I am writing this article in honor of Dr. Henry “Hank” Shimbashi, a practicing dentist and researcher from Edmonton, Alberta who passed away this week. Dr. Shimbashi was a very influential friend of comprehensive restorative dentists and his research is used every day in offices like mine where problems with the bite and TMJ’s are treated.
As a result of his research, the Shimbashi number was established to indicate an ideal relationship between the upper and lower jaws. When there is an optimal position of the lower jaw relative to the upper jaw, the muscles which are connected to them will also be at their optimal length and can function ideally.
If the relationship between the upper and lower jaws is altered, one or more of the many muscles of the head, neck and face may be overworked causing them to go into spasm — i.e., be painful. This can happen if the lower jaw is too close to or far from the upper jaw, too far forward or back, or shifted in any direction relative to the upper jaw.
Dr. Shimbashi’s research measured muscle activity in over 500 patients. He found that there was an ideal vertical dimension at which the jaw muscles functioned at their maximum potential. In addition, at this ideal position, patients had no symptoms of muscle pain. This vertical dimension was found to be universally applicable in all age groups and all races.
This simple number which we use is the measurement from the gum line of the upper front tooth to the gum line of the lower front tooth. Dr. Shimbashi found this ideal distance to be approximately 19 mm plus or minus one mm (about three quarters of an inch) when a patient bites. In our office, we often see patients with bite problems whose Shimbashi number is significantly less than ideal measuring as little as 10 mm or even less. In such patients, the lower front teeth are often nearly completely covered by the upper teeth. Such patients are much more likely to develop tooth and pain problems resulting from their bad bites.
So what is your Shimbashi number? If you have any questions about your bite as a result of this article, please feel free to call our office at 908.359.6655 or via our website at www.DesignsForDentalHealth.com