Ergonomic Risk Factors Associated with Clinical Dentistry
Lance M. Rucker, DDS, and Susanne Sunell, BA, Dip. DH, MA
Copyright 2002 Journal of the California Dental Association.
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Ergonomics has formed an integral aspect of dental education at the University of British Columbia since the early 1980s. However, studies continued to indicate that dentists are at risk for developing musculoskeletal problems. This provided the impetus for a study of the risk factors associated with these problems. The data analyzed from 421 survey respondents in British Columbia indicates that indeed dentists are experiencing musculoskeletal pain and discomfort. However, it also suggests that dentists can recognize and identify their own postures, practicing positions, and the equipment usage patterns that are associated with increased risks of experiencing musculoskeletal pain and discomfort. Such recognition is the first critical step to avoiding or neutralizing ergonomic habits and work environment layouts that might otherwise unnecessarily shorten professional clinical careers.
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As increasingly sophisticated dental equipment has entered the marketplace, the potential for improving the occupational health of dental practitioners has expanded. Despite this, dental practitioners continue to identify chronic back, neck and shoulder pain as occupational ailments,1 often associated with early retirement from the profession.2 Students continue to develop musculoskeletal disorders, even within educational programs, and recent graduates indicate that they are adjusting practice schedules to accommodate their cumulative trauma disorders.3,4 Despite the evidence of musculoskeletal disorders in dentistry, surprisingly little research has been conducted in this area.
Furthermore, a glance at most photographs depicting practitioners at work in articles and advertisements in professional and popular media betray a continued professional tolerance and acceptance of physically imbalanced, compromised postures and positions used in the performance of clinical dentistry. Seeing such representations, members of the rehabilitation professions (including physiotherapists, physiatrists, occupational therapists, massage therapists, chiropractors, etc.) often erroneously conclude that the daily practice of dentistry necessarily involves frequent, ongoing mechanical compromises to job performance. When physical breakdowns occur, many of these rehabilitation specialists will declare that the dentist is unable to continue clinical work because of such presumptions about the innately health-compromising nature of dental practice.
The literature indicates that both dentists and hygienists are experiencing back, neck and shoulder pain and are, in many cases, attributing these problems to the provision of clinical care.5-7 Studies in median nerve sensitivity and cumulative trauma disorders of the median nerve (such as carpal tunnel syndrome) also identify dental practitioners as being at risk.8,9 Consistent reports of work-related and work-impairing injuries of dentists and dental hygienists indicate an average incidence of more than 60 percent of workers who have experienced work loss during the preceding year related to musculoskeletal pain.10-12
Many factors appear to be instrumental in contributing to musculoskeletal disorders, including medical, occupational, and/or lifestyle factors that are conducive to these disorders. The occupational patterns that appear to be influential include excessive use of small muscles, repetitive motions, tight grips, fixed working positions, raised arms, limited movements and long-term static load on muscles.13 The exact nature of the relationship between these factors and musculoskeletal problems is unclear.14,15
To explore the issues of clinical ergonomics, beginning in the early 1980s a team of University of British Columbia researchers investigated "performance logic," a problem-solving model based on individualized positioning.16 The performance logic approach begins with a proprioceptive exercise to determine the individual operator’s preferred posture and positions for physical and visual control of fine motor activity. In effect, it is based upon the clinician’s individual musculoskeletal requirements, anatomy and physiology, using self-derivational approaches that attempt to neutralize the limitations that might have been imposed by specific equipment and by habituation from prior psychomotor experience.
The performance logic model has been used to integrate clinical ergonomics education throughout the undergraduate dental curriculum at the University of British Columbia since 1983 and was further developed with the addition of surgical magnification systems for preclinical and clinical practice in 1990.17 When an operator’s visual acuity is not matched to optimal, comfortable musculoskeletal positioning, the integration of carefully selected surgical magnification systems into the clinical armamentarium has been found to be especially effective in supporting the operator’s preferred angle of vision while maintaining the optimal musculoskeletal operating posture.18
The current study is an attempt to gain an understanding of the health status of British Columbia dentists regarding the types of musculoskeletal discomfort and pain they are experiencing, and what impact this is having on their professional lives.
