Abutment screw withdrawal after conical abutment settlement: A pilot study

Abstract

Objective This study investigated the effects of abutment screw withdrawal after conical abutment settlement on the stability of the implant–abutment connection. Materials and methods Twenty implants of a conical connection system were used. Two two‐piece abutment designs were used: cone only (n = 10; NI) and cone plus octagonal index design (n = 10; I); for each design, five samples were used with (S) and without (NS) abutment screw withdrawal before a cyclic test. Finally, four groups, namely Gr S(NI), Gr S(I), Gr NS(NI), and Gr NS(I), were included. The cyclic test included cyclic loading of 20–200 N, 30°, and 4‐mm off‐axis to implant axis at 10 Hz for 106 cycles, simulating a clinical time interval of 40 months. The fatigue cycles were recorded. The axial displacement of the conical abutments during abutment settlement, screw withdrawal, and cyclic loading were measured. Abutment morphology was examined through scanning electron microscopy (SEM). Results Only Gr NS(NI) failed the test, indicating that without the index design and abutment screw withdrawal, and connection stability seriously deteriorated. Gr NS(I) exhibited significantly higher axial displacement into the implant after abutment settlement than did Gr NS(NI). It also exhibited continuous axial displacement into the implant after cyclic loading. SEM after cyclic testing in Gr NS(I) revealed marked burnishing on lateral edges of the index, indicating that the index design provides an antitorsional ability. Conclusion Although this study has few limitations, abutment screw withdrawal is feasible in this conical implant–abutment connection system with index design.

Emerging factors affecting peri‐implant bone metabolism

“…114 When an octagonal index was added to the abutments, the bending strength was reduced, and wear, plastic deformation, and fractures were found under SEM. 113,114 Furthermore, marked fritting wear was reported around the edges of the antirotational index. 113,114 In summary, no perfect implant shoulder geometry is able to avoid some micromotion at the implant-abutment level.…”

“…113,114 Furthermore, marked fritting wear was reported around the edges of the antirotational index. 113,114 In summary, no perfect implant shoulder geometry is able to avoid some micromotion at the implant-abutment level.…”

“…Pure conical connections had the highest magnitude of micromotion compared with three other connection designs 112 ; in general terms, while butt joint connections tend to wear, conical connections tend to rotate 107,112 and friction occurs vertically with axial displacement into the implant. 113 A study analyzed the behavior of a pure conical versus a conical with an antirotational index. 114 The authors reported failures of pure conical abutments under lateral cyclic loading with torsional moment and stated that there is no antirotational capacity in a purely conical connection.…”

Effect of the prosthetic index on stress distribution in Morse taper connection implant system and peri-implant bone: a 3D finite element analysis

“…Apart from the index design, a screwless conical connection design has been demonstrated clinical success [27], however, lower mechanical resistance was observed when compared with the screw-retained conical connection design [28]. Recently, the feasibility of abutment screw withdrawal after conical abutment settlement was evaluated to solve the difficult problems of screw loosening and screw fracture [29]. Although the conical implant-abutment connection system with index design passed the cyclic test, additional studies should be conducted to test the clinical feasibility [29].…”

“…Recently, the feasibility of abutment screw withdrawal after conical abutment settlement was evaluated to solve the difficult problems of screw loosening and screw fracture [29]. Although the conical implant-abutment connection system with index design passed the cyclic test, additional studies should be conducted to test the clinical feasibility [29]. Furthermore, Shash et al reported that a novel one-piece implant structure could enhance the biomechanical stability of implant-bone system due to no implant-abutmentscrew joint [30]; yet they are not commonly used for broad implants.…”