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

History of Lasers

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, Townes, working with Schawlow at Bell Laboratories,

published the first theoretic calculations for a visible light maser –

or what was then called a LASER.

In May 1960, Theodore Maimen at Hughes Aircraft company made

the first laser. He used a ruby as the laser medium.

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.

The first gas laser was developed by Javan et al in 1961. This was

the first continuous laser and used helium – neon.

2

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.

In 1968 Polanyi developed articulating arms to deliver CO2 laser to

remote areas.

Polanyi in 1970 applied CO2 laser clinically.

In 1990 Ball suggested opthalmologic application of ruby laser.

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.

3

The radiation emitted by lasers including both visible and invisible light

is more generally termed as electromagnetic radiation. The concept of

stimulated emission of light was first proposed in 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 +vely 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

4

energy in the form of an emitted photon. This process is called

spontaneous emission.

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.

If a collection of atoms includes, more that are pumped into the

excited state that remain in the resting state, a population inversion

exists. This is necessary condition for lasing. Now, the spontaneous

emission of a photon by one atom will stimulate the release of a second

photon in a second atom, and these two photon will trigger the release of

two more photons. These four than yield eight, eight yield sixteen and so

on. In a small space at the speed of light, this photon chain reaction

produces a brief intense flash of monochromatic and coherent light

which is termed as ‘laser’.

Properties of Laser

1. Coherent: Coherence of light means that all waves are in certain

phase relationship to each other both in space and time

5

2. Mono- chromatic: Characterized by radiation in which all waves are

of same frequency and wavelength.

3. Collimated: That means all the emitted waves are parallel and the

beam divergence is very low. This property is important for good

transmission through delivery systems.

4. Excellent concentration of energy: When a calcified tissue for eg.

dentin is exposed to the laser of high energy density, the beam is

concentrated at a particular point without damaging the adjacent

tissues even though a lot of temperature is produced ie 800-900oC.

5. Zero entropy.

Laser Design

The laser consist of following components.

1. A laser medium or active medium: This can be a solid, liquid or

gas. This lasing medium determines the wavelength of the light

emitted from the laser and the laser is named after the medium.

2. Housing tube or optical cavity:

Made up of metal, ceramic or both.

6

This structure encapsulates the laser medium.

Consists of two mirrors, one fully reflective and

the other partially transmittive, which are

located at either end of the optical cavity.

3. Some form of an external power source: This external power

source excites or “pumps” the atom in the laser medium to their

higher energy levels. A population inversion happens when there are

more atoms in the excited state rather than a non-excited state.

Atoms in the excited state spontaneously emit photons of light which

bounce back and forth between the two mirrors in the laser tube, they

strike other atoms, stimulating more spontaneous emission. Photons

of energy of the same wavelength and frequency escape through the

transmittive mirror as the laser beam. An extremely small intense

beam of energy that has the ability to vaporize, coagulate, and cut

can be obtained if a lens is placed in front of the beam. This lens

concentrates the emitted energy and allows for focussing to a small

spot size.

7

Laser Light Delivery

Light can be delivered by a numbered of different mechanisms.

Several years ago a hand held laser meant holding a larger, several

hundred pound laser usually the size of 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 routinly in

dentistry.

1. Articulated arms

Laser light can be delivered by articulated arms, which are very

simple but elegant. 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

does have some disadvantages that include the arm counter weight and

the limited ability to move in 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

8

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

micros 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, one the beam is

no longer collimated and coherent when emitted from the fiber which

limits the focal spot size and second disadvantage is that the light is no

longer coherent.

Patient to laser

Another method of delivering laser light to the patient is actually

to bring the patient up to the laser. Eg: Slit lamp used in the

ophthalmologist gist has been doing this for quite some time. The

ophthalmic laser microscope is simply a slit lamp with a laser built into

it. The doctor simply images what he wants on the cornea or retina and

then pushes the foot pedal to deliver laser beam to the target.

Once the laser is produced, its output power may be delivered in

the following modes.

9

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. Gated: 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. Pulsed: Lasers can be gated or pulsed electronically. This type of

gating permits the duration of the pulses to be compressed producing

a corresponding increase in peak power, that is much higher than in

commonly available continuous wave mode.

