Noise Levels in Dental Offices and Laboratories in Hamedan, Iran

Abstract

Objective: Noise pollution is one of the most important situations requiring a solution by the contemporary world. The National Institute for Occupational Safety and Health has identified noise as one of the ten leading causes of work-related diseases and injuries. Dentists and dental auxiliaries are exposed to different noise levels while working in den-tal offices or laboratories. The purpose of this study was to measure the noise level made by different dental instruments in dental offices and laboratories. Materials and Methods: Measurement of the noise level was performed in 89 dental of-fices and nine dental laboratories. The noise levels were determined using a sound level meter; type SL-4011 (Lutron) ,which was placed at the operator's ear level in dental offic-es and laboratories and also at two-meter distance from the technician's ear in laboratories. Results: The maximum sound level was 85.8 dB in dental offices and 92.0 dB in laborato-ries. In dental clinics, the highest noise was produced by the ultrasonic-scaler (85.8 dB) and the lowest noise (49.7 dB) by the high-volume aspirator, whereas in the laboratory, the highest noise was caused during grinding by the stonecutter (92.0 dB) and the lowest by the denture-polishing unit (41.0 dB). Conclusion: After close evaluation, we believe that the maximum noise level in dental offices, although often beneath the damaging noise level for the human ear, is very close to the limit of hearing loss (85.0 dB). However, laboratory technicians may be at risk if they choose not to wear ear protection (earplugs or earmuffs).

Full text

2009; Vol. 6, No. 4 181
Original Article
Noise Levels in Dental Offices and Laboratories in Hamedan,
Iran
F. Mojarad 1~,T. Massum 2, H. Samavat 3
1 Associate Professor, Department of Pedodontics, School of Dentistry, Hamedan University of Medical Sciences, Hamedan, Iran
2 Assistant Professor, Department of Pedodontics, School of Dentistry, Hamedan University of Medical Sciences, Hamedan, Iran
3 Associate Professor, Department of Medical Physics, School of Medicine, Hamedan University of Medical Sciences, Hamedan,
Iran
~ Corresponding author:
F. Mojarad, Department of Pe-
dodontics, School of Dentistry,
Hamedan University of Medical
Sciences, Hamedan, Iran.
FarzadMojarad@yahoo.com
Received: 13 November 2008
Accepted: 25 March 2009
Abstract:
Objective:
N
oise pollution is one of the most important situations requiring a solution by
the contemporary world. The National Institute for Occupational Safety and Health has
identified noise as one of the ten leading causes of work-related diseases and injuries.
Dentists and dental auxiliaries are exposed to different noise levels while working in den-
tal offices or laboratories. The purpose of this study was to measure the noise level made
by different dental instruments in dental offices and laboratories.
Materials and Methods: Measurement of the noise level was performed in 89 dental of-
fices and nine dental laboratories. The noise levels were determined using a sound level
meter; type SL-4011 (Lutron) ,which was placed at the operator’s ear level in dental offic-
es and laboratories and also at two-meter distance from the technician’s ear in laboratories.
Results: The maximum sound level was 85.8 dB in dental offices and 92.0 dB in laborato-
ries. In dental clinics, the highest noise was produced by the ultrasonic-scaler (85.8 dB)
and the lowest noise (49.7 dB) by the high-volume aspirator, whereas in the laboratory,
the highest noise was caused during grinding by the stonecutter (92.0 dB) and the lowes
t
by the denture-polishing unit (41.0 dB).
Conclusion: After close evaluation, we believe that the maximum noise level in dental
offices, although often beneath the damaging noise level for the human ear, is very close
to the limit of hearing loss (85.0 dB). However, laboratory technicians may be at risk i
f
they choose not to wear ear protection (earplugs or earmuffs).
Key Words: Dental Instruments; Laboratories, Dental; Noise, Occupational
Journal of Dentistry, Tehran University of Medical Sciences, Tehran, Iran (2009; Vol. 6, No.4)
INTRODUCTION
A sound, agreeable or disagreeable, is a stimu-
lus discerned by the sense of hearing. Disa-
greeable or undesired sounds are described as
noises, which may cause undesirable masking
of sounds, may interfere with speech and
communication, may produce pain, injury and
brief or perpetual loss of hearing [1-4].
