Abstract
Introduction
Implant-cement debonding at the knee has been reported previously [1]. The strength of the mechanical interlock of bone cement on to an implant surface can be associated with both bone cement and implant related factors. In addition to implant surface profile, sub-optimal mixing temperatures and waiting times prior to cement application may weaken the strength of the interlock.
Aims
The study aimed to investigate the influence of bone cement related factors such as mixing temperature, viscosity, and the mixing and waiting times prior to application, in combination with implant surface roughness, on the tensile strength at the interface.
Materials and Methods
Tensile tests were carried out on two types of hand-mixed cement, high (HV) and medium viscosity (MV), sandwiched between two cylindrical Cobalt-Chrome coupons with either smooth (60 grit) or rough (20 grit) surface finishes. 144 Specimens were prepared with a cement thickness layer of 2.5 mm in customised rigs (Figure 1). The samples were grouped and tested at two mixing temperatures (23 and 19 degrees), at different mixing times (HV-30s, MV-45s). Waiting times after mixing were varied between early (1.5 min), optimal (4.5 min) or late (8 min); for HV and 4 min, 7.5 min and 11 min for MV cements. All the samples were cured for 24 hours prior to testing. The peak force and stress was calculated for all specimens.
Results and Conclusion
Surface Finish: Rough surfaced samples had significantly higher (p < 0.05) mean tensile forces and stress than smooth samples at both 19 and 23 degrees across HV and MV cement types.
Cement Type: MV cements, when applied to rough samples with waiting times of 4 minutes at 23 degrees, and 11 minutes at 19 degrees, resulted in the highest peak tensile forces, followed by 7.5 minutes at 23 and 19 degrees respectively (Figure 2).
Temperature at different application times for rough and smooth samples: for MV cement, rough samples prepared at 23 degrees, 4 minutes, and smooth samples at 19 degrees, 7.5 minutes were found to be significantly better (p < 0.05) than their counterparts. For HV cement, 23 degrees was found to be better (p < 0.05) for smooth samples at applications times of 4.5 and 8 minutes and 19 degrees for application times of 1.5 minutes. No significant difference was noted for rough samples for the same.
Application times at different temperatures for rough and smooth samples: at both 19 and 23 degrees, there were no differences between application times within the rough sample groups for HV or MV. However, for smooth samples, HV cement, tensile forces were significantly higher (p < 0.05) at 23 degrees in the following order; 8 minutes > 4.5 minutes > 1.5.
The results show that implant surface roughness and cement mixing time, temperature, viscosity and application times affect the strength of the interlock at the interface.
