If the permanent tooth and deciduous (baby) tooth are in the same site at the same time, then the deciduous tooth is considered retained and should be removed ASAP. The reasons for this are because they affect the position of the erupting permanent tooth (causing overcrowding and often problems with occlusion) and also because it leads to food, debris, plaque and tartar buildup between the teeth (as seen in the photos below), which will lead to gingivitis, pain and early onset periodontal disease.