A computer graphics program for measuring two- and three-dimensional form change in developing craniofacial cartilages using finite element methods

Cephalometric assessment of human fetal head specimens

BACKGROUND

Past investigations of prenatal craniofacial growth have largely relied on histological sections. Few studies have taken measurements on three-dimensional representations (3D reconstruction, 3D CT, postmortem) or varying depth levels (ultrasound), and we know of no craniofacial growth studies done on cleared-and-stained specimens of whole fetal heads.

MATERIALS AND METHODS

This study comprised 14 human fetal head specimens cleared and stained with alizarin red and alcian blue. They had been stored in glycerol and represented weeks 8-12 of gestation, with crown-rump lengths ranging from 23-145 mm. These specimens were cephalometrically analyzed in norma frontalis and norma lateralis, which notably included the opportunity for side-to-side comparison.

RESULTS

As the cranial membrane bones progressively approached each other, the orbits, maxilla, and mandible gradually grew wider. Likewise, the sagittal dimensions of the maxilla and mandible increased continuously and synchronically. We noted side-to-side differences ranging from 2-5 mm. Another notable finding concerned the inclination of the maxilla relative to the cranial base, which increased more on the right than on the left side.

CONCLUSION

This is the first investigation presenting side-to-side comparative measurements of human fetal head specimens. Such measurements are essential in the quest toward validating the findings of other imaging techniques such as CT or MRI and-most importantly-intrauterine sonography.

[3D reconstruction of anterior internal vertebral venous plexus of a human fetus: a feasibility study]

Anterior internal vertebral venous plexus have been studied extensively due to their clinical importance in diseases of the spine and obstruction of the inferior vena cava. The aim of this feasibility study was to reconstruct in 3D the lower thoracic area of the anterior epidural space of a 69 mm (crown-rump) human fetus from the Rouvière Collection, circa 1927. Forty slices (spaced by 40 microm) at the level of the tenth and eleventh thoracic vertebrae, and their lower adjacent intervertebral discs, were reconstructed in 3D using the commercial software SURFdriver. In a preliminary study, we had found that the structures of the epidural space are already formed at this stage of development, and that they are comparable to the adult stage (2002). Reconstruction of the microscopic slices in 3D allowed to better visualize spatially the structures of the venous plexus and their anatomical relationships. This technique could be used as a complement to the classically used histological studies.

Three-dimensional reconstruction of urogenital tract from Visible Korean Human

The three-dimensional (3D) modeling from anatomical images is revealed to be a remarkable learning tool in anatomy. This is particularly true for the pelvis area and the urogenital tract. The authors present here a 3D reconstruction of the male urogenital tract from the Visible Korean Human data. The segmentation of 440 anatomical images was arranged in a pile and processed by the SURFdriver software to build an interactive 3D model. Forty-two anatomical structures were reconstructed, including kidneys, ureters, urinary bladder (outer and inner boundaries), urethra, testes, epididymides, ducti deferens, seminal vesicles, prostate, rectum, anal canal, abdominal aorta, superior mesenteric artery, renal arteries, inferior vena cava, renal veins, lumbar vertebrae, intervertebral discs, sacrum, hip bones, femurs, and skin. Three-dimensional models of 42 anatomical structures can be individually and interactively manipulated. In addition, the use is able to control the transparency of the model. The aim of this computerized modeling is to present a learning tool for students and patients. In the near future, it could be the basis of new simulation tools for surgeon's training.

[3D modeling in the field of morphology: methods, interest and results]

The aim of this paper is to show the major role played by the new computerized imaging tools available today in the fields of morphology and anatomy. For anatomical studies or educational purpose, they enhance the classical techniques. The 3D reconstruction, already used in daily clinical practice, will be the basis for computation of validated volumetric protocols enhancing our diagnosis and prognosis means. It is also a fantastic educational tool: the interactivity makes it simple, efficient, attractive and easily accessible and diffusable. For the research, mathematical modeling of embryogenesis and morphogenesis using finite elements method will open new ways for biomecanics and a dynamic quantification approach.

