Effect of Implant Connection Type and Depth on the Seating Accuracy of Hand-Tightened Abutments Hakimeh Siadat, DDS, MSc, 1,2 Simin Belbasi, DDS, 1 Marzieh Alikhasi, DDS, MSc, 1,3 Vahideh Nazari, DDS, 1 & Elaheh Beyabanaki, DDS, MSc 4 1 Dental Implant Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran 2 Department of Prosthodontics, Faculty of Dentistry, Tehran University of Medical Sciences, Tehran, Iran 3 Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran 4 Department of Prosthodontics, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran Keywords Dental implant; implant/abutment connection; implant depth. Correspondence Elaheh Beyabanaki, Department of Prosthodontics, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran. E-mail: e.beyabanaki@gmail.com This project was funded by a grant (#26240) from the Dental Implant Research Center, Tehran University of Medical Sciences. The authors have no financial interest in any company or any of the products mentioned in this article. Accepted June 20, 2017 doi: 10.1111/jopr.12688 Abstract Purpose: Improper seating of abutment on the implant is a common problem. This study investigated the effect of the type of implant/abutment interface on the complete seating of the abutments on the head of implants placed at different gingival depths. Materials and Methods: Three implant systems with three different connections including straight external hexagon, butt-joint internal tri-lobed, and conical internal hexagon were used. Two gingival thicknesses (2 and 7 mm) were created using pink baseplate wax around the straight abutments seated on the implants. After placing the implants in acrylic blocks, the wax was replaced with the gingival mask material to simulate the gingival drape around the implant heads. Afterwards, 15 prosthodontists were asked to hand-tighten the straight abutments in the corresponding implant bodies relying only on their tactile sense. At the final stage, the gingival mask was removed, and the seating quality of the abutments on implant bodies was assessed visually. The effect of implant connection and depth on abutment seating accuracy was analyzed using Kruskal-Wallis and multiple-comparison tests. Results: No significant difference was found regarding the effect of either depth or connection design on the accuracy of the abutment seating (p > 0.05); however, pairwise comparison of the combined effect of the depth and connection design was significant (p = 0.009). Accuracy of abutment seating on the Nobel Active implants at both 2 and 7 mm depths were significantly better than Replace system with 7 mm depth (p = 0.027). The same results were obtained in comparison between Nobel Active system at both 2 and 7 mm depths with Branemark system with 7 mm depth (p = 0.006). Conclusion: An increase in implant placement depth meant a decrease in accuracy of the abutment seating. The internal conical connection design showed the best result in abutment positioning in deep implants as compared with external and internal butt-joint connection designs. Accurate and passive fit of restoration/abutment on the im- plant is a substantial factor for the long-term success of implant prosthesis treatments. 1-6 Poorly adapted abutments can lead to biological and biomechanical complications. Mechanical com- plications may include abutment screw loosening, 7,8 increased incidence of abutment rotation and breakage, 8,9 and preload reduction. 10 Biologic complications may include adverse tis- sue reactions, pain, gingivitis, 4 marginal bone loss, 11,12 and increased microleakage. 6,13 Inaccurate fit between abutment and implant might be the result of several factors such as inadequate clinician experience in positioning the components. 14 However, proper seating of abutment on the implant body is important for avoiding a gap and for achieving successful treatment. 14 The clinical meth- ods to detect the gap in the abutment/implant interface include intraoral radiography 15 and combination of direct vision and tactile sensation with a sharp explorer. 16 Visual examination may be possible if the implant/abutment connection is above or at the free gingival margin. Tactile perception with a sharp explorer may also be considered; however, with an increase in implant depth, tactile perception of the clinician would de- crease. Radiography has been shown to be the most popular and reli- able method for verification of the gap at the implant/abutment 1 Journal of Prosthodontics 00 (2017) 1–5 C  2017 by the American College of Prosthodontists