What goes wrong with Dentists?

Sir Percival Potts, a London surgeon, noted in 1775 the association between cancer of the scrotum and being employed as a chimney sweep. 

         At that time, young boys between the ages of 7 and 10 were employed as sweeps, as they were small and agile enough to crawl up inside chimneys.  They wore no clothes, as it was a hot job, and washed infrequently.  Potts noted that they had an unusually high rate of scrotal cancer, especially compared to their Continental counterparts.  The latter were the same age and gender but (believe it or not) were in the habit of washing daily.  They had a much lower rate of scrotal cancer.  Potts correctly concluded that  the scrotal cancer was related to  exposure to soot, or carbon dust.  In the British tradition of medical education, Potts is  often  credited as one of the fathers of occupational medicine.  However, this title more correctly belongs to an Italian physician, Bernardino Ramazzini, who in 1700 wrote the first important book on occupational diseases and industrial hygiene.  We have him to thank for the eventual passage of factory safety and worker's compensation laws.  He was particularly eloquent on the disorders suffered by sedentary workers, who he said “...all suffer from the itch, are a bad colour and in poor condition...from irregular motions in unnatural postures of the body”.

As dental professionals, you are better clothed and  somewhat older than sweeps, but you do have your own set of occupational vulnerabilities.  Prime among these is  musculoskeletal pain.  As long ago as 1946, a study found that 65% of dentists complained of back pain.  Even after the evolution to seated, four-handed dentistry and ergonomic equipment, studies found back, neck, shoulder or arm pain present in up to 81% of dental operators. Furthermore, being seated has made very little difference to the incidence of pain, though it has changed the parts of the body in which  dentists experience pain.  In the seated posture, pain occurs not only in the back, but also in the neck, shoulders and arms.  This compares to standing dentists reporting low back pain, circulatory problems, such as varicose veins, postural defects and  flat feet.  Moreover, the switch to four-handed dentistry has enabled dentists to work for longer in one position, thus compounding the problem.

A large literature review in 2003 found that  a number of mechanisms lead to work related muscuoskeletal pain  in dental professionals.  These include prolonged static postures, repetitive movements, poor lighting, mental stress, physical conditioning, age and genetic predisposition.  By far the majority of detrimental physiological changes in the body are the result of prolonged static postures.  Dentists frequently assume static postures, for prolonged periods, which require more than 50% of the body's muscles to contract to hold the body motionless while resisting gravity.  The static forces resulting from these postures have been shown to be much more taxing than dynamic, or moving, forces.  When the body is subjected repeatedly to prolonged static postures, it can initiate pain, injury or even career threatening musculoskeletal disorders.  (See flowchart).

I had a chat to a chiropractor friend about this, and he confirmed that he has a lot of clients who are dentists, and that if they are taught how to manage these stresses and understand the effects of posture, it can greatly improve the quality of their working life and risk of musculoskeletal disorders.  Unfortunately, he mostly gets to see dentists only after the rot has begun to set in.  He points out that dentists spend their working lives in the 'head -forward position.'  Ideal posture entails the head, which weighs about 10% of your total body weight, balancing on top of your spine like a golf ball on a tee.  Viewed from the side, your external auditory meatus (ear hole) should be over your shoulder joint. For each 2 cm the head moves forward, the force on your cervical spine doubles.  The average desk worker's head is 6-8 cm in the head forward position, so for the average 70 kg person, this represents a force of 28 kg  or more on the muscles supporting the neck.  This is like having a large watermelon hanging around your neck!  Dentists, who sit for long periods in the head-forward position, have even larger forces.( Persistent head forward position also puts a compression load on your upper thoracic vertebrae, which is associated with the development of Dowager's hump).  Little wonder that the result can be headaches, stiff shoulders and neck, shoulder blade pain,  paratheses and TMJ disorder.

