Further Discussion of the Growth
of the Jaws

All vertical growth of the jaws at the anteroposterior level of gonion angle, displaces the gonion angle downward, whether this growth is at the condyle, the temporomandibular fossa or localized interstitial growth. All posterior horizontal condylar growth causes a forward thrust of the chin. All posterior movement of the glenoid fossa and temporal bone limits the forward thrust of the chin. Any resorption of bone at the gonion angle, of course, limits the distance from sella horizontal to the gonion angle. Also the angle formed by sella horizontal and the mandibular plane has an effect on these considerations. Then the final forward movement of the chin is a composite of the above movements of anatomical parts.

The forward growth of the maxilla and the forward and vertical growth of the hard and soft tissue profiles, of the maxilla, is a completely separate entity, being little influenced by the aforementioned growth processes.

However, the vertical growth of the first molar teeth matches and is pitted against this total growth activity mentioned above. When the total first molar growth (from sella horizontal to the mandibular plane) exceeds the composite growth in the region of the condyles, the mandible rotates posteriorly. When composite vertical growth in the region of the condyle exceeds the vertical growth of the first molar teeth, the mandible rotates forward. When these opposing forces are equal the mandible does not rotate as it moves downward and forward.

To simplify these complex concepts and make them easy to understand, we can go back to the "mechanism of jaw growth and function" concept which was discovered in 1960. This concept states that vertical condylar growth functions against vertical molar growth, and their relationship determines how the mandible rotates, and if it rotates. After forty years this concept is still not well understood. Obviously, when we do not understand these principles, we do not understand how the jaws grow.

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