Discussion : The fracture strength by a torsion test at the implant-abutment interface (2)
For comparison between the mechanical strength of CP-Ti screw implants with internal tube-in-tube implant-abutment connections and that of external hexagonal-type connections, all abutments and CP-Ti implants with external hexagonal-type connections were heavily damaged or destroyed in all phases of loading. A typical fracture curve for CP-Ti implants with external connections is shown. The proportional limit and a parabola-like curve with eternal destruction were drawn. Torsion forces of 0.25, 0.50, 0.75, 1.00, 1.25, and 1.50 N · m were applied to the external CP-Ti implants. Deformation occurred in both the implant and the abutment at each torsion force (Fig. 6). This might have been the result of the abutment connection design or the physical properties of the implant materials. In addition, the deformation effect on the torsional yield strength of the implants and abutments is worth noting, as deformation occurred immediately before torsion fracture in all specimens.
Balfour and O’Brien tested the following three kinds of implants for maximum anti-rotational stability: external hexagon-type 0.7 mm-diameter CP-Ti implants, internal octagon-type 0.6 mm-diameter Ti-6Al-4V implants, and internal hexagon-type 1.7 mm-diameter Ti-6Al-4V implants and abutments. Testing comprised rigidly fixing a calibrated torque gauge to the abutment sleeve and applying torque until failure of the components was apparent. The torques necessary to separate the single-tooth abutments from the implants were 8.7 in.-lb (98.3 N · cm) for the external hexagon-type, 3.3 in.-lb (37.3 N · cm) for the internal octagon-type, and 10.0 in.-lb (192.1 N · cm) for the internal hexagon-type. In the internal octagon and internal hexagon designs, failure was limited to the abutment connections. The Balfour and O’Brien result differed from those reported in this study (4.3 and 3.8 mm diameters, 87 and 70 N · cm, respectively). The results from this study confirmed that the torsional strengths were different depending on the connection dimensions as reported by Balfour and O’Brien. CAMLOG implants (5 and 6 mm diameter) achieved higher torsional strength than 4.3, 3.8, and 3.3 mm diameter. This resulted from a combination of increased implant diameter and thickness of the implant walls.
Conclusions
The forces that led to permanent deformation of the abutment connections were dependent on the implant diameter. The differences between the implants used in this study were obvious, both macroscopically and microscopically. Significantly less force was needed to fracture smaller than larger diameter implants. Furthermore, in the CAMLOG implants only, abutment projections corresponding to anti-rotational notches were destroyed, which could have been due to differences in the strength and tensile properties of the materials.
Serial posts:
- The fracture strength by a torsion test at the implant-abutment interface
- Background : The fracture strength by a torsion test at the implant-abutment interface
- Methods : The fracture strength by a torsion test at the implant-abutment interface
- Discussion : The fracture strength by a torsion test at the implant-abutment interface (1)
- Discussion : The fracture strength by a torsion test at the implant-abutment interface (2)
- Figure 1. Torsion testing device
- Figure 3. The mean value of maximum fracture torque strength
- Figure 4. The mean value of torsional yield strength
- Figure 5. SEM picture of CAMLOG implant after torsion test
- Figure 6. SEM picture of implant with external hexagonal connection