INTRODUCTION

Dentistry is a profession that has a high prevalence of work-related musculoskeletal disorders; symptoms can manifest very early, and often begin in the student phase. Ergonomic interventions in physical, cognitive, and organizational domains have been suggested to prevent their occurrence, but evidence for their effects remains unclear¹.

Dentists work in static positions for long periods of time because they adopt a position in relation to the patient; if associated certain risk factors can produce harmful physiological changes in the body, mainly when assuming abnormal postures. These changes often result in pain, injury, or musculoskeletal disorders^2,3.

Musculoskeletal disorders encompass various pathologies that are the main cause of early worker retirement and can cause symptoms that hinder professional activity, such as pain, fatigue, and even functional deterioration of the spine^4,5,6.

By their nature, ergonomic principles in dentistry play a fundamental role in protecting the health of dental equipment. All professionals must learn and apply its principles from initial education at university. Changing bad habits is always more difficult than learning and starting to work properly⁷.

The risk of developing musculoskeletal disorders in dentistry can be assessed by different methods, with the use of standardized observation methods being preferable8. OWAS (Ovako Working Posture Analysis System), is a method that allows the prevention of disorders caused by the adoption of inappropriate postures during clinical-dental activity; it is relatively simple, clear, and refers to the position of the whole body⁹.

Ovako's Work Posture Analysis System (OWAS) was developed between 1974 and 1978 by the company Ovako Oy together with the Finnish Institute of Occupational Health^10,11, and it is one of the most used methods to identify and evaluate bad work postures. The method consists of two parts, an observation technique to evaluate work postures; the second presents a set of criteria for redesigning methods and workplaces. The criteria were based on evaluations carried out by experienced workers and ergonomics experts taking into account factors such as health and safety, but the main emphasis is on the discomfort caused by work postures¹².

OWAS facilitates observation and can also be an option to evaluate dental work positions; it is a method that is well adapted to the demands of occupational health, it is practical to analyze the workplace and not only identify the observed problems, but also provide guidance for its correction, it also has the additional advantage of requiring only a few seconds to evaluate and record the posture (García, Polli and Campos 2013). It is a simple and useful method, it can be used by personnel from different spheres, such as health, engineering, industry, etc., without specialized training and it is well documented¹¹.

Each of the positions that the professional adopts receives a pre-assigned digit plus the digit of the effort made. Each posture of the body is, therefore, identified by a code made up of six digits, three corresponding to the postures of the trunk, arms and legs, another for the load or force carried out and another two complementary ones corresponding to the one assigned to the work phase in which the observation has been made. The observed positions are registered by means of a code system¹².

The objective of the study was to evaluate the risk of developing musculoskeletal disorders in dental students and generate early corrective measures according to the OWAS method.

 

Material y methods

This was a cross-sectional observational study, which included 90 ninth-semester students of both sexes during patient care at the Comprehensive Clinic of the Faculty of Dentistry which was approved by the Ethics and Research Committee on Human Beings of the Central University of Ecuador. Those who signed the acceptance in an informed consent were evaluated and were observed through videos or photographs during work moments.

The students were evaluated regarding the work postures adopted during the performance of various clinical procedures over a period of 2 months. Observations were made for 20 to 40 minutes with an interval of 30 to 60 seconds of rest. For the analysis of the working position of the 9th semester of the Integral Clinic, the image of the part of a working day that takes the longest in the entire process of student work was selected.

Postures were observed according to the OWAS method: the posture of the trunk was registered in the 1st box; in the 2nd, that of the arms; in the 3rd, that of the lower extremities; in the 4th, the load or force used; and in the 5th and 6th, the phase of the work or task cycle (Figure 1). For the registration we proceeded: 1st. Pointing the work to collect the posture, strength and phase of work recording videos or photographs. 2nd. What was observed was recorded and the results were established¹⁰.

Figure 1. Codes for registering postures and the load or strength performed.

Fuente: National Institute for Safety and Hygiene at Work 201510

For the description of categories in the static load evaluation and its correlation with activities to improve working conditions, they are reclassified into four categories according to the results, which are operational in nature and each have an implication, that is:

• Class 1 = the positions taken during the operation are natural. The load is optimal or acceptable. There is no need to change the position.
• Class 2 = the position or positions taken during operation can affect the motor system. The load is almost acceptable. It is not necessary to change the position immediately, but you should take into account the need for such changes in the near future.
• Class 3 = the position or positions taken during working hours have a negative effect on movement. The load is great. Changes in the workplace should be carried out as quickly as possible.
• Class 4 = the position or positions at work have a very negative effect on movement. The load is very high. Changes in the workplace must take place immediately (Niciejewska and Klimecka-Tatar 2016).
  

 

The result that was obtained after the evaluation of each of the participants gave us the percentages of risk levels for each of the activities analyzed, which in turn lead to the action levels that must be taken into account in order to determine the priority of the relevant operational controls for each level.

