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AMERICAN JOURNAL OF INDUSTRIAL MEDICINE 42:248–257 (2002)
Prevalence of Musculoskeletal Symptoms and
Carpal Tunnel Syndrome Among Dental Hygienists
Dan Anton, PhD,PT,AT C,
1
John Rosecrance, PhD,PT,CPE,
2
Linda Merlino, MS,
3
and Thomas Cook, PhD,PT
4
Background Carpal tunnel syndrome (CTS) and other work-related musculoskeletal
disorders (MSDs) are common problems in general industry as well as dental hygiene. The
purpose of this study is to determine the prevalence of CTS and other MSDs among dental
hygienists. No previous studies involving dental hygienists have combined nerve
conduction studies (NCS) and symptoms in their CTS case definitions.
Methods Dental hygienists (N ¼95) completed a symptom and job factors survey, hand
symptom diagram, and underwent NCS across the wrist.
Results At least one MSD was reported by 93%. Prevalence of CTS was 8.4% utilizing a
case definition of symptoms and NCS, but 42% if defined by symptoms alone. Age, BMI, and
the number of patients treated per day were significant factors associated with CTS.
Conclusions Dental hygienists are exposed to occupational factors that increase the risk
of CTS. A case definition that does not include NCS overestimates CTS prevalence. Am. J.
Ind. Med. 42:248–257, 2002. ß2002 Wiley-Liss, Inc.
KEY WORDS: carpal tunnel syndrome; dental hygiene; musculoskeletal disorders;
Nordic questionnaire; nerve conduction studies
INTRODUCTION
Work-related musculoskeletal disorders (MSD) are
common for dental hygienists [Macdonald et al., 1988;
Osborn et al., 1990a,b; O
¨berg and O
¨berg, 1993; Liss et al.,
1995; A
˚kesson et al., 1999; Lalumandier and McPhee, 2001].
It has been estimated that each year 70% of dental hy-
gienists report musculoskeletal pain [Osborn et al., 1990b],
with the low back, neck, and shoulder, the most frequent sites
of musculoskeletal pain [O
¨berg and O
¨berg, 1993; A
˚kesson
et al., 1999]. The prevalence of one of these MSDs, carpal
tunnel syndrome (CTS), has been reported to be greater
among dental hygienists than in the general population
[Macdonald et al., 1988; Osborn et al., 1990a; Liss et al.,
1995; Atroshi et al., 1999; Lalumandier and McPhee, 2001].
Previous studies on this occupation have shown that the
prevalence of CTS ranges from 6 to 8% [Macdonald et al.,
1988; Osborn et al., 1990a]. According to an evaluation of the
Bureau of Labor Statistics data, dental hygienists ranked first
of all occupations in the proportion of cases of CTS per 1,000
employees [Leigh and Miller, 1998].
Carpal tunnel syndrome and other MSDs may be pre-
cipitated by exposure to several factors specific to the dental
hygiene occupation. For example, during teeth scaling, the
hygienist must repeatedly and forcefully grip a relatively
small instrument to maintain safe contact with the patient’s
teeth. The head, neck, and shoulders of dental workers are
2002Wiley-Liss,Inc.
1
Biomechanics and Ergonomics Facility, Department of Occupational and Environmental
Health, College of Public Health, The University of Iowa, Iowa
2
Department of Occupational and EnvironmentalHealth, College of Public Health,The Uni-
versity of Iowa, Iowa
3
Department of Occupational and EnvironmentalHealth, College of Public Health,The Uni-
versity of Iowa, Iowa
4
Department of Occupational and EnvironmentalHealth, College of Public Health,The Uni-
versity of Iowa, Iowa
Dan Anton is working as a S enior Research Assistant.
John Rosecrance is workinga s a Assistant Professor.
Linda Merlino is working a s a Research Assistant.
Thomas Cook is working as a Professor.
Contract grant sponsor: National Center for Injury Prevention and Control; Contract grant
number: CCR703640-11.
*Correspondence to: Dan Anton, Biomechanics and Ergonomics Facility, #156D IREH;
Oakdale Campus,The University of Iowa, Iowa City, Iowa 52242.
E-mail: dan-anton@uiowa.edu
Accepted 8 May 2002
DOI10.1002/ajim.10110. Published online in Wiley InterScience
(www.interscience.wiley.com)
held in static, often awkward postures while working [O
¨berg
et al., 1995; A
˚kesson et al., 1997]. The occurrence of MSD
may influence their work practices and lead to lost work time
or inefficient productivity.
Previous studies of MSDs on dental hygienists have
either used symptom survey responses alone, or symptoms in
conjunction with vibrometry to determine CTS prevalence
[Macdonald et al., 1988; Osborn et al., 1990a; Conrad et al.,
1993; Liss et al., 1995; Lalumandier and McPhee, 2001].
