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1. LASERS IN DENTISTRY
Introduction
Laser is an acronym, which stands for Light Amplification by
Stimulated Emission of Radiation. Several decades ago, the laser was a
death ray, the ultimate weapon of destruction, something you would only
find in a science fiction story. Then lasers were developed and actually
used, among other places, in light shows. The beam sparkled, it showed
pure, vibrant and intense colors. Today the laser is used in the scanners at
the grocery store, in compact disc players, and as a pointer for lecturer and
above all in medical and dental field. The image of the laser has changed
significantly over the past several years.
With dentistry in the high tech era, we are fortunate to have many
technological innovations to enhance treatment, including intraoral video
cameras, CAD-CAM units, RVGs and air-abrasive units. However, no
instrument is more representative of the term high-tech than, the laser.
Dental procedures performed today with the laser are so effective that they
should set a new standard of care.
This presentation intends to discuss the role of lasers in dentistry.
1

2. History of Lasers
• The first working laser was produced by TH Maiman 35 years ago
He described a laser based on a ruby crystal pumped by a high-power
flash lamp which produced deep red visible light at two wavelength.
• Approximately, the history of lasers begins similarly to much of
modern physics, with Einstein. In 1917, his paper in Physikialische
Zeil, “Zur Quantern Theorie der Strahlung”, was the first discussion of
stimulated emission.
• In 1954 Townes and Gordon built the first microwave laser or better
known as ‘MASER’ which is the acronym for ‘Microwave
Amplification by Stimulated Emission of Radiation’
• In 1958, Schawlow and Townes suggest the possibility to use this
stimulated emission for light amplification.
• In May 1960, Theodore Maimen at Hughes Aircraft company made the
first laser. He used a ruby as the laser medium.
2

3. • One of the first reports of laser light interacting with tissue was from
Zaret; he measured the damage caused by lasers incident upon rabbit
retina and iris.
• In 1961, the first gas laser was developed by Javan et al in 1961. This
was the first continuous laser and used helium – neon.
• In 1964, the Nobel Prize for the development of the laser was awarded
to Townes, Basor and Prokhovov in 1964.
• The neodymium – doped (Nd): glass laser was developed in 1961 by
Snitzer.
• In 1964 Nd: YAG was developed by Geusic.
• The CO2 laser was invented by Patel et al in 1965.
• 1975 – Excimer Laser developed by ‘AYCO’.
• Polanyi in 1970 applied CO2 laser clinically.
• In 1990 Ball suggested opthalmologic application of ruby laser.
3

4. • The use of low-power lasers has recently become known as “Low
Intensity Laser Therapy” (LILT) qualities which distinguish it as a
laser light i.e.
1. Coherence
Unlike white light, which is scattered, laser light energy travels in a
specific wavelength and in a predictable patterns.
↓
i.e. it is coherent
2. Monochromatic
Since lasers are coherent, each traveling in a specific wavelength
from uv to infrared, lasers express one colour
↓
i.e. they are monochromatic
3. Laser light also travels in a collimated or parallel, beam and is
therefore highly directional.
4

5. Other Terminologies
When lasers first appeared as clinical tools, they were divided into
2 groups
Related to their observed
Hard Soft interaction with the tissue
Produces immediate Appeared to cause no visible change in
observable effects on the the tissue at the time of lasing
tissues irradiated
These terms are generally falling from use and it is probably better
now to talk only of
High-power Low-power
is the one capable of produces upto 1000 mw (LILT)
producing 3W and more
Laser Physics
Laser is a device that converts electrical or chemical energy into
light energy.
In contrast to ordinary light that is emitted spontaneously by excited
atoms or molecules, the light emitted by laser occurs when an atom or
molecule retains excess energy until it is stimulated to emit it. The
radiation emitted by lasers including both visible and invisible light is more
5

6. generally termed as electromagnetic radiation. The concept of stimulated
emission of light was first proposed (1917) by Albert Einstein.
He described three processes:
1. Absorption
2. Spontaneous emission
3. Stimulated emission.
Einstein considered the model of a basic atom to describe the
production of laser. An atom consists of centrally placed nucleus which
contains positively charged particles known as protons, around which the
negatively charged particles. i.e. electrons are revolving.
When an atom is struck by a photon, there is an energy transfer
causing increase in energy of the atom. This process is termed as
absorption. The photon then ceases to exist, and an electron within the
atom pumps to a higher energy level. This atom is thus pumped up to an
excited state from the ground state.
In the excited state, the atom is unstable and will soon
spontaneously decay back to the ground state, releasing the stored energy
in the form of an emitted photon. This process is called spontaneous
emission.
6

7. If an atom in the excited state is struck by a photon of identical
energy as the photon to be emitted, the emission could be stimulated to
occur earlier than would occur spontaneously. This stimulated interaction
causes two photons that are identical in frequency and wavelength to leave
the atom. This is a process of stimulated emission.
Laser Design
All lasers have similar fundamental elements:
A. Lasing Medium
- Which maybe solid, a liquid / gas
- Maiman’s laser used a solid medium – ruby crystal.
- As a rule, the lasing medium gives its name to the laser e.g.
 Ruby laser (solid)
 Nd :YAG (solid)
 Dye laser (liquid)
 CO2 (gas) and Argon (gas)
 Semi-conductor lasers
B. Energy Source
The atoms or molecules of the lasing medium need to be excited so
that protons of laser light are emitted. The energy for this maybe provided
7

