Download THE EFFECT OF NOISE-INDUCED HEARING LOSS ON DENTISTS

Volume 7
Number 1
Summer l371
August i :)93
.\-leUical loumal or the
hlamic Republic or Iran
THE EFFECT OF NOISE-INDUCED HEARING LOSS
ON DENTISTS
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PARVIN NASSIRI, Ph.D., FARIDEH GOLBABAI, M.S.P.H.,
AND
MAHMOUD MAHMOUD!, Ph.D.
FrolJl lite DepartlJlent of Occupational Health, School ofPublic Health, T ehrall University of Medical
Sciences, Tehran, Islamic Republic offrail.
ABSTRACT
This paper presents noise problems associated with the use of air-turbine drills
in dental practice. Two hundred and fifty dentists (male and female) were randomly
selected from the faculty of dentistry as well as the dentists who worked private in
Tehran. The results indicated that the mean value of sound pressure level produced
by the high-speed drills was 69.1 db. Most of the energy from the drills lied in the high
frequency range, 6000- 8000 Hertz. Audiological evaluations showed that the loss
of hearing in all age groups and years in dental practice lie in 6000 Hertz which has
a positive correlation with the value of sound pressure level in this frequency. The
hearing loss in the right ear of women was slightly higher than the left one, while this
was not true in men. The hearing loss in the female group was greater than in male
group.
MJIRI,
Vol.
7,
No.2, 83-86, 1993.
Keywords: Dentists,air-turbine drills, noise,heari ng loss,audiometry
INTRODUCTION
normal
age-adjusted
p o p u l a t i o n.' An
important
corroborative study was tllatofWard and Holmberg.' Coles
It is a long time that dentists have had an occupational
et al. concluded that the auditory hazard was very slightand
interest in the subject of noise-induced hearing loss (N1HL).
preventive
This carne with the advent of tlte high-speed turbine dental
Akbarkhanzadeh reported that altllOugh the hearing damage
measures
were
also
recommended,l
drill, which was immediately notable forthe high level and
caused by high-speed drill was slight in 12 dental surgeons
unpleasent high-frequency noise that it emitted.' This soon
using these drills for a number of years, tlle possibility of
led to the speculation that it might be a hazard to the
hazardous effects at least for susceptible ears was not
hearing of dentists using this drill and to tllC advice on
excluded.' Wilson et al. have recently studied the hearing
preventive measures including periodic audiometric
dmnage risk mnong dent ists, and the extent of communication
exmnination.M
interference. The noise levels during dental procedure
The ftrst conclusive evidence that damage to hearing
result in an articulation index of 0.27 to 0.37 and it was
can result from exposure to this noise was published by
concluded that hearing damage risk \Vas slight runong
Taylor and co-workers in 1965 in a carefully controlled
dentists using modern equipment.1O
study of dentists.' These workers also comment on tlle
It has also been estimated that most turbine users are
relatively greater importance of other noise exposures,
exposed to high - speed handpieces ranging from total on
current or previous, nOk�bly the ftring of rifles or shotguns.
times of 12 minutes or 12-45 minutes to 10 minutes per
Forman-France and associates. however. studied 70
hour.'lt is estimated that the sound energy contribution of
dentists from eight specialties and found no significant
a typical dental practice is about 8% of the dentists' average
decrease in hearing thresholds when compared with a
24-hour noise exposure.IO
83
Noise-Induced Hearing Loss
The purpose of Ihe presenl sludy was 10 oblain an up­
of the nature and extent of possible
to-datt.: (lI;sessmcnl
hearing in this country.
o.
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MATERIALS AND METHODS
2,0 denlisl', 60 women 'Uld 190 men,from differelll
2.
spccialtil!s wert.! randomly selected from the faculty of
denlisiry and privale clinics in Tehran. All Ihe subjecls
rilled OUI a queslionnaire which included queslions ahoUi
the work schedule.
•
dcntaJ specially. years in practice;
d!!i
previous history of exposure to industrial noise. gunfire.
