153Musculoskeletal symptoms among dentists inrelation to work postureNavah Z. Ratzon∗, Tal Yaros, Alona Mizlik andTamar KannerDepartment of Occupational Therapy, Tel AvivUniversity, Tel Aviv, IsraelObjective: To determine the effect of work posture on mus-culosketal complaints in Israeli dentists.Methods: The population included 60 male dentists meanage was 46.0 (± SD 8.66), 30 worked in sitting positionand 30 were altering positions. Study population completedthe standardized Nordic questionnaire and informative formconcerning recipient’s practice of dentistry, bio-demographicvariables and questions about workloads.Results: Musculoskeletal symptoms in the last 12 monthswere localized primarily in the lower back and in the neck(55% and 38.3% respectively). There was a signiﬁcant cor-relation between the time spent sitting and the severity of lowback pain (r = 0.41, p = 0.01). On the other hand therewas no signiﬁcant correlation between time spent sitting andother musculoskeletal complaints (r = −0.16).Conclusions: Dentists who work in the sitting positionhave more severe low back pain than do those who alternatebetween sitting and standing despite the fact that those whosat at least 80% of the time worked less hours and had lessof a workload during their working hours. This suggests thataltering position should be recommended to dentists. Anintervention study, however, is needed to demonstrate thatchanging posture will decrease the prevalence of low backpain in dentists.Keywords: Sitting position, altering position, workload, prac-tice of dentistry1. IntroductionWorkload imposition is an important factor in theoccurrence of musculoskeletal symptoms in general∗Correspondence to: Navah Z. Ratzon, OT, Ph.D., Department ofOccupational Therapy, Tel Aviv University, Ramat Aviv 69978, TelAviv, Israel. Tel.: +972 3 6409104; Fax: +972 3 6409933; E-mail:email@example.com speciﬁcally back pain among the working popu-lation [12,26].The life-time history of low back painranges from 51–80% [13,29]. Throughout western so-ciety, low back pain among working population hasincreased dramatically [5,7,19,20,30].Studies note a higher incidence and prevalence ofmusculoskeletal symptoms and back pain among den-tists than other occupational groups [7,14,17,19,23,31].Studies have reported a prevalence of 30 to 70 percentof musculoskeletal pain among dentists [2,16,24,28].Musculoskeletal symptoms among dentists havebeen considered a consequence of the workload ofdental practice. Dentists’ work includes several well-known risk factors for musculoskeletal symptoms ingeneral and speciﬁcally for low back pain. The follow-ing widespread postures among dentists are consideredrisk factors: Forward bent sitting posture, accompa-nied with bending and twisting, and the relative staticwork [1,22]. Damkot et al.  found that not onlysitting and twisting postures effect back pain but theamount of sitting and twisting in seat has a great impacton musculoskeletal pain.There is an agreement that changing position fre-quently is a key to avoid occupationally related muscu-loskeletal problems. Static forces require holding thebody in one position and have been shown to be muchmore taxing than dynamic forces. During a static pos-tural position, more than 50% of the body’s musclesmust be in contraction to sustain the position and resistthe force of gravity. Dynamic movements utilize mus-cles of opposing groups, reducing fatigue and pain [3,10,34].While efforts have continued to improve the er-gonomic design of the dental furniture, the dentist him-self has receivedless attention . The purposeof thisstudy is to determine the prevalence of musculoskeletalsymptoms among Israeli dentists and explore the rela-tionship of work posture, bio-demographicfactors, andworkload factors with those symptoms.Work 15 (2000) 153–158ISSN 1051-9815 / $8.00 2000, IOS Press. All rights reserved