4. Super pulsed: The duration of pulse is one hundredth of

microseconds.

5. Ultra pulsed: This mode produces an output pulse of high peak

power that is maintained for a longer time and delivers more energy.

6. Q-scotched: Even shorter and more intense pulse can be obtained

with this mode.

10

Focussing

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 used. This mode can also be referred as cut mode. Eg. While

performing biopsies.

The other method is the defocused mode. By defocusing the laser

beam or moving the focal spot away from the tissue 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.

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

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.

11

Non contact mode: Fiber tip is placed away from the target tissue.

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: Agon, HO : YAG,

Nd:YAG

Laser Types

I. Based on wavelength.

1. Soft lasers

2. Hard lasers

II.

12

Based on the type of active / lasing medium used

1. ArF excimer

2. KrF excimer

3. XeCl excimer

4. Argon ion

5. KTP

6. Ruby

7. Nd: YAG

8. HO: YAG

9. YSGG

10. Er: YAG

11. CO2

13

I.

1. Soft Lasers: With a wave length around 632mm Soft lasers are

lower power lasers.

Eg: He Ne, Gallium arsenide laser.

These are employed to relieve pain and promote healing eg. In

Apthous ulcers.

2. 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 Palet 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.

CO2 lasers have an affinity for wet tissues regardless of tissue color.

14

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, although their penetration depth is only about 0.2 to 0.1mm.

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 cannot 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.

Of all the lasers for oral use, CO2 is the fastest in removing tissue.

15

As CO2 lasers are invisible, an aiming helium – neon (He Ne) beam

must be used in conjunction with this laser.

Nd: YAG Laser: Here a crystal of Yttrium – aluminum – garnet is

doped with neodymium. Nd: YAG laser, has wavelength of 1,064 nm

(0.106 ) 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: hemoglobin 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 wavelength is delivered fiber optically and many sizes

of contact fibers are available. Carbonized tissue remains often build

of 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. Special tips, the coated

sapphire tip, can be used to limit lateral thermal damage. A helium-

neon-aiming beam is generally used with Nd: YAG wavelength.

16

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.

Most dental Nd: YAG lasers work in a pulsed mode. At higher

powers and pulsing, a super heated gas called a plasma can form on

the tissue surface. It is the plasma that can be responsible for the

effects of either coagulation, vaporization or cutting. If not cooled

(e.g. by running a water stream down the fiber) the plasma can cause

damage to the surrounding tissues.

Suffer from dragability

The Nd:YAG beam is readily absorbed by amalgam, titanium and

non-precious metals, requiring careful operation in the presence of

these dental materials.

Argon Lasers

Argon lasers are those lasers in the blue-green visible spectrum.

They operate at 488nm or 514.5nm, are gas like CO2 lasers and are

easily delivered fiber optically like Nd:YAG.

17

Argon lasers have an affinity for darker colored tissues and also a

high affinity for hemoglobin, making them excellent coagulators. 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.

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.

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.

18

Er: YAG laser

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.

Pulpal response to cavity preparation with an Er: YAG laser was

minimal, reversible and comparable with pulpal response created by

a high-speed drill.

Ho: YAG laser [Holmium YAG lasers]

Has a wavelength of 2,100 nm and is a crystal

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.

19

Ho: YAG laser has an affinity for white tissue and has ability to pass

through water and acts as a good coagulator.

Laser interaction with biologic tissues

Light can interact with tissues in four different mechanisms

1. Reflected

2. Scattered

3. Absorbed

4. Transmitted

Reflection: Reflected light bounces off the tissue surface and is

directed outward. Energy dissipates after reflection, so that there is little

danger of damage to other parts of mouth and it limits the amount of

energy that enters the tissue.

Scattering: occurs when the light energy bounces from molecule to

molecule within the tissue. 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. It converts light

energy to heat energy The absorption properties of tissue and cells

20

depends on the type and amount of absorbing pigments or

chromophores. Eg. Hemoglobin, water, Melanin, Cytochromes etc.

Transmission: Light can also travel beyond a given tissue boundary.

This is called transmission. Transmission irradiates the surrounding

tissue and must be quantified. Its effects should be considered before

laser treatment can be justified.

