Related Experiment Video
Updated: Jan 14, 2026
An Improved Mechanical Testing Method to Assess Bone-implant Anchorage
Published on: February 10, 2014
Impact of implant abutment connection designs and cyclic loading on screw stability in dental implants: A systematic
Sara Reda Sammour1, Xie Ziqi2, Toru Ogawa3
1PhD student, Division of Advanced Prosthetic Dentistry, Tohoku University, Graduate School of Dentistry, Sendai, Japan; Assistant lecturer, Prosthodontic department, Faculty of Dentistry, Tanta University, Tanta, Egypt.
Statement Of Problem:
Screw loosening is a common mechanical complication that can compromise the long-term success of implant-supported restorations. Implant-abutment connection design and cyclic loading influence load transfer, preload retention, and joint stability; however, their specific contributions to screw loosening under functional conditions remain unclear.
Purpose:
The purpose of this systematic review and meta-analysis was to evaluate the effect of implant-abutment connection geometry on abutment screw stability under cyclic mechanical loading.
Material And Methods:
This manuscript followed the Preferred Reporting Items for the Systematic Review and Meta-Analyses (PRISMA) statement. Electronic searches were conducted in the PubMed, Scopus, and Web of Science databases for in vitro studies assessing screw loosening after cyclic loading. Studies that evaluated implant-abutment assemblies with clearly specified connection designs using commercially available implants were included. Two reviewers independently screened and extracted data and assessed methodological quality. Random-effects meta-analyses were performed to estimate the mean removal torque loss ratio for each connection type. Meta-regression explored potential sources of heterogeneity. Designs not suitable for meta-analysis were evaluated qualitatively.
Results:
A total of 21 in vitro studies met the inclusion criteria. Most applied cyclic loading ranging from 50 000 to 3 000 000 cycles, with forces between 100 and 300 N. Meta-analysis of studies on external hexagon connections revealed a significant pooled torque loss of 23.9% (P=.016) with high heterogeneity (I²=87.6%). The pooled torque loss was 19.2% for the internal hexagon (P=.074), 16.6% for Morse taper (P=.057), and 16.0% for conical connections (P>.05). Narrative synthesis indicated that hybrid conical connections retained preload more effectively than conventional internal hexagon designs. Angled abutments increased torque loss, and Morse taper hybrids generally showed superior stability.
Conclusions:
All connection types experienced preload loss under cyclic loading, with external hexagon systems showing the greatest average loss. Conical and Morse taper designs preserved preload better than flat-to-flat hexagon connections. Mechanical stability was affected by connection geometry, abutment angulation, and screw material.
