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Growth movements during prenatal development of human facial morphology
Insights
Human facial development rapidly progresses between 7 and 12 weeks post-conception (pc). Early cartilage growth significantly influences craniofacial morphology, impacting later bone development.
Area of Science:
- Developmental Biology
- Craniofacial Morphology
- Embryology
Background:
- Human facial morphology rapidly develops after primary palate formation, achieving human-like characteristics by 10-12 weeks post-conception (pc).
- The craniofacial skeleton is primarily cartilaginous between 7 and 12 weeks pc, preceding complete ossification.
Purpose of the Study:
- To review major growth movements and developmental changes in craniofacial tissues between 7 and 12 weeks pc.
- To understand the role of primary cartilages in establishing human facial appearance.
Main Methods:
- Review of craniofacial development during a critical embryonic period (7-12 weeks pc).
- Examination of experimental animal studies (rats) exposing embryos to teratogens to assess effects on cartilage growth and subsequent bone development.
Main Results:
- Rapid forward growth of facial regions occurs between 7 and 12 weeks pc, establishing relationships to the cranial base.
- Early cartilaginous growth (7-10 weeks pc) is crucial for typical human facial appearance before bony skeleton formation.
- Altered Meckel's cartilage growth in rats affected the developing bony mandible's size and shape.
Conclusions:
- Growth movements of the chondrocranium and Meckel's cartilage are vital for spatial arrangement of facial bones during craniofacial development.
- Significant growth alterations during the primary cartilaginous stage can cause irreversible effects on later craniofacial morphology.
Abstract:
After formation of the primary palate, human facial morphology develops rapidly and by 10-12 weeks pc the face has characteristics that appear typically human. The objective of this study was to review major growth movements and developmental changes in craniofacial tissues between 7 and 12 weeks pc. During this period (20 - 80 mm CR length), the upper and lower facial regions grow forward rapidly to achieve relationships to the cranial base that are similar to those present later prenatally and postnatally. Initial ossification of facial bones is present but the primary cartilages form the continuous craniofacial skeleton through the entire period. Rapid directional growth of the cartilaginous components between 7 and 10 weeks appears to be important to development of the typically human facial appearance prior to the formation of the continuous bony skeleton. The effects of altered primary cartilage growth on bony skeletal patterns were examined in experimental animal studies in which embryonic rats were exposed to teratogens. Reduction in the length of Meckel's cartilage or alteration in the shape of the cartilage was found to affect the size and shape of the bony mandible that developed later. Therefore, growth movements of the chondrocranium and Meckel's cartilage appear to play an important role in spatial relocation of developing facial bones during formation of craniofacial morphology. The results suggest that significant alterations in growth during this period when the primary cartilages form the continuous skeleton may produce significant irreversible effects on later prenatal and postnatal craniofacial morphology.