prevalence of musculoskeletal symptoms and carpal tunnel syndrome among dental hygienists

AMERICAN JOURNAL OF INDUSTRIAL MEDICINE 42:248–257 (2002)

Prevalence of Musculoskeletal Symptoms andCarpal Tunnel Syndrome Among Dental Hygienists

Dan Anton, PhD, PT, ATC,1� John Rosecrance, PhD, PT, CPE,2 Linda Merlino, MS,3

and Thomas Cook, PhD, PT4

Background Carpal tunnel syndrome (CTS) and other work-related musculoskeletaldisorders (MSDs) are common problems in general industry as well as dental hygiene. Thepurpose of this study is to determine the prevalence of CTS and other MSDs among dentalhygienists. No previous studies involving dental hygienists have combined nerveconduction studies (NCS) and symptoms in their CTS case definitions.Methods Dental hygienists (N¼ 95) completed a symptom and job factors survey, handsymptom diagram, and underwent NCS across the wrist.Results At least one MSD was reported by 93%. Prevalence of CTS was 8.4% utilizing acase definition of symptoms andNCS, but 42% if defined by symptoms alone. Age, BMI, andthe number of patients treated per day were significant factors associated with CTS.Conclusions Dental hygienists are exposed to occupational factors that increase the riskof CTS. A case definition that does not include NCS overestimates CTS prevalence. Am. J.Ind. Med. 42:248–257, 2002. � 2002 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; Oberg and Oberg, 1993; Liss et al.,

1995; Akesson 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 [Oberg and Oberg, 1993; Akesson

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.

1Biomechanics and Ergonomics Facility, Department of Occupational and EnvironmentalHealth, College of Public Health,The University of Iowa, Iowa

2Department of Occupational and Environmental Health,College of Public Health,TheUni-versity of Iowa, Iowa



Dan Anton is working as a Senior Research Assistant.John Rosecrance is working as a Assistant Professor.Linda Merlino is working as 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: [email protected]

Accepted 8 May 2002DOI10.1002/ajim.10110. Published online inWiley InterScience

(www.interscience.wiley.com)

held in static, often awkward postures while working [Oberg

et al., 1995; Akesson 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 (0¼ no problem;

10¼major 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 (0–2¼ none; 3–7¼moderate; 8–10¼severe), 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 intoa multivariatemodel

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 andAnthropometric Variables

Table I shows the demographics of the dental hygienists

in this study (n¼ 95). 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/m2) 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 andJob 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

TABLE I. Demographic/Anthropometric, Clinical Practice, and SpecificDental Procedure Factors for Dental Hygienists (n¼ 95)

Mean (SD) Range

Age (years) 37.6 (7.9) 23^58Education (years) 15.7 (1.2) 12^20Anthropometric dataHeight (m) 1.7 (0.1) 1.5^1.8Weight (kg) 66.4 (11.7) 45^109Bodymass index (kg/m2) 24.0 (4.0) 17^34Body fat (%) 31.4 (6.0) 18^45

Clinical practice dataEmployment as DH (years) 12.7 (8.8) 1^38Daysworkedper week (days) 3.8 (1.0) 1^5.5Hoursworkedper week (hr) 31.0 (8.4) 8^45Patients per week 37.6 (13.8) 8^90Patients per day 9.7 (2.2) 5^18Minutes per patient (min) 51.5 (9.7) 27^69

Specific dental proceduresHard calculus patients perday 2.6 (1.4) 1^6Hard calculus patients per week 9.9 (6.2) 1^30Time probingper week (hr) 2.7 (1.8) 0^9Time scaling per week (hr) 16.7 (7.0) 4^32Time polishing per week (hr) 4.7 (3.0) 0^13Time flossing per week (hr) 1.8 (1.1) 0^5Time teaching per week (hr) 2.7 (1.8) 0^9

TABLE II. Prevalence of Job-Related Conditions During the Past12 MonthsforAll Dental Hygienists From theModified Nordic Questionnaire (N¼ 95)*

Job-relatedache, pain, etc

% ‘‘YES’’ (n)Condition

preventedworkSaw physicianfor condition

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)

*Numberreportingdifferedslightlydependingon location.

