**Core Concept**
Ludwig's Angina is a severe infection of the submandibular space, characterized by rapid swelling and potential airway compromise. It often involves the spread of bacteria from the oral cavity to the deeper tissues.

**Why the Correct Answer is Right**
The commonest cause of Ludwig's Angina is a polymicrobial infection, typically involving anaerobic bacteria such as *Fusobacterium necrophorum*, *Peptostreptococcus* species, and *Bacteroides* species. These bacteria often originate from the oral cavity, where they can colonize the teeth, gums, and mucous membranes. The infection can then spread to the submandibular space, leading to the characteristic swelling and potential airway compromise.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because while dental infections are a common source of Ludwig's Angina, they are not the most frequent cause. The polymicrobial nature of the infection makes it difficult to pinpoint a single causative agent.
* **Option B:** This option is incorrect because while *Staphylococcus aureus* can cause skin and soft tissue infections, it is not typically associated with Ludwig's Angina.
* **Option C:** This option is incorrect because while *Streptococcus pyogenes* can cause severe infections, it is not the most common cause of Ludwig's Angina.

**Clinical Pearl / High-Yield Fact**
Ludwig's Angina is a medical emergency that requires prompt recognition and treatment. The "Dreaded Four" - difficulty swallowing, difficulty speaking, drooling, and drooping eyelids - can indicate impending airway compromise, necessitating immediate intubation and surgical intervention.

**Correct Answer: D. Polymicrobial infection**