"LASER HAZARDS AND SAFETY IN DENTISTRY"

Laser hazards can be classified into:

1. BEAM HAZARDS: These include injuries associated with the radiation itself. The laser prod
uces an intense, highly directional beam of light. If directed, reflected, or focused upon an object,
laser light will be partially absorbed, raising the temperature of the surface and/or the interior of
the object, potentially causing an alteration or deformation of the material. Therefore, these inclu
de damages caused to the eye and skin by direct exposure.

2. NON-BEAM HAZARDS: These non-beam hazards, in some cases, can be life-

threatening. The only fatalities from lasers have been caused by non-
beam hazards. A few examples of non-
beam hazards include fire/explosion, electric shock, and laser-generated air contaminants.

CAUSES OF LASER ACCIDENTS: Laser hazards may be listed as follows:

 Ocular
 Skin
 Injury to non-target tissues
 Fire
 Respiratory

1. OCULAR EFFECTS: The primary ocular injury that may result from a laser accident is a ret
inal or corneal burn. The coherence and low divergence angle of laser light, aided by focusing fr
om the lens of an eye, can cause laser radiation to be concentrated into an extremely small spot o
n the retina. A transient increase of only 10 °C can destroy retinal photoreceptor cells. If the laser
is sufficiently powerful, permanent damage can occur within a fraction of a second, literally fast
er than the blink of an eye. Even low-
intensity beams can cause damage because of the focusing effect of the lens and cornea. A laser
beam can be focused to an intensity on the retina, which may be up to 200,000 times higher than
at the point where the laser beam enters the eye. Most of the light is absorbed by melanin pigmen
ts in the pigment epithelium just behind the photoreceptors and causes burns in the retina. Irrever
sible retinal burns resulting in permanent blindness can occur by conversion of incident radiation
to heat energy within a fraction of a second. Damage from a laser beam may be due to direct exp
osure to the beam or diffuse reflection, or when wavelength-
specific eyewear is not used. A pulsed laser will cause more damage than a continuous beam of e
qual power because the peak power is greater than the average output power. The body's protecti
ve "blink reflex" response is triggered only by visible light. So people exposed to high power Nd
:YAG laser emitting invisible radiation may not feel pain or notice immediate damage to their ey
esight. A pop or click noise emanating from the eyeball may be the only indication that retinal da
mage has occurred. Some visible wavelengths affect red and green cones resulting in color blind
ness. Emissions below 400 nm are absorbed by the cornea and lens, leading to cataracts. The eye
focuses visible and near-
infrared light onto the retina. Sufficiently powerful emissions in this spectral region ( nm) will pe
netrate the eyeball and heat up the retina, causing retinal injury. Nm wavelength lasers cause lens
 damage, nm wavelengths cause corneal, aqueous, and lens damage, NM wavelengths cause corn
eal damage.

PRECAUTIONS:

 Use of glasses for protection (patient, operator, assistants): Protective eyewear in the for
m of spectacles or goggles with appropriately filtering optics can protect the eyes from th
e reflected or scattered laser light with hazardous beam power, as well as from direct exp
osure to a laser beam. Eyewear must be selected for the specific type of laser to block or
attenuate in the appropriate wavelength range. For example, if the eyewear is marked as n
m, it means that the eye exposed to all wavelengths between these two outer limits is prot
ected. The wavelengths that the eyewear is specific for should be printed on it. Lightweig
ht goggles with plastic filters are used and these are made of polycarbonate with a dye mi
xed into the material, or with an absorbing or reflecting coating. For higher power, glasse
s containing a lamination of filter glass and polymer layers are used. Glasses must cover t
he entire peri-
orbital region and should be free of any surface scratches. The protocol for use is “patient
first on and last off“ i.e., as soon as the patient is seated, protective eyewear is put on, wh
ich is not to be taken off until the end of the procedure. The eyewear should be examined
now and then for cracks of the protective material.
 Requirements of Safety Glasses: A high level of attenuation of incident laser light by the
glass, achieved by absorption and/or reflection, adequate protection against beams comin
g from the side, durability of the glass, even under conditions of strong heating by an inci
dent laser beam, absence of photo-
bleaching, low tendency for scratches, a label with clear indications concerning the kind
of protection (to avoid that glasses are used in cases where they do not provide adequate
protection), ease of wearing, sufficiently large viewing angle, and a lightweight for avoidi
ng pain due to excessive pressure on the skin.

MAXIMUM PERMISSIBLE EXPOSURE: The maximum permissible exposure (MPE) is the

highest power or energy density of a light source that is considered safe, i.e., that has a negligible
probability for creating damage. A calculation of the MPE for ocular exposure takes into accoun
t the various ways light can act upon the eye. For example, Infrared light with a wavelength long
er than about 1400 nm is absorbed by the transparent parts of the eye before it reaches the retina,
which means that the MPE for these wavelengths is higher than for visible light. In addition to th
e wavelength and exposure time, the MPE takes into account the spatial distribution of the light.
An MPE is usually expressed in terms of the allowable exposure time (in seconds) for a given irr
adiance (in watts/cm2) at a particular wavelength. Collimated laser beams are especially dangero
us because the lens focuses the light onto a tiny spot on the retina. In the MPE calculation, the w
orst-
case scenario is assumed, in which the eye lens focuses the light into the smallest possible spot si
ze on the retina for the particular wavelength and the pupil is fully open.

