Exploring Ductility in Dental Ceramics

Abstract

Two damage regimes—“brittle” and “ductile”—have been identified in the literature on ceramic grinding, machining, grit blasting, and wear. In the brittle regime, the damage mechanism is essentially crack formation, while in the ductile region, it is quasiplasticity. Onset of the brittle mode poses the greater threat to strength, so it becomes important to understand the mechanics of ductile–brittle thresholds in these materials. Controlled microcontact tests with a sharp indenter are employed to establish such thresholds for a suite of contemporary computer-aided design/computer-aided manufacturing dental ceramics. Plots of flexural strength S versus indentation load P show a steep decline beyond the threshold, consistent with well-established contact mechanics relations. Threshold dimensions occur on a scale of order 1 µm and contact load of order 1 N, values pertinent to practical grit finishing protocols. The ductile side of ceramic shaping is accessed by reducing grit sizes, applied loads, and depths of cut below critical levels. It is advocated that critical conditions for ductile shaping may be most readily quantified on analogous S( P) plots, but with appropriate machining variable (grit size, depths of cut, infeed rate) replacing load P. Working in the ductile region offers the promise of compelling time and cost economies in prosthesis fabrication and preparation.

Brittle–Ductile Threshold in Lithium Disilicate under Sharp Sliding Contact

“…A detailed flexural strength S versus normal scratch load P N plot (red circles) is shown in Figure 4. For comparison, the flexural strength S versus Vickers indentation load plot (blue triangles) from a previous study (Alves et al 2022) is also included. The solid blue slope to the right is the theoretical prediction of the dependence of S on indentation load P using equation 5 with material property data in Figure 1D, whereas the bold red slope represents the prediction of S versus normal scratch load P N with 90% confidence bounds using equations 5 to 7.…”

“…We have applied the indentation theory of sliding contacts to predict the brittle-ductile threshold as well as the dependence of flexural strength on the normal scratch load in an LDS material. It is well-established that in axial loading with a "sharp" indenter, indentation cracks begin to dominate the (Alves et al 2022). Again, filled symbols represent failure origins at indentation sites, whereas unfilled symbols show failures away from these sites.…”

Criterios para la elección de biomateriales protésicos según sus propiedades fisicoquímicas para los sectores anterior y posterior. Una revisión exhaustiva

“…The optical results obtained with these materials were similar to the natural tooth appearance. However, due to their low mechanical strength and brittleness these reinforced ceramics were limited to the exclusive use of crowns in the anterior sector ( 26 ). Some studies show fracture-related failures of the veneering feldspathic ceramic.…”

“…Lithium disilicate ceramics contain feldspar responsible for translucency, quartz that composes the crystalline phase, kaolin that provides plasticity and lithium disilicate to improve strength; they are ceramics with excellent optical properties, with a translucency of 75%. Thus, they provide optimal esthetic characteristics for the rehabilitation of the anterior segment 26 .…”

“…Crystalline aluminum oxide is used to increase the strength of dental ceramics (so-called dispersion hardening). The technique developed by Dr. Sadoun made it possible for the first time to produce anterior bridges with up to 3 teeth 26 .…”