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.

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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.

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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.

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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.

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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

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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.

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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

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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

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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.

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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

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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

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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.

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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

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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 deep in the infrared range

of the electromagnetic opectrum.

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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.

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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 )

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.

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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).

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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.

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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 m.

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.

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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.

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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

SourceReflected

ScatteredAbsorbed

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.

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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

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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.

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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 – 60 o denaturation occurs

>60 o coagulation and necrosis

At 100 o C water inside tissue vaporizes

>300 o C carbonization and later phyrolysis withvaporization 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

tissues surfaces and causes ablation and severe heating which can lead to

tissue damage.

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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

4. Tricalcium phosphate takes place.

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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

1-3m 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.

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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.

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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.

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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

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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)

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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 2.94m 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.

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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.

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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.

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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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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.

35

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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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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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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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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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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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.

41

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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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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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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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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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

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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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 5m in size. Particle from laser plume

however may be as small as 0.3m 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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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

Key switch

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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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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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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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