Evaluation of two 3D virtual computer reconstructions for comparison of cleft lip and palate to normal fetal microanatomy

Cleft lip and palate reconstructive surgery requires thorough knowledge of normal and pathological labial, palatal, and velopharyngeal anatomy. This study compared two software algorithms and their 3D virtual anatomical reconstruction because exact 3D micromorphological reconstruction may improve learning, reveal spatial relationships, and provide data for mathematical modeling. Transverse and frontal serial sections of the midface of 18 fetal specimens (11th to 32nd gestational week) were used for two manual segmentation approaches. The first manual segmentation approach used bitmap images and either Windows-based or Mac-based SURFdriver commercial software that allowed manual contour matching, surface generation with average slice thickness, 3D triangulation, and real-time interactive virtual 3D reconstruction viewing. The second manual segmentation approach used tagged image format and platform-independent prototypical SeViSe software developed by one of the authors (F.W.). Distended or compressed structures were dynamically transformed. Registration was automatic but allowed manual correction, such as individual section thickness, surface generation, and interactive virtual 3D real-time viewing. SURFdriver permitted intuitive segmentation, easy manual offset correction, and the reconstruction showed complex spatial relationships in real time. However, frequent software crashes and erroneous landmarks appearing "out of the blue," requiring manual correction, were tedious. Individual section thickness, defined smoothing, and unlimited structure number could not be integrated. The reconstruction remained underdimensioned and not sufficiently accurate for this study's reconstruction problem. SeViSe permitted unlimited structure number, late addition of extra sections, and quantified smoothing and individual slice thickness; however, SeViSe required more elaborate work-up compared to SURFdriver, yet detailed and exact 3D reconstructions were created.

Comparison of mandibular morphology in Korean and European-American children with Class III malocclusions using finite-element morphometry

The purpose of this study was to determine whether the morphology of the mandible differed in subjects of diverse ethnic origin exhibiting Class III malocclusions. Lateral cephalographs of 147 children of either Korean or European-American descent aged between 5 and 11 years were compared. The cephalographs were subdivided into seven age- and sex-matched groups, traced, and eight mandibular homologous landmarks digitized. Average mandibular geometries, scaled to an equivalent size, were computed using Procrustes superimposition and subjected to ANOVA. Graphical analysis using a colour-coded finite element (FEM) programme was used to localize differences in morphology. Results indicated that the overall mean Korean and European-American mandibular configurations differed statistically (P < 0.001) and statistical difference was maintained at all age-wise comparisons. Comparing Korean and European-American Class III mandibular configurations for local size-change, FEM analysis revealed that the Korean condylar and mental regions generally were smaller (approximately 15-20 per cent decrease in size, respectively). However, an antero-posterior increase in the size of the mandibular corpus was most apparent in the incisor alveolus region (approximately 35 per cent increase in size). For shape-change, the Korean and European-American mandibular configurations were fairly isotropic except in the symphyseal and incisor alveolus regions. Dissimilarities in mandibular morphology are identifiable particularly in the dento-alveolar regions in subjects of diverse ethnic origin exhibiting Class III malocclusions. These differences may reflect genetic and/or environmental influences that might determine the severity and prevalence of the condition, and its subsequent clinical management.

Morphologic determinants in the etiology of class III malocclusions: a review

Morphospatial disharmony of the craniomaxillary and mandibular complexes may yield apparent mandibular prognathism, but Class III malocclusions can exist with any number of aberrations of the craniofacial complex. Deficient orthocephalization of the cranial base allied with a smaller anterior cranial base component has been implicated in the etiology of Class III malocclusions. Whereas the more acute cranial base angle may affect the articulation of the condyles resulting in their forward displacement, the reduction in anterior cranial size may affect the position of the maxilla. As well, intrinsic skeletal elements of the maxillary complex may be responsible for maxillary hypoplasia that may exacerbate the anterior crossbite seen in the Class III condition. Conversely, with an orthognathic maxilla, condylar hyperplasia and anterior positioning of the condyles at the temporo-mandibular joint may produce an anterior crossbite. Aside from the skeletal components, soft tissue matrices, particularly labial pressure from the circumoral musculature, may influence the final outcome of craniofacial growth of a child skeletally predisposed to Class III conditions. Indeed, as some Asian ethnic groups demonstrate an increased prevalence of Class III malocclusions, it is likely that the skeletal components and soft tissues matrices are genetically determined. Presumably, the co-morphologies of the craniomaxillary and mandibular complexes are likely dependent upon candidate genes that undergo gene-environmental interactions to yield Class III malocclusions. The identification of such genes is a desirable step in unraveling the complexity of Class III malocclusions. With this knowledge, the clinician may elect an early course of dentofacial orthopedic and orthodontic treatments aimed at preventing the development of Class III malocclusions.

