Evaluation of occupational and non-occupational risk factors associated with carpal tunnel syndrome in dentists

Abstract

BACKGROUND:

Musculoskeletal disorders are very prevalent among dentists. Of these disorders, carpal tunnel syndrome (CTS) is notable.

OBJECTIVE:

The aim of this study was to investigate the relationship between the occupational and non-occupational risk factors and CTS among dentists.

METHODS:

It is a cross-sectional study. We evaluated 106 dentists from dental schools in Tehran. We collected data by a general questionnaire, a hand diagram, and physical examination. A nerve conduction velocity (NCV) test was used to confirm the diagnosis of CTS. The analysis was performed using an independent T-test and logistic regressions on SPSS software.

RESULTS:

The prevalence of CTS among dentists was 17.9%. Significant risk factors of CTS included: vibration exposure greater than two hours per day (OR: 2.5), a wrist diameter ratio of greater than 0.7 (OR: 10.14), and female sex (OR: 13.38).

CONCLUSIONS:

Exposure to the hand-arm vibration should be considered as an occupational risk factor for CTS in dentists. Female dentists should take more preventive measures.

Keywords

Musculoskeletal disorders vibration wrist

1 Introduction

Musculoskeletal disorders are the most common form of occupational diseases and are the leading causes of disability and lost workdays [1]. Carpal tunnel syndrome (CTS) is one of the most prevalent types of occupational musculoskeletal disorders [2]. CTS is a clinical disorder caused by pressure on the median nerve at the wrist [3, 4]. CTS is a common disease with a cumulative incidence rate estimated at 8%in the general population [5, 6]. In an epidemiologic study, the researchers reported an incidence rate of about12 cases per 1000 person-years [7].

CTS typically occurs in adults aged 30–60 years old and its prevalence in women is three times higher than in men [8, 9]. Colles’ fracture, edema caused by infection, trauma, and tumors may be of the etiologies of this syndrome. Systemic conditions such as obesity, diabetes, hypothyroidism, lupus erythematosus, Reynaud’s phenomenon, pregnancy and use of birth control pills may also be potential contributors to CTS. Inflammatory conditions such as gout, rheumatoid arthritis, and granulomatous infections can lead to a diffuse inflammation of the synovial tendon, which may contribute to the development of CTS [8, 10].

Anthropometric factors (e.g. smaller size of carpal tunnel) or genetic factors such as ethnicity and gender are possible risk factors for this syndrome. Systemic disorders or anthropometric factors can increase the risk of CTS, even without any biomechanical risk factors such as repetitive movements [11].

Repetitive movements, applying high force, mechanical stresses and, vibration exposure are suspected as ergonomic risk factors for developing CTS. Dentists working in clinical departments at universities are usually at high risk for developing occupational musculoskeletal disorders.

However, since the discomfort is gradual and slow, it might be ignored until it has led to disability. According to the innate aspects of clinical work of dentistry, which is delicate, intricate and requires precise performance of wrist muscles and fingers; it seems that dentists are at increased risk for the development of CTS. Dental tools are equipped with cooling systems and usually are vibrating [12]. Also, dental tools require repetitive hand movements. Performing delicate handy work and long-term wrist flexion, performing wrist and finger bending movements, the use of MB spa dextrose hand gloves, and applying high force in some dental procedures such as tooth extractions, make dentists susceptible to CTS development [13].

This study aimed to investigate the occupational and non-occupational risk factors for CTS development in dentists and compare these risk factors between dentists with and without CTS.

2 Materials and methods

This analytical-cross-sectional study was conducted on 106 dentists (specialists and residents) working at the treatment centers of the Universities of Tehran, Shahid Beheshti, and Islamic Azad University in Tehran, Iran. Inclusion criteria included dentists with at least one year of experience of general or specialized dentistry and dentists who did not have underlying risk factors of CTS, and history of trauma or wrist surgery.

Different specialists such as endodontists, periodontists, oral and maxillofacial surgeons, orthodontists, pediatric dentists, prosthodontists, oral diseases specialists, restoration specialists, and general dentists were included in the study. We collected data by visiting different sectors of dentistry schools under the study. Qualified dentists gave us informed consents.

