The cavosurface angle formed in cast metal restorations is
**Core Concept**
The cavosurface angle in cast metal restorations refers to the angle formed between the surface of the restoration and the surrounding tooth structure. It is an important consideration in restorative dentistry as it affects the marginal seal and the longevity of the restoration.
**Why the Correct Answer is Right**
The correct answer is **90 degrees** because it allows for the best marginal seal and the least amount of stress concentration around the restoration. A 90-degree angle is ideal because it provides a smooth transition between the restoration and the tooth structure, reducing the risk of marginal leakage and fracture. This is achieved by using a beveled preparation, which helps to eliminate sharp angles and creates a more favorable environment for the restoration.
**Why Each Wrong Option is Incorrect**
**Option A:** A 45-degree angle is not ideal because it can lead to marginal leakage and stress concentration, which can compromise the longevity of the restoration.
**Option B:** A 120-degree angle is not recommended because it can create a weak point in the restoration, making it more susceptible to fracture.
**Option C:** A 135-degree angle is not suitable because it can lead to excessive stress concentration, which can cause the restoration to fail prematurely.
**Clinical Pearl / High-Yield Fact**
When preparing a tooth for a cast metal restoration, it is essential to maintain a 90-degree cavosurface angle to ensure a strong and durable restoration that will last for many years.
**Correct Answer:** D. 90 degrees