Finite-element morphometry of soft tissues in prepubertal Korean and European-Americans with Class III malocclusions

The purpose was to test the hypothesis that soft-tissue morphology differs consistently in people of diverse ethnic origin exhibiting Class III malocclusions. Lateral cephalographs of 70 Korean and 71 European-American children aged between 5 and 11 years were traced and 12 homologous, soft-tissue landmarks digitized. The total sample was subdivided into seven age- and sex-matched groups, and Procrustes superimposition was used to generate average geometries scaled to an equivalent size. Statistical differences were tested by ANOVA. Graphical analysis using a colour-coded finite-element (FEM) program was used to localize differences in morphology. Procrustes' results indicated that the overall mean Korean and European-American soft-tissue configurations differed statistically (p<0.001), and this difference was also true in all seven age groups tested (p<0.001). On comparing mean Korean and European-American Class III soft-tissue configurations for local size change, FEM analysis revealed that whereas the Korean mental regions generally were smaller (approx. 43% on average), local increases in size were apparent for the lower lip (approx. 29% on average). For shape change, the mean Korean and European-American soft-tissue configurations were fairly isotropic except in the region of the columella, lower lip and the anterior part of the mental region. Features of the soft-tissue integument in individuals of diverse ethnic origins appear to be associated with the underlying skeletal Class III morphology.

Comparison of numeric techniques in the analysis of cleft palate dental arch form change

OBJECTIVE

Quantitative descriptions of form (size and shape) changes are significant to the understanding of the development, treatment planning, and prognosis of patients born with cleft lip and palate. This study compared the results of traditional dental arch form change measurements, such as width, depth, perimeter, and area, with four numeric methods: finite element scaling analysis, macroelement method, Euclidean distance matrix analysis, and conventional least-squares and resistant-fit theta rho Procrustes analyses.

DESIGN

Using tooth cusp landmarks on maxillary study casts, form change measurements of a male with complete bilateral cleft lip and palate at ages 2, 5, and 6 years were made comparing each age to the next older.

RESULTS AND CONCLUSIONS

With the exception of the 2- to 5-year resistant-fit analysis, all numeric method: 1) provide comparable results, 2) provide more detailed descriptions than do traditional methods, and 3) provide results that correlate well with the reported effects of increased lip pressure due to lip closure surgery. The use of finite-element scaling analysis on study casts is somewhat limited since: 1) there is more than one solution at teeth shared by many finite elements, 2) gross averaging of form change occurs within triangular elements, and 3) solutions can vary with the choice of element location. The use of the macroelement method circumvented the above finite element limitations without compromising finite-element advantages. Procrustes results vary with the chosen superposition algorithm. The choice of the most appropriate Procrustes method required some a priori knowledge of form difference. The large number of results obtained by Euclidean distance matrix analysis and the nongraphic presentation of these results hamper quick interpretation but may be best suited for definitive statistical analysis. The graphic representation of both the magnitude and direction of: 1) landmark displacement in the Procrustes analyses (once size difference is eliminated), and 2) the rate of form change in the macroelement method provide an intuitive appreciation of how and where the casts differ.

Finite element analysis of the cranial base in subjects with Class III malocclusion

The association between cranial base morphology and Class III malocclusion is poorly understood. This study analyses local shape- and size differences in cranial base configurations of Class I and Class III subjects, employing finite element (FEM) analysis. Seventy-three prepubertal European-American children with Class III malocclusion were compared to their counterparts with a normal, Class I molar occlusion. Lateral cephalographs were traced, checked and subdivided into age- and sex-matched groups. Thirteen points on the cranial base were identified and digitized, providing a geometrical cranial base representation. Average cranial geometries were scaled to an equivalent size and a FEM analysis, capable of depicting and quantifying local shape- and size-change, employed to highlight regionalized, morphological differences. While the anterior cranial base was more homogeneous for shape-change, significant, localized anisotropy in the posterior regions of the cranial base and around sella turcica was evident. For size-change, areas of negative allometry were located posteriorly, but dilations in the mid- and anterior cranial base also were apparent. It is concluded that morphological alterations within the petro-occipital complex accompanied by changes in the sphenoidal and ethmoidal regions induce deviation from a normal cranial base configuration to one associated with deficient orthocephalization and an appearance of Class III malocclusion.