Methods
In a new dental clinical ergonomic study, 421 responses (representing a 43 percent response rate) were received from surveys sent to all dentists practicing in British Columbia who had graduated between the years 1987 and 1996, regardless of the dental school attended. Almost half (48 percent) of the respondents were graduates of the University of British Columbia Faculty of Dentistry and thereby constituted a study group for the effects of integrated clinical ergonomics education during their entire undergraduate training program. A subset of this study group (since 1990) had also utilized surgical magnification. These were telescopes that supported optimized declination angles and working distances during all phases of the dentists’ preclinical and clinical training.
The surveys consisted of a combination of open-ended and closed-ended questions asking the respondents to rate items and to address issues important to the understanding of their work patterns, symptoms, and identified (or suspected) health risk factors. The questionnaires asked respondents for information about their practice ergonomics, practice management issues, lifestyle, and perceived control of their work environment, as well as questions about specific musculoskeletal symptoms.
The questionnaire data was analyzed through descriptive and inferential statistics. The analysis included comparisons of groups (and subgroups) with respect to a number of variables including symptoms, practice patterns, equipment characteristics and psychosocial factors. To calculate measures of association between the respondent attributes, Spearman rank correlation coefficients (rS) were used when the data was ordinal and the Pearson chi-squared statistic (c 2) when the data was nominal. An alpha (p value) of 0.05 was applied to these tests.
The data is based entirely on the perceptions and self-reports of dentists as to their practices, their equipment configurations, their posture and positioning profiles, their medical histories, their personal exercise habits, and their musculoskeletal symptoms. The questionnaire required about 45 minutes to complete.
Results
About two-thirds of the 421 dentist respondents were male (67 percent). Among the dentists, the vast majority were general practitioners (91 percent). All graduated between 1986 and 1997. Two-thirds (66 percent) had been in practice for five or more years. Almost all (94 percent) commonly practiced seven or more hours each day, and 86 percent practiced four or more days each week. Eighty-one percent of the dentists practice more than 40 weeks each year. Not surprisingly, given the target graduation period, the respondents were fairly young. Seventy percent were 30 to 39 years of age, and only 11 percent were older than 40. If anything, this would suggest a fairly healthy study population. This suggestion is well-supported by the respondents’ subjective ratings (on a scale of 1 to 5) of overall health: 87 percent claimed good to excellent overall health, 12 percent average overall health, and only 1 percent below average overall health.
In spite of this overall positive subjective bill of health, in the section that addresses musculoskeletal health status by specific anatomical areas, the respondents (dentists) identified a multitude of localized pains that which they subjectively perceived as work-related (Table 1).
Nearly one in 10 dentists (9 percent) experienced episodes of hand pain, which they perceived as work-related, on at least a weekly basis. Nearly one in five dentists (18 percent) experienced episodes of shoulder pain on at least a weekly basis. Nearly one in four (24 percent) dentists experienced episodes of neck pain on at least a weekly basis. Nearly one in five dentists (19 percent) experienced episodes of upper back pain on at least a weekly basis. Thirteen percent of dentists experienced episodes of mid-back pain more often than once a month. More than one in six dentists (17 percent) experienced episodes of lower back pain on at least a weekly basis.
One in three dentists (34 percent) attributed their musculoskeletal symptoms entirely to their clinical work. Another 54 percent attributed their musculoskeletal symptoms partially to their clinical work, and only 7 percent felt that their symptoms were related solely to factors other than their clinical work.
As to the outcomes of their work-related problems, only 13 dentists (4 percent of the respondents) had decreased their number of working days per week. Nineteen percent of the dentists experienced decreased ability to perform recreational activities, and 14 percent showed decreased abilities to perform activities at home. Other sequelae included painful performance of recreational activities (14 percent) and painful performance of activities at home (13 percent). Seven percent of practitioners purchased specialized equipment to deal with their work-related problems, but only 5 percent actually redesigned their operatories. Three out of five respondents (60 percent) reported that they just "lived with the pain (tolerated it)." A total of 13 dentists (4 percent of the respondents) recorded the loss of a total of 99 work days during the previous 12 months as a result of their musculoskeletal symptoms. Only one in three dentists (33 percent) indicated that they have not experienced any work-related problems.
