Rotational Load Fatigue Performance of an Implant System with an Internal Conical Connection and Microthreads.

PURPOSE: This in vitro study investigated the effect of implant geometry and diameter on the rotational load fatigue performance of an implant system with an internal conical connection with microthreads. MATERIALS AND METHODS: Regular (4.2 mm) and wide-diameter (4.8 mm) Astra Tech EV implants with straight (S) and conical (C) geometries were tested with their corresponding titanium abutments, comprising four test groups: 4.2-mm S (Group 1), 4.2-mm C (Group 2), 4.8-mm S (Group 3), and 4.8-mm C (Group 4). Five samples were included in each group. Customized brass implant holders and abutment holders were machined. A rotational load fatigue machine was used to apply a sinusoidally varying load to the implant-abutment interface at an angle of 45 degrees to produce an effective bending moment of 35 Ncm at a frequency of 14 Hz (air temperature: 20°C). The number of cycles to failure was recorded, with the upper limit set at 5 × 106 cycles. Results were analyzed using ANOVA. Failed samples were examined with a scanning electron microscope to evaluate the mode of failure. RESULTS: Of the 20 total samples, 2 failed, with Groups 1 and 2 each reporting one failure. Abutment and abutment screw fracture were observed in the failed sample in Group 1, while implant and abutment screw fracture occurred in the failed sample in Group 2. All wide-diameter implants ran beyond the cut-off without failure, but abutment screw loosening was noted in one sample in Group 3. No significant difference was found between implant groups of different geometries and diameters. Damage to the abutments and the implant internal surface were noted in all failed samples. CONCLUSIONS: While no significant differences were found between the test groups, failures were observed only in the regular-diameter group. The abutment and abutment screw fractured deep within the implant, and the implant fractured below the simulated bone level. These modes of failure may pose a significant clinical challenge during retrieval of these components.

Cooperative motility, force generation and mechanosensing in a foraging non-photosynthetic diatom.

Diatoms are ancestrally photosynthetic microalgae. However, some underwent a major evolutionary transition, losing photosynthesis to become obligate heterotrophs. The molecular and physiological basis for this transition is unclear. Here, we isolate and characterize new strains of non-photosynthetic diatoms from the coastal waters of Singapore. These diatoms occupy diverse ecological niches and display glucose-mediated catabolite repression, a classical feature of bacterial and fungal heterotrophs. Live-cell imaging reveals deposition of secreted extracellular polymeric substance (EPS). Diatoms moving on pre-existing EPS trails (runners) move faster than those laying new trails (blazers). This leads to cell-to-cell coupling where runners can push blazers to make them move faster. Calibrated micropipettes measure substantial single-cell pushing forces, which are consistent with high-order myosin motor cooperativity. Collisions that impede forward motion induce reversal, revealing navigation-related force sensing. Together, these data identify aspects of metabolism and motility that are likely to promote and underpin diatom heterotrophy.

Load fatigue performance of a single-tooth implant abutment system: effect of diameter.

PURPOSE: This study investigated the load fatigue performance of narrow-, regular-, and wide-diameter CeraOne (Nobel Biocare) single-tooth implants and abutments. MATERIALS AND METHODS: Five samples of each implant-abutment combination in 3 different widths were tested at 3 applied screw torque levels (recommended torque, recommended torque +20%, and recommended torque -20%). A rotational load fatigue machine was used to apply a 21-N load, at an angle of 45 degrees to the long axis of the specimens. This loading produced an effective bending moment of 35 Ncm at the abutment-implant interface. An upper cyclic limit was set at 5 x 10(6) load cycles for all specimens. RESULTS: Two-way analysis of variance revealed a significant difference between narrow-diameter and wide-diameter implant test groups but no significant difference between the 3 torque levels for each implant diameter. In the narrow-diameter group, 6 of the 15 specimens failed (5 abutment screw failures and 1 implant failure). In the regular-diameter group, 3 of the 15 specimens failed (2 implant failures and 1 abutment screw failure). There were no failures in the wide-diameter group. DISCUSSION: The results of this study indicate that the abutment screw is not the only potential failure location. The possibility of implant fracture clinically has been previously reported for prostheses supported by both single- and multiple-implant prostheses. CONCLUSION: The wide-diameter CeraOne single-tooth implant system demonstrated superior load fatigue performance. For clinical situations with significant functional loading, the narrow-diameter implants would be at a greater risk of fatigue failure.