**Core Concept**
The presence of a missing tooth in a child, especially when associated with a history of trauma and endodontic treatment, necessitates a thorough evaluation to identify the underlying cause. Supernumerary teeth, which are extra teeth that develop in addition to the normal complement of teeth, can sometimes hinder the eruption of adjacent teeth, leading to missing teeth. Identifying supernumerary teeth is crucial to plan the appropriate treatment.

**Why the Correct Answer is Right**
In this scenario, the child has a missing tooth #11, which erupted at an unusually late age. The history of trauma and endodontic treatment for tooth #21 suggests that there may be an underlying anatomical issue. A supernumerary tooth is a possible cause of the delayed eruption of tooth #11. Taking a radiograph is essential to rule out the presence of a supernumerary tooth, which can be hidden beneath the gum or between the roots of adjacent teeth. This evaluation will help determine the correct treatment plan, whether it involves orthodontic treatment, space creation, or prosthetic rehabilitation.

**Why Each Wrong Option is Incorrect**

**Option B:** Planning a removable partial denture (RPD) without evaluating the underlying cause of the missing tooth may not be the most appropriate treatment. An RPD may not address the underlying issue and may not provide a stable or aesthetically pleasing result.

**Option C:** Advising a fixed partial denture (FPD) without evaluating the underlying cause of the missing tooth may not be feasible. An FPD requires the presence of healthy adjacent teeth to support the prosthesis, and the presence of a supernumerary tooth may compromise the stability of the FPD.

**Option D:** Advising orthodontic treatment, space creation, and an FPD without evaluating the underlying cause of the missing tooth may not be the most efficient treatment plan. Orthodontic treatment can be lengthy and may not address the underlying issue if a supernumerary tooth is present.

**Clinical Pearl / High-Yield Fact**
When evaluating a child with missing teeth, it's essential to consider the possibility of supernumerary teeth, which can hinder the eruption of adjacent teeth. Taking a radiograph is a crucial step in identifying supernumerary teeth and planning the appropriate treatment.

**✓ Correct Answer: A. Take radiograph and rule out a supernumerary tooth**