In June 1998 Dr. Peter H. Buschang and Dr. Joel Martins published an article entitled, "Childhood and Adolescent Changes of Skeletal Relationships" in the Angle Orthodontist.

Our primary purpose in discussing this excellent article is to highly compliment the authors on this singularly important contribution to the literature. Also we hoped to suggest additional concepts which may enhance our understanding of the growth of the craniofacial complex. The authors used an analysis which correctly relates growth to vertical and horizontal landmarks—a valid plan. If we might suggest a basic change in the stable landmarks from which all points in the craniofacial complex can be accurately measured, it might further complement the work of the authors of this article.

Fig. 1: Showing variations in the position of the glenoid fossa with relation to sella, and variations in the N-S-Ba angle. The saddle angle can vary as much as 25° and the angle between the SN and Frankfort planes as much as 14°

The analysis used is based on or tied to the SN to Frankfort angle which varies as much as 13.5°. Then, SN-7° would leave 6.5° of variation. Please see Fig. 1. If we were to establish a line through sella parallel to Frankfort (please see Article 24), we would have a stable landmark from which to vertically measure all points in the craniofacial complex.

The "great divide," a line downward from sella perpendicular to Frankfort (please see Article 1) is a stable landmark from which all points in the craniofacial complex can be accurately measured horizontally.

When an analysis is based on the SN to Frankfort angle, as in this case (SN–7°), we cannot favorably compare subjects with high SN–Fr angles with subjects with low SN–Fr angles. By using the "SN horizontal" which is parallel to Frankfort, we automatically eliminate the problem of inaccurate measurement.

Figure 2 Showing the effect of a small gonion angle on the effectiveness of the growth of the condyles (45% effective)

Figure 3 Also showing the effect of a large gonion angle on the effectiveness of the growth of condyles (240% effective)

There is another concept which would also complement the study under discussion. The forward bending of the ascending ramus (reduction of the gonion angle) was first reported by George Schudy in his post doctoral thesis published in the AJODO in 1972. This is a phenomenon closely related to mandibular length, condylion-gnathion distance, and has a distinctly important relationship with the treatment of malocclusion. Please see Fig. 2 & 3.

It is obvious that the reduction of the gonion angle, due to growth, limits the increase in condylion-gnathion length. This phenomenon, usually found in low angle morphology, could literally cause a Class II occlusion were it not for the interdigitation of teeth. The reduction of this angle can vary up to 14°, and has about a 13 mm effect on the length of the mandible.

Since a Class II occlusion is established at 7 or 8 years of age, and the reduction of the gonion angle occurs from about 13 to 17, the occlusion of the teeth may help to cause the reduction of the gonion angle—just a puzzling thought!!?

When we use sella horizontal to measure vertically, and the "great divide" to measure horizontally (see the Schudy Chronicles Articles 1 and 24), we are using completely stable landmarks. Regardless of how much anatomical structures move vertically or horizontally, they can be accurately measured.

To properly evaluate the effects of overall growth on the dental condition, it is necessary to study the period from about 14 to 17. This period normally coincides with the post treatment period, at least in males. This is the period when growth affects occlusion most. This is the period when post treatment growth either improves the excellent treatment or causes disastrous effects on poorly treated cases.

The authors ask two questions, (1) "Are developmental changes of AP relationships determined either by maxillary or mandibular growth?", (2) "Are anterior or posterior growth changes more closely associated with the development of vertical relationships?"

Our answer to the first question is: The developmental changes of AP relationships are not determined by either maxillary growth or mandibular growth, but instead, by the relationship between AP and vertical growth.

Example: If condylar growth is 5 mm vertically and 2 mm posteriorly, the upper molars grow downward 3 mm and the lower molars do not grow vertically, the chin will move forward 4 mm. However, if the lower molars grow 2 mm vertically, then the chin will move foreward only 2 mm.

Our answer to the second question is: The posterior growth changes are more closely related to the development of the vertical relationships. In fact, the posterior vertical growth changes cause the development of vertical relationships.

When we establish stable marks for accurately measuring vertical and horizontal growth, and when we point out the effects of gonion reduction on mandibular length, hopefully we have added an additional dimension to the magnificent discussion of growth during childhood and adolescence.

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