The ethical committee of the University of Social Welfare and Rehabilitation Sciences approved the study. All procedures performed in studies involving human participants were in accordance with the ethical standards of the University and with the 1964 Declaration of Helsinki.

2.1 Assessments

2.1.1 Questionnaires

The data recorded in the questionnaires included: sex, age, height, weight, hand dominance, history of trauma or wrist surgery, and history of systemic diseases associated with CTS (history of hypothyroidism, diabetes mellitus, radiculopathy of the cervical nerves, lupus, rheumatoid arthritis, gout, granulomatous infections, cervical rib conditions, tuberculosis, present pregnancy, and the use of birth control pills). We asked if they had recreational activities (such as golfing, tennis, music, working with computer and mouse, gardening, weaving, and knitting), and regular weekly exercise. In addition, we asked about the history of wrist pain, work experiences (years), the average number of work hours per week, rest time after each procedure, the exposure to vibration (no exposure, exposure less than 1 hour per day, exposure between 1-2 hours per day and exposure more than 2 hours per day), and repetitive movements.

2.1.2 Hand diagram

The dentists were asked about symptoms such as pain, tingling, and numbness in fingers 1, 2, 3 and were asked to identify the corresponding locations on the hand diagram for these symptoms.

2.1.3 Physical examination

Physical examination included Tinel’s sign and Phalen test. The diameter ratios of the subjects’ wrists were measured. We calculated the diameter ratio of the wrist by dividing the anterior-posterior depth to width of the wrist [14]. In 1998, Radecki P. defined the ratio of 0.7 as the increased incidence point of developing CTS [15]. Wrist ratio was measured using a caliper. A ratio larger than 0.7 was considered as a positive risk factor.

2.1.4 Diagnostic criteria

A specialist physician identified the suspicious CTS cases, and the diagnosis was confirmed by electro-diagnostic studies.

The probability of CTS diagnosis was considered to be in one of the four categories according to the hand diagram [16 –19].

Classic group: Symptoms such as itching, burning, numbness, and pain in palm, wrist, and at least in two fingers 1, 2 or 3

Plausible group: Symptoms such as itching, burning, numbness, and pain in wrist, and at least in two fingers 1, 2 or 3 (sparing the palm)

Possible group: Symptoms in at least one of the fingers 1, 2 or 3 and there might be pain in the back of the hand

Unlikely group: Without any symptoms, and not any points of discomfort on the hand diagram

We considered participants in classic and plausible groups as suspicious CTS cases regardless of the results from Tinel’s sign and Phalen test. Participants in the possible group were identified as CTS suspected, too, if only the clinical examinations (Tinel’s sign and Phalen test) were positive.

The suspected CTS subjects were referred to perform electro-diagnostic studies to confirm the diagnosis.

2.2 Statistic analysis

Chi-square test, independent t-test, and logistic regression on SPSS software were used to analyze the data.

3 Results

In this study, 106 dentists were studied, of which 67 (63%) were female and 39 (37%) were male. 19 dentists (17.9%) had CTS in at least one hand (determined by NCV testing). Among them, 17 (89.4%) were female and 2 (10.5%) were male. All CTS diagnosed cases had the syndrome in their dominant hands.

The ratio of female to male dentists with CTS (female: male ratio) was 8.5:1. The mean wrist diameter ratio in dentists with CTS was 0.72±0.04, which was significantly higher than the mean wrist diameter ratio of dentists without CTS which was 0.68±0.02 (P = 0.01). In addition, the mean BMI of dentists with CTS (22.57) was significantly lower than the mean BMI of dentists without CTS (24.73) (P < 0.05). The mean of other variables - including age, exercise per week and entertainment per week - were not significantly different between the two groups of dentists with CTS and without CTS (P > 0.05).

Among the occupational factors assessed, mean time of exposure to vibration was significantly higher in the dentists with CTS (3.53±1.26) compared to dentists without CTS (2.83±1.30), (P = 0.039). In addition, the number of patients visited per day for dentists without CTS was significantly higher than those for dentists with CTS (P < 0.05). Other occupational variables including hours worked per day, rest time at work, specialty, force applied, repetitive movements and work experience were not significantly different in both groups (P > 0.05), (Table 1).

