| Background:Induced by the orthodontic force,the anterior teeth maybe retracted.This process is accompanied by the remodeling of periodontal tissue around the root.There is a popular belief in orthodontics that the remodeling of alveolar bone keeps the same pace with orthodontic tooth movement,and maintain the quality and quantity of the alveolar bone as before.Abuabara A reports that the bone apposition occurs on the tension side and bone resorption on the pressure side.This theory was always thought to be the rule of the remodeling of alveolar bone.Retraction of anterior teeth with extraction of 4 first premolars was always made for the treatment of adolescent patients with bimaxillary protrusion,so as to change the soft tissue profile and achieve beautiful effect.For the past few years,Cone beam computed tomography(CBCT)has been proved that it can be used to accurately measure the height and thickness of alveolar bone.Futher more,it possess high accuracy and reliability on the measurement of linear distance of alveolar bone.Many researchs have used CBCT to study the changes of alveolar bone after En masse retraction of incisors.A large number of studies have challenged the alveolar bone remodeling theory.They summary that the rate of biological remodeling of alveolar bone is inconsistent during the palatal movement of anterior teeth,which is mainly manifested as bone resorption,but bone apposition is very little.Another research by Hyo-Won Ahna found that the thickness of palatal alveolar bone decreased significantly in the case of retraction of anterior teeth with Enhanced anchorage,and dehiscence occurred.More and more researchers contradicts the classic theory of alveolar bone remodeling.In addition,their conclusions of these studies on alveolar bone remodeling after tooth extraction reported currently are also very different from each other,correction in adolescents.Therefore,the mechanism of alveolar bone remodeling after tooth movement still needs to be studied further.Objective:This study aims to investigate the changes in alveolar bone thickness and related influencing factors after the retraction of anterior teeth,treated by 4 first premolars extraction in adolescents with bimaxillary protrusion.So as to provide references for clinical orthodontic treatment and related studies.Contents:1.The remodeling of alveolar bone due to retraction of upper incisors in adolescents.2.The remolding of alveolar bone due to retraction of upper anterior teeth in adolescents: a meta analysis.Methods:1.47 cases about retraction of anterior teeth,treated by 4 first premolars extraction in adolescents with bimaxillary protrusion were collected retrospectively.CBCT and cephalometric lateral radiographs datas of all patients were extracted respectively before treatment(T0)and 6 months after the space of tooth extraction closure(T1),then save them as DICOM format and import to Dolphin imaging 11.9 software.The labial and palatal alveolar bone thickness at cervical 1/3(L1),middle 1/3(L2),and apical 1/3(L3)levels of all these 94 maxillary central incisors were measured respectively.In addition,the datas of cephalometric measurements of 47 cases were analyzed for the inclination changes and the different adduction disntance of crown and root of maxillary central incisors.In the end,SPSS19.0 software was used to analyze the values before and after the measurement,and the paired samples were tested by t test,the test standard =0.05.The relationship between the changes of alveolar bone morphology and the inclination changes of upper central incisor,the different adduction disntance of crown and root were obtained.2.An English electronic search of Science Direct,Medline,Pubmed,Web of Science,Springerlink,Embase,Google Scholar,Cochrane Library with these Search terms: incisor retraction,En masse retraction,Extraction space closure,retraction of maxillary incisors,bimaxillary protrusion,orthodontic treatment,Bone remodeling,Alveolar bone thickness,bone reconstruction;And an chinese electronic search of CNKI,CMCI,VIP,CBM with these same Search terms;And the hand searching were performed from American Journal of Orthodontics,The Angle Orthodontist,J Pract Stomatol,Chinese Journal of Orthodontics.Retrieve range from building library until oct.31,2018.All the existing literatures on the changes of alveolar bone thickness after the incisors retraction in adolescent patients with bimaxillary protrusion were scaned.The quality of the obtained literatures was evaluated,and the included literatures were finally studied by Meta-analysis,So as to draw the conclusion on the quantitative changes of alveolar bone thickness according to the existing clinical studies.Thus to provide reference in clinics and some similar studies.Results:1.The results of 47 cephalometric measurements and CBCT data of 94 maxillary central incisor were analysised by statistical softwate respectively.(1)The results of cephalometric analysis show that: After the upper incisors retracted,the inclination of maxillary central incisors in 47 adolescents significantly decreased(5.48±1.96)°(p<0.05),The crown retracted(1.38±0.34)(mm)more than apical(p>0.05).This indicated that the inclination was improved,but the torque was under control.(2)Labial alveolar bone thickness of 94 maxillary central incisors in 47 adolescents were significantly increased(p<0.05).Palatal bone thickness at crest level(L1)and midroot level(L2)were statistically significant decreased(p < 0.05),There were no statistically significant difference at apical level(L3)of palatal bone thickness(p>0.05).2.The alveolar bone thickness of 106 maxillary central incisors at different location were analyzed by random effect model,results are as follows:(1)WMD [95% CI,p] increase between post-retraction(T1)and the Initial(T0)groups amounted to 0.12 mm [-0.13 to – 0.37 mm,p> 0.05] in labial alveolar bone thickness at crest level(S1),There were no statistically significant difference;(2)WMD [95% CI,p] decrease between postretraction(T1)and the Initial(T0)groups amounted to﹣0.72 mm [-1.0 to – 0.44 mm,p< 0.05] in lingual alveolar bone thickness at crest level(S1),There were statistically significant difference;(3)WMD [95% CI,p] increase between post-retraction(T1)and the Initial(T0)groups amounted to 0.28 mm [-0.05 to 0.62 mm,p> 0.05] in labial alveolar bone thickness at midroot level(S2),There were no statistically significant difference;(4)WMD [95% CI,p] decrease between post-retraction(T1)and the Initial(T0)groups amounted to﹣1.07 mm [-1.32 to – 0.81 mm,p< 0.05] in lingual alveolar bone thickness at midroot level(S2),There were statistically significant difference;(5)WMD [95% CI,p] increase between post-retraction(T1)and the Initial(T0)groups amounted to 0.5mm [-0.04 to 1.04 mm,p> 0.05] in labial alveolar bone thickness at apical level(S3),There were no statistically significant difference;(6)Due to the greater heterogeneity,the changes in lingual alveolar bone thickness at apical level(S3)fail to get.So this group is not suitable for combined analysis.Conclusions:1.It is a hot topic in orthodontics about the mechanism of alveolar bone remodeling,but the details still remain unknown;This study reveals that: The remodeling of alveolar bone did not keep the same pace with the tooth movement during the six-month observational period.Retraction of the anterior teeth should be carefully monitored.Palatal bone thickness at crest level(L1)and midroot level(L2)will decreased during en mass retraction.Within its limitations,the conclusions should be seriously consider.Thus,Long-time and Larger-sample researches were needed to study the mechanism of alveolar bone remodeling.2.Based on the existing evidence,we can find the significant decrease at cervical,middle level of the palatal alveolar bone thickness after retraction of the maxillary central incisors.Within its limitations,much more well-desigh,large-sample and Long-time studies were needed in the future. |
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