Musculoskeletal Disorders among Brazilian Dentists in São Paulo

OBJECTIVE: This study aimed at investigating the relationships between health and work-related musculoskeletal disorders (WMSDs) in dentists, and the relationship with socio-demographic, work and health variables. METHODS: We conducted a cross-sectional study of 204 dentists who work in public clinics in the state of São Paulo, Brazil. We used a self-administered survey that included questions on sociodemographic and health aspects, work-related factors, and the Nordic questionnaire. RESULTS: WMSDs were often reported in the neck, shoulder, lower back, and hand/wrists. Logistic regression analysis revealed that there was a correlation between reports of WMSD in the neck and age (OR = 9.48) and health problems (OR = 6.71). Moreover, strong associations were found between MSDs in the shoulders, gender (OR = 5.88) and breaks between appointments (OR = 4.17). CONCLUSION: We concluded that the health problems diagnosed, work-related activities and gender contributed to musculoskeletal disorders in dentists in this clinic.


INTRODUCTION
Oral health-related problems affect much of the population in Brazil and abroad, and dentists are often exposed to a greater number of patients in clinics and consequently, an intense workload. In addition, the dental market has become very competitive and has influenced the daily life of these professionals, with changes in their professional exercise requiring great physical effort and increased work days [1,2].
In Brazil, most dentists that previously were dedicated to work only in the public service or just in private practice today exert exhaustive working hours in both types of services. It is also observed that these professionals often work in stressful conditions, spending hours in nonergonomic awkward postures and performing accurate and repetitive movements [3].
These conditions lead this category of professionals to develop health problems resulting from the exercise of the profession, particularly musculoskeletal disorders. Such diseases are characterized by the presence of discomfort, disability or persistent pain in the joints, muscles, tendons and other parts caused or aggravated by repetitive movements and inadequate prolonged postures or bodily forces [4].
Various case definitions for musculoskeletal disorders are cited in the literature. Some rely on the subject's reported frequency, duration or intensity of pain [5] while others define cases as any report of pain in the specified time period. Physical examination findings have also been included in the definition, however, many MSDs have no detectable physical findings.
The high prevalence of musculoskeletal disorders is also observed in other studies, more frequently affecting the neck, lower back and shoulders [4,[6][7][8][9][10][11]. Some studies have found that musculoskeletal disorders in dental professionals significantly contribute to reduced productivity, departure because of health problems and abandonment of the profession [9].
According to the International Dental Federation (IDF), Brazil has the largest number of dental professionals in the world; in absolute numbers, there were almost 220,000 registered professionals by the year 2009. However, few studies have been performed in Brazil to assess musculoskeletal disorders in dentists [2,7,12] and the questionnaire of perception of work-related factors was not applied earlier in this group of professionals, but only in dental students [13] and dental hygiene technicians [14].
The objective of this study was to investigate the prevalence of musculoskeletal disorders in dentists who work in clinics of the National Health System in the state of São Paulo and describe the relationships between work related risk factors and the prevalence WMSDs.

Ethical aspects
The study was approved by the Ethics Committee for Research on Humans of the Araçatuba School of Dentistry, Paulista State University and performed with the understanding and written consent from each participant.
An exploratory cross-sectional study was conducted in public health services of the National Health System that provide dental care in the northwest health region of São Paulo. São Paulo is a state located in southeastern Brazil, with the highest concentration of dentists in Brazil (33.0%). The northwest health region covers 40 municipalities in the region, with about 346 dentists working in the dental offices of Family Health Units, Emergency Care Units and specialized dental clinics in this health region.
The sample consisted of 204 dentists who were active in the municipalities in that period and were working 20 or 40 hours per week in the public health service, and the survey response rate was 69,4%. The sample excluded patients with congenital or acquired physical disabilities involving the upper or lower limbs, joint or spine, pregnant and lactating women.

Data collection
Data collection was performed for four months in 2016. The data relating to socio-demographic variables, work and health of dentists were obtained through a structured questionnaire designed specifically for this study. Sociodemographic variables include age, gender and marital status. The work-related are: work location, working hours, breaks between calls and clinical time. In relation to health, there was the body mass index (BMI), physical activity, diagnosis of any disease in the last 12 months and use of pain medication.
To evaluate musculoskeletal symptoms, the Nordic Questionnaire developed by Kuorinka et al. [15] was used with the aim of standardizing the measurement of reporting musculoskeletal symptoms. The Brazilian version of the Nordic questionnaire was validated and adapted by Barros and Alexandre in 2003 [16]. This instrument consists of the rear view of a human figure, divided into nine anatomical regions: neck, shoulders, upper and lower back, elbows, wrists / hands, hips / thighs, knees and ankles / feet. It includes questions about the presence of musculoskeletal pain in any of the nine anatomical areas impediment to perform normal activities and need for consultation by a healthcare professional. The period of 12 months prior to the study was considered as the occurrence time for musculoskeletal symptoms.
The questionnaire on risk factors at work that can contribute to musculoskeletal disorders (work-related) was also applied to identify how much work activities contribute to the development of musculoskeletal disorders. This tool was originally developed by Rosecrance et al. [17] in the US. It was adapted and validated in 2009 for the Brazilian culture by Colucci and Alexandre [18]. It consists of 15 questions that seek to assess the perceptions of individuals related to different risk factors at work and their contribution to workrelated musculoskeletal disorders. The subjects were asked to indicate on a scale from 0 to 10 (0 = none and 10 = a lot) how much each variable contributed to the development of pain and injury related to their current tasks at work. Responses were classified in scale with three categories that indicate the severity of symptoms in ascending order: the first 0-1 indicates the absence of symptoms, the second 2-7 indicates minimal to moderate symptoms and the last 8-10 indicates more severe symptoms.

