Linear coefficient of thermal expansion of metal used for metal ceramic restoration range from:
**Core Concept**
The linear coefficient of thermal expansion (CTE) is a critical property of materials used in metal-ceramic restorations. It refers to the change in length of a material per unit length per degree change in temperature. Different materials have varying CTE values, which must be matched to ensure compatibility and prevent cracking or debonding of the ceramic layer.
**Why the Correct Answer is Right**
The correct answer, **C. 13.5-14.5 x 10^-6/°C**, corresponds to the typical CTE range of metals commonly used in metal-ceramic restorations, such as gold alloys (e.g., Au-Ag-Cu) and palladium alloys. These materials have a CTE close to that of ceramics, which allows for minimal thermal stress and prevents cracking or debonding of the ceramic layer. The CTE value of 13.5-14.5 x 10^-6/°C ensures that the metal substrate expands and contracts at a similar rate to the ceramic layer, maintaining the integrity of the restoration.
**Why Each Wrong Option is Incorrect**
**Option A:** A CTE range of 11.5-12.5 x 10^-6/°C is too low for most metal-ceramic restorations, as it may lead to excessive thermal stress and cracking of the ceramic layer.
**Option B:** A CTE range of 10.5-11.5 x 10^-6/°C is even lower than Option A and would be more prone to thermal stress and debonding.
**Option D:** A CTE range of 16.5-17.5 x 10^-6/°C is too high, which would cause the metal substrate to expand and contract more rapidly than the ceramic layer, leading to potential cracking or debonding.
**Clinical Pearl / High-Yield Fact**
When selecting materials for metal-ceramic restorations, it is essential to match the CTE of the metal substrate to that of the ceramic layer to prevent thermal stress and ensure the longevity of the restoration.
**✓ Correct Answer: C. 13.5-14.5 x 10^-6/°C**