**Core Concept:** Distal extension removable partial dentures (RPDs) are dental prostheses used to replace missing teeth on the posterior mandible. Abutments are teeth or dental implants that support the RPD and prevent it from dislodging.

**Why the Correct Answer is Right:** To prevent the dislodgement of an abutment in a distal extension RPD, it is essential to consider factors that contribute to stability and retention. A well-designed RPD should have a sufficient base, adequate retention mechanisms, and appropriate support from the abutments.

**Why Each Wrong Option is Incorrect:**

A. **Incorrect**: Having a "short abutment" may lead to inadequate retention and stability, increasing the risk of dislodgement.

B. **Incorrect**: A "non-carious abutment" refers to a tooth without carious lesions, which may compromise the stability of the RPD. In this context, a carious abutment would be preferable as it offers better retention.

C. **Incorrect**: A "too-long abutment" might interfere with the patient's oral function and aesthetics, making the RPD uncomfortable and unsightly. A balanced length of abutment is crucial for optimal function and patient satisfaction.

D. **Incorrect**: A "spaced abutment" refers to an abutment with a significant gap between teeth. This spacing can lead to poor retention and stability, increasing the risk of abutment dislodgement.

**Clinical Pearl:** The correct abutment selection in a distal extension RPD includes carious abutments with an appropriate length and width, ensuring adequate retention, stability, and patient comfort. The abutment should not interfere with oral function and aesthetics. Adequate space between abutments prevents dislodgement and enhances the overall success of the distal extension RPD.

**Correct Answer:** D. A "carious abutment with appropriate length and width" contributes to optimal retention, stability, and patient comfort in a distal extension RPD, thus preventing abutment dislodgement and ensuring the prosthesis' success.