An 18yr old male patient reported with chief complaint of pain and swelling in the right lower jaw and mild difficulty in opening mouth since one week. A general examination revealed fever and increased pulse rate. Intra-oral examination showed signs of inflammation around the gingiva of partially impacted third molar tender on palpation with opposing tooth impinging. The most likely diagnosis is

**Core Concept**
The patient presents with signs and symptoms suggestive of an acute inflammatory process involving the third molar tooth, which is partially impacted and tender to palpation. This clinical scenario is consistent with a diagnosis of **pericoronitis**, a common condition affecting the gingiva surrounding a partially erupted or impacted third molar tooth.

**Why the Correct Answer is Right**
Pericoronitis is characterized by inflammation of the gingiva surrounding the third molar tooth, often caused by bacterial accumulation and infection. The presence of fever and increased pulse rate suggests a systemic inflammatory response, which is consistent with an acute infection. The opposing tooth impinging on the partially impacted third molar tooth may have contributed to the development of pericoronitis. The clinical signs and symptoms, including pain and swelling in the right lower jaw, mild difficulty in opening the mouth, and tenderness of the gingiva, are all consistent with a diagnosis of pericoronitis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the clinical presentation does not suggest a diagnosis of **periodontitis**, which is a chronic inflammatory condition affecting the supporting structures of the teeth, including the periodontal ligament and alveolar bone.

**Option B:** This option is incorrect because the patient's symptoms do not suggest a diagnosis of **abscessed tooth**, which is typically characterized by a localized collection of pus in the pulp chamber or periodontal tissues, often associated with severe pain and swelling.

**Option C:** This option is incorrect because the patient's symptoms do not suggest a diagnosis of **osteomyelitis**, which is a bone infection that can occur as a result of a dental infection, but typically presents with more severe symptoms, including high fever, chills, and swelling of the entire face.

**Clinical Pearl / High-Yield Fact**
A key clinical pearl is that partially impacted third molar teeth are a common cause of pericoronitis, and that prompt removal of the offending tooth or correction of the impaction can prevent recurrence of the condition.

**Correct Answer: C**

✓ Correct Answer: D. Pericoronitis