**Core Concept**
The patient's presentation is consistent with a mandibular odontogenic keratocyst (OKC), a type of jaw cyst that can cause bony expansion and paresthesia of the inferior dental nerve (IDN). OKCs are known for their aggressive behavior and potential for recurrence.

**Why the Correct Answer is Right**
The next investigation of choice would be a **CT scan of the mandible**, which would provide detailed information about the extent of the lesion, its relationship to surrounding structures, and any signs of cortical bone expansion or perforation. This is particularly useful in OKCs, which can have a thin, incomplete corticated border and a characteristic "honeycomb" or "soap bubble" appearance on CT scans.

**Why Each Wrong Option is Incorrect**
**Option A:** An MRI of the mandible might be useful in assessing the relationship of the lesion to the IDN, but it is not the most appropriate next step in this case, given the need for detailed bony anatomy and cortical assessment.
**Option B:** A panoramic radiograph (OPG) has already been taken, which shows the multi-locular radiolucency without root resorption, but it may not provide sufficient detail for further assessment.
**Option C:** A biopsy of the lesion would be useful in confirming the diagnosis, but it should not be the next step without further imaging to assess the extent of the lesion.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that OKCs are known for their high recurrence rate, often due to incomplete excision, so a thorough preoperative assessment, including imaging, is crucial to ensure complete removal and minimize recurrence risk.

**Correct Answer: C. Biopsy**