. Laser Delivery Systems ARTICULATED ARM Before the introduction of Nd:YAG laser in 1990, most dental lasers used bulky articulated arm for their delivery system. It consists of a series of hollow tubes with mirrors at each joint (called a knuckle ) that reflect the energy down the length of tube. This joint allows the delivery arm to be bent in such a way as to bring the handpiece close to the target tissue. The laser energy exits the tube through the handpiece. Most commonly used with CO2 laser.

12. WAVEGUIDE Waveguide is a single, long semiflexible tube without knuckles or mirrors. It consists of an inner reflective lumen along which the laser energy is transmitted and exits through a handpiece at the end of the tube which can be used either in contact or non-contact mode.

13. OPTICAL FIBERS The American Dental Laser dLase Nd:YAG system was the first such instrument to use a fiberoptic delivery system. This fiberoptic technology allows for contact with the target tissue. The fiberoptic cables are attached to a small handpiece similar in size to a dental turbine and are available in sizes ranging from 200 -1000 μm in diameter. Fiberoptic cables also are relatively flexible.

14. Emission Modes Once the laser is produced, its output power may be delivered in the following modes. Continuous wave: In this mode, the laser emits radiation continuously at a constant power levels of 10 to 100 W, e.g. CO2 laser. Chopped: 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 500 ms . 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.

15. Super-pulsed: The duration of pulse is one hundredth of microseconds. Ultra-pulsed: This mode produces an output pulse of high peak power that is maintained for a longer time and delivers more energy in each pulse than in the super-pulsed mode.

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17. LASER-TISSUE INTERACTION Absorption The desired interaction is the absorption of laser energy by the intended target tissue. This amount of energy that is absorbed by the tissue depends on the tissue characteristics, such as pigmentation (melanin of skin, hair and hemoglobin in blood), proteins and water content; and also on the laser wavelength and emission mode. Argon has a high affinity for melanin and hemoglobin in soft tissue. Transmission This interaction is inverse of absorption; transmission of laser energy directly through the tissue without effecting it.

18. Reflection The incident laser beam redirects itself without affecting the target tissues. Scattering , Scattering of the reflected light weakens the intended energy and possibly produces no useful biologic effect; may transfer heat to the adjacent tissues.

19. b. Photochemical interactions: The basic principle of photochemical process is that specific wavelength of laser light is absorbed by naturally occurring chromophores (tissue compounds), which are able to induce certain biochemical reactions. Photosensitive compounds, when exposed to laser energy, can produce a single oxygen radical for disinfection of the root canals. c. Photothermal interactions: The radiant energy absorbed by tissue substances are transformed into heat energy, which then produces the requisite effects

20. d. Photomechanical and photoelectrical interactions: These include photodisruption , photoplasmolysis and photoacoustic interactions. The pulse of laser energy on the dental tissues can produce a shock wave (photo acoustic effect of laser light), which may explode or pulverize the tissues with mechanical energy. Photoplasmolysis describes the removal of tissues through the formation of electrically charged ions.

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22. Classification of Lasers Traditionally, lasers have been classified according to: The wavelength . The physical construction of the laser (e.g. gas, solid-state, liquid or semiconductor diode) and The type of medium which undergoes lasing (e.g. erbium: yttrium aluminum garnet, etc.). Tissues on which it is used: Soft and hard tissues . The degree of hazard to the skin or eyes following inadvertent exposure.