However, the use of symptom surveys alone lacks adequate
predictive power and may overestimate prevalence [Rempel
et al., 1998]. The primary purpose of this study was to assess
the prevalence of musculoskeletal symptoms and CTS
among dental hygienists, as well as to determine which risk
factors are associated with CTS. A secondary purpose was to
examine the extent to which prevalence estimates change
with different case definitions of CTS.
MATERIALS AND METHODS
Dental hygienists attending a continuing education con-
ference were invited to participate in a survey, to undergo
nerve conduction studies across the wrist, and to have their
body composition evaluated. All subjects were thoroughly in-
formed of the procedures and gave consent prior to parti-
cipation. The Institutional Review Board at the University of
Iowa (Iowa City, IA) approved this study.
The self-administered questionnaire used in this study
was a generic symptom and job factors survey, consisting of
questions regarding demographic data, work-related pain,
missed work, problematic job factors, and specific hand
symptoms. This questionnaire has been used by the investiga-
tors in previous studies [Bingham et al., 1996; Zimmermann
et al., 1997], and has good test-retest reliability [Rosecrance
et al., 2002]. In the first section of the survey, age, height,
weight, gender, handedness, years as a dental hygienist, and
work schedule were queried. The second section consisted of
questions about work-related musculoskeletal disorders in
the past 12 months and was a modification of the Standar-
dized Nordic Questionnaire [Kuorinka et al., 1987]. Nine
parts of the body were identified on a diagram and the dental
hygienists were asked if in the past 12 months they had a job-
related ache, pain, discomfort, or other complaint in these
regions. If they answered, ‘‘yes’’ for any of the regions, the
subjects were also asked whether the complaint prevented
them from doing a day’s work or if they saw a physician for
the problem.
In the third section of the survey, the dental hygienists
were asked to rate on a 0–10 scale (0 ¼no problem;
10 ¼major problem) whether they felt any of 15 job factors
could contribute to work-related pain and injury. Examples of
job factors included grasping small objects or performing
repetitious tasks. They were also asked about clinical prac-
tice factors specific to dental hygiene. These factors included
an estimate of the number of hours worked per week, the
number of patients seen per day, the number of patients seen
per day with heavy calculus, work time spent performing
certain procedures, such as scaling and polishing, the hand
predominantly used for scaling, and the ‘‘clock’’ position
most often used when treating a patient. For example,
position ‘‘9’’ would be directly to the right side of the patient
and position ‘‘12’’ would be looking down from the patient’s
head.
The fourth section of the survey consisted of a hand
diagram and survey to evaluate symptoms consistent with
CTS [Franzblau et al., 1993]. Subjects were instructed to rate
hand or wrist symptoms, such as numbness, tingling, or ache,
on a 0–10 scale (0–2 ¼none; 3– 7 ¼moderate; 8–10 ¼
severe), and shade on a hand diagram where the symptoms
were located. There were also questions regarding the
duration of the hand symptoms, nocturnal symptoms, and
aggravating activities. In the final section of the survey,
subjects completed an employment history regarding the
type of work and time at the current and previous jobs.
Subjects were asked if they had diabetes, hypothyroidism,
rheumatoid arthritis, alcoholism, or any chronic illness, as
well as if they used tobacco products. Finally, they were
asked about hobbies and non-work activities.
After completing the questionnaire, standardized NCS
[Stevens, 1997] were performed bilaterally with a Cadwell
5200A nerve conduction stimulator (Cadwell Laboratories,
Inc., Kennewick, WA). An orthodromic, midpalmar—wrist
median sensory latency was initially recorded. The bipolar
hand held stimulator was placed over the midpalm and the
recording electrode was placed 8 cm proximal to the cathode
over the median nerve 2 cm proximal to the distal wrist
crease. The ground electrode was placed over the back of the
hand. If the median latency was 2.2 ms or greater, an 8 cm
orthodromic, ulnar sensory latency was also recorded, with
the stimulator placed over the ulnar aspect of the palm and the
recording electrode over the ulnar nerve proximal to the wrist
crease. The sensory latency was defined as the time interval
between the stimulus artifact until the peak of the negative
aspect of the mixed nerve action potential. If the median
nerve sensory latency was unattainable (due to conduction
block), the median motor latency for the abductor pollicis
brevis was performed. An onset motor latency equal to or
greater than 4.4 ms was considered abnormal.
For subjects that had median and ulnar latency mea-
surements recorded, the median-ulnar latency difference
(MULD) was calculated. Median mononeuropathy was de-
fined as a difference equal to or greater than 0.5 ms, which is
considered a conservative measurement within the carpal
tunnel [Redmond and Rivner, 1988]. Ulnar latencies were
examined to assure that they were not prolonged in conjun-
ction with median latencies. Hand temperature was moni-
tored by placing a surface thermistor (TH-8 Thermalert,
Physitemp Instruments, Inc., Clifton, NJ) in the palmar web
Musculoskeletal Disorders Among Dental Hygienists 249
space between the thumb and index finger. Although tem-
perature was monitored and NCS were performed in a warm
room, no attempt was made to warm hands or correct the
latencies for temperature. The use of the MULD as a defini-
tion of median mononeuropathy precludes the need to tem-
perature correct latency values.
