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Biomedical subjects

D J Halazonetis

Publications and source records attributed to D J Halazonetis.

7 recordsLinked to original sources
PubMed1996

Computer experiments using a two-dimensional model of tooth support.

The purpose of this investigation was to study the factors that may affect the position of the center of resistance and center of rotation. A two-dimensional computer model of the periodontal ligament was developed. The model permitted the simulation of an isotropic (responding in the same manner regardless of the direction of the applied force) and nonisotropic periodontal ligament and allowed changes in root shape and in position and direction of force application. The center of resistance was found to depend on the distribution of root surface area. For a model of the upper central incisor, it was located at 42% of the root length measured from the alveolar crest. The presence of anisotropy in the periodontal ligament significantly affected the position of the center of resistance, which was in this case also affected by the direction of the applied force. Forces passing through the center of resistance produced translation of the modeled tooth in a direction not necessarily the same as the direction of the applied force. Tipping forces produced much larger stresses than forces causing translation. Simulation of periodontal involvement resulting in loss of attachment increased the stresses exerted on the periodontal ligament. The model permitted easy assessment of various factors that may influence the position of the center of resistance of teeth and revealed a potentially large variability in the position of the center of resistance and center of rotation, caused by variation of the properties of the periodontal ligament.

Alveolar Process↗
PubMed1994

Changes in cheek pressure following rapid maxillary expansion.

The purpose of the present investigation was to study the effects of rapid maxillary expansion on the pressures exerted by the cheeks on the maxillary arch. The sample consisted of 15 patients (five males, ten females) who received either a Hyrax or Haas type expansion appliance for treatment of a bilateral maxillary constriction of more than 5 mm. The median age of the sample was 12 years. Buccal pressures were measured at the upper first molar on the left and right side, before and after active expansion, and also after an average of 3-4 months of retention with the appliance in place. Buccal pressures on the maxillary first molar averaged approximately 3 g/cm2 before expansion and increased significantly to a value of approximately 9 g/cm2 after expansion. Pressure change was approximately 0.6 g/cm2 for each millimetre of expansion. During the 3-4-month period of stabilization of the appliance, the pressures remained at the post-expansion levels and no adaptation of the soft tissues was observed. These results lead to the conclusion that cheek pressures on the maxillary arch may be implicated in the relapse occurring after rapid expansion, even after the usual 3-month period of stabilization.

Adaptation, Physiological↗
PubMed1991

Quantitative description of the shape of the mandible.

The purpose of this study was to provide quantitative data on the shape of the mandible at the period around the pubertal growth spurt and to test the hypothesis that early mandibular shape may influence the amount and direction of subsequent mandibular growth. Longitudinal data from lateral cephalograms of 55 white female and 39 white male subjects were used. The mandibular outline from articulare to gnathion was analyzed into cosine curves, according to the Fourier equation. The resulting Fourier coefficients, representing mandibular outline shape, were analyzed statistically in relation to age, sex, craniofacial pattern, and mandibular growth rotation. Statistically significant growth changes of the Fourier coefficients were observed, especially during the postpubertal period, indicating a decrease in the gonial angle with age. Sex-related differences in shape were observed at all ages, male subjects showing a more rounded shape of the mandible than female subjects. Mandibular shape, as represented by the Fourier coefficients, was correlated to cephalometric variables, indicating mandibular inclination, but only poorly to cephalometric variables, indicating anteroposterior jaw relation. Total rotation of the mandible during growth could not be predicted by mandibular shape.

Cephalometry↗