**Core Concept**
Polycarboxylate cement is a type of dental cement that combines the properties of chemically and physically setting materials. It is composed of a mixture of polycarboxylate resin, water, and powder, which reacts to form a hard, durable bond between tooth structure and restorative materials.

**Why the Correct Answer is Right**
Polycarboxylate cement is used for luting or cementing metal or ceramic restorations, such as crowns, bridges, and orthodontic brackets, onto tooth structures. The cement forms a strong bond between the restoration and tooth due to its ability to penetrate and adhere to the tooth structure. This is achieved through the reaction of the polycarboxylate resin with the calcium ions present in the tooth structure, resulting in a strong and durable bond.

**Why Each Wrong Option is Incorrect**
**Option A:** Polycarboxylate cement is not used for orthognathic surgery, as it is not suitable for load-bearing applications.
**Option B:** While polycarboxylate cement can be used for temporary restorations, it is not the primary choice for this application.
**Option C:** Polycarboxylate cement is not typically used for endodontic procedures, such as obturation or apicoectomy.

**Clinical Pearl / High-Yield Fact**
It is essential to note that polycarboxylate cement has a relatively low pH, which can lead to acid etching of the tooth structure. This can result in a weaker bond and increased risk of restoration failure.

**Correct Answer: C. For luting or cementing metal or ceramic restorations onto tooth structures.**