Mandibular rotation and enlargement.

In a previous article, a theoretical mechanism for neutralization of condylar incremental growth was postulated. It was labeled counterbalancing rotation. The postulate resulted from the reasoning that condylar relocation along a segment of a circle around pogonion would be unable to enlarge the radius. In this article, the relationship between condylar relocation and mandibular enlargement is quantified. To this goal, counterbalancing proportion is defined as the percentage of condylar incremental growth, detected by implants that has contributed to the enlargement of the condylion-to-pogonion dimension. This proportion proves to vary widely in the 21 cases documented by Björk and Skieller. In addition, a relationship between this proportion and the Angle classification is observed. It is concluded that counterbalancing rotation indeed must be considered a mechanism capable of neutralizing condylar incremental growth and may have clinical implications.