Class II with extractions
A class II malocclusion can be corrected after extraction of the upper first premolars. The anterior segment from canine to canine can be distalized at once. However during initial levelling of the crowded incisors the overjet may increase. To avoid “round tripping” the canines can be distalized first. Distalization by sliding mechanics in combination with skeletal anchorage results in bite deepening. This may be favourable to close an anterior open bite but in the majority of the class II cases an increased overbite complicates the elimination of the sagittal overbite. Furthermore it has been demonstrated that during distalization of the canines friction is generated at the bracket-archwire interface. Thanks to this friction the sagittal overbite reduces spontaneously during canine retraction as long as there is no occlusal contact with the lower incisors. Therefore it might be helpful to add a slight intrusive force to the upper incisors by an auxiliary .016” or .017” square stainless steel wire inserted in the tube of the Bollard anchor. The auxiliary arch can be ligated to the main arch wire between 11 and 21 (when the incisors are retruded) or on both sides between the lateral incisor and the canine (when the incisors are protruded).
Class II without extractions
As described in our paper in the AJODO from September 2007 we initially distalized the molars first without bonding the premolars. The premolars follow spontaneously part of the movement of the molars thanks to the stretching of the supracrestal fibres. Friction generated by the molars at the tube-archwire interface also pulls the canines and the incisors backward, which results in a reduction of the sagittal overbite until contact with the lower incisors is obtained. To distalize the posterior teeth we use a piece of closed coil in combination with a sliding tube (Dentaurum ref 480-803-00 (.018”) or 480-809-00 (.020”)).
Recently we prefer to distalize the molars and premolars simultaneously. The distal wing of the bracket should be well fixed by a stainless steel ligature or a selfligating bracket can be used. As the canines are not bonded a level arm is generating some bite opening effect on the incisors. If the overbite is too important an intrusive auxiliary wire can also be used.
An upper molar which is overerupted in an extraction space of a lower molar can be intruded using skeletal anchorage. When the intrusive force is applied to the labial surface of the molar this results in a labial crown tipping. Therefore a triple tube is welded to a molar band parallel to the long axis of the tooth (Dentaurum ref 726-204-00). A 1.1 mm (.045”) stainless steel wire with a 90° bend and a double hook (0.6 mm wire) is inserted in the headgear tube first. In front of the vertical slot of the fixation unit of the Bollard anchor a second bend is made so that the arch wire passes through both holes of the cylinder and can be tightened by the blocking screw. The intrusive force is generated by a 150 grams Sentalloy closed coil springs (GAC ref 10-000-02).
The surgeon should be informed that the Bollard anchor will be used for molar intrusion: he should bend the round bar at the connection with the miniplate so that the fixation unit is positioned at some distance anterior from the molar in order not to interfere with the upwards movement of the tube.
From a biomechanical view the “crossed cantilever” offers the best control: the uprighting moment is generated by a separate spring fixed to the bone anchor. Extrusion of the lower molar and occlusal interference with the upper molar are responsible for jiggling forces and increased mobility. This can be avoided by adding an intrusive force to the distal part of the molar tube. However both springs often cause irritation of the mucosa of the cheek and complicate oral hygiene. Therefore we use now the prefabricated Sander Spring (Forestadent ref 307-1010). This spring consists of a .016x.022” stainless steel wire and a .017x.025” superelastic titanal wire connected by a square tube. The stainless steel wire is fixed into the vertical slot of the cylindrical fixation unit while the titanal part of the spring is inserted into a large edgewise bracket on the molar. By opening the angle of the stainless steel wire just below the fixation unit some intrusion force can be added to the molar in order to compensate for the extrusion generated by the uprighting spring.
Class III orthopedics
When Bollards with hooks are fixed to the infra zygomatic crest and in the lower canine region, continuous class III intermaxillary forces can be applied to the maxilla. However surgery in the upper jaw is complicated by a reduced height of the alveolar bone and the thin external cortical bone. This is responsible for a higher failure rate in these young patients. Because the surgery is more delicate than in adult patients and because 4 anchors have to be placed, we now advise a short total anaesthesia (one day clinic). In the mandible the Bollard with hook should be placed between the lateral incisor and the canine. Therefore we have to wait until the lower canines have mostly completed their eruption. Starting from the age of 12.5 to 13 years the observed clinical changes are clearly reduced. Initially forces of 150 grams on each side are used and over the first 10 weeks gradually increased up to 250 grams. The patients should be well instructed not to touch repeatedly the anchors with their tongue or fingers and not to play guitar with the elastics.