Proper Ergonomic Positioning: It’s Only Human

As a busy private practitioner in Aurora, Colo., Dr. Michael Dougherty has a vested interest in dental ergonomics. He offers courses practical applications of ergonomic principles in dentistry, including office design, equipment selection, and working postures and behaviors. He bases all his training on the feel-based intuitive method of body and instrument positioning called proprioceptive derivation (pd). He took some time to answer some questions and his responses and observations provide valuable, practical tips for dental professionals who want to work healthier and more productively.

pd dental procedure

DC: Please explain the concept of proprioceptive derivation.

MD: Proprioceptive derivation (pd) in health care is the process of deriving the best positioning of the operator’s body, patients, instruments, equipment, and physical space for optimal ergonomic functioning. In dentistry, pd involves an innate introspective process to derive more natural body positioning for performing dental procedures while also considering patient positioning, instrument and equipment design, as well as the layout of the environment in which the dental procedures are performed.

The process of applying the principle of pd allows the participant (the self-appraiser) to decide for him or herself the best use of the body for clinical practice. The individual uses feedback from proprioceptive neurons to discern the least physical effort and most efficient way to perform procedures in the mouth. In using the pd process, the eyes are masked to avoid distractions from visual clues and to focus attention on all muscles of the body while specific dental procedures are mimed. Past operating positioning habits and positioning previous experience with dental instruments and equipment are disregarded.

Reference Posture—the critical features

When individuals decide proprioceptively how they wish to sit for the performance of a finite task in free space, without the influence of equipment or environment, most are inclined to assume a remarkably similar posture – the Reference Posture.
Here are typical features:

  • The dentist is seated in a natural and comfortable upright posture, with the base of the pelvis and the mid-point if the knee cap on the same horizontal plane, and with the upper plane of the thigh in a downward slope from posterior to anterior; both feet are firmly planted on the floor.
  • Shoulders are level, and the upper arms and elbows hang loosely at the side of the body.
  • Forearms are elevated above the horizontal plane, with operating fingers at a Preferred Performance Point, at the level of the heart or upper thorax, and in the mid-sagittal plane.
  • The sight-line and the light-line are withing 15″ of each other.

Reference Posture

The outcome of applying pd results in skillful use of the body and ensures that human performance is measurable and verifiable. It reflects the essential principle of ergonomic functioning—using the least human effort needed to resist the effects of gravity that contribute to body disorders, errors in procedures and outcomes due to fatigue, stress, and strain, and the waste of material resources.

DC: Describe the procedure for “proprioceptively deriving” optimal working position, instrument location, etc. for the dental practitioner.

MD: Pd tests are strictly feel-based and involve miming health care procedures with masked eyes in open space that is, in areas unrestricted by objects). Masked eyes reduce sensory input so that the individual’s self-appraisal of how s/he performs imagined dental procedures focuses on perceiving any strain associated with body position and paths of motion. This includes establishing the best position for the operating point in the patient’s mouth to ensure optimal precision of the dental operation being “performed.”

Once the operating point is determined, the paths of motion for locating instrument supports, holders, monitors, switches and other technologies are identified in relationship to the operating point, again through masked miming procedures. This involves assessing the strain in the body, particularly of the eye, neck, and foot muscles, in regard to the frequency, duration, and time that it takes to access whatever equipment, instruments, switch, monitor, or materials that are needed to perform the operation.

The appraisal process next considers procedures from both the patient’s and assistant’s perspectives by having the dental care provider assume these roles. Participant appraisers do this, still masked, to better understand the stresses and strains and motion paths experienced during procedures from both the patient’s and the assistant’s points of view.

  • positions for the operator’s body, limbs, and fingers while in use and at rest
  • the points on the body, including fingertips and feet, that come in contact with patients and objects for stable control and sightings of the operating points
  • human supports and material objects that account for pd body space, paths of motion of body parts, and location of instrument supports

Importantly, the pd process is human-centered rather than object-centered because it focuses on discerning the safest and most efficient way to perform dental procedures from the operator’s, the patient’s, and the assistant’s perspectives.

DC: What are the most common ergonomics no-no’s you see in dental practice?

MD: The most common ergonomic mistake I see is in malpositioning of the body of the seated operator. These “no-no’s” are observed mostly with operators who work from the side of the patient at or less than 9:30 position and place the patient’s mouth below the apex of their heart (- 10 cm. from a line connecting their arm pits). As a result of poor positioning, I see body twisting, leaning, slumping, head ducking, elbows raised for long durations, and finger work not in the body mid-line. Although learning pd procedures does not make one completely immune from these no-no’s, pd practitioners report that the amount of time they spend in a compromised body condition goes from approximately 60% down to 10% with pd skill.