It is renowned that high sound levels have ad-
verse effects on extra-auditory systems; name-
ly, physical consequences (quickened pulse,
increase in blood pressure, constriction of
blood vessels, low productivity) [1-9] and
psychical consequences (nervousness, mental
fatigue and emotional exacerbation) [1-5]. Ex-
posure to noise levels above 80 dB is asso-
ciated with these consequences, which de-
pends on the intensity of the noise, distance to
the source, total duration of the noise, and the
individual’s age, physical condition and sensi-
tivity [1,2,5].
Noise or sound intensity, is measured in deci-

J
ournal o
f
D
182
b
els (dB).
sure 10 ti
m
decibels,
a
cibels [10
noted that
lent to a
d
is a logari
t
is not atta
i
[12].
Noise pol
l
situations
r
porary w
o
Occupatio
n
nized nois
e
work-relat
e
Dentists a
n
to differe
n
tal offices
The objec
t
noise leve
l
pieces and
es and lab
o
MATERI
A
Noise lev
e
89 dental
in the city
The noise
D
entistr
y
, Teh
Ten decib
m
es greater
t
a
hundred ti
m
,11]. As a
a 3-decibel
d
oubling of
t
hmic unit
i
i
nable: 100
l
ution is o
n
r
equiring a
o
rld [13].
T
n
al Safety
e
as one of
e
d diseases
n
d dental
a
n
t noise lev
e
or laborato
r
t
ive of this
l
produced
other dent
a
o
ratories.
A
LS AND
e
l measure
m
offices an
d
of Hameda
n
level wa
s
Fig 1. So
u
ran Universi
t
els means
t
han zero d
e
m
es greate
r
guideline,
noise incr
e
sound int
e
i
n which s
i
dB + 100
n
e of the
m
solution b
y
T
he Nation
a
and Heal
t
the ten lea
d
and injurie
a
uxiliaries
a
e
ls while w
o
r
ies [2,13].
study was
t
by differe
n
a
l engines i
n
METHO
D
m
ents were
d
nine dent
a
n
in 2008.
s
measure
d
u
nd level mete
r
ty
o
f
Medical
a sound p
r
e
cibels and
r
than zero
d
it should
e
ase is equi
v
e
nsity. Deci
i
mple addit
i
dB = 103
m
ost impor
t
y
the cont
e
a
l Institute
t
h has rec
o
d
ing cause
s
s [2,14,15].
a
re vulner
a
o
rking in d
e
t
o measure
n
t dental ha
n
n
dental of
f
D
S
performe
d
a
l laborato
r
d
using so
u
Sciences
r
es-
20
d
e-
be
v
a-
bel
i
on
dB
t
ant
e
m-
for
o
g-
s
of
a
ble
e
n-
the
n
d-
f
ic-
d
in
r
ies
u
nd
level
tralia
soun
d
an
o
soun
d
At t
h
level
from
soun
d
ator’
s
simil
a
altho
u
woul
d
oper
a
tors
right
posit
e
High
-
ultra
s
amal
g
the e
q
The
l
instr
u
with
o
of th
e
it w
a
ning
f
At
d
meas
u
plac
e
nois
e
anot
h
This
mete
r
ing
e
creas
tiple
micr
o
[2] a
n
ist’s
the
e
tech
n
oper
a
The
n
terva
l
m
eter; Lut
r
(Fig 1). T
h
d
s similar t
o
bjective r
e
d
levels [1]
.
h
e dental
o
mete
r
) w
a
the denti
s
d
s at the in
t
s
ear. This
s
a
r to that r
e
u
gh the o
p
d
tend to
b
a
ting positi
o
a
re right-h
a
ear would
e
ear.
