2018 Volume 31 Issue 4 Pages 320-329
This study examined the effect of inserting an implant at a specific angle of inclination on its maximum bending load and the strain in its collar portion. Implant bodies and abutments were made from cold-worked JIS type-2 titanium (GWGW), JIS type-4 titanium (G4G4), and Ti-6Al-4V alloy (G5G5). The implant bodies and abutments of the same material were used in combination. Strain gages were fixed to the collar portions of the two-piece implants at angles of inclination of 10°, 20°, and 30°. Loads were applied using a universal testing machine while the maximum bending load on the implant and the strain in its collar portion were measured. In addition, the inside of the implant was observed by CT before and after measurement of maximum bending load.
Based on the results of these tests the following conclusions were drawn.
The maximum bending load of the GWGW, G5G5, and G5G5 implants was the highest at an angle of inclination of 10° and decreased as the angle of inclination was increased. When the angle of inclination was increased from 10° to 20°, the maximum bending load decreased by 58.5%, 60.9%, and 60% in the GWGW, G4G4, and G5G5 implants respectively. Furthermore, the maximum bending load at an angle of inclination of 30° decreased by 75.8%, 78.2%, and 76% in the GWGW, G4G4, and G5G5 implants, in comparison with that at an angle of inclination of 10°. Based on the strain measurements, when a load of 300 N was applied, the strain in the collar portion of all implants was 0.1% or less at an angle of inclination of 10°, 20°, and 30°. This was also observed for the implants with an angle of inclination of 10° and 20° when a load of 400 N was applied and for those with an angle of inclination of 10° when loads of 500 N and 600 N were applied. However, when a load greater than or equal to 400 N was applied to implants with an angle of inclination of 30°, the strain exceeded 0.1%. The GWGW implant exhibited the highest strain. CT observation of the implant before the bending test showed adaptability with an excellent abutment and implant body. After the bending test measurement, the abutment fractured at the boundary of the taper part and part of the screw. When the screw did not fracture, plastic deformation and cracking of the abutment were observed. Hence, the experimental findings suggest that when inserting an implant at an angle of inclination greater than 20°, it is essential to select an implant with a collar portion made of a high-strength material.
