Nasal Cavity and Paranasal Sinuses: The Maxillary Sinus and Dental Relations

Overview

The nasal cavity and the four paired paranasal sinuses form the upper respiratory framework of the face. For dentistry the maxillary sinus is paramount: its floor lies directly above the roots of the upper premolars and molars, so it is routinely involved in extractions, implants, and sinus lift procedures.

Boundaries of the Nasal Cavity

The cavity is divided by the nasal septum into two halves, each with four walls:

• Roof: nasal bones, cribriform plate of the ethmoid (olfactory nerve fibres), and body of the sphenoid.
• Floor: palatine process of the maxilla and horizontal plate of the palatine bone (the hard palate) — the roof of the mouth.
• Medial wall: the nasal septum (septal cartilage, perpendicular plate of ethmoid, vomer).
• Lateral wall: the most complex, bearing the three conchae (superior, middle, inferior) that overhang the corresponding meatuses.

Drainage Pathways of the Lateral Wall

• Sphenoethmoidal recess (above superior concha): sphenoid sinus.
• Superior meatus: posterior ethmoidal air cells.
• Middle meatus: frontal sinus (via frontonasal duct), anterior/middle ethmoidal cells, and the maxillary sinus (via the semilunar hiatus).
• Inferior meatus: the nasolacrimal duct — the reason a runny nose accompanies crying.

The Maxillary Sinus (Antrum of Highmore)

The largest paranasal sinus, a pyramid within the body of the maxilla.

• Apex: extends into the zygomatic process.
• Base: the lateral wall of the nasal cavity.
• Floor: closely related to the roots of the maxillary premolars and molars — the roots may project into the sinus, separated only by a thin plate of bone or, at times, only mucosa.
• Ostium: opens high on the medial wall into the middle meatus, so drainage is against gravity, predisposing to stasis and infection.

Innervation and Blood Supply

• Sensory supply is from branches of the maxillary nerve (CN V2): infraorbital, and the anterior, middle, and posterior superior alveolar nerves — the same nerves that supply the upper teeth, which is why sinusitis can mimic toothache.
• Arterial supply is chiefly from the maxillary artery (infraorbital, greater palatine, and posterior superior alveolar branches) and the sphenopalatine artery, a common source of severe epistaxis.

Clinical Relevance

• Oroantral communication/fistula: extraction of an upper molar whose roots project into the sinus can open a passage between mouth and antrum; small ones close spontaneously, larger ones need surgical closure.
• Displaced root or implant into the sinus: a recognised complication of upper posterior extraction and implant placement.
• Maxillary sinusitis of dental origin: periapical infection of an upper molar can perforate the thin floor and seed the sinus.
• Sinus lift (augmentation): elevating the sinus mucosa (Schneiderian membrane) to graft bone before implant placement relies on precise knowledge of the sinus floor.
• Referred pain: because the sinus and the upper teeth share CN V2 innervation, sinusitis frequently presents as poorly localised pain in several upper teeth simultaneously.

Study Points

• Match each meatus to the sinuses and duct that drain into it.
• Explain why the maxillary sinus is prone to poor drainage and infection.
• Describe the anatomical basis of oroantral communication and dental sinusitis.