Screw loosening and changes in removal torque relative to abutment screw length in a dental implant with external abutment connection after oblique cyclic loading

Abstract

PURPOSEThis study investigated the effects of abutment screw lengths on screw loosening and removal torque in external connection implants after oblique cyclic loading.MATERIALS AND METHODSExternal connection implants were secured with abutment screws to straight abutments. The abutment-implant assemblies were classified into seven groups based on the abutment screw length, with each group consisting of five assemblies. A cyclic load of 300 N was applied at a 30° angle to the loading axis until one million cycles were achieved. Removal torque values (RTVs) before and after loading, and RTV differences were evaluated. The measured values were analyzed using repeated measures of analysis of variance with the Student-Newman-Keuls multiple comparisons.RESULTSAll assemblies survived the oblique cyclic loading test without screw loosening. There was a significant decrease in the RTVs throughout the observed abutment screw lengths when the abutment-implant assemblies were loaded repeatedly (P<.001). However, the abutment screw length did not show significant difference on the RTVs before and after the experiment when the abutment screw length ranged from 1.4 to 3.8 mm (P=.647).CONCLUSIONWithin the limit of this experiment, our results indicate that the abutment screw length did not significantly affect RTV differences after oblique cyclic loading when a minimum length of 1.4 mm (3.5 threads) was engaged. These findings suggest that short abutment screws may yield stable clinical outcomes comparable to long screws in terms of load resistance.

Biomechanical evaluation of peak reverse torque (PRT) in a dynamic compression plate-screw construct used in a goat tibia segmental defect model

“…The intracortical fractures occurred in the trans cortex more frequently during the placement of the non-self-tapping screws [36] as compared with the self-tapping screws [5]. The position most commonly associated with the fractures were position no.…”

“…The length of the NST and ST screws ranged between 18 and 24 mm in our study and all of the screws were placed bicortical. Previous research on a different length of the orthodontic implants (1.4–3.8 mm) did not show any significant correlation between the length of the implant and PRT as long as the implant was longer than 1.4 mm, which was considered as implants’ minimal length [36]. The minimal length of the cortical screw is considered when at least 3 threads of the implant can be placed through the far cortex in order to achieve the rigid fixation [1].…”

Effect of cyclic loading on the stability of screws placed in the locking plates used to bridge segmental bone defects

“…Recently, orthopedic studies found it to be valuable to assess primary stability of locking hole inserts placed in locking plates subjected to cyclic loading as well as to evaluate and compare osseointegration of non‐self‐tapping and self‐tapping screws placed in a dynamic compression plate 18,19 . Another study on dental implants used PRT to evaluate the primary stability of various lengths of dental implants subjected to cyclic loading 27 . PRT measures the torque required to remove the implant from the tissue or orthopedic plate, thus indirectly assesses the stability of the screw and bone or screw and plate interface 17 .…”

Abutment screw loosening in implants: A literature review

“…Of these two studies, the first one concluded that when a minimum length abutment screw was used (1.4 mm; 3.5 threads) there was hardly any difference in screw loosening post oblique cyclic loading compared with longer abutment screws. [ 10 ] The other study concluded that under thermal stress, there was no significant effect on torque when a minimum length screw was used (1.4 mm; 3.5 threads). [ 11 ]…”