and 4 o'clock. For left-handed dentists, seated to the
right of the patient, the operator's zone is between 1
and 4 o'clock position and the assistant's zone
between 8 and 10 o'clock. Whenever the treatment site
is on the lingual surfaces of anterior teeth, the dentist
(right or left-handed) generally uses the 12 o'clock
The transfer zone is from 4 to 8 o'clock.
Instruments and materials are passed and received in
this zone over the chest and at the chin of the patient.
All instruments and materials are located in the
The static zone, from 11 to 2 o'clock, is a non-
traffic area where equipment, such as nitrous oxide,
can be placed with the top extending into the assistant's
zone. When an object is heavy, or material or an
instrument is objectionable if held near the patient's
face, you may pass or hold it in the static zone. As an
example, anesthetic syringes are sometimes passed to
the dentist in this area so that the patient will not be
alarmed at the sight of the syringe. Part of this area can
also be used when the provider is positioned in the 12
o'clock position as previously mentioned.
Dentists and dental assistants should sit with their
back straight and head relatively erect. This helps
prevent curvature of the spine. The patient should be
lowered to a position that places the treatment site as
close to the dentist's elbow level as possible. When the
patient is properly positioned, the dentist's eyes should
be 14 to 16 inches from the treatment site.
As the assistant, you should sit as close as possible
to the back of the patient's chair with your feet directed
toward the head of the chair. This position lets you
reach the treatment site, hose-attached instruments,
and instruments and materials from the mobile cart or
instrument tray without leaning, twisting, or
overextending your arms. In this position you are also
able to observe the patients responses throughout the
procedure. Adjust your stool so that your eye level is 4
to 6 inches above the dentist's eye level. Like the
dentist, the assistant should sit in an erect position. The
assistant's chair may have a curved, movable armrest.
This armrest may be adjusted in front to support the
body just below the rib cage. Using this armrest as a
brace, you are able to lean slightly forward from the
hips only. Place your feet firmly on the foot-support
ring at the base of the assistant chair so that your feet
are parallel to the floor. The mobile cart or instrument
tray should be placed toward the head of the patient's
chair, and positioned to allow you easy access to the
needed instruments and materials.
PASSING AND RECEIVING
INSTRUMENTS AND MATERIALS
To increase production while reducing stress and
fatigue of the dentist and the assistant, you and the
dentist will need to work together as a team. You must
be able to anticipate the dentists needs and fulfill those
needs without unnecessary delay. To accomplish this,
you must know the sequence of the treatment
procedure and have the required instruments and
materials ready at the proper time. When you assist in
four-handed dentistry, you must also irrigate with air
and water as well as aspirate with the high-volume
evacuator throughout the procedure. To enable you to
pass and receive items efficiently during the
procedure, we will begin with instrument transfers.
Instrument exchange between the dentist and
assistant takes place in the transfer zone near the
patient's chin. As the assistant, you must anticipate the
dentist's needs, and be ready when signaled by the
dentist to pass the next instrument and receive the used
one in a smooth motion. An alert assistant does not
need a verbal command to make the exchange, but
should be constantly ready when the exchange signal
occurs. Ideally, the instrument transfer is
accomplished with a minimum of motion involving
movement only of your fingers, wrist, and elbow.
During the transfer, the dentist should not move the
finger rest or eyes from the treatment site. When the
exchange is completed, the dentist pivots the working
hand back to the working position.
You should arrange the instrument setup in an
orderly fashion. Usually the instruments are set up
from left to right, in the sequence in which they are to
be used. You should return them to their original
position following use in case they need to be reused.
Let's assume that you are assisting a right-
handed dentist and, therefore, are seated on the left
side of a patient.
Since your right hand is busy
aspirating, you must learn to transfer instruments
with your left hand. The one-hand instrument
exchange is discussed next.
ONE-HAND INSTRUMENT EXCHANGE.
The actual instrument transfer is divided into four
stagesworking, signal, pre-transfer, and mid-
In the working stage, pick up the next instrument
to be used from the instrument tray with your left