WORK A Journal of Prevention, Assessment & Rehabilitation

ELSEVIER

Work 11 (1998) 263-275

Prevalence and risk factors of upper extremity cumulative trauma disorder in dental hygienists Orit Shenkar a , Jonathan Mann b , Adele Shevach c , Pnina Ever-Hadani d , Patrice L. Weiss a,* a School

of Occupational Therapy, Faculty of Medicine, Hadassah-Hebrew University, P.O. Box 24026, 91240 Mount Scopus, Jerusalem, Israel hDepartment of Community Dentistry, School of Dental Medicine, Hadassah-Hebrew University, Jerusalem, Israel cOral Hygiene Program, School of Dental Medicine, Hadassah-Hebrew University, Jerusalem, Israel d Braun School of Public Health and Community Medicine, Hadassah-Hebrew University, Jerusalem, Israel

Abstract Cumulative trauma disorder (CTD) refers to a number of conditions arising from overuse of joints or soft tissues. The common risk factors that contribute to the development of these disorders are related to personal and occupational variables. Job analysis of the tasks performed by the dental hygienist have shown that this occupation is particularly at risk. The objectives of this study were to determine the prevalence of CTD symptoms amongst dental hygienists in Israel and to identify which arc the factors that are related to CTD. A questionnaire including items concerning demographic data, employment history, professional occupational information, use of instrumentation, and CTD symptomatology was mailed to all 530 registered dental hygienists. Two hundred forty-six hygienists (46%) returned the questionnaire; 63% of the respondents were classified as CTD 'sufferers', Age, year of graduation, hours worked per week, and frequency of changing instruments were found to be significantly related to CTD symptoms. Hygienists at high risk included those aged 50 years or more (Odds ratio, OR = 6), those who graduated before 1986 (OR = 3), those who work more than 34 h per week (OR = 2.5) and those who change two or fewer instruments per patient (OR = 2). The major recommendation resulting from this study is to make dental hygienists aware that they work in a high-risk profession. It is hoped that increased awareness of the risk will spur the hygienist to make appropriate work practice, administrative, and engineering modifications and to seek treatment at the first indication of CTD symptoms. © 1998 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Cumulative trauma disorder; Risk factors; Dental hygiene

* Corrcsponding author,

e-mail: [email protected]

1051-9815/98/$ - see front mattcr PIISI051-9815(98)00043-6

(C)

1998 Elscvier Science Ireland Ltd. All rights reserved.

264

o. Shenkar et al. /

1. Introduction The term cumulative trauma disorder (CTD) (also known as repetitive strain injury, overuse syndrome, and repetitive motion disorder) includes a wide variety of related conditions, all of which arise from overuse of the joints or soft tissues (Williams and Westmorland, 1994). CTD and its relation to work has been, in recent years, the topic of a much study since it poses a considerable threat to both employee well being and employer productivity. The common risk factors which contribute to the development of CTD can be categorized as those related to personal background (e.g. anthropometric characteristics, age, hereditary factors) and those related to work (e.g. repetitive motion, force, static posture, awkward positioning, vibration, temperature, work load) (Armstrong et aI., 1987; Putz-Anderson, 1988). The relationship between CTD and work related factors has been the subject of considerable study. Silverstein et aI. (1987) evaluated 652 workers doing 39 jobs in seven different industrial sites. The jobs were categorized according to their force and repetition requirements. All subjects completed a structured interview and a standardized physical examination by examiners who were blind to the subjects' medical history and exposure. The prevalence of carpal tunnel syndrome (CTS) was 0.6% for workers in low-force/lowrepetition jobs and 5.6% for those in highforce /high-repetition jobs. Repetition appeared to be a greater risk factor for the development of CTS than was force. Schreuer et aI. (1996) examined the effect of typing frequency and speed on the prevalence of upper extremity CTD among female typists using a clinical evaluation, a typing test and a personal interview. They found that 40% of the 100 subjects suffered from symptoms related to CTD. Age, hours worked per week, typing speed, and years worked as a typist were all significantly associated with the development of CTD. Dentists and other dental care workers appear to be another professional group that is highly susceptible to CTD. Millerad and Ekenvall (1990) used telephone interviews to compare the preva-

