Put ice on the nearby cheek for 15 minutes, 3-4 times a day. Avoid biting on that area of the teeth. Many books have been written on this subject in recent years. When you go to the dentist, he drills out the decayed part, and then fills the cavity with something hard which, hopefully, will last awhile. The most common substance used for this filling is amalgam.
Mercury tends to evaporate slowly over a period of time.
This influx of mercury, swallowed with your food day after day, is not the best for your health. They are more expensive, but less harmful. They do not gradually melt away, as does mercury in amalgam. This deadly poison should be avoided at all costs. If your dentist offers to give you fluoride treatments, you would do well to politely decline the opportunity.