THE EFFECT OF CEMENT AND SCREW ON THE RESISTANCE OF AN IMPLANT CROWN TELESCOPICALLY ENGAGED TO A HEXAGONAL-SHAPED ABUTMENT UNDER COMPRESSIVE DYNAMIC CYCLIC FATIGUE LOADING

Purpose: To investigate the resistance of an implant crown telescopically engaged to a geometrically defined hexagonal abutment with and without cement under compressive dynamic cyclic fatigue loading. Materials and Methods: 40 crowns, 9 mm in height, were cast from prefabricated plastic copings, each telescopically engaged to a 3-mm-high machined hexagonal abutment. 20 crowns were retained with zinc phosphate cement, and 20 crowns were retained with a screw. A vertical load of 15 kg was applied to all samples under oscilla)on. A Periotest was used to measure the mobility of the implant crown in Periotest values (PTV). Test endpoints were defined by the following: fatigue cycles ≥ 20 million; crown PTV > 10; or if samples became visibly loose or component fracture. Results: Cement-retained crowns failed on average at 2.60 x 10⁶ cycles ± 2.27, while screw-retained crown samples failed at 2.17 x 10⁶ cycles ± 1.27 with no significant difference (P > .05). Implant and abutment screw fractures were the most prevalent mode of failure in the cement-retained group, while in the screw-retained group, failures were caused by the loosening of one or both screw joints. The rate of increase in PTV was higher in the screw-retained group than in the cement-retained group. Conclusions: Under the experimental conditions, an implant crown telescopically engaged vertically to a 3-mm-tall hexagonal abutment, under compressive dynamic cyclic fatigue loading with or without cement, demonstrated no differences in resistance or failure outcomes. A cement-retained implant crown with telescopic engagement to the abutment is more rigid, resulting in more implant and abutment screw fractures than loosening.