Morphometry of the cranial base in subjects with Class III malocclusion

The significance of the cranial base in the development of Class III malocclusion remains uncertain. The purpose of this study was to determine whether the form of the cranial base differs between prepubertal Class I and Class III subjects. Lateral cephalographs of 73 children of European-American descent aged between 5 and 11 years with Class III malocclusion were compared with those of their counterparts with a normal, Class I molar occlusion. The cephalographs were traced, checked, and subdivided into seven age- and sex-matched groups. Average geometries, scaled to an equivalent size, were generated based on 13 craniofacial landmarks by means of Procrustes analysis, and these configurations were statistically tested for equivalence. Bivariate and multivariate analyses utilizing 5 linear and angular measurements were undertaken to corroborate the Procrustes analysis. Graphical analysis, utilizing thin-plate spline and finite element methods, was performed for localization of differences in cranial base morphology. Results indicated that cranial base morphology differed statistically for all age-wise comparisons. Graphical analysis revealed that the greatest differences in morphology occurred in the posterior cranial base region, which generally consisted of horizontal compression, vertical expansion, and size contraction. The sphenoidal region displayed expansion, while the anterior regions showed shearing and local increases in size. It is concluded that the shape of the cranial base differs in subjects with Class III malocclusion compared with the normal Class I configuration, due in part to deficient orthocephalization, or failure of the cranial base to flatten during development.

Facial growth after primary periosteoplasty versus primary bone grafting in unilateral cleft lip and palate

A cephalometric evaluation of long-term changes resulting from two different surgical techniques for the correction of unilateral cleft lip and palate (UCLP) was undertaken on a sample of 19 males with primary bone grafting, and 42 males with primary periosteoplasty from the Science Academy of the Czech Republic, Prague. Lateral cephalometric radiographs collected at approximately 10 and 15 years of age were traced, digitized, and analyzed using the finite-element method. Facial growth and development between the two groups were compared. Significant differences between the two groups were found in the upper face, the posterior part of the maxilla, the anterior bony chin, and nasal bone areas. The periosteoplasty group demonstrated significantly greater vertical development between anterior cranial base and the maxilla. The bony chin was larger and a greater inferior displacement of the posterior palate were found in the periosteoplasty group. An increased proclination in the nasal bone was observed in the bone graft group. This investigation both confirms the findings of a previous study of these sample populations, and provides additional important details regarding the differences between the groups.

Use of the boundary element method for biological morphometrics

Tensorial morphometric assessments of form difference can aid in the understanding of the cause of the form difference by providing reference frame independent, anisotropic, non-homogenous descriptions. The majority of biological and prosthetic structures cannot be adequately analyzed by current methods due to the paucity of anatomical landmarks and methodological requirements of subdivision through the domain. Internal subdivisions can be eliminated with the boundary element method (BEM). A non-landmark (NL) method can be developed by the combination of elliptical Fourier analysis (EFA) and BEM. The appropriateness of NL and BEM was investigated. The growth of the female rat neural skull from 7 to 14 postnatal days was calculated with respect to increase in area. Linear and quadratic BEM landmark analysis were made using 10 and 5 elements, respectively. Five hundred linear BEM elements were constructed from the EFA equations for NL. The form change tensors were obtained by the solution of the Laplace equation using boundary displacements as the essential boundary conditions. For comparison, simplex triangular finite element analysis (FEA), quadrilateral FEA and macroelement analysis were made on the same structure. Results correspond well to the two major growth process in this time period; (1) high cerebellar growth, and (2) relatively higher facial versus neural growth. The results in other regions are close to the biologically observed 36% increase in area. The average difference between BEM, NL versus FEA is 1.9 and 2.8%. Trends in results with position are almost identical for BEM, NL, MEM and quadrilateral FEA. The morphometric landmark BEM technique requires an additional numerical scheme to eliminate the singularities near the boundary.(ABSTRACT TRUNCATED AT 250 WORDS)

