Preclinical Paediatrics · MU Sofia

3. Ossification, lines of fusion and defects in the formation of the maxillofacial region.

Explains how the lower and upper jaws ossify, covering the intramembranous formation of the mandible from Meckel's cartilage template and the maxilla from centres in the maxillary processes. Lists the lines of fusion of the face and the environmental factors that can disturb development in weeks 4 to 7. Classifies facial clefts, from unilateral and bilateral cleft lip to median cleft and cleft lip and palate.

Inside: 1 section · 16 flashcards · 4 min

Topic 3 of 40 in the MU Sofia syllabus for Preclinical Paediatrics (Dental Medicine, Year 3). The free AceMed note covers it in 1 section, about 526 words (4 min of reading), with 16 flashcards.

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  1. OSSIFICATION, LINES OF FUSION AND DEFECTS IN THE FORMATION OF THE MAXILLOFACIAL REGION

OSSIFICATION, LINES OF FUSION AND DEFECTS IN THE FORMATION OF THE MAXILLOFACIAL REGION

Ossification of Lower Jaw (Week 7)

  • Mandible has intramembranous ossification
  • Meckel’s Cartilage is the cartilage of 1st branchial arch of mandibular prominence which is not replaced by bone but it degenerates as bony mandible forms
  • Cartilage forms a template
  • Template itself does not ossify
  • Both cartilages do not meet at midline but are separated by a thin line of cartilage called symphysis
  • On the lateral aspect of symphysis, condensation of mesenchyme forms
  • Intramembranous ossification occurs at week 7, spreads anteriorly and posteriorly to form the mandible bone, bone developing anteriorly to midline of developing lower jaw
  • Ramus develops from rapid ossification posteriorly into mesenchyme of first arch

Ossification of Upper Jaw

  • Maxilla starts with centres of ossification developing in mesenchyme of maxillary processes of first branchial arch
  • Ossification spreads posteriorly below the orbit towards developing zygoma and anteriorly towards the future incisor regions and superiorly to form the frontal process
  • Ossification spreads into palatine process to form the hard palate
  • Union between palatal process and main body of developing maxilla is medial alveolar plate- together with lateral plates- development of maxillary teeth
  • Zygomatic cartilage appears in developing zygomatic processes and contributes to development of maxilla
  • Lateral dimensions of mouth are formed by connection point of mandibular and maxillary processes

Lines of Fusion

Upper Lip: 2 maxillary processes + 2 medial processes

Nasolacrimal Groove: 2 maxillary processes + 2 lateral nasal processes

Part of Maxilla, Upper Lip, Primary Palate, Premaxillary Process: 1 medial nasal process + 1 medial nasal process

Lower Jaw Arising from Mandibular arch at 30-35 days: 1 mandibular process and 1 mandibular process

Genetic and Congenital Defects:

Face develops during the short span from the 4th to 7th prenatal weeks

  • Environmental factors can cause a facial or pharyngeal arch defect which would probably affect these tissues before the 4th week
  • Irradiation
  • Chemical
  • Hormonal
  • Dietary
  • Stress related factors

Mild developmental defects of face are comparatively common.

Failure of facial prominences to merge or fuse results in abnormal developmental clefts.

  • These clefts are due to disruption of the many integrated processes of induction, cell migration, local growth and mesenchymal merging

Types of Facial Clefts

  • Unilateral Cleft Lip
  • Partial cleft located in line of fusion of medial nasal and maxillary process
  • Most common on left side. Strong familial tendencies
  • Bilateral Cleft Lip
  • Rare bilateral cleft lip results in a significant midline defect of upper lip and may produce a protuberant mass

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