Fundamentals of Laser Dentistry Kirpa Johar
Ablated enamel 35
Abscesses of periodontium 94
Absorption 3
of laser 5
Access cavity preparation 88
Accessories for CO2 unit 108
Activation of
fluoride gel 22
stannous fluoride gel 56
Adhesion and margin seal of laser prepared cavities 36
Advantages of
low level laser therapy 132
nd: YAG laser application 97
Aggressive periodontitis 94
Aluminum 57
Ankyloglossia 113, 114
Apical sealing 87
Application of
agent 67
gel 69
desensitizing gel post-bleaching 68
fluoride gel on tooth 22
gel 69
gingival barrier 69
rubber dam 41
thin layer of stannous fluoride gel in cervical area 56
tolonium chloride solution 136
ion laser 7
laser unit 48
Arsenide 57
Articulated arm of CO2 unit 108
Assisted teeth whitening 68
Bacterial plaque 55
Basic scheme of laser 3
Beam delivery system 4, 16
Benefits of ultrashort laser pulses 40
Bio-active and biocompatible glasses 56
Bleaching 63
mechanism of teeth 64
Bonding of fixed orthodontic appliance 122
Calcification 54
Calcium hydroxide 55, 76
Camphoroquinone absorption coefficient curve 47
Caries 63
resistance 24
Causes of tooth discoloration 62
Cavity preparation
using lasers 33
with numerous pulses in
dentin 36
enamel 36
Ceramic scissor 102
Cervical recession causing hypersensitivity 54
Chemical breakdown of carbamide peroxide 65
gingivitis 99
periodontitis 94
Classification of
different wavelengths of light 13
light 12
Clinical procedure of laser 68
Closure of diastema with orthodontic appliance 124
laser unit 108
surgical laser 77
Complications in wound-healing process 107
Composition of light cured filling materials 46
access cavity preparation 88
bleaching 64
pulp capping 76
therapy 95, 107
treatment 22, 55
Cosmetic facial laser surgery 112
Crown lengthening procedure 70
Cryosurgery 107
hard tissues 23
office in 21st century 140
Dentin hypersensitivity 56
Dentinal receptor mechanism 54
Dentist's team vision 140
Dentistry 130
Development of laser-assisted cavity preparation 32
handpiece 8
laser 8, 85, 96
handpiece used for teeth whitening 66
handpiece with metal guides 102
machine 96
tip 8
unit 113
machine 6
Direct pulp capping 76
Diseases of
jaw joint 130
nerval structures 130
Display of cavity 41
Distribution of water in tissue 38
Dye lasers 6, 7
Effect of
argon lasers 27
CO2 lasers on caries 25
different laser wavelengths on eye 13
er: YAG 29
laser on periodontal tissues 99
laser beam on eye 13
nd: YAG laser on periodontal tissues 97
temperature on target tissue 6
Electrotomy 107
Embeded tooth exposed 79
Emission modes 5
Endodontic problems 82
Er : YAG laser 8, 98
unit 78, 97
and erbium-chromium lasers 9
hand piece 41
Excimer laser 7
Extrusion of canine 123
Finishing and restoration of cavity 42
Formaldehyde 55
Four level system 4
Frenectomy 113
Frequency-doubled alexandrite laser 100
Full mouth laser-assisted bleaching 67
Function of laser involving 2
Gallium 57
Gas lasers 6
Gaussian beam and laser resonator 4
guard 67
hyperplasia in relation to maxillary posterior region 104
inflammation and bleeding on probing 98
Gingivitis 92, 94
Glass-ionomer cement 56
Granuloma interna 63
Helium-neon laser 57
Hemostasis techniques 110
Ho:YAG laser 41
Home bleaching 64
Host crystals 9
Iatrogenic discoloration 63
of laser beam on skin 13
on skin 13
Indications of pad technique 135
Infantile oral soft tissue 79
Inflamed gingival margins 99
Insertion of laser fiber into periodontal pocket 98
Intraoperative bleeding 106
Kinetic cavity preparation 33
Labial vestibuloplasty 115
activation of bleaching gel 70
biopsy 115
bleaching of non-vital teeth 67
bonding 122
crown lengthening procedure 70