154 N.Z. Ratzon et al. / Musculoskeletal symptoms among dentists in relation to work posture2. Materials and methodsThe population included 60 male dentists both selfemployed and salaried dentists who had at least 4 yearsof experience, worked at least 18 hours per week andhad at least ﬁve patients per working day. Mean age ofstudy population was 46.0 (± 8.66, range of ages 32–67). The dentists were selected by randomly calling 49of 490 dentists who were listed in the yellow pages ofJerusalem. Thirty dentists reported that they worked atleast 80% of the time in a sitting position, 13 reportedalternating between sitting and standing positions (<40% of working time in sitting position and < 90% ofworking time in standing position). In order to recruitmore dentists in the alternating group,we called another49 dentists at random and found 8 who worked in thealternating position, and ﬁnally recruited an additional9 dentists from the University clinic where the use ofthe alternating position is universal.Only 3 dentists refused to attend the study, 2 dentistswho worked in sitting position and one who worked inthe alternating position. Three dentists did not ﬁt thedeﬁnition of the two groups.The investigation consisted partly of the Standard-ized Nordic Questionnaire for the analysis of muscu-loskeletal symptoms in nine anatomical regions andfor the survey of low back symptoms during the pre-vious 12 months and speciﬁcally the previous sevendays  and partly of speciﬁc questions concerningrecipient’s practice of dentistry, bio-demographic vari-ables and questions about workloads (ergonomicwork-load, time workload and human workload). The vari-able ergonomic workload included self report informa-tion about the comfort/discomfort of work station ingeneral and chair design speciﬁcally, body mechanism(twisting the trunk), and reasonable/poor light and aircirculation. The variable time load was the value ofmultiplying months of experience with mean weeklyworking hours divided by number of annual weeks.The variable human workloadincluded referral to num-ber of clients per hour, number of sessions in whichparallel treatments are given to several clients, controlover number of clients and dentists’ assistant.2.1. Data analysisIndependent variables-t-test was used to compareage, BMI, time workload and severity of symptoms oflow back pain between sitting position and altering po-sition group. Mann-Whitney test was used to comparephysical activity, ergonomic load and human workloadbetween sitting position and altering position groups.Pearson and Spearman correlations were used to ex-plore the association between musculoskeletal symp-toms and low back pain and bio-demographicvariablesand workload factors. Univariate analyses were carriedin order to determine whether musculoskeletal symp-toms, low back pain, age, sitting position, and workloads defer on the main three practice areas of dentistry(maxillo-facial surgery, oral rehabilitation and generalpractice).A probability level of p < 0.05 was accepted asstatistically signiﬁcant.3. ResultsThe population included 60 male dentists, mean ageof study population was 46.0 (± SD 8.66), and meanyears of experience 19.24 (± SD 5.7). Only a minorityof Israeli dentists (22% of the sample) alternated theirposition (spent less than 40% of their working time in asitting position and not more than 90% of their workingtime in standing position).Reported musculoskeletal symptoms in the last 12months were predominately localized in the lower backand in the neck (55% and 38.3% respectively). Themost frequent reported musculoskeletal symptoms inthe last 7 days were the neck and shoulders (28.3% and15% respectively). The highest percentage of reportedpain which prevented dentists from doing normal workin the last 12 months was in the two anatomical regionslow back and neck (8.3% each) (Table 1).There was no statistical difference in the occurrenceof symptoms in the last 7 days and in number of daysin the last 12 months from which the dentist was pre-vented from doing normal work between the sittingposition group and the altering position group. Onlyone anatomical region, the low back (in the last twelvemonths) showed statistical difference between the twogroups. The severity of symptoms among dentists withsitting position was higher than among dentists whoused the altering position (8.16 (± 6.28), 2.73 (± 4.52)respectively; t = 3.84p = 0.00).There was a signiﬁcant statistical difference betweenage, time load, and human load between the sittingpositiongroupand the altering position group. Alteringposition group had higher mean scores on all the threevariables (Table 2).The three major practice areas of dentistry amongthestudypopulationwere generalpractice (36%), Maxillo-Facial Surgery (27%) and Oral Rehabilitation (25%).
