Abstract: PURPOSE: To analyze 8-year cone-beam CT (CBCT) data of early, delayed and late implantation around maxillary area of patients with single dental implant after tooth extraction, and to investigate the effect of implantation at different times on implants, in order to provide valuable information for correct selection of appropriate implant timing after tooth extraction. METHODS: Clinical data of 68 patients who received single-tooth implant after tooth extraction in our hospital from January 2010 to December 2010 were retrospectively analyzed. According to different implantation times, the patients were divided into three groups: group A (n=25), group B (n=24) and group C (n=19). All patients were followed up for 8 years, and the buccal bone defects were recorded. The adjacent bone level and bone defects were analyzed based on CBCT images and posteroanterior(PA) radiographs. The data were processed with SPSS 18.0 software package. RESULTS: The success rate of mini-implants was 92.59%(150/162). Univariate analysis of variance showed that there was significant difference in the success rate of implantation among three groups(P<0.05). Paired comparison showed that the success rate of implantation among three groups was the highest in group C, followed by group B and group A (P<0.05). 8-year CBCT image data of 51 patients included 16 in group A, 20 in group B and 15 in group C. The adjacent bone levels showed no significant difference between CBCT and PA images(P>0.05). Insertion torque and pullout torque showed no significant difference among three groups(P>0.05). Implant timing, insertion torque and pullout torque were the high-risk factors affecting implant success rate(P<0.05). After 8 years of implant placement, there was no significant difference in bone level among three groups (P>0.05). In the second stage of operation, bone defect rate of group C was significantly less than that of group A and B (P<0.05). The average maxillary bone level of implants with no bone defects was lower than that of implants with dehiscence-type defects (P<0.05). CONCLUSIONS: Implant placement time after extraction has no impact on adjacent bone level, but different implant times can affect the success rate of implant; moreover, the indication of immediate implant should be strictly controlled.

Key words: Cone-beam CT, Time of implantation, Dental implant