Dental Zirconia

The emergence of zirconia material was initially based on its strong bending strength and ceramic material, which has good biological safety and can replace metal prostheses. However, the initial zirconia has poor light transmittance, which affects an important demand feature of dental restorations, that is, aesthetics. Therefore, the initial zirconia can only be used for the inner crown, which must rely on the craftsman's porcelain stacking operation, and get a relatively satisfactory aesthetic effect by relying on the hair color and transparency of the porcelain powder after sintering. However, the shortcomings of zirconia inner crown can also be imagined, that is, the restoration uses two layers of different ceramic materials, and its coefficient of thermal expansion is different after all. Whether there is a problem in long-term use needs to be confirmed. In addition, skilled, experienced, and even aesthetically tasted technicians are needed to make a restoration with both function (morphology) and aesthetics (hue and transparency). Besides, obviously, it takes time.

The following are some characteristics of beautyzir brand utex Pro Series zirconia products:

Indications

Thickness

Color

Translucency

Chemical Composition

Suggested crystallization curve

Zirconia has been used in dental restorations for nearly two decades. At present, more and more zirconium block manufacturers have entered the market, and a variety of zirconia block products are dazzling. The greatest credit is due to the unremitting efforts of the raw material manufacturers of zirconia powder and the zirconia products with various performance and beautiful specifications launched by the manufacturers of zirconia blocks according to the characteristics of different raw materials.

For patients, we need to find a good stomatologist to help them recover their function and beauty; For a dentist, a reliable technician is needed to realize the restoration he or she wants to give the patient; For technicians, if they want to have a suitable zirconium block, they can meet the needs of doctors through design, cutting, dyeing, sintering, external dyeing, etc; For zirconia block manufacturers, they want to have raw materials with both performance and beauty to make products that satisfy technicians; For raw material manufacturers, they have developed raw materials that meet the requirements of zirconia block manufacturers, such as easy color matching, easy molding, easy semi sintering, and both performance and beauty. The ultimate goal of these four divisions of labor is to return to the original point, that is, through the relay of efforts in different fields, to bring maximum benefits to patients, but also to get their own benefits.

The work of dentists, the processing level of technicians, and the work of raw material manufacturers are not listed here for the time being. Let's talk about the performance and quality of dental zirconium blocks at present.

What are the most important properties of dental zirconia?

Generally speaking, there are strength, fracture toughness, light transmittance, chromogenic performance and cutting performance. Of course, the lower the radioactive index is, the better, the lower the chemical solubility is, the better, the higher the anti-aging performance is, and so on. This is what dental zirconia must have.

Here we mainly talk about intensity and transparency. Strength in function; Aesthetically, transparency and hue are the hair color effects (of course, there are forms, but they are not shown here). In order to make a successful prosthesis that satisfies patients both functionally and aesthetically, both are indispensable.

What zirconia blocks are on the market?

There is no zirconia block that can meet the different needs of all dental restorations. We know that we need to wear basketball shoes to play basketball, football shoes to play football, badminton shoes to play badminton, etc. This is because different sports have different demands on the foot for force and stress, and also include the demand for foot protection. The same is true of zirconia. High strength, suitable for molars, long unit bridge; High transparency is suitable for anterior teeth restoration with high aesthetic requirements. Of course, some people say that zirconia with high strength and transparency can be applied? The idea is plump, and the reality is bony. The limitations of things can be seen everywhere in the world, and raw material manufacturers are constantly exploring, exploring towards the ideal, and need to wait. The good news is that zirconia raw materials with both strength and light transmittance have appeared one after another. For example, products with strength of about 1100mpa and light transmittance of about 47% have appeared in the market.

Different manufacturers of zirconium blocks have slightly different names for their products, most of which are named after the degree of transparency, such as high permeability zirconia, ultra permeability zirconia, ultra permeability zirconia, etc; There are also names from applications, such as zirconia for anterior teeth, zirconia for implants, etc.

The color of zirconia has also gradually developed from the original only natural color (white) to correspond to vita16 color. Some manufacturers have also introduced their unique colors to meet the color needs of different markets and ethnic groups. The appearance of colored zirconium blocks can reduce or simply abandon the subsequent technician dyeing operation, which not only reduces the technician operation steps, but also significantly maintains the performance of zirconia itself and avoids the adverse factors of strength reduction that may be caused by dyeing operation. In the future, colored zirconia blocks will completely replace colorless zirconium blocks.

Back to the transparency of zirconia, companies use transparency to distinguish specifications, that is, high transparency, ultra transparency, ultra transparency, etc. to name products. First of all, we need to know that there is no standard in the dental ceramic material industry to specify what is high transparency, super transparency and extreme transparency. These names are stipulated by each manufacturer. This is like people from all over the world communicating in their own dialects. Some can understand each other, and some don't know what it means. Therefore, it is not necessarily true that the transparency of manufacturer a is lower than that of manufacturer B. Then we need to communicate in words that everyone understands. The degree of transparency is expressed by transmittance, and the intensity is expressed by three-point bending strength.

For convenience, here I divide the light transmittance of dental zirconia into five grades. The higher the grade is, the higher the light transmittance is, that is, the more transparent it is. We expect zirconia of grade 6 and above to appear in the future.

What factors are related to the light transmittance and strength of zirconia in materials?

Generally speaking, the transparency of zirconia is inversely proportional to its strength. The better the transparency, the lower the strength.