For developing the following equipment inventory, the authors have chosen to characterize usage of specified equipment for more than half of the time (in clinical practice) as a significant part of the clinician’s working profile. Almost all dentists use adjustable operating lights (91 percent) and operating stools whose height can be adjusted in 10 seconds or less (83 percent) and which move easily across the floor (95 percent). In 7 percent of the operatories, there is carpeting under the operators’ stools. Few use arm rests on the operating stools (3 percent), and only 37 percent use lumbar supports. Sixty-five percent work in equipment settings where they can position themselves freely around the dental chair.
Most dentists position their operating stools so that their hips are at the same level as their knees (76 percent) or slightly higher than their knees (15 percent). Only 1 percent commonly stand when they work.
Seventy-eight percent use handpieces for more than half of their practicing time, and most (91 percent) use intraoral mirrors most of the time. Four-handed dentistry involving a chairside dental assistant is the usual practice mode for 89 percent of dentists.
For the performance of maxillary (upper arch) treatment, 85 percent of dentists position the patient fully supine with the maxillary plane approximately vertical (Table B) Eighty-three percent position the operatory light source at increased angles toward the patient’s feet (Table C).
Among the respondents, 59 percent use surgical magnification systems of some kind. Of those using such systems, most have been using them for more than three years.
Posture and Positioning Profiles
Sixty-three percent of the dentists position their hands at about elbow height during clinical operation. Some 21 percent operate with hands at heart height, and only 14 percent operate with hands below the elbows.
Only about a third (32 percent) position themselves and arrange their access to their work so that they do not commonly raise their dominant elbows from a relaxed position at their sides. Sixty-six percent report that they raise the dominant elbow approximately 45 degrees for the majority of their work, and a few (2 percent) even as much as 90 degrees. Their data profile for the nondominant arm is nearly the same (36 percent, 57 percent, and 6 percent, respectively).
When positioning themselves around the head of the patient, only 38 percent of dentists never use the 7 to 8:30 o’clock range, 72 percent never use the 1:30 to 3 o’clock range, and 88 percent never use the 3:30 to 5 o’clock range.
Fifty-nine percent of the dentists keep their legs beneath the patient chair during treatment. Only 4 percent operate with their legs at the side of the patient chair (which requires a torso twist to access the patient’s oral cavity), and 33 percent operate with their legs split at the head of the patient chair (which limits their ability to shift positions freely in the clock positions for optimal access to the oral cavity).
Only 9 percent indicated that they never tip their shoulders to the side (Figure 1) during practice, and 16 percent reported that they avoid rotation of their torsos (trunks) relative to their lower body during patient treatment.
Most (88 percent) use intraoral finger rests for instrument stabilization, and 25 percent usually use extraoral hand rests on the patient’s face to stabilize further and/or to offset the fatigue of supporting the forearms during fine motor manipulations required for intraoral treatment.
Correlations of Postural and Positional Profiles with Musculoskeletal Symptoms
The correlations of association of musculoskeletal symptoms with various aspects of the practice and behaviors of dentists are shown below. In the interest of simplicity and clarity, only the p values (inversely reflective of the strength of the correlation) are indicated for all associations. The lower the p value, the stronger the association. Only statistically significant variables of .05 or less are recorded.
* Increased time with the clinician’s legs directly beneath the patient chair is associated with decreased reports of upper back pain (p=.034). Dentists whose operating lights are positioned farther away from their sightlines (towards the patient’s feet) for maxillary work were more likely to experience lower back pain (p=.008).
* Use of surgical magnification is associated with a decrease of pain in the lower back (p=.034).
* Increased use of lumbar supports on operating stools is associated with decreased reports of leg pain (p=.007).
Posture and Positioning Profiles
The following significant associations were found in the postural and positioning profiles.
* The more likely clinicians are to raise the dominant elbow while they work, the more likely they are to experience musculoskeletal symptoms in many regions of the body. Dentists who utilize such positions more than 50 percent of the time are more likely to experience pain in the hands (p=.001), shoulders (p=.007), neck (p=.001), and upper back (p=.003).
