Symptoms of the neck and upper extremities in dentists.

MILERAD L. Symptoms of the neck and upper extremities in dentists. Scand J Work Environ Health 1990;16:129-34. Symptoms of the neck, shoulders. arms, and hands of 99 dentists and a referencegroup of 100pharmacists werestudied by means of a telephone interview. Forty-four percent of the dentistsand 26 % of the pharmacistsreported symptoms of the neck[relativerisk (RR)2.1, 95 070 confidenceinterval (95 % CI) 1.4-3.1]. Symptomsof the shoulder were reported by51 % of the dentists and 23 % of the pharmacists (RR2.2. 95 % CI 1.5-3.3). Musculoskeletal symptoms in the forearm were present almost exclusively in the dentists (12 versus I %) . Numbnessand paresthesia were morecommon among thedentists than amongthe referents (RR4.2, 95 % CI2.3-7.7). Unilateral Raynaud's phenomenon in the dominant hand occurred in sixdentistsand onepharmacist. The high frequencyof symptoms from the neck, shoulders, and upper extremities of the dentists was probably related to their difficult work positions withcervical flexion and rotation, abducted arms, and repetitiveprecision-demandinghandgrips.

Dentistr y work demands high precis ion and is often performed with the arms abducted and unsupported and the cervical spine flexed for ward and rotated (I ). A high sta tic load is induced on the sho ulder-neck region and shoulder jo int by thi s po sture (2). Static load of long duration may cause symptoms from the musculoskeletal system. Denti sts have a high frequency of symp tom s from the neck and shoulder regions (3). The prevalence of cervical spondylosis is higher among dentists than among farm er s, and dentists also ha ve a higher pre valence of glenohumeral joint osteoarthrosis th an fa rmers (4). Lately, wor k with high-speed rotating handpieces and ultrasound equip ment ha s been discussed in relation to reduced sensor y per ception (5) and Raynaud's phenomenon (6).
Th e objecti ve o f the present study was to describ e and eva luate further the occurrence o f mu sculo skeletal symptoms from the shoulder-neck region and upp er extremities and to investiga te whether or not Raynaud 's phenomenon or neurological symptoms in the hands occur excessively among dentists. We also studied a reference group with the same method s to obtain appropriate relative risks.

Subjects
One hundred dentists in Sto ckholm were randoml y selected from the dentist register in the Stockholm region. The criteria for inclusion were as follow s: practice after becoming qualified . and (iii) accessible via the den tist register or telephone directory of the Stockholm ar ea. On e hundred pharmac ists in the same age span as th e dentists were selected from all the pharmacists in Sto ckholm. Pharmacists were chosen as referents since they have a ph ysically ligh t and varied work that cannot be expected to entail high static or dynamic load on the neck, shoulders, or arms. Mo reover, the socioeconomic ba ckground of dentists and pharmacists is similar, and th e two groups can be expected to ha ve compa rable medical kno wledge.
The subjects were asked by letter if they were willing to participate in the study, and the study design was approved by the local ethics committee.

Questionnaire
The dentists and pharmacists were interviewed on the telephone by a physician according to a questionnaire. The questionnaire included questions on the work situation for th e dentists only since pharmacists were chosen as referents because they have a ph ysicall y varying and light wor k. The questionnaire was otherwise identical fo r both groups. Th e work-related questions concern ed the years in clinical dentistry; workhours per da y; minutes per day with high-speed drills , other drills, or ultrasound devices; and sitt ing or standing work position. Gener al questions included handedness, vibration exposure during leisure time, smoking habits, and diseases other than musculoskeletal diseases. Symp tom -related questions included symptoms of the neck , shoulders, upper arm s, forearms , and hands at any time before the interview ("lifetime prevalence"). Neck and shoulder sym ptoms were furthe r anal yzed according to the Nordic questionnaire for the evalu ation of musculoskeletal symptoms (7) as to duration during th e last 12 months and during the last 7 d, effect on work performance an d leisure-time activities, an d sick leave. Information on Raynaud's phenomenon was asked in such detail that the coldinduced symptoms could be graded according to the Taylor-Pelmear symptom scale (8). Neuro logical symptom s of the hands, such as numbness and pa resthesia, were described as to location (median, ulnar or both nerves), an d it was registered if the sym ptoms were radiating from the neck or on ly localized in the hands .