8. by an electric discharge, high powered xenon-flash lamps or even another
laser.
C. Optical resonator / housing tube
Is an arrangement of mirrors which both amplify the effect of the
laser and ensure that when the light does emerge from the laser, it
possesses the unique.
Laser Light Delivery
Light can be delivered by a number of different mechanisms.
Several years ago a hand held laser meant holding a larger, several hundred
pound laser usually the size of a desk, above a patient. Although the idea
was comical at the time, it is becoming more feasible as laser technology is
producing smaller and lighter weight lasers. In the more future it is
probable that hand held lasers will be used routinely in dentistry.
1. Articulated arms
Laser light can be delivered by articulated arms, which are very
simple but elegant devices. Mirrors are placed at 45o
angles to tubes
carrying the laser light. The tubes can rotate about the normal axis of the
mirrors. This results in a tremendous amount of flexibility in the arm and in
delivery of the laser light. This is typically used with CO2 laser. The arm
8

9. does have some disadvantages that include the arm counter weight and the
limited ability to move in a straight line.
2. Optical Fiber
Laser light can be delivered by an optical fiber, which is frequently
used with near infrared and visible lasers. The light is trapped in the glass
and propagates down through the fiber in a process called total internal
reflection.
Optical fibers can be very small. They can be either tenths of
micrnos or greater than hundreds of microns in diameter.
Advantages of optical fiber is that they provide easy access and transmit
high intensities of light with almost no loss but have two disadvantages.
Disadvantages
(1) The beam is no longer collimated and coherent when emitted from the
fiber which limits the focal spot size.
(2)The light is no longer coherent.
9

10. Mode of Delivery of Laser
Once the laser is produced, its output power may be delivered in the
following modes.
1. Continuous wave: When laser machine is set in a continuous wave
mode the amplitude of the output beam is expressed in terms of watts.
In this mode the laser emits radiation continuously at a constant power
levels of 10 to 100 w. Eg: CO2 laser
2. 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 500ms.
3. Gated: The term superpulsed is used to describe the output of a gated
high peak power laser with a short pulse duration, typically between
hundreds of microseconds (1ms = 1x10-6
sec.). The pulse produced
during superpulsing can have a repitition rate of 50 to 250 pulses per
second that permits the laser output to appear almost continuous during
use.
4. Pulsed: Lasers can be gated or pulsed electronically. This type of
gating permits the duration of the pulses to be compressed producing a
10

11. corresponding increase in peak power, that is much higher than in
commonly available continuous wave mode.
5. Super pulsed: The duration of pulse is one hundredth of microseconds.
6. 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 superpulsed mode. The duration of the ultra pulse is
slightly less.
7. Q-scotched: Even shorter and more intense pulse can be obtained with
this mode. Several hundreds of millijoules of energy can be squeezed
into nano second pulses.
8. Flash-Lamp pulsing: In these systems, a flash – lamp is used to pump
the lasing medium, usually for solid state lasers.
Focusing
Lasers can be used in either a focussed mode or in a defocused
mode.
A focussed mode is when the laser beam hits the tissue at its focal
points or smallest diameter. This diameter is dependent on the size of lens
11

12. used. This mode can also be referred as cutting mode. Eg. While
performing biopsies.
The other method is the defocused mode. In which the mode is
moved away from the total plane. This beam size that hits the tissue has a
greater diameter, thus causing a wider area of tissue to be vaporized.
However, laser intensity / power density is reduced. This method is also
known as ablation mode. Eg. In Frenectomies; In removal of inflammatory
papillary hyperplasias.
In contact mode, the fibre handpiece is placed in contact to the
tissue whereas in the non-contact, the handpiece is placed away from the
target tissue.
Contact and Non contact modes
In contact mode, the fiber tip is placed in contact with the tissue.
The charred tissue formed on the fiber tip or on the tissue outline and
increases the absorption of laser energy and resultant tissue effects. Char
can be eliminated with a water spray and then slightly more energy will be
required to provide time efficient results. Advantage is that there is control
feed back for the operator.
12

13. Non contact mode: Fiber tip is placed away from the target tissue. In the
non contact mode the clinician operates with visual control with the aid of
an aiming beam or by observing the tissue effect being created.
So generally laser can be classified as
Dental Lasers
Those work in
both
Solely in the non Contact & focussed Non contacted
contact mode & defocused
Eg: CO2 Eg: Argon, Ho : YAG, Nd:YAG
Laser Types
I. Based on wavelength.
1. Soft lasers
2. Hard lasers
II. Based on the lasing medium
Lasers can be classified according to the state of the active medium i.e.,
1. Solid eg: Nd:YAG, Diode
2. Liquid eg: Dye
3. Gas eg: CO2, Argon, Er:YAG
13

14. III.Based on the potential danger posed to the exposed skin and to the
unaccomodated eye.
I. Based on wavelength:
Soft Lasers: Soft lasers are lower power lasers; with a wave length around
632mm. Eg. He-Ne, Diode.
These are employed to relieve pain and promote healing eg. In
Apthous ulcers.
Hard lasers: Lasers with well known laser systems for possible surgical
application are called as hard lasers. Eg: CO2, Nd: YAG, Argon, Er:YAG etc.
CO2 Lasers
The CO2 laser first developed by Patel et al in 1964 is a gas laser and
has a wavelength of 10,600 nanometers or 10.6 µ deep in the infrared range
of the electromagnetic opectrum.
14

