**Core Concept**
The release of mercury vapour from amalgam is a concern due to its toxic effects on the nervous system and kidneys. Amalgam is a mixture of mercury with other metals like silver, tin, and copper, used in dental restorations.

**Why the Correct Answer is Right**
The release of mercury vapour occurs due to the oxidation of mercury within the amalgam. When amalgam comes into contact with saliva or water, the mercury reacts with oxygen to form mercury oxide, which then decomposes to release mercury vapour. This process is accelerated by factors like temperature, humidity, and the presence of certain metals. The mercury vapour can then be inhaled, causing systemic toxicity.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specifically address the mechanism of mercury release from amalgam. While temperature can influence the rate of release, it is not the primary cause.
**Option B:** This option is incorrect because it is too vague and does not provide a clear explanation for mercury release. While amalgam is indeed a mixture of metals, the release of mercury vapour is not simply a result of its composition.
**Option C:** This option is incorrect because it is incomplete and does not provide a clear mechanism for mercury release. While saliva and water can interact with amalgam, they are not the sole cause of mercury vapour release.

**Clinical Pearl / High-Yield Fact**
A key factor in minimizing mercury vapour release from amalgam is the use of well-premeasured capsules and proper handling techniques. This can help reduce the risk of mercury exposure and toxicity.

**Correct Answer: C. Contact with saliva or water.