Abstract: Objective  To study the changes of maxillofacial bone and related factors affecting the position of maxillary permanent incisor germs after treatment with modified block appliance. 
Methods  A total of 20 patients with deciduous anterior crossbite were selected and the modified block appliance was used to correct deciduous anterior crossbite. The maxillofacial changes before and after treatment were compared, and the influencing factors of changes in permanent incisor germs position after correction were analyzed by correlation analysis. 
Results  Before and after treatment, there were significant differences in 19 parameters of patients with deciduous anterior crossbite except SNA, SNB, NP-FH, L1-NBMM, MP-SN, FH-MP, facial axis angle, D1i-Y and A-Y(P＜0.05). After treatment, the correlation analysis of occlusal maxillofacial index and permanent tooth germ position index showed that there was a positive correlation between permanent tooth germ position and maxillary position and deciduous tooth position. 
Conclusion  The modified block appliance is effective in correcting deciduous anterior crossbite. After treatment, the maxillary growth forward and the increase of anterior teeth protrusion are conductive to the change of the position of permanent incisor germs forward and downward, as well as to the establishment of normal overbite relationship in mixed dentition period.

Key words: orthodontics, correction； tooth germ； tooth, deciduous, orthodontic appliances, malocclusion, angle class