-
speed han
d
s
onic scal
a
g
amators,
a
q
uipment t
e
l
evel of the
u
ment was
o
ut cutting
e
noise lev
e
a
s recorded
f
ree.
d
ental labo
r
u
red simi
l
e
d near the
t
e
intensity
h
er reading
was to si
m
r
radius of
t
e
xpose
d
to
ed in inten
s
operators
e
o
phone wa
s
n
d 30.0 c
m
(operator’s
)
e
quipment
n
ical perso
n
a
tions and c
n
oise was
m
l
and the
m
r
on SL-401
h
e sound l
e
o the hum
a
e
producibl
e
.
o
ffice, the
m
a
s placed a
t
s
t’s ear i
n
t
ensity they
s
ound level
e
ceived by
t
p
posite ea
r
b
e impacte
d
o
ns. Since
a
nded, it i
be affecte
d
d
pieces, lo
w
a
rs, high-
v
a
nd backg
r
e
sted.
noise was
m
at maxi
m
operations
.
e
l of the hig
when the
r
atories, th
l
a
r
ly. The
t
echnician’
s
reaching
was take
n
m
ulate the p
e
t
he operat
o
the same
n
s
ity, in a s
i
e
xist. In d
i
s
located 6.
0
m
[16,17] a
w
)
ear, or 3
[17]. In a
d
n
nel might
ould be at
r
m
easured o
v
m
aximum i
n
Mo
ja
2009; V
o
1, 30-130
d
e
vel meter
r
a
n ear a
n
d
p
e
measure
m
m
icrophon
e
t
a 15 cm
n
order to
influence
t
was belie
v
t
he dental
a
r
(of the
o
d
due to t
h
most of th
s obvious
d
more tha
n
w
-speed ha
n
v
olume a
s
r
ound nois
m
easured
w
m
um runni
n
. For mea
s
g
h-volume
a
aspirator
w
e noise le
microph
o
s
ear to sim
u
the eardr
u
n
two mete
r
e
rson withi
n
o
r who was
n
oise, alth
o
i
tuation wh
e
i
fferent stu
d
0
inches [1
]
w
ay from t
0.0 cm a
w
d
dition, ot
h
be close
t
r
isk.
v
er a 30-se
n
tensity in
a
rad et al.
o
l. 6, No. 4
d
B, Aus-
r
eacts to
p
rovides
m
ent of
e
(sound
distance
capture
t
he oper-
v
ed to be
a
ssistant,
o
perator)
h
e usual
e ope
r
a-
that the
n
the op-
n
dpieces,
s
pirators,
es were
w
hile the
n
g speed
s
urement
a
spirator,
w
as run-
vel was
o
ne was
u
late the
um
and
r
s away.
n
a two-
also be-
o
ugh
d
e-
e
re mul-
d
ies, the
]
, 5.0 cm
h
e dent-
w
ay f
r
om
h
er non-
t
o noisy
cond in-
decibels

Mojarad et al. Noise Levels in Dental Offices and Laboratories
2009; Vol. 6, No. 4
183
was recorded. The mean of the maxima was
determined and the overall highest maximum
was recorded. This was repeated at least three
times [1].
The location of the air compressor in the den-
tal office and the laboratory was also recorded.
The sound levels measured in dental laborato-
ries were those produced by the procedures
mentioned below:
1- Compressed air through a blast nozzle
2- Acrylic special tray grinding using an acryl-
ic-trimming bur
3- Cutting stone casts with a large bur
4- Denture polishing unit in operation using
pumice on brush wheels
5- Mixing gypsum using vacuum mixing ma-
chine and vibration
6- High-speed lathe with a carbide bur cutting
and grinding metal
7- Porcelain grinding by an abrasive wheel in a
slow-speed handpiece
8- Sandblasting (aluminum oxide air abrasion)
on metal casting
All data collected from the checklist were ana-
lyzed using the Statistical Package for Social
Sciences (SPSS) version 13 and Microsoft Ex-
cel spreadsheet were used for data entry and
analysis.
RESULTS
The results of the sound level measurements at
the operator’s ear level in dental offices are
shown in Table 1.
