Cavosurface angle for amalgam is:
**Core Concept**
The cavosurface angle for amalgam restorations is a critical factor in preventing marginal breakdown and ensuring the longevity of the restoration. A proper cavosurface angle helps to minimize stress concentrations at the margin, thereby reducing the risk of microleakage and secondary caries.
**Why the Correct Answer is Right**
The ideal cavosurface angle for amalgam restorations is 90 degrees. This angle provides a smooth, rounded transition from the cavity preparation to the tooth surface, reducing the likelihood of marginal defects and ensuring a more durable restoration. A 90-degree angle also allows for better adaptation of the amalgam material to the tooth structure, minimizing the risk of marginal leakage.
**Why Each Wrong Option is Incorrect**
**Option A:** A 45-degree cavosurface angle is not ideal for amalgam restorations, as it can lead to increased stress concentrations at the margin and a higher risk of marginal defects.
**Option B:** A 135-degree cavosurface angle is not a standard or recommended angle for amalgam restorations, and may lead to poor adaptation of the material to the tooth structure.
**Option C:** A 180-degree cavosurface angle is not feasible or desirable, as it would result in a sharp, angular transition that could compromise the integrity of the restoration.
**Clinical Pearl / High-Yield Fact**
The cavosurface angle is a critical factor in the success of amalgam restorations, and a 90-degree angle is generally considered the most ideal. When preparing a cavity for amalgam, it is essential to maintain a smooth, rounded transition from the cavity to the tooth surface to ensure a durable and long-lasting restoration.
**Correct Answer: C. 90 degrees**