OPTICAL DENSITY: Eyewear is rated for optical density (OD). Optical Density (OD) is a me
asure of the radiation permitted to pass through a filter and it's determined by the filter. For exam
ple, an OD of 2.0 allows 1/100 of the laser light energy to pass through the filter. The OD specifi
ed on the glasses is the minimum OD sufficient to protect the user against momentary intrabeam
or specular reflection exposure.

2. Use of wet gauze packs to avoid reflection from shiny metal surfaces.

3. The patient and the dentist should wear the eyewear before the laser is switched on and
should not take them off until the laser is switched

NON-TARGET TISSUE DAMAGE

Laser-induced damage to the non-target tissue (oral tissue) can result from thermal interaction of
radiant energy with tissue proteins. This interaction can cause cell destruction by denaturation of
cellular enzymes and structural proteins, interrupting basic metabolic processes. Histologically,
the thermal effect of absorbed radiant energy manifests as thermal coagulation necrosis for
wavelengths above 400 nm. Other non-thermal tissue interactions are thought to induce injury
through photochemical and photoacoustic mechanisms.

Photochemical damage due to short wavelength light is caused by chemical reactions triggered
in the tissues and can accumulate over hours. Prolonged exposure to low power density from
Nd:YAG lasers can result in excess thermal necrosis that may not be apparent at the tissue
surface. The extent of damage depends on factors such as:

 Laser beam size

 Absorption coefficient
 Scattering coefficient
 Exposure time
 Size of the exposed area

PRECAUTIONS

 Focus the beam on target tissues

 Avoid using glass mirrors as they absorb heat and can shatter; use Rhodium coated
mirrors for safety
 Ensure continuous monitoring of adjacent tissues during the procedure

SKIN DAMAGE

Potential risks to the skin are secondary to risks to the eyes because skin injuries often do not
have the severe consequences (such as partial loss of vision) that eye injuries do. Skin injuries
may affect only the external dead layer of skin cells and more penetrating damage usually heals
eventually. Large-area exposures that can lead to serious skin infections and complications are
not common with laser use because the beam is relatively small.

Laser radiation can affect the skin thermally or photochemically. The pain from thermal injury to
the skin by most lasers is enough to alert the user to move out of the beam path. However, high-
power visible and IR lasers are now capable of producing significant burns to the skin in much
less than one second, and users are unable to move out of the beam path before serious injury
occurs.

LASER CLASSIFICATION

CLASS Use in Dentistry Risks Safety Measures

Class I Caries Detection No implicit risk Blink Response
Class I Possible risk with magnified
Scanner Laser safety labels
M beam
Sight aversion
Class II Aiming beams Possible risk with direct viewing
response
Class II Significant risk with
M magnified beam
Class III Photodynamic antimicrobial
Eye damage Safety eye wear
R chemotherapy devices
Class III
Mucosal scanning devices Skin risk Protective clothing
B
Eye and Skin Damage, Non-
Protective eye wear,
Class IV All surgical lasers target tissue damage, Plume
Safety personnel
Hazard

LASER SAFETY SIGNS

Laser Area Signs are used to mark the area designated as a laser hazard zone. The signs vary
according to the classification of the laser or laser system. The signal word “CAUTION” is used
on all signs associated with Class 2 lasers. The signal word “DANGER” is used with all signs
associated with all Class 3a, Class 3b, and Class 4 lasers. All signs and labels shall be
conspicuously displayed in locations where they will best serve to warn onlookers.

SAFETY MEASURES

ENGINEERING CONTROLS

 Stable mounting (beam not at eye level)

 Protective housings, enclosures
 Interlocks on housings, lasers, doors, etc.
 Control of the beam path (beam tubes, beam stops, etc.)
 Remote firing
 Emergency buttons
 Fume extraction systems
 Warning lights
 Filters
 Switch guards, covers
 Alignment aids
ADMINISTRATIVE CONTROLS

 Laser Safety Office or person-in-charge

 Registration of laser equipment and users
 Designated laser-controlled areas
 Warning signs
 Standard operating procedures
 Emergency and accident reporting procedures

PERSONAL PROTECTIVE EQUIPMENT

 PPE as a last resort

 Appropriate laser protective eyewear to protect the eyes
 Suitable clothing to protect the skin

CONCLUSION

Laser use in dentistry is proven to be beneficial in treating a wide range of dental conditions and
as a therapeutic tool in tissue management. Safety regarding the use of lasers is not optional and
should be the highest priority of all staff members involved in surgical procedures. Prevention of
accidents requires thorough knowledge of their causes and the application of measures to avoid
them.