Data analysis
Descriptive analyzes were performed for sociodemographic characterization of the population through measures of central tendency (single, mean and median frequencies) and dispersion (standard deviation). Statistical chi-square tests, Fisher and the maximum likelihood ratio for bivariate analysis to evaluate statistical associations between the dependent and independent variables were performed. The independent variables are the five body regions with higher prevalence of reported musculoskeletal symptoms in the last 12 months: neck, shoulders, upper and lower back and wrist / hand, and the socio-demographic, work-related and health as dependent variables, in addition to the work factors associated with musculoskeletal disorders (workrelated).
The multivariate logistic regression model included all variables that were associated to the level of p < 0.01. After adjusting the multiple logistic regression model with a 95% confidence interval, the p values were estimated. All statistical analyzes were performed using the SPSS version 21.0.

RESULTS
More than half of the study participants were women (62.3%) with mean age of 43 years (SD 9.51) and with a stable relationship (71.9%). Most worked in clinics for an average of 21 years (SD 9.48). Much of the sample worked in public and private services (63.7%), with a workload of more than 8 hours per day (41.4%). In addition 38.4% said they did not take breaks between daily appointments, and among those who did, they had only 1 or 2 (45.9%) daily breaks.
As seen in Table 1, most had normal BMI (53.0%), but there is a considerable portion being overweight (35.9%). The majority (66.7%) practiced physical activity for more than 1 year (69.4%) and three times a week (41.9%). Twenty six percent of respondents had some health problem diagnosed in the last year and 62.3% of these were related to musculoskeletal disorders. Most respondents (60.1%) made use of analgesics (22.0%), anti-inflammatory drugs (33.3%) or a combination of both (30.1%). Table 2 shows that 81.4% of the sample reported pain in the last 12 months. More than half of dentists had pain in the neck (55.4%), shoulders (52.0%) and upper back (50.5%), while 46.1% had sore hands and wrists and 48.8% at the lower back. Musculoskeletal pain in the lower regions (hips, thighs, knees, ankles and feet) were observed in less than 30% of respondents. Regarding the impediment to perform their normal activities, it can be seen in Table 2 that 40.2% of dentists reported that pain interfered with such performance in the last 12 months. Just over half (50.5%) of dentists sought care with a health professional because of musculoskeletal disorders. Forty one point seven percent reported pain in some body area in the last 7 days.
Regarding the problems related to risk factors at work that can contribute to musculoskeletal symptoms, most participants reported moderate or minor problems (77.9%). The issues that had higher scores (average above 6) were "Bending or twisting the back uncomfortably," "Keep working when they are in pain or injury", "Working in the same position for long periods" and "Working in inadequate positions / tight spaces. "   The bivariate analysis of the Nordic Questionnaire variables ( Table 3) shows the following statistically significant associations (p < 0.05): a) neck pain in the last 12 months were associated with age, years of work, healthrelated problems, the use of pain medication and problems related to risk factors related to work b) shoulder pain was associated with gender, breaks between daily care and use of pain medication c) lower-back pain was associated with breaks in between daily care and medication use. e) pain in the upper back was associated with years of work, use of medication for pain and problems related to risk factors related to work f) pain in the wrists and hands were associated with drug use and problems related to risk factors related to work.
The multiple logistic regression model shows that being older (OR = 9:48) and related health problems (OR = 6.71) increased the risk of developing neck pain; and individuals from the female gender (OR = 5.88) that did not take breaks between sessions (OR = 4.17) had a higher risk of having shoulder problems ( Table 4). In addition, individuals who did not take breaks between sessions (OR = 6.87) also had a higher risk of musculoskeletal symptoms in the lower back.

