environmental medicine neuropathy female dental personnel ... · sonic scalers. the exposure varies...

Occupational and Environmental Medicine 1995;52: 116-123

Neuropathy in female dental personnel exposedto high frequency vibrations

Ingrid Akesson, G6ran Lundborg, Vibeke Horstmann, Staffan Skerfving

AbstractObjective-To evaluate early neuropathyin dental personnel exposed to high fre-quency vibrations.Methods-30 dentists and 30 dentalhygienists who used low and high speedhand pieces and ultrasonic scalers were

studied, and 30 dental assistants and30 medical nurses not exposed to vibra-tion (all women). Vibrotactile sensibility,strength, motor performance, sensori-neural symptoms and signs, and vascularsymptoms in the hands, as well as

mercury concentrations in biologicalsamples and cervicobrachial symptoms,were studied.Results-The two groups exposed tovibration had significant impairments ofvibrotactile sensibility, strength, andmotor performance, as well as more fre-quent sensorineural symptoms. In thedentists there were significant associa-tions between the vibrotactile sensibilityand strength, motor performance, super-ficial sensibility, and sensorineuralsymptoms. There were no associationsbetween these findings and cervico-brachial symptoms, mercury concentra-tions, or smoking. There was no increaseof vascular symptoms of the hands in thegroups exposed to vibration.Conclusion-Dental hygienists and den-tists had a slight neuropathy, which maybe associated with their exposure to highfrequency vibrations, and which may bedetrimental to their work performance.Thus, development of safer equipment isurgent.

Department ofOccupational andEnvironmentalMedicine, UniversityHospital, S-221 85Lund, SwedenI AkessonV HorstmannS SkerfvingDivision ofHandSurgery, Departmentof Orthopedic Surgery,Lund University,General Hospital, S-214 01 Malmd, SwedenG LundborgCorrespondence to:Ingrid Akesson, Departmentof Occupational andEnvironmental Medicine,University Hospital, S-22185 Lund, Sweden.

Accepted 15 September 1994

(Occup Environ Med 1995;52:116-123)

Keywords: vibrations; dentists; sensory and motorfunction

The vibration in many hand held tools orwork pieces may cause a complex of vascular,neurological, and musculoskeletal distur-bances.'-3 The neural effects may occur inde-pendently of the circulatory disturbances.3The pathophysiological mechanisms involvedin the peripheral neural changes are not fullyunderstood.' 3 Dental personnel are oftenexposed to vibrations, particularly high fre-quency hand vibrations of 6000-40 000 Hz,4caused by high speed hand pieces and ultra-sonic scalers. The exposure varies consider-ably among different categories of personnel.

Thus, dentists in particular use high speedhand pieces, whereas in dental hygienists theuse of ultrasonic scalers is particularly fre-quent.

Circulatory disturbances have been sus-pected in dentists.4 Impaired vibrotactile per-ception has been found in dentists56 and indental technicians7 (dental hygienists have notbeen studied). Further, carpal tunnel syn-drom has been reported in dentists8 and dentalhygienists.9

Vibration is not the only possible explana-tion of these neurological findings. Dentalwork involves repeated and monotonousmovements of the hands that may causecarpal tunnel syndrome.'0 Also, dental per-sonnel have a high prevalence of disorders ofthe neck and shoulders," which may be asso-ciated with peripheral symptoms. There isalso exposure to mercury vapour,'2 which maycause disturbances of the peripheral nervoussystem. I

Peripheral vascular and sensorineural disor-ders of the fingers and hands might seriouslyaffect the ability to fulfil the high precisiondemands of dentistry; especially dentists anddental hygienists need extremely good fingermobility and tactile sensitivity. Such work alsorequires good hand strength. Disturbances ofthese functions may make it impossible tocontinue working in these professions.The aim of our study was to investigate,

through a battery of tests, the occupationalrisk of development of neurological and func-tional disturbances of the hands among dentalhygienists (not studied before) and dentists,who use hand held tools with high frequencyvibrations. Associations between the differentoutcome variables were also analysed, as wellas the possible associations with mercuryexposure and musculoskeletal symptoms.

Subjects and methodsSUBJECTSDental personnelThe group studied consisted of dental hygien-ists and dental assistants, 30 in each group,who were all women. Also 30 women dentists(general practitioners) were studied. The den-tists had a mean (range) age of 40 (28-57);duration of employment 13-6 (1-2-30) years:the dental assistants had an age of 37-3(25-57) years; duration of employment 15X1(2-7-39) years: the dental hygienists had anage of 41-5 (28-52) years; duration ofemployment 7-5 (2-8-17-7) years. Also therewas exposure to vibration during the educa-

116

on May 8, 2021 by guest. P

rotected by copyright.http://oem

.bmj.com

/O

ccup Environ M

ed: first published as 10.1136/oem.52.2.116 on 1 F

ebruary 1995. Dow

nloaded from

http://oem.bmj.com/

Neuropathy in female dental personnel exposed to high frequency vibrations

tion period, two years for the dental hygienistsand five years for the dentists.The dentists comprised all the female gen-

eral practitioners in an earlier study of dentalpersonnel in the public dental health servicein the county of Blekinge.'2 The dental assis-tants (also exposed to mercury vapour) weresampled by stratified matching (sex and age ±5 years) from the same population. The den-tal hygienists were the only six in Blekinge"and 24 from the county of Malmohus. Thedental hygienists from Malmohus wereselected to match the total group by age to thedentists. All invited subjects participated.

