Microscale resolution fracture toughness profiling at the zirconia-porcelain interface in dental prostheses

Abstract

The high failure rate of the Yttria Partially Stabilized Zirconia (YPSZ)-porcelain interface in dental prostheses is influenced by the micro-scale mechanical property variation in this region. To improve the understanding of this behavior, micro-scale fracture toughness profiling by nanoindentation micropillar splitting is reported for the first time. Sixty 5 μm diameter micropillars were machined within the first 100 μm of the interface. Berkovich nanoindentation provided estimates of the bulk fracture toughness of YPSZ and porcelain that matched the literature values closely. However, the large included tip angle prevented precise alignment of indenter with the pillar center. Cube corner indentation was performed on the remainder of the pillars and calibration between nanoindentation using different tip shapes was used to determine the associated conversion factors. YPSZ micropillars failed by gradual crack propagation and bulk values persisted to within 15 μm from the interface, beyond which scatter increased and a 10% increase in fracture toughness was observed that may be associated with grain size variation at this location. Micropillars straddling the interface displayed preferential fracture within porcelain parallel to the interface at a location where nano-voiding has previously been observed and reported. Pure porcelain micropillars exhibited highly brittle failure and a large reduction of fracture toughness (by up to ~90%) within the first 50 μm of the interface. These new insights constitute a major advance in understanding the structure-property relationship of this important bi-material interface at the micro-scale, and will improve micromechanical modelling needed to optimize current manufacturing routes and reduce failure.

Investigations into the interface failure of yttria partially stabilised zirconia - porcelain dental prostheses through microscale residual stress and phase quantification

“…These results include those presented in Figure 4, as well as those obtained from the re-evaluation of ring-core FIB milling data previously reported by Lunt et al [31,32]. Micro-scale mechanical testing of the YPSZ-porcelain interface has recently been performed to determine the spatial variation of fracture toughness through micropillar splitting [15], as well as the Young's modulus and yield strength from micropillar compression [14] ( Figure 6b). The results of recent energy dispersive spectroscopy studies have also been included to provide insight into the elemental variation in the near-interface region (Figure 6c) [14].…”

“…The results of this study can therefore be used as a firm basis to optimise models of YPSZ-porcelain prosthesis manufacture, and ultimately aid in reducing failure rates in future. [14,15]. c) Spatial variation of seven highest weight % elements obtained using energy dispersive spectroscopy [14].…”

“…The underlying relationships that exist between phase, microstructure and mechanical properties in YPSZ mean that isolated examination of the residual stress is insufficient to understand fully the nature of the near-interface failure. Recent studies have revealed distinct variations in fracture toughness, yield strength and Young's modulus within the near-interface YPSZ, at the locations where high magnitude stresses have previously been reported [14,15].…”

Residual strain mapping through pair distribution function analysis of the porcelain veneer within a yttria partially stabilised zirconia dental prosthesis

“…Recent studies into the origin of this behaviour have suggested that failure arises from modifications to the microstructure (and mechanical behaviour) of porcelain within the first few microns of the interface [4][5][6][7] . Although elemental diffusion is known to influence this weakened near interface region, the primary driving force behind many of these mechanical changes is the tensile residual stress (or strain) which is generated during manufacture [8][9][10].…”

Fracture of Silicon: Influence of rate, positioning accuracy, FIB machining, and elevated temperatures on toughness measured by pillar indentation splitting

“…This technique is based on indentation with a sharp indenter on pillars produced using focused ion beam (FIB) machining with an aspect ratio (height-to-diameter) greater than 1. This allows local interrogation of materials toughness with high resolution [9,10]. In sufficiently brittle materials, a crack nucleates underneath the indenter during loading, and at some critical instability, the crack extends out to the pillar surface.…”