The results of the sound level measurements
taken in the dental laboratories at the techni-
cian's ear level and two meters away are tabu-
lated in Table 2. The results (Table 1 and 2)
indicated that the maximum sound levels in
dental offices and laboratories were 85.8 dB
and 92.0 dB, respectively.
In dental clinics, the highest noise was pro-
duced by the ultrasonic-scaler (85.8 dB) and
the lowest noise (49.7 dB) was created by the
high-volume aspirator (Table 1).
The highest noise in laboratories was caused
by engines during grinding by the stonecutter
(92.0 dB) and the lowest noise by the denture-
polishing unit (41.0 dB) (Table 2).
DISCUSSION
Immoderate noise can damage hearing and
create physical and psychological nervousness
[6-9]. In this study, noise levels of the hand-
pieces and engines used in dental offices and
laboratories in Hamedan were measured (Ta-
ble 1 and 2).
The total noise levels in dental laboratories
(Table 1) were much higher than the dental
clinics (Table 2). The mean maximum envi-
ronmental noise level for laboratories was 58.0
dB, compared to the mean maximum value of
55.0 dB for dental clinics. We know the envi-
ronmental noise level also depends on the
number of operators, the time of day, noise
from outside the office or laboratory through
open windows (crowded streets and traffic)
and finally radio and TV in some dental offic-
es or laboratories.
Kilpatrick proposed a number of sounds in the
dental office that may be hazardous to the
dentists’ hearing [18]:
1. High-speed turbine
2. High-volume aspirator
3. Ultrasonic scaler
4. Mixing devices for stone, amalgam and other
substances
5. Continuous loud music
The high-speed turbine handpiece was intro-
Table 1. Noise level of each device measured (dB) near the
operator’s ear in dental clinics.
Devices Min (Max) dB
Back ground noise 20.00 (55.00)
High-volume aspirator 49.70 (61.61)
Ultrasonic-scaler 56.20 (85.80)
High-speed handpieces 62.71 (82.64)
Low-speed handpieces (angled-
design) 61.03 (79.62)
Low-speed handpieces (straight) 63.00 (76.80)
Amalgamator powder 40.50 (75.50)
capsule 42.50 (75.50)

Journal of Dentistry, Tehran University of Medical Sciences Mojarad et al.
2009; Vol. 6, No. 4
184
duced in 1957 and is thought to generate the
greatest potentially hazardous sound level
[19]. The early models of the ball-bearing type
were found to produce noise levels of 80 to 94
decibels at 12 inches [6], the change from ball-
bearing to air-bearing handpieces happened in
the 1960s. Some studies found that with the
advent of air bearings in the drills, the noise
level decreased by about 10 decibels [20-22].
A cartridge-type ball-bearing drill from the
early 1960’s produced a higher noise (8.5 dB)
compared to an air-bearing drill or a modern
sealed head ball-bearing drill (5.0 dB) [23].
Subsequently, return of ball-bearing handpiec-
es took place. Presently, manufacturers claim
that most handpieces produce less than 75 de-
cibels noise. Recuperated design and air ex-
haustion have resulted in quieter instruments
than before [19].
In this study the maximum noise level were
respectively, low-speed straight handpiece
(76.8 dB), low-speed angle handpiece (79.6
dB) and the high-speed turbine angle hand-
piece (82.6 dB) was increased. This is concor-
dant with antecedent studies mentioning that
the high-speed turbine handpiece generates a
higher noise level than the low-speed hand-
piece [6,18,2]. Sound pressure levels of the
noise created by the dental drill ranged from
maximum 61.0 dB to max 82.0 dB, which is
almost within safe limits [23]. It was con-
cluded that the risk of damage to the dentists’
hearing due to dental turbine noise is insignifi-
cant.
There are several opinions regarding the ef-
fects of dental drill noise and other noises on
dentists’ hearing. Some found that a consider-
able loss of hearing results from noise prob-
lems in dental practice [1,20,24], whereas oth-
ers have found no significant shifts in auditory
thresholds [1,25,26].
