Figure 1. Dental arch models according to the severity of tooth irregularity expressed as arch length discrepancy (ALD). C1, Ideal arch dentition (ALD, 0 mm); C2, mildly crowded dentition (ALD, 3 mm); C3, moderately crowded dentition (ALD, 7 mm); C4, severely crowded dentition (ALD, 10 mm). Fiducials with a diameter of 1.5 mm were attached at 5 locations on the model base located 4 mm below the dentogingival junction. Two posterior fiducials were located below the mesiobuccal cusp of the first molars and 1 anterior ball marker was located below the contact point between the central incisors. Two canine fiducials were located directly below the cusp tips of the right and left canine teeth.