Work 11 (1998) 263-275

lence of neck and upper extremity symptoms in dentists to a control group of pharmacists. In the group of dentists, 44% reported symptoms of the neck and 51 % reported symptoms of the shoulder, significantly more common than amongst the pharmacists; numbness and paresthesia were the most common symptoms. Suggested causes of these symptoms included the dentists' awkward work position (cervical flexion and rotation, abducted arms) and their repeated use of precision-grip tools. Stockstill et aI. (1993) used a postal questionnaire to examine the prevalence of upper extremity neuropathy amongst dentists licensed in Nebraska. Twenty-nine percent of the more than 1000 respondents reported symptoms of peripheral neuropathy. Of these, 25% reported pain, 15% numbness, and 17% tingling. This prevalence is high enough to suggest the possibility of an occupational component to the etiologic factors. Analysis of the tasks carried out by dental hygienists demonstrate that these workers are as susceptible as dentists to the development of CTD (Atwood and Michalak, 1992; Stern and Dahl, 1992; Sanders and Turcotte, 1997). The analysis paints a distinctly unhealthy portrait of the worker at risk. Hygienists sit or stand for prolonged periods and, as shown in Fig. 1, maintain the head, neck and shoulders in fixed positions for long intervals. They frequently twist and bend forward at the waist, and repeatedly engage in combinations of awkward and excessive movements of the upper extremities (forearm supination and pronation in combination with wrist extension, wrist flexion and extension up to 90° together with radial and ulnar deviation to 10-15°, and sustained modified pen grasp) with varying amounts of force and often accompanied by vibration. Indeed, dental hygienists develop CTD symptoms at an alarming rate. Atwood and Michalak (1992) mailed a questionnaire to 900 Connecticut dental hygienists and found that 93% of the 355 hygienists who replied (39% response rate) experienced some degree of pain. Sanders and Turcotte (1997) distributed a survey to a sample of 95 dental professionals (primarily dental hygienists and dental assistants) and found that 96% noted pain during or after work. Sixty-two percent of

0. Shenkar et al. / Work II (1998) 263-275

265

fication is considered to be of utmost importance in order to determine ways to decrease the incidence of this family of injurious conditions. The objectives of the present study were thus twofold. First, to determine the prevalence of CTD symptoms among dental hygienists working in Israel in order to ascertain whether the high rates observed in other countries were also present here. Second, and more importantly, to identify which personal and work related factors caused the dental hygienist to be at risk for the development of CTD. 2. Methods 2.1. Subjects

,

_:.:":':'.'

....._--_.

Fig. I. Typical posture of a de ntal hygie nist at work. T he head is brought fOIw ard by fl exio n o f the neck, the shoulder girdle is protracted, the arms a re abducted and the elbows fl exed.

the 28 hygienists partIcipating in an ergonomics course reported symptoms in the neck and 81 % reported symptoms in one or both shoulders (Oberg and Oberg, 1993). Of the 78 hygienists who agreed to participate in a carpal tunnel syndrome educational program, 65-90% suffered from a variety of symptoms including pain, numbness, clumsiness, weakness and fatigue (Scoggins and Campbell, 1995). In all of the above studies, the symptoms were attributed to the work carried out by the dental professionals. The studies described above demonstrated the very high prevalence of CTD amongst dental care professionals. These results were, however, descriptive in nature and did not permit the identification of personal and work related factors which cause the dentist or dental hygienist to be at risk for the development of CTD. Risk factor identi-

The Israeli Dental Hygienists Association has a membership of 530 registered dental hygienists, all of whom are female. The names and addresses of all members were received from the association's office and all were mailed a questionnaire. The response rate to the first mailing was 25 % (130 respondents). This increased to 41 % (an additional 85 respondents) after a second mailing. Although the total number of respondents was large enough to permit all desired statistical analyses, a response rate of 41 % is relatively small and we were concerned about the possibility that some systematic bias would invalidate the results. For example, perhaps those suffering from CTD were more or less likely to return the questionnaire. We therefore made phone calls to 31 randomly-selected hygienists who had not responded by mail and completed the questionnaire in a telephone interview. Statistical analysis ( X 2) revealed no significant differences in any of demographic, personal and work related factors between the 215 hygienists who responded by mail and the 31 who were interviewed by phone. We therefore included this group in all subsequent analyses and concluded that our sample was representative of Israeli dental hygienists. With the inclusion of the final 31 respondents, the total response rate was 46%. 2.2. Questionnaire

