10/09/2009 A New View on the Control of the Morphogenesis of the Skull

Resident: J. Hencler
Date: 10/09/2009

Article title: A New View on the Control of the Morphogenesis of the Skull
Author(s): J. Van Limborgh
Journal: Acta Morphol. Neerl.-Scand. 8 (1970) 143-160

Major topic: Development and morphogenesis of the skull

Type of Article: Review

Main Purpose:
Review and compare theories of skull development.

Findings:
There are 3 main problems concerning the control of the morphogenesis of the skull.
1. In the embryonic phase, is there any association between development of the skull and other primordial structures of the head?
2. Once the skull is formed, how are endochondral and intramembranous bone growth coordinated?
3. In which way is coordination between skull growth and other structures realized?

Key points in the article discussion:
Controlling factors include intrinsic genetic factors, epigenetic factors, and environmental factors. Intrinsic genetic factors are the genes inherent to the skull tissues. Epigenetic factors are genetically determined factors that manifest themselves in an indirect way. Epigenetic factors may originate from adjacent structures and have a local influence such as the brain or eyes or may be produced by distant structures and have a general influence such as hormones. Environmental factors originate from the external environment. Data now available suggest that processes of skull differentiation are mainly controlled by local epigenetic factors originating from adjacent structures of the head. Very few intrinsic genetic factors are involved. 3 theories concerning control of skull growth are as follows:
1. Sicher (1952): growth of the skull is largely controlled by intrinsic genetic factors. Only the modeling of the surface-configuration and the internal structure of the bones would be subjected to additional influences from local environmental factors, including muscular forces.
2. Scott (1962): Intrinsic growth-controlling factors are only present in the cartilage and in the periosteum. Growth of the sutures is secondary and entirely dependent on extra-sutural influences. Cartilaginous parts of the skull should be viewed as growth centers and sutural growth may be modified by local environmental influences.
3. Moss’ Functional Matrix Theory of Growth (1966): Growth of the skull is entirely secondary. Neither bone nor cartilage is the determinant for growth of the craniofacial skeleton but instead control lies in the adjacent soft tissues. Growth of the face occurs as a response to functional needs and neurotrophic influences and is mediated by the soft tissues in which the craniofacial bones are embedded.

Summary of conclusions:
This article found that none of the 3 relevant theories on the control of skull growth were satisfactory but that each of them contains certain points that are significant.
1. Growth of synchondroses and the resulting endochondral ossification is almost exclusively controlled by intrinsic genetic factors.
2. Intrinsic factors controlling intramembranous bone growth (growth of sutures and periosteum) are small in number.
3. Cartilaginous skull parts must be seen as growth centers.
4. Extent of sutural growth is controlled by both the cartilaginous growth and growth of the other head structures.
5. Extent of periosteal bone growth largely depends on the growth of adjacent structures.
6. The intramembranous process of bone formation can be additionally influenced by local environmental factors, muscle forces inclusive.

Assessment of article:
This was an interesting article that explained all 3 growth theories. Presently, Moss’ Functional Matrix Theory is generally accepted. This article was long and presented a very detailed review of the development, growth, and morphogenesis of the skull. Anyone interested in the finer detail of craniofacial growth should refer to this fabulous, intellectually stimulating article.