(AI d!l fe) 280
&00
R>OO 2000 3000 4000 eooo 11000
frcqucnt.:y (Hz)
Fig. I. Mt.!an sound prl!ssure It.:vcl and octave banu analysis of air
and any incidents thaI might llave a.ffected their hearing.
turbinl! drills.
The noise measurements wen.: made by Rion sound
level meier :.md the narrow band. OClave and one-third
Fig. I shows thl! mean uverall sound pressure level
octave filter set madd SA-56A. All noise measurements
were taken at the position or
dentists' cars. Routine
of
in the ul!ntal
Illcasurcmcnts associared with octave hand analyses
high-speed drills which have been made
audiometric testing was performed on each subject with
Ihe usc of Madsen audiameler Iype 0·B40 con!inning 10
clinics in Tehran. The maximum sound pressure level was
IECI78 and ANSI-3.6-1969 siandard and was calihralcd
52dh wilh slandard devialion of 11.3 db canCcnlITllcd in 6
10 ISO-R389-127/B,S. 2497 rccammcndalian. Ii was
KHz,and 50.6 db wilh Ihc slandard devialian or 10.2 db in
calibraled before Ihe survey according 10 Ihe calibralion
K KHz and the minimum sound pressure level W<L"; 41.3 db
procedure recommended in the Madsen operating manual.
in 2 KHz.
Each deniiSI was inslrucled 10 usc Ihe audiomeler bUllon,
Hearing sensilivily al 2,0, 500,1000,2000,4000,6000,
Audiological Measurements
and 8000 Herlz was delermined for lef! car and Ihen righl
A lalal af250 dentisls were examined, 24 perce III af lhe
ear. Thc audiomelric findingsfOrlhc dCnliSIS were adjusled
siudied group were fernaleand 76 perceni m,�e. The largesl
for age. producing age-corrected auditory thresholds.11
percenlage (73.2%) of lhe studied population consisled of
general praclilianers. The age r;U1ged from 20 10 65 years.
The years in denial praclice ranged from rive 10 39 years.
RESULTS
Table I summarizes Ihe individu;� chamclerislics of lhe
slUdied populalian. The mean heming Ihreshald oflhe righl
Enviromnental Measurements
and len ears of Ihe dentisls in six groups according
The main noise sources in tl1e visited dental clinics and
10 Ihe
years in denial praclice are presenled in Fig,2.
Ihe faculty of denlisiry were idenlificd as Ihe high· speed
drills. In addition, some noise levels were measured from
aspirmors,air conditioning and background mnbient noise.
DISCUSSION
As these levels were not a main hazard,the main attention
.. was given lllihe high-speed denial drills,
Ii is believed
Ihal Ihe high-speed drills are a hazard III
Table I. Mean value and standard deviation of individual characteristics of studied dentists
Dentists
Age
"
Specialist
n
41
General
II
142
60
84
142
Tolal
n
40.76
48
190
9.55
16.92
16.22
10.88
n
7.76
10
19
Specialist
42.54
40.15
7.79
14.83
Years in 9.1
"
60
19
9.04
5.45
Tolal
33.36
39.39
30.71
41
Practice
male
Female
General
16.4
48
190
P. Nassiri, Ph.D., et al.
found a significant loss of hearing.ls.lf;
Most of the energy from high-speed dental drills is
concentrated in the higher frequencies. above 3000 Hz. The
sound pressure level me;l<ured was 52 db at 600n and 50.6
db at 8000 Hz.
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- - -
'.!:--=---=:-:-=-=-;;-:-;;=-=
;-
The damage ri.sk criteria for continuous eight hour
exposure is 90 dbA." Depending on the individu,� and the
type of dental prnctice. variations of IOta! exposure time for
eiglll hours ranged between 1 2 wlll45 minutes.' Thus on the
haSjis of the Icnght of exposure ;Uld noi�e intl..!nsity. air­
turbine drills in proper working ordl!r should hl! safe
regarding dmnnge to hearing.
