There are some minor differences between the deciduous maxillary central incisor and that of the permanent maxillary central incisor. The deciduous tooth appears in the mouth at 8–12 months of age and shed at 6–7 years, and is replaced by the permanent tooth around 7–8 years of age. The permanent tooth is larger and is longer than it is wide. The maxillary central incisors contact each other at the midline of the face. The mandibular central incisors are the only other type of teeth to do so. The position of these teeth may determine the existence of an open bite or diastema. As with all teeth, variations of size, shape, and color exist among people. Systemic disease, such as syphilis, may affect the appearance of teeth.