ControlsThe control group consisted of 30 femalemedical nurses with a mean (range) age of41-7 (26-60) years and duration of employ-ment 8-2 (0 3-28) years from the blood cen-tres at two hospitals and some occupationalhealth service centres in the same area.The work of the control group was physi-

cally light and varied, with demands of skilful-ness in precision, hand mobility, and tactilesensitivity. The controls had no occupationalexposure to vibrations from hand held tools orto mercury. From now on, when not consid-ered separately, dentists and hygienists arereferred to as the exposed groups, dentalassistants and controls as the non-exposedones.

QUESTIONNAIRETwo standardized forms were used in theinterviews of the participants by a physio-therapist and a technician, both experienced.One form contained questions related to

work that concerned working hours a day,years of employment, and use of ultrasonicdevices. Also, smoking habits (current, ciga-rettes a day; ex-smokers; never-smokers;snuff takers), rheumatoid arthritis, and dia-betes were asked for. No diabetic was encoun-tered. One subject (a control) had a history ofrheumatoid arthritis, but no symptoms andsigns at the time of examination. Questionsabout symptoms that related to vibration ofthe arms or hands (sensorineural and vascu-lar) were asked, and the subjects were classi-fied (table 5). Subjective symptoms (such asnightly numbness in the median nerve regionof the hand) related to carpal tunnel syn-drome were asked for, and any surgery forthat syndrome was noted.

Symptoms (ache, pain, discomfort)thought to originate from the musculoskeletalsystem during the past 12 months and theprevious seven days, and sick leave because ofthese during the preceding 12 months weredetermined by a form based on three stan-dardised Nordic questionnaires (general, andspecific for neck and shoulders).l4

TEST OF NEUROMUSCULAR FUNCTIONVibrogramTests were performed by the method ofLundborg et al.'5-'7 The perception thresholdswere recorded at different frequencies ofvibration (8, 16, 31-5, 65, 125, 250, and

500 Hz). The frequencies were automaticallychanged through this frequency range. On thebasis of these perception thresholds, a vibro-gram curve (tactilogram) was obtained.Vibrograms were recorded from the secondand fifth fingers of both hands, more than twohours after the end of exposure to vibration.

Sensibility indexA sensibility index (SI) was used as a measureof sensitivity disturbance, according to amethod described by Lundborg et al.17 Theindex was obtained by dividing the area underthe vibrogram curve by the median of theareas under the control's curves (no ageadjustment).

In some situations, depending upon the rel-evance of a particular issue, an SI-sum wascalculated by addition of the SIs for individualfingers, either for the dominant and non-dom-inant hands separately, or for both handstogether.

Two point discrimination (2PD)Discriminatory tactile sensation was deter-mined as described by Moberg.'819 The testwas performed on the index and little fingersof both hands.

Tactile identification testTests were performed according to a methoddescribed by Sperling and Jonsson.'0Discrimination between six different shapeswas tested blindly at four different sizes.

Muscular strengthDynamometer tests (Martin vigorimeter,Tuttlingen, Germany) were performed in trip-licate (maximal values used). The mediumrubber bulb (diameter 4-5 cm) was used tomeasure the maximum grip strength of eachhand, the small bulb (4 cm) to test key andpinch grip involving the thumb and the indexand the middle fingers. The tests were per-formed in a standardized position with theforearm supported.

Manual performanceThe dominant hand was tested. The subjectshad to pick up and transfer a selected set ofsmall sized dental equipment, 28 pieces(burs, matrix band, grind discs, dowels, etc)with a pair of tweezers from one petri-glasscup to another. The time was measured; thebest of three attempts was used.

MONITORING OF MERCURYMercury concentrations in whole blood(HgB), and plasma (HgP) and mercury andcreatinine in urine (HgU) were determined asalready described.'2

STATISTICSThe perception thresholds of vibrotactilefunction could be obtained only for values upto 150 dB. Thresholds greater than that givecensored readings with 150 dB as therecorded values (mostly at frequencies of125, 250, and 500 Hz). When censoredreadings occurred we have presented medians

117



.bmj.com

/O

ccup Environ M


ebruary 1995. Dow

nloaded from

http://oem.bmj.com/

Akesson, Lundborg, Horstmann, Skerfving

Table 1 Results of vibrograms in the index and little fingers of the dominant and non-dominant hands of dentists, dentalhygienists, dental assistants, and controls; n = 30 in each group

Threshold

Dentists Dental hygienists Dental assistants Controls

Mean or Mean or Mean or Mean orFrequency median >150 dB median >150 dB median >150 dB median >150 dB

Finger Side No (Hz) (dB) (n) (dB) (n) (dB) (n) (dB) (n)

Dominant:Index 8 99-5* 100-3** 99 0** 94-7

16 106-8* 106-7* 105-2 102-531-5 113-7* 111-2 111-8 108-563 112 3 1110 110.0 107-7125 110-0* (0) 107-5 (1) 105-0 (0) 105-0 (0)250 115-0 (0) 115-0 (2) 110-0 (0) 110-0 (0)500 130-0 (5) 130-0 (8) 127-5 (4) 130-0 (1)SI (range) 0-87* (0-34-1-22) 0-89 (0-26-1 19) 0-93t (0-46-1-22) 0 99 (0-73-1-39)

Little 8 98-8 97-5 97 7 95-516 104-8 105-8 103-8 102-331-5 112-3 113-0 109-7 109-563 115-3* 115-0 109-2 110-7125 110-0* (0) 110-0 (1) 105 0 (0) 105-0 (0)250 115-0* (3) 112-5 (4) 107-5 (1) 110-0 (0)500 140-0* (4) 132-5 (7) 130-0 (3) 130-0 (2)SI (range) 0-87* (0-33-1-14) 0-87* (0-26-1-26) 0.99 (0-43-1-43) 0-98 (0-67-1-24)

