In 1972, my father and I had our heads under the open hood of a 1969 Oldsmobile 442, listening to an idling 500-horsepower 455-cubic inch engine clunk and clatter. We both speculated as to the problem, and, after the tear-down the micrometer showed an extremely worn crankshaft. The noise from the engine of this muscle car was caused by the piston connecting rod slop and the piston hitting the head/valve at the top of the stroke cycle. The engine was out of centric relationship. The piston could travel past its terminal border position; parts were colliding, and eventually the system broke down.
In the September issue, Drs Rinchuse and Kandasamy offered readers some lessons about orthodontic gnathology (Rinchuse DJ, Kandasamy S. Myths of orthodontic gnathology. Am J Orthod Dentofacial Orthop 2009;136:322-9).
The gnathology lesson I learned from that engine is quite simple. Would it be kinder to the mandible and supporting tissues if, in dynamic movement, (1) the condyles were centered in a terminal border position? (2) the condyles were allowed to stay in contact with the articular eminence during excursive movements? (3) all posterior teeth contacted exactly at the same instant, allowing a stable mandibular position? and (4) the anterior teeth protected the posterior teeth from colliding during excursive movements?
I’ve been in practice over 30 years and have followed gnathologic concepts for 13 years. I must admit this raised the bar and enhanced my appreciation for how truly difficult practicing our specialty can be. Also, and most important, I realized that I am working in a dynamic and not a static field.
I have examined the posttreatment mounted models of all my patients for the last 12 years. This examination is quite revealing and has afforded clearer insight of the importance of anterior coupling to the dynamic occlusion. Specifically, it has shown the importance of proper anterior tooth length.
I want to thank Drs Rinchuse and Kandasamy for their most stimulating article and ask a final question. When you finish treatment and release the patient to “start your mandible,” is the clunking and clattering noise you hear because your patient is chewing? Or maybe you don’t hear it because you’re not listening.