* Furthermore, the more likely dentists are to raise the nondominant elbow while they work, the more likely they are to experience musculoskeletal syndromes in many regions of the body: in the hands (p=.037), arms (p=.034), neck (p=.005), and upper back (p=.004).
* The greater the percentage of time dentists spend practicing with their shoulders tipped to the side, the more likely they are to experience pain in the hands (p=.017), arms (p=.026), shoulders (p=.001), neck (p=.001), upper back (p<.001), and lower back (p=.006).
* The greater the percentage of time dentists spend practicing with their torsos (trunks) rotated to any discernible degree, the more likely they are to experience pain in the hands (p=.047), shoulders (p=.003), neck (p=.003), upper back (p<.001), and lower back (p<.001).
* Dentists who spent a greater proportion of their practice working with an assistant (4-handed) were less likely to experience shoulder pain (p=.041).
* Dentists who use the 7 to 8:30 o’clock range a greater percentage of the time in practice reported increased pain in their hands (p=.044), arms (p=.009), and upper backs (p=.050). Dentists who use the 3:30 to 5 o’clock range a greater percentage of the time in practice reported increased pain in their arms (p=.009), upper backs (p=.048), and legs (p=.039).
The statistical comparison for the effects of integrated clinical ergonomics education comparing University of British Columbia graduates to the control group of non-University of British Columbia graduates confirms that the former group is less likely to have lower back pain (p=.05) than the latter.
Furthermore, the University of British Columbia graduates are indeed practicing the performance logic posture and positioning profiles they were taught during their clinical ergonomics training at University of British Columbia. That is, the majority of the performance logic posture and positioning elements are significantly characteristic of the practice habits and styles of the University of British Columbia graduates. The data also identifies that many key ergonomic posture and positioning profiles elements are not being practiced by those dentists (non-University of British Columbia) whose dental school curricula did not include performance logic experience.
Discussion
In the dental health field, there has been much attention directed toward carpal tunnel syndrome as a focus of primary concern with regard to work-related musculoskeletal symptoms. The current study has provided information that has directed attention to other important areas as well. Dentists continue to be at risk for a variety of musculoskeletal symptoms. However, there appear to be specific equipment, postural, and positioning variables that clinicians can adjust to decrease their risks.
The correlations of increased musculoskeletal symptoms with use of the certain positions around the patient chair (7 to 8:30, and 3:30 to 5) may be related to the effects of the torso-twisting and elbow-raising compromises identified in the same posture and positioning profiles section. This is not surprising, given the distorted body postures often associated with the use of such positions around the patient chair.
The compromising effects of operatory light positioning towards the patient’s feet are probably the result of violations of the physics of light lines and sight lines, which is especially dramatized by the use of an intraoral mirror. This issue may be challenged by some traditional dental assistant programs in which the more classic but erroneous directions found in textbook references train assistants to use direct lighting of the maxilla (with the light positioned away from the sightline of the dentist) for treatment on that arch. Although direct maxillary lighting may improve unshadowed viewing from the perspective of the chairside assistant, it virtually guarantees a compromised view for the dentist and results in the dentist tipping the head and torso to bring the eye line closer to the light line, in an attempt to see better.
The correlation of increased use of surgical magnification with decreased risks for experiencing low back pain should be considered in the context that most of the users of surgical magnification in the study were University of British Columbia graduates with systems that allowed for appropriate declination angles for their optimal working postures. Most systems in use by dentists today are limited in their abilities to produce optimal declination angles,17,19 and the reductions of musculoskeletal symptoms for such users may not be the same as those generated in the University of British Columbia study.
To be sure, there are many things beyond postural and equipment-related ergonomic high-risk factors that are important elements in the dental professionals’ exposure to increased musculoskeletal symptoms. For example, the study also confirmed health factors such increasing age, smoking, and certain pre-existing medical conditions (such as diagnoses of spinal curvature or certain eye problems) as co-factors in higher risk.
