**Core Concept**
Root planning is a crucial procedure in periodontal therapy aimed at removing the damaged or infected portion of the periodontal ligament and the cementum covering the root of a tooth, which has become diseased due to periodontitis. This procedure helps in eliminating the primary site of bacterial accumulation and facilitating the regeneration of the lost periodontal ligament and bone.

**Why the Correct Answer is Right**
The main aim of root planning is to remove the **subgingival calculus and the infected cementum**, which have become a source of bacterial accumulation and inflammation. This process helps in restoring the health of the periodontal ligament and the surrounding bone by allowing for the growth of new tissue. The removal of infected cementum also helps in reducing the bacterial load and preventing further destruction of the periodontal ligament and bone.

**Why Each Wrong Option is Incorrect**
* **Option A:** The removal of the tooth itself is not the aim of root planning, but rather a last resort in cases of severe periodontal disease.
* **Option B:** The removal of the overlying epithelial attachment is not the primary goal of root planning, although it may be a secondary benefit.
* **Option C:** The removal of the periodontal ligament is not the aim of root planning, as the goal is to regenerate the lost tissue rather than remove it.

**Clinical Pearl / High-Yield Fact**
Root planning should be performed with an ultrasonic scaler or a curette, taking care to avoid damaging the underlying periodontal ligament and bone. The procedure should be gentle and atraumatic to prevent further damage and promote healing.

**Correct Answer: C. The infected cementum.**