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Biomedical subjects

P E Lestrel

Publications and source records attributed to P E Lestrel.

At least 19 recordsLinked to original sources
PubMed1994

Skeletal jaw relationships: a quantitative assessment using elliptical Fourier functions.

Elliptical Fourier functions (EFF) were generated for the boundary outlines of the hard tissue craniofacial complex including the maxilla, mandible, and cranial base in order to quantitatively describe adult patients (n = 98) who were initially classified into nine skeletal groups by a combination of conventional cephalometric measures and clinical judgement. The mean residual fit of the EFF-predicted points and the original digitized data for the individual subjects ranged from .42 mm to .61 mm with a mean of .52 mm suggesting an accurate fit. Visual inspection of the individual plots confirmed this. Predicted classifications from a step-wise discriminant analysis based on EFF amplitudes were compared with the original classifications. The discordance rates for A-P and vertical plane classification were 21% and 13% respectively with an overall discordance rate of 33%. In general, a cluster analysis using EFF amplitudes did not identify clusters very similar in membership to the original groups; however, it was marginally successful in identifying members of the more severe groups and, like discriminant analysis, appeared to be more sensitive to vertical morphological differences. The overall lack of agreement between classifications and clusters based on EFF amplitudes and the original classifications may indicate that traditional skeletal categories such as those used in this study do not actually represent discrete groups.

Adolescent↗
PubMed1993

Longitudinal study of cranial base shape changes in Macaca nemestrina.

The primate cranial base (CB) represents a complex irregular structure even when limited to two dimensions, making it difficult to describe quantitatively using the conventional metrical approach composed of angles and distances. Consequently, a curve-fitting procedure, elliptical Fourier functions (EFF), was utilized, which accurately defines the form of complex two-dimensional morphologies. A longitudinal Macaca nemestrina sample consisting of 14 females and 15 males was utilized. Lateral headfilms, 1 to 8 years, were available (275 headfilms). Because the x-rays were not always taken at precise one-year intervals, a number of headfilms were excluded, which reduced the sample to 181. The CB boundary outline was carefully traced onto acetate sheets and 54 points located. The observed points were digitized and used to compute size-standardized EFF's with 20 harmonics. From each EFF, a set of 150 expected distances to the CB boundary was generated using the centroid as an origin. Superimposition of the CB's on the centroid also provided a detailed picture of the relative shape changes with respect to that center. Statistically significant shape differences were found as a function of age and sexual dimorphism. These age changes consisted of a gradual anteroposterior lengthening with a concomitant narrowing in the superoinferior direction. Specifically, a lengthening of the dorsal clivus and an anterior migration of the hypophyseal fossa could also be discerned. Thus, Fourier descriptors provide a particularly powerful method for documenting, both visually and numerically, the shape changes of complex two dimensional morphologies.

Animals↗
PubMed1993

Quantification of function regulator therapy using elliptical Fourier functions.

The application of various functional appliances to correct antero-posterior skeletal discrepancies in the treatment of Class III malocclusion has received increased attention. In this context, elliptical Fourier functions (EFF) are particularly useful for eliciting boundary-outline information. This longitudinal study was undertaken to visually and numerically describe the shape alterations arising as a response to treatment with the FR-3 appliance of Fränkel. The subjects chosen were Caucasians (n = 14) from the Glasgow Dental Hospital and School who presented with Class III incisor relationships. Lateral cephalometric head-films were available prior to the initiation of treatment, at the end of active treatment, and at least one year out of retention. Maxillary and mandibular boundary outlines were carefully traced. A set of points, 42 on the maxilla, and 78 on the mandible, were precisely located. These points were then digitized and used to compute EFF's with 20 harmonics. These equations were then standardized for size. Subsequently, 102 maxillary and 150 mandibular closely spaced points on the outline were calculated from the EFF's. After superimposition on the centroid, expected vectors were then computed to these points from the centroid. Statistically significant dento-alveolar shape changes could be discerned with treatment. These involved a localized anterior repositioning of the maxillary incisal aspect with a concomitant posterior displacement of the mandibular incisal aspect. There was no evidence of shape changes in the basal areas of either the maxilla or mandible. This method of fitting Fourier descriptors, specifically EFF's, provides a precise numerical and visual description of the changes arising from functional regulator therapy.