N.Z. Ratzon et al. / Musculoskeletal symptoms among dentists in relation to work posture 155Table 1Occurrence of musculoskeletal symptoms in the last twelve month and at thelast 7 days among study population and occurrence of dentists prevented fromdoing workDentists Last 12 month Last 12 month prevented Last 7 days(N = 60) Frequency (%) from doing normal work Frequency (%)Frequency (%)Neck 23 (38.3) 5 (8.3) 17 (28.3)Shoulders 15 (25) 4 (6.7) 9 (15)Upper back 12 (20) 2 (3.3) 8 (13.3)Low back 33 (55) 5 (8.3) 6 (10)Elbows 4 (6.7) 1 (1.7) 2 (3.3)Wrists/Hands 4 (6.7) 2 (3.3) 3 (5)Hips/Thighs 3 (5) 1 (1.7) 1 (1.7)Knees 6 (10) 1 (1.7) 1 (1.7)Ankles/Feet 3 (5) 0 (0) 1 (1.7)Table 2Comparison of independent sample variables between sitting position dentistsand altering position dentistsVariables Sitting position Altering position P valuesMean(SD) (N = 30) Mean(SD) (N = 30)Age 43.2 (6.5) 48.7 (9.7) 0.01BMI 25.14 (2.18) 25.31 (2.44) NSPhysical activity 0.63 (0.49) 0.63 (0.49) NSErgonomic load 2.13 (0.68) 2.13 (0.50) NSTime load 190.01 (91.15) 271.86 (138.49) 0.00Human workload 3.35 (1.07) 4.01 (0.91) 0.01Analysis of variance was submitted with practiceof dentistry and each of the following variables sepa-rately: musculoskeletal symptoms, low back pain, sit-ting position, age and workloads as factors; practiceof dentistry being a between subject factor, and eachof the others (second effect) being a within subjectfactor. Three practice areas of dentistry groups didnot differ from each other in the dependent variablesmusculoskeletal symptoms and low back pain and inthe independent variable ergonomic workload. Never-theless, these three groups signiﬁcantly differed fromeach other in working position [F(2, 50) = 15.96,p < 0.00], workload [time load: F(2, 50) = 5.03,p < 0.01, human load: F(2, 50) = 7.65, p < 0.01]and age [F = (2, 50) = 3.33, p < 0.04).Table 3 showed signiﬁcant correlations between in-dependent variables age and time load and the depen-dent variable musculoskeletal pains. Furthermore, lowback pain correlated only with working position, mean-ing that the higher the percentage of time the dentistspent in sitting position the higher he scored on the lowback pain.There was a correlation between low back pain andmusculoskeletal pain (r = 0.38, p < 0.01).There was a negative correlation between sitting andage (r = −0.38, p < 0.01), meaning that the youngerTable 3Correlations between bio-demographic variables and workload andmusculoskeletal and low back painVariables Musculoskeletal pain Low back pain(n = 60) (n = 60)Age 0.23∗ 0.09BMI 0.03 0.03Sitting −0.16 0.41∗∗Ergonomic load 0.08 −0.01Time load 0.22∗ 0.06Human workload 0.12 0.09∗p < 0.05; ∗∗p < 0.01.the dentist is the higher is the percentage of time he wassitting while he treated his patients (was not shown inthe table).4. DiscussionThe most frequent percentage of reported pain anddiscomfort among Israeli dentists was the occurrenceof low back pain in the last twelve months. The second,anatomical region that was reported was the neck. Theresults support the ﬁndings of similar previous studiesin other countries like the ﬁndings of Marshal et al. ,Rundcrantz et al.  and others who suggested thatpain and discomfort were predominately localized in
156 N.Z. Ratzon et al. / Musculoskeletal symptoms among dentists in relation to work posturethe lower back and in the neck. The frequency of lowback pain among Israeli dentists was 2.29 times morethan the frequency of such problems among Israeli in-dustrial workers; regarding the neck region, the fre-quency of pain among Israeli dentists was 3.48 timesmore than among industrial workers . Neverthe-less, those prevented from doing normal work duringlast 12 months showed relatively low percentage (8.3%for low back and neck), meaning that the existing ofmusculoskeletal problems did not interrupt work. Thiscoincides with nowadays-clinical trend which advisespatients to stay active in order to reduce back pain .This is in