Statistical methods
Data were analyzed using SPSS software (version 23.0; SPSS, IBM; Chicago). As for the reliability of the projection method, the intraclass correlation coefficient (ICC) for absolute agreement, single measure, based on 2-way random effects, was calculated. The Shapiro-Wilk test was used to assess the data distribution. Two-way repeated measure ANOVA was used to analyze the influence of the interaction of treatment and time on buccal STV. Paired t-test was used to verify the difference of STVC between extraction and non-extraction side during each period. One-way repeated measure ANOVA was used to analyze the difference of STV at different time points.For the hard tissue, the descriptive statistics of the HTVC were calculated. Pearson correlation coefficient was used to verify the correlation between the HTVC and the STVC to answer whether the volume decrease of the maxillofacial hard tissue would cause soft tissue change.