by Harold L. Meador, D.D.S., B.S.D., F.A.A.P.

BIOMECHANICS/ERGONOMICS (The following material comes from "Performance Logic.") The concept of Performance Logic (Human-Centered Ergonomics) was introduced to dentistry by Dr. Daryl L. Beach of the Human Performance and Informatics Institute, Osaka, Japan. It was first introduced to North American Dentistry by the Center for Human Performance and the efforts of its principals, Dr. Hector DiNardo, Dr. David Hanson, Dr. Robert McDonald and Dr. Robert Oblinger. In the 1980s, the University of Maryland, Baltimore and the University of British Columbia introduced this concept to dental education. I first learned of the benefits of Performance Logic in a course offered by the Center for the Study of Human Performance in Dentistry at the University of Maryland in 1988, as taught by Dr. DiMardo and Dr. Michael Belenky, Center Director. Ergonomics is the study of natural and consistent movement. It is based on the premise that the control of physical stress is the acquired ability to relax muscles not necessary to the performance of the task at hand. The myocentric position (balanced position) is the position from which a planned act can be initiated with the potential for the highest degree of movement control and perception. The axioms on which ergonomics is founded are helpful in understanding the neutral position of the body: 1. The proprioceptive senses take precedence over the visual senses. 2. Delicate work is best done in the mid sagittal plane. 3. The height (on the mid sagittal plane) is determined by the delicate nature of the work. 4. The attitude of the hand is determined by the delicate nature of the work. 5. The more delicate the work, the more joint segments are set. The more physical the work, the fewer joint segments are set. 6. In doing irreversible work in the seated position the operator leans forward. 7. In repetitive delicate work mankind seeks the myocentric (balanced) position. 8. In this atmosphere we perceive best in relation to the vertical. 9. Mankind stabilizes by tri-podding. 10. Physical stress alters judgment ("fatigue makes cowards of us all,"-Vince Lombardi). Careful study will require the body position to be evaluated and to see how it conforms to these axioms in the proper execution of scaling motions. It should be added that after taking "Performance Logic," the author struggled for several months to adapt the ideas to the needs of the practicing periodontist. "Performance Logic" had been developed with the general dentist in mind. However, axioms #3 and #5 would indicate a need for change in applying these principles to periodontics due to the difference in the physical nature of the work.

POSTURE Posture is defined as "the position or carriage of the body as a whole." A concept of posture needs to be framed by ergonomics and include the anatomy of the joints and muscles in both static and dynamic relationships. Proper posture for the hygienist is applying the principles of both neutrality and ergonomics to the body position when at work. This should include the legs, torso, head, shoulders, arms, elbow, wrist, hand, fingers, and thumb.

Posture streaming video (47 secs.)

Anatomy This brief overview of the anatomy of the upper extremity will include the joints of particular interest {30 & 33}. Joints There are three major joints in the upper extremity: the shoulder, the elbow and the wrist. The shoulder and elbow joints will be considered first. {Figure 2.4}. In the shoulder, the acromio-clavicular joint is a small synovial articulation of the plane type, between the lateral end of the clavicle and the medial border of the acromion process of the scapula. The head of the humerus joins the scapula in the glenoid cavity. The elbow joint is a large synovial joint of the hinge type in which the radius and ulna of the forearm articulate with the distal of the humerus. Figure 2.4: Bones and joints of the right shoulder and arm (anterior view)

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