Systolic and diastolic blood pressure was measured from
the right upper arm with an automatic electronic digital mo-
nitor (HEM-705CP, Omron Healthcare, Inc., Vernon Hills,
IL). Body composition analysis was determined by near-
infrared light interactance, a method shown to have good re-
liability [Cassady et al., 1996]. The infrared spectrophot-
ometer (Futrex 5000A Spectrophotometer, Futrex, Inc.,
Gaithersburg, MD) consisted of a small DC powered multi-
key micro-processing unit with a cable connected to a hand-
held transducer probe. The probe was placed in an attachment
that prevented interference from external light before it was
placed on the right biceps of each subject. The infrared light
reflected from the test site was converted to optical density
measurements, and a percent body fat and lean body mass
were calculated.
Three different case definitions of CTS were used in this
study. The first, based solely on responses to the hand sym-
ptom survey and hand diagram, was positive if the subject
rated greater than two on the 0–10 scale (‘‘moderate’’ or
greater) symptoms of numbness, tingling, burning, or aching,
and shaded two out of the four fingers of the median dis-
tribution of either hand (CTSsymp). The median distribution
was defined as the palmar aspect of digits 1 –4, as well as the
distal phalanx of each of these digits dorsally. Additionally,
the symptoms must have occurred sometime in the past 12
months, have been present for at least 1 month, and have
occurred while practicing as a dental hygienist. This case
definition of CTS is comparable with the ‘‘classic or probable
CTS’’ symptom definition reported by Rempel et al. [1998].
The second case definition in the present study included
all of the conditions of the first, in addition to symptoms that
were either worse at night or woke the subject (CTSnoct).
The third case definition of CTS required the symptoms of the
CTSsymp definition, and abnormal NCS findings (CTSncs).
A MULD equal to 0.5 ms or greater, or a median motor lat-
ency equal to 4.4 or greater was considered an abnormal
NCS. Other investigators of CTS have used this definition
[Franzblau et al., 1993].
Data Analysis
Means and standard deviations, or frequencies and per-
centiles were calculated for the demographic and occupa-
tional variables for all of the dental hygienists, as well as by
case and non-case status for various definitions of CTS.
Additionally, means and standard deviations, or frequencies
and percentiles were obtained for the modified Nordic Ques-
tionnaire and job factors. Percent time performing various
dental hygiene procedures was converted to number of hours
per week based on the number of hours worked per week
reported by the dental hygienist. Crude prevalence rates were
obtained for the three case definitions of CTS and median
mononeuropathy. For the CTSncs and CTSnoct case defin-
itions, Wilcoxon Rank Sum or independent t-tests were used
to assess the relationship between cases and non-cases.
Crude odds ratios (OR) with their 95% confidence in-
tervals (CI) were determined by logistic regression for the
demographic, job factors, and clinical practice related vari-
ables. Variables that were univariately significant at conven-
tional levels (P<0.15) were entered into a multivariate model
using stepwise logistic regression. For variables that were
collinear (bodyfat and BMI; patients per day and patients per
week), the stronger age and BMI adjusted representation was
retained for multivariate modeling. The likelihood ratio test
was used to calculate P-values. A parsimonious model, tak-
ing into account the sample size, was chosen. All analyses
were performed with SAS, Version 8 for PC (SAS Institute,
Cary, NC).
RESULTS
All of the 109 conference participants responded to the
survey (100% response rate). One dental assistant, one in-
structor, two administrators, and nine dental hygiene students
were removed from the analysis to assure that the sample
included only practicing dental hygienists. Although, one
male dental hygienist attended the conference, he was also
excluded from the data analysis. Because the conference
ended before all volunteers could be tested, only 89 (93%) of
the dental hygienists were able to participate in nerve con-
duction testing, blood pressure measurement, and body com-
position testing.
Demographic and
Anthropometric Variables
Table I shows the demographics of the dental hygienists
in this study (n ¼95). The mean and median age of the sub-
jects was 38 years (SD 7.9), and the average time practicing
as a DH was 12.7 years (SD 8.8). The mean body mass index
(BMI; kg/m
2
) was 24.0 (SD 4.0) with body fat averaging
31.4% (SD 6.0). Only 6.3% used tobacco products. A
medical history of thyroid problems was reported by 9.6% of
the DH with no other CTS confounding co-morbidities (i.e.,
diabetes, etc.) reported. Ninety-five percent of the subjects
were right handed, and an equal percentage used their right
hand for scaling. Over 69% of the subjects preferred working
primarily in the 10, 11, or 12 o’clock position. The subjects
worked an average of 31.0 hr/week (SD 8.4), and spent the
majority of this time performing the procedures of scaling
(mean 16.7 hr, SD 7.0) and polishing (mean 4.7 hr, SD 3.0).
