Time.
Almost all types of zirconium are sintered in two hours at a temperature of 1450 to 1550 degrees. This rule applies to materials from any manufacturer. According to the standard, sintering takes approximately eight hours, of which the zirconium is gradually heated during three hours, and gradually cooled during the same time. This program is used to create small bridges and single crowns.
For large structures with stabilizers (special supports that prevent the product from deforming during sintering), a long program is used, approximately 18 to 20 hours. The scheme is the same: two hours at peak temperature, and still time for slow heating and cooling. For volumetric structures, rapid sintering is fraught with deformation and the appearance of cracks.
There is also a quick cycle lasting from one to two hours. At the same time, the temperature increases sharply; thirty minutes are allotted to the maximum mode, followed by rapid cooling. To speed up the latter, a smooth opening of the stove is provided. This method cannot be called standard; moreover, it implies restrictions on the length of the structure (up to three units). Added to this is the likelihood of nuances associated with the color and transparency of zirconium.
Advantages of metal-free ceramic bridges
Orthopedic dentists often recommend bridges made of zirconium dioxide to their patients, since this material gives the structures such positive qualities as:
- very high aesthetics and its long-term preservation (only with high-quality manufacturing): the material does not absorb dyes, less plaque settles on it than on tooth enamel,
- does not provoke “blueness” of the gums, like metal ceramics,
- biocompatibility, very low risk of allergies,
- the highest strength: several times higher than the strength of ceramics, and also stronger than some metal alloys,
- have a thinner layer of ceramics on top (compared to metal ceramics): because the metal is gray - under very thin ceramics it can be seen through,
- possibility of installation in any part of the row on natural teeth, as well as on dental implants,
- low thermal conductivity (compared to metal-ceramics): therefore, the supports under the prosthesis will not react so sharply to hot and cold food. But still, you shouldn’t get carried away with extremely hot and cold drinks / dishes, because... you can burn your gums and natural teeth,
- the supporting teeth do not need to be sharpened much,
- low risk of secondary caries and odor from under the crowns: from the inside, the structure fits very tightly to the supports, without gaps,
- very long service life: it is 20-25 years.
Selection of oven and heating elements.
The most popular furnaces are furnaces with SiC (silicon carbide) and MoSi2 (molybdenum disilicide) heating elements. In the first case, these are the most budget models, but have a number of disadvantages. These include increased sensitivity at work, intolerance to sudden temperature changes and the inability to speed up the process. If such an oven is opened when it is not completely cooled, cracks may appear or it may become deformed. The operating temperature of SiC is lower than that of MoSi2. In such furnaces, you should also not use acid-based dyes for zirconium.
If you want to avoid technical problems from distracting you from your work, pay attention to stoves with MoSi2 heaters. Their surface is protected by a layer of silicon from oxides formed during heating, which makes the elements more reliable in operation. An additional advantage is that as a result, the color of the material does not suffer during processing.
Recommendation:
During prolonged operation at low temperatures, the silicon layer is quickly destroyed. To restore it, it is recommended to turn on the “cleaning” cycle at maximum heating. MoSi2 furnaces are capable of operating in extreme conditions for fast sintering. To allow the elements to cool faster, the oven door can be opened. IMPORTANT! The fast cycle requires the use of a special cup that can withstand sudden temperature changes. The standard one may burst.
The price of furnaces with MoSi2 elements is not much higher than the price of SiC furnaces. We also recommend purchasing equipment care products, the cost of which starts from 25 euros and depends on the volume. For example, pay attention to nacera clean from Doceram. They are needed to improve the process of purification from oxides. This is an important point, because Removing foreign substances and restoring the protection layer of heating elements improves the quality of processing, preventing color changes or loss of translucency of products.
One of the most important features is the presence of Tungsten in the heating element. This strengthens and gives reliability to the heating elements by an order of magnitude, while eliminating the problem of zircon turning yellow after sintering, which occurs after 1-2 years of operation of those furnaces that do not contain Tungsten! Therefore, it is advisable to choose stoves with heating elements that contain tungsten.
Technical features of zirconium as a dental material
Zirconium dioxide (ZrO2), or simply zirconium, is a white crystalline zirconium oxide. Currently, it is the most studied ceramic material in dentistry. Many specialists are introducing this material into their practice, with varying degrees of success. The main question that all experts are now asking is: is the use of zirconium a new trend or a temporary fad?