Adolescent↗
PubMed1993

Fourier analysis of shape changes in the Japanese skull: occipital view.

Photographs (norma occipitalis) of Japanese adult skulls (n = 171) were mathematically described with Fourier analysis to assess shape changes over time. The materials used were adult male skulls excavated from the Kanto District and covered four age-periods; Jomon (2000-1000 BC). Kamakura (14C. AD), Muromachi (15C. AD). and Edo (18C. AD). Mean raw data values, containing both size and shape information of each vector, were compared for the four age-periods. Statistically significant differences among the four age-periods were found using an ANOVA. The form of the Jomon skulls displayed the most difference among the four groups. This trend was especially evident at the parietal margin. Fourier analysis was subsequently undertaken to detect the presence of secular changes in skull form after standardization for size. Once the effect of size was removed, the occipital shape of the Jomon skulls was found to be essentially similar to those of the more recent age-periods.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1992

Shape changes due to functional appliances.

Functional appliances are now routinely used in orthodontic treatment to correct anteroposterior skeletal discrepancies, based on the assumption that existing functional patterns can be modified to yield a new morphological pattern. However, the mechanisms by which this correction occurs remain in dispute as current measurement procedures, primarily mathematical, do not adequately describe shape changes. This paper introduces a new measurement method, Fourier descriptors, to clinical dentistry.

Adolescent↗
PubMed1989

Some approaches toward the mathematical modeling of the craniofacial complex.

It is increasingly recognized by quantitative morphologists that the use of the conventional metrical approach (CMA), consisting of linear distances, angles, and ratios, to describe the size and shape of complex morphological forms as well as the shape changes between forms, is a procedure that is inherently deficient. Conventional metrics were designed to measure regular geometric objects and were never intended to describe the shape of complex irregular forms. A number of new methods have been developed to describe complex irregular shapes that attempt to circumvent the difficulties with CMA. These procedures fall into two categories, those dependent on homologous-point representations and those based on boundary representations. Three of these new methods, 1) biorthogonal grids, 2) finite element scaling, and 3) elliptical Fourier analysis, are reviewed here. While all three methods represent major improvements over CMA as shape and shape change descriptors, they must be considered as promising preliminary numerical models rather than final definitive pronouncements. Each method has constraints that preclude it from being the method of choice. It is apparent that a generalized model for the characterization of complex morphological forms remains to be developed.

Animals↗
PubMed1989

Carapace growth of the turtle Chrysemys scripta: a longitudinal study of shape using Fourier analysis.

Because the majority of morphological structures encountered in Biology are irregular in form, conventional metrics composed of distances, angles and ratios, are inefficient shape descriptors. To circumvent this drawback in the application of morphometrics to describe 2 dimensional shapes, an alternative procedure based on Fourier analysis was developed and applied to the turtle carapace. Once size differences were controlled for, the presence of shape changes with age could be demonstrated. This study showed that small systematic differences in the phase angle are associated with increase in carapace asymmetry. The differences were not visually apparent in the original data. These results reinforce the need for precise shape descriptors that are capable of measuring a large percentage of the informational content that is present in all biological forms.

Age Factors↗
PubMed1982

A Fourier analytic procedure to describe complex morphological shapes.

Most time-dependent processes such as growth are characterized by changes in size and shape. An accurate assessment of such morphological changes at specific points in time and over time has remained problematic. The conventional metrical approach, consisting of a comparatively few and subjectively chosen distances, angles, and ratios remains an inefficient descriptor of complex shapes. This is not to say that conventional metrics have no utility (their use depends on the application), but rather that they cannot measure more than a fraction of the informational content present in complex shapes. An alternative approach to conventional metrics has been developed using a Fourier analytic procedure. The Fourier function chosen provides an accurate representation of the morphological form. As the Fourier coefficients are orthogonal it is possible to partition out the effect of size to facilitate comparisons based solely on shape. The application of this Fourier procedure to describe morphological shapes is illustrated with data drawn from craniofacial as well as postcranial skeletal materials.

Aging↗
PubMed1980

A cephalometric study of mandibular cortical bone thickness in dentulous persons and denture wearers.

