**Core Concept**
Addition poly silicone impression materials undergo a minimal dimensional change when disinfected due to their unique chemical structure. This characteristic is essential for maintaining the accuracy of dental impressions, which is critical for the fabrication of accurate dental restorations.

**Why the Correct Answer is Right**
Addition poly silicone impression materials exhibit a low dimensional change upon disinfection because they are not affected by the disinfecting agents, such as glutaraldehyde or hydrogen peroxide. This is due to the absence of a cross-linking mechanism that is susceptible to degradation by these agents. As a result, the material's network structure remains intact, minimizing any dimensional changes. In contrast, other impression materials, such as polysulphide and polyether, undergo significant dimensional changes when exposed to disinfectants.

**Why Each Wrong Option is Incorrect**
**Option B:** Agar-agar impression materials undergo significant dimensional changes when exposed to heat, which is often used in the disinfection process. This makes them unsuitable for precise dental impressions.
**Option C:** Polysulphide impression materials are susceptible to dimensional changes when exposed to disinfectants, such as hydrogen peroxide, which can break the cross-links between the polymer chains.
**Option D:** Polyether impression materials also undergo significant dimensional changes when exposed to disinfectants, such as glutaraldehyde, which can degrade the material's network structure.

**Clinical Pearl / High-Yield Fact**
When selecting an impression material for a dental restoration, it is essential to consider the material's dimensional stability, especially when disinfection is required. Addition poly silicone impression materials are an excellent choice due to their minimal dimensional change upon disinfection, ensuring accurate and reliable impressions.

**✓ Correct Answer: A. Addition poly silicone**