The questionnaire was based on previous CTD

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O. Shenkaret at. / Work 11 (1998) 263-275

sUlveys (Armstrong et aI., 1987; Schreuer et aI., 1996) and recommendations made by Sanders and Turcotte (1997). The first section included items on general demographic data (such as age, family status, number of years since graduation). The second section included questions regarding employment history (such as numbers of hours worked per day, days per week), professional occupational information (numbers of patients seen per day, length of appointments), and instrumentation (frequency of using scalers, frequency of sharpening instruments). At the end of this section, subjects were asked whether they had suffered from pain or other CTD related symptoms (pain, stiffness, pricking, weakness, swelling, numbness, sensitivity) in the upper extremities (shoulder, arm, elbow, forearm, wrist, hand or fingers) on more than three occasions in the last year or on one occasion lasting more than 1 week. Subjects who answered negatively to this question were thanked for their participation and were designated as 'nonsufferers'. Those who positively answered were designated as 'sufferers' and proceeded to the third section of the questionnaire. The last section referred to symptoms (presence, location, effect on daily activities, seeking for medical help), and changes that were made in the work environment. Content validity of the questionnaire was established by a five member panel of experts (two occupational therapists, one dental hygienist, one dentist and one health care epidemiologist) (Benson and Clark, 1982) and it was then pretested on 10 dental hygienists. Based on feedback from these respondents, minor changes were made to the questionnaire to enhance its clarity. 2.3. Data analysis

Data Analysis was carried out with the aid of the PC-SPSS (Windows version 7.5) computer program. Standard descriptive statistical procedures were first used to describe the population. A univariate analysis between the dependent variable (being a 'sufferer' or a 'non-sufferer') and each of the independent variables was performed using the X 2_ test. Logistic regression analysis was

then performed on the independent variables that showed significance in the univariate analysis. Odds ratios (DRs) were calculated for each of the independent variables. 3. Results Details concerning frequency distributions for the variables pertaining to demographic data and employment history are shown in Table 1. The 246 women who participated in the study ranged in age from 21 to 69 years (mean ± S.D. = 35.3 ± 9.1), although more than 70% were under the age of 39 years. Almost 75% of subjects were married and the number of children was about equally divided amongst the three categories used to characterize this variable (no children, 1-3 children, > 3 children). Israel is a country with a relatively high immigration rate and more than 32% were not native born. The number of years of education ranged from 10 to 20 (14.4 ± 1.4). Over 40% of the respondents graduated since 1992. As expected from a population as diverse as the one under study, there were large variations in subject height which ranged from 150 to 200 cm (163.5 ± 6.3) and weight which ranged from 38 to 99 kg (58.7 ± 9.5). Calculation of the body mass index (BMO (Gibson, 1990) showed that 50% of subjects had scores less than 20 and they were regarded as underweight. More than 90% of the subjects were right hand dominant. Variables describing employment history also showed a wide range of values. Occupational experience in the field of dental hygiene ranged from 1 to 38 years (8.1 ± 6.1), with 36% of subjects having worked in this profession for over 10 years. More than 65% of the respondents had worked in some other occupation prior to their work as dental hygienists, from as little as 1 year to as much as 33 years. There did not appear to be any significant change in the subjects' work routine over the last 5 years with a mean number of working days per week of 4.4 (S.D. = 1.3), mean number of working hours per week ranging of 27.9 (S.D. = 11.6), mean number of patients treated per day of 11.3 (S.D. = 5.0) and mean length of treatment time of 31.1 min (S.D. = 7.0).

