How Does the Human Head Grow?
At age 3 months the human embryo is 1 year old (9 months of intrauterine life and 3 months post partum). At age 3 months the skull has reached approximately one-half of its final diameter. While at age 3 months the skull has reached about one-half of its growth, the face is just beginning to grow, the mandible has reached approximately 40% of its growth, and the body has reached about 30% of its growth.
The skull is destined to grow about the same, regardless of whether the person grows to five feet or seven feet. Cephalometric radiograms are seldom done before age 6 years. At age 6 years, the mandible has reached approximately 90% of its growth. Then, for most patients, the orthodontist deals with about 10% of total facial growth. Also, what is even more frightful is that post treatment growth includes an appreciable segment of total growth. This segment of growth will nearly always have an adverse effect on poorly treated cases. However, post treatment growth will nearly always improve the superiorly treated case. The growth of the mandible in nearly all cases will drive all upper teeth forward (translate the molars and bicuspids forward and tip the incisors forward). Also this late growth will reduce the overjet, sometimes improve the overbite and usually improve the interdigitation. For all of these favorable changes to occur, the case must have been carefully treated and retained.
When we view the overall picture and really believe these facts down to the depths of our hearts, then we realize our awesome responsibility. We know that we should get down to a study of the "nitty gritty" details of comprehensive orthodontic treatment.
Unless we measure growth increments we will never know how the patient grew between birth and age 6 years. We will never know that the growth of the mandible was primarily in a horizontal direction for the first 3½ years of life and that in some cases the glenoid fossa moves posteriorly as much as 10 mm during this time. Please see Fig. 1. In this illustration the glenoid fossa was directly under the sella turcica at age 3 months and moved posteriorly 10 mm in 3½ years. This horizontal growth of the condyles was responsible for the forward positioning of the chin. Please see Fig. 2.
Fig. 1: Case No. 2768 at age 3 months and age 3 years, 6 months. Please note that at age 3 months the temporo-mandibular joint is directly beneath sella turcica. By age 3.5 years the joint moved 10 mm dorsally in relation to sella. Please note the remarkable growth of the mandible. (From the Broadbent Study of Case Western Reserve University, Cleveland, Ohio, U.S.A.)
Fig. 2: This is the same patient shown in Fig. 1. Please note (1) the lingual movement of the lower incisors, (2) primarily horizontal component of growth of condyles, and (3) rare instance of an occlusal curve in deciduous dentition. (From the Broadbent Study of Case Western Reserve University, Cleveland, Ohio, U.S.A.)
When we try to relate our treatment to the overall growth and welfare of the individual, it helps us to respect the work we do, and should give us renewed intensity.
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