Objectives: studying in 172 patients in othordontic department of Vietnam-Cuba Hospital to identify reason of transposition, rotated and impacted tooth, and the reality of dental arch length. Methods: cross-sectional analysis. Results: Lack of space causes 68,6 percent of tooth anomalies cases. The rate of space lacking of both arches was 75,6 percent, while that in upper arch and lower arch were 16 percent and 8,4 percent, respectively. Conclusions: The main reason of transposition, rotated and impacted tooth is the lack of space. The highest rate of space lacking of both arches was the highest number.