Non-dominant:Index 8 97 3 97.9 95.3 94-8

16 104 8 105-0 103-5 101-831-5 110-7 110 7 108 0 108 063 110-7 109-7 107-0 107-2125 108-5* (0) 107-6* (0) 103 2 (0) 103-5 (0)250 115-0 (1) 115-0 (0) 105-0 (0) 110-0 (0)500 130-0 (3) 1350 (3) 127-5 (2) 130-0 (0)SI (range) 0-92* (0-49-1-15) 0 93 (0-63-1-32) 1 00 (0-37-1 20) 1-00 (0-70-1-27)

Little 8 97-8* 97 3 95*3 94-116 105-5* 105-2* 103-8 101-431-5 111-7 111-3 109-3 108-863 112-0 111-3 109-5 110.0125 105-0 (0) 110-0* (1) 105-0 (0) 105-0 (0)250 115-0 (1) 115-0* (1) 110-0 (0) 110-0 (0)500 130-0 (4) 132-5 (3) 125-0 (2) 130-0 (0)SI (range) 0-91 (0-46-1-12) 0-89* (0-39-1-20) 0-97 (0-49-1-22) 0-98 (0-63-1-34)

Medians in italics. Tests on dental personnel v controls; when means are given, t tests were used and when medians, two sample ranksum tests: * P < 0-05, ** P < 0 01, *** P < 0 001. Dominant v non-dominant hands were tested by paired t tests;t P < 0 05. SI = sensibility index.

(together with frequencies), arithmetic meansare otherwise given. We tested differencesbetween groups by means of Gehan's test2'(generalised Wilcoxon's two sample rank sumtest) that handles censored readings; t testswere used otherwise.To compare the occurrence of musculo-

skeletal symptoms among dental personnelwith controls, we used a logistic regressionwith adjustment for age. Comparisons of SIbetween groups with or without muscu-loskeletal symptoms in various regions duringthe past seven days, and vascular or sen-sorineural symptoms (graded 0-4), 2PD (2-8mm) were tested by the Wilcoxon's two samplerank sum test. Muscular strength of the handsand manual performance were nearly nor-mally distributed, and comparisons weremade by two sample t tests. Differencesbetween groups, for the proportion of errorsin the tactile discrimination test, were testedby means ofZ tests.We studied associations between continu-

ous variables like age, perception thresholds,SI, manual performance, muscular strength ofthe hands, HgB, HgP and HgU by linearregression. To test individual differences inthreshold values for the dominant hand v thenon-dominant hand, we used paired t tests.Fisher's exact test was used to test for associa-tions between smoking and vascular or sen-sorineural symptoms. The significance levelused was 5%; two tailed tests were used.

ResultsNEUROMUSCULAR FUNCTIONVibrogramThe dentists and dental hygienists had, incomparison with the controls, increased per-ception thresholds for many different frequen-cies (table 1). In the control group, there wasno association between age and the thresholdsfor the various frequencies in the different fin-gers. Thus, no age correction of the vibro-grams of the dental personnel was performed.

In the index finger of the dominant hand,the dentists had significantly increased per-ception thresholds for the frequencies 8, 16,315, and 125 Hz, and for the little finger ofthe same hand for 63, 125, 250, and 500 Hz(table 1). In the non-dominant hand, theindex finger had significantly increasedthresholds for 125 Hz, and the little finger for8 and 16 Hz. Dental hygienists had signifi-cantly increased thresholds for the index fin-ger of the dominant hand for 8 and 16 Hz. Inthe non-dominant hand, the index finger hadsignificantly increased thresholds for 125 Hz,and in the little finger for 16, 125, and250 Hz. Dental assistants differed signifi-cantly from the controls only in the index fin-ger of the dominant hand for 8 Hz.When the vibrograms of the dominant and

the non-dominant hand were compared forthe different frequencies, the dominant handconstantly has higher average perceptionlevels than the other hand, for all the different

118



.bmj.com

/O

ccup Environ M


ebruary 1995. Dow

nloaded from

http://oem.bmj.com/


Table 2 Test of two point discrimination (2PD), tactile identification, manual performance among dentists, dentalhygienists, dental assistants, and controls; n = 30 in each group

Two point discrimination(subjects with 2PD >4 mm)

Tactile identificationDominant Non-dominant (mean error proportion)finger finger

Dominant Non-dominant Manual performancesGroup II V II V hand hand (mean SD)

Dentists 3 4 2 5 0 16 0 19 45-5 (11-2)tDental hygienists 0 3 0 2 0-20 0-21 42-4 (9 0)tDental assistants 3 2 0 2 0-20 0-23 38-3 (5.6)**Controls 0 2 0 3 0-20 0-18 43-6 (9-4)

Dental personnel groups v controls (t test; * P < 0 05, ** P < 0 01, *** P < 0-001); dentists and dental hygienists v dental assistants:tP < 0-05.

