Influence of interlayer design on residual thermal stresses in trilayered and graded all-ceramic restorations

Abstract

Residual thermal stresses are formed in dental restorations during cooling from high temperature processing. The aim of this study was to evaluate the influence of constructive design variables (composition and interlayer thickness) on residual stresses in alumina- and zirconia-graded restorations. Restorations' real-like cooling conditions were simulated using finite elements method and temperature-dependent material properties were used. Three different designs were evaluated: a bilayered restoration (sharp transition between materials); a trilayered restoration with a homogenous interlayer between core and veneer; and a trilayered restoration with a graded interlayer. The interlayer thickness and composition were varied. Zirconia restorations presented overall higher thermal stress values than alumina ones. Thermal stresses were significantly reduced by the presence of a homogeneous interlayer. The composition of the interlayer showed great influence on the thermal stresses, with the best results for homogeneous interlayers being observed for porcelain contents in the composite ranging between 30%-50% (vol.%), for both alumina and zirconia restorations. The interlayer's thickness showed a minor contribution in the thermal stress reduction. The graded interlayer showed an optimized reduction in restorations' thermal stresses. The use of graded interlayer, favoring enhanced thermal stress distributions and lower magnitude is expected to reduce the risk of catastrophic failure.

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].…”

Coroas cerâmicas bi-layers: Uma revisão de literatura sobre tipos de cerâmicas, processamento cerâmico e tensão residual

“…As restaurações de zircônia apresentaram valores de tensão térmica maior do que as de alumina. As tensões térmicas são significativamente reduzidas pela presença de uma camada intermediária homogênea, reduzindo a chance de falhas catastróficas 6 .…”

“…Vários estudos na literatura têm mostrado uma elevada incidência de fratura da porcelana sobre a zircônia, decorrente desta incompatibilidade térmica 5 . Tal condição pode ser desencadeada devido a tensão residual constituídas em coroas bi-layers com coping de zircônia com aplicação de porcelana, durante o resfriamento do processamento cerâmico a alta temperatura 6 .…”

Porous Zirconia Blocks for Bone Repair: An Integrative Review on Biological and Mechanical Outcomes

“…In this way, biocompatible materials composed of zirconia with desired properties such as strength, fracture toughness, chemical stability, and high biocompatibility have been designed for biomedical applications [6,[16][17][18][19][20][21][22]. In medicine, zirconia has been used for orthopedic implants and prostheses [7,20,[23][24][25].…”