23. 23 ACCORDING TO WAVELENGTH Excimer laser (wavelength 150–350 nm ) Visible light laser (wavelength 350–750 nm ) • Ruby laser • Argon laser • Helium-neon laser Infrared laser (wavelength 750–12000 nm ) • Neodymium: Yttrium- aluminium -garnet ( Nd:YAG ) • Holmium: Yttrium aluminium garnet ( Ho:YAG ) • Erbium-doped yttrium aluminium garnet ( Er:YAG ) • Carbon dioxide laser

24. 24 2. ACCORDING TO THE TYPE OF LASER MEDIUM Gas laser (argon, helium-neon, carbon dioxide) Solid-state laser ( Nd:YAG , Er:YAG , Er:Cr:YAG , Ho:YAG ) Semiconductor laser (Gallium-Arsenide, Gallium- Aluminium -Arsenide, Indium-Gallium- Aluminium -Phosphide) 3. ACCORDING TO TISSUES TO BE LASED Soft tissue laser Hard tissue laser

25. 26 THE MODIFIED CLASSIFICATION Class 1 : Safe under all conditions; maximum permissible exposure (MPE) cannot be exceeded when viewing a laser with naked eye or with microscope. Class 1M : Safe under all conditions, except when passed through microscopes and telescopes. Class 2: Safe because of blink reflex; applies to visible light lasers (400–700 nm). Laser pointers and measuring instruments are in class 2. Class 2M: Safe because of blink reflex, if not viewed through optical instruments. Class 3R : Visible continuous lasers are limited to 5 mW (for pulsed lasers, this limit varies). 3R is considered safe with restricted beam viewing. Class 3B : 3B laser is hazardous if exposed directly (direct viewing need protective eyewear). The accessible permissible emission limit (AEL) for continuum laser is 0.5W and wavelength 400–700 nm. Class 4 : Lasers exceeding 3B level of AEL; mostly unsafe for eyes and skin.

26. TYPES OF LASERS 27 SOFT TISSUE LASERS The soft tissue lasers are athermic , low energy lasers that generally utilize the semiconductor laser diodes. Their wavelength stimulates cellular activity. They aid in tissue regeneration and wound healing by increasing collagen production by fibroblast stimulation. Soft tissue lasers are used to relieve pain, inflammation, edema and also accelerate healing

27. 28 In dentistry, soft tissue lasers are used for: • Desensitization of hypersensitive dentin • Healing • Reducing pain and promoting healing of ulcers, etc. The examples of soft tissue Lasers are: • Helium – Neon (He-Ne) • Gallium – Arsenide (Ga- Ar ) • Gallium – Aluminium –Arsenide (Ga-Al- Ar )

28. 29 b. Hard Tissue Lasers The hard tissue lasers are thermic and of high energy, that are utilized in surgery as precise energy source, i.e. cut, coagulate. These are mostly used for caries removal, cavity preparation and etching of enamel and cementum surfaces. The examples of hard tissue lasers are: • Carbon dioxide • Neodymium: Yttrium aluminium garnet ( Nd:YAG laser)

29. A . CARBON DIOXIDE (CO2 ) LASER Carbon dioxide laser (active medium CO2 and nitrogen) produces a beam of infrared light centering in 9.4 μm to 10.6 μm . CO2 laser was thought to be suitable for selected surface applications on teeth, such as sealing of pit and fissures, welding of ceramic materials to enamel and prevention of dental caries. As principally absorbed by water molecules, it can cut many hard and soft tissues (used both for hard tissues ablation and soft tissue surgeries). The wavelength has the highest absorption in hydroxyapatite out of any dental laser. Therefore, structures adjacent to surgical site must be shielded from laser beam.

30. Advantages • Excellent hemostasis, reduce bacteremia • Minimum postoperative pain/discomfort • Remove tissue quickly and efficiently • Minimize mechanical trauma Disadvantages • Lack of feed back (CO2 laser used in a non-contact mode) • Black-brown pigmentation of the treated tissues • Costly

31. B. ARGON LASER The argon laser uses argon gas as the active medium, which generate coherent visible light with primary wavelengths of 488 and 514 nm. The 514 nm (blue green color) light wavelengths have peak absorption in red pigment such as hemoglobin; thus, laser light is well absorbed in pigmented tissues with abundance of hemoglobin, hemosiderin and melanin. Argon laser light is not well absorbed by enamel and dentin or other non-pigmented tissues.