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Work 11 (1998) 263-275

Dental hygienists are employed in three different types of clinics which differ in their work

267

load; working in a periodontal clinic is considered to make a heavier physical demand on the hygien-

Table 1 Details concerning frequency and frequency distributions for the variables pertaining to demographic data, employment history, and working habits % Frequency

Variable

Category

Frequency

Age (years)

20-39 40-49 50-69 Married Non-married (single, divorced, widowed) 0 1-3 >3 Israel Africa and Asia Europe and America 1954-1986 1987-1991 1992-1997 27 Right

172 50 21 184 62

70.8 20.6 8.6 74.8 25.2

76 89 81 166 23 56 78 66 100 115 75 40 222 24 62 50 43 86 27 90 42 70 64 55 51 50 72 61 49 45 42 189 170 142 135 118 9 237 111 133

30.9 36.2 32.9 67.5 9.3 23.2 31.8 27.3 40.8 50.0 32.6 17.4 90.2 9.8 25.7 20.7 17.8 35.7 17.0 56.6 26.4 28.5 26.0 22.4 20.7 20.3 29.3 24.8 19.9 18.3 17.1 76.8 69.1 57.7 54.9 48.0 3.7 96.3 45.5 54.5

Marital status

Number children

Country of origin

Year of graduation

Body mass index

Hand dominance

Left Years worked as dental hygienist

Former profession

Hygienists who worked in periodontal clinics

Hygienists who worked in orthodontic clinics

Hygienists who worked in general clinics

Type of instrument used Scaler used with

1-3 4-6 7-9 > 10 Secretary Allied health Other 1996 1995 1994 1993 1992 1996 1995 1994 1993 1992 1996 1995 1994 1993 1992 Cavitron or manual Both All patients When needed

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O. Shenkilr et aL / Work 11 (1998) 263-275

Table 1 (Continued) Variable

Category

Frequency

% Frequency

Type of hand instruments used

Universal Gracy Both Thin Thick 1-2 2:3 Every day When needed Rarely Yes Yes No Not comfortable Comfortable Very comfortable

106 34 106 177 62 134 110 15 180 50 246 238 8 22 78 146

43.1 13.8 43.1 74.1 25.9 54.9 45.1 6.1 73.5 20.4 100.0 96.7 3.3 8.9 31.7 59.3

Instrument handle width Number of instruments changed for each patient Sharpen instruments

Use gloves Change gloves between patients Comfort with gloves

ist while working in an orthodontic clinic is considered to be less physically demanding. It is noticeable that number of hygienists increased with the years although the most prominent change had occurred in the general clinic such that they now represent more than 75% of hygienists. Variables describing work habits were less variable. The majority of subjects (96%) reported that they use both a scaler and hand instruments. Over 50% used the scaler only when needed. Information about handle size indicated that 75% of subjects preferred using a thin handle. Fifty-five percent used one or two instruments for each patient, while the remaining respondents used three or more. Sharpening instruments was done by 74% just when needed. All the hygienists reported that they wore gloves, with 97% of them changing gloves after each patient. Fifty-nine percent reported no discomfort while wearing gloves. 3.1. Categorization of subjects

On the basis of the questionnaire, 155 (63%) of the respondents belonged to the group labeled 'sufferers', i.e. those who reported having suffered from pain or other symptoms in the upper extremities (shoulder, arm, elbow, forearm, wrist, hand or fingers) on more than three occasions in

the last year or on one occasion lasting more than 1 week. The remaining 91 subjects (37%) belonged to the group labeled 'non-sufferers'. 3.2. Description of the 'sufferers'

As shown in Table 2, 25% of the subjects labeled as 'sufferers' reported the presence of a variety of symptoms, more than half being orthopedic in nature. Fifty-six percent reported the occurrence of symptoms during the last 2 years, with the symptoms often appearing for the first time while the respondent was at work. In some cases (37%) the onset of symptoms was sudden but 56% reported a gradual onset. Ninety-two percent of the 'sufferers' reported symptoms primarily on their right (dominant) side; the location of symptoms was about equally divided between the shoulder and the wrist, hand and digits. Sixty percent of the respondents reported that the symptoms were severe enough to disrupt the performance of daily activities, including household chores, feminine hygiene and dressing. In more than 83% of cases the performance of work tasks was impaired and 65% suffered from symptoms while at rest. Sixty-two percent of the 'sufferers' sought medical intervention with more than half consulting a physician, 24% being treated in occupational and/or physical therapy

O. Shenl«lr et al. / Work 11 (1998) 263-275

269

Table 2 Details concerning frequency and frequency distributions for the variables describing the group of 'sufferers' Variable