15. • CO2 lasers have an affinity for wet tissues regardless of tissue color.
• The laser energy weakens rapidly in most tissues because it is
absorbed by water. Because of the water absorption, the CO2 laser
generates a lot of heat, which readily carbonizes tissues. Since this
carbonized or charred layer acts as a biological dressing, it should
not be removed.
• They are highly absorbed in oral mucosa, which is more than 90%
water. High absorption in small volume results although their
penetration depth is only about 0.2 to 0.3nm. There is no scattering,
reflection, or transmission in oral mucosa. Hence, what you see is
what you get.
• CO2 lasers reflect off mirrors, allowing access to difficult areas.
Unfortunately, they also reflect off dental instruments, making
accidental reflection to non-target tissue a concern.
• CO2 lasers can not be delivered fiber optically Advances in
articulated arms and hollow wave guide technologies, now provide
easy access to all areas of the mouth.
• Regardless of the delivery method used, all CO2 lasers work in a
non-contact mode.
15

16. • Of all the lasers for oral use, CO2 is the fastest in removing tissue.
• As CO2 lasers are invisible, an aiming Helium – neon (He Ne) beam
must be used in conjunction with this laser.
Nd: YAG Laser: Here crystal of Ytrium – aluminum – garnet are doped
with neodymium. Nd: YAG laser, has wavelength of 1,064 nm (0.1064 µ)
placing it in the near infrared range of the magnetic spectrum.
• It is not well absorbed by water but are attracted to pigmented tissue.
Eg: haemoglobin and melanin. Therefore various degrees of optical
scattering and penetration to the tissue, minimal absorption and no
reflection.
• Nd: YAG lasers work either by a contact or non-contact mode. When
working on tissue, however, the contact mode in highly recommended.
• The Nd:YAG laser is delivered fiber optically and many sizes of
contact fibers are available.
1. Carbonized tissue remnants often build up on the tip of the
contact fiber, creating a ‘hot tip’. This increased temperature
enhances the effect of the Nd:YAG laser, and it is not necessary
to rinse the build up away.
16

17. 2. Special tips, the coated sapphire tip, can be used to limit lateral
thermal damage.
3. A helium-neon-aiming beam is generally used with Nd: YAG
wavelength.
• Penetration depth is ~ 2 to 4m, and can be varied by upto 0.5-4mm in
oral tissues by various methods.
• A black enhancer can be used to speed the action.
• The Nd-YAG beam is readily absorbed by amalgam, Ti and non-
precious metals, requiring careful operation in the presence of these
dental material.
Uses:
- Soft tissue removal
- Haemostasis
- Coagulation
Argon Lasers
• Argon lasers are those lasers in the blue-green visible spectrum
(thus they can be seen).
17

18. • They operate at 488nm(blue) or 514.5nm (green), or 496nm
(blue/green) ARGON is easily delivered fiber optically.
• Argon lasers have an affinity for darker colored tissues and also a
high affinity for haemoglobin, making them excellent coagulators.
Thus argon lasers focused on bleeding vessels stop the
haemorrhage. It is not absorbed well by hard tissue, and no
particular care is needed to protect the teeth during surgery.
• In oral tissues there is no reflection, some absorption and some
scattering and transmission – travel fiber-optically is unaffected by
H2O.
• Argon lasers work both in the contact and non contact mode
• Like, Nd: YAG lasers, at low powers argon lasers suffer from
‘dragability’ and need sweeping motion to avoid tissue from
accumulating on the tip.
• Enhances are not needed with Argon lasers.
• Argon lasers also have the ability to cure composite resin, a feature
shared by none of the other lasers.
18

19. • Argon is highly absorbed by Hb, strongly absorbed by melanin and
poorly absorbed by H2O.
• The blue wavelength of 488 nm is used mainly for composite
curing, while the green wavelength of 510nm is mainly for soft
tissue procedures and coagulation.
Erbium: YAG laser
• Is a promising laser system because the emission wave length
coincides with the main absorption peak of water, resulting in good
absorption in all biological tissues including enamel and dentin.
This is the 1st
Laser to be cleared by the FDA on May 7, 1997 for
use in preparing human cavities.
• Have a wavelength of 2.94 µm.
• A number of researchers have demonstrated the Er: YAG lasers
ability to cut, or ablate, dental hard tissue effectively and efficiently.
The Er: YAG laser is absorbed by water and hydroxyapatite, which
particularly accounts for its efficiency in cutting enamel and dentin.
19

20. • A variety of restorative materials such as Zn phosphate, Zn
carboxylate, glass ionomer cements and silver amalgam can be
effectively removed by the Er: YAG cases.
• Pulpal response to cavity preparation with an Er: YAG laser was
minimal, reversible and comparable with pulpal response created by
a high-speed drill.
• Er: YAG can also be used for bone ablation and has indications in
soft tissue surfaces where no coagulation effect is desired such as
removal of hyperplastic gingival tissue, periodontal surgery and
abrasion of large benign lesions of the oral mucosa and skin.
Ho: YAG laser [Holmium YAG lasers]
• Is thallium and holomium doped, chromium sensitized YAG crystal
• Has a wavelength of 2,100 nm
• Delivered through a fiber optic carrier.
• A He-Ne laser is used as an aiming light
• Dragability is less compared to Nd: YAG and argon lasers
• Like Nd: YAG, can be used in both the contact and non-contact
modes and are pulsed lasers.
20

