| Objective:To assess the changes of third molar angulation and eruption space in orthodontic patients with and without extraction treatment and to provide theoretical support for orthodontists when making treatment plan and dealing with the third molar.Methods:The Cochrane library, PubMed, Embase, CNKI,BM, VIP and Wanfang database were searched from 1st January 1990 to 28th February 2015. Additionally, we hand searched the professional journal, the related academic conference and System for Information on Grey Literature in Europe. What’s more, we used google search engine to find out leaked studies and try to identity all the studies about third molar angulation and position changes in patients treated with extraction and non-extraction. The related randomized controlled trials and controlled clinical trials were screened out in accordance with the inclusion criteria. Then we assessed the methodological quality of the included trials. Meta-analysis was conducted with Review Manager 5.3.3 and Stata 13.0 software. Heterogeneity among the included studies was assessed with Q Test and I2 statistic. Where there was significant heterogeneity, heterogeneity could be explored by conducting subgroup analysis and sensitivity analysis. The publication bias was assessed by the Begg’s funnel plot and the Egger’s linear regression analysis.Results:A total of 21 retrospective studies were included in this meta-analysis. There were 13 Chinese literatures and eight English studies. The position of the third molar was evaluated by measuring the angulation and eruption space of the third molar. This meta-analysis separately compared the maxillary third molar eruption space (4 studies), the mandibular third molar eruption space (12 studies), the maxillary third molar angulation (11 studies), the mandibular third molar angulation (15 studies). Subgroup analysis was done for subsets of participants (first premolar extraction patients, second premolar extraction patients and first molar extraction patients). The results were as follows: 1 The change of maxillary third molar eruption spaceThe meta-analysis revealed that significant differences were found in maxillary third molar eruption space(WMD=1.94mm,95%CI[1.38,2.50]), and moderate heterogeneity was detected (I2=41%, p=0.17).Subgroup analyses:first premolar extraction (WMD= 1.44mm,95%CI [0:83,2.05]), second premolar extraction(WMD=2.35mm,95%CI [1.26, 3.44]), first molar extraction(WMD=2.53mm,95%CI [1.26,3.79])。 2 The change of mandibular third molar eruption spaceThe meta-analysis revealed that significant differences were found in mandibular third molar eruption space(WMD= 1.90mm,95%CI [1.53, 2.28]), and significant heterogeneity was detected (I2=51%, p=0.02).Subgroup analyses:first premolar extraction(WMD=1.80mm,95%CI [1.32,2.28]), second premolar extraction(WMD=2.02mm,95%CI [1.31, 2.74]), first molar extraction(WMD=2.52mm,95%CI [1.72,3.32])。 3 The change of maxillary third molar angulationThe meta-analysis revealed that significant differences were found in maxillary third molar angulation(WMD=5.29°,95%CI[3.95,6.63]), and no heterogeneity was detected (I2=0%, p=0.9).Subgroup analyses:first premolar extraction(WMD=4.86°,95%CI [2.94,6.79]), second premolar extraction(WMD=5.08°,95%CI [2.34, 7.81]), first molar extraction (WMD=12.09°,95%CI [4.45,19.73])。 4 The change of mandibular third molar angulationThe meta-analysis revealed that significant differences were found in mandibular third molar angulation (WMD=3.31°,95%CI[1.91,4.71]), and significant heterogeneity was detected (I2=69%, p< 0.0001).Subgroup analyses:first premolar extraction(WMD=3.44°,95%CI [1.31,5.58]), second premolar extraction(WMD=3.35°,95%CI [1.21, 5.48]), first molar extraction (WMD=4.57°,95%CI [2.81,6.33]).Conclusions:We suggest that extraction treatment have a positive effect on the third molar eruption compared with non-extraction treatment. Moreover, the effect of extraction treatment seems more significant in maxillary third molar than that in mandibular third molar. In addition, the first molar extraction patients have a greatest improvement in the third molar eruption, and the second premolar extraction patients have a greater improvement than the first premolar extraction group. Due to the limitations in this study, the conclusions above need to be validated by further clinical trials. |
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