32. These characteristics make argon laser very useful for cutting, coagulating and providing hemostasis on gingival and oral mucosa. The argon laser is primarily used for root planing and curettage, gingival retraction, gingivectomy/ gingivoplasty , frenectomy, treatment of oral lesions, tissue welding and for caries detection. c. Neodymium: Yttrium Aluminium Garnet ( Nd:YAG ) Laser Nd:YAG laser systems are usually large and bulky. This system emits its pulsed energy at 1064 nm (near infrared) and this energy is directed through a 320 μ silica fiber, using the high peak powers and free running pulse emission.

33. When this beam is used in non-contact, defocused mode, this can penetrate deep and is used for hemostasis, treatment of aphthous ulcers or pulpal analgesia. The main disadvantage is the direct exposure of pulp by laser light through crown or root, leading to denaturation of pulp tissues. The common clinical applications are for cutting and coagulation of the dental soft tissues. It has an affinity for pigmented tissues (more for melanin and less for hemoglobin). It minimizes the heat build-up in tissues.

34. d. Erbium Laser Erbium laser is a promising laser system because of its emission wavelength (Er:YAG-2940 nm and Er:Cr:YAG-2780 nm), which coincides with main absorption peak of water, resulting in good absorption in all biologic tissues including enamel and dentin. Infrared laser systems like carbon dioxide or Nd:YAG laser have reported the presence of zones of carbonization and necrosis due to high temperatures. Er:YAG laser treatment does not induce any thermal changes. A high steam pressure then leads to micro-explosions with erupting particles. Er:YAG laser can be used for the removal of healthy hard tissue

35. e. Semiconductor/Diode Laser Gallium-Arsenide (GaAs) 904 nm , Gallium- Aluminium -Arsenide ( GaAlAs ) 780–890 nm and Indium-Gallium- Aluminium Phosphide ( InGaAlP ) 630–700 nm are the common diode lasers. In diode lasers, the active medium is sandwiched between silicon wafers. The discharge of current from one silicone wafer to another releases photons from the active medium. Diode lasers are used for the treatment of dentin hypersensitivity, wound healing and for relieving postsurgical pain.

36. 37 Advantages of laser • Interaction with diseased tissue is selective and precise • Damage to surrounding tissues is minimum • Easy osseous tissue removal and contouring • Provide good hemostasis • Help reduction in pain • Minimal need for anesthesia • No whining sound or vibration of dental drill • Less chair time • Fast healing • Less antibiotics and analgesics required

37. 38 Disadvantages of laser • High cost • Delivery systems are bulky • Difficult access to the surgical area • Precise selection of wavelength is mandatory for different procedures

38. The rapid development of laser technology coupled with better understanding of interactions with biological tissues, has widened the scope of applying this technology in endodontics. In endodontics, laser energy is being tried in the following procedures: Analgesia Reducing permeability of dentin and fusing dentin plug at apical end Sterilization of endodontic instruments Pulp testing (assessment of flow of pulpal blood by laser Doppler flowmetry) Pulp capping and pulpotomy Preparation of access cavities and root canal walls Disinfection of root canals APPLICATION OF LASER TECHNOLOGY IN ENDODONTICS

39. viii. Obturation of root canals ix. Removing gutta-percha and separated instruments x. Endodontic surgery xi. Endodontic mishaps xii. Laser bleaching xiii. Stimulate healing and relieving postoperative pain xiv. Retrograde cavity preparation

40. 41 i . ANALGESIA Certain wavelengths of laser energy interfere with the sodium pump mechanism, change cell membrane permeability, alter temporarily the endings of sensory neurons and block depolarization of C and Aδ fibers of the nerves. The pulsed Nd:YAG laser has been successfully used for achieving analgesia. II. REDUCING PERMEABILITY OF DENTIN AND FUSING DENTIN AT APICAL END It is established that the laser irradiation of 10 pulses/ second for two minutes on dentin melts normal dentinal surface and closes the exposed dentinal tubule orifices without creating any surface cracks. The dentin surface after Nd:YAG laser treatment showed no protrusive rods (protrusive rods are a measure of open dentinal tubules).

