Effect of Screw Head Design on Implant Abutment Screwhead Deformation after Repeated Closing and Opening Cycles

Abstract

The implant has gained worldwide acceptance in recent years and its usage is increasing daily. Opening and closing of the prosthetic components of the implant are done with various designed screws. The head of screw, in two very common designs is in the shape of hexagons and stellar. The purpose of this study is comparing the rate of the head screw transformation in the hexagonal and the stellar shape after consecutive opening and closing. Materials and Methods Two fixtures were used. The fixtures were then fixed vertically in plaster blocks using Die Stone, then placed on each abutment sample, and the torque value of N.Cm25 was applied by using the abutment screw which has been recommended by manufacturing firm. Six abutment screws out of total twelve screws of related firm are used in each fixture. The samples were examined by 50-magnification under Nicon stereo microscope model C-DS. The amount of changes of the head screw (outline) in different shapes was recorded by AutoCAD software .Then, the difference of the area of consecutive samples between the hexagonal and stellar geometric shapes of the screw was calculated. Statistical analysis was performed using spss24 software and P <0.05 was considered significant. Results By increasing the number of opening and closing, the screw area decreased in both hexagonal and stellar geometrical shapes, and at all stages except stage 0 to 50, the changes in stellar screw were greater than the hexagon screw. In stage 0 to 50 the area changes were 0.15 and were less in the stellar screw than in the hexagon screw. These changes were statistically significant at 100 to 200 and 200 to 300 stages (P <0.05).The area in the hexagonal screw from stage 0 to 300 decreased by 2.81 units and in the stellar screw by 4.15 units. There was a statistically significant difference between the area values in the number of different opening and closing in both types of hexagonal and stellar screws (P <0.001). Also, the area of the head of both screws in all numbers of openings and closings was significantly different of each other (P <0.001). Conclusion By increasing the number of opening and closing the screw area in both hexagonal and stellar geometrical forms has decreased. Also, the amount of area changes in all stages was higher than hexagonal screw, comparing with stellar screw except the 0-50 cycle. The headof screw in stellar shape has more depreciation comparing with hexagonal shape (at the number of openings and closing over 100 times).