Abstract: Objective　 To evaluate the accuracy of linear measurements of dental implants obtained from digital periapical radiographs (DPR) by the paralleling and bisecting-angle technique, and provide references for DPR in peri-implant bone tissue assessment. Methods One hundred and sixty patients with 210 implants were divided into two groups randomly: paralleling technique group (80 patients with 98 implants) and bisecting-angle technique group (80 patients with 112 implants). DPRs were taken after implant placement immediately and the diameter and length of implants on DPRs were measured using SOPRO Imaging 2.20 software by blind method. Then the measurements were compared with the actual size of the implants. SPSS software was used to conduct t-tests to obtain the level of significance. And the accuracy of two measurement methods was evaluated. Results In the paralleling group, the mean differences between measurements and actual values were 0.14±0.10mm in diameter and 0.20±0.15mm in length, with the magnification of 1.58% in horizontal direction and 2.13% in vertical direction. In the bisecting-angle group, the mean differences were 0.37±0.22mm in diameter and 1.04±0.47mm in length, while the horizontal and vertical magnification were 3.90% and 10.65% respectively. Paralleling DPR showed a better accuracy than bisecting-angle DPR in measuring the diameter and length of implants (P<0.05）. Conclusion Paralleling DPR can obtain a more precise measurement of the diameter and length of the implants, which may be considered as a clinically reliable radiographic examination for implant treatment.

Key words: Bisecting-angle technique, Digital periapical radiograph, Implant, Paralleling technique