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AbstractIt is often claimed that occlusal variation (“malocclusion”) is under strong genetic control. This study of a large age-standardized series of families (parents and offspring) shows that the genetic contribution to occlusal variation is quite low. On average, only about 10 percent of the variation in overjet, overbite, crowding, tooth rotations, and molar relationships results from nonenvironmental causes. In contrast, about 60 percent of the variation in measurements of arch size and shape is attributable to heredity.

AbstractAlthough lower incisor tooth shapes, defined as mesiodistal length divided by labiolingual width, have been proposed as important factors in lower incisor crowding, the question of whether or not these ratios are more useful than simple measurements of incisor mesiodistal length has not been addressed. In order to test this question, we measured mesiodistal and labiolingual incisor dimensions and lower incisor crowding (defined as the crowding index proposed by Little) on dental casts from two groups: 100 pretreatment orthodontic patients and 100 Hutterites from a religious isolate in Canada. The orthodontic patients are our primary interest. The Hutterites serve mainly to test whether or not results are consistent in another population of different ethnicity, age distribution, and occlusal status. In each population, incisor crowding is correlated with the tooth shape ratios, confirming the general observations of Peck and Peck. However, mesiodistal incisor lengths have slightly higher correlations with crowding than the shape ratios. In multiple regression equations to predict crowding in each population, incisor mesiodistal lengths are the most important variable, and neither the tooth shape ratios nor labiolingual widths significantly improve the equations. Although statistically significant, none of the correlations is higher than 0.30, and they are thus of little clinical value. The use of tooth size measurements or ratios as a guide to clinical procedures is an oversimplification of a complex problem.

AbstractOrthodontic forces can be treated mathematically as vectors. When more than one force is applied to a tooth, the forces can be combined to determine a single overall resultant. Forces can also be divided into components in order to determine effects parallel and perpendicular to the occlusal plane, Frankfort horizontal, or the long axis of the tooth. Forces produce either translation (bodily movement), rotation, or a combination of translation and rotation, depending upon the relationship of the line of action of the force to the center of resistance of the tooth. The tendency to rotate is due to the moment of the force, which is equal to force magnitude multiplied by the perpendicular distance of the line of action to the center of resistance. The only force system that can produce pure rotation (a moment with no net force) is a couple, which is two equal and opposite, noncolinear but parallel forces. The movement of a tooth (or a set of teeth) can be described through the use of a center of rotation. The ratio between the net moment and net force on a tooth (MF ratio) with reference to the center of resistance determines the center of rotation. Since most forces are applied at the bracket, it is necessary to compute equivalent force systems at the center of resistance in order to predict tooth movement. A graph of the MF ratio plotted against the center of rotation illustrates the precision required for controlled tooth movement.

AbstractIt is often claimed that occlusal variation (“malocclusion”) is under strong genetic control. This study of a large age-standardized series of families (parents and offspring) shows that the genetic contribution to occlusal variation is quite low. On average, only about 10 percent of the variation in overjet, overbite, crowding, tooth rotations, and molar relationships results from nonenvironmental causes. In contrast, about 60 percent of the variation in measurements of arch size and shape is attributable to heredity.

AbstractAlthough lower incisor tooth shapes, defined as mesiodistal length divided by labiolingual width, have been proposed as important factors in lower incisor crowding, the question of whether or not these ratios are more useful than simple measurements of incisor mesiodistal length has not been addressed. In order to test this question, we measured mesiodistal and labiolingual incisor dimensions and lower incisor crowding (defined as the crowding index proposed by Little) on dental casts from two groups: 100 pretreatment orthodontic patients and 100 Hutterites from a religious isolate in Canada. The orthodontic patients are our primary interest. The Hutterites serve mainly to test whether or not results are consistent in another population of different ethnicity, age distribution, and occlusal status. In each population, incisor crowding is correlated with the tooth shape ratios, confirming the general observations of Peck and Peck. However, mesiodistal incisor lengths have slightly higher correlations with crowding than the shape ratios. In multiple regression equations to predict crowding in each population, incisor mesiodistal lengths are the most important variable, and neither the tooth shape ratios nor labiolingual widths significantly improve the equations. Although statistically significant, none of the correlations is higher than 0.30, and they are thus of little clinical value. The use of tooth size measurements or ratios as a guide to clinical procedures is an oversimplification of a complex problem.

AbstractOrthodontic forces can be treated mathematically as vectors. When more than one force is applied to a tooth, the forces can be combined to determine a single overall resultant. Forces can also be divided into components in order to determine effects parallel and perpendicular to the occlusal plane, Frankfort horizontal, or the long axis of the tooth. Forces produce either translation (bodily movement), rotation, or a combination of translation and rotation, depending upon the relationship of the line of action of the force to the center of resistance of the tooth. The tendency to rotate is due to the moment of the force, which is equal to force magnitude multiplied by the perpendicular distance of the line of action to the center of resistance. The only force system that can produce pure rotation (a moment with no net force) is a couple, which is two equal and opposite, noncolinear but parallel forces. The movement of a tooth (or a set of teeth) can be described through the use of a center of rotation. The ratio between the net moment and net force on a tooth (MF ratio) with reference to the center of resistance determines the center of rotation. Since most forces are applied at the bracket, it is necessary to compute equivalent force systems at the center of resistance in order to predict tooth movement. A graph of the MF ratio plotted against the center of rotation illustrates the precision required for controlled tooth movement.

AbstractIt is often claimed that occlusal variation (“malocclusion”) is under strong genetic control. This study of a large age-standardized series of families (parents and offspring) shows that the genetic contribution to occlusal variation is quite low. On average, only about 10 percent of the variation in overjet, overbite, crowding, tooth rotations, and molar relationships results from nonenvironmental causes. In contrast, about 60 percent of the variation in measurements of arch size and shape is attributable to heredity.

