Motion economy refers to the way energy can be conserved, and strain on the body reduced, by refining specific motions. Motion can be classified into five categories according to the length of the motion.
Class I is a fingers only movement, such as picking up a small cotton pellet.
Class II is a fingers and wrist motion, as used when transferring an instrument to the operator.
Class III includes the fingers, wrist, and elbow, as when reaching for a hand piece.
Class IV requires movement of the entire arm and shoulder, as when reaching into the mobile cabinet.
Class V requires the entire torso to be moved, as when turning to activate the electro-surgery unit.
The latter two motion classifications, IV and V, are the most strenuous, and eliminating these will conserve energy and reduce stress.
The stool is adjusted to allow the operator’s feet to rest firmly on the floor, thighs parallel to the floor and to provide adequate support for the back.
The patient’s chair is lowered so that the chair back is nearly in the operator’s lap over the thigh area. The operator should be able to move freely in the operator’s zone of activity. The patient’s head is positioned so that the mouth is as close as possible to the operator. Elbows should be close to the side of the body. The lower part of the arms are nearly parallel to the floor. The shoulders are parallel to the floor. Back is straight. Neck is not bent or strained. Distance from the operator’s eyes to the patient’s mouth should be no less than 14”.
The operator’s chair position changes in relation to the area of the mouth that is being treated. Adjustment of the operator’s position within the zone of activity can greatly improve visibility and reduce back and neck strain caused by bending and leaning.
The stool is positioned as close to the patients’ chair as possible. The body support is positioned to come around the left side and to support the assistant’s torso when it is leaning forward, thus reducing stress on the back and neck. The front edge of the stool or the assistant’s knees should be nearly even with the patient’s mouth to ensure that the assistant is in line with the patient’s oral cavity. Legs are parallel to the side of the chair, and are facing the direction of the patient’s head. Torso is centered on the stool or more bluntly, cheeks on the seat. Feet rest on the rim of the stool and are parallel to the floor.
When seated, the assistant’s eye level should be 4-6” higher than the operator’s eye level. In general, the assistant’s eye level should be just over the top of the operator’s head. The eye level should be slightly higher for working on the mandibular arch.
Avoid excessive bending or extending the arms to reach for materials or instruments. Maintain a relatively straight back and neck.
The assistant’s chair position remains the same regardless of the treatment site. Although the zone for the assistant extends from 2 to 4 o’clock when he/she assists a right-handed operator, the assistant remains relatively stationary regardless of the quadrant being treated.
To see more clearly in the mandibular arch, it is possible to raise the stool slightly, but it seldom will require movement back and forth within the zone of activity.
Most dental operating lights are designed to illuminate the mouth when placed 3-5’ away from the operative site. If the lights are placed too closely, they can interfere with vision and inhibit ease of movement in the transfer zone as well as create unnecessary heat.
When the operator is working on the mandible, the light is raised to a higher position so that its beam can be tilted down toward the mandibular teeth. For the maxilla, the entire light can be lowered and the beam can be aimed more parallel to the floor.
The assistant must be observant during the procedure to detect any potential for patient or operating team discomfort. Frequently, glance around the zones of activity. If the operator or the assistant must lean over, if the arms are raised needlessly, or if the visibility is not good, pause for a few seconds. Suggest to the operator that the team or the patient needs to be repositioned. If necessary, reposition the light. To continue to work in a stressful position will cause body fatigue and will ultimately make the dental staff uncomfortable and inefficient.
After the patient is seated, lower the arm of the chair. Offer to store personal items in a safe location nearby, out of the way of treatment. Position the patient napkin. Within an aseptic chair, the patient is automatically placed into the supine position. The base is raised about 10-12”. The chair tilts the patient until the patient’s calves are parallel to the floor and the chair back tilts an additional 45 degrees until the patient is in the supine position.
Have the patient move to the upper-most portion of the chair nearest the operator. Lower the operating light to a position the assistant can reach when seated. Position the mobile cabinet directly in from the assistant’s knees and as close to the chair as possible. Extend the working area over the knees or lap, depending on whether the top of the cabinet is a forward, back or side moveable.
Some patients have special needs and are not able to be seated in a routine manner. Special attention should be given to the young patient, to older adults, the pregnant patient, or those who are physically challenged.
The video segments are excerpts from the videotape entitled, “Clinical Dynamics of Four‑Handed Dentistry,” and used with the permission of Health Sciences Products, Birmingham, Alabama. The entire video tape can be purchased at: