Medial movement of the palatopharyngeal arches medial and posterior to the palatoglossal arches is also involved in closing the oropharyngeal isthmus. By closing the oropharyngeal isthmus, food or liquid can be held in the oral cavity while breathing.
The teeth are attached to sockets (alveoli) in two elevated arches of bone on the mandible below and the maxillae above (alveolar arches). If the teeth are removed, the alveolar bone is resorbed and the arches disappear.
The gingivae (gums) are specialized regions of the oral mucosa that surround the teeth and cover adjacent regions of the alveolar bone.
The different types of teeth are distinguished on the basis of morphology, position, and function (Fig. 8.278A).
In adults, there are 32 teeth, 16 in the upper jaw and 16 in the lower jaw. On each side in both maxillary and mandibular arches are two incisor, one canine, two premolar, and three molar teeth.
The incisor teeth are the “front teeth” and have one root and a chisel-shaped crown, which “cuts.”
The canine teeth are posterior to the incisors, are the longest teeth, have a crown with a single pointed cusp, and “grasp.”
The premolar teeth (bicuspids) have a crown with two pointed cusps, one on the buccal (cheek) side of the tooth and the other on the lingual (tongue) or palatal (palate) side, generally have one root (but the upper first premolar next to the canine may have two), and “grind.”
The molar teeth are behind the premolar teeth, have three roots and crowns with three to five cusps, and “grind.”
Two successive sets of teeth develop in humans, deciduous teeth (“baby” teeth) (Fig. 8.278B) and permanent teeth (“adult” teeth). The deciduous teeth emerge from the gingivae at between six months and two years of age. Permanent teeth begin to emerge and replace the deciduous teeth at around age six years, and can continue to emerge into adulthood.
The 20 deciduous teeth consist of two incisor, one canine, and two molar teeth on each side of the upper and lower jaws. These teeth are replaced by the incisor, canine, and premolar teeth of the permanent teeth. The permanent molar teeth erupt posterior to the deciduous molars and require the jaws to elongate forward to accommodate them.
All teeth are supplied by vessels that branch either directly or indirectly from the maxillary artery (Fig. 8.279).
All lower teeth are supplied by the inferior alveolar artery, which originates from the maxillary artery in the infratemporal fossa. The vessel enters the mandibular canal of the mandible, passes anteriorly in bone supplying vessels to the more posterior teeth, and divides opposite the first premolar into incisor and mental branches. The mental branch leaves the mental foramen to supply the chin, while the incisor branch continues in bone to supply the anterior teeth and adjacent structures.
All upper teeth are supplied by anterior and posterior superior alveolar arteries.
The posterior superior alveolar artery originates from the maxillary artery just after the maxillary artery enters the pterygopalatine fossa and it leaves the fossa through the pterygomaxillary fissure. It descends on the posterolateral surface of the maxilla, branches, and enters small canals in the bone to supply the molar and premolar teeth.
The anterior superior alveolar artery originates from the infra-orbital artery, which arises from the maxillary artery in the pterygopalatine fossa. The infra-orbital artery leaves the pterygopalatine fossa through the inferior orbital fissure and enters the inferior orbital groove and canal in the floor of the orbit. The anterior superior alveolar artery originates from the infra-orbital artery in the infra-orbital canal. It passes through bone and branches to supply the incisor and canine teeth.