Musculoskeletal Disorder Hazards

Awkward Postures

Posture is a term used for the position of various parts of the body during an activity. For most joints, a good or “neutral” posture means that the joints are being used near the middle of their full range of motion. The further a joint moves towards either end of its range of motion, or the further away from neutral, the more awkward or poor the posture becomes and the more strain is put on the muscles, tendons and ligaments around the joint. For example, when arms are fully outstretched, the elbow and shoulder joints are at the end of their range of motion. If an individual pulls or lifts repeatedly in this position, there is a higher risk of injury. The use of awkward postures is perhaps the greatest risk factor for those in the dental field. Researchers have confirmed the presence of awkward postures specifically in the neck, back, shoulders, hand and wrist for dental professionals. Awkward postures are often adopted due to improper seating, improper patient positioning and/or poor work techniques. Common awkward postures in dental practice include elbow and wrist flexion and thumb hyperextension, which have been shown to stress neurovascular structures and ligaments.

Static Postures

Static postures are defined by those which are held for a long period of time and may result in fatigue and injury. Oxygen is delivered to the muscles and joints by blood. When a posture is held for a prolonged period of time there is a reduction in blood flow to the tissues. This results in a reduction of nutrient and oxygen supply with lactic acid and other metabolites accumulating, which can  result in pain and tissue damage. Researchers have found that even 30 degrees of forward shoulder flexion or abduction can cause a significant impairment in blood circulation within the shoulder / neck region. Furthermore, dental practitioners have been observed statically holding postures requiring greater than 50% of the body’s musculature to contract. This  results in increased muscular effort which can lead to muscle overload, decreased blood flow and increased pressure on muscles and joints. Static gripping for duration's exceeding 20 minutes was also noted during instrumentation tasks within dental practice. 

Force

Force refers to the amount of effort created by the muscles as well as the amount of pressure placed upon a body part. All tasks require workers to use their muscles to exert some level of force, however, when a task requires them to exert a level that is too high for a particular muscle, it can damage the muscle or related tendons or joints and/or other soft tissue. An example of a gripping task requiring high force application could be holding small instruments for a prolonged period of time. This task is commonly performed with a pinched grip where the fingers are on one side of the object and the thumb is on the other. This form of gripping is undesirable as it requires a much greater force application than a power grip (object in the palm of the hand). Researchers have suggested that excessive use of a pinch gripping is the greatest contributing risk factor in the development of MSDs among dental hygienists. Additionally, scaling procedures involving both waving and rotary motion power strokes have been classified as the most demanding task required of hygienists . 

Repetitive Movements

The risk of developing an MSD increases when same or similar parts of the body are used continuously, with few breaks or chances for rest. Highly repetitive tasks can lead to fatigue, tissue damage, discomfort, and, eventually injury. This can occur even if the level of force is low and the work postures are not awkward. During instrumentation, there is a constant alternation between wrist flexion, extension, and forearm rotation. Repetitive gripping is experienced throughout the day in order to write, clean and hold instruments, and expose radiographs. Such high usage of wrist and forearm musculature has been linked to an increased risk of fatigue and overuse.

Repetitive motions are extremely prevalent in clinical practice, particularly when performing scaling, root planning and polishing. Three critical components to consider include:

  • Frequency
    • refers to how many times an action is repeated
    • examples include: repetitive wrist motions, the number of cleanings performed in a day, the number of instruments gripped by one hand
  • Duration
    • refers to how long an action is performed
    • examples include: length of time spent holding an instrument, length of time sitting in a static posture, the total length of a work day
  • Recovery time
    • refers to the time which breaks a repetitive cycle
    • examples include: time between clients, scheduled breaks, time spent stretching 

Vibration

Although vibratory tools are used in the dental field research has shown that the daily vibration exposure of dentists is relatively low with respect to the exposure action value (European Union Vibration Directive). A long work history in dental filling and root treatment as well as high BMI seem to be associated with frequent finger symptoms perceived as vibration-related by dentists. However, vibration exposure in dentistry may be of concern when one must grip vibratory tools for prolonged periods of time. The reason is that when holding a vibrating tool, muscles begin to tire due to over stimulation. As this occurs, the operator must squeeze harder in order to continue to operate the tool which in turn increases internal force application of the surrounding musculature. 

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