June, 2009
Distal Propeller: Innovation in Molar Distalization Appliance Design
An Appliance with New Concepts in the Innovation of Molar Distalization Appliance Design
Dr. Ashok Kumar Jena MDS, PGDHM, FPFA and Dr. Sujit Panda MDS
Distalization of the maxillary molars is one of the treatment modalities to correct the Class-II molar relationship and various molar distalization appliances have been proposed in the literature. [1-13]The evidence suggests that the distal movement of the molar is mainly due to tipping and rotation of the crown, [6,9,14-20] which is undesirable. The tipping of the molar is mainly due to the distal force coronal to the center of the resistance. However, the flexible nature of the appliances and the loose joint between distalization appliance and the attachment on molar could be the other factors contributing to the tipping and rotation. However, a more rigid appliance with a solid joint between appliance and the attachment on molars could cause distal movement of the molars with minimal tipping and rotation. Thus, to overcome the undesirable effects of the previously designed molar distalization appliances, the rigid “Distal Propeller’ appliance has been designed with the aim to distalize the molars bodily and without rotation.
Steps for appliance fabrication
Bands were adapted to the maxillary first molars and first premolars on either side, and transferred them to the working model (Fig 1). Then, an 11mm hyrax screw was adapted as shown in (Fig 2). The arrow marks on the hyrax screw can be kept either to the right or left side. The distal legs of the hyrax screw were soldered to the molar bands. The mesial legs of the hyrax screw were soldered to the premolar bands and also incorporated in the acrylic for the palatal anchorage. The finished appliance is shown in (Fig 3).
Case Report
A 12 year-old female patient presented with Class-II Div-2 malocclusion and moderate crowding in the mandibular anterior region. (Fig 4) Cephalometric measurements as mentioned in table-1, revealed mild Class-II skeletal relationship with favorable growth pattern of the mandible. Non-extraction treatment was planned. The “Distal Propeller” appliance was placed to move the maxillary first molars distally. (Fig 5) The patient was advised to open the screw ¼ turn in every 5 days. The patient was recalled in every four weeks for check-up. After 3 months, Class-I molar relationship on both sides was achieved. (Fig 6) The appliance was removed and a Nance acrylic button was cemented on the same day. (Fig 7) The nature of tooth movement and changes in the facial skeleton by the appliance is shown in table 2. The cephalometric superimposition is shown in figure 8.
Figure 1. Adapted bands on the first premolars and first molars.
Figure 2. Adapted hyrax screw on the working model.
Figure 3. The “Distal Propeller” appliance
Table 1. Pre-treatment cephalometric parameters
| Parameters | Values |
|---|---|
| SNA | 840 |
| SNB | 800 |
| ANB | 40 |
| AO-BO | +1 mm |
| FMA | 260 |
| SN-GoGn | 210 |
| Y-axis | 630 |
| Basal plane angle | 240 |
| Upper incisor – SN | 980 |
| Upper incisor – NA | 80 / 1mm |
| Lower incisor – NB | 250 / 4mm |
| IMPA | 1000 |
| Nasolabial angle | 1070 |
| Upper lip – E-line | -1mm |
| Lower lip – E-line | -1mm |
Table 2. Skeletal and dentoalveolar effects of the appliance
| Parameters | Pre | Post |
|---|---|---|
| FMA | 260 | 270 |
| SN-GoGn | 210 | 22.50 |
| Basal plane angle | 240 | 250 |
| Y-axis | 630 | 640 |
| Total anterior facial height | 105.58mm | 108.53mm |
| Palatal plane to maxillary incisor edge perpendicular distance | 28.16mm | 27.90mm |
| Palatal plane to maxillary 1st premolar centroid perpendicular distance | 21.07mm | 21.07mm |
| Palatal plane to maxillary 1st molar centroid perpendicular distance | 16.11mm | 15.68mm |
| Palatal plane to long axis of maxillary incisor angle | 820 | 760 |
| Palatal plane to long axis of maxillary 1st premolar angle | 900 | 92.50 |
| Palatal plane to long axis of maxillary 1st molar angle | 1020 | 1040 |
| Pterygoid vertical to maxillary incisor edge perpendicular distance | 47.49mm | 48.79mm |
| Pterygoid vertical to maxillary 1st premolar centroid perpendicular distance | 30.99mm | 32.05mm |
| Pterygoid vertical to maxillary 1st molar centroid perpendicular distance | 15.85mm | 12.51mm |
Figure 4. Pre-treatment intra-oral photographs.
Figure 5. The appliance in patient’s mouth
Figure 6. Intra-oral photographs after molar distalization
Figure 7. Intra-oral photographs after removal of the appliance
Figure 8. Cephalometric superimposition
Discussion
The Class-II molar correction by this appliance was almost by bodily distal movement of molars. This could be due to the rigidity of the appliance and the solid joint between appliance and molar attachment. Approximately 75% of the regained space was due to distal movement of the molar and 25% was due to the anchorage loss. The amount of anchorage loss by this appliance was less when compared to the anchorage loss by other appliances. [14-18,21-23], Most of the conventional molar distalization appliances cause mesial marginal ridge elevation of molars during distalization and resulting downward and backward rotation of the mandible. However, the effect of this appliance on the rotation of the mandible was negligible. The other advantage of this method of molar distalization is that the amount and rate of tooth movement is controlled. This appliance is also easy to fabricate and insert, and is also well tolerated by the patient.
Conclusion
The initial clinical and cephalometric findings are encouraging. However a clinical study with large sample is necessary to provide evidence based conclusions.
References
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Contributed by:
Dr. Sujit Panda MDS
Reader in Orthodontics Dept. of Orthodontics & Dentofacial Orthopedics RAMA Dental College, Hospital & Research Centre Lakhanpur, Kanpur-208024 India.
Co-Author
Dr. Ashok Kumar Jena MDS, PGDHM, FPFA
Asst. Professor Unit of Orthodontics Oral Health Sciences Centre. Post Graduate Institute of Medical Education and Research Sector-12, Chandigarh-160012 India.