41. 42 Lasers can effectively treat dentin hypersensitivity. The laser treatment is also effective in fusing the dentin at the apical end. III. STERILIZATION OF ENDODONTIC INSTRUMENTS A significant reduction in the microbial loads due to raised temperatures has been reported after the sterilization of endodontic instruments by lasers. Carbon dioxide, argon and Nd:YAG lasers effectively sterilize the instruments used in endodontics.

42. 43 IV. PULP TESTING (ASSESSMENT OF FLOW OF PULPAL BLOOD BY LASER DOPPLER FLOWMETRY) Laser Doppler flowmetry is a non-invasive technique that detects net red blood cell movement in small volumes of a tissue and monitor the total blood flow through that tissue It utilizes light beam from a He-Ne laser (632.8 nm) , which is carried to and from the tissues by a fiberoptic probe that carries light by one fiber and receives back the scattered light (by moving red cells which undergo frequency shift according to the Doppler principle) by another fiber to the instrument. Lasers ( Nd:YAG ) has also been used to differentially diagnose types of pulpitis from normal pulp

43. 44 V. PULP CAPPING AND PULPOTOMY For direct pulp capping, an energy level of 1 W at 0.1 second exposure time with one second pulse intervals is applied until the exposed pulps are completely sealed. It is established that laser therapy stimulates odontoblast activity (calcium and collagen production), leading to secondary dentin formation. Carbon dioxide laser has been very effective in pulp treatment procedures. It sterilizes and heals the irradiated area, reduce inflammation and the size of blood clot, ensuring close contact of the pulp with the capping materials (fast mode for hemostasis, disinfection and sealing of exposed pulp tissue). Nd:YAG , Er:YAG and Er:Cr:YAG have also been tried successfully in pulp capping and pulpotomies. These are equally effective in hemostasis and coagulation of exposed pulp.

44. 45 VI. PREPARATION OF ACCESS CAVITIES AND ROOT CANAL WALLS Various Lasers in different forms have been tried for preparation of access cavities and root canal walls ( Er:Cr:YSGG —2780 nm, Er:YAG —2940 nm). The root canals prepared with Lasers are cleaner as compared to conventional techniques. TECHNIQUE The apical region of canal is initially hand instrumented with a No. 15 K-file. The laser energy set at 150 mJ through fiberoptic was inserted into root canal up to working length. The canal is prepared circumferentially in apical third, middle third and the coronal third, sequentially increasing the size, as required.

45. 46 The Er:YAG laser is equally effective for debris removal, producing a cleaner surface with a higher number of open tubules compared to other lasers Photon Induced Photoacoustic Streaming (PIPS) Technology Photon induced photoacoustic streaming (PIPS) harness the power of the Er:YAG laser to create photoacoustic shock waves within the irrigating solutions introduced in the root canal. The shock waves effectively stream the solutions through the entire canal system. The canals are left clean and the dentinal tubules are free of smear layer. Photon induced photoacoustic streaming (PIPS) is equally effective for final rinsing prior to obturation

46. 47 PIPS technology eliminates the need to introduce the tip into the root canals. Unlike traditional laser techniques (placement of tip at 1.0–5.0 mm from apical constriction) PIPS tip is placed at the coronal chamber, allowing acoustic waves to spread into the root canals. A combination of laser wavelength is being used in twinlight endodontic treatment (TET). The procedure facilitates clean canals with open dentinal tubules free of smear layer.

47. VII. DISINFECTION OF ROOT CANALS Various studies have confirmed the efficacy of diode and Nd:YAG lasers in eradicating bacterial load from the root canals An average of 34% decrease in colony forming units (CFU) for Actinomyces and 15.7% for Pseudomonas aeruginosa with 5 Hz laser treatment and a decrease of 77.4% for Actinomyces and 85.8% for Pseudomonas with 10 Hz laser have been reported. Photoactivation disinfection (PAD)/light activated disinfection (LAD)/photodynamic antimicrobial chemotherapy (PACT) work on the principle that photosensitive molecules get attached to the membrane of the bacteria. The specific wavelength of laser irradiation leads to the production of singlet oxygen, which may cause bacterial cell wall to rupture, killing the bacteria.