The dental hygienists in this study treated an average of
250 Anton et al.
10 patients a day (SD 2.2), and about 3 of these patients a day
required scaling of hard calculus. The most frequent non-
work activities reported include home computing (17.0%),
weight lifting (12.7%), and sewing (11.7%).
Musculoskeletal Symptoms and
Job Factors
The results of the modified Nordic questionnaire are
shown in Table II. Approximately 93% of the dental hygie-
nists stated that they had at least one job-related ache, pain, or
discomfort in the 12 months prior to the survey. The majority
of the symptoms were in the wrist/hand region (69.5%), neck
(68.5%), and upper back (67.4%). The low back and shoul-
ders were also frequent sites of discomfort. Approximately
one third of the dental hygienists saw a medical, osteopathic,
or chiropractic physician for job-related neck or upper
back pain, and a slightly smaller proportion (26.3%) sought
medical advice for the low back. A very small percentage
missed work because of MSD symptoms, with shoulder pain,
the most frequent (5.3%) cause of missed work.
Table III displays the results of the job factors survey that
subjects rated as most likely to contribute to work-related
pain. The most problematic job factors included working
in the same position for long periods (mean 6.9, SD 2.9),
bending or twisting the back in an awkward way (mean 6.6,
SD 2.9), and performing the same task repeatedly (mean 6.4,
SD 3.2). Working in awkward or cramped positions, handling
or grasping small objects, and insufficient breaks during the
day were the other factors rated greater than 5 out of 10. After
controlling for the effects of age and BMI, none of these job
factors were associated with prevalent CTSncs.
Carpal Tunnel Syndrome
The overall prevalence of a CTS case defined solely on
symptoms (CTSsymp) was 44.2%, and decreased to 23.2% if
a more conservative definition including nocturnal symp-
toms (CTSnoct) was included (Fig. 1). The prevalence of
TAB L E I . Demographic/Anthropometric, Clinical Practice, and Specific
Dental Procedure Factors for Dental Hygienists (n ¼95)
Mean (SD) Range
Age (years) 37.6 (7.9) 23^ 58
Education (years) 15.7 (1.2) 12 ^20
Anthropometric data
Height (m) 1.7 (0.1) 1.5 ^1.8
Weight(kg) 66.4(11.7) 45^ 109
Body mass index (kg/m
2
) 24.0 (4.0) 17^ 34
Body fat (%) 31.4 (6.0) 18 ^45
Clinical practice data
Employmenta s DH (years) 12.7 (8.8) 1^ 38
Days workedper week (days) 3.8 (1.0) 1 ^5.5
Hours workedper week (hr) 31.0 (8.4) 8^ 45
Patients per week 37.6 (13.8) 8^ 90
Patients per day 9.7 (2.2) 5^ 18
Minutes per patient (min) 51.5 (9.7) 27^ 69
Specific dental procedures
Hard calculus patients perday 2.6 (1.4) 1 ^6
Hard calculus patients per week 9.9 (6.2) 1 ^ 30
Time probingper week (hr) 2.7 (1.8) 0 ^ 9
Time scaling per week (hr) 16.7 (7.0) 4 ^32
Time polishing per week (hr) 4.7 (3.0) 0^ 13
Time flossing per week (hr) 1.8 (1.1) 0 ^5
Time teaching per week (hr) 2.7 (1.8) 0^ 9
TAB L E II . Prevalence of Job-Related Conditions During the Past12 Months
forAll Dental Hygienists Fromthe Modified Nordic Questionnaire (N ¼95)*
Job-related
ache, pain, etc
% ‘‘YES’’ (n)
Condition
prevented work
Saw physician
for condi tion
Neck 68.5(65) 3.2 (3) 36.8 (35)
Upper back 67.4 (64) 4.2 (4) 32.6(31)
Low back 56.8 (54) 4.2 (4) 26.3 (25)
Shoulders 60.0(57) 5.3 (5) 23.2 (22)
Elbows 21.1 (20) 0 (0) 12.6 (12)
Wrist/hand 69.5 (66) 3.2(3) 21.1 (20)
Hips/thighs 19.0 (18) 0 (0) 10.5 (10)
Knees 13.7 (13) 0 (0) 4.2 (4)
Feet 15.8 (15) 0 (0) 5.3 (5)
*Numberreportingdifferedslightlydepending onlocation.
