**Core Concept**
Ludwig's angina is a severe infection of the submandibular space, characterized by rapid progression and potential airway compromise. It involves the spread of infection to the surrounding fascial spaces, leading to severe swelling and potential life-threatening complications.

**Why the Correct Answer is Right**
Ludwig's angina primarily involves the submandibular space, which is a fascial space located beneath the mandible. The infection spreads to the sublingual space, the submental space, and the digastric space, leading to significant swelling and potential airway compromise. The involvement of these spaces is due to the lymphatic and vascular connections between them.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to Ludwig's angina, which does not typically involve the parotid space.

**Option B:** The pretracheal space is not primarily involved in Ludwig's angina, although it can be affected in severe cases.

**Option C:** The pterygoid space is not a primary site of involvement in Ludwig's angina.

**Option D:** The buccal space can be involved in dental infections, but it is not a primary site of involvement in Ludwig's angina.

**Clinical Pearl / High-Yield Fact**
In Ludwig's angina, early recognition and management are crucial to prevent airway compromise. A high index of suspicion is required, especially in patients with a history of dental infections or trauma.

**Correct Answer: D. The submandibular, sublingual, submental, and digastric spaces.**