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What is Increased collum angle is seen in and explain in detail?
Collum angle
The angulation of the root to the crown, particularly of the single rooted anterior teeth is  known as Collum angle. It is the angle formed by the intersection of the long axis of the crown and root and it is measured using the lateral cephalogram.
Dental features of class II div 2 include a class II molar and canine relationship, deep traumatic bite, retroclined upper four incisors or retroclined central incisors with a labial inclination of the laterals and supra-erupted, upright lower incisors. The tooth size may be  small, and upper incisors may have increased collum angle between the crown and the root.
The maxillary incisors in class II division 2 malocclusions are about 12° more vertical than those in normal occlusion. The mandibular incisors are upright in a class II division 2 malocclusion, but to a lesser extent than the upper incisors.