| Background In the clinical work of orthodontics,it is always an important means to open up tooth space and improve class II relationship.However,the regression of the maxillary dentition should not only consider the sagittal direction of the maxillary tuberosity,but also consider the height and width of the maxillary tuberosity and the influence of the third molar on the maxillary tuberosity.Some scholars have shown that,in patients with maxillary third molars,it is recommended to remove the maxillary third molars.The extracted part can make room for the distant molars,and the phenomenon that the alveolar bone remodeling process is accelerated and the local bone density is reduced after tooth extraction is helpful to the distant molars.So,how will the bone mass of the maxillary tuberosity change after the removal of the third molar?Objective The purpose of this study was to investigate the changes of bone mass of the maxillary tuberosity before and after the extraction of the third molar.The three-dimensional shape of the maxillary tuberosity was described by the measurement and analysis of CT.The influence of the extraction of the third molar on the bone mass of the maxillary tuberosity was evaluated by the comparative study of CT before and after the extraction.The influence of the extraction of the third molar on the bone mass of the maxillary tuberosity was evaluated by the different treatment methods during the extraction The effect of regression.Materials and Methods A total of 20 patients who underwent orthodontic treatment,ambushing of one or both maxillary third molars on one or both sides of the maxillary third molar,and whoneeded to retract the maxillary molar were collected from January 2018 to September 2019.All patients agreed to use their imaging data for clinical research.Anchor nails were implanted between the second premolar of the maxilla and the first molar,CT images were taken at two points before and after the third molar was removed,and the length,width,and height of the maxillary tuberosity at different levels were measured.Describe the anatomical structure of the maxillary tuberosity;compare the CT data at the same level before and after tooth extraction,measure the changes in bone mass absorption,and evaluate the impact of the extraction of the embedded third maxillary molar on the bone mass of the maxillary tuberosity and the retraction of the maxillary molars;CT data of the same level of buccal bone fragments and non-buccal bone fragments during molar grinding are divided into two groups,each group is divided into different layers,and the different layers of each group are compared between groups to evaluate the extraction of the maxillary third molar In the process,the removal of buccal bone pieces affected the maxillary tuberosity bone mass and the impact of maxillary molar retraction.Use SPSS16.0 for statistical analysis of the data.Results 1.The average length of L2,L4 and L6 plane of maxillary tuberosity before tooth extraction was 22.10 mm,24.70 mm and 26.97 mm respectively(P < 0.05 by ANOVA);the average height of H2,H4 and H6 was 8.80 mm,8.59 mm and 6.88 mm(P > 0.05 by ANOVA;the difference between H2,H6 and H4,H6 plane was significant(P < 0.05);the average width of W2,W4 and W6 was 11.57 mm,9.12 mm and 7.77 mm(Analysis of variance,P < 0.05).2.The self-control results of different layers before and after extraction showed that: maxillary tuberosity The length of△ l2、△ l4、△ l6 layers was-1.34 ± 0.80 mm,-1.23 ± 0.65 mm,-0.85 ± 0.24mm(t test,P < 0.05);the height of △ h2、△ h4、△ h6 layers was-0.52 ± 0.32 mm,-0.71 ± 0.37 mm,-1.00 ± 0.29mm(t test,P < 0.05);The width of △ w2、△ w4、△ w6 layers were-1.11 ± 0.44 mm,-1.17 ± 0.36 mm and-1.74 ± 0.59 mm respectively(t test,P < 0.05).3.In the extraction of the third molar,the buccal bone was not retained in 15 extraction sites.0.27 2.P value of W4 < 0.05,P > 0.05).17(85%,95% CI: 67.85-100%),15(75%,95% CI: 54.21-95.79%),7(35%,95% CI: 12.1-57.9%),and 7(46.7%,95% CI:18.07-75.26%),6(40.0%,95% CI: 11.92-68.08%),5(33.3%,95% CI: 6.31-31.48%)in the group without buccal bone flap P value of W2 and W4 plane is less than 0.05.Conclusions In this clinical study,the difference of bone mass of the maxillary tuberosity before and after the removal of the third molar was studied.The results showed that:(1)the height and width of the maxillary tuberosity in the adolescent group decreased with the distance from the second molar,and the length increased with the distance from the CEJ plane.(2)The length,width and height of the maxillary tuberosity in the adolescent group were smaller than those before extraction.(3)The method of extraction with buccal bone slice retained in the adolescent group was helpful to preserve the width and height of the maxillary tuberosity after extraction,and the proportion of the buccal bone slice retained group that could safely retreat to 4mm was 75%,while the proportion of the buccal bone slice not retained that could safely retreat to 4mm was 40%. |
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