DISCUSSION
Studies on musculoskeletal disorders in dentists have been performed for over 40 years and have generated important proposals for changes in the working process of these professionals, even with the change of standing work position for seated [16]. Their knowledge is still incipient in Brazil, although there are many studies on the prevalence of musculoskeletal complaints in other countries.
Some of these studies show a high prevalence of pain in the regions of the neck, shoulders and back, as found in this study. For example, in the study of 268 Polish dentists, 60.1% reported lower back pain, and neck pain (56.3%), lower extremities (47.8%) and wrists / hands (44.0%) [8]. In a similar study with dental professionals in Denmark, lower back pain was also the most reported problem prevalent in two-thirds of the study sample [6].
The most affected area reported by Brazilian dentists in our study was the neck (55.4%), as conducted by Alexandre et al. [12] with 298 Brazilian dentists. This author found that dentists had higher risk of developing musculoskeletal disorders, particularly back pain, tendinitis and arthritis than the general population and other health professionals such as doctors. Barbosa et al. [11] also found that dentists in the state of Minas Gerais were 1.5 times more likely to report musculoskeletal problems than other health professionals.
Occhionero et al. [19] conducted a systematic review of musculoskeletal disorders in health workers and showed that for dentists, the neck is the most affected area of the body in all the analyzed studies, with prevalence from 26% to 73%, and greater than 50% in 7 of the 12 reviewed studies. This high incidence of neck pain can be explained by the fact that dental professionals work most of the time with the neck flexed at 30 degrees [20], and that many dentists do not use indirect vision with a clinical mirror to work in the jaw region of the patient [21]. The use of a clinical mirror facilitates and eases movements to examine the oral cavity, as verified in the study by Santos and Barreto [7], in which indirect vision was associated with lower frequencies in neck pain.
The high prevalence of musculoskeletal disorders found among dental professionals can also be explained by exposure to awkward postures during the visits, the management of vibrating tools, excessive working hours, often without breaks, and the precise movements performed [7,9,[22][23][24]. Our study found similar results, probably because the dentists who participated worked in both the public and private service, with work days of over 8 hours, without breaks between sessions.
The realization of pauses between sessions is essential to alternate the muscle groups and keep work productive. Detailed analyses on rest breaks in the dental practice were made by some authors, which found that more than 30% Musculoskeletal disorders and dentists | Soares et al. of dentists work without breaks [8,25]. In our study, it was observed that the lack of breaks increased the likelihood of these professionals to present shoulder and lower back pain. The guidelines of the American Association of Industrial Hygienists (AAIH) recommends at least 6 minutes rest every hour for professionals who perform repetitive movements [26].
Wazzan et al. [27] found that only 37% of oral health professionals who suffer from neck and lower back pain sought medical attention, and concluded that these symptoms among dental professionals were not severe enough to require medication. In our study, more than half of dentists routinely used drugs for pain, and only 50.5% sought medical care because of musculoskeletal symptoms.
The reason for the difference in musculoskeletal symptoms between men and women is unclear, although researchers claim that women can pay more attention to their health and well-being, and that they may have a lower pain threshold or have less resistance to muscular stress [10]. On the other hand, according to these authors, women experience a double workday in their day-to-day, especially those living with a partner and children. They are burdened by household chores with less time for leisure activities and necessary rest, and therefore suffer the effects caused by occupational tasks more than men [28].
According to the published literature in scientific journals, the activities related to work that most commonly cause problems for health professionals are lifting heavy equipment, working in the same position for a long time and repetitive movements [29]. The variables that were perceived as greater risk factors for muscular-skeleton disorder symptoms in our study were related to the working position -bending the back uncomfortably, working in the same position for long periods and in inadequate positions, corroborating with previous studies on the subject.
There are no previous studies in the literature that have evaluated the perception of dentists regarding the association between risk factors and symptoms of musculoskeletal disorders. Garcia et al. [13] found that there was a strong association with the neck region in dental students. In addition, Anton et al. [14] applied the same instrument used in our study to oral hygiene technicians, and found that the main problems reported were related to the working posture and repetitive movements.
A few years ago, newly trained dentists worked intensely, more than 8 hours a day in the early years of their careers. But what can be observed in our study is that even with the average of 21 years of clinical practice professionals have two employment relationships and exert an intense workload. The organization of work in dentistry has changed along with the exchanges in the labor market in Brazil, causing increased workdays, shift work, and the number of employment relationships. Moreover, the absence of breaks and costs of productivity becomes routine in the life of these professionals, which together may influence their health [30].
The results of our study demonstrate the need to develop ergonomic practices for the improvement of working conditions of Brazilian dentists. The practice of ergonomics becomes essential to determine the best way to achieve success in the profession without abandoning the clinical practice because of health problems or even leaving the profession.

CONCLUSION
Given the cross-sectional design of the study, it is not possible to establish a cause and effect relationship for the associations found between the symptoms of musculoskeletal disorders and other variables. Research based on questionnaires completed by respondents themselves allow for the occurrence of self-report bias. In addition, the nonprobability and non-randomized sample compromises the legitimacy of the answers by dentists, making it difficult to generalize the results for the rest of these professionals throughout Brazil.