Table 1
Comparison of quantitative variables in two groups of dentists with CTS and without CTS

Variable CTS Mean Std.Deviation P value

Age (year) No 37.24 10.84 0.971

Yes 37.16 8.66

BMI No 24.73 4.62 0.021

Yes 22.57 3.24

Entertainment time (hour/week) No 3.57 6.78 0.258

Yes 2.42 3.06

Sport time (hour/week) No 1.19 2.21 0.691

Yes 1.00 1.85

Job duration (hour/day) No 4.43 6.28 0.980

Yes 4.39 5.49

Experience (year) No 7.42 8.41 0.797

Yes 6.94 6.87

Patients visited (per day) No 7.06 6.00 0.011

Yes 4.73 2.70

Exposure time to vibration (hour/day) No 2.82 1.30 0.039

Yes 3.52 1.26

Variable	CTS	Mean	Std.Deviation	P value
Age (year)	No	37.24	10.84	0.971
	Yes	37.16	8.66
BMI	No	24.73	4.62	0.021
	Yes	22.57	3.24
Entertainment time (hour/week)	No	3.57	6.78	0.258
	Yes	2.42	3.06
Sport time (hour/week)	No	1.19	2.21	0.691
	Yes	1.00	1.85
Job duration (hour/day)	No	4.43	6.28	0.980
	Yes	4.39	5.49
Experience (year)	No	7.42	8.41	0.797
	Yes	6.94	6.87
Patients visited (per day)	No	7.06	6.00	0.011
	Yes	4.73	2.70
Exposure time to vibration (hour/day)	No	2.82	1.30	0.039
	Yes	3.52	1.26

Chi-square test showed significant relationship between CTS and sex, exposure to vibration over 2 hours per day, and wrist diameter ratio greater than 0.7. Table 2 shows the prevalence of each of the qualitative variables assessed in dentists with CTS and without CTS.

Table 2

Comparison of qualitative variables studied in two groups of dentists with CTS and without CTS

Variable	CTS		Total	P value
	No	Yes
Gender
Female	74/6%	25/4%	67	0.009
Men	94/95	5/1%	39
Wrist ratio
≤0.7	92.30%	7.70%	52	0.010
> 0.7	72.20%	27.80%	54
Total	87	19	106

Logistic regression tests showed the risk of CTS so that the determining factors in the final stage included sex, exposure time to vibration per day, and the wrist diameter ratio greater than 0.7. Positive coefficients of these three variables showed that the likelihood of CTS increases in female dentists, dentists with wrist diameter ratio greater than 0.7, and time of exposure to hand and arm vibrations higher than two hours per day. Therefore, the only proven occupational risk factor was exposure to hand-arm vibration.

The odds ratio for sex was 13.38 (CI 95%:2.52, 71.10), the odds ratio for exposure to hand-arm vibration was 2.25 (CI 95%:1.23, 4.10), and finally, the odds ratio for wrist dimension was 10.14 (CI 95%: 2.61, 39.35), (Table 3).

Table 3

Risk of CTS and significance value of the relationship between independent variables in the final model

Risk factor	CTS (Yes)	CTS (No)	OR	P value	CI 95%
Gender (female)	17	50	13.38	< 0.001	2.52, 71.10
Hand-arm vibration exposure time (hour)	17	76	2.25	< 0.001	1.23, 4.10
Wrist diameter (mm)	15	39	10.14	< 0.001	2.61, 39.35

The Nagelkerke R Square value was 0.39, indicating that 39%of changes in the dependent variable (carpal tunnel syndrome) were due to changes in the independent variables (sex, time exposure to vibration and wrist diameter ratio).

The general formula of logistic regression: $\begin{matrix} Time of vibration = The time of exposure to \\ hand - arm vibration per day (h) \end{matrix}$ $\begin{matrix} \frac{p}{1 - p} = Ln (2.6 \times {Sex}^{1}) + 0.81 \\ \times Time Vibration + 2.32 \times Wrist diameter ratio \end{matrix}$ $Sex = {\begin{matrix} female = 2 \\ male = 1 \end{matrix}$

4 Discussion

In our study, occupational and non-occupational risk factors for developing CTS were assessed in dentists. The results showed that vibration exposure more than two hours per day (odds ratio: 2.5), a wrist diameter ratio of greater than 0.7 (odds ratio: 10.14), and female sex (odds ratio: 13.38), would increase the risk of CTS development in dentists.