AbstractAlthough lower incisor tooth shapes, defined as mesiodistal length divided by labiolingual width, have been proposed as important factors in lower incisor crowding, the question of whether or not these ratios are more useful than simple measurements of incisor mesiodistal length has not been addressed. In order to test this question, we measured mesiodistal and labiolingual incisor dimensions and lower incisor crowding (defined as the crowding index proposed by Little) on dental casts from two groups: 100 pretreatment orthodontic patients and 100 Hutterites from a religious isolate in Canada. The orthodontic patients are our primary interest. The Hutterites serve mainly to test whether or not results are consistent in another population of different ethnicity, age distribution, and occlusal status. In each population, incisor crowding is correlated with the tooth shape ratios, confirming the general observations of Peck and Peck. However, mesiodistal incisor lengths have slightly higher correlations with crowding than the shape ratios. In multiple regression equations to predict crowding in each population, incisor mesiodistal lengths are the most important variable, and neither the tooth shape ratios nor labiolingual widths significantly improve the equations. Although statistically significant, none of the correlations is higher than 0.30, and they are thus of little clinical value. The use of tooth size measurements or ratios as a guide to clinical procedures is an oversimplification of a complex problem.

AbstractOrthodontic forces can be treated mathematically as vectors. When more than one force is applied to a tooth, the forces can be combined to determine a single overall resultant. Forces can also be divided into components in order to determine effects parallel and perpendicular to the occlusal plane, Frankfort horizontal, or the long axis of the tooth. Forces produce either translation (bodily movement), rotation, or a combination of translation and rotation, depending upon the relationship of the line of action of the force to the center of resistance of the tooth. The tendency to rotate is due to the moment of the force, which is equal to force magnitude multiplied by the perpendicular distance of the line of action to the center of resistance. The only force system that can produce pure rotation (a moment with no net force) is a couple, which is two equal and opposite, noncolinear but parallel forces. The movement of a tooth (or a set of teeth) can be described through the use of a center of rotation. The ratio between the net moment and net force on a tooth (MF ratio) with reference to the center of resistance determines the center of rotation. Since most forces are applied at the bracket, it is necessary to compute equivalent force systems at the center of resistance in order to predict tooth movement. A graph of the MF ratio plotted against the center of rotation illustrates the precision required for controlled tooth movement.

AbstractAllometric scaling, a widely used approach for studying the relationship between size, shape, and function in organisms, is examined in both concept and application. Several methodological conventions are unnecessary or misleading, and a number of theoretical assumptions are unjustified. Some alternatives are suggested. Dependence on a power function as the method for evaluating the biological consequences of size has masked the complexity of the problem.

AbstractMuch of the literature in functional morphology is concerned with attempts to understand the mechanical nature of evolutionary adaptations, i.e. how organisms are like machines. It is argued that a more justifiable orientation would be to evaluate the constraints which limit the mechanical efficiency of structures, in other words, why organisms are different from machines.

AbstractA new approach is presented for the evaluation of cephalometric measurements in which a measurement is considered to be a diagnostic test for the presence or the absence of some component of malocclusion. This approach allows cephalometric measurements to be judged by the criteria that are generally used for clinical diagnostic tests, including determination of sensitivities, specificities, positive and negative predictive values, and, most important, receiver operating characteristic (ROC) curves. In this study, ROC curves are generated for the relationship between several skeletal cephalometric measurements and anterior dental open bite in a sample of 1541 orthodontic patients. The overbite depth indicator is found to be a better diagnostic criterion for the presence of dental open bite than any other commonly used skeletal cephalometric measurement or ratio. ROC curves are of substantial value for evaluating the diagnostic information of cephalometric measurements. (AM J ORTHOD DENTOFAC ORTHOP 1992;101:234-43.)

AbstractThe Drosophila position-specific integrins (PS integrins or PS antigens) comprise two heterodimeric complexes, αPS1βPS and αPS2βPS. With the cloning of αPS1 described here, we complete the characterization of the primary structure of the three PS integrin subunits. We have purified the αPS1 subunit, obtained peptide sequence and isolated genomic and cDNA clones. The encoded αPS1 protein contains pattern of the cleaved alpha integrins, three putative metal binding domains and shows the other characteristic features of alpha integrins. Regions of sequence variation indicate that αPS1 is distinct from all other alpha chains. The transcript analysis shows that the patterns of both αPS1 mRNA and protein expression are the same, suggesting that the gene is controlled transcriptionally. We compare the gene structures of the DrosophilaαPS1, αPS2, the human αPS1and αPS2 (p150,95) and the C. elegans F54G8.3 integrins. We find several positions and phases of introns conserved which, supported by conservation also in the amino acid sequence, indicates that they all derive from a common ancestral gene.

AbstractBackgroundThyroglossal duct cysts (TGDCs) are common in children but also present in adults. This study evaluates the preoperative management and postoperative outcomes in patients with a resected TGDC.MethodsA retrospective analysis was performed on patients with a surgically treated TGDC. Clinicopathologic variables and treatment outcomes were obtained by chart review.ResultsA total of 79 patients (44 pediatric and 35 adult) were identified. The majority of patients in both groups presented with a neck mass. Compared with children, adults were significantly more likely to undergo preoperative imaging and fine-needle aspiration biopsy. Malignancy was not identified in any patient on preoperative workup or postoperative pathology.ConclusionsAdults with a TGDC are more likely to undergo preoperative imaging and biopsy. The infrequent occurrence of TGDC cancer or concurrent thyroid pathology suggests that the diagnosis of a TGDC may be made on clinical grounds in adult patients although ultrasound (±fine-needle aspiration biopsy) may be a useful supplementary modality.

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