agreement with results obtained by Guay who reported that the severity of back and neck pain israrely such that it interrupts work.While the occurrence of low back pain in the lasttwelve months was the highest, the occurrence of painin this region in the past 7 days was only the third witha frequency of 10%. It would be expected that theproportion of musculoskeletal symptoms in the nineanatomical regions will diverge more or less identicallyin the past 12 months and in the past 7 days, but it didnot. The frequency of low back symptoms in the last 7days was even lower than point prevalence of 15% (as itappears in literature) among population who states thatthey are having low back symptoms . The authors ofthis article have no explanation for this discrepancy un-less there is a seasonal effect over different anatomicalregions.Regarding working position and musculoskeletalsymptoms, the fact that only the low back region (inthe last twelve months) showed statistical differencebetween the sitting group and the altering group can bedue to the very low frequencies of occurrence in otheranatomical regions. The lack of difference betweengroups concerning the neck was perhaps a result ofbody mechanism, which enforce dentists in both work-ing positions use neck muscles in an awkward way. Inspite of these explanations, it seems that dentists whoused sitting positions experienced more severe symp-toms than dentists who used altering position, eventhough altering position dentists were older, and hadhigher workloads (time and human workload) whichwould be considered to be more of risk . Althoughage and workloads were higher among altering positiongroup we did not control for it since it acted against ourresearch hypothesis. Indeed, for dentists, special bodytechniques like alternating between sitting and stand-ing reduced back pain. These ﬁndings support Wag-ner’s  article, which recommended altering posi-tion to reduce fatigue by shifting muscular support toopposing groups.A speciﬁc causal relationship of occupational re-quirements to musculoskeletal pain is difﬁcult to es-tablish and it is more accurate to look for multifac-torial etiology for musculoskeletal symptoms. Bio-demographic variables and environmental variablesmight give a better perspective for the understanding ofmusculoskeletal problems.4.1. AgeStudies note an association between musculoskele-tal problems and age [9,24]. Indeed such correlationwas found but the correlation coefﬁcient was low, andno correlation was found between low back pain andage. It seems that low correlation on one hand and nocorrelation on the other was partially due to interferingvariables like practice of dentistry, different workingpositions and ergonomic workloads, all factors whichcontributed to muscuskeletal symptoms and were inde-terminate to the age effect.4.2. Ergonomic workloadThe effectiveness of ergonomic workload is contro-versial; on one hand the effectiveness of ergonomicwork site was proven to avoid recurrent episodes of painand disability  and on the other hand ergonomicsvariables showed a low predictive value for recoveryor for the development of pain and discomfort .Moreover, in spite of improvements of the ergonomicdesign of dental equipment and in the work environ-ment, musculoskeletal pain and discomfort did not im-prove [16,24]. Indeed this research did not show acorrelation between ergonomic workload and muscu-loskeletal symptoms. Yet, one should remember thatthe variable ergonomic workload was self-reported andunlike time workload and human workload,which wereinformative variables, ergonomics might need to relyon a professional analysis.4.3. Time workloadSince dentists are working on a ﬁxed schedule whichis planned weeks or days in advance we expected timepressure to be a risk factor to low back pain . No sig-niﬁcant correlation was found between time workloadand back pain in this study but time load did correlatesigniﬁcantly with musculoskeletal symptoms.