Tissue effects on laser irradiation

When radiant energy is absorbed by tissue 4 basic types of

interactions occurs.

Laser effects on Dental Hard Tissues

The absorption and transmission of laser light in human teeth is

mainly dependent on the wavelength of the laser light.

For eg. – Ultraviolet laser light is well absorbed by teeth.

In water and in hydroxyapatite, there is a very low absorption at a

wavelength of 2m in comparison to high absorption of laser energy at

3m and 10m.

The laser effects can be grouped as:

1. Thermal effects:

21

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

with vaporization of bulky

tissues.

2. Mechanical effects:

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.

3. Chemical effects:

Here molecules can be associated directly with laser light of high

photon energies.

Histologic Results:

22

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.

Microcracks and zones of necrosis and carbonization are unavoidable.

Because of drying effects, the microhardnes of dentin increases. The

crystalline structure of hydroxyapatite changes and a transformation of

apatite to tricalcium phosphate takes place.

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.

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

23

cavities areas of carbonization and microcracks were observed. Ablating

enamel always cracked and deep zones of debris appeared.

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. Thermal side effects increase as photon energies of excimer

lasers decrease.

Laser Effects On Dental Pulp:

Recent histologic evidence suggests that a normal odontoblasts

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.

24

Application of Lasers in Dentistry:

Application Possible Laser Types

Basic research

Laser tissue interaction

Technical development of applications

of lasers in dentistry

All types

All types

Measurement and diagnosis

Holography

Laser Doppler fowmetry

Spectroscopy (caries diagnosis)

He Ne, diodes

He Ne, diodes

Various types

Oral and Maxillofacial Surgery

Cutting and Coagulation

Photodynamic therapy

CO2, Nd: YAG, Ar, dye

Dye, Au-Cu vapour

Conservative dentistry

Preventive dentistry (fissure sealing)

Caries treatment

Composite resin light Curing

Tooth surface conditioning

CO2, Nd:YAG, ruby

CO2, Nd:YAG, Er: YAG, Excimer

Ar, dye, HeCd

Excimer, CO2, Nd:YAG, Er:YAG

Endodontics

Root canal treatment

Apicoectomy

Nd: YAG, CO2, Excimer

CO2, Nd:YAG

Periodontics

25

Laser sealing of affected root surfaces

Excision of gingival soft tissues

CO2, excimer

CO2

Analgesic effect and bio-stimulation

Stimulation of wound healing

Low power laser radiation with analgesic

Effects

He Ne, diodes

Nd: YAG

Other applications:

Laser processing of dental materials

Welding of dental alloys

Cobalt – chrome – molybdinum

Nickel – chrome – aluminum

Silver Palladium

Titanium alloys

Welding of ceramic materials

Still under investigation

Advantages of laser welding:

1. High bond strength and corrosion resistance since laser welding is a

form of sweating that does not use solders of different materials.

2. Reduced oxidation when argon gas is used for welding.

26

3. Decreased thermal influence and greater precision in processing than

with soldering or other techniques.

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 Oaya used as YAG laser at energy

densities of 10 to 20 J/cm³ and demonstrated that the lased

enamel surface was more resistant to in vitro

demineralization than non lased enamel.

Stern and Sognnaes demonstrated in vivo that enamel

subjected to 10 to 15 J/cm² 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.

27

Lobene and Collogues 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 laser in prevention of caries.

Lasers can be 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.

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.

2. Diagnosis: Lasers can be used to detect incipient carious lesion

which cannot be diagnosed clinically and radiographically.

28

Transilliumination 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.

3. Laser Doppler Flowmetry: Pulpal blood flow can be assessed using

laser doppler flowmentry. He Ne and diodes can be used.

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)

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

29

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.

30

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 then 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

this 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.

31

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.

32

The polymerization of light activated bases and or liners

can also be accomplished with the argon laser.

Advantages : A wide verity of fiber sizes provides access to all location

of cavity preparation.

Pit and Fissure Sealant Therapy:

Advantages are similar to those offered for curing composite

resins.

Desensitization:

Lasers are effective tool in the treatment of hypersensitivity.

