Thermal residual stresses in bilayered, trilayered and graded dental ceramics

Abstract

Layered ceramic systems are usually hit by residual thermal stresses created during cooling from high processing temperature. The purpose of this study was to determine the thermal residual stresses at different ceramic multi-layered systems and evaluate their influence on the bending stress distribution. Finite elements method was used to evaluate the residual stresses in zirconia-porcelain and alumina-porcelain multi-layered discs and to simulate the ‘piston-on-ring’ test. Temperature-dependent material properties were used. Three different multi-layered designs were simulated: a conventional bilayered design; a trilayered design, with an intermediate composite layer with constant composition; and a graded design, with an intermediate layer with gradation of properties. Parameters such as the interlayer thickness and composition profiles were varied in the study. Alumina-porcelain discs present smaller residual stress than the zirconia-porcelain discs, regardless of the type of design. The homogeneous interlayer can yield a reduction of ~40% in thermal stress relative to bilayered systems. Thinner interlayers favoured the formation of lower thermal stresses. The graded discs showed the lowest thermal stresses for a gradation profile given by power law function with p=2. The bending stresses were significantly affected by the thermal stresses in the discs. The risk of failure for all-ceramic dental restorative systems can be significantly reduced by using trilayered systems (homogenous or graded interlayer) with the proper design.

Zirconia surface modifications for implant dentistry

“…These coatings often undergo delamination and fracture caused by the coating/substrate bonding issue, mismatch in coefficient of thermal expansion (CTE), and the abrupt changes in physical properties at the coating/substrate interface. To overcome such issues, Zhang et al [105,106] proposed a bio-inspired strategy regarding transition in chemical composition and properties, as seen in Figure 6 [107][108][109]. That strategy relies on a functionally graded calcium phosphate-based glass/zirconia (CPG/Y-TZP) system with a low elastic modulus and a flexural strength similar to, or even higher than that recorded for Y-TZP [4,110,111].…”

“…The osteoconductive CPG coating can speed up the osteointegration process and prevents micromotion at the implant/tissue interface [4,105,112] In addition, the residual outer surface CPG layer acts as an encapsulation layer, preventing hydrothermal degradation of the Y-TZP interior, and can be further transformed to a carbonate apatite (CHA) layer by immersing in mineral precipitate solution or simulated body fluid (SBF) since the newly formed bone is directly attached to a CHA layer. Despite the aforementioned advantages of this system, there is only a few studies on CPG/Y-TZP, contrasting to a vast literature on glass infiltrated zirconia structures [4,104,[107][108][109][110][111][112][113][114].…”

Functionally graded ceramics for biomedical application: Concept, manufacturing, and properties

“…Therefore, new FGCs materials have been successfully designed and developed to combine an aesthetic, low elastic modulus and low hardness glass veneer with a high strength ceramic core, without a sharp interface between the materials. Fabris et al compared the thermal residual stresses generated inside “traditional” ceramic restorations, made by a strong ceramic framework and an external aesthetic veneer with those of multi‐layer ceramics. In particular way, 3 different multi‐layer designs were analysed by finite elemental analysis: (i) a conventional two‐layer (zirconia core—feldspathic porcelain veneer); (ii) a three‐layer structure, with a step‐wise transition from the bottom zirconia layer to the upper porcelain one; (iii) a graded structure, with a continuous transition between the 2 layers.…”

A comparative evaluation of shear bond strength between feldspathic porcelain and lithium di silicate ceramic layered to a zirconia core– An in vitro study

“…Once the temperature comes down, the phases are reversed automatically. Rare earth metal oxides such a magnesium oxide (MgO), calcium oxide (CaO) and yttrium oxide (Y2O3) are used to stabilize the zirconium from reverting back to the monoclinic phase and stabilized in a metastable state of tetragonal zirconia polycrystal and the Commonly used stabilizer in dental zirconia blocks is the yttrium oxide ( 10 , 11 ).…”