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Table 1 Inclusion criteria

From: Three-dimensional assessment of teeth first-, second- and third-order position in Caucasian and African subjects with ideal occlusion

Adult age (not less than 18 years) No previous orthodontic treatment
Regular arch form with little or no crowding Complete dentition to second molars
No bridges or implants Centred midlines
No gingival recession No joint or muscle pathologies
No ectopic teeth No supernumerary teeth or tooth agenesis
At least four of Andrews’ six keys with bilateral molar and canine class I occlusion always present Presence of minimal diastems and/or small premolar rotation or little irregularity (Little’s index less than 3) at incisors in some individuals
Overbite and overjet within normal limits 2 mm ± 1 mm No anterior or posterior cross-bite
No markedly visible intra-oral or extra-oral symmetry