This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
The process in which a material melts to form a crystalline phase and a liquid phase known as: 
Select and explain. 
A. Incongruent melting, B. Congruent melting, C. Sintering, D. Ceramming
A: Incongruent melting
Answer: A: Incongruent melting 
Explanation: When feldspar is heated at temperatures between 1150°C and 1530°C, it undergoes incongruent melting to form crystals of leucite in a liquid glass. Incongruent melting is the process by which one material melts to form a liquid plus a different crystalline material. 
This tendency of feldspar to form leucite during incongruent melting controls thermal expansion during the use of porcelains for metal bonding.
Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, 12th ed page no 430