FUNCTIONAL MOVEMENTS OF THE MANDIBLE – Part 3
by Clayton A. Chan, D.D.S.
This short posting appear as a 3rd part to an original posting made on the former genR8TNext internet forum under the subject: Re: [CROWNS] TMD/Wear, No Anterior Guidance on Monday, September 04, 2000 9:44 AM.
Dental literature comments much on the studies of masticatory movements, chewing forces, tooth contact patterns and swallowing. Masticatory movements have been studied by Luce (1889), Hildebrand (1931), Sheppard (1959) Koivumaa (1963), Hickey et al, (1963), Byron (1964), and Ahlgren (1966, 1976). These studies showed that the masticating is a highly complex neuromuscular activity that varies from individual to individual, each possessing their own characteristic chewing patterns developed from early childhood in the mixed dentition stage. The masticatory muscles develop accommodations and compensations to the developing vertical dimensions that have formed as each tooth develops and grows into the dental arches. A mandibular position is then accommodated to those acquired occluding positions that allows the best fit of the teeth, yet compensations are continually made by the surrounding musculature as well as the joints to meet the dominating factors of hard structures the intercuspating teeth. Posselt, 1952 as well as many others as Ingervall, 1964; Cohen, 1965; Hodge and Mahan, 1976; Reider, 1978, all reported that the this anterior posterior discrepancy existed in 90% of the population with a distance between the retruded and the intercuspal position of 0.25 mm – 2.25 mm on average. If there is that much slipping and sliding of the mandible, no wonder there is so much available business for us aesthetic dentists. I guess that is why many of us see anterior wear and recommend treatment for those areas. What we all are trying to determine is how best to minimize the potential breakage factors which impacts the time spent in redoes, our patients feelings of unhappiness and perceptions of what we have done, the effort we dentist stress ourselves over in wondering why our bonding materials and restorative materials are not holding up.
“The discrepancy between centric relation and maximum intercuspation is a reality which every clinician performing occlusal therapy must accept.” (Pameijer, 1970.) He wrote: “The question – ‘at which mandibular relation maximum intercuspation should occur in order to obtain a harmonious entity with the neuromuscular system’? then needs to be answered.”
He further wrote: “The chewing process consists of a series of acquired reflex movements, modified by the size and consistency of the bolus of food. The system itself is protected by neuromuscular reflexes, called nociceptive reflexes, which prevent damage by traumatic functional forces.” Studies have shown that almost every chewing cycle ends with tooth contact; most of these contacts occur with the teeth in maximum intercuspation in normal healthy schemes; those with non-healthy occlusal scheme, unhealthy condyles and discs, lacking adequate support to the masticatory system during chewing and swallowing cycles, will result in destructive tooth contacts. “Tooth contacts in centric relation (where ever that is defined) rarely occurs in chewing and swallowing”, since chewing and swallowing are functional movements that do not confine themselves to border movements.
© 2009 Clayton A. Chan, DDS. All Rights Reserved.