TAB L E I II . Job Factors Rated by Dental Hygienists as Most Likely to
Contribute to Work-Related Pain (0 ¼no problem; 10 ¼major problem;
N¼95)
Mean (SD)
Training 1.4 (2.0)
Tool use 4.6 (3.1)
Workschedule 4.2 (3.0)
Heavy material handling 1.1 (2.2)
Work when injured 3.9 (3.4)
Environment 2.2 (2.6)
Workoverhead/away from body 4.2 (3.3)
Worknear physical limits 4.3 (3.4)
Bend/twist back 6.6 (2.9)
Continuous positions 6.9(2.9)
Awkwardpositions 6 (3.1)
Insufficientbreaks 5.8 (3.2)
Grasping small objects 5.9 (3.3)
Workingfast 4.7 (3.3)
Repetition 6.4(3.2)
Musculoskeletal Disorders Among Dental Hygienists 251
CTS was 8.4%, when the case definition included classic
symptoms and NCS indicating median mononeuropathy
(CTSncs), and assuming that the six dental hygienists who
did not undergo NCS did not have CTS.
Table IV shows a comparison of demographic and dental
factors by case and non-case status for the two more stringent
definitions of CTS (CTSncs and CTSnoct). For CTSncs,
cases were 11 years older than non-cases (P¼0.0004), had
a higher BMI (P¼0.0017), and higher body fat percentage
(P¼0.07). Although, there was a difference in body weight,
there was no significant difference in height between cases
and non-cases (P¼0.58). CTSncs cases also saw about two
more patients a day than did non-cases (P¼0.34), which
translated into 12 more patients per week (P¼0.44). None of
the other clinical practice variables showed significant
differences.
None of the demographic factors were significantly
associated with CTSnoct, but BMI approached significance
(P¼0.08) with cases having a higher BMI than non-cases.
The only occupational factor that showed a significant diff-
erence between cases and non-cases was number of patients
with hard calculus treated per week (P¼0.01). The number
of patients treated per day was greater for the CTS cases and
approached statistical significance (P¼0.07).
The crude associations of dental factors with CTSncs
and the associations adjusted for age and BMI are presented
in Table V. Age, BMI, patients treated per day, patients treat-
ed per week, and years worked were univariately associated
with CTSncs. Although, the generic job factors of handling
small objects and use of tools approached significance with
crude analyses, none of these factors were significant when
adjusted for age and BMI (data not shown). None of the non-
work activities were associated with case definitions of CTS.
Since, BMI and percent body fat are collinear, one model was
constructed that included percent body fat, but not BMI,
which after adjustment for age, did not remain significant
(OR: 1.23, 95% CI: 1.00–1.52). Patients per day, age, and
BMI were retained in the final model (OR: 1.73, 95% CI:
1.00–2.99).
DISCUSSION
Musculoskeletal Symptoms
The results of this study are consistent with previous
findings that work-related musculoskeletal symptoms are
common in the dental hygiene profession [Osborn et al.,
1990b; O
¨berg and O
¨berg, 1993; Liss et al., 1995; A
˚kesson
et al., 1999]. Over 90% of dental hygienists experienced at
least one musculoskeletal complaint in the previous 12
months. Since, this study was carried out at a continuing
education program on ergonomics, it is possible that the high
percentage complaining of work-related pain was due to
selection bias. However, a study by A
˚kesson et al. [1999] also
noted that over 90% of dental hygienists had symptoms of
MSD. Comparable to the results of other investigators [Liss
et al., 1995], the present study found the neck as one of the
regions most frequently associated with discomfort. The
current 69% prevalence of wrist and hand symptoms is
comparable to that noted in other studies. A
˚kesson et al.
[1999], using a similar questionnaire, noted a prevalence of
64%, and Lalumandier and McPhee [2001] reported 75.1%
of dental hygienists in their sample had hand problems.
Carpal Tunnel Syndrome and
Case Definitions
The results of this study also reinforce that CTS is a
significant health problem in the dental hygiene population.
The prevalence of CTS for dental hygienists was found to be
only slightly greater than previously reported by other
investigators [Macdonald et al., 1988; Osborn et al., 1990a;
Liss et al., 1995], even when a more stringent case definition,
CTSncs, was used. The results were most comparable to the
large sample study by Macdonald et al. [1988], who found
that 8.7% of dental hygienists had a ‘‘medical history’’ of
CTS. Although, those investigators suggested that the pre-
valence of CTS was possibly an overestimate of true cases,
the results of this study reinforce that a prevalence of 8–9% is
FIGURE1. Flowdiagram of thenumber ofdental hygienistsfittingdifferent case definitionsof carpal tunnelsyndrome.