21. • Ho: YAG laser has an affinity for white tissue and has ability to
pass through water and acts as a good coagulator.
Laser – tissue interaction
Source
Reflected
Scattered
Absorbed
Transmitted
- When laser strikes a tissue surface, it can be reflected, scattered,
absorbed or transmitted.
Reflection: Reflected light bounces off the tissue surface and is directed
outward.
 Because the energy dissipates so effectively after reflection,
there is little danger of damage to other parts of the mouth.
 It also limits the amount of energy that enters the tissue.
Scattering: occurs when the light energy bounces from molecule to
molecule within the tissue.
21

22.  It distributes the energy over a larger volume of tissue,
dissipating the thermal effects.
Absorption: occurs after a characteristic amount of scattering and is
responsible for the thermal effects within the tissue.
Transmission: Light can also travel beyond a given tissue boundary. This
is known as transmission.
• It irradiates the surrounding tissue and must be quantified.
• The distance the energy transmits into the tissue is called
penetration depth.
• Co-agulation where as depth is the deepest level where alterations in
the tissue will occur because of the laser’s energy
E.g. CO2, Nd-YAG and Argon have similar co-agulation depths but
different penetration depths.
Naturally, the temperature and tissue effects are greatest near the
light source and decrease exponentially as tissue depth increases.
°C J/cm2
Tissue effect
>175
100-150
90-100
>5000
1000-5000
1000
Rapid cutting
Carbonization
Vaporization
22

23. 70-80
60
50
37
500
200
10
0
Welding
Co-agulation
Hyperthermia
Normal
Lasers and soft tissues
• The absorption of laser light by different elements of tissue is
extremely wavelength dependent.
• H2O, a major constituent of soft tissue strongly absorbs wavelengths
of 2nm / above and therefore these penetrate little in soft tissues, the
greater part of which is made up of H2O.
Hard tissues
Many researchers felt that lasers were obvious replacement for the
dental drill, as
• Lasers are ‘non-contact’ and their use produces much less vibration
than conventional drills.
• They are much quieter than drills, usually producing only a muted
‘popping sound’ which is generally well-tolerated.
• They can sterilize as they cut.
23

24. • They can also be used to seal tissues at the periphery of the cut.
Therefore cut dentinal tubules were sealed rather than left-open as
pathways for micro-organisms, reducing the possibility of post-
operative hypersensitivity.
1. Thermal effects:
The best known laser effect in dentistry is the thermal vaporization
of tissue by absorbing laser light i.e. the laser energy is converted into
thermal energy or heat that destroys the tissues.
From 45o
– 60o
 denaturation occurs
>60 o
 coagulation and necrosis
At 100o
C  water inside tissue vaporizes
>300 o
C  carbonization and later phyrolysis with
vaporization of bulky tissues.
Above 300°-800°  used to cut cavities.
When the high peak-power of a pulsed – laser is greater, a super-
heated gas called the ‘plasma’ may form.
↓
Which can absorbed the incoming laser beam, allowing less energy
to reach the surface. This hot plasma, can then quickly conduct heat to the
24

25. tissues surfaces and causes ablation and severe heating which can lead to
tissue damage.
Flowing water down the fiber and onto the tissue has been used in
an attempt to control this plasma (which pulsed Nd-YAG).
2. Mechanical effects / Effect of heat build-up
High energetic and short pulsed laser light can lead to a fast heating
of the dental tissues in a very small area. The energy dissipates explosively
in a volume expansion that may be accompanied by fast shock waves.
These shock waves lead to mechanical damage of the irradiated tissue.
Histologic Results:
A. With continuous wave and pulsed CO2 lasers.
When continuous wave and pulsed CO2 lasers were used, structural
changes and damage in dental hard tissue were reported.
1. Microcracks.
2. Zones of necrosis and carbonization are unavoidable. Because of
drying effects
3. The microhardnes of dentin increases. The crystalline structure of
hydroxyapatite changes and a transformation of apatite
25

26. 4. Tricalcium phosphate takes place.
B. Nd: YAG Lasers
The Nd: YAG laser shows low absorption in water as well as in
hydroxyapatite. Therefore the laser power diffuses deeply through the
enamel and dentin and finally heats the pulp. In dentin, at the laser impact,
zones of debris and carbonization are surrounded by an area of necrosis can
be seen. Microcracks appear when energies above a threshold of 100mj /
pulse are used. But the appearance and the extent of the side effects are not
predictable.
C. Er: YAG Laser
In dentin, shallow cavities were surrounded by a zone of necrosis of
1-3µm thickness when water-cooling systems were used. In deeper
cavities, areas of carbonization and microcracks were observed. Ablating
enamel always cracked and deep zones of debris appeared.
D. Excimer Lasers
No pathologic changes in the tissue layers adjacent to the dissected
areas were found after the ablation.
The ablation effects of dental hard tissues are predictable. Compared
to conventional diamond and burs, however, the effectiveness is low.
26