Statistical analysis
The ratio between the frequency of positive answers (yes to a symptom question) from the dentists and pharmacists was defined as the risk ratio (RR), which described the relat ion between the symptoms of the exposed dentists and those of the unexposed pharmacists.
The risk ra tio was calculated with the 95 070 confidence  interval (95 % CI) (9). When the frequency of symptoms was low, Fisher's exact test was used with a level of significance of P < 0.05.

Results
Ninety-nine of the 100 dentists and all of the pharmacists participated in the study . The age distribution was similar for both groups, as were smoking habits (table  I). Both groups had similar, low exposure to vibrating tools during leisure time. The frequency of diseases other than those of the musculoskeletal system was similar for the groups, and hypertension was the most common diagnosis, with six cases among the dentists and seven among the pharmacists . The mean employment time was 19 (SD 5.9) years for the dentists and 20.3 (SD 4.8) yea rs for the pharmacists. The mean week ly worktime fo r the dentists was 40 (SD 7.2) h. Eighty-five dentists worked in a sitting position only, II reported both sitting and standing, and three used only the standing position. The employment time of both the dentists and pharmacists was correlated with age (correlation coefficient 0.84 and 0.89, respectively).

Neck
The dentists had a higher freque ncy of cervical symptoms than the pharmacists (table 2). Among the female dentists the rate of symptoms increased with age (48 % in the age group of 35-44 years and 73 % in that of 45-55 years) . No such relation to age was observed among the female pharmacists or among the ma le dentists or pharmacists. The influence of emp loyment time in dentistry on the symptoms could not be estimated , as it was strictly correlated with age. The dentists with neck symptoms also had shoulder and arm symptoms more often than pharmacists with neck symptoms (table 2). Twenty-six dentists and 10 pharmacists with neck symptoms during the last 12 mon ths had ha d symptoms more than 30 d . Twentytwo dentists and 11 pharmacists were currently experiencing neck symptoms, an d 14 and 4 , respectively, had received me dical treatment. Seven dentists but no pharmacist reported changing their work routines or reducing their workhours because of neck -shoulder Table 3. Symptoms in the shoulders of the dentists and pharmacists with the relative risk (RR)   symptoms. Five denti sts but no pharmacist had been on sick leave (two of them more than 30 d) because of neck-shoulder symptoms during the 12 months preceding the interview. The female denti sts reported neck symptoms 1.4 times more often than the male denti sts (95 010 CI 1.0-2.0), and corre sponding symptoms were reported 1.8 times more often among the female than the male phar macists (95 Cl io C I 0.8-3 .9).

Shoulders, upper arms, elbows
Symptoms of the shoulders and the corresponding data from subjects with no concomitant neck problems are shown in tab le 3. The shoulder on the dominant side was as often affected as that on the nondominant side.
Four denti sts and one pharmacist repo rted symptoms from the glenohumeral joint of the dominant side, and two dent ists reported the same symptoms on the nondominant side. The upper arm and elbow symptoms were mainl y localized in the dominant arm (12 of 14 denti sts and 6 of 6 pharmacists). Eight dentists and four pharma cists reported elbow disorders. Lateral epicondylitis was the most commonly reported diagnosis for the arm with seven cases among the dentists (all on the dominant side) and four among pharmacists (three on the dominant side) .

Forearm
Symptoms of the for earm are pre sented in table 4. Eighty-three percent of the dentists with such symptom s also had neck and shoulder symptoms on the same side. The sympt oms were generally localized in the dominant side (75 010) . Only one pharmacist had forearm symptoms.

