372 CHARLES R. STOCKARD AND A. L. JOHNSON 



Figure 5 illustrates the cast from an extreme case of man- 

 dibular prognathism in a child. The exact similarity to the 

 bulldog jaws (fig. 4) is obvious. For comparison, a cast 

 illustrating the normal dental occlusion of the human mouth 

 is shown in figure 3. 



The human achondroplasic dwarf very commonly presents 

 mandibular prognathism caused by the same conditions as 

 are responsible for prognathism in the bulldog. The under- 

 shot condition may be due, however, to entirely different 

 causes. The upper facial arrangement may be flat and 

 short, as is the type in certain human families, and yet be 

 associated with a large, long lower jaw which necessarily 

 projects beyond the upper. The orthodontist, in attempting 

 to correct malocclusion, continually finds that two patients 

 with apparently similar kinds and degrees of malocclusion 

 respond very differently to the same mechanical treatments. 

 Some patients are much less responsive to one method than 

 others, and some truly achondroplasic cases may not respond 

 at all, or at least not in the ordinarily expected way. 



THE QUESTION OF PERMANENCE AND AGE OP ESTABLISHMENT 

 FOR DENTAL OCCLUSION 



With such facts as those presented in the foregoing section 

 in mind, we have attempted to determine whether there may 

 be a definite relationship between some of the skull indices 

 and the degree of perfection in dental occlusion. It seemed 

 important also to determine the periods of growth at which 

 the dental occlusion in the long jaws of the dog is established. 

 In both man and the dog the permanent dentition with adult 

 sized teeth becomes stabilized sometime before the jaws have 

 completed their growth. The jaws of the prepubescent child, 

 and of the puppy until it is 5 months old, are too small to 

 accommodate freely the adult sized permanent teeth, with the 

 result that they appear in crowded and misplaced arrange- 

 ment until the growth of the jaw to adult size supplies the 



