Dental hygienists at risk for nerve damage

By Anne Harding

NEW YORK (Reuters Health) - About one-quarter of experienced dental hygienists who use high-frequency ultrasound instruments will develop a type of nerve damage that blunts the sense of touch and causes weakness, a new study has found.

Such symptoms have been reported in individuals working in dentistry since the 1980s, Dr. Martin G. Cherniack of the Ergonomics Technology Center at the University of Connecticut Health Center told Reuters Health. The current study is the largest and most technically advanced to date on the topic.

Cherniack and his team performed a battery of tests of nerve function and symptoms in 94 experienced dental hygienists who had worked in the field for at least five years.

Nearly 45 percent, they found, had chronic numbness and tingling, known as paresthesia, in their hands. Twenty-seven percent had a distinct set of symptoms including a lowered threshold for sensing vibration, a perception of weakness in the hands, and loss of strength as measured by pinch force.

About two-thirds of the hygienists in this group had paresthesias, compared to 39 percent of the rest of the study participants, and they also had a greater overall exposure to vibration than those who did not have the symptoms.

Such symptoms indicate damage to small fiber nerves that is completely distinct from carpal tunnel syndrome, Cherniack said.

Vibration from industrial power tools like jackhammers is known to cause nerve damage, he added. But very high vibrations like those produced with dental instruments called cavitators and dental drills are sometimes not even perceptible to the people using them, and are generally thought not to pose nerve damage risk.

"There's been an assumption that high frequency instruments are not so harmful," he added. "We're much more dubious about that."

Cherniack said he suspects posture, grip and technique play a role in whether or not a person will develop the symptoms. "These are fields which are facing major labor shortages," he added. "One of the reasons is that people are leaving or retiring at relatively young ages due to neuromuscular and skeletal reasons."

It would be possible to prevent this type of nerve damage once the responsible frequency is identified, he added, as it is relatively simple to filter out high frequency vibrations using engineering techniques.

For now, Cherniack said, dental hygienists experiencing numbness, tingling and weakness in their hands should see a physician. "When there's this sort of experience of hand weakness or numbness in the hands, it isn't necessarily carpal tunnel syndrome. It is important to try to get it evaluated-it's too simplistic to send everyone off to surgery."

SOURCE: American Journal of Industrial Medicine, May 2006.