Final answer:
Thermal expansion is the change in volume or length of dental materials due to hot food and cold drinks. Dental fillings can expand differently from tooth enamel, causing pain and potential cracks. Metal fillings are being replaced by composite fillings to minimize the effects of thermal expansion.
Step-by-step explanation:
The change in volume or length of dental materials due to hot food and cold drink is referred to as thermal expansion. Dental fillings, such as metal fillings, can expand differently from tooth enamel when exposed to temperature changes, leading to pain and potential cracks in the fillings. Composite fillings, made of porcelain, have smaller coefficients of expansion and are closer to the expansion coefficients of teeth, which is why they are replacing metal fillings.