48. It is established that this technique effectively destroys bacteria remaining in the canal spaces after using conventional irrigants in root canal treatment. viii. Obturation of Root Canal Spaces Argon laser has been used as a heat source to compact the gutta-percha during root canal obturation. The quality of apical seal achieved has not been established yet.

49. 50 ix. Removing Gutta-percha and Separated Instruments Nd:YAG laser has successfully used to remove gutta percha and broken files from the root canals. Nd:YAG and Er:YAG lasers are effective in removing zinc oxide sealers and other filling materials. Biolase laser is used to remove gutta-percha and other filling materials following the hydrokinetic process. x. Endodontic Surgery Lasers have been tried in endodontic surgery to irradiate the surgical site during apicoectomy. effectively achieves hemostasis and visualization of the operating field. Er:YAG laser in a low-output power, when used in apical surgery, lead to smooth and clean surface devoid of charring

50. 51 xi. Endodontic Mishaps Accidental perforation of pulp chamber is a common feature during tooth preparations. Such perforations may occur anywhere along the root during endodontic procedures. Lasers have been tried to sterilize the affected area and seal the perforation effectively. Nd:YAG laser has been observed to be effective in disinfecting the area of perforation and removing the attached organic/ inorganic smear layer followed by sealing the area with laser irradiated composites Nd:YAG laser was tried to seal the vertical root fracture fragments and other cracks.

51. 52 The crack surfaces were filled with tricalcium phosphate and melted by the laser irradiation (various studies confirmed the presence of tricalcium phosphate along the crack lines). A few authors have successfully tried melting bioactive glass paste over the crack site using carbon dioxide laser (higher temperature of laser could melt bioactive glass paste in a very short span of time). xii. Laser Bleaching The procedure utilizes 30–35% hydrogen peroxide, which is usually applicable in routine bleaching. Laser whitening gel has a unique mix of thermal absorption crystals integrated into gel of highly processed fumed silica and 35% hydrogen peroxide.

52. 53 xiii. Stimulate Healing and relieving Postoperative Pain Laser causes an anti-inflammatory effect in the irradiated area, which accelerates healing and decreases pain. It has got a stimulating action on bone morphogenic proteins, which further stimulates undifferentiated mesenchymal cells into osteoblasts, resulting in increased osteogenesis. Laser also stimulate fibroblasts for more collagen production, accelerate cell reproduction and also cause increased prostaglandin levels, which help in healing and regeneration of tissues

53. 54 xiv. Retrograde Cavity Preparation Er:YSGG and Cr:YSGG laser have been used for rootend cavity preparation. The root-surface cracking that produced by ultrasonic retropreparation tips/ conventional preparation using a bur have been overcome by lasers

54. REFERENCES 55 Lasers in dentistry- dcna oct 2004 Lasers and light amplification in dentistry – dcna oct 2000 Lasers in endodontics:a review- iej vol 33 Endodontics-ingle Pathways of pulp- cohen Lasers in conservative dentistry and endodontics- A review- IOSR journal of dental and medical science A contemporary apprise on LASERS and its applications in dentistry- international journal of oral health and medical research Laser in endodontics- international journal of oral health and medical research- jun 2015

55. LASERS in conservative dentistry Guided by : Presented By: Dr. Yogesh Sahu Patatri Mitra Dr. Praveen Mishra Dr. Abhishek Pal Dr. Shruti Sharma

56. Lasers in conservative dentistry 58

57. CARIES DETECTION 59

58. Quantitative Light-induced Fluorescence 60 The loss of mineral from an area of enamel results in a change in its optical properties, with an increase in the scattering of incident light and a decrease in the amount of fluorescence. There’s a direct correlation between the amount of mineral loss and decrease in fluorescence allowing for quantification of mineral loss. In the case of the QLF the visible light has a wavelength of 370 nm , which is in the blue region of the spectrum. Principle

59. 61 The resultant auto-fluorescence of human enamel is then detected by filtering out the excitation light using a bandpass filter at w> 540 nm by a small intra-oral camera. This produces an image that is comprised of only green and red channels (the blue having been filtered out) and the predominate colour of the enamel is green.

