Axial Displacements and Removal Torque Changes of Five Different Implant-Abutment Connections under Static Vertical Loading

Abstract

The aim of this study was to examine the settling of abutments into implants and the removal torque value under static loading. Five different implant-abutment connections were selected (Ext: external butt joint + two-piece abutment; Int-H2: internal hexagon + two-piece abutment; Int-H1: internal hexagon + one-piece abutment; Int-O2: internal octagon + two-piece abutment; Int-O1: internal octagon + one-piece abutment). Ten implant-abutment assemblies were loaded vertically downward with a 700 N load cell at a displacement rate of 1 mm/min in a universal testing machine. The settling of the abutment was obtained from the change in the total length of the entire implant-abutment unit before and after loading using an electronic digital micrometer. The post-loading removal torque value was compared to the initial torque value with a digital torque gauge. The settling values and removal torque values after 700 N static loading were in the following order, respectively: Ext < Int-H1, Int-H2 < Int-O2 < Int-O1 and Int-O2 < Int-H2 < Ext < Int-H1, Int-O1 (α = 0.05). After 700 N vertical static loading, the removal torque values were statistically different from the initial values, and the post-loading values increased in the Int-O1 group and Int-H1 group (α = 0.05) and decreased in the Ext group, Int-H2 group, and Int-O2 group (α = 0.05). On the basis of the results of this study, it should be taken into consideration that a loss of the preload due to the settling effect can lead to screw loosening during a clinical procedure in the molar region where masticatory force is relatively greater.

Review of the Mechanical Behavior of Different Implant–Abutment Connections

“…Five studies (Cashman et al (2011), Ferreira et al (2012), Bernardes et al (2014), Al-Otaibi et al (2017), Kim et al (2020)) [ 20 , 35 , 36 , 42 , 47 ] have investigated the mechanical behavior of different connections as a function of time and tightening and untightening sequences. The studies were designed to test if multiple tightening and untightening sequences of abutment screws influenced the loss of preload.…”

Strategic Use of CAD-CAM Interim Restoration for the Recovery of the Vertical Dimension of Occlusion in the Posterior Partially Edentulous Jaw

“…Even though this digital method can overcome the challenge of occlusal changes in the initial period after the delivery of restorations, a reliable connection between the implant and abutment should be confirmed to decrease the axial displacement of the abutment under functional loading [10,12,26]. The implant screw must be tightened with adequate torque to achieve the optimum preload [12,27,28]. In the present study, the abutment screw was retightened when the interim restoration was removed for taking the second impression, three months after the abutment connection.…”

“…Moreover, compressive force by long-term occlusal loading could generate plastic deformation of the interface of connection [11]. This settling phenomenon induces the axial displacement of the prosthesis [12]. The amount of settling of abutments to implants varies in all implant systems, and it has been reported that the implants with internal conical connection have higher settling values than those with external hexagonal connection [9,12].…”

“…This settling phenomenon induces the axial displacement of the prosthesis [12]. The amount of settling of abutments to implants varies in all implant systems, and it has been reported that the implants with internal conical connection have higher settling values than those with external hexagonal connection [9,12]. Mandibular dislocation was reported in partially edentulous patients without molar supports [13].…”

Abutment screw loosening in implants: A literature review

“…[ 25 ] recommended increasing the torque value to above 30 Ncm to reduce screw loosening, stating that the torque value should be more than the value recommended by the manufacturer. Kim KS and Lim YJ[ 48 ] studied the abutment settling into the implants and the torque value removal under static loading. They concluded that loss of preload due to the settling effect can lead to screw loosening.…”