The !irst step in our study was to exclude all dentists
with a known exposure 10 noiscor any hiswry ofear Liiscase.
present
01'
pas\. leaving 250 dentists (191J male and 60
female) forthe survey. Comp;uison uf the gnlup aUdiogr:uns
shows that there is a definite threshold at the higher
frequencies ill thl! drill noise expnsl!d. in women. greater
loss of he;u'jng exists al (i KHi'. in Ihe group of 20-24 an<.J
- - -
-�-=-=:-:-;;;--:-=-:;;-;-;;;;--;;!
Illore than 3U years of deillal practice. Then. we Illeasurell
the average hearing loss in those practiced more than \()
yenrs ;Uld compared it with thost.! practiced less than )()
years. At i\ KHz. in female dentists. there was 0.93 db (right
car) 'Uld 5.2 db (left ear) difference in hearing threshold
level. The difference is statistically significant for left car.
P<O.025. The dilTen.:nces indicating that the right ear shows
- .- --
....
!:-=---=:-:-=-=-;;-:-;;�'-;!
;-
greater loss than left ear me statistically significant ill
fem,�e dentists (P<Il.05).
Thl! :tudiograms of male dentists. although shuwing a
.� ....
changl! in the thresholLi urhearing, aJ'l! not ;L';; severe as those
in Ihe female group. Among the six studied groups. the
greatest hearing loss l!xisted in the group with 2U-24 years
of practice which was similm to the female hearing loss.
The differences between the right and left ear uf noise·
'.!:--=--=:-:-=-=-::-,.:::-:-:::-::!
exposed male dent ists with morc th;Ul I IJ years and less I II
ycms of dental practicl! were as follows:
The right car exceeded 3.72 db while the left car
exceede<.J 1.34 Lib. the difference is significant for the right
car. P<11.025.
It is concluded from this study that the average sound
,.0-=_,--,_=-=_=-.=_,.-,._=--=_':-:'_
pn:ssure level meaSllfl!L1 in clinical settings were Il.!ss· than
...
_
-
-
_
.
_
-
-
Fig. 2. Hearing threshold level or noise-exposed male and femille
dentists at.:..:ordinl! 10 the years in Llcntal practice.
the permissible limits hut till! nois-induced hl!aring loss
was ohserved both in male and female dentists. The loss.
being at the 6 KHz frequency rl.!gioll. is heyond thl! speech
frequency range and is undl!ll.:cted by till! dentists. Huwever,
thl! continued noise l!xposure may indicate a gradual
dentists' hearing. The factors to he considered in acollstic
cncroachmenl on the frequencies of the speech range.
trauma are intensity and frequency of sound, length of
exposure. and interval between exposure.
ACKN()WLED(;EMENT
Different opinions exist about the effects of the noise
generated by high-speed drills on the dentists' hearing
Thl! authors wish to acknowle<.Jge the cooperation of
acuity �·OInc investigators found no cvidence thal lhe uscof
such a drill is detrimental to hearing.I�.14 yet others have
the Iranian Dental Association who made significanl
cOllirihution towan.l the success or this study.
Noise-Induced Hearing Loss
Sincere thanks are extended to the dentists who
gunfire on dentists' heuring. J Am Denl Assoc 79: 1383-7,
participated in this research project.
1969 ..
9. Akburkhanzadeh F:Effects of high-speed drill noise on dentists'
hearing. Iranian J Pub I Health 7(4): 168-79,1978.
The authors also would like to express theirappreciation
to Mr. lamshid Pirnazar for his assisHmce in audiological
10. Wilson CF, Vaidyanathan TK, Cinotti WR, Cohen SM, Wang
5J: Hearing damage risk and communication interferem:e in
examination ,md to Mr. Ah,und Dorosti-Motalagh for his
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contribution in processing of data.
dental practice. J Dent Res 69(2):489-93, 1990.
11. Berger EH, Wan.! WD, Morill, JC, Royster LH: Noise ilnd
Hearing Conservation Manual. Am lOll Hy!: Ass!)/.: 193-194,
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86