Table 3 Test of muscular hand strength among dentists, dental hygienists, dental assistants, and controls; n = 30 in eachgroup

Muscular strength (bar: mean (SD))

Full hand grip Pinch grip Key grip

Dominant Non-dominant Dominant Non-dominant Dominant Non-dominant

Dentists 0-86***t (0 25) 0 83***t (0 20) 0-61 (0 11) 0 58 (0 09) 0-51** (0 10) 0-50**t (0 09)Dental hygienists 0 87***t (0-17) 0.91* (0 20) 0.57* (0 08) 0 59 (0-08) 0-51* (0 11) 0-49***t (0 09)Dental assistants 0 97** (0-17) 0Q95* (0 20) 0-62 (0.05) 0-61 (0.06) 0 54 (0 08) 0 54 (0-07)Controls 1 11 (0-18) 1-03 (0-19) 0-62 (0 08) 0-61 (0-10) 0 57 (0-06) 0 56 (0 06)

Dental personnel groups v controls (t test; * P < 0 05, ** P < 0 01, *** P < 0-001); dentists and dental hygienists v dental assistants:tP < 0 05; 1 bar = 100 kPa.

groups. Interestingly, the differences, aremore apparent for both the dentists and thedental hygienists, and for all frequencies, thanfor the dental assistants and the controls,although not significantly different. For thecontrols the differences are minor.

Sensibility indexThere were no significant differences in SIs foreither hand between the different smokinggroups with and without exposure to vibration.

For the dentists there was an impaired SIfor all fingers tested on the dominant hand,and for the index finger on the non-dominantone, compared with the controls (table 1).Among the dental hygienists, an impairmentwas found for the little fingers of both hands.Also among the dentists, there was a slight,but significant decrease of SI in the dominanthand (sum of both fingers) with increasingduration of exposure. One year of exposurewas associated with an average SI decrease of0 018 (P = 00 17). No such significant associ-ation was found in the non-dominant hand,nor in any of the hygienists' hands. There wasa tendency for the dominant hand to havelower SI than the non-dominant one, but thedifferences were not significant for the den-tists or the dental hygienists.

Two point discriminationThere were no significant differences betweenthe groups (table 2). For the dentists therewere significant associations between a high2PD (>4 mm) and a low SI (for the indexfinger of the dominant hand average SI = 0-60at >4 mm v 090 at <4 mm, P = 0049; andfor the little fingers; dominant hand 070 v0-89, P = 0 035; non-dominant 0-69 v 0-95,P = 0-0022; for the non-dominant index fin-ger there was a non-significant trend). Theother subgroups showed no significant effects.

Tactile identification testThere were no significant differences betweenthe groups (table 2).

Muscular strengthMuscular strength was significantly loweramong the dentists and the hygienists thanamong dental assistants, who in turn hadlower values than the controls (table 3). Therewere significant associations between the fullhand grip and the SI of the little finger of thedominant hand within the dentist group (P =

0014), and with SI of the index finger of thenon-dominant hand in the hygienists (P =

0041). Also, among the dentists, the pinchgrip was significantly associated with the SIfor the index finger of the dominant hand(P = 0025). The other subgroups had no sig-nificant associations. No such significant asso-ciation was seen for the key grip.

Manual performanceThe dentists, hygienists, and controls did notdiffer significantly from each other, whereasthe dental assistants had a significantly betterperformance (table 2). For the dentists, ahigher SI for the index finger of the dominanthand displayed a borderline association with abetter performance test (P = 0 054); an SIincrease of 0-1 corresponded to an averagedecrease of the manual performance test oftwo seconds; total test time was about40 seconds.

SYMPTOMSMusculoskeletal symptomsThe dentists and the dental hygienists had, incomparison with the controls, higher frequen-cies of ache, pain, or discomfort within thepast seven days in the neck and upper limbs(table 4). Symptoms in the past 12 monthsshowed the same general pattern (not in

119



.bmj.com

/O

ccup Environ M


ebruary 1995. Dow

nloaded from

http://oem.bmj.com/


Table 4 Frequencies of musculoskeletal symptoms during the previous seven days among dentists, dental hygienists,dental assistants, and controls: n = 30 in each group

Muscuoskeletal symptoms

Hands or Upper Lower Feet orGroup Neck Shoulders Elbows wrists back back Hips Knees ankles

Dentists 11 14** 3 9* 5 1 0 3 2 3Dental hygienists 15* 12* 6** 10* 6 3 2 2 0Dental assistants 4 8 0 0 4 6 1 1 0Controls 6 5 0 3 1 4 2 2 2

Dental personnel v controls with a logistic regression model, with adjustment for age, or Z test: *P < 0 05, ** P < 0 01.

table). There were no significant associationsbetween reported symptoms of the neck,shoulders, or elbows in the past seven daysand the corresponding SI-sums for the testedfingers in the entire group or in any of thesubgroups. The shoulders and elbows of thedominant side and the non-dominant sidewere tested separately.Among the dentists the average SI-sum was

only slightly lower among those with necksymptoms than in those without (3-43 v 3-63,NS); within the hygienist group those withneck symptoms had a slightly higher SI-sumthan those without (3-63 v 3-54; NS). Thesame pattern was noted for symptoms of theshoulders and elbows (NS).

There were no significant associationsbetween symptoms of the neck or shouldersand grip strength, manual performance, or

2PD.Carpal tunnel syndrome was found in only

one dentist and one dental hygienist (both inthe dominant hand). Both had had surgery,and the dental hygienist had a relatively highSI (0-83), the still symptomatic dentist a lowone (0-53) in the relevant index finger. In thedentists the dominant hand showed a signifi-cant association between hand symptoms dur-ing the past seven days and the SI-sum for thecorresponding side (1-41 v 1-85, P = 0-0015).The same association was found for the non-dominant hand (1-43 v 1-90, P = 0-013).Among the dental hygienists there was thesame trend (NS). In the non-exposed groupsthere was no such association. In the dentists,there were some significant associationsbetween hand symptoms and grip strength(dominant side, P = 0-0083; non-dominant,P = 0-0050), and 2PD (dominant side,P = 0-019).