The head -forward position is exacerbated when you are working with your hands outstretched, as in dentistry. Even with the best ergonomic equipment, dentists often find themselves in sustained awkward postures with forward bending and repeated rotation of the head, neck and trunk to one side.  Over time, the muscles responsible for rotating the body to one side become stronger and shorter, while the opposing muscles become weaker and elongated.  The stressed, shortened muscles can become ischaemic and painful, exerting asymmetrical forces on the spine that can cause misalignment of the spinal column and decreased range of motion in a particular direction.  Ligaments and muscles eventually adapt to this position, making it uncomforatable to assume  correct posture. Studies have found that for a majority of dentists, neck rotation to the right with side bending to the left is a difficult movement to perform, yet it is one that they contort themselves into for long periods. If you recall the anatomy of the brachial plexus, it becomes obvious that working with the arms extended puts abnormal stresses on important nerves, so it is little wonder that neck and arm paratheses can result.  Within the cervical discs, increased pressure  and altered forces from the weight of the head forward position lead to degenerative changes, putting the disc at risk of injury.  A 'new' injury is rarely really 'new'; it is just the end result of a long period of  subclinical damage.

Further, muscle  imbalance  tends to develop between the abdominal and low back muscles over time, and this is especially problematic in seated dentistry.  Repeated leaning towards a patient can cause strain and overexertion in the low back extensors, while the deep stabilizing muscles (transversus abdominus) tend to become weaker. The lumbar lordosis flattens, causing the nucleus in the spinal disc to migrate posteriorly toward the spinal cord.  Over time the posterior wall of the disc weakens, predisposing to disk herniation - next time you lunge for that low shot on the tennis court, for instance.

         Take note of the posture of older people, or look at photos of your parents when they were married and as they were 50 years later.  The 'aged' posture is generally a head- forward one, from years of reaching and leaning.  The shoulders are rolled forward,  the  chest is sunken, and the
bottom has dropped or disappeared, because of loss of abdominal support and  tightened chest muscles.  The abdomen protrudes, from loss of abdominal tone, and the waist is thicker, from the sunken chest pushing the viscera outwards.  Most people could be as straight at 80 as at 20, if they could maintain their normal muscle flexibility and strength balances.  Height loss with age  (in the order of 2-3cm) is due more to posture than to intervertebral disc compression.  Of course, osteoporosis  and genes also play a part in this, but the movement that contributes to better posture also helps prevent  this.

         All this sounds rather depressing, doesn't it.  Do you have a problem?  If so, is it too late to change?

Ask a significant other to observe you standing when you are off guard, or better still to take a photo.  Your ear holes should be over your shoulder joints and if you are standing, you should be able to draw a straight line down from your ear holes through your shoulders, hips, knees and ankles.  A tall order, as it were.

When I began researching this article, I thought this topic would be  a relatively simple one.  However, it is a huge area, and an important one, as musculoskeletal disorders among dentists can be severe enough to demand early retirement. Most dentists are self-employed, making even taking time off sick difficult, let alone time for self-care. It also appears that  the ergonomics of dentistry is not taught very extensively in dental school, yet prevention of these problems would appear paramount.  I will therefore devote another column to this next month, but in the meantime will leave you with a a simple exercise that you should do a couple of times per hour.  It is called the Brugger Relief Position, developed by a German neurologist (see illustration) and will help to correct the damage that those long hours spent in the head-forward position may be doing.

Sit at the edge of your chair. Put your knees apart slightly and your feet under your knees.  Arch your back.  Rotate your arms outward so your palms face forward.  Tuck in your chin.

Hold this position while taking a deep breath in through your abdomen.

(with thanks to Dr Adam Meredith, North Sydney Spine and Health Centre, www.spineandhealth.com.au)

Fig.1.Brugger’s Relief Position

Examples of chairside directional stretches.

A. Neck and shoulder combination. With the elbow at shoulder height and at a 90-degree angle, gently pull the arm across the front of body with opposite arm. Look over the shoulder being stretched and hold for two to four breathing cycles. Repeat.

B. The untwister. With the knees wider than shoulder width, bend to the left side, resting the full body weight through the left elbow on the left knee. Stretch the right arm overhead and look toward the ceiling. Hold for two to four breathing cycles. Repeat.

C. Upper trapezius stretch. Anchor the right hand behind the seat of the chair. Gently bring the left ear toward the left armpit. Hold for two to four breathing cycles. Repeat.

D. Downward squeeze. Assume a neutral head posture (ears over the shoulders) and do not let the head move forward throughout the exercise. Lift the chest upward, position the arms at the sides with fingers pointing upward and palms facing forward. Roll the shoulders back and down, squeezing the shoulder blades downward and together. Hold for one long breath cycle. Repeat five times.