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Biomedical subjects

G F Walker

Publications and source records attributed to G F Walker.

At least 19 recordsLinked to original sources
PubMed1987

A biometric comparison of face shape with denture tooth form.

Dentist and patient preferences are often used to select replacement teeth in prosthodontics. Face shape compared with inverted tooth form classifications based on Leon William's work are currently used. Shapes of teeth and faces have been referred to as square, ovoid or tapered, or some combination of these. Six patients, three male and three female, were selected as being classically square, tapered or ovoid in facial form. Three sets of dentures had been made for each patient with tapering, ovoid and square denture teeth. Using a standardized photographic technique, full face views with profiles and close-ups of the teeth were taken. Then from standardized enlarged tracings, key anatomic and derived points were marked, digitized and computer analysed. The face shapes and inverted tooth forms were digitized in the same manner. A comparison of tooth moulds versus the actual denture teeth shows a highly significant difference (P less than 0.001) between set and unset denture teeth. There is also a significant difference (P less than 0.001) between facial form and denture teeth using temporal zygomatic and gonial widths for faces, compared with incisal, contact, and cervical widths for the teeth.

Denture Design↗
PubMed1985

A morphometric analysis of the craniofacial configuration in achondroplasia.

Human achondroplasia can be viewed as an experimental model for studying the effects of abnormal endochondral bone formation on the development of the skull as a whole. In this study, lateral cephalograms of 25 adult males and 26 adult females with achondroplasia were converted to a two-dimensional coordinate model of craniofacial morphology and analyzed using 66 linear, angular, and area variables. Lateral cephalograms of 951 normal adults were used for comparison. Two sample t-tests were used to compare achondroplastic cephalograms with normal cephalograms. Multivariate statistical analysis included Hotelling's T2 and discriminant function analysis. Selected variables were graphed as profile patterns in which mean values were expressed as standard deviation units (Z scores) relative to the norm. Finally, Calcomp plots were used for visual inspection and for comparison of the average cephalometric tracings of male and female achondroplastic subjects with normal male and female subjects, respectively. Significant findings in achondroplasia included enlarged calvaria, frontal bossing, large frontal sinuses, occipital prominence, normal anterior cranial base length, strikingly shortened posterior cranial base length, an acute cranial base angle, a short nasal bone that was deformed and depressed, short upper facial height, recessed maxilla, posterior tilt of the nasal floor, and a prognathic mandible that was anteriorly displaced but of normal size with a normal gonial angle and a high coronoid process. The finding of normal anterior cranial base length in achondroplastic subjects was surprising since the cranial base is preformed in cartilage and hypoplasia and shortening would be expected. Since the brain is enlarged in achondroplasia, the expanding frontal lobes may possibly influence the growth of the anterior cranial base, since it is known to follow a neural pattern of growth. Cribriform plate length was strikingly reduced, but anterior sphenoidal length was strikingly increased, compensating for the shortened cribriform plate length and suggesting that growth in the length of the anterior cranial base takes place primarily by adaptation at one site--namely, the sphenoethmoidal synchondrosis. Strikingly short posterior cranial base length was interpreted as resulting from hypoplasia of bone that is preformed in cartilage with possible early closure of the spheno-occipital synchondrosis. The exaggerated closure of the cranial base angle in achondroplasia may be related to an increased brain size and possibly earlier than normal closure of the intersphenoidal synchondrosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Achondroplasia↗
PubMed1983

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.

Adult↗
PubMed1982

Principal components of craniofacial growth for white Philadelphia males and females between 6 and 22 years of age.

Three principal components, explaining 83 percent of the common variation for 999 males and females between 6 and 22 years of age, describe ontogenetic patterns of relationship for seven facial dimensions, including sella-nasion, sella-basion, nasion-prosthion, infradentale-menton, articulare-gnathion, gonion-gnathion, and articulare-gonion. Accounting for 65 percent of the variation, a general component associated with both size and shape defines size-required changes in proprotion during growth. Independent patterns of regional variation associated with alveolar remodeling (second component) and condylar growth (third component) describe specific sources of facial modification. Mean multivariate component scores reveal that sexual dimorphism, which progressively favors males over females with age, results from accumulating differences in size and related proportional changes in shape. The timing of the condylar growth spurt, as evident from variation in ramus height, produces secondary dimorphism which diminishes following the adolescent phase in males. Significant age effects are indicated for alveolar remodeling and mandibular growth of the condyle.

Adolescent↗
PubMed1982

Racial variation of cephalometric measurements in Hawaii.