Raynaud's phenomenon
The prevalence of Raynaud 's phenomenon among the denti sts and pharmacists is shown in tab le 5. In both gro ups the women reported a higher prevalence than the men. The male dent ists had a higher frequency of Raynaud 's phenomenon than the male pharmacists (P < 0.05). No such difference was ob served for the women . A possible influence of smoking on Raynaud 's phenomenon was not analyzed, since few subjects were smokers (table 1). Six dentist s and one pharmaci st had Raynaud's phenomenon localized exclusively in the More than half of the subjects with Raynaud's phenomenon also had neurological symptoms localized in the same hand or hands.

Neurological symptoms
The reported occurrence of neurological symptoms in the hands is shown in table 6. The relative risks of the dentists compared with those of the pharmacists were high, especially for symptoms localized in the dominant hand only. Among the subjects with neurological symptoms in the hands, combined symptoms from the sensory distribution areas of the median and ulnar nerves were the most comm on in both the dentists and th e pharmacists (27 versus 7, respectively). Symptoms in the median area alone were more often reported by the dentist s than the pharmacists, and these symptoms were mainly localized in the dominant hand . Nineteen dentists and four pharmacists had neurological symptom s without an y relation to Raynaud' s phenomenon or cervicobrachial symptoms (table 6). The distribution of the symptoms is shown in table 7.