Category

Frequency

% Frequency

Presence of non-CTD-related symptoms

Yes No

38 117

24.5 75.5

Nature of these non-CTD-related symptoms

Orthopedic Thyroid Vitamin B12 deficit Diabetic Rheumatologic

20 7 5 4 2

52.6 18.4 13.2 10.5 5.3

Occurrence of CTD symptoms

The last 1-2 years The last 3-4 years The last 5-6 years The last 7-8 years The last 9-10 years More than 10 years ago

57 17 6 3 7

56.4 16.8 10.9 5.9 3.0 6.9

First appearence of CTD symptoms

During work During rest Following trauma Following vacation Following change of job Do not remember

87 33 8 3 2 22

56.1 21.3 5.2 1.9 1.3 14.2

Onset of CTD symptoms

Gradually Suddenly Following trauma Do not remember

87 57 6 4

56.5 37.0 3.9 2.6

Side of CTD symptoms

Right Left

142 13

91.6 8.4

Location of CTD symptoms

Shoulder Arm Elbow Forearm Wrist Hand Fingers

75 1 4 4 27 22 22

48.4 0.6 2.6 2.6 17.4 14.2 14.2

Symptoms disturb 'sufferer' during

ADL Work Rest

94 128 102

60.6 82.6 65.8

Type of medical intervention

Physician Occupational and/or physical therapy Alternative medicine Other

61 23

63.5 14.8

8 4

8.3 4.1

11

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o. Shenkaret at. / Work 11 (1998) 263-275

Table 2 (Continued) Category

Diagnosis

Not diagnosed Tendon inflammation Other

53 21 81

34.2 13.5 52.3

Did work habits change as a result of symptoms?

Change Did not change

71 84

45.8 54.2

In what way did work habits change?

Work practice Administrative Engineering

49 13 9

69.0 18.3 12.7

and 8% visited a practitioner of alternative medicine. Thirty-four percent of those whose saw a physician were not given a specific diagnosis but 14% were diagnosed as suffering from tendon inflammation. Approximately half of the 'sufferers' had made changes of one type or another in the work setting. Of these, 70% had made changes in their work practice including modifying the position of hygienist and/or of the patient, exercising and stretching between appointments, and changing the way of holding instruments. Approximately 18% had made administrative changes including an increase in the number of breaks and a decrease in the number of patients treated per day. The remaining 12% had made work station changes, such as modifying the chair's placement and height and the location of the hand instrument tray. 3.3. Significant differences between 'sufferers' and 'non-sufferers'

Amongst the various demographic factors examined in this study, both age (P = 0.020) and year of graduation (P = 0.014) appeared to affect the rate of suffering. Thus, 86% of respondents aged 50 years and older suffered from CTD whereas fewer than 60% of those younger than 39 years belonged to the 'sufferers' category. The highest rate of CTD symptoms occurred for those who graduated between the years 1987 and 1991. Those who graduated prior to that period

Frequency

% Frequency

Variable

(1954-1986) and following that period (1992-1997) showed significantly lower rates. One work load factor that significantly affected the rate of 'suffering' was the number of hours worked per week (P = 0.018); the rate of 'suffering' among subjects who worked at least 34 h per week was 74%, compared to 59% amongst those who worked fewer than 33 h per week. Another work load factor was the number of patients treated per day during the previous year (P = 0.021); the highest rate of 'suffering' (72%) was observed amongst hygienists who treated 11 or more patients per day, compared to 58% amongst those who treated fewer than 10 patients per day. The work style factor that significantly affected the rate of 'suffering' was the frequency with which instruments were changed (P = 0.011); the highest rate of 'suffering' (71 %) was observed amongst hygienists who changed instruments in low frequency (1-2 instruments per patient), compared to 55% amongst those who changed more than three instruments per patient. Multivariate analysis (logistic regression) was then used to examine the relative contribution of these variables in accounting for variation in the dependent variable (i.e. 'sufferers' vs. 'nonsufferers'). As shown in Table 3, the analysis showed that the following variables were significantly related to CTD: age (P < 0.05), year of graduation (P < 0.05), number of hours worked per week (P < 0.001) and frequency of changing instruments (P < 0.05). Finally, OR values were calculated in order to

O. Shenkaret al. / Work 11 (1998) 263-275

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Table 3 Variables that were significantly related to CTD according to the logistic regression and odds ratio Variable

