Congenital, Genetic, and Endocrinologic Influences on Dental Occlusion

Abstract

Employment of studies on individuals who have experienced congenital, genetic, and endocrinologic influences on dental occlusion affords an opportunity to study and observe current concepts of occlusal and centric relationships in the general population. In Down's syndrome one rarely finds a satisfactory occlusal relationship as well as a so-called centric relationship. Patients who are educable and trainable have no problem with mastication despite the occurrence of minor or major occlusal disharmonies and a complete absence of centric relationship. When permanent tooth agenesis occurs, one finds a significantly different pattern of occlusal relationship from that found in the general population. There is an unusually high incidence of Class II occlusal disharmonies with accompanying closed bites. In pituitary dwarfism different segments of the dentofacial complex are differentially retarded, resembling the postcranial skeleton. The teeth, on the other hand, although retarded in emergence, formation, and alignment, are advanced in respect to skeletal age and jaw formation and demonstrate an independence of epithelial growth by growth hormone secretion. Congenital X-linked ectodermal dysplasia is accompanied by partial and complete agenesis of teeth. The affected individuals, because of tooth agenesis, are essentially edentulous. When making dentures for these individuals there is no precise guideline for occlusal relationships or centric relationship. When dentures are constructed approximations for occlusal and so-called centric relationship are established. In no single case in my experience has the patient had any difficulty in adapting to the dentures. When the dentures are made for young children they must be remade as many times as is necessary to accommodate the anteroposterior growth of the maxilla and mandible. The osseous defects in Morquio's syndrome are severe and grotesque, yet the craniofacial complex is relatively free from any gross abnormalities. The cranial and facial size and proportions are at or near normal values (with the possible exception of cranial length). All of the patients studied showed a slight protrusion of the premaxillary region yet the occlusion was functional and acceptable in appearance. The cases of Duchenne muscular dystrophy all manifested varying degrees of open bite. Although there was no apparent occlusal relationship of the teeth in any of these individuals, they had no problem with mastication. As one examines the occlusal relationship of individuals affected by congenital, genetic, and endocrinologic influences it becomes apparent that our present standards of evaluating occlusal and so-called centric relationships require re-examination. Many years ago Angle stated in the introduction of his text, Malocclusion of the Teeth, “that no two normal human dentures have been created that were exactly alike.” Angle did not realize that the ideal rarely or never exists in nature, yet the term normal and ideal are profusely used in dental literature today. The concept of ideal occlusion has permeated the whole field of dentistry, not only in orthodontics but also in fixed and removable prosthodontics. When one examines large numbers of young children one rarely finds a so-called ideal occlusion in the primary, mixed, or permanent dentitions. What one finds is an occlusion that is not static and that changes with the growth and development of the child. The congenital, genetic, and endocrinologic disorders described in this article demonstrate the independence of these influences upon growth and development of the dentofacial complex and occlusal relationships. With the general growth and development of the dentofacial complex, in the above disorders environmental factors play an important role in the accentuation of the occlusal disharmonies. It becomes obvious that statisfactory occlusal relationships as well as centric relationships are not observed in the above disorders, yet it has no apparent effect on mastication and the nutritional status of these individuals.