HE L5.2

Chapter 5: Development of Orofacial Structures

Overview of Orofacial Development

• Timing: Orofacial structures develop from the fourth to the twelfth week of prenatal development, covering the later embryonic to early fetal periods.

• Continuation: This chapter continues the discussion on embryonic development, focusing on the stomodeum, face, and neck—where the last chapter concluded.

Palatal Development

Palatal Development: Time Table

• Fifth Week: Formation of the palate begins.

  • Palette consists of primary and secondary structures.

• Twelfth Week: Finalization of the palate.

Detailed Development Timeline:

• Fifth to Sixth Week:

  • Primary Palate: Formed from the intermaxillary segment derived from fused medial nasal processes.

• Sixth to Twelfth Week:

  • Secondary Palate: Formed from the fusion of palatal shelves from maxillary processes.

• Twelfth Week:

  • Final Palate: Completed fusion of all three processes (primary and secondary palates).

Palatal Development Process Overview

• Fusion Mechanism: Involves the joining of swellings from various embryonic surfaces, akin to the fusion of the neural tube.

Primary Palate Formation

• Fifth Week: Intermaxillary segment forms and serves as a partial separation between the oral and nasal cavities.

Secondary Palate Formation

• Sixth Week:

  • Creation: Bilateral maxillary processes develop into palatal shelves (or lateral palatine processes).

• Development Process:

  • Shelves grow vertically and deep into the stomodeum alongside the developing tongue.

  • The tongue, initially occupying the nasal and oral cavity, moves aside as it develops, allowing shelves to reposition horizontally.

  • Elongated shelves move medially and fuse to form the secondary palate.

Features of the Secondary Palate

• Contributes to the posterior two-thirds of the hard palate and incorporates certain maxillary teeth.

• The median palatine raphe and suture indicate the fusion line of the palatal shelves.

Performance of Epstein Pearls

• Definition: Small white papules on the palate of an infant represent epithelial tissue trapped during fusion.

Final Palate Completion

• The fusion of the posterior part of the primary palate and secondary palate culminates in a final palatal structure.

Developmental Disturbances

Cleft Palate

• Occurs due to a failure in fusion of palatal shelves with each other and/or the primary palate. This results in various levels of disability.

Cleft Uvula

• Description: Cleft uvula (or bifid uvula) represents the simplest form of a cleft palate.

Nasal Cavity and Septum Development

• Develops concurrently with the palate, from the fifth to the twelfth week of prenatal development, aiding in respiratory system formation.

• Nasal Septum: Formed from fused medial nasal processes, it grows inferiorly and connects with the palate.

• Fuses with the final palate to become a cohesive structure.

Clinical Consideration

Deviated Septum

• A condition where the nasal septum is displaced, resulting in unequal separation and potential blockage of nasal cavities.

Tongue Development

Timing and Origin

• Period: Development occurs between the fourth to eighth weeks of prenatal growth, arising from branchial arch structures.

• Early Development: Begins as a median swelling, the tuberculum impar, supplemented by lateral swellings.

Development Timeline:

• Fourth to Eighth Week:

  • Body: Formation of tuberculum impar and lateral lingual swellings.

  • Base: Copula forming over the second branchial arches.

• Eighth Week: Merging of the anterior body and copula to complete the tongue.

Body of Tongue Development

• Swellings: Lateral lingual swellings merge, hiding the tuberculum impar, forming the anterior two-thirds of the tongue.

• Median Lingual Sulcus: Indicates the fusion line of lateral swellings and is a visible marking of development.

Base of Tongue Formation

• Copula Development: Overgrows the second branchial arch to form the posterior third of the tongue, eventually coalescing with the body during the eight week period.

Completion Markers

• The sulcus terminalis forms a boundary between the tongue's body and base indicating completion by the eighth week.

Developmental Disturbances in Tongue

Ankyloglossia

• Commonly known as "tongue-tied," caused by a short lingual frenum attachment preventing full movement of the tongue.