Category

Number of cases

% Sufferers

Odds ratio

Significance level

Age (years)*

20-39 40-49 ~ 50

172 50 21

57.6 70.0 85.7

1 2.13 5.95

0.077 0.013

1992-1997 1987-1991 1954-1986

100 66 78

54.0 75.8 66.7

1.34 2.92

NS 0.005

::; 33 34

150 85

58.7 74.1

1 2.65

0.004

>3

109 134

55.0 70.9

2.12

0.014

Year of graduation*

Number of hours worked per week** Frequency of changing instruments (per patient)*

~

1-2

* Significance level, P < 0.05. ** Significance level, P < 0.001.

determine threshold levels associated with the development of CTD. The measurement was carried out for each of the variables that generated significant results during the logistic regression analysis. The major findings were that dental hygienists over the age of 50 have six times more chance and those who graduated during the years 1954-1986 have three times more chance of belonging to the 'sufferers' group. Those who work more than 34 h per week have 2.5 times more chance and those who change 1-2 instruments per patient have two times more chance of belonging to the 'sufferers' group. 4. Discussion Two hundred forty-six dental hygienists (46%) responded to a questionnaire surveying their demographic data, employment history, professional occupational information, the use of instrumentation, and CTD symptomology. Sixty-three percent of the respondents were classified as CTD 'sufferers', i.e. suffered from pain or other CTD related symptoms (pain, stiffness, pricking, weakness, swelling, numbness, sensitivity) in the upper extremities (shoulder, arm, elbow, forearm, wrist,

hand or fingers) on more than three occasions in the last year or on one occasion lasting more than 1 week. Age, year of graduation, hours worked per week, and frequency of changing instruments were the variables that were significantly related to CTD symptoms. 4.1. Comparisons with other studies

There are some notable comparisons between the frequency of CTD 'sufferers' in the present study with those found by previous surveys of typists, computer workers and dental care professionals. Atwood and Michalak (1992) found that 63% of the 355 dental hygienists questioned in their study suffered from pain in the trunk and upper extremities and an additional 30% had pain as well as physical symptoms, for a total of 93% of all respondents. Scoggins and Campbell (1995) found similarly high rates, ranging from 65% to 90% of hygienists who agreed to participate in a CTS educational program. Millerad and Ekenvall (1990) found that up to 51 % of the 100 dentists surveyed had symptoms in the neck and/ or the upper extremities. Schreuer et al. (1996) reported that 40% of 100 female typists

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O. Shenkar et al. / Work 11 (1998) 263-275

had pain and/or other symptoms and 60% of 688 computer operators reported significant discomfort since the commencement of their current jobs (Chan, personal communication). Differences and similarities in the prevalence of CTD related symptoms reported in the above studies can be attributed to a number of factors. First, the various studies used somewhat different methods to survey the workers (mailed questionnaires, telephone surveys and personal interviews). Second, the jobs examined in the above mentioned studies consisted of quite different tasks. All of these jobs require that the worker remain in fixed postures for lengthy intervals, stabilize the proximal musculature, and perform repetitive and precise movements of the hands and digits. In addition to these potentially harmful elements, dental care treatment is characterized by the need to grip thin-handled tools for long periods and manipulate vibrating electrical tools. Moreover, dental care professionals work directly with patients, many of whom respond to their ministrations with considerable anxiety. It may be that this emotional component exacerbates the physiological and biomechanical stresses of the job (Sanders and Turcotte, 1997). There are some important differences in the work carried out by dentists and dental hygienists. Most of the work of the latter is performed while seated and involves the recurrent use of a relatively small number of tools (Stern and Dahl, 1992; Sanders and Turcotte, 1997). In contrast, dentists sit or stand and execute a much more varied number of procedures (Stockstill et aI., 1993). Given the many elements which appear to cause a worker to develop CTD (Williams and Westmorland, 1994), it is not surprising that dental hygiene is one of the professions most susceptible to this condition. A third factor to consider in looking at variations in CTD prevalence is that the studies on dental hygienists were conducted in two different countries, the United States and Israel. The average number of hours worked per week by the American dental hygienists (32 h) was higher than their Israeli counterparts (28 h). In contrast, work intensity, as measured by the number of patients per day and the time spent with each patient, was