1. Alumina plays a certain toughening role in zirconia, but the higher the alumina content, the greater the impact on transparency. The high content of alumina has good mechanical properties, but the transparency is greatly reduced.

2. The content of stabilizer yttrium oxide also has a great relationship with transparency and strength.

3. The size and agglomeration state of zirconia powder also have a certain relationship with transparency and strength.

In addition, the mechanic operation process also has a certain impact on the strength and transparency of zirconia, which will be discussed in the future.

How is the transparency of zirconia detected?

It is explained by the remaining transmittance of a certain amount of light after passing through a certain thickness of zirconia.

For a simple example, the light of a flashlight shines on a stainless steel plate with a certain thickness. At the other end of the stainless steel plate, you can't see the flashlight. The transmittance of this steel plate is 0%; If you replace the stainless steel with a glass plate with a corresponding thickness, you can certainly see the beam of hand lightning at the other end of the glass plate. If the glass is transparent enough, the light intensity you see across the glass plate is almost the same as what you see after removing the glass plate, then the transmittance of the glass plate is close to 100%.

At first, the transmittance of zirconia was more than 20%. With the continuous efforts of zirconia raw material manufacturers, dental zirconia raw materials with 35%, 44%, 47%, 50% light transmittance and certain strength have also appeared in succession.

Generally speaking, for zirconia blocks on the market now, the light transmittance of products with ordinary light transmittance is about 30% - 35% (1mm thick sample, 740nm wavelength), and the three-point bending strength is 1200-1400mpa;

For high transmittance products, the light transmittance is about 40-45%, and the three-point bending strength is 1000-1200mpa; The light transmittance of ultra-high transmittance products is about 48-50%, and the three-point bending strength is 600-1000mpa. There is also the need to shade metallic zirconia in planting and restoration. Instead, this kind of zirconia needs to be extremely opaque, with a light transmittance of about 20% or less, and a strength of about 1000MPa.

Aesthetically, we need zirconia with high transparency and close to natural tooth hair color, and sometimes we need extremely opaque zirconia to achieve aesthetic purposes. The market demand is diverse, and raw material manufacturers and zirconia block manufacturers are also making unremitting efforts.

In order to make zirconia restorations more beautiful and closer to the gradual hair color of patients' natural teeth, most zirconium block manufacturers have also introduced multi-layer color zirconia blocks (or gradual discoloration), which simulate the anatomy and histological structure of natural teeth. Even zirconia blocks with fluorescence also appear.

Histologically, the hard tissues of natural teeth implanted in alveolar bone include enamel, dentin and cementum. Soft tissue is dental pulp (nerves, blood vessels, connective tissue) that fills the pulp cavity. For restorations, cementum does not need to be considered. What needs to be considered is the comprehensive hair color effect of enamel, dentin and dental pulp, of which the most important is the hair color effect of enamel and dentin. As we all know, almost all enamel is composed of hydroxyapatite, with high transparency; There are many organic substances in dentin, and there are differences in structure. The transparency is much worse than that of enamel. Structurally, the distribution of enamel and dentin at the cutting end of the tooth, one third of the cutting end, the body and one third of the neck is different, reflecting that the hair color of each longitudinal layer of the tooth is different. To be more specific, the anterior teeth and posterior teeth are different. Each tooth position in the anterior teeth is also different, and each tooth position in the molar is also different. In more detail, the hair color of the teeth of the same person is also different when he is young, middle-aged and old. This is an irresistible law, and it is also the myriad customs the world gives us.

The multi-layer color zirconia block simulates the gradual hair color of natural teeth. The multi-layer color zirconia block can correspond to most applications, save dyeing operations, and fully meet the aesthetic requirements of posterior teeth restoration and some anterior teeth.

As we talked about the structure of natural teeth, how many layers of multi-layer color should correspond to the hue of natural teeth?

Some people will say that the more layers, the better. This may be the case in business publicity, but it is not the case in actual use. The aforementioned natural teeth are colorful, with different histological structures and crown heights. As we all know, the crown height of the maxillary and mandibular central incisors is between 9 and 12mm, and that of the posterior molars is about 7 to 8mm. There is no multi-layer zirconia block that can perfectly cope with the front and rear teeth of patient a at the same time, nor can it meet the needs of patient B, C, D... At the same time. The gradient from 4 layers to 6 layers can meet most needs in appearance. More important than the number of layers are the hair color of each layer, the thickness distribution of each layer, and the cutting position. Future development trend I personally believe that due to the different shapes and heights of teeth, there will be multilayer zirconium blocks for anterior teeth, multilayer zirconium blocks for premolars and multilayer zirconium blocks for posterior molars, which can more aesthetically cover the existing multilayer zirconium block products.

Before the zirconia restoration is put into the patient's mouth to realize its chewing, phonation and aesthetic functions, it has gone through many processes, such as the production of raw materials by the raw material manufacturer, the production of zirconia block manufacturer, the preparation of dental molds by the dentist, the design of the processing Institute, the selection of appropriate zirconium blocks, cutting, dyeing, sintering, external dyeing, grinding and polishing, and the grinding of the dentist. As long as one of the processes goes wrong, It will affect the current visible quality of the prosthesis or the changes in the future quality that are not visible at present.

Zirconia restorations are worn in the mouth of patients. Choose the zirconia material that is most suitable for the individual patient, adopt the most correct design and processing, and help the patient restore function and beauty. The greatest satisfaction of patients is the manufacturer of zirconia raw materials, zirconia blocks, oral cavity technicians, and prosthodontics, and the significance of realizing their respective values.

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