TABLE III. Job Factors Rated by Dental Hygienists as Most Likely toContribute to Work-Related Pain (0¼ no problem; 10¼major problem;N¼ 95)

Mean (SD)

Training 1.4 (2.0)Tool use 4.6 (3.1)Work schedule 4.2 (3.0)Heavymaterial handling 1.1 (2.2)Workwhen injured 3.9 (3.4)Environment 2.2 (2.6)Work overhead/away frombody 4.2 (3.3)Work near physical limits 4.3 (3.4)Bend/twist back 6.6 (2.9)Continuous positions 6.9 (2.9)Awkwardpositions 6 (3.1)Insufficient breaks 5.8 (3.2)Grasping small objects 5.9 (3.3)Working fast 4.7 (3.3)Repetition 6.4 (3.2)


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 (P¼ 0.0004), had

a higher BMI (P¼ 0.0017), and higher body fat percentage

(P¼ 0.07). Although, there was a difference in body weight,

there was no significant difference in height between cases

and non-cases (P¼ 0.58). CTSncs cases also saw about two

more patients a day than did non-cases (P¼ 0.34), which

translated into 12 more patients per week (P¼ 0.44). None of

the other clinical practice variables showed significant

differences.

None of the demographic factors were significantly

associated with CTSnoct, but BMI approached significance

(P¼ 0.08) 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 (P¼ 0.01). The number

of patients treated per day was greater for the CTS cases and

approached statistical significance (P¼ 0.07).

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; Oberg and Oberg, 1993; Liss et al., 1995; Akesson

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 Akesson 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. Akesson 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 andCase 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. Flowdiagramofthenumberofdentalhygienistsfittingdifferentcasedefinitionsofcarpal tunnelsyndrome.

252 Anton et al.

TABLE

IV.DistributionforDemographic/Anthropom

etric,ClinicalPractice,andSpecificD

entalProcedureFactorsbyC

aseand

Non-CaseStatusforTwoC

arpalTunnelSyndrom

eDefinitions

Classicsym

ptom

sand

nerveconductionstudies

Classica

ndnocturnalsym

ptom

s

Casemean(SD)

Noncasemean(SD)

P-value*

Casemean(SD)

Noncasemean(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

Height(m)

1.64(0.07

)1.66(0.06)

0.58

1.66(0.07

)1.66(0.06)

0.84

Bodymassindex(kg/m2 )

29.7(4.7)

23.4(3.4)

0.0017

26.0(5.2)

23.4(3.5)

0.08

Bodyfat(%)

35.9(6.7)

31.0(5.8)

0.07

33.3(7.4)

30.9(5.5)

0.16

Clinicalpracticedata

Yearsw

orkedasDH

(years)

21.8(7.9)

11.8(8.4)

0.004

12.2(8.2)

12.8(9.0)

0.87

Daysworkedperweek(days)

4.1(1.1)

3.8(1.0)

0.44

3.9(1.0)

3.8(1.0)

0.78

Hoursw

orkedperweek(hr)

33.1(8.1)

30.8(8.5)

0.39

31.1(8.7)

31.0(8.4)

0.83

Patientsperweek

48.1(27.5)

36.2(11.9)

0.44

41.9(19.5)

36.3(11.5)

0.45

Patientsperday

11.2(4.2)

9.5(1.9)

0.34

10.6(2.8)

9.4(1.9)

0.07

Minutesperpatient(min)

49.4(16.4)

53.4(17.9)

0.84

48.7(11.7)

52.3(9.0)

0.12

Specific

dentalprocedures

Hardcalculuspatientsperweek

9.6(9.2)

9.9(6.0)

0.43

13.6(8.0)

9.0(5.2)

0.01

Hoursprobingperw

eek(hr)

2.5(2.8)

2.7(1.7)

0.35

2.7(2.0)

2.7(1.8)

0.84

Hoursscalingperweek(hr)

18.7(7.0)

16.5(7.0)

0.49

17.0(6.4)

16.6(7.2)

0.89

Hourspolishingperweek(hr)

5.0(3.1)

4.6(3.0)

0.55

4.5(3.2)

4.7(2.9)

0.81

Hoursflossingperweek(hr)

2.3(1.4)

1.8(1.0)

0.24

1.9(1.2)

1.8(1.0)

0.91

Hoursteachingperw

eek(hr)

2.8(1.7)

2.7(1.8)

0.55

3.0(1.8)

2.6(1.8)

0.26

*P-valuebasedonWilcoxonRankSum.

