Is fatigue mechanism implicated in intraoral fracture of narrow dental implants? A retrieval analysis study

Abstract

Abstract Purpose This study aimed to perform a thorough failure analysis of two fractured narrow dental implants (NDIs) after medium-term in vivo use. Materials and Methods The top parts of two fractured NDI fixtures were retrieved from two different locations at two different times from the same patient. The first NDI fixture (NDI-specimen-1) was 12 months in service while the second NDI fixture (NDI-specimen-2) was 17 months in service. In both cases, the top parts of the fractured NDI fixtures that were attached to prosthetic components were retrieved and subjected to thorough, non-destructive (light microscopy [LM] and scanning electron microscopy [SEM]), and destructive testing (metallography, energy dispersive X-ray spectroscopy [EDS] and hardness testing). Results LM and SEM revealed that both the retrieved fractured NDI fixtures failed because of fatigue, characterized by beach and ratchet marks. Macroscopic examination revealed that fatigue cracks initiated at the internal thread surfaces of the implants and propagated around them until final fracture. Both samples fractured near the end of the retaining screw and followed the root of the internal thread (crest of the retaining screw). Both optical and SEM analyses revealed a uniform distribution of irregularly shaped grains with diameters ranging from approximately 2 to 5 µm. EDS analysis showed that the NDI-specimen-1 was made using Ti-14%Zr with traces of Si and Al and its microhardness was 288 ± 5 HV. Conclusion In both cases, the fracture occurred by a fatigue failure mechanism; thus, an increase in fatigue resistance will be beneficial for the longevity of NDI.