**Core Concept**
When considering fixed prostheses, particularly in dentistry, the material properties of the cement used can significantly impact the overall success of the restoration. The compressive strength, tensile strength, and shear strength of the cement are critical factors in determining its suitability for a particular application.

**Why the Correct Answer is Right**
The correct answer highlights the importance of understanding the material properties of dental cements. In fixed prostheses, the cement is often the weakest link in the restoration. This is because cements typically have lower strength values compared to other materials used in dentistry, such as metals or ceramics. The tensile strength of a material is its ability to withstand stretching forces without breaking, and the cement's low tensile strength makes it prone to cracking or failure under stress. This is particularly relevant in fixed prostheses, where the cement is subjected to various forces, including compressive, tensile, and shear forces.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the maximum compressive strength of a cement does not necessarily make it more difficult to remove the prosthesis. In fact, cements with high compressive strength can be more challenging to remove due to their increased bonding strength.

**Option B:** This option is incorrect because low shear strength is not directly related to the difficulty of removing a prosthesis. Shear strength is the ability of a material to withstand forces that cause it to deform by sliding along a plane parallel to the direction of the force.

**Option D:** This option is incorrect because increasing the thickness of cement can actually increase the likelihood of flaws and defects, rather than reducing them. Thicker cement layers can lead to a higher risk of porosity, shrinkage, and other defects that can compromise the integrity of the restoration.

**Clinical Pearl / High-Yield Fact**
When selecting a dental cement for a fixed prosthesis, it is essential to consider the material properties of the cement, including its compressive strength, tensile strength, and shear strength. The cement should be chosen based on the specific requirements of the restoration, taking into account the forces it will be subjected to and the desired level of bonding strength.

**✓ Correct Answer: C. Cement is weakest phase in fixed prosthesis**