excision of ulcer 117
frenectomy 124
gingival depigmentation procedure 72
lingual frenectomy using diode laser 114
periodontal therapy 96
pulp capping 77
pulpotomy 78
root canal sterilization 84
tooth exposure 122, 123
cable stripper 102
classes 13
cured materials 50
furnishes pocket debridement and establishes coagulation 101
in implant dentistry 111
integral part of 21st century dental office 140
photo polymerization 47
protective eyewear 17
radiation safety 15
education 12
goggles 17
officer 19
cavity 34
root canal sterilization 83
root canal therapy 89
therapy 95, 101, 107
tissue interactions 5
used in pad 135
veneer and enamel modification 35
warning sign 12
Light cure composite resin 42
Limitations of ultrashort pulse laser systems 40
frenectomy 114
vestibuloplasty 115
Lower output power lasers 57
Luxation of tooth after bone cutting 118
Main components of laser 3
Marketing laser dentistry 141
Maximum permissible exposure 12
Metal guide being fed to hand piece 103
Middle output power lasers 57
Mucocele in relation to lower lip 117
Natural pulpal defense mechanisms 54
Nd: YAG laser 41, 84, 97
periodontal diseases 94
ulcerative periodontitis 94
Nomination of laser safety officer 19
Operculectomy 79
Oral and maxillofacial surgery 108
Oxalate containing products 56
Parts of er:YSGG laser unit 34
Pericoronitis 112, 113
Peri-implantitis 111
Periodontitis 92, 94
Periodonto pathogenic bacteria 93
Photo polymerization reaction 46
Photodynamic therapy 134
Pre-eruption trauma 63
Preventive dentistry 23
Properties of
laser light 38
light 2
Protection of eyes 18
Pulpotomy 78
Pulse repetition rate 38
Q-1000 soft laser 131
Reaction of bacteria to laser light 83
Recurrent aphthous ulcer treatment 115
Reflection of laser by target tissue 5
Removal of caries 42
Requirements of root canal filling material 89
Root canal
filling 89
preparation 85
shaping 88
sterilization 82
goggles 103
in laser treatment 87
Scalpel 107
Several kinds of extrinsic discolorations 62
fluoride 55
monofluorophosphate 55
laser therapy 132
lasers applications 78
lesions 130
Solid state lasers 8, 9
Strawberry flavored fluoride gel 28
Stripping of laser cable 102
Strontium 55
Supporting periodontal therapy 95
diseases 63
factors of metabolic illness 93
Target tissue 5
Temporary filling material 77
Terra quant solo soft laser 130
Tetracycline staining 62
Theories of dentin hypersensitivity 54
Thermal diffusivity K 38
Three level system 4
Types of laser 41
Vestibuloplasty 115
Wound healing 128
Chapter Notes

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Basic Physics and Concepts of Lasers used in DentistryCHAPTER 1

  • ❖ Introduction
  • ❖ Properties of Light
  • ❖ Function of Laser Involving Optical Concepts
  • ❖ Laser Tissue Interactions
  • ❖ Laser Media
  • ❖ Pumping Methods and Schemes
  • ❖ Laser Concepts
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The word laser represents an elegant Acronym as “Light Amplification by Stimulated Emission of Radiation”. It was demonstrated for the first time in 1960 by Maiman.
Typical lasers, which emits in the visible and the adjacent areas of the UV and IR wavelengths comprise of a large number of Individual laser materials and laser oscillator setups working in the continuous wave or pulsed mode.
The development and application of lasers, emitting rather collimated or more or less intensive beams of narrow bandwidth coherent light, in association with optical and electro-optical components, has been recognized as a new field of optical science called photonics, comprising of aspects of quantum optics, electro-optics and linear and non-linear optics.