Anterior cranial base morphology in mice with midfacial retrusion

The role of the anterior cranial base in the morphogenesis of class III malocclusions remains uncertain. This study was conducted to determine whether morphologic deficiencies occur in the anterior cranial base in the Brachyrrhine (Br) mouse mutant showing severe midfacial retrusion, which is characteristic of a class III malocclusion. Crania from three groups of C3H/Hej, 3H1 Br/+, and 3H1+/+ mice, each consisting of 15 animals, were collected at 1, 3, and 5 days of age (total = 135). The anterior cranial base from each specimen was subjected to computerized reconstruction and ten landmarks were digitized from each model. The landmark configurations were compared using Procrustes analysis. Significant differences between models were determined at each age. In order to localize differences between forms, average landmark configurations derived from Procrustes analysis were subjected to finite-element analysis. Size-change values for the 3H1 Br/+ animals showed magnitudes that increased in an anteroposterior direction when compared to the 3H1 +/+ and C3H/Hej animals at all ages. The largest values were located posteriorly along the ossifying front of the presphenoid. In five of six comparisons, the size-change values separated into two distinct clusters. The posterior region of the anterior cranial base was divisible into two subclusters, one located superiorly and the other inferiorly. These data suggest that midfacial retrusion in the Br mouse may be caused, in part, by growth deficiencies in the posterior region of the anterior cranial base, particularly the presphenoidal and sphenoethmoidal regions.

Recent advances in primary palate and midface morphogenesis research

During the sixth week of human development, the primary palate develops as facial prominences enlarge around the nasal pits to form the premaxillary region. Growth of craniofacial components changes facial morphology and affects the extent of contact between the facial prominences. Our recent studies have focused on developing methods to analyze growth of the primary palate and the craniofacial complex to define morphological phases of normal development and to determine alterations leading to cleft lip malformation. Analysis of human embryos in the Carnegie Embryology Collection and mouse embryos of cleft lip and noncleft strains showed that human and mouse embryos have similar phases of primary palate development: first, an epithelial seam, the nasal fin, forms; then a mesenchymal bridge develops through the nasal fin and enlarges rapidly. A robust mesenchymal bridge must form between the facial prominences before advancing midfacial growth patterns tend to separate the facial components as the medial nasal region narrows and elongates, the nasal pits narrow, and the primary choanae (posterior nares) open posterior to the primary palate. In mouse strains with cleft lip gene, maxillary growth, nasal fin formation, and mesenchymal replacement of the nasal fin were all delayed compared with noncleft strains of mice. Successful primary palate formation involves a sequence of local cellular events that are closely timed with spatial changes associated with craniofacial growth that must occur within a critical developmental period.

Sexual dimorphism in the baboon facial skeleton

Baboons exhibit marked sexual dimorphism in many aspects of their morphology. Dimorphism is especially pronounced in the face. We use finite-element analysis to investigate the ontogeny of sexual dimorphism in a cross-sectional sample of baboon (Papio sp.) faces. This method provides detailed quantitative information about size and shape changes at anatomical landmarks in the face during growth. Allometric results suggest that sexual dimorphism in facial size and shape is produced by ontogenetic scaling: males and females share a common ontogenetic trajectory. Analyses of growth in time, which complement allometric analyses, show that female growth slows much earlier than male growth, accounting for the differences between sexes. Local size and local shape follow similar patterns of growth, but changes in these variables are slower in females. Local and global facial size are much more dimorphic than local and global facial shape.

Comparison between two finite-element modelling methods for measuring change in craniofacial form

Finite-element modelling of form change is a useful morphometric technique for measuring differences between anatomical patterns. Two different finite-element algorithms currently are used. One method requires normalized coordinates as input data, while the second method uses globalized coordinates as input data. This study determines whether the two finite-element methods provide equivalent measures of three-dimensional form change when applied to the nasal septa of embryonic mice. Computer models of the nasal septa from mice of 15 and 17 days gestation were generated. Homologous landmarks were identified so that each nasal septum was represented by a tetrahedral finite-element. These elements were subjected to both finite-element modelling methods. Results show that the two algorithms use different interpolation functions and yield dissimilar intermediate results, but generate identical strain matrices as well as equivalent principal extensions, directions of form change, variables of form change, and graphical displays. Therefore, results are directly comparable from studies using either finite-element modelling method.