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 restorative properties of zirconium. Below are the results of observation of 15 thousand monolithic zirconia structures in the form of various restorations, starting with dentures for the entire dentition and ending with single implants and abutments.
Tetragonal zirconium (after sintering) is stronger and stronger than metal. At the same time, it does not have significant flexible properties and is more prone to splitting than deformation. These properties can find good use in dentistry, and especially in implantology.
The key to producing a quality zirconia restoration is high precision. If the specialist follows the instructions, the resulting restoration will sit better and the lack of pliability will ensure durability. This is especially important for implant-supported restorations, since passive seating is of paramount importance for the efficiency and durability of their service due to the complete immobility of the implants (Fig. 1a, 1b) .
Zirconium does not deform under pressure, which often affects the structure during medical and dental procedures, and also poorly conducts heat.
This allows the creation of large-sized restorations that will not reshape in the ceramic oven as is the case with traditional porcelain-fused-to-metal 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.2a, b, c)
Undyed tetragonal zirconium is usually white in color and has a transparency similar to that of dental hard tissues. In the past few years, a more transparent material with a lower aluminum content has appeared. The final appearance of zirconia restorations is influenced by various staining fluids, staining and sintering techniques.
However, in general, zirconia restorations, especially monolithic ones, can give excellent results in terms of aesthetics without compromising their strength (Fig. 3a, b) . In the case of a veneered zirconia structure, the basic structure constitutes the main part of the structure and is robust; only minimal use of the veneer for shading and the addition of pink gingival ceramics is required (Fig. 4a, b) . The lingual surfaces and the inner surface of the pons of the bridge can be completely left without veneer, since nothing needs to be hidden, as in the case of a metal framework.
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The round is the main part of the structure and is durable, only minimal use of veneers for shading and the addition of pink gingival ceramics is required (Fig. 4a, b) . The lingual surfaces and the inner surface of the pons of the bridge can be completely left without veneer, since nothing needs to be hidden, as in the case of a metal framework.
Monolithic zirconium restorations also give good results from the point of view of aesthetics in a limited space, and not as a compromise option, but as a good aesthetic solution where this would have been impossible in the era of metal ceramics (Fig. 5 a - d) .
Solid zirconium also provides a conservative preparation. For good esthetics, the preparation volume should be approximately 1 mm of tissue. This enables the practitioner to preserve most 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 in the 70s. XX 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.
The properties of zirconium, which are explained by its atomic bonds, make this material quite biocompatible. The high density (up to 6.1 x 10³ kg / m³) and high chemical resistance ensure a low accumulation of bacteria on the monolithic parts of the restoration, even in poor oral conditions.
Good wear resistance guarantees a high survival rate of the restoration. According to the data of several orthopedic dentists from 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, zirconium (especially monolithic polished zirconium) is non-abrasive, and recent research in this field indicates that of the numerous restorative materials, monolithic zirconium is the safest for opposing teeth, and in some cases even safer than natural enamel.
Dental clinics and laboratories have already entered the digital age. Many procedures can already be performed using digital technologies, and every year there are more and more of them. It just so happened that the production of zirconium restorations for the first time became possible precisely in digital form. As digital technology advances, CAD systems for zirconia restorations remain at the forefront of progress.
This allows you to easily integrate these technologies into the manufacturing process of zirconium restorations - from planning (digital computed tomograms), virtual impressions and designs (oral scanners) to monitoring the patient's medical record (storing and exchanging 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 provisional restoration that meets the needs of both clinician and patient,
as well as creating an exact replica of the final zirconia restoration with predictable results.
Despite the many positive aspects of the material, many doctors find it difficult to introduce 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 ceramics, so such restorations often chipped and cracked almost immediately after installation. This prompted experts to use zirconium more cautiously.
Nowadays, to get around this problem, many doctors resort to the use of monolithic zirconia restorations. Creation of monolithic or minimally veneered zirconia restorations requires training in new skills (especially for dental technicians), and these skills are not limited to the ability to work with digital technologies. An intimate knowledge of the material is a key factor in creating effective zirconia restorations.
Minimal adjustments, the use of a water turbine, various degrees of cooling and heating in ceramic ovens are just a few of the skills that dental technicians must learn.
The second reason zirconium is so slow to integrate into dental practices is the lack of formal training in how to use it. In the Internet age, zirconium has exploded in popularity as a dental material through online advertising, and researchers in the field have lagged far behind.
Long-term clinical trials started 5 years ago were outdated even before they were published. The statistics regarding cermets do not provide clear conclusions in favor of the choice of monolithic zirconium restorations. Due to the lack of clinical studies, many doctors do not want to openly popularize the material, even though they use zirconium in their practice. On the other hand, companies selling similar products confuse doctors even more with slogans like "the only material that will give you the result you want."
However, they have neither scientific evidence nor instructions for achieving this "necessary result." The lack of official educational programs creates a lot of misconceptions, for example, that zirconium degrades at low temperatures and has pronounced abrasive properties. None of these beliefs are true, but they all made experts suspicious of zirconium. No tutorial has been released on the use of the material, and it is unlikely that anyone will find a seminar or course that is not related to a particular supplier 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 after working for 7 years and installing about 15 thousand monolithic zirconium restorations, I am sure that zirconium is serious and for a long time.
Quite possibly, this is the material every dentist has dreamed of. It can satisfy both the patient's requirements "without metal and grayness", as well as the doctor's requirements for strength, durability and aesthetic component.
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.
