These teeth must be kept symmetrical in reasonable limits.Minor asymmetries are allowed,because bilateral asymmetry between maxillary central incisors was found not to exceed 0.3 to 0.4 mm in mesiodistal width.The shape and outlines of the central incisors studied were strictly same in only 14% of the subjects,were similar in 23%(one or two dimensions not exceeding 0.2 mm),and were different(differences in all three dimensions,one of which was more than 0.2 mm) in 63% of subjects.

• Dental midline
• Maxillary canines