Introduction-
Prior to 1985, low back pain was the most commonly reported musculoskeletal disorder (MSD) or repetitive injury for dentists and dental hygienists. Since then, there has been a rise in MSDs from extended workdays, awkward postures, prolonged standing/unsupported sitting, and a host of other problems caused by poorly designed workstations, improper work habits, and instruments that are difficult to manipulate. The current workstation in most dental offices
requires that the practitioner lean forward, flex his neck forward and laterally, hold his shoulders abducted and his arms flexed, with this position being held statically for most of the workday.
Dentists need to tightly grip thin, sharp instruments and make a high volume of short, forceful movements with the muscles of their wrists and hands to treat heavy calculus and other conditions. The human body is not built to handle these kinds of stresses, and the positions in which dentists repeatedly put themselves through their work place them at great risk for developing MSDs.
Conditions can vary from mild recurrent symptoms to severe and incapacitating. Early symptoms of MSDs include pain, swelling, tenderness, numbness, tingling sensation, and loss of strength. These injuries result in costly insurance payments, extended periods of time away from work, and decreasing work performance, job satisfaction, and energy levels. For many dental practitioners, musculoskeletal pain and the development of repetitive strain injuries have caused them to take a leave of absence, shorten their work hours, reassign their duties to other dental staff, or undergo surgery, and some dentists have been forced into premature retirement. Until recently, this problem has not been given much attention, but with increasing numbers of dentists developing painful symptoms, changes must be made to the way they practice to allow for longevity in their careers.
Some Signs of MSDs
•Decreased range of motion
•Loss of normal sensation
•Decreased grip strength
•Loss of normal movement
•Loss of coordination
Some Symptoms of MSDs
•Excessive fatigue in the
shoulders and neck
•Tingling, burning, or other pain
in arms
•Weak grip, cramping of hands
•Numbness in fingers and hands
•Clumsiness and dropping of
objects
•Hypersensitivity in hands and
fingers
Some Risk Factors for MSDs
•Repetition
•Forceful exertions
•Awkward postures
•Contact stress
•Vibration
•Poorly designed
equipment/workstation
•Improper work habits
•Genetics
•Medical conditions
•Poor fitness level
•Physical/mental stress
•Lack of rest/recovery
•Poor nutrition
•Environmental factors
•Poor lighting
Off theJob Activities That Can Contribute to MSDs
•Home computer use
•Repetitive activities using the
fingers
•Sports activities
•Prolonged/awkward postures at
home
•Use of household tools
•Activities involving repeated
heavy lifting, bending, twisting, or reaching
MSD 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 mligaments 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 (OHSCO, 2007).
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 (Jarvholm, 1989). 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 (Park 2009). Static gripping for durations exceeding 20 minutes was also noted during instrumentation tasks within dental practice (Sanders, 1997).
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 (OHSCO, 2007).
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 (Sanders, 1997). Additionally, scaling procedures involving both waving and rotary motion power strokes have been classified as the most demanding task required of hygienists (Horstman, 1997).
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 (OHSCO, 2007).
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, 2010). 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.
Health Effects
Wrist
The risk factors associated with dental work that most commonly affect the wrists are chronic repetitive movements, awkward and static positions, mechanical stresses to digital nerves such as sustained grasps on instrument handles, extended use of vibratory instruments and inadequate work breaks. The wrist is in constant demand, often sustaining excessive and repeated stresses and strains. The safest position for the wrist is a straight or neutral position. Special care should be used to avoid bending the wrist downwards (flexion) or outwards (ulnar deviation).
Carpal Tunnel Syndrome (CTS)
CTS is one of the most common problems that affect the hand and wrist. CTS occurs when the median nerve, which runs from the forearm into the hand, becomes pressed or squeezed at the wrist. The median nerve controls sensations to the palm side of the thumb and fingers (although not the little finger), as well as impulses to some small muscles in the hand that allow the fingers and thumb to move.
Tendonitis of the Wrist
Tendonitis is an inflammation of tendons, which are the structures that attach muscle to bone. Tendonitis of the wrist is accompanied by pain, swelling and inflammation on the thumb side of the wrist, and is made worse with grasping and twisting activities (e.g. polishing and scaling). People with this disorder have often noted an occasional “catching” or snapping when moving their thumb
Guyon’s Syndrome
Guyon's canal is a space at the wrist between the pisiform bone and the hamate bone through which the ulnar artery and the ulnar nerve travel into the hand. Compression of ulnar nerve occurs in this space at the base of the palm. It is commonly caused by repetitive wrist flexing or excessive pressure on palm/base of hand. It is characterized by pain, weakness, numbness, tingling, burning in the littlefinger and part of the ring finger.
Neck
Pain and discomfort are the most common complaints reported in the neck/shoulder region amongst dental professionals. Studies have also shown that female dentists reported neck symptoms 1.4 times more often than male dentists (Mangharam, 1998).