Vascular symptomsVascular symptoms were found in 19 women(table 5). There were no significant associa-

tions between smoking and vascular symp-toms. No significant differences in the preva-lence of vascular symptoms between thesubgroups were found. There were no signifi-cant associations between duration of expo-sure to vibration and vascular symptoms.

Vascular symptoms showed a significantassociation with a low SI-sum (all four fin-gers) among the dental assistants (with symp-toms, SI-sum 3-28 (n = 6); withoutsymptoms, 4-05 (n = 24); P = 0-0 17), but notin the controls, or the groups exposed tovibration.

Sensorineural symptomsEighteen subjects had sensorineural symp-toms, 27% among both the dentists andhygienists, 3% in both the dental assistantsand controls (table 5). There were no signifi-cant associations between age and smokingand occurrence of sensorineural symptoms.Among the dentists, however, there was anassociation between increased age and sen-sorineural symptoms (P = 0-048), not presentin any other subgroup.A combination of persistent numbness,

reduced manual dexterity, and reduced grip(stage 4) was found in seven dentists and fivedental hygienists, but in neither the dentalassistants nor the controls (table 5). Both den-tists and hygienists differed significantly fromthe unexposed groups.Among the dentists those with any sen-

sorineural symptoms showed an average SI-sum for both hands of 3-19 (n = 8), and thosewithout symptoms 3-69 (n = 22; P = 0-024).There was no significant difference in any ofthe other two groups.

In the dentists only there was a significantassociation between musculoskeletal symp-toms of the hands during the past seven daysand sensorineural symptoms (P = 0-0031).Thus nine dentists had musculoskeletalsymptoms, and six of those had sensorineural

Table 5 Frequencies of vascular and sensorineural symptoms in arms or hands among dentists, dental hygienists, dentalassistants, and controls; n = 30 in each group

Symptoms

Vascular (stage) Sensorial stage§Group 0 1 2 3 4 0 1 2 3 4

Dentists 24 4 1 1 0 22**t 0 1 0 7Dental hygienists 26 2 0 2 0 22**t 2 0 1 5Dental assistants 24 5 0 0 1 29 0 1 0 0Controls 27 2 1 0 0 29 0 1 0 0

Dental personnel v controls: ** P < 0-01; dentists and hygienists v dental nurses: tP < 0-01, by the Wilcoxon's two sample rank sumtest.tStage: 0 = no symptoms, 1 = episodic blanching of one or more finger tips, 2 = episodic blanching of one or more fingers for< 15 min, mostly during winter, 3 = attacks of blanching affecting most or all fingers >15 min, even during summer, 4 = asin stage 3, symptoms every day, with trophic skin changes in the finger tips.§Stage: 0 = no symptoms, 1 = with (tingling)paraesthesia during and shortly after exposure to vibrations, 2 = as in stage 1, with (tingling) paraesthesia at night, 3 = with (tingling)paraesthesia or numbness most of the time, 4 = persistent numbness, reduced manual dexterity and grip function.

120



.bmj.com

/O

ccup Environ M


ebruary 1995. Dow

nloaded from

http://oem.bmj.com/


Table 6 Mercury concentrations (mean (SD; range)) in urine (HgU), plasma (HgP), and blood (HgB) for dentists,dental hygienists, dental assistants, and controls

Mercury concentrations

HgU HgB HgP

Group n (ugig creatinine)f n (p4g/l)t n (u1gll)tDentists 29 3-4 (2-1; 1-1 1) 30 3-5 (1-2; 1-4-6-5) 30 1-5 (0-8;0-6-42)Dental hygienists 27 3-6 (1-9; 0 72-8 0) 29 2-9 (0-9; 1-24-9) 29 2-9 (0 9; 0 5-2 7)Dental assistants 30 5-5 (3-8; 1-3-18) 30 3-4 (1-3; 1-4-6-5) 30 2-0 (1-0; 0-8-5 5)Referents 28 3 5 (2-3; 0-76-10) 29 2-9 (1-5; 0 70-78) 29 1-6 (1 0; 04-5 2)

Dental personnel group v controls: P < 0 05 (t test).tI pg/g creatinine = 0-56 nmol/pmol creatinine; t 1 pg/l = 5 0 nmol/l.

symptoms as well. Among the remaining 21dentists without musculoskeletal symptoms,only two had sensorineural symptoms.

MONITORING OF MERCURYOn the whole, there was a significant increaseofHgB with age (P = 0 0 12); neither HgP nor

HgU showed such a trend (not in table).None of the subgroups separately showed a

significant increase of HgB with age. Only U-Hg in dental assistants was significantly differ-ent (higher) from the controls (table 6).

Neither vibrograms (sum of all four SIs inboth hands in each person), nor 2PD, tactilediscrimination test (hands separately), manualperformance (dominant hand), or strength(hands separately) showed any significantassociations with HgB, HgP or HgU.

DiscussionThe most interesting findings in our study are

the increased vibrotactile perception thresh-olds (at low and high frequencies), thedecreased strength, particularly in the domi-nant hand, and the impairment in the manualperformance test, for the groups exposed tovibration. The group with the longest dura-tion of exposure-the dentists-showed more

frequent and obvious sensorineural symp-

toms, impairment of discriminatory tactilesensation, and associations between the vibro-tactile sensibility and grip strength, motorperformance, 2PD, and the occurrence ofsensorineural and other symptoms of thehands.The study was a cross sectional one. Thus,

the possibility of a healthy worker selectionmust be considered: it is possible that some

dentists and hygienists may have left the pro-fessions because of musculoskeletal or neuro-

logical symptoms.The controls without vibration or exposure

to mercury were selected on the basis of simi-lar socioeconomic conditions and varied workpostures. It turned out, however, that an

important fraction of the controls had workwith relatively high workload on the hands,which may have caused an underestimate ofthe risk of hand symptoms in the othergroups.