27. Thermal side effects increase as photon energies of excimer lasers
decrease.
Laser Effects On Dental Pulp:
Recent histologic evidence suggests that a normal odontoblast layer,
stroma and viable epithelial root sheath can be retained following laser
radiation provided damage threshold energy densities are not exceeded. If
pulp temperatures are raised beyond the 5°C level, research has shown that
the odontoblasts layer may not be present. Characteristics of the
dentinogenesis process related to root development, predentin and
reparative dentin formation, dentinal bridge presence, typically reflect the
overall trauma that has been induced in the odontoblasts.
Laser in Restorative Dentistry and Endodontics
Lasers find numerous applications in restorative dentistry and
endodontics ranging from prevention of caries to antibacterial action in
root canals.
1. Prevention of carries:
• Yamamoto and Ooya used Nd-YAG laser at energy densities of 10
to 20 J/cm2
and demonstrated that the lased enamel surface was
more resistant to in vitro demineralization than non lased enamel.
27

28. • Stern and Sognnaes demonstrated in vivo that enamel subjected to
10 to 15 J/cm² Ruby laser showed a greater resistance to dental
caries than the controls.
• Stern concluded that energy levels below 250 J/cm² did not
permanently alter the pulp but necrosis could occur when energy
level, reached 1800 J/cm² or higher.
• Lobene and Colleagues in their experiment with CO2 laser, observed
that CO2 irradiation to tooth enamel caused small amounts of
hydroxyapatite to be converted to more insoluble calcium
orthophosphate apatite. This paved the way for widespread use of
laser in prevention of caries.
• Another study, laser dentin closed resembled e.g. because of
increase in Ca and phosphate contents.
• Lasers can be thus used for removal of incipient caries, sealing pits
and fissures. The CO2 and Nd:YAG lasers can remove the organic
and inorganic debris found in pits and fissures. Following the
removal a synthetic hydorxyapatite compound is attached to enamel
using the laser. Power densities used are low and it did not alter the
health of pulp tissue.
28

29. • In 1985 Terry Myers used Nd:YAG laser for debrident of incipient
caries.
• When a topical fluoride treatment was performed after argon laser
conditioning of enamel, an even more dramatic reduction in enamel
acid demineralization was observed.
CO2 lasers:
Florin has shown that a continuous wave CO2 laser homogenesizes the
enamel surface by melting structural elements. The tissue in the laser –
induced zones of fusion was harder than adjacent, un-irradiated enamel,
which would increased the caries resistance.
Argon:
• Argon irradiation of root surfaces significantly increased the
resistance of cementum and underlying dentin to continual artificial
caries attack.
• Lased cementum and dentin seem to have an increased affinity for
uptake of fluoride, phosphorous and calcium ions.
2. Diagnosis: Lasers can be used to detect incipient carious lesion which
cannot be diagnosed clinically and radiographically. Transilliumination
29

30. using lasers is used for this purpose. The lesion appears as a distinct
dark red area easily differentiated from the rest of the sound tooth
structure. Decalcified area appears as a dull, opaque, orange color. Also
enamel fractures and recurrent decay around metallic and resin
restoration can be diagnosed.
• Quantitative measurement of the fluorescence emission pattern
induced by laser, the technique of laser-induced fluorescence, has
been used in the assessment of caries.
• This non-destructive method is more effective than micro-
radiography.
Cavity preparation:
The use of lasers for cavity preparation has been under scrutiny for
20yrs as many investigators found that pulpal necrosis would occur with
use of lasers.
The reasons for necrosis are:
1. The heat produced
2. Total power output (J/cm²)
30

31. The search for laser that can be used to cut hard tissues begun in
1964 by Dr. Leo Goldman who used laser on his brother Bernard’s teeth.
The subsequent search included many laser wavelengths such as CO2 but
its disadvantages include cracking with flaking of enamel surface.
Nd:YAG 10 J/cm² has shown to inhibit incipient carious lesions but
at higher densities it causes irreversible pulpal damage. Other lasers such
as Ho: YAG, ArF, Nd:YLF and Er: YAG have been investigated.
Er: YAG at the wavelength of 2.94µm has shown most promising
results. A number of researchers have demonstrated the Er:YAG laser’s
ability to cut or ablate dental hard tissues effectively and efficiently. The
Er:YAG laser is absorbed by water and hydroxyapatite, which partially
accounts for its efficiency in cutting enamel and dentin.
• It has generally been assumed that if pulpal temperature rises
less than 5.5°C, the procedure would be safe and would not
cause irreversible histologic damage to the pulpal tissues.
Researchers who conducted in vivo animal studies reported
that the pulpal response to cavity preparation with an
Er:YAG laser was minimal, reversible and comparable with
the pulpal response created by a high speed drill.
31

32. • The temperature rise with these type of laser was less than
3°C.
• Moreover, a water coolent can be used which not only cools
the tooth during ablation but also increase the efficiency of
ablation.
• In a study by Timothy Smith, patients reported little or no
pain during the treatment with dental laser. With many
people reporting fear of pain as their chief reason for not
seeking dental care, lasers may offer a more acceptable
treatment technique.
Etching the Enamel:
The laser absorbed by enamel causes the enamel surface to be
heated to a high temperature, generating micro cracks in the surface and
thus aids in enhancing adhesion of composite to the tooth structure. The
surfaces appear similar to acid etched surfaces.
The Nd:YAG laser is not readily absorbed but absorption can be
increased by using a dye on enamel surface.
32