Myofascial Pain Disorder (MPD)
MPD is characterized by pain and tenderness in the neck, shoulder, arm muscles, and a restricted range of motion. Possible causes include overloaded neck/shoulder muscles.
Cervical Spondylosis
This disorder is characterized by intermittent/chronic neck and shoulder pain or stiffness, headaches, hand and arm pain, numbness, tingling, and clumsiness. Possible causes include age-related spinal disc degeneration leading to nerve compression and spinal cord damage, arthritis, and time spent with the neck in sustained awkward
postures.
Disc Problems
In a seated posture the pressure in the lumbar discs increases by 50% as compared to standing. Additionally, sitting in an unsupported posture can cause twice the amount of stress as compared to standing. During bending (forward flexion) and twisting (rotation) motions of the spine, the pressure on the lumbar discs increases by 200% (Fisk, 1987). This type of pressure on the disc can lead to a bulge or herniation, causing compression on a spinal nerve.
Some Tips for Working With Good Posture:
(1) Always try to maintain an erect posture. By positioning your chair close to the patient, you can minimize forward bending/excessive leaning over the patient. Keep your feet flat on the floor to promote a neutral or anterior tilt to your pelvis, which keeps your back aligned and promotes the natural curvatures of your back. Remember that your head weighs as much as a bowling ball, and when you lean forward and flex your neck, you force your muscles to hold up the weight of your head, rather than the bones and discs in your spine.
(2) Use an adjustable chair with lumbar, thoracic, and arm support. Having a good chair is essential in maintaining good posture, because what you sit on provides the base of support from which you work all day long. When you think about it, you work 8 or more hours per day, 5 days per week, 4 weeks per month, and about 11 months out of the year, which makes a highquality chair with adjustable features well worth the cost of saving your back, neck, arms, and hands. You should look for important features like adjustable height, width, tilt, backrest, seat pan, and armrests, because in most dental offices many people of different sizes use the same workstation.
(3) Work close to your body. Position your chair close to your patient, and position your instrument tray close to you. This way, you don’t have to overextend yourself to reach your patient or your instruments, putting excessive stress on your back, shoulders, and arms. Think of the 90° rule of having your elbows, hips, knees, and ankles all forming 90° angles. If you find yourself reaching out far beyond these angles too often, then you’re not properly positioned and you should adjust the position of your chair/instrument tray.
(4) Minimize excessive wrist movements. Be conscious of how you position and move your wrists, and try to keep them in a neutral position (palms facing each other, shoulder width apart with wrists straight), which puts your muscles and tendons in a much better relationship to perform the work. You will have to move your wrists into various positions as you work on your patients, but try to be aware of these movements so you can minimize potentially damaging hand positions.
(5) Avoid excessive finger movements. When you combine the excessive forces needed to hold your instruments with the amount of repetitions that you perform each day, you can see the tremendous toll that this takes on the small muscles of your fingers. Retrain yourself to use your shoulders and arms to position your hands, rather than making the small, forceful movements with your fingers.
(6) Alternate work positions between sitting, standing, and side of patient. Switching positions allows certain muscles to relax while shifting the stress onto other muscles and increasing your circulation. When you work on alternate sides of the patient or rotate the position of your instrument table, you allow each side of your body to share the stress, rather than performing the same motion in the same way, which causes cumulative trauma in the overused side.
(7) Adjust the height of your chair and the patient’s chair to a comfortable level. If your chair is too low and the patient’s chair is too high, this causes you to elevate your shoulders and can lead to neck problems and pinched nerves. Alternately, if your chair is too high and the patient’s chair is too low, you’ll have to flex your neck down and bend your wrists back to compensate, which can lead to neck and hand problems. Remember the 90° rule and keep your elbows at a 90° angle with your wrists straight and shoulders relaxed.
(8) Consider horizontal patient positioning. If your workstation allows the patient to be reclined into a horizontal position, this allows you to sit above the patient’s head with good ergonomic posture, and you can use each arm equally in more natural positions. If the workstation does not accommodate this position, consider buying a quality reclining chair for the patient when you replace the old one.
(9) Check the placement of the adjustable light. Position the adjustable light so you don’t have to strain your neck to be able to see in the patient’s mouth. It is important to adjust this light with each new patient because of the different height of each person. The light should be adjusted again when a new dentist uses the workstation because his/her sitting eye height is different, and this will affect his/her ability to see into the patient’s mouth
(10) Check the temperature in the room. Make sure the temperature in your workspace is not too cold because this will decrease the circulation and blood flow to your extremities. Most often, the dental work environment is damp and cold, so be certain to wear gloves and warm up your hands before working on a patient.
Referernces-
1) Ergonomics in Dentistry, Part 1 | Dentistry Today
2) Occupational Health Clinics for Ontario Workers