Anatomy of Teeth

Tooth Structure

• Teeth are attached to the cementum of the roots by the periodontal ligament
• Gingiva covers the alveolar bone
• Enamel is very hard, white to off-white, and highly mineralized, acting as a barrier to protect teeth
• Enamel can be degraded by acids from food and drink
• Dentin is yellow in appearance and greatly affects the color of the tooth due to the translucency of enamel
• Dentin is less mineralized and less brittle than enamel, and is necessary for supporting enamel
• Two main characteristics distinguishing dentin from enamel are that it forms throughout life and is sensitive

Periodontium

• Periodontium refers to the tissues surrounding and supporting teeth
• The four principal components of the periodontium are:
  • Gingiva
  • Periodontal ligament
  • Cementum
  • Alveolar bone
• Alveolar bone is surrounded by gingival subepithelial connective tissue
• Cementum overlays the root and is attached to the adjacent cortical surface of the alveolar bone by the alveolar crest, horizontal fibers of the periodontal ligament, and oblique fibers of the periodontal ligament

Palatine Aponeurosis

• Supports the integrity of the soft palate
• Provides attachment to palatal muscles
• Composed of the expanded tendons of the tensor veli palatini and encloses the musculus uvulae
• Thin, firm fibrous plate attached to the posterior border of the hard palate
• Is an autonomous neural crest structure
• Supports the muscles of the soft palate and gives strength

Scaphoid Fossa and Spine of Sphenoid

• Scaphoid fossa is a small, oval, shallow depression in the pterygoid processes of the sphenoid, above the pterygoid fossa
• Spine of sphenoid is a triangular process that projects from the postpart of each great wing of the sphenoid, fitting into the angle between the squama and petrous portion of the temporal bone

Muscles of the Palate and Pharynx

• Palatoglossus muscle:
  • Innervation: Pharyngeal plexus
  • Origin: Palatine aponeurosis
  • Insertion: Side of the tongue
  • Action: Elevates the back of the tongue and draws the soft palate inferiorly, closing the oropharyngeal isthmus
• Palatopharyngeus muscle:
  • Innervation: Pharyngeal plexus
• Pharyngeal plexus:
  • Innervates all muscles of the soft palate except the tensor veli palatini
  • Formed by pharyngeal branches from the glossopharyngeal nerve and the vagus nerve

Tongue

• Connected to the mucosa of the floor of the oral cavity via the lingual frenulum
• Sublingual folds lateral to the lingual frenulum are formed by sublingual glands and ducts of submandibular glands, shaping the mucosa
• Sublingual caruncle is located at the confluence of the sublingual folds and the lingual frenulum
• Fimbriated folds flank the lingual frenulum
• Deep lingual veins are visible deep to the surface of the mucosa between the lingual frenulum and the fimbriated folds

Innervation of the Tongue

• Except for the palatoglossal muscle, the tongue is entirely innervated by the hypoglossal nerve
• Somatic afferents:
  • Areas anterior to the vallate papillae: Lingual nerve
  • Areas posterior to the vallate papillae: Glossopharyngeal nerve
• Taste buds are innervated by:
  • Areas anterior to the vallate papillae: Facial nerve (chorda tympani)
  • Areas posterior to the vallate papillae: Glossopharyngeal nerve

Lingual Papillae

• Projections of mucosa on the presulcal part of the dorsum
• Four types:
  • Fungiform
  • Filiform
  • Foliate
  • Vallate
• All carry taste buds except for the filiform papillae

Extrinsic Tongue Muscles

• Palatoglossus muscle:
  • Elevates the back of the tongue and draws the soft palate inferiorly, closing the oropharyngeal isthmus
  • Aids in the initiation of swallowing
• Innervation: Pharyngeal branch of the vagus nerve
• Motor fibers from the cranial accessory nerve

Intrinsic Tongue Muscles

• Only attach to other structures in the tongue
• Named by direction in which they travel
• Affect the shape and size of the tongue
• Have a role in facilitating speech, eating, and swallowing
• Motor innervation via the hypoglossal nerve
• Four paired intrinsic tongue muscles:
  • Longitudinal
  • Transverse
  • Vertical
  • Inferior longitudinal

Blood Supply of the Tongue

• Arteries of the tongue:
  • Lingual artery
  • Dorsal lingual artery
  • Root of the tongue is also supplied by:
    • Tonsillar and ascending palatine branches of the facial artery
    • Ascending pharyngeal artery
• Veins of the tongue:
  • Lingual vein
  • Union of dorsal lingual vein, deep lingual vein, and vena comitans of the hypoglossal nerve