Department of Civil and Environmental Engineering, University of Connecticut, Storrs, CT 06269, USA.
Department of Preventive and Restorative Sciences, University of Pennsylvania, School of Dental Medicine, Philadelphia, PA 19104, USA.
Dent Mater. 2024 Aug;40(8):1267-1281. doi: 10.1016/j.dental.2024.06.007. Epub 2024 Jun 13.
During the manufacturing of Porcelain Veneered Zirconia (PVZ) dental crowns, the veneer-core system undergoes high-temperature firing cycles and gets fused together which is then, under a controlled setting, cooled down to room temperature. During this cooling process, the mismatch in thermal properties between zirconia and porcelain leads to the development of transient and residual thermal stresses within the crown. These thermal stresses are inherent to the PVZ dental crown systems and render the crown structure weak, acting as a precursor to veneer chipping, fracture, and delamination. In this study, the introduction of an intermediate functionally graded material (FGM) layer at the bi-material interface is investigated as a potentially viable alternative for providing a smoother transition of properties between zirconia and porcelain in a PVZ crown system.
Anatomically correct 3D crown models were developed for this study, with and without the FGM layer modeled at the bi-material interface. A viscoelastic finite element model was developed and validated for an anatomically correct bilayer PVZ crown system which was then used for predicting residual and transient stresses in the bilayer PVZ crown. Subsequently, the viscoelastic finite element model was further extended for the analysis of graded sublayers within the FGM layer, and this extended model was used for predicting the residual and transient stresses in the functionally graded PVZ crown, with an FGM layer at the bi-material interface.
The study showed that the introduction of an FGM layer at the bi-material interface has the potential to reduce the effects from transient and residual stresses within the PVZ crown system relative to a bilayer PVZ crown structure. Furthermore, the study revealed that the FGM layer causes stress redistribution to alleviate the stress concentration at the interfacial surface between porcelain and zirconia which can potentially enhance the durability of the PVZ crowns towards interfacial debonding or fracture.
Thus, the use of an FGM layer at the bi-material interface shows a good prospect for enhancing the longevity of the PVZ dental crown restorations by alleviating the abrupt thermal property difference and relaxing thermal stresses.
在制造烤瓷氧化锆（PVZ）牙冠的过程中，贴面-核系统经历了高温烧制循环并融合在一起，然后在受控的环境中冷却至室温。在冷却过程中，氧化锆和瓷之间的热性能不匹配会导致牙冠内部产生瞬态和残余热应力。这些热应力是 PVZ 牙冠系统固有的，使牙冠结构变弱，成为贴面碎裂、断裂和分层的前兆。在这项研究中，在双材料界面处引入中间功能梯度材料（FGM）层被认为是一种可行的替代方案，可以在 PVZ 牙冠系统中提供氧化锆和瓷之间性能更平滑的过渡。
本研究开发了具有和不具有双材料界面处 FGM 层的解剖学正确的 3D 牙冠模型。为解剖学上正确的双层 PVZ 牙冠系统开发并验证了粘弹性有限元模型，然后该模型用于预测双层 PVZ 牙冠中的残余和瞬态应力。随后，将粘弹性有限元模型进一步扩展到 FGM 层内的梯度子层分析中，并使用该扩展模型预测具有双材料界面处 FGM 层的功能梯度 PVZ 牙冠中的残余和瞬态应力。
研究表明，与双层 PVZ 牙冠结构相比，在双材料界面处引入 FGM 层具有降低 PVZ 牙冠系统内部瞬态和残余应力影响的潜力。此外，研究表明，FGM 层引起的应力重新分布可以缓解瓷和氧化锆之间界面表面的应力集中，这可能会增强 PVZ 牙冠的耐久性，防止界面脱粘或断裂。
因此，在双材料界面处使用 FGM 层通过缓解突然的热性能差异和减轻热应力，显示出增强 PVZ 牙科冠修复体寿命的良好前景。