33. Curing of Composites and GIC:
Currently, photoactivated dental resins employ a diketone, such as
camphoroquinone, and a tertiary amine reducing agent to initiate
polymerization. This photoinitiator system is sensitive to light in blue
region of the visible spectrum with broad peak activity in the 480nm
region. The argon laser’s monochromatic wavelengths of 488nm and
514.5nm have been shown to be effective in the initiation of
polymerization of dental resins.
Advantages:
• Enhanced physical properties like increased tensile strength due to
enhanced or more thorough polymerization.
• Improved adhesion
• Reduced microleakage
• Reduced exposure time. Argon laser polymerization requires a
10sec cure cycle while visible light activation usually takes
approximately 40sec.
• The polymerization of light activated bases and or liners can also be
accomplished with the argon laser.
Advantages : A wide varity of fiber sizes provides access to all location of
cavity preparation.
33

34. Pit and Fissure Sealant Therapy:
Advantages are similar to those offered for curing composite resins.
Bleaching:
Lasers also find use in bleaching of vital and non-vital teeth.
Two-laser assisted whitening systems have been cleared by the
FDA. The laser is used to enhance the bleaching material.
e.g. i) Argon of 488 nm for 30 sec to accelerate the activity of its
bleaching gel.
ii) Both Argon and CO2 are used. CO2 is employed with another
peroxide based solution to promote penetration of the bleaching
agent into the tooth to provides bleaching below the surface.
Treatment of fractured teeth: Lasers have the potential to fuse the
segments of fractured teeth.
Pulpotomy: Recent development.
Removal of Old restoration:
• Composites and cements can be ablated.
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35. • Gold crowns and cast fillings cannot be removal as laser beam is
reflected.
• Ceramics cannot be ablated.
Lasers in endodontics
1. Diagnosis of blood flow in the dental pulp
Laser Doppler Flowmetry (LDF) was developed to assess blood
flow in microvascular system e.g. retina, skin. This original technique
utilized a light beam from a He-Ne laser emitting at 032.8nm, which when
scattered by moving red cells, underwent a frequency shift, according to
the Doppler principle. A fraction of the light back-scattered from the
illuminated area was frequency shifted in this way. This light was detected
and processed to produce a signal that was a function of the red cell flux.
• Other wavelengths of semiconductor lasers have also been used :
780 nm and 180-820nm.
• In general, infra-red (780-910nm) has a greater ability to penetrate
enamel and dentin than shorter wavelength red light (632.8nm).
• Non laser light (576nm) has also been used for the detection of
pulpal perfusion.
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36. • Lasers are usually at a low-power level of 1-2 mW and no reports
on pulp injury by this method have been reported.
• Another diagnostic application of lasers in endodontics is the
application of an excimer laser system emitting at 308nm for
residual tissue detection within the canals.
2. Dentinal hypersensitivity:
To date, most of the therapies for this, have failed to satisfy one or
more of the criteria like,
 non-irritant to the pulp
 painless on application
 easily carried out
 rapid in action
 be effective for a long time
but some authors report that lasers may now provide reliable and
reproducible treatment, documenting success rates of upto 90%
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37. The lasers used for the treatment of dental hypersensitivity are divided into
two groups:
low output power lasers middle output power lasers
e.g. He-Ne e.g. Nd-YAG
Gallium / Al / arsenide - CO2
(Ga Al As)
Mechanism causing a decrease in hypersensitivity is mostly
unknown, but it is thought that the mechanism for each laser is different.
a) In the case of low output-power lasers – A small fraction of the laser’s
energy is transmitted through enamel and dentine to reach the pulp
tissue.
• He-Ne laser irradiation may affect the electric activity / action
potential / and not affect peripheral Ag or C-fiber nociceptors.
• Using CO2 at moderate laser energies, mainly sealing of dentinal
tubules is achieived, as well as reduction of permeability. CO2 laser
irradiation may cause dentinal dessication, yielding temporary
clinical relief of dentinal hypersensitivity.
• The sealing depth achieved by Nd:YAG laser irradiation on dentinal
tubules measured less than 7nm.
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38. Note: It is necessary to consider the severity of dentinal hypersensitivity
before laser use.
3. Pulp capping and pulpotomy
• Melcer et al (1987) first described laser treatment of exposed
pulp tissues using the CO2 laser in dogs to achieve hemostasis.
• Lasers facilitate pulpal healing after irradiation at 2W for 2s.
CO2 laser was found to be a valuable aid in direct pulp capping
in human patients (Moritz 1998).
• Ist laser pulpotomy using CO2 on dogs by Shoji (1985). No
detectable damage was observed in the radicular patients of
irradiated pulps with the CO2 laser. Wound healing of the
irradiated pulp seems to be better than that of controls at 1 week,
and dentine bridge formation in the irradiated pulp was
stimulated at 4 and 12 after operation.
• If a laser is used for these procedures, a bloodless field would be
easier to achieve due to the ability of the laser to vaporize tissue
and coagulate and seal small blood vessels.
• Moreover, the treated wound would be sterilized.
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39. • No laser damage was found in tissues, with the presence of
secondary dentine and a regular odontoblast layer by Wilder
Smith et al (1997).
Lasers used for this are mainly CO2 and Nd:YAG.
Note: An approximate parameter should be selected as if the laser energy is
too strong, the treatment will be unsuccessful.
4. Modification of root canal walls
• Laser removes the smear layer and replaces it with an
uncontaminated chemical sealant, or sealing it by melting the
dentinal surface.
• Using CO2 laser irradiation, the dentine permeability was
reduced and a wide range of morphological changes were
observed by (Tanji 1994).
• Nd:YAG within fiber / fiber optic laser was used to seal the
entrance to the root canal at the apex of the tooth in vitro
(Weichman 1972).
• First, debris and smear layer were removed using appropriate
laser parameters and dentin permeability was reduced.
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40. • Since absorption of Nd:YAG laser irradiation is enhanced by