N.Z. Ratzon et al. / Musculoskeletal symptoms among dentists in relation to work posture 1574.4. Human workloadThe highest human workload score was amongmaxillo-facial surgeons even though the existence ofdental assistance is more common among them, a factwhich should minimize stress and fatigue while achiev-ing maximum efﬁciency in the practice of operativedentistry. In fact, the signiﬁcant increase in the fre-quency of musculoskeletal pain reported by maxillo-facial surgeons may be due to the reduction of move-ment associated with greater utilization of dental assis-tant or with longer periods working without taking abreak .4.5. Practice of dentistryAlthough practice of dentistry did not explain thevariance of musculoskeletal symptoms and low backpain, still dentists who specialized in maxillo-facialsurgery suffered almost twice as much from muscu-loskeletal pain (3.06) than dentists who specialized inoral rehabilitation (1.60) and general practice (1.86).Maxillo-facial surgeons had more time and humanworkloads than oral rehabilitation and general prac-tice. The mean scores of low back pain among gen-eral dentists (6.63) was approximately twice as muchas the mean scores of dentists (3.7) and oral rehabilita-tion dentists (3.03). The analysis of variance showedthat general dentists used the sitting position 3.21 timesmore than maxillo-facial surgeons and 1.44 times morethan oral rehabilitation dentists. These data were re-ﬂected in the correlation analysis which was discussedabove.4.6. LimitationsDentists’ population was taken from the Jerusalemdistrict, which initially had been only one district inIsrael. To what degree this represents the population ofdentists in Israel is not clear. However the distributionof muscoloskeletal complaints is comparable with thatfound in other studies [17,25,30].The use of a questionnaire as a diagnostic tool formusculoskeletal symptoms and low back pain is as ac-curate as any other devices, since rarely are diagnosesfor musculoskeletal symptoms and low back pain sci-entiﬁcally valid . The Nordic questionnaire is incommon use and yet the Nordic questionnaire has nodetails about the frequency or duration of the inabilityto work. Nor does the questionnaire indicate whetherthe person has been on sick-leave or has just sloweddown his speed of work.Subsequently, this is a retrospective study and thecorrelation we found does not necessarily represent thecause for the symptoms. A prospective study is neededto conﬁrm the results of this study.Despite these cautions in the interpretation thesedata, a number of potentially signiﬁcant ﬁndings doemerge. The severity of low back pain among dentistswith sitting position was higher than among dentistswho used the altering position.Practice of dentistry differed from each other inworking position, workload and age. As for the asso-ciation between musculoskeletal symptoms and backpain with bio-demographic and workload factors, ageand time load correlated with musculoskeletal symp-toms and low back pain correlated signiﬁcantly onlywith working posture.5. ConclusionsDentists who work in the sitting position have moresevere low back pain than do those who alternate be-tween sitting and standing, despite the fact that thosewho sat at least 80% of the time worked less hours andhad less of a workload duringtheir working hours. Thissuggests that altering position should be recommendedto dentists. An intervention study, however, is neededto demonstrate that changing posture will decrease theprevalence of low back pain in dentists.References Andersson, G.B.J., The epidemiology of spinal disorders, in:The Adult Spine: Principles and Practice, Frymoyer, J.W.,eds., Raven Press, New York, 1991, pp. 107–146. Bassett, S., Back problems among dentists, J Cand Dent Assoc49 (1983), 251–256. Buckle, P., Stubbs, D.A. and Baty, D., Musculoskeletal dis-orders and associated work factors, in: The Ergonomics ofWorking Postures, Corlett, E.N., Wilson, J.R. and Manenic, I.,eds., Taylor and Francis, London, pp. 19–30. Burdorf, A. and Sorock, G., Positive and negative evidence ofrisk factors for back disorders, Scand J Work Environ Health23 (1997), 243–256. Clemmer, D.I., Mohr, D.L. and Mercer, D.J., Low-back in-juries in a heavy industry I. Workers and workplace factors,Spine 16 (1991), 824–830. Damkot, D.K., Pope, M.H., Lord, J. and Frymoyer, J.W., Therelationship between work history, work environment and lowback pain in men, Spine 9 (1984), 395–399. Fish, D.R. and Morris-Allen, D.M., Musculoskeletal disordersin dentists, N Y State Dent J 64 (1998), 44–48.
