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Anatomy and Physiology of the Oral Cavity

Overview

Boundaries of the Oral Cavity

  • Anterior: vermilion border of the lips

  • Posterior: junction of hard and soft palate (superiorly), the line of the circumvallate papillae or linea terminalis (inferiorly), and the retromolar trigones laterally

Subunits

  • Lips, buccal mucosa (mucosal lining of the cheek), upper (maxillary) and lower (mandibular) alveolar ridges, retromolar trigone, hard palate, floor of mouth, and oral tongue (anterior two-third of tongue, anterior to circumvallate papillae)

Function

  • Intake and mastication of food and beverages, oral phase of deglutition, communication (speech), protection from noxious substances

Anatomy of the Lip

Surface Anatomy

  • Vermilion: composed of nonkeratinized squamous epithelium underlying capillaries give its characteristic color, no hair follicles, or sebaceous glands

  • Vermilion border: transition point from external skin to internal mucous membrane

  • Philtrum ridges and Cupid’s bow (on upper lip)

  • Oral commissure: lateral junction between upper and lower lip

Perioral Musculature

  • Innervated by branches of facial nerve (CN VII)

  • Modiolus: tendinous thickening at each oral commissure that serves as an attachment site for several upper and lower lip muscles

  • Muscles that insert on modiolus: orbicularis oris (forms a sphincter around the mouth, purses the lips, presses lips against teeth), buccinator (presses the lips and cheek against the teeth), levator anguli oris (superiorly elevates the commissure), depressor anguli oris (depresses and laterally moves commissure), zygomaticus major (elevates and laterally moves commissure), risorius (draws the commissure laterally)

  • Muscles that insert on upper lip: levator labii superioris (elevates upper lip), levator superioris alaeque nasi (dilates nostril and elevates upper lip), zygomaticus minor (elevates and pulls the commissure laterally)

  • Muscles that insert on lower lip: depressor labii inferioris (depresses lower lip and pulls it slightly laterally), mentalis (elevates lower lip), platysma (lip depressor)

Sensory Innervation

  • Upper lip: infraorbital nerve (CN V2)

  • Lower lip: mental nerve (CN V3)

Vascular Supply

  • Inferior and superior labial arteries from facial artery

Lymphatic Drainage

  • Primarily to submandibular lymph nodes

  • Midline lower lip also to submental lymph nodes

  • Upper lip also to preauricular, infraparotid, and perifacial lymph nodes

Teeth

Layers of the Teeth (Four Major Components)

  • Enamel: hardest, white outer part, mostly made of calcium phosphate, formed by ameloblasts (amelogenesis)

  • Dentin: layer underlying the enamel, formed by odontoblasts (dentinogenesis)

    1. Unlike enamel, dentin continues to form throughout life and dentin is sensitive.

  • Pulp: inner structure with blood vessels and nerves running through it

  • Cementum: surface layer of the tooth root composed of connective tissue that binds tooth roots to gingiva and alveolar bone, formed by cementoblasts

Periodontal Ligament

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