Th 134899

The male/female difference in ergonomics

Jan. 1, 2003
I am excited that the good people of PennWell (the parent company of Dental Equipment & Materials) are publishing a new journal � Woman Dentist Journal. I have a real "soft spot" for women dentists.

Jeff Carter, DDS

I am excited that the good people of PennWell (the parent company of Dental Equipment & Materials) are publishing a new journal — Woman Dentist Journal. I have a real "soft spot" for women dentists. I suppose it is sexist to confess to any extra compassion for women in dentistry over their male counterparts because dentistry is rigorous and demanding on all practitioners U but I do anyway.

When I went to dental school in the 1970s, female dental students were often regarded as confused hygienists who had become disoriented and accidentally stumbled onto the wrong side of the school. I remember disparaging remarks that female dentists would not be full-time practitioners because they would have babies and would not be fully committed to running a successful practice. Yet today, we are approaching enrollments in dental schools where the ratio of male to female students is nearly 1:1. What progress has been made!

A few months ago, a speaker at a dental marketing course talked about the dwindling supply of dentists nationwide. He relayed that numerous dental school closures have drastically reduced the future supply of dentists. He also noted that the large number of women dentists would make the shortage even more dramatic. Why? Most of them do not want to be full-time practitioners, he said, because they would have babies and they would not be fully committed to running a successful practice. Yeah, that's real progress!

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My concerns are the ergonomic challenges women encounter with equipment and facilities as dentists. Obviously, it has nothing to do with ability or motor skills, but rather the fact that women dimensionally, on average, are smaller than men. Well-designed dental equipment and dental facilities should facilitate effective use by the widest range of users. Unfortunately, economics and engineering principles often can limit the accommodation results.

Consider Table 1 which lists anthropometric statistics that compare the 50th percentile female dentist and 50th percentile male dentist on key physical dimensions affecting dental equipment placement and office design.

So what? After all, the dimensions are within a few inches of each other in all categories. However, unlike the design requirements of more generic office space occupied by lawyers and accountants, dental office design is "inch-specific." It is quite possible in a dental office that a few inches can impose significant ergonomic challenges. An operatory layout can, in fact, be developed utilizing the above table and interpreting the ergonomic implications of these dimensions.

Operator stools

For the average woman operator, the stool adjustment must position the seat height at 15.7" for the operator's thighs to be parallel to the floor and feet to be flat on the floor surface. For example, A-dec's Cascade 1601 operator's stool (seen at right) has a height adjustment range of 18.8" to 25". Right now you may be thinking, "What? How is that going to work?" Relax. The 1601 stool comes with an optional short cylinder (no extra charge) that changes the height adjustment range to 15.25" to 18.5." By combining ergonomic principles with anthropometric data, we can select equipment that is optimally sized. The average-sized woman dentist would require the optional "short cylinder" to make her A-dec operator's stool functional and ergonomic. Before purchasing new operator stools from any manufacturer, make sure you can lower or raise the seat to a position where your thighs are parallel to the floor.

Patient chair

If you are the average-sized woman dentist, the backside of the dental patient chair headrest must be reclined and lowered into your 21.3" "lap height." Most patient chairs on the market will accomplish this position, but the chair back declination angle is critical. For example, the A-dec Decade 1021 chair will lower the back of the headrest to a height of 13" above the floor. Of course, patients would be miserable in this position and feel like they were standing on their heads. As you tilt the chair back upward and the leg rest area downward, a definite point is reached where the patient feels comfortably reclined. We have all been in dental patient chairs for extended periods of time and have probably experienced the crossover point where you go from being comfortable to an uncomfortable sensation of too much blood flow to your head.

If you are purchasing new patient chairs, do the following to ensure you don't have to violate the crossover point to gain proper ergonomic positioning for the operator. Sit in your ergonomically height-adjusted operator stool with thighs parallel to the floor. Lower the patient chair back until the back of the headrest comes into contact with your lap. Slide out from under the patient chair and position yourself as a patient would in the patient chair. Are you comfortable, or have you passed the crossover point into the uncomfortable zone? If you are still comfortable in the patient chair, this would be a crucial positive factor in favor of purchasing the chair.

Surrounding work-surface heights

Assuming we have a properly adjusted operator's stool and a properly reclined patient chair, the next step is to examine your surrounding work-surface heights. Remember our average-sized woman "lap height" was 21.3" above the floor. The average human head is 7.5" from front to back (sagittal measurement). If we add the head dimension to the chair back/headrest thickness and lap height, we are at 30.8." This assumes a minimal thickness for the chair back/headrest. Ergonomically, the supporting surfaces should be in the same plane as the oral cavity. In this example, the oral cavity is 30.8" above the floor. Therefore any adjacent surfaces would ideally be 30.8" above the floor also. In design, we routinely create side cabinets and assistant work-surface heights at 32." The 32" height is slightly above our ideal. Would you notice a discrepancy of 1.2"? Yes, but it still may fall within an acceptable range. I would not consider a discrepancy of 3" or more as being acceptable.

The problem is really the forearm angle to access items placed on a 32" countertop. The average-sized woman operator has a seated elbow height of 23.8." Healthy ergonomics dictate we work with elbows at our sides and not elevated. If your elbow is at 23.8" and you are manipulating objects at 32" on a flat counter surface, you can't reach past the point where your wrists hit the side of the counter, unless you elevate your elbows through prolonged contraction of the deltoids. If the elbow height/work surface discrepancy becomes too much, you create the problem that small children (without booster chairs) experience at the dinner table. The edge of the table "digs" into children's forearms and wrists as they try to reach upward and it is uncomfortable.