The other “no-no” that I see is dentists purchasing dentist chairs solely on the basis of how comfortable the chair is when they sit in it. Dental equipment should be purchased based on how compatible it is with the operating process which, ideally, would be pd. Dentists need a set of evaluation criteria upon which to base their purchase of products for their ergonomic effects. Thus, they should go through the self-assessment I’ve discussed above before purchasing equipment if, in fact, they want to practice in the most ergonomic manner.

DC: What are some of the notable ergonomic modifications in today’s operatory equipment?

MC: Notable ergonomic modifications in today’s operatory equipment include stable dual lighting, touch-less adjustable headrests, a non translating lift for the patient support, the single multipurpose foot controller, and the integration of handpieces, technologies and instrument holders at the shoulder of the patient’s support. Also notable are the improvements in lighted evacuation equipment.

The weight, length, and diameters of early electric handpieces sent pd ergonomics backwards. However, the specifications for many electric handpieces and air-driven handpieces are getting closer to a pd range.

Another example of notable modifications of instruments that are often claimed to be ergonomic but are not pd, are sensing instruments with large-diameter handles. For example, the explorer is a sensing instrument, and sensing ability is compromised by the greater amount of finger contact surface used with large diameter handles. Also, the large diameter makes it more difficult to position.

DC: When designing and equipping the treatment room, what specifics should dentists be looking for?

MD: First, when designing and equipping the treatment room, the dental clinic owner/dental care provider should look for GEPEC pd-Acceptable components that have been determined to be human-centered by engineers and worldwide dentists. GEPEC is the first and only organization that evaluates products for their ergonomic compatibility with the user based upon a principle of body use. Pd surfaces (operator supports, patient supports, assistant supports) are level and non-tilting because humans physically related best to level, non-tilting surfaces.

In regard to an operator’s seat, it should create no pressure on the bottom of the thighs, have moderate posterior and lateral gluteal support, and the center of the axis of rotation of the seat should be between the ischeal tuberosities and above knee height. Bars at the base of the support that restrict foot movement are unacceptable. Operator back supports are optional and may be needed by some providers with disabilities. If the operator support has a back, it should not interfere with the fee range of motion of the elbows and the fully upright spine. Elbow supports are also not indicated when practicing under pd conditions since the use of elbow supports implies that the operator chooses to lean and/or extend his/her elbow far from their side. Further, delivery systems should provide either dual lighting or shadowless intraoral lighting, and all magnification should reflect pd conditions including working length and declination.

DC: For practitioners experiencing work-related pain, what’s the first step for determining the source and finding a remedy?

MD: If practitioners’ pain is suspected as being work-related (e.g., the person’s condition gets worse or is aggravated by performing work-related tasks), then management by using the process of pd care and pd-compatible clinics is indicated. The treatment setting where practitioners work must first be considered as equipment and physical space may not allow for natural upright positioning of the spine and natural paths of body and limb motion. The first step for practitioners with work-related pain who want to learn about using pd is to participate in an introductory course about pd which involves the self-assessments described above. Participants will derive the best treatment method for themselves through exercises, will experience how it feels to practice in a pd manner, and will be able to compare this with the way they have recently treated or currently treat patients to decide about changing to a pd practice.

DC: How would you characterize the progress toward establishing ergonomic standards in the dental industry?

The American Dental Association has included ergonomics as part of its wellness program. However, manufacturer interests tend to still govern what is debated and, therefore, the emphasis is on products that are not necessarily developed based on pd principles and best use of the human body for the practice of dentistry. Today those of us practicing pd dentistry are more convinced that a principle of pd is needed in health care as we are experiencing a global financial adjustment that has illuminated waste and self serving businesses. The public is witnessing the interface of an emerging survival-safety-health (SSH) economy with a group-personal choice economy that now seems to be leading to great waste recognized by world leaders.. Commitment to human centered standards in the dental industry and in dental clinics would be a demonstrable move toward the SSH economy.

DC: Are manufacturers interested?

MD: Definitely, yes. Most engineers agree with the principle of pd. However, I believe that the Dental Trade Association remains resistant to a single ergonomic pd standard for equipment and stands behind their dealers to market products that are equipment-centered as opposed to a human-process centered.

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