[Intrusion of the anterior teeth with the segmented-arch technic of Burstone--a clinical study]

The purpose of this study was to examine the efficiency of intrusion mechanics as described by Burstone. Thirty-one cases of deep bite with an overbite equal to or more than 4 mm were analysed by means of cast models, lateral cephalometric views and dental films of the front teeth prior to and after intrusion. The following parameters were considered: 1. Extent of the intrusion relative to a selective point of force application, 2. duration of the intrusion, and 3. amount of root resorption. The average extent of the intrusion in the case of the upper front teeth was 2.3 mm, and in the case of the mandible 3 mm. The rate of intrusion per month was 0.53 mm in the maxilla, and 0.54 mm in the mandible. Analysis of the point of force application showed that the centre of resistance must be presumed to be more distal than previously assumed. For an average treatment time of 4.3 months in the maxilla, and 5.5 months in the mandible, the apical root resorption was minimized by applying dosed force using a calculable force system. A buccal root torque arch employed in three cases permitted, in class II/1 cases, a combined movement comprising lingual tipping of the crown and intrusion, the intrusion component being clearly delayed in comparison with tipping. The segmented arch technique allows an objective intrusion of anterior teeth. This depends on choosing the appropriate point of force attachment and the correct amount of force.