Comparison of the effects of double distal jet appliance use on dentofacial structures with the single distal jet appliance in the treatment of class II malocclusion

The principle of distalization involves the posterior movement of maxillary molars in non-extraction orthodontic treatments. It is commonly preferred by clinicians to compensate for Class II dental and Class II skeletal discrepancies. Numerous appliances have been developed for molar distalization; however, their indications and contraindications must be carefully evaluated, and appliance selection should be based on the specific needs of each patient. This study utilized data from 34 patients treated with molar distalization between 2021 and 2023 at the Department of Orthodontics, Faculty of Dentistry, Uşak University. The first group (n = 17) consisted of patients treated with the Single Distal Jet (SDJ) appliance, and the second group (n = 17) included those treated with the Double Distal Jet (DDJ) appliance. The purpose of this study was to comparatively evaluate the dentofacial effects of these two distalization systems on skeletal and dental structures. Each patient had lateral cephalometric radiographs taken before (T0) and after (T1) distalization. From these radiographs, 36 reference points and 11 planes were identified, resulting in 33 cephalometric parameters selected for comparative analysis based on the biomechanical principles of the two appliances. To assess measurement error, the measurements of 10 randomly selected patients were repeated by the same researcher 15 days after the initial evaluation. No significant measurement error was detected. Both appliances achieved effective molar distalization. However, patients treated with the DDJ appliance demonstrated greater distal movement in a shorter period of time. Although both angular and linear anchorage loss were statistically insignificant in both groups, the DDJ group exhibited a greater amount of molar extrusion, leading to a statistically and clinically significant increase in vertical dimension (p < 0.05). Analysis of variance revealed a significant difference only in the extrusion of the maxillary first premolar, which was found to be higher in the SDJ group. This difference originates from the working mechanics of the appliances. In the SDJ, distalization of the maxillary second molar is achieved through indirect force transmission: the force is applied to the maxillary first molar, which compresses its periodontal ligament and subsequently transfers the distalizing force to the second molar. In contrast, in the DDJ, the anchorage force is distributed across four teeth, causing simultaneous periodontal ligament compression in multiple units. This configuration enhances the efficiency of force transmission, resulting in faster and greater molar distalization. From a biomechanical standpoint, the SDJ group showed greater premolar mesialization and extrusion, whereas the DDJ group showed greater molar extrusion. No statistically significant differences were observed between the groups regarding angular or linear values of anterior anchorage loss. When distalization and mesialization amounts were combined to calculate percentage anchorage loss, the SDJ group was found to be more disadvantageous. Therefore, it is recommended that the distalization force be applied directly, as in the DDJ system, to improve control and efficiency. Although the vertical skeletal parameters did not show a significant difference between groups in the analysis of variance, the DDJ group exhibited an intragroup increase in vertical dimension. As with any distalization appliance, the DDJ system has both advantages and disadvantages that can be optimized through appropriate patient selection. According to the data obtained from this study, further research is required to address the potential challenges of distalization in cases where the maxillary second molar has erupted, since its presence may complicate the biomechanics of distal movement and prolong treatment duration.