**Question:** Areas which are not clearly visible in OPG is/are:

A. Root apices
B. Third molars
C. Cervical part of long bones
D. Mandibular canal

**Core Concept:** Orthopantomography (OPG) is a dental radiographic technique that provides a panoramic view of the teeth, jaw bones, and associated structures. It offers a wide field of view but has some limitations due to its inherent characteristics.

**Why the Correct Answer is Right:**
A. Root apices are not clearly visible in OPG due to their small size and proximity to the surrounding structures. In an OPG, the image quality is compromised as the film is exposed to a wider area, and the resolution is lower than that of other imaging modalities like CBCT or CT scans.

B. Third molars, also known as wisdom teeth, are not always visible in OPG because they may be impacted or positioned too far posteriorly to be captured by the OPG beam. In such cases, additional imaging, such as CBCT, is required.

C. The cervical part of long bones, particularly the phalanges and metacarpals, may not be clearly visible in OPG due to their small size and the limited field of view of the OPG machine.

D. The mandibular canal, which contains the inferior alveolar nerve and vessels, may not be clearly visible in OPG because of its narrow dimensions and proximity to the teeth and bone. OPG is not suitable for detailed evaluation of the mandibular canal and related structures.

**Why Each Wrong Option is Incorrect:**
A. Option A focuses on the limitations of OPG in imaging root apices, which is a key aspect of the question.
B. While third molars are not always visible in OPG, Option B incorrectly mentions the entire long bones, which are not relevant to the question.
C. Option C highlights the limitations of OPG in imaging small structures like the cervical part of long bones, which is relevant to the question.
D. Option D correctly emphasizes that OPG is not suitable for detailed evaluation of the mandibular canal and related structures, which is relevant to the question.

**Clinical Pearl:** OPG is a valuable tool for assessing the oral and maxillofacial region, but it has specific limitations. A thorough understanding of these limitations is crucial for accurate diagnosis and treatment planning. In cases where specific details are necessary, additional imaging modalities like CBCT or CT scans should be considered.