Evaluation Of The Efficiency Of Pendulum Appliance For Molar Distalization And Of That Related To Second Molar Eruption Stage

Dental crowding is a kind of malocclusion which is often met clinically. And the permanent molar mesial movement following the deciduous molar loss premature is one of the main causes. The malocclusion resulting from the maxillary molar mesial movement often shows as maxillary dental crowding and molar distal relationship. For these cases, by means of maxillary molars distalization we can correct the molar relationship and gain space for relieving dental crowding. The traditional distal movement techniques, such as extraoral traction with the headgear , have the major disadvantage of heavy dependence on the patient cooperation ,and moreover, they are unsuitable for such cases as ClassⅢmalocclusion. In 1992, Hilgers introduced the pendulum appliance for maxillary molar distalization. As a technique depending no patient cooperation, the pendulum appliance was widely applied and developed home and abroad. The treatment effects and the mechanism of this appliance were studied by many researchers. And it was suggested that the pendulum appliance could effectively move the maxillary molars distally. However, a controversy existed concerning the influence of second molars on the distal movement of the first molars and the best time to start therapy with the pendulum appliance, which was less investigated in domestic studies. Thus, the purpose of this study is to assess the efficiency of the pendulum appliance for molar distalization related to second molar eruption stage, while a further evaluation on the overall treatment of the pendulum appliance is also made. The method as follows: 1. collection of cases: 19 adolescent patients who would be treated by maxillary molar distalization were selected as the subjects. The panoramic radiograph of each patient showed maxillary second and third molars present with the third molars at the budding stage. All the patients were divided into 2 groups according to the different eruption stage of their upper second molars. 2. Treatment method: All the patients were treated with pendulum appliance for maxillary first molars distalization. 3. Cephalometric analysis: Cephalometric headfilms were obtained at pretreatment and posttreatment at time of pendulum appliance removal, and 29 cephalometric items were measured. 4. Statistical analysis: The statistical package(SPSS11.5) was used to analyze differences between the paired pretreatment and posttreatment cephalometric measurements and to determine significant differences of the treatment changes between the upper second molar erupted and unerupted group. The results as follows: 1. Analysis of overall treatment effects: In all patients, the molar distal relationship was corrected to super ClassⅠrelationship at posttreatment with pendulum appliance. In the sagittal plane, the maxillary first and second molars moved and tipped distally, and the maxillary first premolars and incisors reciprocally moved mesially and flared slightly. Increases in dentoalveolar vertical dimensions for the upper second molars, the first premolars and incisors also were observed, whereas the first molars were intruded slightly by an amount that was not statistically significant. In addition, there was a increase in overjet and a decrease in overbite. The sagittal skeletal effect of pendulum treatment was not significant. Significant increases in the vertical dimension were indicated by a slight opening of the mandibular plane angle relative to SN plane and by an increase in lower anterior facial height. 2. Comparative analysis of treatment effects between the upper second molar erupted and unerupted group: The amount of the first molar distal movement in those who had no second molar erupted was more than in those with second molar erupted, but the difference between two groups was not statistically significant. The degree of the first molar distal tipping in the second molar unerupted group is more than in the second molar erupted group( p﹤0.01), whereas the second molar distally tipped more in the second molar erupted group than in the second molar unerupted group( p﹤0.05). The upper first molars extruded significantly more in the second molar erupted group. Compared to the no erupted second molar group, in the second molar erupted group , the upper incisors flared more resulting in a more increase in overjet( p﹤0.05), with the incisors more tipping labially( p﹤0.01). So we can draw conclusions as follows: 1. The pendulum appliance can distalize the upper molars effectively. 2. The pendulum appliance primarily affects the maxillary dentition, and there are minor effects on the skeletal components. 3. During the distalization of maxillary molars, there was reciprocal anchorage loss in the premolars and incisors in a mesial direction. 4. The erupted upper second molars have no significant effect on the upper molar distalization. 5. It influences the distal tipping of maxillary molars whether the maxillary second molars are erupted or not. The erupted second molars can relieve the distal tipping of the first molars, but there are more distal tipping in themselves, which is suspected to be related to the presence of the third molar bud and should be paid attention to in clinical treatment. 6. The erupted maxillary second molars give more burden to the anterior anchorage, resulting in more anchorage loss. So the anterior anchorage must be controlled clinically. Concerning the anchorage, the best time to start therapy with a pendulum appliance for young patients is before the eruption of the maxillary second molars. 7. For the patients who have maxillary second molars erupted, the upper first molars would extrude after molar distalization. Thus, for those cases with high mandibular plane angles, it should be cautioned in using this appliance. Now, there are some questions remained to be solved: According to the present results, we suspect that the distal tipping of the second molars is related to the the presence of the third molar, which is needed to be proved. Moreover, it is required to be investigated further whether the presence of the third molars affects the maxillary molars distalization and the upper anterior anchorage loss. The present study has some clinical significance: By a further evaluation on the overall treatment of the pendulum appliance and the efficiency of the pendulum for molar distalization related to second molar eruption stage in our study, some conclusions mentioned above were drown from our results. And the conclusions would provide theoretical basis for the pendulum appliance being effectively applied to the clinical treatment.