In our study, the ratio of female to male in CTS patients was 8.5:1. It is consistent with previous studies conducted in Iran [19]. This result also supports the findings of previous studies in other nations [20, 21]. However, a study conducted by Haqiqat in Iran, found no significant difference between genders with CTS [22]. Besides, in a study by Maghsoudipour et al. on 439 industrial workers, no relationship was found between gender and CTS. They concluded that male workers had more exposure to occupational risk factors for CTS compared to female workers in their study [23]. Some previous researchers assumed that more women’s participation in housework added more biomechanical loads, which might contribute to or worsen upper limb repetitive stress disorders [24].

The mean age of our patients diagnosed with CTS was 37.2 years. In a previous study on a general population, the highest frequency of CTS occurred in the age group of 40 to 49 years [19]. Also, a meta-analysis for the evaluation of occupational risk factors for CTS showed that incidence of the syndrome increases with age [25]. The Becker study revealed that being aged 41 to 60 years old, significantly influenced the risk of CTS [26]. Our patients in the lower age group were busier in their jobs, and maybe less experienced, so, this may account for a higher risk of developing CTS at younger ages. Another study in line with our results explained the carpal tunnel syndrome (CTS) as a disease of the century, with increasing the incidence and predominant age ranging from 25 to 40 years [27].

The mean BMI in dentists with CTS was significantly lower than the mean BMI in dentists without CTS. These results disagree with the results of previous studies [26 –28]. It might be attributed to the relationship of BMI with sex in our study and high socioeconomic status of female dentists in our society who are so concerned about their weights.

In our study, a significant relationship was found between CTS and wrist diameter ratio. The mean wrist diameter ratio of dentists with CTS was significantly higher than the mean wrist diameter ratio of dentists without CTS. This study confirmed the results of previous studies [14 , 28].

Out of 106 dentists studied, 19%had CTS, and in 93%of these cases, CTS was observed in the dominant hand. The study showed a significant relationship between the dominant hand and prevalence of CTS. These findings are inconsistent with a previous study conducted in Iran [29].

We did not find a significant relationship between repetitive movements and CTS in our subjects. However, in the study conducted by Katz et al., the relationship between biomechanical risk factors and the occurrence of CTS was observed. They stated that there is strong evidence for an association between increased risk of CTS and factors such as repetitive movements and force application [30]. The explanation for this discrepancy might be the similarity of the maneuvers between our cases.

We did not find a significant relationship between regular exercise and entertainment activities (such as tennis, music, and golf) with CTS prevalence. The reason for that observation might be due to the low number of dentists with regular exercises or hobbies. Also, another study conducted on dentists had the same conclusion [31].

Our study showed that the number of patients visited per day by dentists without CTS was significantly higher than that in dentists with CTS. The pain and numbness in dentists with CTS might cause the dentists to visit fewer patients to attenuate their symptoms. Also, our results revealed that there is no significant relationship between working hours per week and CTS. These findings are inconsistent with the results of a previous study conducted in Iran [29]. More extensive sample studies are required to test the effect of working hours on CTS development in dentists.

Although we did not find a significant relationship between the prevalence of CTS and the specialty field of the dentist, pediatric dentists displayed the highest incidence of CTS (5 dentists) followed by restorative dentists (4 dentists). Lack of cooperation of younger patients may result in awkward working postures for dentists. However, small oral cavities are more challenging for therapists, resulting in poor posture and placing more pressure on the wrists. The higher prevalence of CTS among restorative dentists might be due to longer procedure times and more repetitive movements.

