ArticleLiterature Review

The role of function in the development of human craniofacial form?A perspective

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Abstract

As an anatomical region the head combines great diversity of function with close integration of structure. Consequently no structural component has autonomy of form. There is a sequence of maturation of functions and their related structural components, and in this sequence the nervous system and its supportive structures mature first. The nasal airway matures next in response to increasing body mass, and the masticatory system constitutes the last major functional system to reach maturity. The later the maturation of the function, the greater is the requirement for its related morphology to adapt to preceding skeletal templates. These matters of developmental sequence, and extrinsic as well as intrinsic craniofacial functions, are paramount considerations in interpreting the form of any component of head anatomy.

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... The innervation pattern of the cranial nerves precedes basicranial and neurocranial expansion, with both of the latter processes in turn positively allometric to ethmomaxillary expansion (Lieberman, Ross, and Ravosa, 2000), which tracks increasing body mass. These integrated and constrained processes occur prior to formation of full dental eruption and development of adult masticatory function in Homo (Kean and Houghton, 1987). ...
... In humans, the development of the brain and neurocranium outpace masticatory function, the brain being 90% of its adult size in comparison to 40% for the jaws at age 5 (Washburn, 1947;Hanken and Hall, 1998). Thus, formation of the craniofacial complex is hierarchical and masticatory factors are constrained to accommodate prior states in the ethmomaxillary, basicranial, and neurocranial regions (Kean and Houghton, 1987). ...
... For example, modules such as the face are genetically programmed autonomously, apart from the dermatocranium and basicranium (through differential Hox gene induction patterns, Kuratani, 2005). There is intermodular hierarchical organization: the structure of the face follows the more rapidly expanding dermatocranium and nasal region (Kean and Houghton, 1987;Franciscus and Trinkaus, 1988). The S/D/B modules occupy specific cranial regions. ...
... The potential accommodative capacity of the maxillary sinuses is particularly important with regard to variation in nasal morphology given that the relative independence of the nasal cavity may vary across different regions of the nose. For example, although there are potentially important population-specific differences in superior nasal breadth related to respiratory function and air-conditioning capacity of the nasal cavity (e.g., Franciscus, 2003), variation in the breadth of the superior nasal region may be constrained by neural structures and visual organs (Kean and Houghton, 1987). In contrast, air-filled spaces in place of bone and vital organs (i.e., the maxillary sinuses) are unlikely to impose the same constraints on other aspects of nasal morphology. ...
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... It is therefore apparent from details of palatal morphology in humans that the ante- rior portions of this element comprise two functionally independent (in terms of facial functional capsules) laminae (Moss and Greenberg, 1967). With respect to palatal morphogenesis, as the extent of inferior drifting of the palatal nasal lamina is regu- lated primarily by body size and the height of the nasal airway ( Kean and Houghton, 1987;Burke and Hughes-Lawson, 1989), whereas depositional activity orally is pre- sumably more a function of the extent of upward maxillary rotation associated with elongation of the posterior face (Björk and Skieller, 1976), it might be expected that a general thickening of this element might accompany posterior facial hyperplasia. The ''posterior facial hyperplasia'' model there- fore posits that the vertical dimension of the hard palate is structurally linked to that of the posterior facial skeleton. ...
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Even though the temporomandibular joint is loaded in function, it often arthroses under heavy use. The effects of stress to the joint are not well understood. This study utilizes three-dimensional photo-elastic stress analysis to visualize the intensity and direction of stresses within the mandibular condyle generated by various occlusal forces. Functional stresses were shown to concentrate in the condylar neck, but were reduced within the condylar head due to its elliptical shape. Stress directions within the condyle were found to be non-preferential, varying with different mandibular positions. This supports the idea that the condyle is designed to receive light varied forces rather than heavy, cyclical unidirectional forces.
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Mathematical models have been developed to predict hypothetical forces acting on the mandibular condyles during mastication, but no direct measurements of condylar forces in vivo have been reported. This preliminary study presents the technical development of an instrumented prosthesis which was implanted in the mandibular ramus of a baboon, and some preliminary data collected while measuring with this prosthesis the condylar forces exerted during simulated mastication under general anaesthesia. Simulated mastication was induced by stimulating the motor tracts of the trigeminal nerve bilaterally, and the forces in response to increasing amperage were recorded. The pathogenesis of TMJ degeneration may be more fully understood by directly measuring the direction and magnitude of forces acting on the condyles during function. In addition, the future development of a total TMJ replacement for traumatized, deranged, or degeneratively impaired joints, must be accomplished with reliably engineered prostheses based upon direct force measurements.
Article
It is evident that chondrocyte determination is an example of cellular aging. This possible leads to the erroneous view that chondrocytes have a "weak" genetic control mechanism. If such was the case, chondrocranial growth and development would be a very "shaky" process indeed. It is recognized however that chondrocranial growth is under predominantly genetic and tissue interaction influence especially during the early phase of growth. These control factors plus other epigenetic and local environmental influences are responsible for the harmonious growth of the chondrocranium.