All methods but the mercury determina-tions had a subjective component, which mayhave made it impossible to observe minoreffects. The reproducibility of the vibrogramperformance was good. The vibrograms, how-ever, at the highest frequencies (125, 250, and

500 Hz) sometimes reached the maximumlevel of 150 dB, above which it was not techni-cally possible to record. Thus, there is a riskthat vibrotactile neuropathies are underesti-mated in such cases.The sensorineural and vascular symptoms

were scored according to schemes routinelyused for a long time at the department, andwhich, when used in parallel with the stagingssuggested by Bramner et al and Gemne et al ina follow up study of the present groups,2223were found to give very similar results(unpublished data). The screening question-naires for supposed musculoskeletal symp-toms of the hands may also recordneuropathies and circulatory disturbances.

In the dentists, there was a decrease ofvibrotactile perception with increasing dura-tion of vibration exposure. We did not adjustfor age. In some other studies, there was anage effect,'72425 mainly at high frequencies,26but the present effect associated with vibra-tion occurred mainly at low ones. We did notsee an age effect in the groups without expo-sure to vibration, probably because the ageeffect is less pronounced in women than inmen (due to occupational exposure and othervibrational exposure), and occurs mainly athigher ages.

There were impairments of vibrotactile per-ception in both the dominant and-althoughless pronounced-non-dominant hands. In thedentists, however, the effect in the non-domi-nant hand may be due to firmly holdingcrowns, stabilisation splints, and removableorthodontic appliances with this hand, and byusing vibrating tools during adjustments beforeinstallation. A similar pattern has beenrecorded in dental technicians.7 The presenteffect in the little finger of the dominant handmay be due to exposure to vibration, as a gripthat involves all five fingers is often used duringwork with low speed hand pieces and ultra-sonic devices in the lingual area of the lowerjaw.Our results are in accordance with earlier

findings of vibrotactile perceptual distur-bances in small studies of dentists"5 andphysiotherapists.2' The physiotherapists useultrasonic therapeutic devices, although withdifferent energy characteristics than the pre-sent ultrasonic scalers.We found that the grip forces were lower

among the groups exposed to vibration.Impairment was noted in the full hand andkey grips. Decreased muscle strength has pre-viously been found in lumberjacks exposed to

121



.bmj.com

/O

ccup Environ M


ebruary 1995. Dow

nloaded from

http://oem.bmj.com/


vibration, particularly in those subjectivelymost affected by vibration disease.28 29Workers exposed to vibrations often complainof decreased muscular force.29 It seems thatthis is a constant phenomenon, not only pre-sent during work.28 The impaired musclefunction in the full hand grip, which alsoengages the local muscles of the hand, may bebased on an injury to muscle tissue, nerve tis-sue, or a combination of both induced byvibration. Experimental studies have shownthat vibration may damage nerve fibres30 31and infraneural microvessels32 as well as musclefibres.33The relation between impaired SI and

decreased muscle strength in the full handgrip may support the theory that impairedmuscle function is secondary to sensibility dis-turbance. One cannot exclude, however, adirect injury to hand muscles induced byvibration. Recent experimental studies haveshown degenerative phenomena of variousdegrees in muscles in the feet of rats exposed tovibration.33

There is a demand for manual dexterityamong dental personnel. Thus it is reasonableto compare the results of the manual perfor-mance test mainly within these three groups.The dental assistants had a better manual per-formance than the other two groups. Thismight be due to a deterioration of the manualperformance induced by vibration in theexposed groups, which is supported by theassociation between SI and manual perfor-mance. The difference is probably not due tomusculoskeletal factors as there was no asso-ciation between such symptoms and manualperformance.Our results show no significant differences

in the 2PD tests between the groups. Thiscorresponds with the work of Lundborget al.'5 16 Changes in 2PD are known to occuronly at an advanced stage in a nerve lesion,and usually involve degeneration and regener-ation of fibres. For the dentists, there was anassociation between a low SI and high 2PD.The pathophysiological mechanisms involvedin peripheral neural changes induced by vibra-tion are not fully understood.' Damageinduced by vibration has been seen in themicrovascular structures of the nerves,32 aswell as in the nerve fibres.303' 34 High fre-quency vibrations from hand held tools maydamage the mechanoreceptive units.35

Only two cases of carpal tunnel syndromewere encountered in a dentist as well as in ahygienist who had normal vibrograms. Thus,carpal tunnel syndrome induced by work wasnot the cause of the sensory disturbances.There was no association between the expo-sure to vibration and gross vascular symp-toms, which is in accordance with earlierfindings.4The work of the dental personnel includes

static muscle load with rotation and flexion ofthe cervical spine and flexion of the elbow.Also, some operations involve repetitive force-ful hand grips. Accordingly, many hygienistsand dentists reported musculoskeletal symp-toms from the neck, shoulders, arms, and

hands. Ekenvall et al suggested that muscu-loskeletal load might give rise to neuropathy.This is not supported by our studies. Therewere no associations between symptoms ofthe neck, shoulders, or arms and a low SI,high 2PD, sensorineural symptoms, reducedstrength, or manual performance. Symptoms,in the hands of mainly the dentists were asso-ciated with a low SI, sensorineural symptoms,high 2PD, and reduced strength. No suchassociations were seen among the dental assis-tants or controls, although a relatively highpercentage of the controls had symptoms ofthe hands. The dental assistants did not showany signs of neuropathy in the vibrograms forfrequencies above 8 Hz, and did not report anincreased frequency of sensorineural symp-toms. Detailed clinical examination of ourgroups, however, did not show different fre-quencies of musculoskeletal symptoms ordiagnostic patterns in dental assistants anddentists (unpublished data). Hence, it is likelythat the main part of the subjective and objec-tive hand phenomena were caused by theexposure to vibration, and not by muscu-loskeletal load associated with work.

