Abstract
BackgroundThe purpose of this in-vitro study was to evaluate the effect of dynamic cyclic loading on screw loosening of retightened abutment screw versus new abutment screw in both narrow and standard implants.MethodsSeparate acrylic resin blocks containing implant assembly (fixture, abutment, abutment screw, metal tube capping the abutment). Samples were divided into two main groups according to the diameter of implant: group 1 (GI 4.5-mm diameter) and group 2 (GII 3-mm diameter). Each group is subdivided into two subgroups according to the suggested option to manage screw loosening either by retightening (GIA, GIIA) or using new screws (GIB, GIIB). One hundred thousand cycles of eccentric dynamic cyclic loading (DCL) were applied before and after retightening or replacing the screw; then, removal torque loss (RTL) ratio was calculated, tabulated, and analyzed by t-student, ANOVA, pair wise Tukey’s tests.ResultsThere were differences between GI and GII regarding the incidence of screw loosening process. Removal torque loss ratio was higher in GIB and GIIB where the old abutment screws were replaced by new screws for both standard implants (SIs) and narrow diameter implants (NDIs). There was significant effect of retightening and replacing the abutment screws after exposure to DCL.ConclusionsWithin the limitations of this in-vitro study, it can be conclude that screw loosening process occurred in both SIs and NDIs but with higher values in NDIs. It is better to retighten the screw of NDIs and SIs than replacing it with a new screw.
Highlights
Oral implantology has undergone a well-deserved rebirth or rediscovery and implants considered the treatment of choice in an increasing number of carefully selected cases.After osseointegration is achieved, long-term clinical follow-ups reported biological or mechanical complications [1]
The titanium abutment was screwed to the fixture, sprayed, and three dimensionally (3D) scanned to accurately get the desired design and dimensions of the metal tube that fit the abutment head; this was achieved by the Computer Aided Design Computer Aided Manufacturing (CAD/ CAM) software (Dent create Exocad), with flat occlusal surface (10 mm in diameter) parallel to horizontal plane and perpendicular to implant fixture long axis to permit contact with the testing machine piston in a flat horizontal plane with small rounded hole exactly opposite to the abutment screw hole that facilitates screw driver accessibility
The results of this study showed that the screw loosening process occurred in both standard implants (SIs) and narrow diameter implants (NDIs) with nonsignificant difference; this can be due to use of various abutment screw diameter
Summary
Long-term clinical follow-ups reported biological or mechanical complications [1]. One of the systematic reviews evaluated the survival rate of implant-supported single crowns concluded. Screw loosening may cause implant or screw fracture, inadequate occlusal force distribution, and possible osseointegration failure. Screw loosening would lead to micro motion at the implantabutment interface while chewing [3]. Sones [4] reported that the failure of components, especially if abutment screws cannot be retrieved, might necessitate the disuse of the involved implant and require conversion or remake of the prosthesis. The purpose of this in-vitro study was to evaluate the effect of dynamic cyclic loading on screw loosening of retightened abutment screw versus new abutment screw in both narrow and standard implants
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