Light is a form of Electromagnetic energy that travels in waves at constant velocity. The basic unit of this radiant energy is called a Photon or a particle of light. A wave of photons can be defined by two basic properties:
Amplitude: Defined as total height of the wave oscillation from the top of the peak to the bottom. It is the measurement of the energy in the wave. The unit of energy is Joule.
Wavelength: It is the distance between any two corresponding points on the wave. It is the measurement of physical size measured in Meters.
Frequency: The measurement of a number of wave oscillation per second. It is inversely proportional to the wavelength, shorter the frequency, higher the wavelength.
Ordinary light is usually diffuse, not focused, e.g. light produced by a table lamp is a warm white glow. It is polychromatic, noncollimated and incoherent type.
Real light waves are circumscribed and hence subject to diffraction, i.e. the distribution of amplitude over the cross section varies during propagation.
In case of confined light distribution called a beam, the direction of propagation is not sharply defined but is distributed over a certain range of vectors.
Light produced by laser has opposite properties. It is monochromatic, coherent and collimated type.
Laser light has the property of one specific color which is finely focused called Monochromatism. The precision of the monochromatic beam is due to additional characteristics: collimation and coherency.
Collimation refers to the beam having specific spatial boundaries which ensures that there is a constant beam size and shape that is emitted from the laser unit.
Coherency refers to unique property of lasers. The light waves are a specific form of electromagnetic energy that are physically identical. They are all in phase with one another, i.e. they have identical amplitude and identical frequency (Table 1.1).
Table 1.1   Laser light differs from ordinary light
Laser light
Ordinary light
• Monochromatic
• Directional
• Coherent
Interaction Between Light and Matter
Threefold interaction between light and matter has three important features: Absorption, spontaneous emission and stimulated emission.
Absorption (Fig. 1.1) is the process indicated by the transfer of an electron from energy level E1 to E2.
Spontaneous emission (Fig. 1.2) is the mechanism for the reciprocal electronic transition E2 to E1, which is the result of typical radiative decay of excited electronic states of atoms or molecules.
It is comparable to radioactive decay of excited or unstable nuclear states.3
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Fig. 1.1: Absorption
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Fig. 1.2: Spontaneous emission
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Fig. 1.3: Stimulated emission
Stimulated emission (Fig. 1.3) represents the decay mechanism, that can only occur if a photon interacts with an atom in the excited state causing the emission of a second, identical photon.
The higher the energy of a photon, the shorter the wavelength. All dental lasers emit either a visible light beam or an invisible infrared light beam in the portion of the nonionizing spectrum called thermal radiation.
Basic Scheme of a Laser
The basic scheme (Figs 1.4A and B) of each laser comprises of laser medium, which is excited by an external source. Light can travel to and fro many times along a defined axis by being repeatedly reflected by mirrors of different reflection [R] forming an optical oscillator or Resonator (also called cavity). The laser oscillator stores light via multiple reflection of its mirrors, but also emits light through the partially transmitting out-coupling mirror. The laser light oscillates and is amplified during each pass through laser medium. If the resonator is filled with radiation at one instant of time, it emits a beam.
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Fig. 1.4A: Basic scheme of laser
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Fig. 1.4B: Main components of a laser
Population Inversion
Population inversion is a situation in which the occupation of a higher energy level is greater than the occupation of a certain lower level under nonlinear optical conditions, so that net amplification takes place.4
This inversion cannot be achieved by strong pumping of two-level system because the probabilities of absorption and stimulated emission are the same. Hence three-level and four level systems are required in order to realize inversion and hence amplification.
For lasing, the upper laser level should have a higher population density. Pumping always has to be done at a shorter wavelength than the laser activity.
In a three-level system (Fig. 1.5), the atoms or molecules are raised from ground level O to level 2 by a pumping mechanism. If the material is such that after reaching level 2 decays rapidly in a radiative or non-radiative manner to the longer life time level 1, population inversion can be obtained between level 2 and level 1.