60. 62 Argon ion laser emitting blue green light (λ–488 nm) was used. This source produces diffuse monochromatic light (Light of a characteristic wavelength) and when a tooth is exposed to this light source, fluorescence of the enamel occurring in the yellow wavelength is observed (540 nm) through a yellow high pass filter to exclude tooth scattered blue green light. Demineralized areas appear as dark spots.

61. DIAGNODent Laser Device 63 A chairside, battery-powered quantitative diode laser fluorescence device by KaVo , which uses laser fluorescence to detect incipient caries. It measures the fluorescence of bacterial products within carious lesions — namely, porphyrins— rather than crystalline disintegration. This theory is supported by the fact that the DIAGNODent device does not detect lesions produced in the laboratory by means of acidic buffers, which produce no microbiological activity. The device generates a laser beam that is absorbed by materials within the tooth and is subsequently re-emitted as infrared fluorescence.

62. 64 This device makes use of laser autofluorescence technology, but instead of using blue light it uses red light, of wavelength 655 nm , output < 1mW . This red light identifies caries as having an increased fluorescence over sound tooth . Source of light is a diode laser that emits light at 655 nm wavelength from a fiber optic bundle directed onto the occlusal surface of a tooth. Light is transported to the angulated tip within a central fiber. Around the central fiber, additional fibers are concentrically arranged to collect fluorescent light from dental hard tissues. The reflected and ambient lights are eliminated by a filter.

63. 65 Display value: Therapy: 0 - 14 No special measures. 15 - 20 Usual prophylactic measures. 21 - 30 More intensive prophylaxis or restoration from 30 Restoration and more intensive prophylaxis. Interpretation of values

64. Optical coherence tomography 66 It is a non contact, non invasive imaging technique use to obtain high resolution cross sectional images Infrared ray of 830 nm is used. It is based on low coherence (white light) interference of electromagnetic waves which was initially used in measurement of optoelectronic components. It can detect morphological changes of tooth surface during demineralization It can determine lesion depth.

65. Preventive effects 67 Laser energy has the potential to alter the enamel to make it less susceptible to subsurface demineralization. CO2 laser is used- long wavelength easily absorbed by enamel. The most effective wavelength is – 10,600nm Nd:YAG is used as pit & fissure sealant. It removes inorganic & organic debris in pit & fissure without damaging surrounding healthy enamel.

66. 68 Two features are important for Laser to help in caries prevention: MINIMUM ENERGY DENSITY IS REQUIRED TO AVOID DAMAGING SOFT TISSUES ESPECIALLY PULP. THE ABILITY TO DIRECT LASER BEAM WITHIN RESTRICTED SPACE BY MEANS OF FLEXIBLE BEAM GUIDE. THE ENAMEL SURFACE GETS SEALED & BECOME LESS SUSCEPTIBLE TO DIFFUSIO N . THE COMPOSITION OF ENAMEL IS ALTERED , WHICH REDUCES ITS SOLUBILITY & PERMEABILITY.

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68. CAVITY PREPARATION 70 CO2 Laser has been successfully used to remove carious dentin without damaging pulp. Nd:YAG is also being used for removing caries. Advantages: Laser induced analgesia Less postoperative sensitivity Access to subgingival caries is improved. Er:YAG laser has shown more promising results. It is absorbed by water & hydroxyapatite, which partially accounts for its efficiency in cutting enamel and dentin .