greater for Israeli hygienists (11 patients per day and 31 min per each patient) than for American hygienists (9 patients per day and 49 min per each patient). Despite these differences, the prevalence of CTD in the two studies was similar. It may be that the lower number of work hours offset the increased work intensity of the Israeli hygienists. Finally, one of the most important factors affecting prevalence data is how CTD and 'suffering' is ascertained. The type of symptoms included in the definition of 'suffering' (pain only or a wider range of symptoms, such as stiffness, pricking, weakness, swelling, numbness, sensitivity), their location (primarily upper extremities or upper extremities, neck and back), and their duration (within the year prior to the study or for longer) will certainly influence the prevalence. Not surprisingly, those studies that focused on a narrower range of symptoms, and more circumscribed location and duration detected a lower prevalence of CTD. 4.2. Limitation of survey data

The fact that survey data rely on the subjective reporting of respondents raises the question of the validity of a primarily subjective method of data collection. Angel and Gronfein (1988) addressed this issue in a study of the correlation of individuals' subjective reports of their health with those determined by a physician. In this study, data from 6913 people aged 27-74 years were collected by the United States Center for Health Statistics. Each subjects rated his or her health on a five point scale (excellent to poor) which was then compared to a physician's rating of any disease conditions in accordance with the International Classification of Disease guidelines. There was a significant correlation between the patient's subjective report and the physician's objective report. 4.3. CTD risk factors

Multivariate analysis (logistic regression) was carried out in order to identify those variables that were significantly related to CTD. From

0. Shenkilr et al. / Work 11 (1998) 263-275

observation of the OR measurements of the different variables it is possible to rank these variables according to the level of risk for the development of CTD symptoms. It was found that hygienist age was the greatest risk factor, followed by year of graduation, and number of hours worked per week. The frequency with which instruments are changed was the least important risk factor. As in other study populations [industry workers (Armstrong et at, 1987) and typists (Schreuer et at, 1996)], age was found to be a significant CTD risk factor for dental hygienists, and those aged 50 years and above were six times more likely to be classified as 'sufferers' than those aged 20-39 years. Age related susceptibility to CTD can be explained, in large part, by the physiological and anatomical changes that accompany the aging process. 'Woo and Buckwalter (1987) studied the soft tissues of rabbits and mice and found that the structure of the periosteum changed with age, including alterations to elastic fibers, synovial fluid and bone flexibility. The year of graduation was also a significant risk factor and hygienists who graduated between 1954 and 1986 had a threefold risk for the development of CTD symptoms when compared to those who graduated between 1992 and 1997. The OR measurement was not significant when hygienists who graduated between 1987 and 1991 were compared to those who graduated between 1992 and 1997. There is no doubt that the age and year of graduation risk factors are related and, from the results of the OR measurement, it is clear that age is the more significant factor of the two. Further research aimed at examining older new graduates would help to distinguish their relative impact. Amongst the work load factors, the number of hours worked per week was a significant risk factor and hygienists who work more than 33 h per week were 2.5 times more likely to belong to the 'sufferers' group. In a study of 973 newspaper workers Bernard et at (1994) found that increases in the work hours as well as work under pressure and additions in work load were strongly related to the occurrence of musculoskeletal disorders in the upper extremities. Onishi et at (1982) found a

273

significant correlation between worker fatigue and day of the week. EMG recordings from the trapezius muscle of computer operators demonstrated higher levels of fatigue at the beginning of the week (after the weekend) relative to much lower levels at the end of the work week, indicating the cumulative effect that work has on the musculoskeletal system. On the other hand, in a study of 50 subjects whose work was characterized by repetitive motions and who suffered from problems in the upper extremities, Feely et at (1995) showed that workers retained many symptoms following both short and long periods of rest. They suggested that this result indicated that their subjects had already sustained a chronic level of impairment. Clearly, further study of the appropriate number of rest breaks, their duration and their effect on workers already suffering from CTD vs. those who have not yet developed overt symptoms is needed. Finally, the frequency with which dental hygienists changed instruments was a significant CTD risk factor, with those who changed only one or two instrument per session being two times more likely to belong to the 'sufferers' group when compared to those who replaced their tools three or more times per treatment session. Each tool requires a rather different grip and is operated in a somewhat different manner (Stern and Dahl, 1992; Wilkins, 1994). The very fact that tools are successively set down and picked up gives the hygienist multiple small breaks (so-called micropauses) which provide an important interval of rest. Indeed, changing instruments during the treatment session appear to provide relief from the partial ischemia and sensory disturbances that are caused by holding narrow diameter tools for prolonged periods (Putz-Anderson, 1988; Stern and Dahl, 1992; Williams and Westmorland, 1994). 4.4. Implications for the dental hygienist As indicated above, the tasks performed by dental hygienists make them a professional group which is at great risk for the development of CTD. They remain in fixed postures for prolonged periods with their heads, necks and