Discussion
In the present study the dentists reported symptoms of the neck and upp er extremities more often than the pharmacists. The design of the study was cro ss-sectional , and a potential source of error thu s was the " healthy worker effect," ie, dentists who had given up clinical dentistry because of symptoms were not accessible for an interview . This poss ibility may have led to an underestimation of the relative risks. On the other hand, self-reported symptoms ma y be exaggerated in all' expo sed group and, ther efore , lead to an overestimation of the relati ve risks. In th e present study the interviewer knew if the subject was a dent ist or a pharmacist , since work-related question s were included in the questionnaire. Howe ver, the interviews were performed according to a standardized format , and this standardization can be expected to minimize any influence of observer bias on the result s. Potentially confounding or modifying factors such as age, smoki ng habits, nonprofessional vibrati on exposure , and disea ses other than those of the musculoskeleta l system were similarl y distributed in the dentist and reference groups. It is therefore not likely that these factors would explain our results, and the high occurrence of symptoms in the denti st group was probably related to differences in the work situation. However, we could not find any relat ion between symptom s and "exposure time" (eg, period of employment) among the dentists. Age and exposure time were closely related, but apart from the neck symptoms of the female dentists, there was no ob vious connection between symptoms and age. The age group studied (35-55 years) was limited and may have contributed to the lack of "age-response" or " dose-response" relationships.
The high frequency of neck complaints found among the dentists in thi s study was similar to that found in a previous study (3). The dentists also seemed to have more serious and long-term symptoms which 132 influenced their work capacity and leisur e-time activities. Neck symptoms were also more often combined with symptoms from the should ers and arm s among the denti sts. The work posture with flexion and rotation of the cervical spine is a probable explanation for these symptoms. According to a previous study, dentists also have a high pre valence of cervical spondylosis (4), and even if the relation between cervical symptoms and radiographic cervical spondylosis is indistinct (10), both may be relat ed to a high musculo skeletal load (4, II) .
Neck problems were more common among the female than the male dentists in the present study, although the relative risks in relation to female and male ph armacists were comparable . It is difficult to find comparable work situations for men and women with similar high musculoskeletal static componen ts. To our knowledge, the present study is the first to demonstrate that the sexes seem equally prone to develop neck symptoms when subjected to equal work-related musculoskeletal strain.
In conformity with pre vious studies (3, II) , we found an increased risk for shoulder symptom s among the denti sts. These symptoms were reported as often for the dominant as for the nondominant side, and this finding may reflect the work position with both arm s abducted (I). At 30°or more of abduction the perfusion of the supraspinatus tendon ma y decrease since the intramuscular pressure increa ses (12). The static contraction of a muscle in an abducted position may also cause impairment of the blood flow in the muscle (13). Decreased blood flow in the tendon of the supraspinatus muscle may cause degeneration of the tendon and rotator cuff tendinitis (14), which is a common cause of shoulder pain. In sit-down dentistry the work area is higher than elbow height. This situation may cause an elevation of the shoulder girdle. The static elevation of the shoulders may cause chronic myalgia in the descending part of the trapezius muscle, often referred to as tension neck syndrome (I5).
Symptoms of the arms and elbows were also more common among the dentists than among the pharmacists. In contrast to shoulder symptoms, they were almost exclusively located on the dominant side. Dentists work with repetitive simultaneous power and precision-demanding grips without support for the arm. The high frequency of complaints from the arm and elbow may be due to a need for stabilization of the unsupported wrist.
The prevalence of Raynaud's phenomenon has been estimated to be about 5 0J0 for men (16) and 20070 for younger women (17). Thus the prevalences found in our study were within the normal range for young women in pharmacy and for female dentists. The finding of an increased prevalence among male dentists only is difficult to explain, especially as the increase could not be attributed to un ilateral symptoms. Unilateral Raynaud's phenomenon is unusual in the general population and can, according to the definition (18), not be defined as Raynaud 's disease, but is presumed to be secondary to other diseases. The prevalence of symptoms exclusively localized in the dominant hand was high in the present study among the dentists, even if the difference between the dentists and the pharmacists was not significant. A similar tendency towards unilateral Raynaud's phenomenon in the dominant hand has previously been reported for male dentists (6). It is unknown whether or not high-frequency vibration can induce Raynaud's phenomenon, and the technical recommendations of the standard of the International Organization for Standardization only apply to frequencies between 5.6 and 1400 Hz (19), whereas the frequencies of high-speed equipment in dentistry are between 1000 and 40 000 Hz. Even if dentists have an increased prevalence of Raynaud's phenomenon, the explanation may be circulatory disturbances secondary to carpal tunnel syndrome or cervical nerve root compression (20) rather than highfrequency vibration . Occupational groups with repetitive hand movements have an increased frequency of carpal tunnel syndrome (21), and repetitive hand movements also characterize dentistry work. The symptoms may thus be secondary to other diseases possibly occurring more often in dentists than in pharmacists.
In this study neurological symptoms in the hands were common among the dentists. Only four referents had neurological symptoms not combined with Raynaud's phenomenon or neck-shoulder pain on the same side, whereas 19 dentists had such symptoms without any relation to radiating pain from the neck or Raynaud's phenomenon. The symptoms mainly occurred in the dominant hand or in both hands. The cause of 4 neurological symptoms in the hands cannot be clarified in a telephone interview, but carpal tunnel syndrome is common in occupations with repetitive hand movements (21). In this study, the majority of neurological symptoms of the dentists were also localized in the area innervated by the median nerve. A peripheral nerve injury in the fingers cannot be excluded, however. Healthy dentists have a reduced perception for vibration in the dominant hand in comparison with that of the nondominant hand, and exposure to highspeed rotating handpieces has been discussed in relation to this finding (5). In addition, the extensive use of handtools in dentistry work can cause a chronic extrinsic compression of the nerves in the hand, and therefore may cause an entrapment of digital nerves (22). Whatever the cause of the symptoms, neurological disturbances are potentially serious in an occupation in which precise hand movements are necessary.
We conclude that dentists have a higher than expected risk for musculoskeletal symptoms in the neck and upper extremities. The probable reason for the high risk is their difficult work positions with the arms abducted and elevated , the cervical spine flexed and rotated , and repetitive precision-demanding handgrips. These work positions can be improved by preventive measures directed towards the workplace, eg, arm or hand support, appropriate construction of the dentist's chair, and appropriate design of the work unit. Another possible preventive approach is ergonomic education of the dentists and improvement of the work organization. The high occurrence of neurological symptoms in the hands is an observation that needs further evaluation. If the symptoms are due to peripheral nerve damage in the fingers as a result of exposure to high-frequency vibration, preventive measures are possible since these vibrations can easily be dampened. In contrast, if the symptoms are caused by nerve entrapment at the wrist or elsewhere, prevention may not be so simple.