Edge and Centroid Relationship

What is Edge and Centroid Relationship:

Incisor edge centroid relationship

courtesy: Kumar – textbook of Orthodontics

It is a measure as the distance between the perpendicular projections of lower incisor edge and centroid of upper incisor root on maxillary plane.

  1. What is Edge in Edge Centroid relationship: The tip of the crown most prominent lower incisor
  2. What is Cnetroid in Edge Centroid relationship: The Mid-Point on root axis of most prominent upper incisor

For stable occlusion the lower incisor edge should 2mm in front of  the centroid of the upper incisor. But when the Lower incisor Centroid is behind the upper incisor centroid it should be corrected to get Stable Occlusion.

Classification of Incisor Edge – Centroid Relationship in Different Mal occlusions:

Class I:

  • Normal Inter Incisal Angle
  • Lower incisal angle lies ahead of upeer incisor Centroid (normal overbite of 0-2mm)

Class II Div 1: 

  • Interincisal Angle is decreased because of protrusion of maxillary incisors
  • Lower incisor edge lies in line with or behind the upper incisor centroid

Class II Div 2:

  • Interincisal Angle is increased
  • Lower incisor angle lies behind the upper incisor Centroid

 Treatment of Abnormal Incisor Edge-Centroid Relationship:

Treatment or Correction of Edge-Centroid Relationship is done with the help of Removable or Fixed appliances depending on the severity of the case.

  • Mild cases are treated with Removable appliances
  • Severe cases are treated with Fixed appliances

Mild Cases: Upper Anterior Bite planes are used in correcting mild Edge-Centroid discrepancies. Another easy way is to Extract Premoalrs and Retract the upper incisors to establish normal Edge-Centroid relationship.

Severe Cases: Palatal movement of Upper incisors and Labial movement of lower incisors simultaneously is used to achieve normal Edge-Centroid relation ship in severe cases.


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