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 position.

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 assistant's zone.

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 patient’s 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 dentist’s 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

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 stages - working, signal, pre-transfer, and mid- transfer.

In the working stage, pick up the next instrument to be used from the instrument tray with your left