The black gap in the middle of teeth may be caused by the following two reasons: the first one, tooth decay. Because it is hard to clean off the food and soft scale in the tooth gap when brushing, so there will be soft scale accumulated for a long time to corrode the teeth, and it is very easy to have caries in the tooth gap, at this time, the patient can find the black gap in the tooth gap through self-examination, and need to go to the hospital for filling treatment in time to remove the black part and fill it with resin again. Secondly, there is an accumulation of tooth stain or tartar in the gap, because if this position is not cleaned, it is not good to develop caries and then there will be calculus, also need to carry out full mouth scaling or sandblasting to remove the tooth stain in the gap.