There were no associations between mer-cury concentrations in blood cells, bloodplasma, or urine and the functional tests.Effects of mercury on the peripheral nervoussystem occur only at higher exposures.36Further, the dental assistants had the highestconcentrations of mercury, but showed littledifference in the functional parameters.The decrease of strength was rather severe,

and the impairment in tactile sensitivity andperformance, although not great, was stillnotable. They constitute a serious problemamong dentists and dental hygienists as theseprofessions require excellent hand function-precision, sensibility, fine manipulation, andgrip force. The dentists were more affectedthan the hygienists. This may be partlybecause the dentists had longer durations ofexposure. Also, the dentists use mostly highspeed and low speed hand pieces, whereas thedental hygienists handle ultrasonic scalers andlow speed hand pieces to a greater extent. Theproblem is particularly serious, as the dura-tion of exposure every day is limited. Dentistsand hygienists use vibrating tools for onlyabout 75 minutes a day.37 This is in accor-dance with recordings made of the presenthygienists (unpublished data).

It is obvious that dental devices with lowerexposure to vibration must be developed. Adrawback is that too little is known about theconduction of energy from the instruments tothe hand, and about how to reduce this. Onesimple measure, that can be applied to alreadyexisting devices, is to teach the personnel touse only minimum grip force, as this wouldreduce the transmitted energy.'8

These studies were supported by grants from the SwedishWork Environment Fund and the Medical Faculty, LundUniversity. Support was also given by the County Council ofBlekinge and the County Council of Malmohus. Valuableassistance was given by Ms Ingrid Hallberg, Dr Carl-GunnarLingstrom, Dr Kjell Martensson, Ms Vivi Svensson, MrAnders Ekholm, Ms Gudrun Persson, Dr Andreis Schutz, andMs Nancy Simonsson.

122



.bmj.com

/O

ccup Environ M


ebruary 1995. Dow

nloaded from

http://oem.bmj.com/

123Neuropathy in female dental personnel exposed to high frequency vibrations

1 National Institute for Occupational Safety and Health.Criteria for a recommended standard. Occupational exposureto hand-arm vibration. Cincinnati, OH: US Departmentof Health and Human Services. Public Health Service,Centers for Disease Control, Division of StandardsDevelopment and Technology Transfer, 1989. (DHHS(NIOSH) Publ No 89-106).

2 Pyykko I. Clinical aspects of the hand-arm vibration syn-drome. A review. Scand _J Work Environ Health1986;12:439-47.

3 Lundstrom R. Hand-arm vibrationer. Kunskapslaget forbedomning av skaderisker. Hand-arm vibration. Currentknowledge for risk evaluation. Uppsala: Ord and FormAB, 1989. (In Swedish).

4 Andersson R, Bergstrom B, Dandanell R, Engstrom K,Grave B, Magnusson L, et al. Underswkning av vibrations-miljon och skaderisker vid arbete med tandldkarborrar medhoga varvtal och ultraljudsverktyg. Study of the vibration-exposure and the occupational risks in work with dental drillswith high acceleration levels and ultrasonic devices.Link6ping: Saab-Scania TH 1983;64:1-15. (InSwedish).

5 Lundstrom R, Lindmark A. Effects of local vibration ontactile perception in the hands of dentists. Journal OfLow Frequency Noise and Vibration 1982;1: 1-11.

6 Ekenvall L, Nilsson B, Falconer C. Sensory perception inthe hands of dentists. Scand J Work Environ Health1990;16:334-9.

7 Hjortsberg U, Rosen I, 0rbsek P. Lundborg G, Balogh I.Finger receptor dysfunction in dental techniciansexposed to high-frequency vibration. Scand _J WorkEnviron Health 1989;15:339-44.

8 Shapiro I, Sumner A, Spitz L, Cornblath D, Uzzel B, StiipI, et al. Neurophysiological and neuropsychologicalfunction in mercury-exposed dentists. Lancet 1982;i:1 147-50.

9 MacDonald G, Robertson M, Erickson J. Carpal tunnelsyndrome among California dental hygienists. DentalHygiene 1988:322-8.

10 Wieslander G, Norback D, Gothe CJ, Juhlin L. Carpaltunnel syndrome (CTS) and exposure to vibration,repetitive wrist movements and heavy manual work: acase-referent study. BrJ7 Ind Med 1986;46:43-7.

11 Rundcrantz B-L, Johnsson B, Moritz U. Cervical pain anddiscomfort among dentists. Epidemiological, clinical,and therapeutic aspects. Swed Dent_ 1990;14:71-80.

12 Akesson I, Schutz A, Attewell R, Skerfving S, Glantz P-O.Mercury and selenium status in dental personnel-impact of amalgam work and fillings. Arch EnvironHealth 1991;46:102-9.

13 Albers JW, Cavender GD, Levine SD, Langolf GD.Asymptomatic sensorimotor polyneuropathy in workersexposed to elemental mercury. Neurology 1982;32:1168-74.