252 Anton et al.
TAB L E IV. Distribution for Demographic/Anthropometric, Clinical Practice, and Specific Dental Procedure Factors by Case and Non-Case Status forTwo Carpal Tunnel Syndrome Definitions
Classic symp toms and nerve cond uction studi es Classic and no cturnal symp toms
Case mean (SD) Non c ase mean (SD)
P
-value* Case mean (SD) Non c ase mean (SD)
P
-value*
Demographics/Anthropometrics
Age (years) 47.5(5.0) 36.6 (7.5) 0.0004 37.3 (7.3) 37.6 (8.1) 0.95
Education (years) 16.0 (1.8) 15.6 (1.2) 0.87 15.8 (1.4) 15.6 (1.2) 0.61
Weight(kg) 80.7(15.4) 65.0(10.4) 0.0002 73.2(16.3) 64.4(9.1) 0.06
Heig ht (m) 1.64 (0.07) 1.66 (0.06) 0.58 1.66 (0.07) 1.66 (0.06) 0.8 4
Body mass index (kg/m
2
) 29.7 (4.7) 23.4 (3.4) 0.0017 26.0 (5.2) 23.4 (3.5) 0.08
Body fat (%) 35.9 (6.7) 31.0 (5.8) 0.07 3 3.3 (7.4) 30.9 (5.5) 0.16
Clinical practice data
Years worked as DH (years) 21.8 (7.9) 11.8 (8.4) 0.004 12.2 (8.2) 12.8 (9.0) 0.87
Days workedper week (days) 4.1 (1.1) 3.8 (1.0) 0.44 3.9 (1.0) 3.8 (1.0) 0.78
Hours worked per we ek (hr) 33.1 (8.1) 3 0.8 (8.5) 0.39 31.1 (8.7) 31.0 (8.4) 0.8 3
Patientsperweek 48.1(27.5) 36.2(11.9) 0.44 41.9(19.5) 36.3(11.5) 0.45
Patients per day 11.2(4.2) 9.5 (1.9) 0.34 10.6 (2.8) 9.4 (1.9) 0.07
Minutes per patient (min) 49.4 (16.4) 53.4 (17.9) 0.84 48.7(11.7) 52.3 (9.0) 0.12
Specific dental procedures
Hard calculus patients per week 9.6 (9.2) 9.9 (6.0) 0.43 13.6 (8.0) 9.0 (5.2) 0.01
Hours probing per week (hr) 2.5 (2.8) 2.7 (1.7) 0.35 2.7(2.0) 2.7 (1.8) 0.84
Hours scaling per week (hr) 18.7 (7.0) 16.5 (7.0) 0.49 17.0 (6.4) 16.6 (7.2) 0.89
Hours polishing per week(hr) 5.0(3.1) 4.6 (3.0) 0.55 4.5 (3.2) 4.7 (2.9) 0.81
Hours flossingper week (hr) 2.3 (1.4) 1.8 (1.0) 0.24 1.9 (1.2) 1.8 (1.0) 0.91
Hours teaching per week(hr) 2.8(1.7) 2.7 (1.8) 0.55 3.0 (1.8) 2.6 (1.8) 0.26
*
P
-valuebased on WilcoxonRank Sum.
253
a reasonable estimate. In studies using questionnaire method-
ology similar to the present one, both Osborn et al. [1990a]
and Liss et al. [1995] determined that 7.0% had been pre-
viously diagnosed with CTS.
The high prevalence of CTS and other MSD symptoms
among dental hygienists found in this study and reported in
previous research indicates that ergonomic interventions are
important to consider in this occupational group. Interven-
tions could range from ergonomic education to redesign of
the workstation. A recent report indicated that education in
ergonomic principles is lacking in the majority of dental
hygiene programs in the US [Beach and DeBiase, 1998].
This is the first study of dental hygienists that has utilized
both NCS and classic symptoms to establish a case definition
of CTS. Some investigators have suggested that symptom
surveys, including hand diagrams, are adequate to determine
a CTS case in surveillance studies [Franzblau et al., 1993].
Osborn et al. [1990a] reported that a high percentage of their
population of dental hygienists had at least one classic CTS
symptom (63%). In contrast, the present study found that the
prevalence of CTS was 44.2% from a more liberal case
definition based on the symptom survey and hand diagram,
with nocturnal symptoms excluded. It is important to note
that the classic symptom definition used in the present study
was more restrictive than in Osborn et al. [1990a], because at
least two of the four fingers innervated by the median nerve
were required to have symptoms instead of any one finger. In
the present study, prevalence was 23% with the inclusion of
nocturnal symptoms, which is comparable to the findings of
Osborn et al. [1990a] of 21%. In contrast, Liss et al. [1995]
reported a prevalence of only 11%, based on a questionnaire
case definition similar to CTSnoct in the present study. It is
possible that since Liss et al. [1995] included the question,
‘‘Have you ever hurt your wrist/hand in an accident,’’ and
restricted cases lasting longer than seven days, the number of
cases was sufficiently limited.
In the current study, the estimate of the prevalence of
CTS was considerably lower if results from NCS were in-
cluded in the definition. Thus, the prevalence of CTS may be
substantially overestimated if a case is based solely on symp-
toms [Lalumandier and McPhee, 2001], even when a more
restricted definition including nocturnal symptoms is used
[Stevens et al., 1999]. Nevertheless, in the current study, the
prevalence of CTS was found to be approximately twice that
reported for the general population [Atroshi et al., 1999].
