**Core Concept**
In endodontics, access cavity preparation is a critical step in root canal treatment, requiring precise removal of tooth structure to facilitate effective cleaning and shaping of the root canal system. The maxillary and mandibular incisors have unique anatomical features that demand careful consideration during access cavity preparation.

**Why the Correct Answer is Right**
The most common error during access cavity preparation is **over-preparation of the tooth structure**, particularly in the maxillary and mandibular incisors. This can lead to unnecessary removal of sound tooth structure, compromising the tooth's integrity and potentially causing post-operative sensitivity or fractures. In these anterior teeth, the incisal edge and lingual/palatal surfaces are particularly susceptible to over-preparation.

**Why Each Wrong Option is Incorrect**
* **Option A:** While inadequate access cavity preparation can hinder root canal treatment, it is not the most common error seen in maxillary and mandibular incisors.
* **Option B:** Insufficient removal of tooth structure can be a problem in other areas of the mouth, but it is not the primary concern in anterior incisors.
* **Option C:** This option is incomplete and does not provide a valid distractor.

**Clinical Pearl / High-Yield Fact**
To avoid over-preparation, use a **"step-back" approach** when accessing the root canal, removing tooth structure in increments and verifying the canal's position before proceeding.

**Correct Answer:** C.