14 Kuorinka I, Jonsson B, Kilbom A, Vinterberg H, Biering-Sorensen F, Andersson G, et al. Standardised Nordicquestionnaires for the analysis of musculoskeletal symp-toms. Appl Ergon 1987;18:233-7.

15 Lundborg G, Sollerman C, Stromberg T, Pyykko I, RosenB. A new principle for assessing vibrotactile sense invibration-induced neuropathy. Scand J Work EnvironHealth 1987;13:375-9.

16 Lundborg G, Lie-Stenstrom AK, Sollerman C, StrombergT, Pyykko I. Digital vibrogram: a new diagnostic tool forsensory testing in compression neuropathy. J7 Hand Surg1986;5:693-9.

17 Lundborg G, Dahlin LB, Lundstrom R, Necking LE,Stromberg T. Vibrotactile function of the hand in com-pression and vibration-induced neuropathy. Sensibilityindex-a new measure. Scand J Plast Reconstr Surg HandSurg 1992;26:275-9.

18 Moberg E. Objective methods for determining the func-tional value of sensibility of the hand. J Bone joint Surg

Br 1958;40:454-76.19 Moberg E. Criticism and study of methods for examining

sensibility in the hand. Neurology 1962;12:8-19.20 Sperling L, Jonsson B. Funktionstestning av arbets- och

skyddshandskar. Test of hand function at work with pro-tective gloves. In: Sperling L, Jonsson B, Holmer I, eds.Handfunktion och handskydd vid arbete med handskar.Hand function and hand protection at work with gloves.Solna: Arbetarskyddsverket. Arbete och Halsa 1983;30:65-76. (In Swedish).

21 Gehan EA. A generalized Wilcoxon test for comparingarbitrarily singly-censored samples. Biometrika 1965;52:203-23.

22 Brammer AJ, Taylor W, Lundborg G. Sensorineural stagesof the hand-arm vibration syndrome. Scand J WorkEnviron Health 1987;13:279-83.

23 Gemne G, Pyykko I, Taylor W, Pelmear PL. TheStockholm workshop scale for the classification of cold-induced Raynaud's phenomenon in the hand-arm vibra-tion syndrome (revision of the Taylor-Pelmear scale).ScandJ3 Work Environ Health 1987;13:275-8.

24 Goff GD. Vibration perception in normal man and med-ical patients. J Neurol Neurosurg Psychiatry 1965;28:503-9.

25 Verrillo R. Comparison of vibrotactile threshold andsuprathreshold responses in men and women. PerceptPsychophys 1979;26:20-4.

26 Lundstrom R, Stromberg T, Lundborg G. Vibrotactileperception threshold measurements for diagnosis of sen-sory neuropathy. Int Arch Occup Environ Health1992;64:201-7.

27 Lundstrom R. Effects of local vibration transmitted fromultrasonic devices on vibrotactile perception in the handsof therapists. Ergonomics 1985;28:793-803.

28 Farkkila M. Grip force in vibration disease. Scand Jf WorkEnviron Health 1978;4:159-66.

29 Farkkila M, Aatola S, Starck J, Pyykko, Korhonen 0.Vibration-induced neuropathy among forestry workers.Acta Neurol Scand 1985;71:221-5.

30 Ho ST, Yu HS. Ultrastructural changes of the peripheralnerve induced by vibration: an experimental study. Br JInd Med 1989;46:157-64.

31 Lundborg G, Dahlin LB, Danielsen N, Kanje M.Vibration exposure and nerve fibre damage. Jf Hand SurgAm 1990;15:346-51.

32 Lundborg G, Dahlin LB, Danielsen N, Hansson HA,Necking LE, Pyykko I. Intraneural edema followingexposure to vibration. Scand J Work Environ Health1987;13:326-9.

33 Necking L-E, Dahlin LB, Friden J, Lundborg G,Lundstrom R, Thornell LE. Vibration-induced muscleinjury. An experimental model and preliminary findings.YHand Surg Br 1992;17:270-4.

34 Takeuchi T, Takeya M, Imanishi H. Ultrastructuralchanges in peripheral nerves of the fingers of three vibra-tion-exposed persons with Raynaud's phenomenon.ScandJ Work Environ Health 1988;14:31-5.

35 Gemne G, Lundstrom R, Hansson JE. Disorders inducedby work with hand-held vibrating tools. A review of cur-rent knowledge for criteria documentation. Solna:National Institute of Occupational Health. Arbete ochHalsa 1993;6:9-10.

36 Clarkson TW, Hursh JB, Sager PR, Syversen TLM.Mercury. In: Biological monitoring of toxic metals. NewYork; Plenum Press, 1988;199-246.

37 Andersson R. Exponeringstider vid anvandning av vibrerandeutrustning inom tandvarden. Exposure time in occupationalexposure to hand-held vibrating tools in dentistry.Link6ping: Landstinget i Ostergotlands lin. Landstings-halsan i Ostergotland, 1986;7:1-4. (In Swedish)

38 Burstrom L, Lundstrom R. Mechanical energy absorptionin human hand-arm exposed to sinusoidal vibration. IntArch Occup Environ Health 1988;61:213-6. on M

ay 8, 2021 by guest. Protected by copyright.

http://oem.bm

j.com/

Occup E

nviron Med: first published as 10.1136/oem

.52.2.116 on 1 February 1995. D

ownloaded from

http://oem.bmj.com/

environmental medicine neuropathy female dental personnel ... · sonic scalers. the exposure varies...

Documents