Will it be used for a long time or, as has happened more than once, will it give way to other, more modern materials? To answer this question, it is necessary to study the restoration properties of zirconium. Below are the results of observation of 15 thousand zirconium monolithic structures in the form of various restorations, from full-arch prostheses to single implants and abutments.
Structural stability
Tetragonal zirconium (after sintering) is stronger and more durable than metal. At the same time, it does not have significant flexible properties and is more susceptible to splitting than deformation. These properties can be used well in dentistry, and especially in implantology.
The key to producing a quality zirconia restoration is high precision. If the technician follows the instructions, the resulting restoration will fit better and the non-flex properties will ensure longevity. This is especially important for implant-supported restorations, since passive fit is of great importance for the effectiveness and durability of their service due to the complete immobility of the implants (Fig. 1 a, b).
Rice. 1a Fig. 1b
Zirconium does not deform under pressure, which often affects the structure during medical and dental procedures, and also conducts heat poorly.
This allows for the creation of large restorations that will not change shape in a ceramic kiln in the same way as traditional metal-ceramic restorations. The maximum operating temperature of zirconium exceeds the temperature in standard ceramic furnaces, which ensures stability and shape retention even after sintering several layers of ceramics (Fig. 2 a - c).
Rice. 2a Fig. 2b Fig. 2v
Quality aesthetics
Uncolored tetragonal zirconium is usually white in color and has a transparency similar to that of dental hard tissue. In the last few years, a more transparent material with less aluminum has become available. The final appearance of zirconia restorations is influenced by various staining fluids, staining and sintering technologies.
However, in general, zirconia restorations, especially monolithic ones, can provide excellent results in terms of esthetics without compromising their strength (Fig. 3 a, b).
Rice. 3a Fig. 3b
In the case of a veneered zirconia structure, the base structure forms the bulk of the structure and is durable, requiring only minimal use of veneers to impart color and the addition of pink gingival porcelain (Fig. 4 a, b).
Rice. 4a Fig. 4b
The lingual surfaces and the inner surface of the pontic can be left completely unlined, since nothing needs to be hidden, as is the case with a metal frame, for example.
Monolithic zirconia restorations also provide good esthetic results in limited spaces, not as a compromise, but as a good esthetic solution where this would not have been possible in the metal-ceramic era (Fig. 5 a - d).
Rice. 5a Fig. 5b Fig. 5c Fig. 5g
Monolithic zirconia also provides conservative preparation.
For good aesthetics, the preparation volume should be approximately 1 mm of tissue. This gives the specialist the opportunity to preserve much of the original tooth structure, which is especially important in the case of intact teeth.
Today, zirconium materials are at the same stage of development as ceramics were in the 70s. twentieth century - in its embryonic state. The more they are studied and used, the faster they will develop and the faster an even better aesthetic result will be achieved.
Biological compatibility
The properties of zirconium, which are explained by its atomic bonds, make this material quite biocompatible. The high density (can reach 6.1 x 10? kg/m?) and high chemical resistance ensure low bacterial accumulation on monolithic parts of the restoration, even in conditions of poor oral health.
Good wear resistance guarantees a high degree of survival of the restoration. According to several orthopedic dentists in our area, some patients with bruxism who wore monolithic zirconium restorations, after some time, stop experiencing the symptoms of this pathology or feel them less, and this is precisely due to the high wear resistance of zirconium, which deprograms bruxism. This statement has not yet been confirmed by clinical trials, but now it sounds logical, and it can be heard from more and more doctors.
The low coefficient of friction makes monolithic zirconia restorations safe for opposing teeth. Despite its hardness, zirconia (especially solid polished zirconia) is non-abrasive, and recent research in the field indicates that, of the many restorative materials, solid zirconia is the safest on opposing teeth, and in some cases even safer than natural enamel.
Rice. 6a Fig. 6b Fig. 7a Fig. 7b Fig. 7c Fig. 7g
Ease of introducing modern digital technologies into the restoration process
Dental clinics and laboratories have already entered the digital age. Many procedures can already be carried out using digital technology, and their number is increasing every year. It so happened that for the first time the production of zirconium restorations became possible in digital form. As digital technology advances, CAD systems for zirconia restorations remain at the cutting edge.
