In Vitro Study of Preload Loss in Different Implant Abutment Connection Designs

Abstract

The stability and integrity of the abutment-implant connection, by means of a screw, is fallible from the moment the prosthetic elements are joined and is dependent on the applied preload, wear of the components and function. One of the main causes of screw loosening is the loss of preload. The loosening of the screw-abutment can cause complications such as screw fracture, marginal gap, peri-implantitis, bacterial microleakage, loosening of the crown and discomfort of the patient. It is also reported that loosening of the screw/abutment may lead to a failure of osseointegration. It is necessary to evaluate and quantify, with in vitro studies, the torque loss before and after loading in the different connections. Aim: evaluate the influence of implant- abutment connection design in torque maintenance after single tightening, multiple tightening and multiple tightening followed by mechanical cycling. Materials and Methods: 180 Klockner implants divided in 4 groups: 15 SK2 external connection, 25 Ncm tightening torque; 15 KL external connection, 30 Ncm tightening torque; 15 Vega internal connection, 25 Ncm tightening torque; 15 Essential internal connection, 30 Ncm tightening torque. In each group removal torque values (RTV) were evaluated with a digital torque meter, in 3 distinct phases: after one single tightening, 10 multiple tightenings and 10 multiple tightenings and cyclic loading (500 N × 1000 cycles). Results: After one single tightening, and for all connections, RTV were lower than those of insertion, but only for Essential and Vega internal connections this result was statistically significant. After multiple tightening, RTV were significantly lower in all connections. After repeated tightening followed by cyclic loading, mean RTV were significantly lower, when compared to insertion torque. The multiple tightening technique resulted in higher RTV than the single tightening technique, except for Vega implant. The multiple tightening followed by cyclic load, compared to the other phases, was the one that generated the lowest RTV, for all connections. Conclusions: The connection design, in our study, did not seem to influence the maintenance of preload. Loading influenced the loss of preload, in the sense that significantly decreased the removal torque values. The multiple re-tightening technique resulted in higher removal torque values than the single tightening technique. Clinically, our results recommend to retighten retaining screws, a few minutes after insertion.

Preload and friction in an implant–abutment–screw complex including a carbon-coated titanium alloy abutment screw: an in vitro study

“…The changes in preload with repeated screw tightening are not consistently described in the literature. Some authors have found an increase in preload with repeated tightening [ 4 , 15 , 22 ], others observed a decrease after retightening [ 18 , 23 – 25 ], and in some studies, the preload did not change [ 9 , 10 ]. These reports of differing preload changes after repeated tightening might be attributed to varying measuring methods, and especially the use of differing materials, which may have individual friction characteristics and wear phenomena.…”

Reverse Torque Value of Angulated Screw Channel Abutment before and after Cyclic Loading: An In Vitro Study

“…Even though a higher risk of mechanical issues is reported in the literature, the screw-retained prosthesis is a reliable treatment and may have some biological advantages over the cement-retained prosthesis [ 18 , 19 , 20 , 21 , 22 , 23 ]. Although angulated SRCs can make it possible for dentists to use screw-retained crowns under the condition that only cement-retained crowns can be used, because of a lack of evidence and long-term clinical outcome data, dentists will be hesitant in using this unfamiliar component.…”

“…One reason for loose screws is an insufficient preload. When the external load is beyond the preload, the abutment screw connection loses stability, affecting the vibration, and micromovement of the interfaces, which causes screw loosening [ 20 , 21 , 22 , 23 ]. An angulated SRC is usually used when the implant is in a suboptimal position; this may cause the implant abutment screw to receive larger lateral forces when functionally loaded, which may increase the chance of screw loosening.…”

Anaerobic adhesives effect on counter‐torque of abutment screws on implants with external hexagon and conical connections: An in vitro study

“…This process occurs because the inside of the screw thread and the implant are not manufactured without irregularities and the micro-roughness of the metal is softened with the tightening force, causing a loss of 2%-10% of the initial torque. 12,13 For this reason, it is necessary to apply torque once more after 10 min to compensate for the effect of this loss. 22 Abutment screw loosening can, over time, result in screw fracture or even implant fracture if there is no prior intervention.…”

“…In all groups, the torque was reapplied after 10 min to compensate the effects generated by the sedimentation phenomenon 12,13 …”