The results of this study showed that there is a significant relationship between the prevalence of CTS and the exposure to vibrating equipment (hand and arm vibration), which suggests that the risk of developing CTS increases with increasing exposure to vibrating equipment (e.g., micro-motors, angel turbines). These findings are consistent with the results of a study in Germany, which evaluated the relationship between CTS and occupational risk factors [25]. Also, the study conducted by Katz et al. revealed the relationship between vibration and a higher risk of CTS at moderate levels of vibration [30]. Another study consistent with our study, suggested that proper ergonomics in the operating field and few strengthening exercises can reduce the onset and progression of the symptoms [32]. According to previous studies carpal tunnel syndrome is the most common self-reported musculoskeletal disorder in dentists [33] and precautions are needed to prevent irreversible changes occurring in dentists [34].

4.1 Limitations

Our study had limitations. First, the sample size was modest. Although we had enough sample size for detecting the difference between dentists with and without CTS, subgroup analysis was not possible especially across different specialties of dentists. Second, our assessment only included the Iranian dentists and our conclusions are limited to the population studied.

5 Conclusion

Female gender, wrist dimension greater than 0.7, and exposure to vibration are critical factors associated with the development of CTS in dentists. The results of our study may impact the health policies for dentists to apply more ergonomic principles to decrease exposure to hand vibrating tools, especially in female dentists.

Conflict of interest

None to declare by all authors.

Funding

This research was not supported by grant funding from any agency in the public, commercial, or not-for-profit sectors.

References

Habib

, and Hassanzade

. Evaluation of ergonomic risk factors by OCRA method in assembly industry. Iran Occupational Health. 2008;5(1):70–76.

Newington

, Harris

, Walker-Bone

. Carpal tunnel syndrome and work. Best Pract Res Clin Rheumatol. 2015;29(3):440–53.

Gelberman

, Rydevik

, Pess

. Carpal tunnel syndrome—a scientific basis for clinical care. Orthop Clin North Am. 1988;19(1):115–24.

Phalen

. The carpal-tunnel syndrome. J Bone Joint Surg. 1966;48A(2):211–28.

Stevens

, Witts

, Smith

, Weaver

, The frequency of carpal tunnel syndrome in computer users at a medical facility. Neurology. 2001;56(11):1568–70.

Adams

, Franklin

, Barnhart

. Outcome of carpal tunnel surgery in Washington State workers’ compensation. Am J Ind Med. 1994;25(4):527–536.

Nordstrom

, DeStefano

, Vierkant

, Layde

. Incidence of diagnosed carpal tunnel syndrome in a general population. Epidemiology. 1998;9(3):342–5.

Jerry

. Campbell’s operative orthopaedics. 9th ed. Vol 4. St Louis. Mosby; 1998:3685-94.

de Krom

, Knipschild

, Kester

, Thijs

, Boekkooi

, Spaans

. Carpal tunnel syndrome: Prevalence in the general population. J Ciln Epidemiol. 1992;4(45):373–6.

10.

Dee

, Mango

, Hurst

. Principles of orthopaedic practice. Vol 1. New York: McGraw-Hill; 1988:673–676.

11.

Franklin

, Haug

, Heyer

, Checkoway

, Peck

. Occupational carpal tunnel syndrome in Washington State, 1984-1988. Am J Public Health. 1991;81(6):741–6.

12.

Werner

, Armstrong

. Carpal tunnel syndrome: ergonomic risk factors and intra-carpal canal pressure. Occupational Health and Industrial Medicine. 1997;6(37):287–90.

13.

Powell

, Winkley

, Brown

, Etersque

. Evaluating the fit of ambidextrous and fitted gloves: implications for hand discomfort. J Am Dent Assoc. 1994;125(9):1235–42.

14.

Kamolz

, Beck

, Haslik

, et al. Carpal tunnel syndrome: a question of hand and wrist configurations? J Hand Surg Br. 2004;29(4):321–4.

15.

Radecki

. A gender specific wrist ratio and the likelihood of a median nerve abnormality at the carpal tunnel. Am J Phys Med Rehabil. 1994;73(3):157–62.

16.

Rempel

, Evanoff

, Amadio

, de krom

, Frazblau

, et al. Consensus criteria for the classification of carpal tunnel syndrome in epidemiologic studies. Am J Public Health. 1998;88(10):1447–51.

17.

