Zirconia- the Wonder Material in Dentistry

INTRODUCTION

The zirconium or zirconia (the Arabic “zargun” which means “gold”), in its purest form exists in two forms: the crystalline form, a soft metal, white, ductile, and the amorphous form, a powder-blue black viz:

Zircon. A zirconium silicate, is the primary source of supply Baddeleyite. A zirconium oxide is a minor source of supply

HISTORY OF ZIRCONIUM

The element was discovered in 1789 by German chemist Martin Heinrich Klaproth and isolated as a metal by the Swedish chemist Jöns Jakob Berzelius in 1824. In the late sixties started a study as a biomaterial called tetragonal zirconia polycrystal (TZP). Their properties were ideal for the preparation of spherical heads of hip prostheses.Because of its high melting point and low thermal expansion,zirconium dioxide was also used to wrap nuclear fuel elements.In 1975 the British physicist Ron Garvie published in renowned business journal Nature his striking work under the title ‘Zirconia: Ceramic Stell’ (zirconia, ceramic steel“?). His research on the possibility of stabilizing the tetragonal structure of zirconium dioxide by adding about 5.5% yttrium oxide material helped to achieve the exceptional mechanical properties and high biological stability.

The resistance to bending, the shear strength and modulus E reached values of steel, therefore, the ceramic Garvie also called ‘ceramic steel’.A few years ago entered the field of dentistry for the performance of ceramic copings for crowns.The zirconia is considered one of the best ceramic products on the market for dental reconstructions, from the 90s, it is increasingly used in the field of dental technology. It is estimated that between 15,000 and 20,000 zirconia structures are made each day worldwide. Zirconia-based restorations are quite versatile and can be used for crowns, bridges and implant abutments in a variety of clinical situations if the appropriate guidelines are followed. The type of zirconia used in dentistry is yttriatetragonal zirconia polycrystal (Y-TZP) material, which is a zirconia oxide. Yttria (Y2O3) is an oxide of the metallic element yttrium (atomic No. 39).Y-TZP is a monophase ceramic material that is formed by directly sintering crystals together without any intervening matrix to form a dense, air-free, polycrystalline structure.Theyttria is added to the zirconia to stabilize the structure and maintain the material’s desirable properties hence, yttria stabilized zirconia.

TYPES OF ZIRCONIA

Three main types of zirconia are available for use in clinical dentistry.

Though they are chemically identical, they have slightly different physical properties (e.g., porosity, density, purity, strength), which may (or may not) be clinically relevant.

1. fully sintered or HIP type of zirconia.
2. partially sintered zirconia,
3. nonsintered or “green state” zirconia.

HIP stands for “hot isostatic pressing,” and is a sintering technique used in the ceramic industry that utilizes high temperatures and pressures to increase density of the material.Due to the similar manufacturing and fabricating processes, both of these types will be considered together (partially sintered or non-HIP zirconia). Blocks of these types of materials are manufactured by utilizing a spray-dried zirconia powder that is then isostatically pressed and incompletely sintered. These materials remain softer than the HIP

zirconia and are easier to mill. After milling, the zirconia is then sintered completely in a furnace at 1,350°C to 1,500°C to achieve its final shape, strength, and physical properties.

PROPERTIES

The zirconium for their properties, hardness and biocompatibility, gives you the option of working in dental surgeries nonmetallic tools (cutters zirconium) to avoid any metal contamination that may be caused.Furthermore, the rotary instruments made of zirconium oxide has advantages in dentoalveolar surgery in terms of temperature control and in economic terms, can be reused a number of times and show no alterations or wear on its cutting blades.The biggest advantage given to zirconium is that the dentist has the option of placing an implant of zirconium oxide rather than a metal one. The zirconium oxide implants are more stable from a mechanical point of view, besides that have opened the possibility of a new generation of color dental implants.The most common application of zirconia is to develop dental veneers, crowns, inlays, though today prosthesis can be made of 14 pieces.

Due to its high biocompatibility, strength and esthetics it is today the best option to perform oral rehabilitations.

ADVANTAGES

Zirconia implants surpass titanium in the following aspects:

Esthetics: While titanium has a dark, metallic color, Zirconium is whitish in appearance. Though most part of the implant is embedded within the bone, titanium sometimes shows a dark line around the gums. There is no such issue with Zirconia.

Hygiene: Ceramic implants and crowns are known to retain less plaque and calculus than titanium. So, they help the patient maintain better standards of oral hygiene and promote healthy gums.

Biocompatibility: Zirconium has decent bio compatibility; it is an inert material with very low allergic potential.

Corrosion Resistance: Zirconia tooth implants have almost a negligible risk of corrosion.

Patient comfort: Some patients are sometimes apprehensive about the idea of having a metal piece fixed into their bone. Ceramic implants solve this problem and provide patients with a comfortable option.

APPLICATIONS

Zirconia (Zirconium Oxide) is a white powdered metal used to create dental frameworks for crowns, bridges and other dental substructures. It replaces gold or stainless steel used in the past, creates the appearance of a whiter more translucent tooth, and is transparent in xrays.

Zirconia has been in use in cosmetic dentistry for many years to acheive the most aesthetic result possible, but has more recently become widely accepted as the dental material of choice.

RISKS

Zirconia implants are relatively new to the market, and are still being highly probed for the associated risks and problems.

One of the major risks with these implants is radioactivity. Zirconium may contain a certain number of radioactive isotopes, the activity of which may lead to an increased chance of various oral cancers.

Usually the Zirconia used in implants has extremely low radiation emission levels, and manufacturers of these are required to produce a declaration of radioactivity for their Zirconium based dental products.

DISADVANTAGES

Abrasive effect: The toughness of zirconia crowns can have an abrasive quality, which causes friction against the root of the affected tooth as well as with other teeth.

Decay under the crown: Though these crowns are meant to last a lifetime, the decay underneath the crown my cause them to loosen and fall.

As with everything in life, advantages often come with a price. This holds true for zirconia crowns too. Still, when you weigh the long list of advantages against a minor setback or two, zirconia crowns surely emerge as a leader.

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