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Why the zirconia become the popular dental restoration material?

2021-08-13 Page view : 29 views

Today, in dentistry, it is usually used a modified yttria (Y2O3) tetragonal zirconia polycrystalline (Y-TZP), because it has great mechanical properties and very good tear resistance than other regular ceramic materials. The addition of yttria is meant to stabilize the transformation of the crystalline structure under the conditions of increased temperature, but also to improve the physical properties of zirconium. Thus, the Y-TZP may reach 1000 Mpa while the fracture toughness of 400-500 MPa is also superior to the regular dental ceramics. One characteristic of Y-TZP zirconia is especially this high resistance to fractures because the tetragonal beads are transformed from the monoclinic phase, which leads to the compression of the forces around the defects, preventing their propagation. The wider ranges of clinical situations were Y-TZP zirconia may be used is related to its superior mechanical properties compared to other dental ceramics. While the first integral ceramic dental restorations were limited to single crown restorations or bridges, these zirconia structures may be used in larger prosthesis both in the anterior or posterior region of the oral cavity being one of the few aesthetic solutions that can be used in the lateral area. All of which added to classical uses like posts and cores or more recently as a material for dental implants.

Dental prosthetic restorations made from zirconia may be obtained using the CAD/CAM technology with two possible methods:

  1. The first technique the prosthetic restorations are milled from zirconia blocks already sintered which means there is no shrinkage to the final structure, but there are some disadvantages such as the reduced life-time of the burs, due to their great wear and the numerous flaws that occur during the machining that may diminish the mechanical properties of the final prosthesis. In this method the Y-TZP blocks are subjected to a first sinterisation at temperatures below 1500℃increase their density. Then the blocks are subjected to a high pressure at the same temperatures in an inert gas atmosphere, which allow the obtaining of a very high density of more than 99% of the theoretical one.
  • The second method the zirconia prosthesis is milled from a block, replicating the form of the final prosthesis but with bigger dimensions so it compensates for the shrinkage that occurs after sintering.

Nowadays there are some types of metal-free ceramics have been researched and developed to meet the requirements from the dental lab technicians and clinicians for natural looking appearance restorations. With the ceramic biocompatibility and good mechanical CAD/CAM properties, zirconia has been successfully used in recent years as a dental biomaterial.

Full-contour zirconia restorations become more widely used today as an alternative to veneered zirconia, due to the reason that its high translucent zirconia cores are generally covered with ceramic veneers that provide a more natural appearance, it is well-known that the current knowledge and scientific data of the zirconia use in dentistry is more popular compared the dental restorations with the metal-ceramic types.