A unified developmental model in which the human mandible is not produced by one ossification mechanism, but by five distinct modes deployed in specific regions and coordinated in part by Meckel’s cartilage.
The review reframes Meckel’s cartilage from a passive scaffold to an active signalling centre and argues that “parachondral” most accurately describes mandibular body formation in vivo.
The categories are defined so that the spatial relationship to cartilage and the cellular mechanism are not conflated.
Direct osteogenic differentiation in mesenchyme; prominent in body, ramus, and coronoid process.
Intramembranous bone forms adjacent to Meckel’s cartilage under its paracrine guidance.
At the symphysis and anterior Meckel’s cartilage midsegment, with chondrocyte-to-osteoblast transdifferentiation.
At the condylar and angular processes; specialised cartilage retains viable hypertrophic chondrocytes and can form chondroid bone.
Bone forms at the surface of Meckel’s cartilage; spatially distinct but mechanistically a form of intramembranous ossification.
Transdifferentiation is treated as the cellular process executing primary-cartilage endochondral ossification, not as an independent mode.
The diagram highlights the major regions used to explain the composite model. It is a conceptual map, not a scale anatomical illustration.
Single-cell and spatial transcriptomic evidence supports paracrine communication from intermediate Meckel’s cartilage to osteoblast progenitors.
One of the MC-derived osteogenic guidance signals highlighted in the model.
Supports the concept of an active cartilage-to-mesenchyme signalling field.
Part of the intermediate MC communication programme.
Included among signals guiding adjacent osteogenic differentiation.
Selected milestones from the review's human developmental timeline.
The composite model links regional anatomy to signalling pathways and transcriptional programmes.
Supports osteoblast differentiation and intramembranous bone formation.
Supports cartilage formation, chondroprogenitor proliferation, and region-specific endochondral programmes.
The review connects regional mechanisms with craniofacial disorders and regenerative strategies while keeping the evidence level explicit.
Used as an example of disruption at a developmental/molecular level; prenatal molecular rescue evidence remains preclinical.
Illustrates how osteogenic transcriptional programmes can disturb mandibular development.
Included as a clinically relevant disorder that can reflect disruption of mandibular growth mechanisms.