black ink, it potential laser effects on root canals.
• Argon laser irradiation can also achieve an efficient clearing
effect on instrumented root canal surfaces. The effect of the laser
irradiation was enhanced in the presence of Ag(NH3)2F.
Others lasers used – Er:YAG
Potassium titanye phosphate (KTP)
Xenon chloride (XeCl)
Ar-Fluoride (F) excimer laser
HO:YAG
Note: The removal of smear layer and debris is possible however, it is hard
to clean all the walls, because the laser is emitted straight ahead, making it
almost impossible to clean or irradiate the lateral root canal walls.
5. Sterilization of root canals
• The Nd:YAG laser is more population for this, because a thin
fibre-optic delivery systems for entering narrow root canals is
available with this device.
Others are : XeCl, Er:YAG, a diode laser
• All the lasers have a bactericidal effect at high power that is
dependent on each laser.
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41. • There appears to exist a potential for spreading bacterial
contamination from the root canal to the patient and the dental
team via the smoke produced by the laser, which can cause
bacterial dissemination (Hardee et al 1994).
Note: Precautions such as a strong vacuum pump system must be taken to
protect against spreading infections when using lasers in the root canal
(McKinley 1994).
Also, sterilization of root canals by lasers is problematic since
thermal injury to periodontal tissues is possible.
6. Root canal shaping and obturation
• Using an Er:YAG laser, root canal orifices were prepared, after
irradiation by an Er:YAG laser, the root canal surface appeared
smooth under SEM. Root canal cleaning and shaping was
achieved by Nd:YAG laser clean and regular root canal walls
achieved.
• The photopolymerization of camphoroquinone – activated resins
for obturation is possible using an Argon laser emitting at 477
and 488 nm.
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42. • The results indicate than an Argon laser coupled to an optical
fibre could become a useful modality in endo therapy.
• AH-26 and composite resin have been used as obturating
materials (AMC 1795) and SEM examinations revealed fewer
voids in laterally compacted resin fillings than in vertical
compaction.
• Argon, CO2 and Nd:YAG lasers have been used to soften gutta-
percha and results (Anic 1995) indicate that the Argon laser can
be used for this purpose to produce a good apical seal.
Note: It is hard to irradiate root canal walls; as after laser irradiation, walls
are rough and uneven. Therefore it is necessary to improve the fibre tip and
the method in order to irradiate all areas of root canal walls.
7. Effect on periodontal tissues
• The threshold level for bone survival 47°C for 1 min.
• No adverse effects on periodontal tissues by lasers were
observed if appropriate parameters were selected. Laser systems
operate in various modes, such as continuous wave, pulsed,
chopped-wave and Q-switched.
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43. • To minimize the rise in tissue temperature within the target and
around areas, use of the Q-switched nanosound pulsed mode is
beneficial.
8. Full root canal treatment
• Clinical follow-up examination of infected teeth at 3-6 months
after laser irradiation and root canal filling revealed that post-
operative discomfort or pain in the laser treated group was
significantly reduced compared to the non-laser treated group
(Koba, 1995, 1999).
• The immediate drying of Nd:YAG laser maybe due to the
evaporating effect of irradiation on the exudates leaving the
suspended materials to precipitate inside the canals followed by
hemostatic and healing effect with subsequent inhibition of the
inflammatory condition of the periapical lesion.
Note: It is useful to use lasers as an adjacent during conventional treatment,
but it is not possible to use lasers alone for treatment.
9. Apicoectomy:
Because of the high heat energy generated by the use of laser, better
sealing ability of hydroxyapatite to the root apex was detected.
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44. • If a laser is used for the surgery, a blood less surgical field
should be easier to achieve due to the ability of the laser to
vaporize tissue and co-agulate and seal small blood vessels.
• If the cut surface is irradiated, the surface is sterilized and sealed.
Moreover, the potential of the Er:YAG laser to cut hard dental
tissues without significant thermal or structural damage would
eliminate the need for mechanical drills.
• The use of Er:YAG laser resulted in improved healing and
diminished post-operative discomfort (Komori 1996, 1997).
With other lasers like CO2 and Nd:YAG did not improve the healing
process.
Note: It take more time to perform with lasers when compared to more
conventional methods.
• Use of Er:YAG laser for retrograde cavity preparation showed
that the working time with the Er:YAG laser is significantly less
than with ultrasonic tools.
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45. 10. Other applications for endodontic treatment
- For treatment of root fractures
- But fusion was not achieved (Arakawa 1996).
- To sterilize dental instruments (Ar, CO2, Nd:YAG)
- Argon laser was able to do so consistently at the lowest energy
level of 1w for 2 min.
Laser Hazards and Laser Safety:
The subject of dental laser safety is broad in scope, including not
only an awareness of the potential risks and hazards related to how lasers
are used, but also a recognition of existing standards of care and a thorough
understanding of safety control measures.
Laser Hazard Class for according to ANSI and OSHA Standards:
Class I - Low powered lasers that are safe to view
Class IIa - Low powered visible lasers that are hazardous only when
viewed directly for longer than 1000 sec.
Class IIb - Low powered visible lasers that are hazardous when viewed
for longer than 0.25 sec.
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46. Class IIIa - Medium powered lasers or systems that are normally not
hazardous if viewed for less than 0.25 sec without
magnifying optics.
Class IIIb - Medium powered lasers (0.5w max) that can be hazardous if
viewed directly.
Class IV - High powered lasers (>0.5W) that produce ocular, skin and
fire hazards.
The types of hazards can be grouped as follows:
1. Ocular injury
2. Tissue damage
3. Respiratory hazards
4. Fire and explosion
5. Electrical shock
1. Ocular Injury:
- Direct emission
- Reflection
Potential injury to the eye can occur either by direct emission from
the laser or by reflection from a specular (mirror like) surface or high
polished, convex curvatured instruments. Damage can manifested as injury
46