Katz

, Stirrat

, Larson

, Fossel

, Eaton

, Liang

. A self-administered hand symptom diagram for the diagnosis and epidemiologic study of carpal tunnel syndrome. J Rheumatology. 1990;17(11):1495–8.

18.

Franzblau

, Werner

, Alers

, Grant

, Olinski

, Johnston

. Workplace surveillance for carpal tunnel syndrome using hand diagrams. Journal of Occupational Rehabilitation. 1994;4(4):185–98.

19.

Choobineh

, Rahimi

, Tavakoli Manesh

, Hosaini

, Tabatabaei

. Epidemiological study of carpal tunnel syndrome among patients referring to Shiraz Chamran and Nemazi hospitals from 2002 to 2006. Iran Occupational Health. 2009;6(3):20–6.

20.

Hulston Michal . Work-related upper limb disorders: recognition and management, A Hodder Arnold Publication; 1997:77–9.

21.

Nordstrom

, Vierkant

, Destefano

, Layde

. Risk factors for carpal tunnel syndrome in a general population. Occup Environ Med. 1997;54(10):734–40.

22.

Haghighat

, Khosrawi

, Kelishadi

, Sajadieh

, Badrian

. Prevalence of clinical findings of carpal tunnel syndrome in Isfahanian dentists. Advanced Biomedical Research. 2012;1, 13–16.

23.

Maghsoudipour

, Moghimi

, Dehghaan

, Rahimpanah

. Association of occupational and non-occupational risk factors with the prevalence of work related carpal tunnel syndrome. J Occup Rehabil. 2008;18(2):152–6.

24.

Yang

, Cheung

. The inclusion of homemakers as an occupation amongst people with upper limb repetitive stress injuries. Work. 2016;55(1):181–6.

25.

Spahn

, Wollny

, Hartmann

, Schiele

, Hofmann

. [Meta-analysis for the evaluation of risk factors for carpal tunnel syndrome (CTS) Part II. Occupational risk factors]. Z Orthop Unfall. 2012;150(5):516–24.

26.

Becker

, Nora

, Gomes

, Stringari

, Seitensus

, Panosso

, Ehlers

. An evaluation of gender, obesity, age and diabetes mellitus as risk factors for carpal tunnel syndrome. Clin Neurophysiol. 2002;113(9):1429–34.

27.

Costa

, Barros

, Campos

, Lima

, Barbosa

. An epidemiological profile of cashiers holders carpal tunnel syndrome in a grocery store chain. Work. 2012;41(Suppl 1):5794–8.

28.

Hlebs

, Majhenic

, Vidmar

. Body mass index and anthropometric characteristics of the hand as risk factors for carpal tunnel syndrome. Coll Antropol. 2014;38(1):219–26.

29.

Borhan Haghighi

, Khosropanah

, Vahidnia

, Esmailzadeh

, Emami

. Association of dental practice as a risk factor in the development of carpal tunnel syndrome. Journal of dentistry (Shiraz, Iran). 2013;14(1):37–40.

30.

Katz

, Stirrat

, Larson

, Fossel

, Eaton

, Liang

. A self-administered hand symptom diagram for the diagnosis and epidemiologic study of carpal tunnel syndrome. J Rheumatol. 1990;17(11):1495–8.

31.

Harutunian

, Gargallo-Albiol

, Figueiredo

, Gay-Escoda

. Ergonomics and musculoskeletal pain among postgraduate students and faculty members of the School of Dentistry of the University of Barcelona (Spain). A cross-sectional study. Med Oral Patol Oral Cir Bucal. 2011;16(3):425–29.

32.

Prasad

, Appachu

, Kamath

, Prasad

. Prevalence of low back pain and carpal tunnel syndrome among dental practitioners in Dakshina Kannada and Coorg District. Indian J Dent Res. 2017;28(2):126–32.

33.

de Jesus Júnior

, Tedesco

, Macedo

, Agra

, Mello-Moura

, Morimoto

. A self-report joint damage and musculoskeletal disorders data among dentists: a cross-sectional study. Minerva Stomatol. 2018;67(2):62–7.

34.

Abichandani

, Shaikh

, Nadiger

. Carpal tunnel syndrome - an occupational hazard facing dentistry. Int Dent J. 2013;63(5):230–6.