that nevertheless require different treatment schemes because they are of different origins:
- In border areas, there are transitional types between 'normal development' and deformity
- An exact diagnosis is required!
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Problems usually affect individual regions, such as the maxilla and/or the mandible.
Base of the skull = border structure between neurocranium and viscerocranium
The development of the base of the skull influences that of the neurocranium and viscerocranium.
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Weeks 5 and 6 of embryonal development.
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- Mesenchymal densification in the area of the axial head mesoderm.
- Transformation of this mesenchymal cover in the area of the base of the skull into a blastema.
- Development of the cartilaginous chondrocranium.
- The skullcap remains membranous.
The chondral base that is open to the top consists of 4 regions (Stark 1975).
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- Trabeculae cranii
- Ala orbitalis (lesser wing of sphenoid bone)
- Ala temporalis (greater wing of sphenoid bone)
- Occipital region
Chondral base of the skull = primary growth centre
Development is influenced by:
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- genetic,
- functional,
- and hormonal factors.
The chondral base is successively transformed into bone by enchondral ossification.
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Problems of chondroblast activity during development may lead to severe deformities, such as Apert syndrome.
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Ala minor ossis sphenoidalis develops from the ala orbitalis.
Sphenoid bone and acoustic labyrinth develop from the ala temporalis (pars squamosa by desmal ossification).
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Together, 1 and 2 form the temporal fossa = glenoid fossa of temporal bone.
The position of the temporo-mandibular joint (TMJ) is pre-determined by the chondral base of the skull in a vertical, sagittal and transverse direction, as well as the angle between the two petrous bones.
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Developmental disorders may lead, for instance, to Goldenhar's syndrome (oculo-auricular dysplasia).
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The trabeculae cranii develop into:
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- Ethmoid sinus
- Ethmoid bone
- Crista galli
- Nasal septum
- Cartilaginous nasal capsule
This area is decisive for the sagittal and vertical development. Developmental problems in this area may lead to disorders, such as Binder's syndrome.
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Desmal ossification of the skullcap occurs parallel to the enchondral ossification of the base of the skull.
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In week 7 and 8 of embryonal growth, centers of ossification develop in both the neurocranium and the viscerocranium, together with musculature.
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The membranous character remains in the area of the sutures.
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A suture consists of an osteogenetic cellular inner layer, covered by a fibrous vascular layer.
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Growth in the area of the sutures by functional forces = musculature.
They lead to distraction of the centers of ossification and reactive appositional bone growth on the margin of the centers of ossification = secondary growth center
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The extent of movement can be concluded from the suture's design.
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Craniofacial sutures = secondary growth center
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Problems lead to craniostenosis with typical skull modifications, also in the viscerocranium.
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