Likewise there are health and fitness factors that seem to be associated with decreased risk of musculoskeletal syndromes among dentists, such as increased frequency of moderately paced physical activities and increased frequency of strengthening exercises. Other findings of the study confirm that certain psychosocial and environmental factors are associated with increased risk of musculoskeletal symptoms for dentists, including less control over day-to-day workload, impairment of opportunities to provide input at work, discomfort in asking co-workers for assistance, and compromised quality of air or temperature in the work environment.
Some practitioners may not have understood the subtle differences among the survey diagrams; they may not have had the awareness and/or ergonomic knowledge to provide accurate data. The questionnaire required about 45 minutes to complete; this time commitment may have affected the response rate. An argument is also commonly made that people with musculoskeletal problems would be more likely than asymptomatic people to respond to a voluntary survey, particularly a lengthy one. These are all possible limitations of our study. However, the incidence of musculoskeletal symptoms reported by the survey respondents closely matches the results of other studies of oral health practitioner populations in other parts of the world.
Self-recognition by a clinician of any one of the signs of high-risk ergonomic profiles might be a cause for alarm, but recognition of multiple factors should be especially concerning. One or more of these signs that are accompanied by symptoms of pain or discomfort in any of the body regions identified in the study are redoubled cause for concern. Just as certain individuals have smoked several packs of cigarettes per day for many decades without having cancer, so it is not unlikely that certain individual clinicians might sustain the self-abuse of the identified high-risk ergonomic profiles and still continue practice without clinically compromising repetitive strain injuries. However, the risks are real and the posture and positing profiles are modifiable and preventable. Most of the negative (high-risk) ergonomic factors associated with musculoskeletal symptoms can be reduced, modified, or eliminated from practice, and most of the positive factors are elements that can be learned, encouraged, and/or acquired.
Appropriate educational measures undertaken as part of the initial basic training programs of dentists can help reduce the high-risk clinical equipment usage factors and posture and positioning profile factors that are associated with increased risks of musculoskeletal symptoms for dentists. What is not yet known is the degree to which such education has similar success in postgraduate and continuing educational contexts. However, there is a need to increase clinician awareness of the factors that are associated with increased musculoskeletal symptoms, so that performer-based, equipment-based, and/or practice management-based programs might be introduced for intervention where feasible.
Given that this study has relied on clinicians’ personal subjective appraisals of practice characteristics, it becomes somewhat easier to alert the at-risk population than it would be if the observations required external monitoring. A self-assessment tool is currently being prepared that can increase clinician self-awareness of identified risk factors for the office and its personnel, and that will point toward solutions to specific identified problems.
Coupling of the posture and positioning profiles/musculoskeletal symptom associations increases the recognition of alternatives related to specific behavioral changes and might help to increase motivation of the dentist to change to healthier practice patterns. What has been perceived more often than not as a hopeless, unavoidable syndrome associated with the dental health occupations now becomes related to equipment variables, to specific behaviors, and to observed "postures and positions associated with the way I do my work." Once we invite and allow for potential variation in work patterns, clinicians who are in pain can begin to make some changes and to see the results of those changes.
By and large, dentists "put up with" their pain because they do not know specifically what has caused it, much less what to do about it. When many of their professional colleagues have similar musculoskeletal symptoms, the logical conclusion is that such symptoms and their sequelae are an unavoidable part of the work of the profession. So they continue to work for their equipment more often than not (rather than making their equipment work for them), and the cycle continues.
The profession might do well to encourage basic, seminar-type educational programs in clinical ergonomics directed toward the recognition, interception, and reduction of identified high-risk patterns of work and lifestyle for all members of the dental team. To date, continuing education programs in dental clinical ergonomics have focused largely on reducing nonpractice risk factors and on palliative therapy for clinicians who have been injured. Few clinicians with high-risk profiles who are not yet symptomatic have either realized their risk level or been motivated to deal with the problems. The challenge for the profession is to raise the awareness level of the asymptomatic group, making real prevention a possibility.
Research initiatives allow us to define and refine ergonomic competencies for the practice of dentistry. This in turn allows professional associations to establish practice standard guidelines, ergonomic accreditation guidelines for educational institutions, operatory layout designs, and equipment integration guidelines for manufacturers. National and international standards bodies (such as the International Organization for Standardization [ISO] and Canadian Standards Association) need evidence to drive the specification of designs and manufacturing tolerances that support optimal ergonomics in the workplace.
