Geoffrey F. Walker

Changes in jaw relations, hyoid position, and head posture in complete denture wearers

In a group of 18 partially edentulous patients provided with immediate complete dentures, changes in hyoid bone position and craniocervical posture were examined on cephalometric radiographs made during 1 year of denture use. The findings indicated that the changes in hyoid bone position largely followed the pattern of forward-upward rotation of the mandible due to ridge resorption. During this course the hyoid position in relation to the cervical spine showed a mean increase. The hyocervical changes, however, showed less variability than the hyomaxillary and hyomandibular changes. The posture of the head and cervical column showed no definite mean changes during the 1-year period. On the other hand, analysis of individual changes revealed that a pronounced decrease in mandibular inclination due to ridge resorption was associated with retroclination of the cervical column and decreased craniocervical angulation. These postural changes may be regarded as adaptive changes to a marked initial change in mandibular position.

Differential diagnosis of adult male black and white populations.

Abstract No Abstract Available. From the Dental Research Institute and Veterans Administration Hospital, University of Michigan, Ann Arbor, Michigan.

Age and Race as Factors in Craniofacial Growth and Development

Large samples of adult American black and white males are being studied to determine the extent to which age and race are important factors in craniofacial mophology and growth. It is shown that a number of dentofacial dimensions continue to change throughout adulthood and that the amount and direction of these changes may be race-specific. Applications in orthodontics and prosthetic dentistry are indicated.

On the use of the SNA and SNB angles in cephalometric analyses

T he SNA and SNB angles have long been recognized as informative indicators of upper and lower facial prognathism and as useful guides in the diagnosis and treatment of malocclusion. As such, these angles play fundamental roles in a number of cephalometric analyses, such as those proposed by Down& 2 and Steiner. 3, 4 It is therefore of considerable interest to determine normative values for these variables. In an attempt to do this, Down+ studied the distribution of these variables in twenty persons with “clinically excellent occlusions, ” ranging from 12 to 17 years of age and about equally divided with respect to sex. He found a mean value of 81 degrees for the XNA angle (ranging from 78 to 84 degrees) and a mean value of 78 degrees (ranging from 75 to 81 degrees) for the SNB angle, and these figures have been generally accepted as representative of “normal variation” despite the fact that they are based on a small sample from a rather special population. Steiner3 chose a set of craniofacial norms, “. . . which express our concept of a normal average American child of average age,” the norms for the SNA and SNB angles being set at 83 and 80 degrees respectively. He implored the reader to “Please bear in mind that these are rough estimates, to be used as a starting point from which to vary and must be modified by other factors . . . age, sex, race, growth potential and mdividual variations within these and other groupings,” lbut he provided little insight into how these modifications should be implemented in practice. In the present article we will investigate, using cephalometric methods, the distribution of the SNA and SNB angles in a large sample of “normal” persons for several age groups and both sexes. The intent is to estimate the norms, and the variation about these norms, for the SNA and SNB angles and to compare these with the values obtained by Downs and Steiner. We shall also investigate sexual dimorphism and the dependence of these angles on age.

Computer Morphometrics in Craniofacial Biology

HIRSCHFELD,(~~~~~) HUXLEY, JOHNSON, KOWALSKI,(~~) MEDAWAR,(‘~) SCOTT and WALKER et u/.,(~~P~~) to name just a few, but the fundamental difficulty is the inherent complexity of craniofacial morphology and structural change. During growth the face

Use of Angular Measurements in Cephalometric Analyses

Most cephalometric analyses make extensive use of angular measurements. This usage is based on the assumption that angular measurements for a particular individual tend to remain relatively constant with respect to time, ie, that they are affected minimally by growth. The tenability of this assumption is challenged in several instances on the basis of the results of a cross-sectional cephalometric study of certain angular variables.

Chromosome surface area: Further evidence for autosomal sexual dimorphism

SUMMARY The karyotypes of 76 males and 84 females, each assembled by the trypsin banding method, are examined in a study designed to investigate sex differences among autosomes. It is shown that female autosomes have consistently larger surface areas than the males, with respect to both the short and long arm measurements. In addition, discriminant function analysis is used to distinguish between the male and female karyotypes. We find that, using autosomal measurements alone, this can be done with a high probability of success. In a recent paper we showed that female autosomes were consistently longer than male autosomes [5]. The karyotypes of 100 males and 100 females, each assembled by the trypsin banding method, were used in this and the average lengths of each of the autosomes were computed separately for each sex. We found the average value for the female cells to be consistently longer than that of the male cells, and that this was mirrored in both the short and long arms. With the single exception of the short arm of chromosome number 19, the arms of the female autosomes were longer than the corresponding arms of the male autosomes. Analysis of the arm ratios and centromere indices of these chromosomes also revealed certain shape differences, but the pattern of these differences proved to be more diffcult to characterize. Discriminant function analysis was also used to differentiate between male and female cells. Depending on which set of measurements was used in the discriminant function analysis, some 75 % of the cells could be correctly classified as either male or female on the basis of autosomal measurements alone. The purpose of the present paper is to report analogous results obtained on the basis of surface area measurements. It is shown that female autosomes have consistently larger surface areas than the male autosomes. Certain “shape” differences also exist, when these are defined in the obvious way using arm ratios and centromere indices. In addition, the technique of discriminant function analysis is used to classify karyotypes as either male or female. Using only autosomal surface area measurements, we again find that this identifica