الفهرس 
Mechanism of screw loosening processOnly 14 pages are availabe for public view
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Abstract
Narrow diameter implants become badly needed in the clinical practice because they offer great advantages to various clinical situations, but they have critical biomechanics that the clinician should take into consideration to get results comparable with standard implants with less complications such as screw loosening process.Screw loosening process occurs in both narrow and standard implants with various degrees and needs effective solution to carefully manage. Retightening the old abutment screw or replacing the old screw with new one are suggested.This in-vitro study was performed to evaluate the screw loosening process by measuring the removal torque value (in Ncm) of the retightened and new abutment screw in both narrow and standard implants.Forty implants were tested in this in-vitro study and divided into two main groups,twenty each, according to the diameter of the implant and so the diameter of the screw.Each group was subdivided into two subgroups, ten each, according to the suggested solution for management of screw loosening; retightening and replacing the old abutment screw.Data analysis was performed in many steps. The initial and postload removal torque loss ratio, after first (RTL1) and second exposure (RTL2) to dynamic cyclic loading were analyzed using SPSS statistical analysis version 20.ANOVA and Turkey’s post hoc test were performed to compare all testing groups.The study showed that removal torque loss ratio was higher in NDIs than Sis indicating that the screw loosening process has higher incidence in NDIs. The results also revealed that removal torque values were higher in GIA & GIIA where the old screws were retightened to the original torque value.The abutment screws of SIs have more survival rate when they are replaced by new ones after exposure to dynamic cyclic loading.