To establish the race-specific norms and investigate the underlying etiological basis of racial differences in malocclusion, cephalometric measurements of Steiner were analyzed for five major racial groups in Hawaii: Caucasians, Japanese, Chinese, Filipinos, and Hawaiians. Subjects consisted of 210 healthy and orthodontically normal individuals of both sexes aged 15 years or older. Analysis of age- and sex-adjusted cephalometric values showed that bone-to-bone relationships are largely comparable among races with an exception of GoGn/SN. Significant racial differences are incisal inclinations in relation to the maxilla, the mandible, or the opposite incisors, with the least inclination for Caucasians and the greatest for Chinese. The result is general tendency of bimaxillary protrusion of non-Caucasians. No significant differences were detected in arch lengths of both jaws among these groups. It is suggested that the observed higher prevalence of mesioclusion in non-Caucasians--especially Orientals--is due to an imbalance of tooth dimension to the alveolar bone.

Adolescent↗
PubMed1980

Roentgen cephalometric analysis of ridge resorption and changes in jaw and occlusal relationships in immediate complete denture wearers.

In eighteen subjects assigned for immediate complete upper and lower dentures, roentgen cephalometric recordings were made before extraction of the residual anterior dentition and 3 weeks, 3 months, 6 months and 1 year after denture insertion. The cephalometric analysis was based on electronic measurements of linear and angular morphological variables and computer head plots generated from 177 reference points (Walker, 1967), derived for each subject for each of the five observation stages. The reduction of the alveolar ridges was most rapid during the first 3 months of denture wear and particularly during the post-extraction period of 3 weeks. The reduction in anterior height of the lower ridge was on average twice as great as that of the upper ridge. The ridge resorption and the accompanying settling of the dentures on the basal seats, measured from lead shots inserted in the dentures, brought about an upward rotation of the mandible with a resulting decrease in occlusal vertical dimension and reduction in overjet of the dentures. In accordance with the amount of ridge reduction, these changes showed great individual variation.

Adult↗
PubMed1977

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 dentofaical 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.

Adult↗
PubMed1977

A cephalometric guide to the diagnosis of midface hypoplasia at the Le Fort II level.

A cephalometric study of the relation of the malar eminence to the A point has been made. It is proposed that the orbital-NA distance is of clinical importance in patients with SNA of less than 79 degrees in whom a Le Fort I osteotomy procedure is contemplated. The measurement of the angle SNO is a significant guide to the malar-maxillary relationship and will assist in complete cephalometric evaluation of these patients.

Adolescent↗
PubMed1977

Computer-based analysis of 227 white males and females to establish range of malar-maxillary cephalometric relationships.

A computer-based analysis was undertaken on 227 white males and females to establish the relationship of the sella-nasion orbitale angle to that of the sella-nasion A point. The ratio of sella-orbitale to sella-nasion was also studied and it was discovered that these results were significantly related to the sella-nasion A-point angle. There was little sexual dimorphism. These results provide objective guidelines to the surgical treatment of people suffering from hypoplastic development of the middle part of the face.

Adolescent↗
PubMed1976

The computer and the law: coordinate analysis of skull shape and possible methods of postmortem identification.

Mechanisms accelerating or retarding the disintegration of soft tissues are briefly discussed, as well as the need to reconstruct the missing profile for postmortem identification purposes. The application of X-ray and computer-based analyses is discussed in the context of providing data to predict and reconstruct the most probable soft tissue profile of a dry skull. In addition, information from extensive studies of the facial bones and profiles of veterans has been applied to methods in forensic medicine of determining age, sex, and racial background of unknown subjects.

Black or African American↗
PubMed1975

A quantitative study of the face in Down's syndrome.

The large number of persons with Down's syndrome among the group of physically and mentally retarded demands that continuing study be directed toward its causes and effects. Much conflicting data are reported in the literature concerning the facial and cranial effects of this syndrome. The cephalic proportions, in profile, of a group of male Caucasian trisomic Mongoloids were compared with the proportions of a control group of male Caucasians of similar age range. Using the areas of the midface, mandible, and endocranium obtained from cephlograms of the two groups, the following ratios were studied: (1) midfacial area/endocranial area (2) mandibular area/endocranial area, and (3) midfacial area/mandibular area. A significant degree of deficiency in midfacial area, mandibular area, and endocranial area was found in the Mongoloid group. In studying the facial proportions, we found that the Down's syndrome group's ratios were significantly smaller in all three areas. The magnitude of the deficiency in the Mongoloid midface, both in gross area and in relation to endocranial area, remained nearly constant with age. The ratio of midfacial area to mandibular area in Mongoloids was much more comparable to that of the normal group than the other two ratios studied. In both groups the ratio of the midfacial area to the mandibular area became smaller with age. The decrease was more rapid in the Down's syndrome group. The findings of this study imply that all areas of the face and skull are deficient in persons with Down's syndrome. The data point to the possibility that the characteristics of this syndrome and the deficiencies described are polygenic in origin. Also, contrary to the majority of reports in the literature, the mandible and the midface grow in approximately the same proportion in both study and control groups

Adolescent↗