In addition to routine airborne debris, airborne particles may be produced occasionally by matrix

failure of molded abrasive cutting instruments. Hard matrix wheels may crack or shatter into
relatively large pieces. Soft abrasive wheels or points may increase in temperature during use,
causing the rubber matrix to debond explosively from the abrasive into fine particles.

Precautions must be taken to prevent eye injury from unusual light sources such as visible
light-curing units and laser equipment. Dental personnel and patients should be protected from
high-intensity visible light with the use of colored plastic shields (attached to the fiber optic tip).
Laser light can be inadvertently reflected from many surfaces in the dental operatory; the
operatory should be closed, and every-one should wear protective goggles (see the earlier
section on laser equipment).

Hazards with cutting instruments

Eye Precautions

The operator, the assistant, and the patient should wear glasses with side shields to prevent eye
damage from airborne particles during operative procedures using rotary instru-mentation.
When high speeds are used, particles of old restorations, tooth structure, bacteria, and other
debris are discharged at high speeds from the patient's mouth. Sufficiently strong high-volume
evacuation applied by the dental assistant near the operating site helps alleviate this problem.
Protective glasses are always indicated when rotary instru-mentation is being used. The dentist,
being in the direct path of such particles, is more likely to receive injury than the assistant or the
patient. If an eye is injured, it should be covered by a clean gauze pad until medical attention
can be obtained. temporary threshold shift. If sufficient time is allowed between exposures,
complete recovery occurs. Extended or continuous exposure is much more likely to result in a
permanent thresh-old shift, with persistent hearing loss. The loss may be caused by all
frequencies, but often high-frequency sounds affect hearing more severely. A certain amount of
unnoticed noise (ambient noise level) is present even in a quiet room (20-40 db). An ordinary
conversation averages 50 to 70 db in a fre-quency range of 500 to 2500 cps.

Air-driven handpieces with ball bearings, free running at 30-lb air pressure, may have noise
levels of 70 to 94 db at high frequencies. Noise levels greater than 75 db in frequency ranges of
1000 to 8000 cps may cause hearing damage. Noise levels vary among handpieces produced
by the same manu-facturer. Handpiece wear and eccentric rotating instruments can cause
increased noise. Protective measures are recom-mended when the noise level reaches 85 db
with frequency ranges of 300 to 4800 cps. Protection is mandatory in areas where the level
transiently reaches 95 db. The effect of exces-sive noise levels depends on exposure times.
Normal use of a dental handpiece is one of intermittent application that generally is less than 30
minutes per day. Earplugs can be used to reduce the level of exposure, but these have several
drawbacks. Room soundproofing helps and can be accom-plished with absorbing materials
used on walls and floors. Anti-noise devices also can be used to cancel unwanted sounds.

Ear Precautions
Various sounds are known to affect people in different ways. Soft music or random sounds such
as rainfall usually have a relaxing or sedative effect. Loud noises are generally annoying and
may contribute to mental and physical distress. A noisy environment decreases the ability to
concentrate, increases proneness to accidents, and reduces overall efficiency. Extremely loud
noises such as explosions or continuous exposure to high noise levels can cause permanent
damage to the hearing mechanism.

An objectionable high-pitched whine is produced by some air-driven handpieces at high speeds.

Normal ears require that the intensity of sound reach a certain minimal level before the ear can
detect it. This is known as the auditory threshold. It can vary with the frequency and exposure to
other sounds. When subjected to a loud noise of short duration, a protective mechanism of the
ear causes it to lose some sensitivity temporarily. This is described as

Inhalation Precautions

Aerosols and vapors are created by cutting tooth structure and restorative materials. Aerosols
and vapors are a health hazard to all present. The aerosols are fine dispersions in air of water,
tooth debris, microorganisms, or restorative materials. Cutting amalgams or composites produce
submicron particles and vapor. The particles that may be inadvertently inhaled have the
potential to produce alveolar irritation and tissue reac-tions. Vapor from cutting amalgams is
predominantly mercury and should be eliminated, as much as possible, by careful evacuation
near the tooth being operated on. The vapors gen-erated during cutting or polishing by thermal
decomposition of polymeric restorative materials (sealants, acrylic resin, composites) are
predominantly monomers. They may be eliminated efficiently by careful intraoral evacuation
during the cutting or polishing procedures.

A rubber dam protects the patient against oral inhalation of aerosols or vapors, but nasal
inhalation of vapor and finer aerosol still may occur. Disposable masks worn by dental office
personnel filter out bacteria and all but the finest particulate matter. Masks do not, however, filter
out mercury or monomer vapors. The biologic effects of mercury hazards and appropriate office
hygiene measures are discussed in online Chapter 18 on Biomaterials

Reading Task: Read an excerpt from the book Sturdevant’s Art and Science of Operative
Dentistry on the hazards with cutting instrument.

Guide question: