Fracture behaviour of zirconia FPDs substructures

Abstract

The purpose of this study was to evaluate the occurrence of superficial flaws after machining and to identify fracture initiation and propagation in three-unit heat-treated machined fixed partial dentures (FPDs) substructures made of hot isostatic pressed (HIPed) yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) after loaded to fracture. Four three-unit HIPed Y-TZP-based FPDs substructures were examined. To evaluate the occurrence of superficial flaws after machining, the surfaces were studied utilizing a fluorescent penetrant method. After static loading to fracture, characteristic fracture features on both mating halves of the fractured specimens were studied using a stereomicroscope and a scanning electron microscope. Grinding grooves were clearly visible on the surfaces of the machined FPDs substructures, but no other flaws could be seen with the fluorescent penetrant method. After loading to fracture, the characteristic fracture features of arrest lines, compression curl, fracture mirror, fracture origin, hackle and twist hackle were detected. These findings indicated that the decisive fracture was initiated at the gingival embrasure of the pontic in association with a grinding groove. Thus, in three-unit heat-treated machined HIPed Y-TZP FPDs substructures, with the shape studied in this study, the gingival embrasure of the pontic seems to be a weak area providing a location for tensile stresses when they are occlusally loaded. In this area, fracture initiation may be located to a grinding groove.

Mechanical performance of implant-supported posterior crowns

“…The clear mist and hackle area in the occlusal part of the broken LP and PT crowns demonstrates that the fracture originated from the fissure. 34,35 Additionally, white lines close to the top of the abutment and white spots on the cusps of the remnants indicate permanent plastic deformation caused by compressive stress that did not lead to catastrophic fracture.…”

“…After testing, all cement and crown remnants were removed from the abutments and photographed to analyze the origin of the fracture. 34,35 The abutments were cleaned with ethanol and prepared for another test group.…”

A 3D numerical simulation of stress distribution and fracture process in a zirconia‐based FPD framework

“…Today there are a number of techniques available for studying fracture in materials13; one frequently applied method is the fractographic analysis method,14–16 which often allows the fracture mechanism to be interpreted and the fracture initiation to be localized 13, 16. However, fractographic analysis can only be applied once the specimen has fractured and cannot identify the stress distribution and fracture propagation during the fracture process.…”

“…However, since the loading conditions and the stress distribution in the oral cavity are complex, three‐dimensional (3D) numerical modeling would provide more information about the stress distributions and fracture processes in all‐ceramic FPDs 20. Moreover, since previous studies have shown that machining ceramic restorations produces grooves, often described as milling trace lines, on the surface of ceramic frameworks16, 21 and that manual grinding may introduce irregularities on ceramic surfaces,22 it is of interest to examine how such grooves/irregularities on the ceramic surfaces affect the fracture process.…”

Fraktur einer kopiergefrästen Implantatbrücke aus Zirkonoxid-Keramik

“…Wesentlicher Vorteil der Kopierfräsverfahren im Vergleich zu aktuellen CAD/CAM-Systemen scheint die erreichbare Individualität der herstellbaren Strukturen zu sein [2, 10]. Schädigungen der Gerüststruktur durch Schleifkorrekturen werden ebenfalls als mögliche Ursachen für Frakturen angesehen[13,29] und können auch hier nicht ausgeschlossen werden. Als materialspezifische Probleme wurden jedoch Abplatzen der Verblendkeramik [4, 8, 23, 24] sowie Frakturen von Brückengerüsten beschrieben [3].…”