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Fig. 1.5: Three level system
In a four level laser (Fig. 1.6), atoms are raised from ground level 0 to level 3. If the atoms or molecules decay rapidly to level 2, it should remain as long as possible so that population inversion can be obtained accordingly between levels 2 and 1. Once oscillation starts, the atoms will be transferred to level 1 via stimulated emission for continuous wave operation. In a four level laser it is necessary that the transition 1 → 0 should be ultrafast to keep level 1 at a lower population than level 2.
Gaussian Beam and Laser Resonator
Gaussian beam represents the shape of a laterally confined wave which is easily treated theoretically as well as practically. Its Amplitude [E] as well as its Intensity [I] profile distribution follow a Gaussian bell curve, which in principle extends to Infinity, although with a very rapid loss of height.
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Fig. 1.6: Four level system
Laser resonators are the active medium contained within an optical enclosure in which the laser light oscillates and is amplified during each pass through the laser medium.
For the beam of laser quality to be generated adequate resonator mirrors have to be put in place in the medium.
Stimulated emission, like that of the laser amplification mechanism, requires the interaction of light with an Inverted laser medium. All the resonator configurations shown are symmetric or half symmetric and stable.
The common stable resonator configuration are:
  • Coplanar (plane mirrors)
  • Over-confocal (large radii of curvature)
  • Confocal
  • Spherical (concentric)
  • Hemi-spheric (half concentric).
Beam Delivery System
The coherent collimated beam of light, must be delivered to the target tissue in a precise manner. Beam is delivered in three ways–fixed beam path, articulated arm path and the fiber.
Two delivery systems are used in dental lasers. One is a flexible hollow wave guide or tube that has interior mirror finish. The laser energy is reflected along this tube and exists through a hand piece, with the beam striking the tissue in a non-contact fashion.
The second delivery system is a glass fiberoptic scale. The fiber fits snugly into a hand piece with the bare end 5protruding or with an attached glass-like tip. This fiber system can be used in contact or non-contact mode.
Emission Modes
Contact mode: In this type the distal end of an optic fiber is placed in direct contact of the target tissue.
Non-contact mode: The hand piece is held away from the tissue and a guide is provided to focus the beam at the desired target tissue.
The laser device can emit the light energy in one of three basic modes. The first is continuous wave, the second is gated pulse mode and the third is free running pulsed mode.
In continuous wave mode the beam is emitted at constant power continuously by continuous pumping. The average power is equal to the peak power.
In gated pulse mode there are periodic alternations of the laser energy which is achieved either by opening or closing of a mechanical shutter in front of the beam path of a continuous wave emission. The duration of this type of laser is normally as small as a few milli seconds.
Free running pulsed mode is unique. The pulses are delivered with high peak power. Large peak energies of laser light are emitted for an extremely short time period.
The important principle of any laser emission mode is that the light energy strikes the tissue for a certain time, producing a thermal interaction.
The light energy from a laser can have four different interactions with the target tissue and these interactions depend on the optical properties of that tissue and the wavelength used.
The first interaction is reflection (Fig. 1.7A) in which the beam redirects itself off the tissue surface without any effect on the target tissue.
The second interaction is absorption (Fig. 1.7B) of the laser energy by the intended target tissue.
The third interaction is transmission (Fig. 1.7C) of the laser energy directly through the tissue, with no effect on the target tissue.
The fourth interaction is scattering (Fig. 1.7D) of the laser light, weakening the energy and possibly producing no useful biologic effect.
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Fig. 1.7A: Reflection of laser by target tissue
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Fig. 1.7B: Absorption of laser by target tissue
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Fig. 1.7C: Transmission of laser by target tissue
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Fig. 1.7D: Scattering of laser by target tissue
The primary and beneficial effect of laser energy is absorption of the laser light by intended biological tissue. Dental laser surgery optimizes these photo-biologic effects. Incisions and excisions accompanying precision and hemostasis, is one of the advantages of lasers. Besides photo thermal effects, lasers also have photochemical and photo-acoustic effects.