69. 71 For the treatment of dentinal hypersensitivity: Dentinal hypersensitivity is characterized as a short, sharp pain from exposed dentin that occurs in response to provoking stimuli such as cold, heat, evaporation, tactility, osmosis, or chemicals. The first mechanism implies the direct effect of laser irradiation on the electric activity of nerve fibers within the dental pulp, whereas the second involves modification of the tubular structure of the dentin by melting and fusing of the hard tissue or smear layer and subsequent sealing of the dentinal tubules. The lasers used for the treatment of dentinal hypersensitivity are divided into two groups: - low output power lasers (helium neon and gallium/ diode) and - middle output power lasers ( Nd:YAG and CO2)

70. 72 Low output power laser therapy is used to support wound healing, shows anti-inflammatory effect, has the ability to stimulate nerve cells. Low output laser uses an output power of only 6 mW , which do not affect the morphology of the enamel or dentin surface but allows a small fraction of the energy to reach the pulp tissue.

71. 73 Treatment of tooth erosion Dental erosion is caused by a series of extrinsic and intrinsic factors. Extrinsic factors largely include the consumption of acidic foods. Carbon dioxide lasers have been mostly used in the prevention of erosion, due to its efficient interaction with hydroxyapatite crystals. The possibility of increasing the enamel resistance to demineralization after laser irradiation was first demonstrated in 1965 with a ruby laser. Some studies showed partial beneficial results with the use of Nd:YAG lasers.

72. 74 For removal of restorative materials The Er:YAG laser is capable of removing all dental cements and composite resin restorations. Lasers should not be used to ablate amalgam restorations, because of the potential release of mercury vapour. The Er:YAG laser is incapable of removing gold crowns, cast restorations and ceramic materials because of the low absorption of these materials and the reflection of the laser light. These limitations highlight the need for adequate operator training in the use of lasers.

73. 75 Etching of tooth surface Laser etching has been evaluated as an alternative to the 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 micro-irregularities make the enamel surface microretentive and offer a mechanism of adhesion without acid etching to composite resin. CO2 & Nd:YAG Laser are also being used for etching

74. 76 Photopolymerisation Argon laser 488nm of wave length is a promising source, as the wavelength of the light which is emitted by this laser is optimal for the initiation of polymerisation of the composite resin. Argon laser wavelength activates camphorquinone , a photo-initiator that causes polymerisation of the resin composites. The argon laser radiation is also able to alter the surface chemistry of both the enamel and root surface dentin, which reduces the probability of the recurrent caries.

75. 77 Studies have also shown the positive effects of the argon laser compared to halogen light: 1) Increased hardness, 2) Increased diametral tensile strength, transverse flexural strength and compressive strength of the polymerised composite resin, 3) Increased depth of curing 4) Reduction in the residual monomer of composite resin.

76. LASER HAZARDS The beneficial effects of Lasers have been accepted in day-to-day practice; however, continuous use may have certain hazards. The hazards can be: Effect on eyes Effect on skin and other tissues Environmental hazards Electrical hazards

77. Effect on Eyes Potential injury to the eye can occur either by direct emission from Laser or by reflection from a specular surface. The primary ocular injury that may result from a Laser accident is a retinal or corneal damage. Retinal injury is possible with emissions in the visible (400–780 nm) and near infrared (780–1400 nm) wavelengths. It may cause ‘ scotoma ’ (loss of vision in the path of visual field; blind spot).

78. b. Effect on Skin and other Tissues Laser may damage skin and other tissues as a result from thermal interaction of radiant energy with tissue proteins. Temperature elevation of 21°C above normal body temperature can produce cell destruction by denaturation of cellular enzyme and structural proteins, which interrupts basic metabolic processes. Factors affecting laser-tissue interaction are: • The relative absorption and transmission of particular wavelength. • The pulse duration and pulse repetition rate.