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 forCarpal 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 CarpalTunnel 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 Akesson 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 considerably 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

TABLE V. Odds Ratios and Confidence Intervals for Demographic/Anthropometric, Clinical Practice, and SpecificDental Procedure Factors for the CTSncs Case Definition

Crude OR 95%CI Adjusted OR 95%CI

Demographics/anthropometricsAge 1.23 1.08^1.39 1.38a 1.09^1.74Education 1.22 0.71^2.10Bodymass Index 1.43 1.17^1.75 1.58b 1.18^2.12Body fat 1.17 0.99^1.38 1.23b 1.00^1.52

Clinical practice dataYearsworked as dentalhygienist

1.14 1.04^1.26 1.08c 0.91^1.28

Daysworkedperweek (days) 1.30 0.58^2.94Hoursworkedper week (hr) 1.04 0.94^1.15Patients per day 1.35 1.01^1.80 1.73c 1.00^2.99Patients per week 1.06 1.01^1.11 1.09c 0.99^1.20Minutes per patient (min) 0.98 0.91^1.05

Specific dental proceduresHard calculus patientsper week (hr)

0.99 0.88^1.12

Hours probingper week (hr) 0.93 0.60^1.44Hours scaling per week (hr) 1.05 0.94^1.17Hours polishingperweek (hr) 1.04 0.82^1.32Hours flossing per week (hr) 1.63 0.85^3.14Hours teaching per week (hr) 1.03 0.70^1.52

aAdjustedforBMIonly.bAdjustedforageonly.cAdjustedforageandBMI.


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

[Oberg et al., 1995; Akesson 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.

REFERENCES

Akesson I, Hansson G-A, Balogh I, Moritz U, Skerfving S. 1997.Quantifying work load in neck, shoulders and wrists in female dentists.Int Arch Occup Environ Health 69:461–474.

Akesson I, Johnsson B, Rylander L, Moritz U, Skerfving S. 1999.Musculoskeletal disorders among female dental personnel—Clinicalexamination and a 5-year follow-up study of symptoms. Int Arch OccupEnviron Health 72:395–403.

Anton D. 2002. A comparison of exposure to risk factors in constructiontrades with contrasting prevalence of Carpal Tunnel Syndrome. IowaCity: The University of Iowa. Doctoral dissertation.

Atroshi I, Gummesson C, Johnsson R, Ornstein E, Ranstam J, Rosen I.1999. Prevalence of carpal tunnel syndrome in a general population.JAMA 282:153–158.

Beach JC, DeBiase CB. 1998. Assessment of ergonomic education indental hygiene curricula. J Dent Educ 62:421–425.

Bingham RC, Rosecrance JC, Cook TM. 1996. Prevalence of abnormalmedian nerve conduction in applicants for industrial jobs. Am J Ind Med30:355–361.

Bramson JB, Smith S, Romagnoli G. 1998. Evaluating dental officeergonomic. Risk factors and hazards. J Am Dent Assoc 129:174–183.

Cassady SL, Duffy AM, Meier KM, Venteicher JM, Zimmerman JB.1996. Reliability of near infrared body composition analysis. Cardio-pulm Phys Ther 7:8–12.

Conrad JC, Conrad KJ, Osborn JB. 1993. A short-term, three-yearepidemiological study of median nerve sensitivity in practicing dentalhygienists. J Dent Hyg 67:268–272.

Franzblau A, Werner RA, Valle J, Johnston E. 1993. Workplacesurveillance for carpal tunnel syndrome: A comparison of methods.J Occup Rehab 3:1–14.

Gerr F, Letz R, Harris-Abbott D, Hopkins LC. 1995. Sensitivity andspecificity of vibrometry for detection of carpal tunnel syndrome.J Occup Environ Med 37:1108–1115.

Hadler NM. 1997. Repetitive upper-extremity motions in the workplaceare not hazardous. J Hand Surg 22-A:19–29.

Hansson GA, Nordander C, Asterland P, Ohlsson K, Stromberg U,Skerfving S, Rempel D. 2000. Sensitivity of trapezius electromyo-graphy to differences between work tasks—Influence of gap definitionand normalisation methods. J Electromyogr Kinesiol 10:103–115.

Jonsson B. 1982. Measurement and evaluation of local muscular strainin the shoulder during constrained work. J Human Ergol 11:73–88.

Kilbom A. 1994. Repetitive work of the upper extremity: Part II—Thescientific basis (knowledge base) for the guide. Intl J Indus Ergon14:59–86.

256 Anton et al.

Kuorinka I, Jonsson B, Kilbom A, Vinterberg H, Biering-Sørensen F,Andersson G, Jørgensen K. 1987. Standardised Nordic questionnairesfor the analysis of musculoskeletal symptoms. Appl Ergon 19:233–237.

Lalumandier JA, McPhee SD. 2001. Prevalence and risk factors of handproblems and carpal tunnel syndrome among dental hygienists. J DentHyg 75:130–134.

Leigh JP, Miller TR. 1998. Occupational illnesses within two nationaldata sets. Intl J Occup Environ Health 4:99–113.

