Final answer:
The most appropriate treatment for a pregnant patient in her first trimester requiring the replacement of a large MOD amalgam restoration is to delay treatment until after the baby is born.
Step-by-step explanation:
The most appropriate treatment for a patient in her first trimester of pregnancy requiring the replacement of a large MOD amalgam restoration with extensive recurrent caries and thermal sensitivity is to delay treatment until after the baby is born. This is because during the first trimester, the developing baby is most susceptible to the potential harms of dental procedures, such as the release of mercury from amalgam fillings. It is important to prioritize the safety of the mother and baby.