Mode of action is by blocking the dentinal tubules resulting in change in

hydraulic conductance.

Bleaching:

Lasers also find use in bleaching of vital and non-vital teeth.

Treatment of fractured teeth:

Lasers have the potential to fuse the segments of fractured teeth.

33

Pulpotomy:

Recent development

Removal of Old restoration:

Composites and cements can be ablated.

Gold crowns and cast fillings cannot be removal as laser beam

is reflected.

Ceramics cannot be ablated.

In endodontics:

For root canal preparation.

1. For Root Canal Preparation: Based on the SEM investigation of

prepared teeth, root canals appeared to be free of soft tissue and

debris. There was no smear layer detectable and there were no cases

of straightening or over instrumentation of the canals. The dentinal

tubules appeared to be open. These were no detectable thermal or

mechanical alteration to the root canal walls. There was a significant

reduction in bacterial growth (disinfection).

2. For sterilization of Files & Reamers

34

3. Apicoectomies:

for soft tissue procedures

for curing the retrograde filling materials.

Lasers in Surgical Systems:

Lasers are an alternative to conventional surgical systems. Stated

best by Apfelberg in 1987, lasers are a “new and different scalpel”

(optical knife, light scalpel).

Advantages:

Easy access to the anatomic site

Possess inherent hemostatic properties.

Capable of ablation of lesions in proximity to normal

structures, with minimal damage to normal structures.

Reduced pain during surgical procedures and less post

operative pain.

Enhanced healing

35

Bactericidal and virucidal effects of laser result in

decreased rates of wound infection.

Certain proven uses for dental soft tissue procedures using

lasers are:

1. Frenectomy

Maxillary midline

Lingual (Tongue tie)

2. Incisional and exasional biopsies.

3. Removal of benign lesions

Fibrous

Papillous

Pyogenic granuloma

Lichen Planus

Erosive lichen planus

Nicotinic stomatites

Verruca vulgaris

Inflammatory papillary hyperplasia

Epuli

4. Gingivoplasty

36

5. Soft tissue tuberosity reduction.

6. Soft tissue distal wedge procedure.

7. Gingivectomy

A. Removal of hyperplasias

1. Dilantin etc

2. Idopathic

B. Crown trough.

8. Aphthous ulcer

9. Operculectomy

10. Removal of hyperkeratotic lesions

11. Removal of malignant lesions

12. Soft tissue crown lengthening

13. Coagulation.

A. Graft donor sites.

B. Seepage around crown preparation.

14. Vestibuloplasty

15. Removal of granulation tissue – periodontal clean out

16. Removal of vascular lesions

A. Hemangioms

B. Pyogenic granuloma

37

17. Removal of lesion in patients with hemorrhagic disorders.A. Hemophelia etc.

18. Implants – Stage II – at the time of recovery.

A. Soft tissue removal

Bio-stimulation and Photodynamic Therapy:

Photodynamic therapy is an experimental cancer treatment that is

based on a cytotoxic photochemical reaction. This reaction requires

molecular oxygen, the photoactive drug dihematoporphyrin ether, a

hematophorphyrin derivative and intense light, which is typically

delivered by a laser. Dihematoporphyrin which is relatively retained in

malignant tissue after several days, is given intravenously to a patient.

Laser light at a wavelength corresponding to the absorption peak of the

drug is used to activate the drug to an excited state. The drug then reacts

with molecular oxygen to produce singlet oxygen, a highly reactive free

radical which ultimately leads to tissue necrosis.

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

38

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 hazards only when

viewed directly for longer than 1000 sec.

Class II - Low powered visible lasers that are hazardous when

viewed for longer than 0.25 sec.

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.

39

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:

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 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 others non target tissues can

result from the 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. Tissue damage can also occur due to cumulative

40

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 breathing 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

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.

41

Particle from laser plume however may be as small as 0.3m in

diameters. Therefore, evacuation of laser plume is always indicated.

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.

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

42

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

Administrative controls:

- Laser safety officer

- Standard operating procedures

- Output limitations

- Training and education

- Medical surveillance

Personal protective equipment:

- Eye wear

- Clothing

- Screens and curtains

43

Special controls:

- Fire and explosion

- Repair and maintenance

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.

44