I had a root canal and cap on my #30 tooth about 8 months ago. The dentist intentionally left a slight gap between the bottom of the cap and gum line. He said going to the gum line could create problems. Since I have had the cap sometimes food is sticking between #30 and 31 on the inside (tongue side) of the teeth near the bottom of the teeth at the gum line. I started going to a new dentist and told him of the problem. He could just barely see something with his magnifier and decided to take a picture with a high power camera and he saw what he believes to be exposed build up material from when the cap was put on. I ask for a copy of the picture but never received it. But what I saw in the picture was a dark substance in the gap between the bottom of the new cap and gum line. It looks like something was there and then someone scrapped/removed it but a little residual is left. It is on the side of the tooth and not really in the back corner between #30 and 31 where the food sometimes sticks. He suggested I go back to the old dentist and have it fixed or it will eventually lead to decay. What is your opinion?