BACKGROUND: Miniscrew plant attachment to maxillary sinus is an important factor for implant safety and bone density can influence implant stability. Studies have explored implantation location of implant anchorage, such as bone thickness or bone density. However, the idea on implantation angle remains controversial. OBJECTIVE: To investigate the relationship between miniscrew implant in the interradicular space between the second premolars and the first molars in the maxilla and the maxillary sinus as well as bone density in the surroundings. DESIGN, TIME AND SETTING: Observation experiment was performed at dinan University from October 2007 to May 2008. PARTICIPANTS: A total of 38 patients with cone beam CT data were selected from Uni-Care Dental Center, Macao, including 11 males and 27 females, aged 18-35 (24.8±3.8) years. METHODS: Three dimensional images were reconstructed from cone beam CT images. For each subject, the buccolingual bone thickness was measured by postulating that the miniscrews would be inserted at 16 positions (10, 12, 14 and 16 mm above the median sagittal planes of the interradicular spaces between the first molars and the second premolars in the maxilla, and 30°, 45°, 60°, 90° from the cortical bone surface). The danger rate representing for implantation sites where buccolingual bone thickness was less than 6 mm was calculated. The density of the bone around the entire circumference of each miniscrew was also measured. MAIN OUTCOME MEASURES: Height of maxillary sinus, buccolingual bone thickness at implantation sites and bone density. The implantation sites could be divided into three groups. Group 2 exhibited the greatest danger rate and bone density and group 1 had the lowest danger rate and bone density.