Development of Face (Mouth, Lips and Gums, Cheeks, Palates)

Development of face

The stomodeumor the primitive buccal cavity is formed by the formation of the cranial and lateral foldings and subsequent cranial flexures. It is separated from the pharyngeal cavity by the oropharyngeal membrane which breakdown following the fusion of the left and right mandibular processes. During the foetal development, the stomodeum becomes greatly elongated as a result of the growth of the maxillary, mandibular and nasal process.

Neural crest mesenchymal cells initially located over the dorsal and rostral surfaces of the procencephalon are brought to the rostral and ventral surfaces of the head as a result of >90 ° cranial flexure. This population of cells called the frontonasal mesenchyme, will form the forehead and nasal regions of the face. At the early stage, the fronto nasal mesenchyme, will form the forehead and nasal regions of the face. At the early stage, the fronto nasal process represents forehead. A thickening of ectoderm on each side o this process forms the olfactory placode (nasal placode).

Each nasal placode invaginates to form the nasal pit which deepens and subsequently contacts the roof of the stomodeum. The nasal pit is circumscribed by two swellings, the medial nasal process and the lateral nasal process derived from fronto nasal mesenchyme.The area between the two medial nasal processes extending dorsally over the forebrain is the frontal prominence. The line of fusion of the two medial nasal process is the philtrum.

Each medial nasal process unites with the maxillary process of the respective side to form the upper jaw and cheek regions. The lateral nasal process fuse with the maxillary process closing the oculo-nasal sulcus and thus completing the socket. The lateral nasal processes become the sides and wings of the nose.

The two mandibular processes unite in front to form the lower jaw. The bifurcation of maxillary and mandibular processes is reduced by the establishment of the lips and cheeks forming the rima oris.

Development of Mouth

The first indication of the embryonic mouth is the stomodeum – an indentation of the ventral surface of the embryo at the level of first branchial arch.

The stomodeum enlarges and becomes deeper. A defnite stomodeal cavity is formed at two weeks of gestation in most of the embryos. Shortly thereafter,the oropharyngeal memberane ruptures which allow the communication between the stomodeum and the floor of the pharynx.

The rupture of the memberane allows structures arising from the pharynx to extend into the adjacent part of the stomodeum. After the rupture of the oral memberane,it is impossible to determine the exact junction of the ectoderm and endoderm in the mouth cavity.

The terminal sulcus on the root of the tongue marked by the presence of circumvallate papillae is the only demarcation. The stomodeal part is lined with the ectodermal epithelium and the pharyngeal part with endodermal epithelium.

Development of Lips and Gums

The maxillary and mandibular prominences that form the jaws are originally solid masses of mesenchyme covered with the ectoderm. At about 3 ½ weeks, in the ectodermal epithelial lining of the mouth, a horse-shoe shaped thickened band of cells appear on each jaw.

The band of epithelial cells begins to grow into the underlying mesenchyme thereby causing bands to become the grooves. Along the course of the original band, the epithelial lamina is formed because of the sufficient penetration of epithelium into the mesenchyme.

Then the lamina splits forming a peripheral layer of tissue to form the lips (labia oris) and a medial layer of tissue to form the gums (gingiva). Thus, the grooves and the lamina are called labio-gingival groove and lateral lamina respectively. The space created by the labio-gingival lamina is called the vestibule.

Development of cheecks

The fusion of the jaws results in the formation of cheeks. The degree of the fusion is a factor determining the size of the opening into the oral cavity (rima oris ).

The labial and buccal muscles differentiating from the mesenchyme of the second branchial arches which migrates between the epidermal covering and mucosal lining of these parts.

Development of Palate

Following the fusions of the facial mesenchyme, the roof of the stomodeum is bounded by the maxillary process laterally and by the medial nasal process and fronto nasal prominence rostrally. A pair of openings from the short nasal cavities enter the roof of the stomodeum.

The mesenchymal cells located between the nasal cavities initially form the medial nasal process and ventral aspect of the frontal prominence. These cell population aggregate in the rostral midline to form the medial palatine process, part of which will become the primary palate. Later, the premaxillary bone is formed within the mesenchyme. The palatine fissures mark the caudal margin of the primary palate. The mesenchyme located superficially between the nasal cavities contributes to the rostral cartilages of the snout, philtrum and median part of the upper lip.

The oronasal cavity is partially partitioned by two vertical tissue masses, the nasal septum which projects from the roof of the cavity ventrally between the two nasal cavities. Broad mesnchymal process grows into the oronasal cavity from the maxillary processes on both the sides. These are lateral palatine processes, which unite with each other and then with nasal septum and medial palatine process. Bone appears in the anterior part of the fused lateral palatine processes forming the hard palate. Ossification fails at the posterior part, which results in soft palate. The medial palatine process forms the premaxillary portion of the upper jaw.

Anomalies in development of Palate

Cleft palate

Cleft palate or Palatoschisis or Congenital Oronasal Fistula is a failure of fusion of lateral palatine process.