Zones of Activity

All treatment activity evolves around the patient. Before equipment selection can be considered, the dental team must be aware of special functional spatial relationships around the patient at chair side. The work area around the patient is divided into four “zones of activity.” Zones of activity are identified using the patient’s face as the face of a clock. The four zones are: the operator’s zone, assistant’s zone, transfer zone, and static zone. The zones are depicted for a right‑handed operator in (Figure 1). The zones are reversed for the left‑handed operator in (Figure 2).

Figure 1. Zones of Activity for a right-handed dentist.
right-handed zone
Figure 2. Zones of Activity for a left-handed dentist.
left-handed zone

The operator’s zone for a right‑handed operator extends from 7 to 12 o’clock, the assistant’s zone from 2 to 4 o’clock, the instrument transfer zone from 4 to 7 o’clock, and the static zone from 12 to 2 o’clock. The operator changes position dependent upon the dental arch and tooth being treated. The assistant seldom moves much in the zone of activity, but may find it necessary to raise the operating stool when working on the mandibular arch to improve the line of sight into the oral cavity.

These zones are self‑explanatory except for the static zone, which is the zone of least activity. Instruments that are infrequently used such as the blood pressure equipment, portable curing light, or the assistant’s mobile cabinet when not in use can be stored in this area.

An awareness of the zones of activity is important since they should serve as guides for the dental team in locating equipment as well as positioning the patient and operating team to facilitate access to the operative field and improve visibility. The second course of this two part series reviews the selection of dental equipment for use in an ergonomic, four‑handed dental practice.