Non-Occupational Factors for
Carpal Tunnel Syndrome
Age was a significant non-occupational factor associated
with the CTSncs cases, but not for CTSnoct cases. This
finding concurs with several studies that have shown age to be
an important risk factor for CTS [Letz and Gerr, 1994;
Rempel et al., 1998]. BMI was found to be the only other
significant risk factor for the CTSncs cases that was not work-
related. Other studies report obesity as an important risk
factor for CTS [Nathan et al., 1992a; Werner et al., 1994].
Although, percent body fat could be considered collinear
with BMI, percent body fat was not significantly associated
with CTSncs after adjustment for age. Since, BMI is a stron-
ger risk factor than percent body fat and is easily obtained, it
appears that there is little benefit in taking the time to measure
body composition with near-infrared light interactance in
surveillance studies on CTS. Regardless, it is possible that a
larger sample would have improved the utility of body com-
position testing.
Occupational Factors for Carpal
Tunnel Syndrome
Some studies have reported that non-work related vari-
ables alone are associated with CTS [Nathan et al., 1992b;
Hadler, 1997]. However, the present findings indicate that
occupational factors are also related, even when non-occu-
pational variables are considered in the model and a relatively
restrictive case definition is used. A greater number of pa-
tients seen per day or number seen per week, both measures
representative of exposure frequency, were associated with
the CTSncs cases (Table V). Exposure duration was measu-
red as the number of years worked as a dental hygienist, and
was also significantly associated on univariate measure. How-
ever, after adjustment for age and BMI, the number of years
worked was no longer associated with prevalent CTSncs. A
longitudinal study by A
˚kesson et al. [1999] indicated that
dental personnel had an increased risk of developing mus-
culoskeletal disorders of the wrists or hands with greater
years of practice. In contrast, the intensity of exposure, mea-
sured as the percent time performing various dental hygiene
procedures, was not found to be significant. In general, these
findings suggest that cumulative exposure of all tasks is more
critical than the performance of specific procedures such as
the amount of time spent scaling.
Other studies on dental hygienists have indicated that
cumulative exposure variables are associated with CTS. As in
the present study, Macdonald et al. [1988] and Liss et al.
[1995] both found that classic symptoms of CTS were sig-
nificantly associated with years worked as a DH. However,
Macdonald et al. [1988] did not find the number of patients
treated per day to be significant. Also in contrast to the pre-
sent study, Macdonald et al. [1988] and Liss et al. [1995]
reported that the number of heavy calculus patients seen per
week was significantly associated with CTS. Working on
patients with hard calculus is representative of work intensity
and was significant for the CTSnoct definition used in the
present study. The difference in these studies and the present
one appears to be largely methodological with factors of
sample size, response rate, and case definition, all notable.
254 Anton et al.
The perception that job factors could contribute to work-
related injury was found to be significant only with crude
analyses. For example, the job factors of handling small in-
struments and using tools approached significance for the
CTSncs definition. These factors may show significance with
a larger sample size. Previous studies have also included
symptoms as predictor variables. Osborn et al. [1990a] noted
that finger paresthesias, nocturnal symptoms, and numbness
upon awakening were significant predicators for a diagnosis
of CTS. In the present study, symptom variables were not
entered into a logistic analysis to avoid the circular effect of
the predictor variables and outcome both based on the same
variables.
Previous studies of CTS in dental hygienists have used
vibrometry to assess median nerve dysfunction, a method
purported to be useful for early detection of CTS [Conrad
et al., 1993]. However, several potential problems limit the
usefulness of vibrometry when used for surveillance pur-
poses in epidemiologic studies. First, Merchut et al. [1990]
found that vibration sense varies consider ably throughout the
day. Since methodological difficulties often make it impos-
sible to test all subjects simultaneously, and testing may take
several days in cross-sectional studies, a measure with great
daily variance may not be appropriate. Secondly, the sensi-
tivity of vibrometry is widely variable depending on the
severity of CTS, with values as low as 10% to as high as 87%
reported [Spindler and Dellon, 1982; Szabo et al., 1984].
Additionally, early CTS may be primarily due to demyeli-
nization, which may not influence vibration sense in mild
cases [Werner et al., 1995]. In contrast, consensus criteria on
epidemiologic studies on CTS recommend the use of NCS in
addition to classic symptoms for case definitions [Rempel
et al., 1998]. In fact, several of the studies on vibrometry have
used NCS as the ‘‘gold standard’’ in order to determine sen-
sitivity and specificity [Gerr et al., 1995; Werner et al., 1995].