Cephalometric measurements of the cortical thickness of the inferior mandibular border and the inferior aspect of the mandibular symphysis were compared in two groups of subjects, one with complete dentition and the other wearing complete maxillary and mandibular dentures. Although the cortical thickness of the inferior mandibular border increased slightly with age in both dentition groups, the cortical thickness was significantly less in denture groups than in their respective dentition groups. The opposite was true with the cortical thickness of the inferior aspect of the mandibular symphysis; a decrease in thickness was noted with age, and a slight increase in thickness was noted with edentulousness. The results suggest that bone remodeling can be expected at sites distant from the residual ridge in denture wearers.

Adult↗
PubMed1978

The mandibular dental arch: part III. Buccal expansion.

The tendency toward relapse in intercuspid width has been examined with those cases having final intercuspid width less than 27 mm showing significantly less relapse than those cases with final intercuspid width of 28 mm or more. The point of contact between the cuspid and first premolar has been introduced as a key point on the arch, determining arch width. An individualized norm has been derived for this measurement as a function of the patient's tooth size, facial pattern, and other variables based upon stable normal occlusions in treated cases. Those cases expanded to a dimension exceeding the norm by more than 1 mm showed a greater propensity toward relapse. The group following the norm was significantly more stable than the over- and underexpansion groups at the .025 significance level. An individual norm for intermolar width based upon the patient's facial pattern (using frontal and lateral X-rays) has been established. Cases showing relapse showed considerably less space between the lower molar and the JAG plane, and greater lower face height than stable cases. The results show that the space available for the permanent dentition can be estimated in advance of treatment based on the patient's own skeletal measurements, thus minimizing unnecessary extractions, relapse, and extended treatment time due to errors in diagnosis.

Adolescent↗
PubMed1978

The cranial base in fetal Macaca nemestrina: a quantitative analysis of size and shape.

The applicability of Fourier analysis to quantitate the midsagittal cranial base has been demonstrated utilizing fetal Macaca nemestrina. This methodology accurately measures the irregular form of the endocranial profile, minimizes the effects of size, and maximizes shape differences. This method provides a quantitative dimension to the descriptive analysis of shape change previously observed with a combined histologic and cephalometric analysis.

Animals↗
PubMed1977

Size and shape of the hominoid distal femur: fourier analysis.

A quantitative description of the shape of the distal femur is provided by Fourier analysis. Fourier analysis also facilitates the separation of the size and shape components which allows the removal of the distorting effect of size. Hence, comparisons between the hominoid groups can be based solely on shape. A sample of 91 hominoid distal femora from the Cleveland Museum of Natural History was used to make comparisons based on size and shape as well as shape only. It is suggested that unless the effect of size is minimized or removed, generally not possible with the traditional metrical approach, measures of biological distance will be distorted.

Animals↗
PubMed1977

A computer program for comparing irregular two-dimensional forms.

A shape comparison of two forms requires a procedure that ensures comparability. A computer program has been written to compute a quantitative measure of shape differences between irregular bounded forms. The curve-fitting procedure, utilizing Fourier's series, is particularly well-suited for two-dimensional closed forms. The program provides several alternate methods to eliminate size difference, ensure a common or neutral center for superimposition and provide a rotational orientation which minimizes shape differences. The program contains numerous user-specified options which control input data transformations, algorithmic processing and output. The algorithmic processing provides: (1) generation of Fourier coefficients based on observed data, (2) two methods of producing Fourier coefficients adjusted for positional orientation, (3) two methods of producing Fourier coefficients adjusted for size standardization, (4) two methods of producing Fourier coefficients adjusted for rotational orientation, (5) a cross-correlation technique which rotationally adjusts two superimposed forms to minimize the shape difference, and (6) various standard statistical measures.

Computers↗
PubMed1976

Fourier analysis of the cranium in trisomy 21.

A comparative study of individuals exhibiting the trisomy 21 syndrome (Down's) and a normal group has shown statistically significant differences in cranial shape (norma lateralis). These differences illustrate the departure from normal growth seen in individuals displaying the trisomy 21 syndrome. Fourier analysis is a preferred method since it is more efficient than conventional techniques in the analysis of complex shapes. Fourier analysis is also attractive because the series terms are orthogonal, hence independent; further, the Fourier approach allows for the control of size differences. A three-way analysis of variance was used to test for significant differences between mean Fourier coefficients. The results showed significant difference between individuals with trisomy 21 and controls. Age differences were also significant, only sex differences tended to be non-significant. Finally, the trisomy 21 sample is twice as variable as the controls.

Age Factors↗