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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 Downloaded from mjiri.iums.ac.ir at 5:52 IRDT on Sunday May 14th 2017 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. Downloaded from mjiri.iums.ac.ir at 5:52 IRDT on Sunday May 14th 2017 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. Downloaded from mjiri.iums.ac.ir at 5:52 IRDT on Sunday May 14th 2017 - - - '.!:--=---=:-:-=-=-;;-:-;;=-= ;- 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 Downloaded from mjiri.iums.ac.ir at 5:52 IRDT on Sunday May 14th 2017 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, REFERENCES 1986. 12. Praml GJ.Sonnahend E: Noise-induced hearing loss caused hy 1. Coles RRA, Hoare NW: Noisc�induced hearing loss and the dentists. Br Dent J 159(7): 209-18,1985. dental turbines. Dtsch-Zahnr.ltl-Z 35(3): 400-6, 1980. 13. Zubick HH. Tolentineo AT, Boffa J: Hearing and the high 2. Mittelman JS:The dental practitioner and hearing,! Am Dent. speed denial handpiece. Am .! Public Health 70(6): 633-5, Assnc 58: 156, 1959. 1980. 3. Rohin IG:Effect of noise mauc by the dcntal lurbinc drill. Dent 14. Lehto T, Laurikainen ET, Aitasulo KJ, Pietila TJ, Helenius Hl, Practitioner 10: 148�52,1960. 4. American Dental Association, Council on Dental Research; Johnsson R: Hearing of dentists in the long run: a IS-year follow-up study. Community Denl Oral Epidcmiol 17(4): Sound hazard of high-speed cutting instrument'), J Am Denl 207-11,1989. Assoc 58: 145, 1959. 5. Kessler HE: Hearing as related to dentistry. Dent Radiogr 15. Sturgeon JH, Mariani RC: Hearing loss: is it a necessary hazard in dental practice. New Dentists 10: 7.1979. Photogr 34 :3-20, 1961. 16. Muller HJ, Sabri ZI, Suchak AJ, McGill S, S<andford, JW: 6. Taylor W,Pearson J,Mair A:The hearing thresholds of dental Noise level evaluation of dental handpieces. .! Oral practitioners exposed to air turbine drill noise. Sr Dent J 118: Rehabilitation 13: 279-92, 1986. 206-10,1965. 17. Occupational Safety and Health Act (1970). Occupational 7. Forman-France B, Abramson AL, Stein T: High-speed drill noise exposure. Federal Register,339( 122) Part n: 22809 (24 noise and hearing: audiometric survey of 70 dentists. J Am June 1974). National Archives of United States Microfilm Dent Assoc 97: 479-82,1978. M 190, Ro1l 239. 8. Ward WD, Holmberg DJ: Effects of high-speed drill noise and 86