47. to sclera, cornea, retina and aqueous humor and also as cataract formation.
The use of carbonized and non-reflective instruments has been
recommended.
2. Tissue Hazards:
Laser induced damage to skin and other non target tissues can result
from the (1) thermal interaction of radiant energy with tissue proteins.
Temperature elevation of 21°C above normal body temp (37°C) can
produce cell destruction by denaturation of cellular enzymes and structural
proteins. (2) Tissue damage can also occur due to cumulative effects of
radiant exposure. Although there have been no reports of laser induced
caroinogenesis to date, the potential for mutagenic changes, possibly by the
direct alteration of cellular DNA through breaking of molecular bonds, has
been questioned.
The terms photodisruption and photoplasmolysis have been applied
to describe these type of tissue damage.
3. Respiratory:
Another class of hazards involves the potential inhalation of
airborne biohazardous materials that may be released as a result of the
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48. surgical application of lasers. Toxic gases and chemical used in lasers are
also responsible to some extent.
During ablation or incision of oral soft tissue, cellular products are
vaporized due to the rapid heating of the liquid component in the tissue. In
the process, extremely small fragments of carbonized, partially carbonized,
and relatively intact tissue elements are violently projected into the area,
creating airborne contaminants that are observed clinically as smoke or
what is commonly called the ‘laser plume’. Standard surgical masks are
able to filter out particles down to 5µm in size. Particle from laser plume
however may be as small as 0.3µm in diameters. Therefore, evacuation of
laser plume is always indicated with a “Smoke Evacuator”.
4. Fire and Explosion
Flammable solids, liquids and gases used within the clinical setting
can be easily ignited if exposed to the laser beam. The use of flame-
resistant materials and other precautions therefore is recommended.
Flammable materials found in dental treatment areas.
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49. Solids Liquids Gases
Clothing
Paper products
Plastics
Waxes and resins
Ethanol
Acetone
Methylmethacrylate
Solvents
Oxygen
Nitrous oxide
General anesthetics
Aromatic vapors
5. Electrical Hazards:
These can be:
- electrical shock hazards
- electrical fire or explosion hazards
Summary of laser safely control measures recommended by ANSI
Engineering controls:
 Protective housing
 Interlocks
 Beam enclosures
 Shutters
 Service panels
 Equipment tables
 Warning systems
49

50.  Key switch
Administrative controls:
 Laser safety officer
 Standard operating procedures
 Output limitations
 Training and education
 Medical surveillance
Personal protective equipment:
 Eye wear
 Clothing
 Screens and curtains
Special controls:
 Fire and explosion
 Repair and maintenance
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51. Conclusion
Laser has become a ray of hope in dentistry. When used
efficaciously and ethically, lasers are an exceptional modality of treatment
for many clinical conditions that dentists treat on daily basis. But laser has
never been the “magic wand” that many people have hoped for. It has got
its own limitations. However, the futures of dental laser is bright with some
of the newest ongoing researches.
Once, our knowledge about optimal laser parameters for each
treatment modality is complete, lasers can be developed that will provide
dentists with the ability to care for patients with improved techniques.
References
 St underwent (3rd
Ed.).
 Lasers in Endodontics – a review (IEJ, 33 : 173-185).
 DCNA 2000 (Lasers and light amplification in dentistry).
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52. CONTENTS
 INTRODUCTION
 HISTORY OF LASERS
 LASER PHYSICS AND DESIGN
 MODE OF DELIVERY OF LASER
 TYPES OF LASER
 LASER INTERACTION WITH BIOLOGIC TISSUE AND ITS
EFFECTS
 APPLICATION OF LASERS IN DENTISTRY
 CONSERVATIVE
 ENDODONTIC
 LASER HAZARDS
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