Limitations
There were several limitations of the present study. Most
importantly was the small sample size. As previously noted,
other risk factors may have been included with a larger
sample. A post hoc, logistic regression power analysis in-
dicated a 51% probability of rejecting the null hypothesis of
no difference between cases and non-cases (PASS 2000,
NCSS, Kaysville, UT). Another drawback of this study was
that testing was conducted at a continuing education program
on ergonomics in dental hygiene practice. Although, this
created the possibility of selection and recall bias, subjects
TAB L E V. Odds Ratios and Confidence Intervals for Demographic/Anthropometric, Clinical Practice, and Specific
Dental Procedure Factors for the CTSncs Case Definition
Crude OR 95%CI Adjust ed OR 95% CI
Demographics/anthropometrics
A g e 1. 2 3 1. 0 8 ^ 1. 3 9 1. 3 8
a
1. 0 9 ^ 1. 74
Education 1.22 0.71^ 2.10
Body mass Index 1.43 1.17 ^1.75 1.58
b
1.18 ^ 2 . 12
Body fat 1.17 0.99^ 1.38 1.23
b
1.00^ 1.52
Clinical practice data
Years worked as dental
hygienist
1.14 1. 0 4 ^ 1. 2 6 1. 0 8
c
0.91 ^ 1.2 8
Days workedper week (days) 1.30 0.58 ^ 2.94
Hours workedper week (hr) 1.04 0.94^ 1.15
Patients per day 1.35 1.01^ 1.80 1.73
c
1.00^ 2.99
Patients per week 1.06 1.01 ^ 1.11 1.09
c
0.99^1.20
Minutes per patient (min) 0.98 0.91^1.05
Specific dental procedures
Hard calculus patients
per week (hr)
0.99 0.88 ^ 1.12
Hours probingper week (hr) 0.93 0.60^ 1.44
Hours scaling per week (hr) 1.05 0.94^ 1.17
Hours polishing per week (hr) 1.04 0.82 ^1.32
Hours flossingper week (hr) 1.63 0.85^ 3.14
Hours teaching per week (hr) 1.03 0.70^ 1.52
a
AdjustedforBMIonly.
b
Adjustedforageonly.
c
AdjustedforageandBMI.
Musculoskeletal Disorders Among Dental Hygienists 255
were not aware that they had the opportunity to undergo NCS,
body composition, or other testing until the day of the pro-
gram. The attendance was typical for dental hygiene con-
tinuing education programs and was representative of dental
hygienists in Eastern Iowa. Additionally, dental hygienists
must regularly accrue continuing education units and this
conference was one of several available conferences. Never-
theless, the sample may limit the generalizability of the study
results. Since, this was a cross-sectional study, no cause and
effect inferences could be made, and a comparison group was
not used to compare exposures.
There were also the inherent limitations of surveys with
possible response bias. A portion of the survey has been stan-
dardized [Kuorinka et al., 1987], and recent evidence in-
dicates that the entire survey has good test-retest reliability
[Rosecrance et al., 2002]. Although, it can be argued that self-
report of exposure has questionable validity [Viikari-Juntura
et al., 1996], it seems reasonable that many dental hygienists
are able to estimate the number of patients they see in a day or
week, especially since their income is often based on these
measures.
Direct assessment of physiological exposure is consid-
ered more accurate [Kilbom, 1994], but there are few studies
that have used these methods with dental hygienists. Bramson
et al. [1998], using forearm electromyography and wrist
goniometry, reported that none of the activities of a dental
hygienist constituted a high ergonomic risk. The investiga-
tors hypothesized that only high forces or extreme wrist
postures contributed to the development of MSD. However,
only the peak root-mean-square electromyography was an-
alyzed in the study, which is solely an indicator of exposure
intensity. The results of the present study suggest that the
accumulation of static work of the hand and wrist muscu-
lature may contribute to the development of CTS or tendo-
nitis. If static work is culpable, alternative electromyographic
data reduction methods may more suitably demonstrate a
relationship. Examples of these direct exposure assessment
methods include the amplitude probability distribution func-
tion [Jonsson, 1982], exposure variation analysis [Mathias-
sen and Winkel, 1991], clustered exposure variation analysis
[Anton, 2002], and gap analysis [Hansson et al., 2000].
Previous studies of other occupations, including dentists,
have indicated that these static activities may be problematic
[O
¨berg et al., 1995; A
˚kesson et al., 1997].
CONCLUSIONS
A large percentage of dental hygienists in this study
reported work-related musculoskeletal disorders, especially
in the wrist/neck, neck, and upper back. The prevalence of
CTS, using a more conservative case definition based on
NCS, was found to be 8.4%, almost 80% lower than a defi-
nition based on symptoms alone. Exposure frequency, as re-
presented by the number of patients treated, was also found to
be significantly associated with prevalent CTSncs. These
findings emphasize the need for ergonomic intervention in
the dental hygiene profession including education, modifica-
tion of instruments, and flexibility in scheduling patients.
ACKNOWLEDGMENT
The authors thank Dr. Trudy Burns for her assistance
with the statistical analysis.
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