This makes it easy to integrate these technologies into the manufacturing process of zirconia restorations - from planning (digital computed tomograms), virtual impressions and design (oral scanners) to monitoring the patient’s medical record (storing and sharing files related to the patient’s medical history).
In addition, digital technology simplifies the fabrication of zirconia restorations. The best illustration is the ability to digitally replicate an exact replica of a temporary restoration that satisfies the needs of both clinician and patient, and to create an exact replica of a definitive zirconia restoration with a predictable outcome.
Despite the numerous positive aspects of the material, many doctors have difficulty introducing zirconium into their own practice, and the reasons for this are clear.
The fact is that when zirconium was just gaining popularity, in restorations it was combined (like metal) with ceramics, sometimes even according to the same rules.
There is no chemical bond between zirconium and ceramic, so these restorations often chipped and cracked almost immediately after installation. This has forced specialists to use zirconium more carefully.
Currently, to circumvent this problem, many doctors resort to the use of monolithic zirconia restorations. Creating monolithic or minimally veneered zirconia restorations requires learning new skills (especially for dental technicians), and these skills are not limited to just the ability to work with digital technologies. In-depth knowledge of the material is a key factor in creating effective zirconia restorations. Minimal adjustments, the use of a water turbine, and varying degrees of cooling and heating in ceramic ovens are just a few of the skills that dental technicians must learn.
The second reason zirconium has been so slow to be integrated into dental practices is the lack of formal training in its use. In the age of the Internet, zirconium as a dental material has gained incredible popularity thanks to online advertising, but researchers in this field have lagged far behind.
Long-term clinical studies that began 5 years ago were outdated before they were published. Statistics regarding metal-ceramics do not provide clear conclusions in favor of choosing monolithic zirconium restorations. Due to the lack of clinical studies, many doctors are reluctant to popularize the material openly, even though they use zirconium in their practice. On the other hand, companies selling similar products further confuse doctors with slogans like “the only material that will give you the results you need.”
However, they have neither scientific evidence nor instructions regarding achieving this “necessary result.” The lack of formal educational programs creates a lot of misconceptions, for example that zirconium breaks down at low temperatures and has pronounced abrasive properties. None of these ideas are true, but they have all made experts suspicious of zirconium. No manuals have been produced on how to use the material, and it is unlikely that anyone will find a seminar or course that is not associated with a specific vendor or product. The result is that many people use zirconium, but no one is aware of its properties.
In conclusion, I want to say that, having worked for 7 years and installed about 15 thousand monolithic zirconium restorations, I am sure that zirconium is here for the long haul. Quite possibly, this is the material that every dentist dreams of. It can satisfy both the patient’s requirements - “without metal and grayness”, and the doctor’s requirements for strength, durability and aesthetics.
Without a doubt, zirconium will soon become one of the most widely used materials. All that is now needed for the successful introduction of zirconium into dental practice is the creation of training materials for specialists.
Temperature
The recommended parameters are set when programming the oven. Zirconium dioxide crystals expand during sintering, which significantly affects their light transmittance. The larger they are, the less light is reflected from the crystal faces in the crown. If you create a certain pressure and set the temperature to 2200-2300°C, the result will be cubic zirconia, with transparency resembling diamond.
In the usual version, heating for zirconium is about 1450-1550°C. The higher the temperature, the more transparent it becomes. But this feature also has a downside: due to the appearance of microscopic voids between the crystals, the structure becomes less durable. Thus, if when heated to 1450 °C the strength of sintered zirconium is approximately 1200-1400 MPa, then after increasing the mode to 1600 °C it decreases to 1000 MPa or more.
From all of the above, we can conclude that even in laboratories and small centers it is impossible to do without several ovens. First of all, in order not to interrupt the work process. So, when sintering a horseshoe (occurs within 18 hours), the remaining work will have to be delayed for a day.
You can insure yourself against unnecessary or unexpected expenses when buying a stove if you take into account a number of nuances in advance. For example, you need to immediately find out the cost of replacing heaters that have a certain service life.