Article
The orbital volume in Dutch rabbits ranged from 3.6 ml at 98 days to 5.8 ml at 540 days of age. By 180 days of age the orbital volume had reached about its maximum of 5 ml and was 25% larger than at 100 days of age. The mean orbital volume was less at 540 than at 450 days of age. At 15 days of age the eye volume was about 20% of adult size, at 100 days of age about two thirds, at 180 days of age about 85% of adult size which was reached at about 300 days of age. The mean bulb volume was less at 540 than at 450 days of age. After evisceration, enucleation, or exenteration, in young rabbits there was a decelerated increase of orbital volume and a direct relationship between the lack of intraorbital mass and the subsequent lack of development of the orbit. The addition of a constant-sized implant in the young rabbit, after evisceration or enucleation of the eye, did not enhance orbital growth. In adult rabbits enucleation of the eye did not subsequently alter the orbital volume. In young rabbits an increase of the eye volume after multiple intrabulbar injections of silicone resulted in increase in orbital volume. The same procedure in adult rabbits increased neither the eye nor the orbital volume. Some clinical correlations are made.
Article
We consider the cranial base to be the primordial determinant of the head form and mandibular shape so common amongst (but not exclusive to) adult Polynesians. The flatness of the cranial base manifests its full influence only when growth of the upper facial skeleton is complete in early adulthood. We argue that during growth and maturation the upper facial skeleton and the maxillary occlusal plane are required to adjust in position to a major extent according to the template set out by the flat cranial base, with consequent obligatory and extreme adjustment in shape and position of the mandible in order that occlusion be maintained. The base is constrained from adjusting its own shape significantly by virtue of its intimate relationship with the brain and the emerging cranial nerves. The structural consequences of these adaptations are seen in the bony profile, which is vertically disposed and orthognathic, and in the large nasopharynx, while functionally the relative inefficiency of the mandible as a lever requires extensive compensatory development of masticatory musculature which influences the shape of the face and vault.
Article
The three dimensional co-ordinates of a large number of landmarks on a series of Polynesian skulls have been obtained by means of a diagraph, and from standard lateral cephalograms. The method is accurate, and a very large amount of data is stored in the concise form of the standardized co-ordinates. A factor analysis of some of these data defines a number of distinct craniofacial segments showing independent variation in positioning, and therefore presumably growth, along defined axes. The segments thus defined relate well to the conclusions of other studies of skull growth and form, and support the view that the basis of cranial variation is the same for all Homo sapiens. It is suggested that the strict independence of the isolated craniofacial segments may be a consequence of the particular method, and may not truly reflect the situation in the growing skull.
Article
Four human adult mandibles were selected, a rosette strain guage was applied in the angle region bilaterally and a single element strain gauge on the posterior surface of both condyles and condylar necks. Each mandible, together with a brass replica of the upper arch and the glenoid fossa, were placed together on a supporting frame and loads were applied to simulate the action of the anterior temporal, masseter and internal pterygoid muscles. Strains were recorded in maximum intercuspation and after insertion of a rubber frame between the lateral teeth. Strains in the angle region were greater on the working side than on the balancing side. However, in the condylar region the balancing side strains were higher than on the working side. This can be attributed to the different orientation of strains on the two sides.
Article
A complete bibliography of all papers dealing with maternal nutrition and fetal growth in both animals and man is beyond the scope of this chapter. Recognizing that animal investigations may be relevant, I have attempted to concentrate on information derived from studies in human beings. References cited may be incomplete in some cases. Usually I have emphasized recent reports for the perspective they provide.
Article
Expected mean values and a range of normal values (plus or minus twice the standard deviation) are presented for the vital capacity and the maximum breathing capacity of female children and adolescents. Although multiple correlation does not demonstrate a particularly higher degree of predictability it is recommended that the above values be based upon the four attributes (age, height, weight, and body surface area) rather than upon a single attribute. This is especially important in the abnormally shaped individual.
Article
Expected mean values and a range of normal values (plus or minus two standard deviations) are presented for the vital capacity and the maximum breathing capacity of male children and adolescents. It is recommended that calculations of the above values be based upon four attributes (age, height, weight, and body surface area) rather than upon a prediction deriving from a single attribute (especially in the individual who does not have a standard height and weight for his age).
Bidy' weight, race and climate The influence of asymmetry of the muscles of Anthropol., 11.533-558. -mastication upon the bones of the face
  • D F Rnberts
Rnberts, D.F: (1953) Bidy' weight, race and climate. Am. J. Phys. Rogers, W.M. (1958) The influence of asymmetry of the muscles of Anthropol., 11.533-558. -mastication upon the bones of the face: Anat. Rec., 131t617-632.
Cheshire cat craniology In: Ar-chaeology at ANZAAS 1984
  • P Houghton
  • M R Kean
Houghton, P., and M.R. Kean (1986) Cheshire cat craniology. In: Ar-chaeology at ANZAAS 1984. G. Ward, ed. Canberra Archaeological Society; and Department of Prehistory, Research School of Pacific Studies, Australian National University, Canberra.