Effects of Temperature on Target Tissue
The thermal effect of laser energy on soft tissue primarily revolves around the water content of the tissue and the temperature rise of the tissue (Table 1.2).
Table 1.2  
Tissue temparature [°C]
Observed effect
Coagulation, protein denaturation
Welding of tissue
Gas Lasers
Laser medium → Gas
Gases are contained within appropriate tubes, which are sealed either by special windows or by di-electric mirrors, e.g. HeNe laser, CO2 laser, Excimer laser, Ion laser.
Dye Lasers
Laser medium → Liquid suspension
Liquid laser media are primarily dyes dissolved in alcoholic solutions. The most prominent and efficient dye is Rhodamine 6G.
Semi-conductor—Diode Lasers
Laser medium → Doped semiconductor crystal
It is based on uniting laser and host properties, thereby containing the highest density of energy state to be potentially inverted (allowing highest amplifications) (Fig. 1.8).
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Fig. 1.8: Diode machine
Solid-state Lasers
Laser medium → Doped crystals
They consist of a host medium with laser ions or molecules embedded in it. The medium chosen is a crystal because it may offer optimum heat transportation properties. The doping ions for solid state lasers are taken out of two groups in the periodic system: either rare earths (such as Nd3+, Yr, Ho, Er) or transitional metals (such as Cr2+, Cr3+, Cr4+, Ti3+).
E.g.:- Nd:YAG (Neodymium: Yttrium, Aluminum Garnet), Er:YAG (Erbium: Yttrium, Aluminum Garnet), Er. Cr: YSGG (Erbium, Cromium: Yttrium Scandium Gadolinium Garnet), Ho: YAG (Holinium: Yttrium, Aluminum Garnet), KTP.
There are a wide range of options for pumping, in order to transfer energy into the laser medium.
The following processes may be employed:
  • Optical pumping by strong lamps or lasers.
  • Electric pumping by gas discharges.
  • Chemical pumping by reactions yielding excited molecules.
  • Impact pumping by inelastic collisions between partners.
  • Electronic pumping by diffusion of carriers in semiconductors.
  • Pumping by acceleration of electrons (free electron laser).
Electronic pumping deals with the semiconductor laser. This is the best laser to date with respect to 7effectivity (>50%), cost and maintenance. It is the cheapest source of monochromatic light of substantial power and is excellent when used for optical pumping.
The following are brief descriptions of the available laser devices that have dental applications. The laser is named according to its active medium, wavelength, delivery system, emission modes, tissue absorption and clinical applications.
Excimer Laser
Excimer laser is a special gas laser based on unstable molecules called Excimer (Excited Dimers). They exist only in the excited state for nanoseconds which is enough for long pulsed laser action.
The emitted beam has the shape of a window. This type of laser represents the most important source of short-wave length radiation.
Wave Lengths
158 nm
193 nm
249 nm
l308 nm
351 nm
Typically mixture of rare gas (e.g. Kr) 5-10%
Halogenide (e.g. F2) 0.1-0.5%
Buffer gas (e.g. He/Ne)
→ Plasma discharge
Operation mode
→ pulsed.
Dye Lasers
→ 500-800 nm (Depending on dye suspension)
→ Liquid suspension of dye.
→ Flash lamp (other laser sources).
Argon Ion Laser
Argon lasers have an active medium of Argon gas that is fiber optically delivered in continuous wave and gated pulse modes. The laser has two emission wavelengths and both are visible to the human eye: 488 nm blue in color and 514 mm blue green in color is very expensive to purchase and to maintain.
  • Polymerization of resin in light cured composites materials.
  • Hemostasis.
  • Treatment of acute inflammatory periodontal disease.
  • Aid in caries detection.
