Which of the following is true of an occlusal rest for a removable partial denture? 1. One-third facial lingual width of the tooth 2. 1.5 mm deep for base metal 3. 2.0 mm labiolingual width of the tooth 4. Floor inclines apically toward the center of the tooth
**Core Concept**
An occlusal rest is a type of support in removable partial dentures that allows for distribution of masticatory forces, thereby reducing the stress on the abutment teeth. The design and dimensions of occlusal rests are crucial to ensure proper function and prevent damage to the surrounding tooth structure.
**Why the Correct Answer is Right**
The correct answer is 3.0 mm labiolingual width of the tooth, which is a standard recommendation for the design of occlusal rests. This width allows for adequate support and distribution of forces while minimizing the risk of tooth damage. The labiolingual width of the occlusal rest should be approximately 2/3 to 3/4 of the labiolingual width of the tooth. This ensures that the rest does not compromise the tooth's integrity and allows for proper occlusal contact.
**Why Each Wrong Option is Incorrect**
**Option A:** One-third facial-lingual width of the tooth is too narrow and may not provide sufficient support for the removable partial denture.
**Option B:** 1.5 mm deep for base metal is not a standard recommendation for occlusal rest depth, which can vary depending on the material and design of the rest.
**Option D:** Floor inclines apically toward the center of the tooth is incorrect, as the occlusal rest should be designed to distribute forces evenly and not create an uneven surface that may lead to tooth damage.
**Clinical Pearl / High-Yield Fact**
When designing occlusal rests, it is essential to consider the labiolingual width of the tooth and ensure that the rest is not too narrow or too deep, which can compromise the tooth's integrity and lead to premature wear or damage.
**Correct Answer:** C. 2.0 mm labiolingual width of the tooth.