 

Results

According to the OWAS posture evaluation method, for dental students in the last semester of career, the highest risk of developing musculoskeletal injuries was in the back, it was predominant to find dental procedures in the sitting position with the torso slightly twisted, inclined towards ahead (49%); with a tilted or turned to the side position (16%); and tilted and turned (3%); that is to say, 68% of the students assume a position that in the long or short term needs consideration due to the risk of developing musculoskeletal injuries (graph 1); however, the adoption of urgent measures is low (3%).

During patient care work, the elbows were below the shoulder joint, but, in laboratory procedures, the arms were eventually placed at shoulder height, 60% at some point generated an unfavorable position for the patient’s arms. Regarding the load on the feet, more than 80% worked sitting, and those who worked standing were with the weight distributed on the 2 legs. For dentistry, the load is not considered a risk factor since the external force codes in relation to the characteristics of dental tools do not exceed 10 kg (graph 1).

 

Figure 2. Percentages according to the risk level by body segment of the sample.

Fuente: Base de datos de la Investigación
Elaborado: Los autores

Discussion

Our study has shown that there is a considerable risk of developing musculoskeletal injuries, mainly in the back; when identified early, prevention of chronic pain in dentistry may require a paradigm shift within the profession regarding clinical work habits, including the proper use of ergonomic equipment, frequent short stretching breaks, and regular strengthening exercise².

We have verified that the greater risk of musculoskeletal injury presented a higher percentage at the level of the back, followed by the arms; in their study, de Oliveira and colls.5, found that the anatomical regions that most professionals reported pain was in the lower back, neck, hands, shoulders, and upper back. Given the severity of musculoskeletal symptoms and their consequences on the health of dentists, it is essential to adopt practices that aim to prevent their appearance; since it directly affects the quality of life of the professional¹³.

Being back problems the highest risk, according to the results obtained; it should be proposed that work chairs for dental professionals and / or students reduce ergonomic risk; however, in a meta-analysis moderate evidence was found that the chairs provide a lower ergonomic risk than conventional seats in an examined population of dental students¹⁴.

In this context, it can be documented that unfavorable body postures can be adopted predominantly during treatment instead of the other examined activities. Furthermore, ergonomics training should be more intensively included in the dental curriculum to prevent musculoskeletal disorders¹⁵.

In this profession, musculoskeletal disorders are among the most common and debilitating occupational diseases and should be diagnosed as soon as possible8, so studies in students are relevant, where the correction of the position will improve the quality of life in the profession.

Certain postures and musculoskeletal disorders have influenced the proposal of reference values for the position of the articular segments. ISO 11226, 'Ergonomics: Assessment of Static Work Postures', provides ideal postures for dental work, such as sitting in an active, symmetrical and vertical posture, with the upper body bent forward, if necessary, from hip joints, maximum 10-20 degrees¹⁰. However, in practice, these ideal postures are not always adopted by professionals. Clinical ergonomic training and education, which sought to rectify such poor working postures, would reduce the occurrence of musculoskeletal disorders; as is the objective of the investigation.

Although ergonomic risks have been established, it must be kept in mind that the etiology of problems in the musculoskeletal system of dentists is multifactorial and, therefore, for its prevention it will be necessary to pay attention to three factors: worker, work and place of work. The measures basically go through a form of work in which they try to space repetitive movements and static postures maintained, frequently alternating the working position, planning various procedures throughout the usual day, using suitable ergonomic equipment and establishing frequent breaks¹⁶.

From the study proposal, it is observed that a limitation of the OWAS method is that it focuses only on exposure to uncomfortable postures during visits, but the high prevalence of musculoskeletal disorders found among dental professionals can also be explained by the handling of vibrating tools, excessive working hours, often without interruptions, and the precise movements performed¹⁷.

Although it has been stated that OWAS overestimates the risk and that it is necessary to review the evaluation parameters¹¹; the results found in our research are related to a high prevalence of musculoskeletal disorders in the dental profession, thus, there seems to be an urgent need to implement preventive strategies even for undergraduate students. As Kumar et al.¹⁸, this can be done very effectively by noticing the mechanisms that lead to musculoskeletal disorders and teaching them the strategies to follow.

A limitation of the study is that only one evaluation method has been used, the results of systematic reviews suggested using more than one technique for postural evaluation14; although, the applicability of the techniques in dentistry in particular needs to be established. There are techniques that are not yet compared to verify agreement or correlation, and that serve as a research vacuum.

From the results obtained on the prevalence, the risk of developing musculoskeletal disorders is considered high and should be taken into account in the ergonomic training of dental students.

 

Conclusions

Through the ergonomic evaluation of OWAS, a higher prevalence of medium risk (2 and 3) of developing musculoskeletal disorders, mainly in the back, was observed in students of the last semester of the Dentistry degree.

Bibliografía

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	Adrián Andree Teran Granja; https://orcid.org/0000-0002-0159-5822
	Alexie Elizabeth Izquierdo Buchelli; https://orcid.org/0000-0003-2841-2819