<prompt> The interincisal angle between deciduous incisors is:100 degrees120 degrees150 degrees170 degrees  <response>: Primary teeth are upright, but permanent teeth incline to the labial surface, thus decreasing the inter-incisal angle from about 150 degrees in the deciduous dentition to 123 degrees in the permanent dentition. This increases the arch perimeter. Ref: Textbook of orthodontics Gurkeerat Singh 2nd ed pg no 46 