The findings of the British Columbia study suggest the value of reviewing ergonomic standards for operatory equipment in dental practices. Indeed, it is possible to define and test certain minimum standards of equipment and layouts to be provided in dental offices to minimize the exposure of dentists to work-related musculoskeletal symptoms. Similarly, there is enough information to begin to refine guidelines for utilization of dental operatories to minimize the exposure of all dental operatory personnel to work-related musculoskeletal symptoms.
Summary
While dentists continue to be at risk for developing musculoskeletal symptoms, the findings of this study suggest several distinct and identifiable clinical equipment usage factors and posture and positioning profile factors that are associated with increased risk of musculoskeletal symptoms for dentists, including the following:
* Torso twist;
* Tipped shoulders;
* Elbow (either dominant, nondominant, or both) raised during operation;
* Operatory light positioned away from the clinician's sight line for maxillary treatment;
* Operating with hands close to face; and
* Increased time practicing in the 7 to 8:30 and 3:30 to 5 o’clock positions.
Certain clinical equipment usage and posture and positioning profile elements are associated with decreased risk of musculoskeletal symptoms for dentists:
* Use of surgical magnification;
* Utilization of four-handed (assisted) delivery;
* Both dominant and nondominant elbows resting at the clinician’s sides during operation;
* Operatory light positioned close to the clinician’s sight line for maxillary treatment; and
* Equipment that is designed and utilized so as to permit the legs of the clinician to be directly under the patient chair during treatment.
The findings of this study suggest that there is a sufficient information base to begin to refine guidelines for utilization of dental operatories to minimize dentists’ work-related musculoskeletal symptoms. It is time dentistry focused its attention on these critical areas to support the health of current practitioners and those of the future.
Authors
Lance M. Rucker, DDS, is the director of clinical simulation and an associate professor and chairman of the Division of Operative Dentistry at the University of British Columbia.
Susanne Sunell, BA, Dip. DH, MA, is with the Department of Dental Hygiene at Vancouver Community College and a candidate for a doctorate in education.
Acknowledgment
The authors wish to acknowledge the funding support of the Workers’ Compensation Board of British Columbia for this research.
References
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13. Meador HL, The biocentric technique: a guide to avoiding occupational pain. J Dent Hygiene 67(1):38-51, 1993.
14. Sommerich CM, McGlothlin JD, Marras WS, Occupational risk factors associated with soft tissue disorders of the shoulder: a review of recent investigations in the literature. Ergonomics 36(6):697-717, 1993.
15. Musculoskeletal disorders and the workplace: low back and upper extremities. National Research Council and Institute of Medicine, January, 2001.
16. Boyd MA, Donaldson D, First-year experience with a performance simulation system. J Dent Ed 47(10):666-70, 1983.
17. Rucker L, McGregor C, Beattie C, Surgical magnification in clinical simulation: enhanced visual control of performance. J Dent Ed 60(2):122, 1996.
18. Chang BJ, Role of advanced surgical telescopes and illumination systems for clinical procedures In, Babbush CA, ed, Dental Implants -- The Art and Science, Chap 24. WB Saunders, Philadelphia, 2000, 495-505.
19. Rucker LM, Surgical magnification: posture maker or posture breaker? In, Murphy DC, ed, Ergonomics and the Dental Care Worker, Chap 8. American Public Health Association, Washington DC, 1998, pp 191-216.
To request a printed copy of this article, please contact/ Lance M. Rucker, DDS, Faculty of Dentistry, The University of British Columbia, 2199 Wesbrook Mall
Vancouver, BC V6T 1Z3, CANADA
Legends
Figure 1. Tipped torso.
Figure 2. Torso twist.
Figure 3. Tipped shoulders
Figure 4. Elbow (either dominant, nondominant, or both) raised during operation.
Table 1. Respondents Experiencing Work-Related Discomfort or Pain During the Past Year
Table 2. Patient Position for Maxillary Treatment
Table 3. Operatory Light Source Position for Maxillary Treatment
