title: Does Abutment Collar Length Affect Abutment Screw Loosening After Cyclic Loading?
abstract: A significant vertical space that is corrected with vertical ridge augmentation may necessitate selection of longer abutments, which would lead to an increased vertical cantilever. This study investigated the influence of different abutment collar heights on single-unit dental implant screw-loosening after cyclic loading. Fifteen implant-abutment assemblies each consisted of an internal hexagonal implant were randomly assigned to 3 groups: Group1, consisting of 5 abutments with 1.5 mm gingival height (GH); Group2, 5 abutments with 3.5 mm GH; and Group3, 5 abutments with 5.5 mm GH. Each specimen was mounted in transparent auto-polymerizing acrylic resin block, and the abutment screw was tightened to 35 Ncm with an electric torque wrench. After 5 minutes, initial torque loss (ITL) was recorded for all specimens. Metal crowns were fabricated with 45° occlusal surface and were placed on the abutments. A cyclic load of 75 N and frequency of 1 Hz were applied perpendicular to the long axis of each specimen. After 500 000 cycles, secondary torque loss (STL) was recorded. One-way ANOVA analysis was used to evaluate the effects of abutment collar height before and after cyclic loading. One-way ANOVA showed that ITL among the groups was not significantly different (P = .52), while STL was significantly different among the groups (P = .008). Post-hoc Tukey HSD tests showed that STL values were significantly different between the abutments with 1.5 mm GH (Group1) and with 5.5 mm GH (Group3) (P = .007). A paired comparison t-test showed that cyclic loading significantly influenced the STL in comparison with the ITL in each group. Within the limitations of this study, it can be concluded that increase in height of the abutment collar could adversely affect the torque loss of the abutment screw.
authors.affiliation: 1  Dental Implant Research Center and Department of Prosthodontics, Tehran University of Medical Sciences, School of Dentistry, Tehran, Iran.
authors.forename: Hakimeh
authors.initials: H
authors.lastname: Siadat
authors.affiliation: 2  Dental Implant Research Center and Department of Endodontics, Tehran University of Medical Sciences, School of Dentistry, Tehran, Iran.
authors.forename: Salma
authors.initials: S
authors.lastname: Pirmoazen
authors.affiliation: 1  Dental Implant Research Center and Department of Prosthodontics, Tehran University of Medical Sciences, School of Dentistry, Tehran, Iran.
authors.forename: Elaheh
authors.initials: E
authors.lastname: Beyabanaki
authors.affiliation: 1  Dental Implant Research Center and Department of Prosthodontics, Tehran University of Medical Sciences, School of Dentistry, Tehran, Iran.
authors.forename: Marzieh
authors.initials: M
authors.lastname: Alikhasi
mesh_terms: D001696:Biomechanical Phenomena; D001732:Bite Force; D003442:Crowns; D000044:Dental Abutments; D003722:Dental Alloys / Q000737:chemistry; D059605:Dental Implant-Abutment Design; D019250:Dental Implants, Single-Tooth; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D006801:Humans; D008422:Materials Testing; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D019415:Torque
chemical_list: D003722:Dental Alloys
keywords: abutment design; dental implant; screw loosening