According to ADA specification No or number 1, the minimum compressive strength for silver amalgam filling after one hour should be
**Core Concept**
The American Dental Association (ADA) specification No. 1 outlines the requirements for dental amalgam. One of the key properties assessed is the compressive strength, which is a measure of a material's resistance to deformation under compressive forces. In the context of dental amalgam, compressive strength is crucial for withstanding the masticatory forces in the oral cavity.
**Why the Correct Answer is Right**
The correct answer specifies the minimum compressive strength required for a silver amalgam filling after one hour. This is based on the ADA specification No. 1, which stipulates that the amalgam should exhibit a minimum compressive strength of 27 MPa after one hour. This ensures that the amalgam can withstand the initial forces applied during mastication. The compressive strength is influenced by the microstructure of the amalgam, which is formed by the reaction between the silver, mercury, and other alloying elements.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not meet the minimum compressive strength requirement specified by the ADA.
**Option B:** This option is incorrect as it is lower than the minimum compressive strength required by the ADA.
**Option C:** This option is incorrect because it exceeds the minimum compressive strength required by the ADA, but it is not the correct answer.
**Clinical Pearl / High-Yield Fact**
It is essential to note that the compressive strength of dental amalgam can be influenced by various factors, including the alloy composition, manipulation technique, and time allowed for setting. A minimum compressive strength of 27 MPa after one hour is a critical requirement for ensuring the longevity and success of the amalgam restoration.
**Correct Answer: D. 27 MPa**