**Core Concept:** Orbital cellulitis is a severe infection of the tissues surrounding the eye and can lead to potentially life-threatening complications. It typically presents as a complication of sinus infections.

**Why the Correct Answer is Right:** Orbital cellulitis is most commonly associated with maxillary sinusitis, which is the most commonly affected sinus due to its proximity to the orbit. The maxillary sinus drainage pathway, known as the inferior meatus, connects to the inferior nasal concha and the pterygopalatine fossa. When the maxillary sinus becomes infected, bacteria can spread through this pathway and invade the orbit, leading to orbital cellulitis.

**Why Each Wrong Option is Incorrect:**

A. Frontal sinusitis: Although orbital cellulitis can occur after frontal sinusitis, it is less common due to the frontal sinus's greater distance from the orbit.
B. Ethmoidal sinusitis: Orbital cellulitis from ethmoidal sinusitis is also less common compared to maxillary sinusitis due to its indirect connection to the orbit via the sphenopalatine ganglion.
C. Sphenoidal sinusitis: Sphenoidal sinusitis is the least common cause of orbital cellulitis due to its deep location and indirect connection to the orbit via the cavernous sinus.
D. Spread from adjacent teeth: While dental infections can lead to orbital cellulitis, the primary cause is usually an underlying sinus infection (maxillary sinus in this case).

**Clinical Pearl:** In cases of orbital cellulitis, it is essential to consider the underlying source of infection. A thorough history and physical examination, including dental examination, are crucial to identify potential sinus infections and initiate appropriate treatment. Prompt intervention is crucial to prevent complications and improve patient outcomes.