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As an average-sized woman dentist, there is an advantage in that many design parameters are based on averaged-sized women because 97 percent of dental staff is female. For example, maximum shelf heights of cabinets are based on the comfortable reach of an averaged-sized female. The top shelf of any cabinet or shelving system should not exceed 74.9" or it becomes unreachable for most staff in the office. If you fix-mount a patient-view monitor in the operatory, most codes would require the bottom-edge of the monitor be 78" above the floor. That places the monitor controls out of the reach of the average-sized female, so don't lose that remote control!

Consider Table 2 that captures what I would call the "nightmare partnership scenario" in office design and equipment selection.

Somewhere out there, I am sure there is a dental practice contemplating a partnership of a woman sized in the 2.5 percentile and a man in the 97.5 percentile. It is sort of similar to what you might have seen in high school where the star center on the basketball team dates the petite head cheerleader. When they slow dance at homecoming, her head almost reaches to the bottom of his shirt pocket.

A 5' 1/2" woman dentist partnering with a 6' 3" man dentist creates many issues and potential conflicts in equipment and design. The practice requires operator stools adjustable from 14.4" to 18.5". This falls outside the typical range of adjustability. The working height of the oral cavity is 28.9" vs. 35.6." We can adjust delivery units to help minimize this 6.7" discrepancy, but we can't adjust side cabinet work surfaces or other fixed dimensions. In the "nightmare scenario," some compromise decisions would have to be made. If you have a choice of partners or associates, it may be to your advantage to take a second or third look at the person sized more closely to you.

Of equal concern to proper equipment selection and design decisions is ergonomic diligence to constantly reconfigure working positions if your office has significantly different-sized operators, no matter their gender. It is all too common for doctors to sit next to the patient and start working unaware of the health consequences of their body position.

The good news in all of this is that Woman Dentist Journal will address many more of these issues. In addition, it will provide a forum for dental manufacturers to market directly to women dentists and provide information that their equipment can accommodate the ergonomic and dimensional requirements of a great group of people.

Dr. Jeff Carter is co-owner of the Practice Design Group, based in Austin, Texas. PDG specializes in providing architectural, interior design and equipment, and technology integration services to dentists nationwide. Dr. Carter may be reached at (512) 295-2224 or by e-mail at [email protected].

Seeing ergonomics from the manufacturer's side

As Dr. Carter points out in his article, the field of dentistry is evolving. An influx of female dentists, Asian dentists, and male assistants has challenged the traditional Caucasian male dentist/female assistant scenario. A growing understanding of the importance of ergonomics (matching the worker's environment and tools to the worker's body) has forced manufacturers to take into consideration just how many different shapes and sizes of worker bodies there are, yet the dental operatory environment has been slow to change. One result is the epidemic of work-related musculoskeletal symptoms and conditions such as carpal tunnel syndrome.

So how does a responsible dental manufacturer respond? At Dentech, we began with the basics. First, we increased the breadth of possible settings and positions for many of our products. We added "tall" and "short" options to our dental stools, so that clinicians could sit low (or high) enough to be in proper position to perform good dentistry. We introduced the Dentech ECO-19 chair, which has a back so thin that even dentists at the lowest end of the height spectrum can sit with their feet on the floor, their knees at the proper 90-degree angle, and still be able to get their legs under the chair so they can access the oral cavity without leaning.

Yet making dental equipment adaptable to a variety of shapes and sizes of dental professionals is just a start. A "build it and they will come" attitude may work for baseball fields, but when it comes to dental equipment, adding ergonomic features simply isn't enough. Having a well-designed stool and not adjusting it properly isn't going to save a dentist's back any more than a smoke detector with no batteries is going to save the dentist's family in the event of a fire. The key to ergonomically designed dental equipment isn't just how it's built, but how it's used.

We believe we have taken the next step with our Inner Circle™ Productivity Program. We realized early on that our sales representatives (and those of the dealers that carry Dentech products) could play a vital role in helping dental professionals protect their health and be more productive by teaching them how to get the most out of their equipment. We began training these representatives to understand the importance of clinicians keeping their motions within the "inner circle" surrounding the oral cavity. We taught our sales reps about classes of movement, neutral positions, and proper posture. We trained them to understand how dentists practice and what they need to do to avoid back, neck, and shoulder problems.

Recently, we expanded the Inner Circle program to include in-office training for dental teams. After all, if we accept that a cookie-cutter approach can no longer be used when making dental equipment, we must also recognize that our obligation extends beyond dropping off a box and cashing the check. Most pieces of dental equipment must be adjusted specifically for each user in order for that person to be positioned properly. This is particularly true for those clinicians (including many women dentists) who fall above or below "average" height ranges for Caucasian males. Odds are, over the years, these clinicians have had to adapt their bodies and their working styles to the equipment, rather than vice versa. The natural response to not being able to reach something is to lean or twist. And once one part of the body is drawn out of proper position, other parts of the body compensate. Even the most awkward positions can seem routine after awhile, but the price may be back and neck pain or even debilitating musculoskeletal problems.

Different body sizes and proportions, preferences of delivery position, variations required by left-handed practitioners, and dentists' individual working styles all must be incorporated in the design and function of the ergonomic operatory. Once dental professionals learn the basic concepts behind ergonomic positioning and understand how to use dental equipment to their advantage, they can put that knowledge into practice within their own operatory environment and enjoy the benefits of increased productivity and greater comfort.

We at Dentech join Dr. Carter in welcoming Woman Dentist Journal to the dialog and promise to continue our efforts to provide whatever support we can to help dental professionals use our products safely and productively.

--- Steven W. White, president, Dentech Corp.