Tiz, I am from a family of teeth-grinders. I have been told that it is hereditary (from a misaligned jaw). However, I am not totally convinced, because I stopped grinding a few years ago for no apparent reason. I have found that during times of stress, I grind aggressively. Not sure if that's true for all grinders, but could explain why your son's grinding slowed down over holiday.
Grinding erodes the tops of your teeth, making them oversensitive to temperature (and sometimes overly sweet tastes, etc.) A toothpaste for sensitive teeth usually helps people who have mild problems with this.
Dentists typically like to stop the grinding by creating a custom night guard for the grinder. The guard properly aligns the jaw and protects the teeth. I tried this solution and bit through two guards. They may have better materials now (my experience was several years ago).
One of my daughters is also a grinder, but it is very sporadic, so we haven't gone the night guard route yet.
Good luck with finding a solution for your son!