The first convincing evidence proving that
damage to hearing may be caused by exposure
to noise produced by a dental drill was pub-
lished by Taylor et al [20] in a carefully con-
trolled study of dentists in Dundee, Scotland.
According to reports from the Occupational
Safety and Health Administration, eight hours
of perpetual exposure to a noise level of 90.0
dB is permissible daily [27]. On the report of
the noise pollution control act in Iran, workers
may be exposed to a maximum noise level of
85.0 dB for eight hours without ear protection.
Based on the overall measurements in this
study and other comparable studies [6,18,28],
we found that the amount of noise dental prac-
titioners are exposed to is still below the limit
of the risk of hearing loss (85.0 dB). Forman-
Franco et al [29] found no statistical decrease
in the hearing thresholds of 70 dentists when
they were compared with a normal, age-
adjusted population. However, dental techni-
cians who spend daily eight hours in large la-
boratories should also be considered at risk.
In dental offices and laboratories, regular
maintenance of the equipment, early repairs,
Table 2. Noise level (dB) measured near the operator’s ear (I) and at two-meter distance (II) in dental laboratories.
Devices I II
Min (Max) dB Mean (SD) Min (Max) Mean (SD)
Compressed air 82 (85) 83.5 (2.12) 82 (82) 82.0 (0.0)
Special tray grinding 70 (85) 77.8 (5.60) 62 (78) 68.6 (6.3)
Stone cutter (grinder) 75 (92) 82.0 (5.00) 70 (89) 75.0 (6.7)
Denture polishing unit 48 (75) 63.2 (10.00) 41 (63) 56.0 (8.8)
Stone mixer (with vibrator and vacuum) 58 (76) 66.0 (6.70) 51 (73) 61.0 (7.6)
Metal cutting 71 (82) 78.2 (4.00) 62 (75) 70.0 (5.2)
Porcelain grinding 73 (80) 76.0 (3.60) 60 (73) 67.2 (5.9)
Sandblaster 52 (79) 70.3 (8.70) 57 (66) 61.7 (3.0)
Background noise 34 (58) 45.88 (9.34) 34 (58) 45.88 (9.34)

Mojarad et al. Noise Levels in Dental Offices and Laboratories
2009; Vol. 6, No. 4
185
replacement of defective items, use of newer
less noisier models and increasing sound ab-
sorption of the room (by 3-5 dB) may have a
4-7 dB decrease in the noise level, consequent-
ly preventing noise-induced hearing loss [5].
The operating room should be made more
acoustically satisfactory by minimizing the
hard surfaces that allow reverberation of sound
[1].
It is, therefore, essential to control noise in
dental environments, emphasizing the fact that
acoustic comfort depends not only on control
of emitted sound levels, but also on the acous-
tic characteristics of the place (hard surfaces
act as noise reflectors, therefore aggravate
sound) [5].
Periodic audiometric checkups should be car-
ried out. When you know you will be exposed
to loud noises, either temporarily or over a
longer period, using ear plugs or ear muffs
may help prevent hearing loss. Properly fitted
earplugs into the outer ear canal and earmuffs
placed over the entire ear decrease the intensi-
ty of the sound reaching the eardrum by 15 to
30 decibels when used separately, and if used
together reduce the noise by 30.0 to 35.0 dB
without interfering with the conduct of a nor-
mal between-person conversation in the labor-
atory [1].
CONCLUSION
After close evaluation, we believe that the
maximum noise level in dental offices, al-
though often beneath the damaging noise level
for the human ear, is very close to the limit of
hearing loss (85.0 dB). However, technicians
may be at risk if they do not wear ear protec-
tion, because properly fitted earplugs and ear-
muffs can reduce noise by 15 to 30 decibels.
ACKNOWLEDGMENTS
This work was supported by a grant from Ha-
medan University of Medical Sciences (No.
470). We wish to thank the Department of Oc-
cupational Health, School of Public Health for
their valuable comments. The authors declare
that they have no conflict of interest.
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