Evaluation of reverse torque values and failure loads of three different abutment designs with internal connections

Saied Nokar, Habib Hajimiragha, Leyla Sadighpour, Azam Sadat Mostafavi


Background: High percentage of biomechanical complications such as screw loosening in dental
implants can be related to implant–abutment (I/A) connection properties which affect the behavior
of implant assembly against functional loads in the oral cavity. The aims of the present study were to
compare the reverse torque values (RTVs) and failure loads of three abutment types with internal
Morse taper connection.
Materials and Methods: In this experimental in vitro study, eighteen implants (4.5 mm × 10 mm
bone level implants, Implantium, Dentium Co, Seoul, South Korea) were divided into three
groups with different abutments: two‑piece (TP) abutment, one‑piece (OP) abutment, and screw
abutment (SA), mounted in stainless‑steel blocks according to ISO 14801. After completion the
torque/detorque protocol, a compressive load (1 mm/min) was applied at 30° off‑axis until failure.
Mean reverse torque/tightening torque (RT/TT) values and failure loads were analyzed with one‑way
ANOVA test and Tukey’s honest significant difference (α = 0.05). Failure modes were evaluated by
radiography and stereomicroscopy.
Results: RT/TT values in the TP group were lower than those in other groups (P < 0.001). Highest
failure loads were observed in SA group (P = 0.002). In radiographic evaluation, all specimens
showed deformation in I/A interface.
Conclusion: I/A connections with larger surface areas may lead to higher RTVs (e.g., OP and
SA groups). Use of an additional screw and indexed area in TP group did not reduce the bending
resistance under static loading.
Key Words: Compressive loading, dental implant–abutment interface, reverse torque

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