79. • The level of radiation exposure. • The relative degree of vascularity of tissue. The deleterious effects of Lasers on enamel and dentin are: • Enamel exhibits gross cratering from 0.1–1.1 mm deep depending on amount of energy delivered to target area. In deeper penetration, dark speckling of exposed dentin can be seen. Examination under polarized light may show crystallographic changes. Dentin shows shallow, irregular craters 0.1 mm deep. Three distinct zones of dentinal destruction are: central zone of complete dentinal destruction; an immediate surrounding area of partial dentinal destruction and a scattered zone of dark speckling beyond first two zones.

80. c. Environmental Hazards Inhaled air borne contaminants can be emitted in the form of smoke or fume generated through thermal interaction of Laser with tissue or through accidental escape of toxic chemical and gases from Laser itself. These damage the functioning of respiratory system. d. Electrical Hazards Because Laser use high currents and high voltage power supplies, these are potentially hazardous. Electrical hazards of Lasers can be grouped as electrical shock hazards, electrical fire hazards or explosion hazards

81. Laser Safety American National Standard Institute (ANSI) has classified Lasers on their safety parameters. • Class I denotes Laser system, which under normal conditions do not pose hazard. • Class II denotes low power visible Laser system, they usually do not present hazard; but may have potential for hazard, if viewed directly or extended period of time. • Class III (a) denotes Laser system having ‘caution’ label that normally would not injure the eye if viewed momentarily; but present hazard if viewed using collecting optics. • Class III(b) denotes Laser system that is hazardous, if viewed directly. • Class IV denotes Laser system that is hazardous not only from direct reflection, but also produce significant skin hazards, etc.

82. 84 ANSI has specified ‘Maximum Permissible Exposure ’, i.e. the level of radiation to which a person may be exposed without hazardous effects on adverse biologic changes. In some applications open beams are required making it necessary to define an area of potentially hazardous laser radiation. This is Normal Hazard Zone (NHZ) which is defined as a space within which the level of direct, scattered or reflected laser exceeds the MPE

83. 85 The safety requirements include: • A Laser warning signal outside the clinic. • Use of barriers within the operatory. • Use of eyewear to protect against reflected Laser light or accidental direct exposure. • The residue left after tissue ablation should be evacuated using high volume suction. • Equipment should be serviced and checked regularly. • The operator should take adequate precautions to prevent injury or damage to adjacent soft and hard tissue or to the pulp and periodontal apparatus.

84. Excimer laser 86 The following limitation of CO2 and Nd:YAG Laser led to the development of Excimer laser. • Vaporization and carbonization of dental tissue. • Thermal side effect, which may damage pulp and periodontal tissue ( Temperature may rise up to 65°C). • Caries removal leads to structural changes such as cracks, zones of necrosis, etc.

85. 87 Excimers work by the process of ablative photo decomposition, which implies bond breaking of molecules with minimal thermal side effects (Temperature increase is approximately 12°C). Residual energy is converted into kinetic energy by expansion of residual gaseous phase. Excimers are emitted in UV spectral range. The available Excimers are: ArF - 193 nm KrF - 248 nm XeCl - 308 nm XeF - 351 nm

86. 88 Argon-fluorine Excimer laser has the following advantages: Thermal effects are minimal (The temperature rise of pulp was 5°C). Prepare cavities in dental hard tissue without side effects. It has bacteriological effect on prepared surface. The possibility of tissue identification during the treatment process in selective removal of affected tissues. The zone of necrosis is small so there is no residual debris. The experiments have observed no carcinogenic effect.

87. REFERENCES 89 Lasers in dentistry- dcna oct 2004 Lasers and light amplification in dentistry – dcna oct 2000 Lasers in endodontics:a review- iej vol 33 Endodontics-ingle Pathways of pulp- cohen Lasers in conservative dentistry and endodontics- A review- IOSR journal of dental and medical science A contemporary apprise on LASERS and its applications in dentistry- international journal of oral health and medical research Laser in endodontics- international journal of oral health and medical research- jun 2015