Objective To measure the mesiodistal and buccolingual alveolar bone mass of back teeth in posterior alveolar crest at different height by cone beam computed tomography（CBCT）, and analyze the safe area of microscrew implanted at back teeth in posterior alveolar crest. Methods 30 cases of adult scan image data were selected for the study of jaw bones scan reconstruction. From the distal of first premolar backward, buccolingual（plate）width and the mesiodistal size between each interfurcal region（including tuber maxillae） were measured from alveolar crest at top of 2, 4, 6, 8, 10 mm. ANOVA and LSD methods were made by SPSS 16.0 software for comparison. Results 1）The mesiodistal bone mass of back teeth in maxilla at the same height with different position had statistically significant difference（P
