Clinical Effects On The Alveolar Bone Of Anchorage Molars After Rapid Maxillary Expansion:a Systematic Review And Meta-analysis

Objective:The purpose of this study was to assess the effects of rapid maxillary expansion(RME)on alveolar bone thickness and vertical alveolar bone height of maxillary first molars and first premolars through Meta-analysis,so as to provide scientific reference for the prevention of complications of patients with rapid maxillary expansion.Methods:An extensive electronic search about the effects on the alveolar bone of maxillary anchorage molars after conventional rapid maxillary expansion or microimplant assisted rapid maxillary expansion was conducted through databases including PubMed,Web of Science,Scopus,Cochrane central register of controlled trials(CENTRAL),China national knowledge infrastructure(CNKI),Wanfang database,China biology medicine database(CBM)up to February 1,2021.On this basis,we personalized the retrieval strategy of each database.Besides,we also searched the grey literature in databases.Also,the reference lists of the included studies were searched manually.There was no language restriction during the literature searching.After independent screening by two researchers,data extraction and the risk of bias assessment were performed.Review Manager 5.3 was used for statistical analysis and heterogeneity test.The standardized mean differences(SMD)with their 95%CI were chosen for the analysis of relevant indicators.For studies with high heterogeneity(I2>50%),we adopted the random effect model.Otherwise,the fixed-effect model was used.We conducted a descriptive analysis of data that could not be combined for analysis.Results:A total of 2361 articles was searched.At last,17 studies were included.Among the 17 articles,6 were randomized controlled trials(RCT)and 11 were non-randomized controlled trials(NRCT).The risk of bias assessment showed that 3 studies took a low risk of bias,13 studies took a medium risk of bias,and the other one took a high risk of bias.The thickness of the buccal alveolar bone of the first molars(SMD 0.79;95%CI:0.64-0.94)was significantly reduced after RME.Similarly,the same was true for the first premolars(SMD 0.51;95%CI:0.29-0.74).And the vertical distance between the buccal tip and the buccal alveolar crest increased significantly after RME(first molars:SMD-0.92;95%CI:-1.16--0.68;first premolars:SMD-1.14;95%CI:-1.49--0.80).The results were statistically significant(P<0.05).However,although the thickness of palatal alveolar bone of maxillary first molars and first premolars increased significantly(first molars:SMD-0.83;95%CI:-1.45--0.21,first premolars:SMD-0.69;95%CI:-1.28--0.11),more clinical trials are needed to confirm the stability of the results due to the high heterogeneity(first molars:I2=77%;first premolars:I2=62%).After microimplant assisted rapid maxillary expansion,the decrease of buccal alveolar bone thickness and vertical height and the increase of palatal alveolar bone thickness were also observed in the maxillary skeletal expansion(MSE)group.The thickness of buccal and palatal alveolar bone and the vertical height of buccal alveolar bone did not change significantly in the C-type expander group.Conclusion:After a systematic review and Meta-analysis of the existing evidence,it is concluded that:1.Rapid maxillary expansion can reduce the thickness of buccal alveolar bone and the vertical height of alveolar bone of maxillary anchorage teeth in a short time.2.After rapid maxillary expansion,the thickness of palatal alveolar bone of maxillary first molars and first premolars increased.But more studies were needed to verify the stability of the results because of the high heterogeneity.3.When using Hyrax appliance and Haas appliance for rapid maxillary expansion,there was no significant difference in the thickness of buccal alveolar bone between the two groups.However,the height of buccal alveolar bone in Haas group was less damaged than that in Hyrax group.4.When the maxillary primary molars were anchorage teeth,no adverse effects of rapid maxillary expansion on the alveolar bone at the maxillary posterior area were observed,such as the decrease of alveolar bone thickness and the increase of bone fenestration and bone cracking.5.Microimplant assisted rapid maxillary expansion has fewer negative effects on alveolar bone than conventional rapid maxillary expansion.