158 N.Z. Ratzon et al. / Musculoskeletal symptoms among dentists in relation to work posture Frymoyer, J.W. and Cats-Baril, W., Predictors of low backpain disability, Clin Orthop 221 (1987), 89–98. Frymoyer, J.W. and Cats-Baril, W., An overview of the inci-dences and costs of low back, Orthop Clin N Am 22 (1991),263–271. Grandjean, E., Fitting the Task to the Man: An ErgonomicsApproach, Taylor and Francis, London, 1988. Guay, A.H., Commentary: ergonomically related disorders indental practice, J Americ Dental Assoc 129 (1998), 184–186. Hildebrandt, V.H., Back pain in the working population:prevalence rates in Dutch trades and professions, Ergonomics38 (1995), 1283–1298. Holzman, P., A new method for analysis of ergonomic effort,Appl. Ergon 13 (1982), 82–87. Kuorinka, I., Jonsson, B., Kilbom, A., Vinterberg, H., Biering-Sorensen, F., Andersson, G. and Jorgensen, K., Standard-ised Nordic questionnaires for the analysis of musculoskeletalsymptoms, Appl Ergonomics 18 (1987), 233–237. Lehto, T.U., Helenius, H.Y.M. and Alaranta, H.T., Muscu-loskeletal symptoms of dentists assessed by a multidisciplinaryapproach, Community Dent Oral Epidemiol 19 (1991), 38–44. Mandel, I.D., Occupational risks in dentistry, JADA 124(1993), 41–49. Marshall, E.D., Duncombe, L.M., Robinson, R.Q. and Kil-breath, S.L., Musculoskeletal symptoms in New South Walesdentists, Aust Dent J 42 (1997), 240–246. Murtomaa, H., Work related complaints of dentists and dentalassistants, Int Arch Occup Environ Health 50 (1982), 231–236. Nachemson, A.L., Spinal disorders. Overall impact on societyand the need for orthepedic resources, Acta Orthop ScandSuppl 241 (1991), 17–22. Nachemson, A.L., Newest knowledge of low back pain: Acritical look, Clin Orthop 279 (1982), 8–20. Nordin, M. and Frankel, V.H., Evaluation of the workplace,Clinical Orthopedics and related research 221 (1987), 85–88. Nordin, M., Ortengren, R. and Andersson, G.B.J., Measure-ment of trunk movements during work, Spine 9 (1984), 465–469. Powell, M. and Eccles, J.D., The health and work of twoprofessional groups: dentists and pharmacists, Dent Practit20 (1970), 373–378. Rundcranz, B.L., Johnsson, B. and Moritz, U., Cervical painand discomfort among dentists. Epidemiological, clinical andtherapeutic aspects, Swed Dent J 14 (1990), 71–80. Rundcranz, B.L., Johnsson, B. and Moritz, U., Pain and dis-comfort in the musculoskeletal system among dentists, SwedDent J 15 (1991), 219–228. Ryden, L.A., Molgaard, C.A., Bobbitt, S. and Conway, J., Oc-cupational low back injury in a hospital employee population:an epidemiologic analysis of multiple risk factors of a highrisk occupational group, Spine 14 (1989), 315–320. Sholrof, B. and Donchin, M., Musculoskeletal symptomsamong industrial workers in Israel, Israel Epidemiology As-sociation, the 13th annual conference, Jerusalem, 1995. Shugers, D., Miller, D., Fishburne, C. and Stricklans, D.,Musculoskeletal pain among general dentists, Gen Dent 4(1987), 272–276. Valkenberg, H.A. and Haanen, H.C.M. The epidemiology oflow back pain, in: American Academy of Orthopedic SurgeonsSymposium on Idiopathic Low Back Pain, White, A.A. andGordon, S.L., eds., St. Louis, CV Mosby, pp. 9–22. Van Doorn, J.W.C., Low back disability among self employeddentists, veterinars, physicians and physical therapists in theNetherlands, Acta Orthopedic Scandinavian Supplement 66(1995), 1–64. Waddell, G., Biopsychosocial analysis of low back pain, Bal-lieres Clinical Rheum 6 (1992), 523–527. Waddell, G., Feder, G. and Lewis, M., Systemic reviews ofbed rest and advice to stay active for acute low back pain, BrJ Gen Pract 47 (1997), 647–652. Wagner, B., Optimal working posture, Quinsense Int 1 (1984),77–78. Westgaad, R.H. and Aaras, A., Postural muscle strain as acausal factor in the development of musculoskeletal illness,App Ergonomics 15 (1984), 162–174.