Well-known large manufacturers offer their products on the market at prices ranging from 8,000 to 12,000 euros, with heating elements costing 400-500 euros per piece. It's easy to calculate the costs, especially when you consider that one oven may require 4 to 6 units. heating elements. You can find high-quality stoves with optimal operating characteristics and reliable assembly within 6,000 euros, where heaters cost from 150 to 250 euros. Some companies use both options.
Advantages of zirconium dioxide sintering furnaces
- The models use new technology. It ensures minimal time for high-temperature firing and sintering. The preparation is completed in just 120 -180 minutes.
- Zirconium sintering furnaces are easy to operate. They are equipped with a special touch screen on which operating modes are switched.
- Modern technologies allow you to quickly connect the oven to a computer and quickly transfer all the necessary information.
Sintering furnaces have compact dimensions - this allows them to be located even in cramped laboratory conditions.
For more information, please contact the contacts listed on the website. Specialists will not only help you choose a furnace for dentistry, but will also provide prompt delivery of equipment in Moscow and other regions of the Russian Federation.
Manufacturing and installation stages
Before any type of prosthetics, patients must undergo diagnostics - visual, X-ray (optimally if it is a computed tomography), functional (best modern on digital devices). At these stages, contraindications are excluded, the shade of new teeth is selected, and bite parameters are assessed. If we look at it step by step, the manufacture and installation of prostheses looks like this:
- taking casts (impressions) from the jaws or undergoing a digital scan on an intraoral 3D scanner,
- creation of a virtual model of the prosthesis: modeling takes place in a specialized computer program. Here, a plaster model is first scanned (which was obtained on the basis of casts), or digital “casts” are used - the latter option speeds up the progress of work,
- milling a blank from a single block of material: model data is sent to a computerized robotic machine, which mills the frame blank. Interestingly, the blank will be 20% larger than the real one - why is this necessary, read on,
- sintering (sintering in a furnace): at high temperatures the material gains high strength, but shrinks by 20% of the volume,
- painting, applying a facing ceramic mass for sintering or pressing ceramics,
- processing the product at high temperature,
- Trying on temporary cement (for a few days maximum),
- final fixation: the finished product is attached to natural teeth and implants using a permanent cement composition. But they can be fixed onto implants with miniature screws, although even at the modeling stage it will be necessary to provide small holes in several crowns. Then these holes will be closed with a composite composition.
Zirconium dioxide is such a strong material that it is not possible to process it manually or use it for casting. Therefore, the only suitable processing method is milling (sawing, cutting) using CAD/CAM systems.
Indications and contraindications for installation
Zirconium dioxide bridges are good because they have a minimum of contraindications - they can be placed on almost all patients, both on the front and chewing teeth. The main indication for prosthetics with a zirconium dioxide bridge is the absence of 1-5 teeth in a row. But along the edges of the empty space, at least one healthy tooth or root should be preserved, which will serve as supports for the prosthesis. Also, an indication may be the presence of several adjacent teeth, the crowns of which are destroyed by 50% or more (and the patient does not want to place single artificial crowns).
Why might a dentist recommend a bridge made of a different material (for example, ceramic)? Often zirconia is opaque and unnaturally white. And if you put a bridge from it on 3 front teeth, then the smile will be lighter in one sector and darker in the other. Therefore, it is better to install a bridge of 4 or 6 crowns on the front teeth. And on the chewing ones you can put a prosthesis made of 3 crowns, because they don't fall into the smile zone.
Contraindications for installation are inflammation in the oral cavity, tooth mobility and bruxism - in this case, strong and involuntary clenching of the jaws will damage the enamel on the antagonist teeth.
Don't know what type of prosthetics to choose?
We will help in the selection, advise where to read more information and compare types of prosthetics.
Consultation with an orthopedic doctor in Moscow clinics is free! Call now or request a call
Working hours: from 9:00 to 21:00 - seven days a week
If the bridge is planned to be installed on implants1, then it can be of absolutely any length - even from 12-14 crowns, i.e. will restore all teeth in a row. But the patient may need gum plastic surgery so that the edges of the prosthesis seem to “hide” under the gum. Or you can supplement the prosthesis with small areas of acrylic gum, then they will not need plastic.
Read on the topic: what is a dental bridge on implants and why is it better than a classic one?
