Growth and Devolpment of Maxilla & Mandible

Development of the Premaxilla

• Premaxilla ossification occurs through two centers: the palato-facial center and the prevomerine (paraseptal) center.
• Palato-facial center appears by the end of 6 weeks, located above the lateral deciduous incisor germ, contributing to the inner wall of alveoli and the palatal part of the premaxilla.
• Prevomerine center begins at 8-9 weeks, forming beneath the anterior vomer and contributing to the nasal paraseptal cartilage.
• Union of maxilla and premaxilla occurs at 8 weeks of intrauterine life.

Accessory Cartilages

• Accessory cartilaginous centers develop in the future zygomatic process and undergo rapid ossification.
• Additional secondary cartilaginous centers form along the alveolar plate and midline of the hard palate.

Growth of the Maxilla

• Growth continues until approximately 10 years of age, primarily through sutural growth, alveolar development, and subperiosteal bone formation.
• Maxilla articulates with skull bones via four main sutures: fronto-maxillary, zygomatico-maxillary, zygomaticotemporal, and pterygopalatine.
• Eruption of permanent teeth, especially upper molars, enhances maxillary arch length.
• The maxillary sinus expands through bone resorption on the sinus side and deposition on the facial surface, a process known as pneumatization.

Development of the Mandible

• The mandible is the strongest facial bone, composed of a horizontal body and two ramus portions meeting at nearly right angles.
• Ossification spreads backward, forming a trough for the inferior dental nerve and eventually the mandibular canal.
• The ramus develops from mesenchyme of the first branchial arch, diverging from Meckel’s cartilage.

Mandibular Cartilages

• Condylar cartilage forms in the 12th week, shaping the condyle and posterior ramus half to the inferior dental foramen.
• Coronoid cartilage appears transiently, contributing to the coronoid process and the anterior ramus half.

Alveolar Process Formation

• The alveolar process initiates growth when deciduous tooth germs reach the early bell stage, forming a bony trough around tooth germs.
• Septa of bone develop between adjacent tooth germs, allowing the formation of the mandibular canal and supporting nerves and blood vessels.

Mandibular Growth Patterns

• Mandibular growth includes secondary cartilage contribution, especially from condylar cartilage, influencing height and overall length.
• Age-related changes occur in the mandible:
  • At birth, the body is a simple shell accommodating various teeth; mental foramen opens below the first deciduous molar.
  • In childhood, body elongation occurs, increasing depth for additional teeth and aligning the mental foramen and mandibular canal with growth.
  • In adulthood, alveolar and sub-dental body depths are equal, with a nearly vertical ramus and narrower angle (110° to 120°).
  • In old age, the mandible reduces in size, involving alveolar process absorption and repositioning of the canal and foramen.