Information for Consideration in an Ergonomic Standard for Dentistry

by Michael Dougherty, DDS

Kadowaki and Kaneco have completed studies comparing the traditional tilting dental chair environment and a new technology and process of performing dentistry that stabilizes the operator and the patient in the most optimum relationship. It is evident from their statistics that the latter is a significantly less stressful and more efficient way to practice dentistry because it resulted in significant differences in a variety of measures used to assess dental practice efficiency and efficacy.

The average number of contacts during treatment on tray handles, light handles, finger switches, charts, operating stools, cabinets, gowns, clothes, and dental chair were reduced from an average of 36.2 per operation to 4.8 per operation with the newer design of delivery. The average number of hand or finger contacts for the assistant were similarly reduced from 46.0 in a dental chair environment to 9.5 in this new stabilized setting. Treatment area time analysis (average) revealed that the percent of treatment time without physical distortion or strain was increased from 39.7% to 98.7%. The percent of dentists reporting subjective musculoskeletal (MSK) symptoms ranged from 78% for those who stood to operate with the dental chair to 76% for those who reclined the dental chair and sat to operate. Only 8% of dentists surveyed who worked with the stabilized future type of delivery reported MSK symptoms. Finally, the time analysis in handling instruments indicated that there was a significant reduction in the average number of pick-ups and in the average time spent picking up instruments with tubing and hand instruments with this new system designed for the proprioceptive sense of the operator.

This new human-centered technology is a break with the past history of performing dentistry with the patient sitting in a reclining chair. It is the result of the life-long pursuit of a better way to practice dentistry by American dentist, Dr. Daryl Beach, of Osaka, Japan. This new system uses an environment that encourages natural human movements and promotes optimal performance of dentistry. The concepts and equipment design advocate a non-articulating support for the reclined patient. This design incorporates dynamic instrumentation at positions just forearms drop away at the shoulder of the patient’s support. The design has come to be called “the shoulder delivery type” in Japan were it outsells “the chair mount delivery type” two to one. Prototypes of a stabilized form of shoulder delivery equipment and instruments have been manufactured by the Morita Corporation in Kyoto, Japan since 1962. This stabilized design has had limited availability in countries outside of Japan.

This new concept of dental care is free of unnecessary distractions and gives the dentist, the assistant, and the patient the most optimum position and context for the activities that occur during dental treatment. The patient is offered a lying or full rest position for treatment. This positioning and a special headrest helps keep the patient’s mouth in a predictable position regardless of the patient’s height. The range of the operator’s support to the patient’s oral cavity constitutes an arc of approximately 120 degrees from behind the patient’s head. The center of this arc is the incisal embrasure of the patient’s maxillary central incisors. This imaginary vertical line is referred to as a skill

axis. The relationship of operator to patient is stabilized and consistently keeps the dentist in a full upright alert seated posture. The dentist’s upright posture allows the best control of the fine stabilized finger movements required when operating in the mouth and on the teeth. By stabilizing the position of the mouth and being able to easily reach necessary equipment and materials, the dentist and his assistants are able to work more accurately, more efficiently, and with less physical and mental wear and tear on both the patient and themselves. According to Dr. Beach, “Performance starts with the spine.” Maintaining the physiologic curves of the erect vertebral column transecting the center of gravity allows for maximum performance.

This stable relationship offers many other advantages over previous chair- based equipment systems. Currently, the treatment room has become a site for detached areas of technology. The addition of clinical microscopes, lasers, curing lights, air abrasion techniques, intraoral video, CAD CAM, root canal apex finders, sonic scalers, radiovisiography, pressure assisted anesthetic devices, separate dental unit water lines, and clinical computer systems has the future treatment room looking like a garage sale. The moving orientation of the head of the dental patient by traditional tilting dental chairs requires buttons, switches, wheels on cabinets and stools, folds, seams, tracks, computer processing of positions, robotics, long tubes, wires, hinged arms, movable lights, trays, and carts. There is a best posture and position to see and articulate the oral tissues. It is also a position from which all present and future technologies can relate and be delivered. The skill axis/oral surface interface is the most important point in the future dental office. Technology may be integrated into this type of treatment room with specifications that it must not intrude into space necessary for a stable and natural human to human interface.

When a dentist establishes routes in an oral procedure there have been limits to his/her maintaining balance due to previous equipment and instrument designs. Some of these specifications are the size and positioning of the headrest, dental mirror- handle angle and dimensions, and the errors induced by a fully adjustable and tilting system without a stable skill axis. The scooting of the operator stool in the attempt to position the operator appears to be an imperfect system for repetitive positioning. A new level of organization is now available with feel based equipment and instruments that relate the process of dental treatments to the dentist. Benefits of this new technology include:

  1. Dramatic improvement in personal health and stamina
  2. Increased confidence and security
  3. Minimized physical stress while treating patients
  4. Heightened awareness of precise operating control
  5. Significantly improved ability to enhance productivity
  6. Increased gentleness and patient comfort

Dentists have been performing dentistry essentially the same since the time and motion studies of the late 1960’s. The current dental student is still unable to consistently develop ways of limiting reach, articulations, and predictable presentations in the course of moving from one surface of a tooth to another because of the equipment and instruments their predecessors have modeled. The physical and mental health of dentists and hygienists have been strained and compromised based on available research. They often have limited themselves to “a peek in the mouth” instead of “a peak performance”. Their success at maintaining an unstrained posture has been mostly left up to personal trial and error in a tilting environment that always requires organization and postural accommodation. The dental chair has been a great contributor towards the performance of dental operations and much of our thinking for over a century. Manufactures have automated, configured, and flexed the “chair” until its concept has been exhausted based on the dental profession’s future needs. It is time to stop thinking in terms of “dental chairs”, “chair time”, and “chairside assistants” and to start thinking in terms of human needs.

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