Letty Moss-Salentijn

Finite element method modeling of craniofacial growth

The application of the concepts of continuum mechanics and of the numerical techniques of the finite element method permits the development of a new and potentially clinically useful method of describing craniofacial skeletal growth. This new method differs from those associated with customary roentgenographic cephalometry in that its descriptions and analyses are invariant; that is, they are independent of any method of registration and superimposition. Such invariance avoids the principal geometric constraint explicit in all analytical methods associated with conventional roentgenographic cephalometry. The conceptual and mathematical bases of the finite element method (FEM) are presented and illustrated by the numerical and graphic descriptions of the two-dimensional growth of the rat skull, for which two sets of longitudinal growth data are used. In practice, the FEM permits analysis of the skull at a scale significantly finer than previously possible, by considering cranial structure as consisting of a relatively large number of contiguous finite elements. For each such element, independently, it is then possible to describe and depict both the magnitude and the direction of temporal size and shape changes occurring in that element relative to itself at some initial time. It is emphasized that such descriptions are completely independent of any local reference frame.

The logarithmic properties of active and passive mandibular growth

Summary The growth of the human mandible in a series of orthodontically normal children was examined by methods designed to demonstrate both the vectors of active and passive growth and the logarithmic attributes of such growth. Both methods are described and illustrated. The individual differences in the vectorial properties of active and passive growth during relatively short periods of time suggest that is is hazardous to predict such growth increments within clinically useful tolerances. Further, all mandibular growth is shown to be logarithmic. As such, mandibular growth shares three logarithmic attributes: Its growth is allometric (expressed by the relative growth equation); growth of all human mandibles is capable of graphic presentation as a unitary logarithmic spiral; and its growth is gnomonic, that is, it changes its size while retaining the same shape. A synthesis of mandibular growth is presented in terms of the interrelationship between active and passive growth processes and their logarithmic attributes.

A minor salivary gland in human gingiva.

Abstract A hitherto unreported observation is presented of a minor salivary gland in the gingiva of an erupted human third mandibular molar. This gland was of a mixed, predominantly mucous nature. The possible mechanisms of its development in this unusual location were discussed.

Statistical testing of an allometric centered model of craniofacial growth

An allometric centered model of craniofacial growth was tested by several computer-assisted statistical methods on the pure longitudinal growth data of twenty-four close-bred female rats and on cross-sectional human cranial growth data. The study demonstrated that such a model was heuristic and, being incapable of exact definition, was deemed inappropriate for further use in modeling of craniofacial skeletal growth. The necessity for vigorous testing of any hypothesis concerning the modeling of craniofacial growth is stressed.

Studies on dentin. 2. Vestigial lacteal incisor teeth of the rat

The presence of a vestigial, lacteal incisor tooth is described in the laboratory rat. This tooth is felt to belong to the same dental generation as the other functional teeth. Accordingly, the rat is described as having a monophyodont, first dentition containing two incisor teeth in each quadrant. These vestigial teeth are then compared with other similar mammalian teeth and are defined as transient, partially formed and non-functional. As such, they are differentiated from other transient teeth. The examination of the fossil record suggests that tooth loss is a general phenomenon in rodents, but that this vestigial tooth probably represents a condition present in forms antecedent to rodents. A critical literature review strongly suggests that the teeth of the recent rat are members of the first dental generation. The presence of such a vestigial tooth and of the postincisive diastema in the rat is felt to be an example of phylogenetic reduction and progressive retardation in the sense of de Beers concepts. These same two phenomena were analyzed with respect to the field theory of Butler and of the Zahnreihen theory of Edmund. Placed within the context of recent data on epithelioectomesenchymal interactions, both theories were supported, and both the vestigial teeth and anodontic diastema were shown to be explicable within these conceptual frameworks.

Cartilage canals in the human spheno– occipital synchondrosis during fetal life

Spheno-occipital synchondroses were studied histologically in eight human fetuses ranging from 100 mm CRL to term. Cartilage canals were present in all seven specimens over 110 mm CRL. With age the canals grew longer and wider and the larger ones developed some branching. The histologic structure, external morphology and spatial arrangement of these cartilage canals were described. Some attributes of cartilage canals were reviewed from available data in the literature and their significance for the present findings discussed. It was suggested that the canals, containing blood vessels and connective tissue elements, actively invade the cartilage of the synchondrosis. It was suggested further that they probably serve as a source of nutrition or as an extension of the perichondrium (and a source of prospective chondroblasts) or both.

A bilateral, superficial location of human sublingual glands: Report of a case

During a routine dissection of a cadaver, the unusual, completely superficial position of both sublingual glandular masses was noticed. Histologically, the glandular masses consisted of a group of minor sublingual glands. It is suggested that the existence of a wide gap between the anterior and posterior parts of the mylohyoid muscle, which was revealed during further dissection, was the primary embryologic anomaly that was responsible for the unusual location of the glands.

An allometric network model of craniofacial growth

This study of cranial skeletal growth kinematics details the conceptual principles underlying the development of an allometric network model of such growth. This model is tested by the analysis of longitudinal rat and cross-sectional human growth data and by comparison of this model with a previously described allometric centered model. It is shown that the network model is superior to the centered model in three ways: (1) The allometric network model permits growth prediction when allometric constants are known; (2) the network model has significantly smaller errors than the centered model; and (3) the network model is capable of displaying growth kinematics of both the neural and facial skulls while in time there are marked transformations, such as relative rotations of two sets of cranial anatomic points.

A stochastic-mechanical model of longitudinal long bone growth.

A typical mammalian long bone will increase in length during the growth phase of the individual. This increase in length does not occur uniformly throughout the bone, since bone tissue is incapable of internal expansion after formation. The growth occurs at two, disc-shaped, regions near either end of the long bone. These regions are called growth plates. These plates are located between the osseous shaft (diaphysis) and osseous tip (epiphysis) whose bone tissues are discontinuous. The present study develops a stochastic-mechanical model for such a bone growth and demonstrates the capability of the model to reproduce the observed overall behavior of longitudinal long bone growth based on realistic information of cellular mitosis, growth and ossification. A numerical analysis was performed on the model under the assumption that the number of cells in the proliferation zone remains constant throughout the growth period. The growth curves thus obtained compare favorably with those growth curves proposed elsewhere essentially on the basis of phenomenological observation. The present model can demonstrate the effects of such parameters as the proliferation rate, initial age distribution and compressive stress on the growth. More importantly, the stochastic-mechanical model so developed permits one to incorporate further experimental evidence and statistical observation at the cellular level into the analysis to improve the solutions.

Studies on dentin 2. transient vasodentin in the incisor teeth of a rodent (perognathus longimembris).

Vascular inclusions regularly occur in the lingual dentin of the constantly erupting teeth of the pocket mouse (P. longimembris). The inclusion of a capillary loop and surrounding perivascular tissues is associated with odontoblasts whose cytodifferentiation is relatively immature. These same cells produce dentinal tubules which are more irregular in their course, more arborescent, with more lateral branches, wider in diameter and less numerous than are the tubules of the labial orthodentin. The patent vascular inclusions are surrounded by a broad halo of incompletely mineralized dentin. With further maturation complete obliteration of the vessels occurs, accompanied by complete dental matrix mineralization. A literature review supports the contention that vasodentinogenesis is related operationally to lower stages of odontoblastic cytodifferentiation although the processes by which this occurs are not yet clear.