CO2 Laser
The CO2 laser is one of the oldest laser. It is a gas-active medium that must be delivered through a hollow tubelike wave-guide in continuous or gated pulse mode. It is well absorbed by water and has a shallow depth of penetration into tissue and effective in soft tissue excision. It is especially useful in cutting dense fibrous tissue.
The CO2 laser cannot be delivered in an optic fiber. Instead, a hollow wave-guide with a hand piece is used. Large lesions can be treated easily using a simple back and forth motion. The loss of tactile sensation is a disadvantage for the surgeon.
9.6 μm IR
10.5 μm IR
mixture of CO2, N2, He ratio depending on the wavelength
typically CO2: N2: He = 0.8: 1:7
→ Plasma discharge
Operation mode
→ Cw, pulsed.
Semi-conductor Lasers/Diode Lasers
It comprises of solid active medium that uses a combination of aluminum, gallium and arsenide to change electric energy into light energy.
The available wavelength for dental use range from about 800 to 980 nm (Fig. 1.9A and B).
Delivers laser energy fiber optically in continuous wave and gated - pulsed mode.8
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Fig. 1.9A: Example of diode laser
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Fig. 1.9B: Diode hand piece
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Fig. 1.9C: Diode laser tip
Advantages of diode lasers are:
  • Excellent hemostasis.
  • Soft tissue surgery can be performed effectively, as it is poorly absorbed by tooth structure.
  • Indicated for cutting and coagulating gingiva and mucosa and for soft tissue curettage or debridement.
  • Flexibility of the delivery system to target issues.
  • Laser units are portable, compact and are lowest priced laser currently available.
Variation from VIS down to IR is commonly between 860 to 980 nm for surgery.
In Ga As - Indium Gallium Arsenide typically for Infrared diodes.
Heterostructure set up (i.e. multiple buyers of different doped semiconductor crystals).
→Most commonly by injection of carriers.
Operation mode
→ CW, pulsed.
Solid State Laser
Nd:YAG, Ho: YAG, Er: YAG and Er, Cr: YSGG.
  • The most important is the Neo-dymium laser based on the rare - earth ion Nd.
  • This ion can be incorporated into different host materials, the most important ones being YAG (Yttrium, aluminum garnet) and several glasses.
  • YAG offers favorable mechanical and thermo-optical properties allowing its use for CW and pulsed lasers, even at high power.
  • Most commercial laser emit the wavelength l064 nm corresponding to transition of energy levels.
  • Excitation is achieved by optical pumping into broad energy bands followed by radiation.
  • It consists of a hollow cavity with gold-coated internal surfaces revealing an elliptical cross section.
  • In medicine, this laser has been used for long time, taking advantage of its greater depth of penetration into the tissue and dispersion in tissue as a result of scattering.
  • Coagulation stops bleeding effectively and immediately after the incision.
  • Another advantage, in comparison with the CO2 laser, is the propagation through silica fibers allowing for endoscopic use or for fibers to be inserted in root canals, etc.
Erbium and Erbium-Chromium Lasers
  • In crystalline Er-lasers, the host crystals are usually YAG (Yttrium Aluminum Garnet), YALO (Yttrium Aluminum Oxide), YSGG (Yttrium Scandium Gadolinium Garnet) or YLF (Yttrium Lanthanum Fluoride).
  • Doping is relatively high, i.e. about 50% of the Y ions in YAG are replaced by Er ions.
  • In medical applications and especially in dentistry, the Er lasers represent highly developed commercial lasers with very high yield and efficiency in tissue removal.
  • It is the type of laser currently used for dental hard tissue ablation (Fig. 1.10).
1.064 μm
2.14 μm
Er, Cr: YSGG
2.79 μm
2.94 μm
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Fig. 1.10: Example of Er:YSGG unit
Host Crystals
YAG (Yttrium Aluminum Garnet)
YSGG (Yttrium Scandium Gadolinium Garnet)
→ Optical by flash lamps or laser diodes.
Operation mode
→ Cw, pulsed