Letz R, Gerr F. 1994. Covariates of human peripheral nerve function. I.Nerve conduction velocity and amplitude. Neurotoxicol Teratol 16:95–104.

Liss GM, Jesin E, Kusiak RA, White P. 1995. Musculoskeletal problemsamong Ontario dental hygienists. Am J Ind Med 28:521–540.

Macdonald G, Robertson MM, Erickson JA. 1988. Carpal tunnelsyndrome among California dental hygienists. Dent Hyg 62:322–327.

Mathiassen SE, Winkel J. 1991. Quantifying variation in physical loadusing exposure-vs.-time data. Ergonomics 34:1455–1468.

Merchut MP, Kelly MA, Toleikis SC. 1990. Quantitative sensorythresholds in carpal tunnel syndrome. Electromyogr Clin Neurophysiol30:119–124.

Nathan PA, Keniston RC, Myers LD, Meadows KD. 1992a. Obesity as arisk factor for slowing of sensory conduction of the median nerve inindustry. A cross-sectional and longitudinal study involving 429workers. J Occup Med 34:379–383.

Nathan PA, Keniston RC, Myers LD, Meadows KD. 1992b. Long-itudinal study of median nerve sensory conduction in industry:Relationship to age, gender, hand dominance, occupational hand use,and clinical diagnosis. J Hand Surg [Am] 17:850–857.

Oberg T, Oberg U. 1993. Musculoskeletal complaints in dental hygiene:A survey study from a Swedish county. J Dent Hyg 67:257–261.

Oberg T, Karsznia A, Sandsjo L, Kadefors R. 1995. Work load, fatigue,and pause patterns in clinical dental hygiene. J Dent Hyg 69:223–229.

Osborn JB, Newell KJ, Rudney JD, Stoltenberg JL. 1990a. Carpaltunnel syndrome among Minnesota dental hygienists. J Dent Hyg 64:79–85.

Osborn JB, Newell KJ, Rudney JD, Stoltenberg JL. 1990b. Muscu-loskeletal pain among Minnesota dental hygienists. J Dent Hyg 64:132–138.

Redmond HD, Rivner MH. 1988. False positive electrodiagnostic testsin carpal tunnel syndrome. Muscle Nerve 11:511–517.

Rempel D, Evanoff B, Amadio PC, de Krom M, Franklin G, FranzblauA, Gray R, Gerr F, Hagberg M, Hales T, Katz J, Pransky G. 1998.Consensus criteria for the classification of carpal tunnel syndrome inepidemiologic studies. Am J Public Health 88:1447–1451.

Rosecrance JC, Ketchen KJ, Merlino LA, Anton DC, Cook TM. 2002.Test-retest reliability of a self-administered musculoskeletal symptomand job factors questionnaire used in ergonomics research. Appl OccupEnviron Hyg 17: (in press).

Spindler HA, Dellon AC. 1982. Nerve conduction studies andsensibility testing in carpal tunnel syndrome. J Hand Surg 7A:260–263.

Stevens JC. 1997. AAEM minimonograph: 26: The electrodiagnosis ofcarpal tunnel syndrome. American Association of ElectrodiagnosticMedicine. Muscle Nerve 20:1477–1486.

Stevens JC, Smith BE, Weaver AL, Bosch EP, Deen HG, Jr., Wilkens JA.1999. Symptoms of 100 patients with electromyographically verifiedcarpal tunnel syndrome. Muscle Nerve 22:1448–1456.

Szabo RM, Gelberman RH, Dimick MP. 1984. Sensibility testing inpatients with carpal tunnel syndrome. J Bone Joint Surg 66A:60–64.

Viikari-Juntura E, Rauas S, Martikainen R, Kuosma E, Riihimaki H,Takala EP, Saarenmaa K. 1996. Validity of self-reported physical workload in epidemiologic studies on musculoskeletal disorders. Scand JWork Environ Health 22:251–259.

Werner RA, Albers JW, Franzblau A, Armstrong TJ. 1994. Therelationship between body mass index and the diagnosis of carpal tunnelsyndrome. Muscle Nerve 17:632–636.

Werner RA, Franzblau A, Johnston E. 1995. Comparison of multiplefrequency vibrometry testing and sensory nerve conduction measures inscreening for carpal tunnel syndrome in an industrial setting. Am J PhysMed Rehabil 74:101–106.

Zimmermann CL, Cook TM, Rosecrance JC. 1997. Operatingengineers: Work-related musculoskeletal disorders and the trade. ApplOccup Environ Hyg 12:670–680.


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