I have a pin in gum line holding a filling, can that break off and if so where does it go in the gum?

Hi Rose Ann.
Pins in teeth are basically used to help hold in a filling when a part of the tooth is missing. The pin isn't visible since it's under the filling. Pins were used a lot more in the past when more silver fillings were done. If you can see the pin (not to be confused with a post which is totally different) then part of the filling or tooth has broken off. The pin is in the tooth, not the gum, though it may look like it's coming out of the gum if the tooth is broken off to the gum line. There are several options once the tooth or filling held by the pin breaks. Usually a full crown is needed to fix the tooth. Sometimes the rest of the pin is removed or other times the remaining part is left as is and used to help secure a buildup in preparation for a crown.  There's no need to worry about the pin hurting your gum. Your dentist will be able to decide what to do about the pin and the best way to restore your tooth. Good luck.