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shoulders maintained rigidly for long intelVals. In contrast, other body parts, notably the hands and fingers, engage in highly repetitive movements, sustain significant pressure from narrow-handled tools, and are often exposed to considerable vibration. In the present study, 63% of the hygienists were categorized as 'sufferers', with symptoms about equally divided between the proximal and distal parts of the upper extremity. The respondents had no particular history of musculoskeletal pathology of either congenital or traumatic origin and there is every reason to believe that their symptoms were primarily related to their work as dental hygienists. These results and this conclusion are fully supported by other studies of dental care professionals (Millerad and Ekenvall, 1990; Atwood and Michalak, 1992; Oberg and Oberg, 1993; Stockstill et al., 1993; Sanders and Turcotte, 1997). The CTD symptoms had a pronounced impact on the hygienist's ability to function in many spheres. Eighty-three percent of the 'sufferers' in the present study reported that their symptoms negatively affected their ability to perform tasks at work and 60% reported a serious disruption to their ability to perform routine activities of daily living. Approximately 65% of the 'sufferers' indicated that they experienced at least some of the symptoms even when at rest. What are dental hygienists doing to cope with these problems? Sixty-two percent of the 'sufferers' who responded to our sUlVey had sought medical intelVention of different types, considerably higher than the percent reported in previous studies which ranged from 27% to 45% (Armstrong et aI., 1987; Granjean, 1988; Atwood and Michalak, 1992; Schreuer et aI., 1995). Approximately 50% of the 'sufferers' in the present study had attempted to alleviate their symptoms by modifying their work environment, with approximately or about 70% making work practice changes, 18% making administrative changes and 12% making engineering changes. The hygienists in the study by Atwood and Michalak (1992) also made changes to their work environment including the periodic performance of stretching exer-

cises, the implementation of regular breaks and modifications to the treatment chair. How many of the 'sufferers' were actually helped in these different ways is not clear and further study of the effectiveness of the various possible interventions, techniques and routines which could prevent, or at least delay or reduce, the onset of CTD related symptoms is certainly needed. Some of the risk factors identified in the present study (number of hours worked per week and frequency of changing instruments) are indeed elements that can be altered once the hygienist is made aware of their negative impact. Other well known suggestions, such as frequent micropauses, should also be promoted. On the other hand, barring discovery of the Fountain of Youth, there is little that can be done to mitigate age, the most significant CTD risk factor found in this study. Dental hygiene is a high-risk profession with regard to the development of CTD. Our major recommendation is that hygienists must be made aware both of their great susceptibility and that the problem will increase dramatically as they get older. Awareness of the problem must start during dental hygiene training and must continue via the regular publication of information regarding the latest developments in CTD prevention, treatment and remediation. The results of Scoggins and Campbell's (1995) educational program for dental hygienists certainly suggest that increased knowledge of CTD and its risk factors results in a significant improvement in the way hygienists perform some of the major components of their work. Increased awareness of the risk should encourage hygienists to make appropriate work practice, administrative and engineering modifications and to seek medical and other help at the first indication of symptoms. References Angel R, Gronfein W. The use of subjective information in statistical models. Am Soc Rev 1988;53:464-473. Armstrong TJ, Fine LJ, Goldstein SA, Lifshitz Y, Silverstein AM. Ergonomic consideration in hand and wrist tendinitis. J Hand Surg 1987;5:830-836. Atwood MJ, Michalak C. The occurance of cumulative trauma in dental hygienists. Work 1992;2:17-31.

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