| Summary: Anchorage is the resistance to unwanted tooth movement and obstructing the success of orthodontic treatment. In order to achieve good effect, we must seriously address the anchorage design issues. Presently, there was little specific quantitative study for the change of anchorage teeth position. And the research on affecting factors such as the face type, existence of the third molar et al was not enough. The aim of this study was to analyze the stability of anchorage molar by measuring the head and the lateral movement of the first molar by cephalometric measures and analysis there was or not relation between the age of patients, face types, sex, the third molar and the first molar mesio movement. it will lay the theoretical basis for the correct clinical treatment.Methods:Lateral cephalometric radiographs of 57 patients(17male,40 female) were selected from orthodontic department, the second hospital of Hebei Medical University. The average age of them is 16.7. The patients were divided into 4 groups according to treatment scheme:extracting the first premolar (group A), extracting the second premolar (group B), non- extraction(group C), extracting the first premolar with implant anchorage (group D). The patients in the group A were subgrouped according to the face typs (high angle; low angle;average angle), age(adult and teenager), sex and whether had the third molars respectivly.The distance of the mesaio contact point of the crown to of the first molar RL line and the distance of mesiocclusion root of the first molar to RL line were measured both pretreatment and posttreatment radiographs, and also the difference distances of the molar movement were compared. To evaluate the pre and posttreatment differences within each group, paired t-tests were used. For pre- and posttreatment differences between the adult and teenager group, male and female group, M3 existing group and M3 no-existing group, independent sample t-tests were used. For pretreatment and posttreatment comparisons among different face types groups, ANOVA were used. Values of P <0.05 were considered statistically significant. All values were analyzed by SPSS 10.0 statistic softwareResult:1 The values of mesaio movement of the 4 groups were as follow:Extracting the first premolar group: U6a(T2-T1) 1.62mm, U6s(T2-T1) 2.14mm, L6s(T2-T1) 2.49mm, L6a(T2-T1) 2.42mm. Those had statistically significant difference between pre and posttreatment. U6/PP(T2-T1) and L6/MP(T2-T1) had no statistically significant difference between pretreatment and posttreatmentExtracting the second premolar group: U6a(T2-T1) 2.97mm, U6s(T2-T1) 3.71mm, L6s(T2-T1) 4.53mm, L6a(T2-T1) 4.22mm. Those had statistically significant difference between pre and posttreatment. U6/PP(T2-T1) and L6/MP(T2-T1) had no statistically significant difference between before and after the treatmentNon-extraction group: U6a(T2-T1) 0.38mm, U6s(T2-T1) 0.61mm, L6s(T2-T1) 0.40mm, L6a(T2-T1) 0.35mm. Those had no statistically significant difference between before and after the treatment (P>0.05)Implants anchorage group: U6a(T2-T1) 0.05mm, U6s(T2-T1) 0.44mm, L6s(T2-T1) 0.49mm, L6a(T2-T1) 0.42mm. Those had no statistically significant difference between before and after the treatment (P>0.05)2 The value of displacement in group B were greater than that of group A. There was statistically significant difference (P < 0.05)3 The ANOVA results among of different face types Low angle U6s-Y(T2-T1) 0.61mm, U6a-Y(T2-T1) 0.59mm L6s-Y(T2-T1) 1.46mm, L6a-Y(T2-T1) 1.40 mm High angle U6s-Y(T2-T1) 4.74mm, U6a-Y(T2-T1) 2.85mm L6s-Y(T2-T1) 5.18mm, L6a-Y(T2-T1) 3.87 mm Average angle U6s-Y(T2-T1) 3.08mm, U6a-Y(T2-T1) 2.51mm L6sY(T2-T1) 2.87mm, L6a-Y(T2-T1) 2.23 mm The differences of them were significant(P<0.05), the higher mandible plane angle, the longer distances of the molar movement is.4 The result of molar displacement for adult versus teenager in group A Adult: U6s-Y(T2-T1) 1.44mm, U6a-Y(T2-T1) 1.03mm. L6s-Y(T2-T1) 1.46mm, L6a-Y(T2-T1) 1.43 mm. Teenager: U6s-Y(T2-T1) 3.71mm, U6a-Y(T2-T1) 2.58mm. L6s-Y(T2-T1) 4.39mm, L6a-Y(T2-T1) 3.26 mm The differences of them were significant (P<0.01), those values for teenager group were greater than those of the adult group.5 The results of molar displacement was no significant statistically difference between in male group and in female group.(P>0.05).6 The results of molar displacement for existence versus no-existence in group A Existence: U6s-Y(T2-T1) 3.79mm, U6a-Y(T2-T1) 2.98 mm L6s-Y(T2-T1) 3.06mm, L6a-Y(T2-T1) 2.13mm No-existence: U6s-Y(T2-T1) 2.19mm, U6a-Y(T2-T1) 1.51mm L6s-Y(T2-T1) 0.53mm, L6a-Y(T2-T1) 0.40mm The differences of changing were significant (P<0.01). The third molar effect on the mesio movement of the first molar in maxilla was more obviously.Conclusion:1 After extracting the first or the second premolars, the loss of molar anchorage occurred and a clear anterior movement was occurred for the first molars. With extraction of first premolars, the range of the maxillary first molars anterior movement measurement was from 1.62mm to 2.14mm. The range of the mandible first molars anterior movement measurement from 2.42mm to 2.49mm, which occupied 1/4 ~ 1/3 of extraction space. In the second premolars extraction group, the range of the maxillary first molars anterior movement measurement was from 2.97mm to 4.53mm. The range of the mandible first molars anterior movement measurement from 4.22mm to 4.53mm, and about 1/3 ~ 1/2 of extraction space was occupied. The measurement of mesio movement of the first molars in group B was 1mm longer than in group A.2 The mini-implants can provide enough anchorage for the first molar, and make the first molar not obviously move forward. Also the angle was not significantly change. Most of the gap was used to adduct the front teeth and to improve the profile appearance.3 The non-extracted patients'the first molars'position and inclinate angle were not apparently change without the device of molar backward.4 The change of the molar mesio movement and face types were significantly related, high angle > average angle > low angle.5 There was no significantly relationship between the change of the molar mesio movement and sex.6 The change of the molar mesio movement and age were significantly related. The change of teenager group was more obviously.7 The presence of third molar made it that the first molar would be more prone to move forward. This phenomenon is more obvious in maxilla than in mandible. |
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