Dental Crowns-What are They and Why are Used
Für eine künstliche Krone wird der natuerliche Zahn präpariert, das heißt, sie wird bis ca. 0,5 mm unter den Zahnfleischsaum rundherum beschliffen. Am Zahnhals wird eine meist stufen oder hohlkehlförmige Stufe gefraest.
Vor dieser Praeparation findet eine Zahnfarbenbestimmung statt damit die neu zu erstellende Krone harmonisch in den Restzahnbestand eingegliedert werden kann.Auch bei der Kaufläche beziehungsweise Schneidekante muss so viel abgeschliffen werden, dass genügend Platz zu den Gegenzaehnen ist .
Dieser so präparierte Zahn wird mit Abformmasse (Silikon oder Polyether)vom Zahnarzt abgeformt. Dieser Arbeitsschritt gehoert zu den wichtigsten Schritten ueberhaupt bei der Herstellung von Zahnersatz, da sogar kleinste Fehler in den wenigsten Faellen nach Herstellung der Arbeitsmodelle korrigiert werden koennen.
Für eine künstliche
Mithilfe dieser Abformung kann der Zahntechniker dann ein Modell erstellen, auf dem er dann den Zahnersatz herstellt. Typischerweise werden gering expandierende Hartgipse, hauptsaechlich “natuerliche Gipse” dafuer verwendet, damit der darauf hergestellte Zahnersatz eine hoechstmoegliche Praezision erreichen kann.
Unter anderem gehoert GC Fujirock zu den besten, das heisst praezisesten und dimensionsstabilsten Hartgipsen, welcher auch in unserem Zahntechiklabor verwendet wird.
Moderner Zahnersatz wird hauptsaechlich aus Vollkeramikmaterialien wie Lithiumdisilikat, Zirkondioxid oder Feldspatkeramik hergestellt. Der Vorteil zu Metallkeramikrestaurationen liegt in der guten Lichtdurchlaessigkeit und Biokompatibilitaet.
Künstliche Kronen können auf Zahnstümpfen, aber auch auf Zahnimplantaten eingegliedert werden wobei auf Zahnimplantaten verschraubte wie auch zementierte Restaurationen einsetzbar sind.
What are dental crowns and bridges?
Dental crowns and bridges are common procedures nowadays, especially with the development of new dental materials and technologies followed with patients’ higher esthetic demands. Sometimes, patients see these prosthodontics at their friends and family and expect the same dental procedures in order to get nicer and more harmonic smile for themselves. It is crucial for patients to understand the types of restorations available on the market, indications, and contraindications for its application, the functional and esthetical properties, so as the price and durability of such restorations.
What are dental crowns?
The most simple way to describe a dental crown is a “cap” that covers prepared tooth or implant. Indications for these restorations are different:
- Extensive destruction of hard dental tissue
- Extensive dental fillings that need to be removed
- Extensive caries lesions
- Restorations after endodontic treatments
- Changing the color of the tooth
- Changing the position of the tooth
Depending on the individual patient’s situation and specific indication considering over-all dental analysis, different types of crowns may be suggested. When talking about the crowns, it is almost impossible to mention Inlays, Onlays, Overlays and veneers. Named restorations cover the tooth partially, depending on the location and proportions of tooth destruction. On the other hand, veneers are not necessarily indicated to reconstruct the lost dental tissue, but more often, to change the color, size, shape and/or position of frontal teeth.
What needs to be done in order to get a dental crown?
After detailed anamnesis, clinical examinations and dental analysis first step is tooth preparation. For a vital tooth, local anesthesia is applied prior tooth preparation, while non-vital tooth does not need anesthetics. Preparation is performed with a high-speed handpiece and diamond burs. After the tooth is prepared the next step is taking impressions. Impressions might be analog, taken with a conventional method that includes silicons for the jaw in which the tooth is prepared for the crown, and another impression of the opposite jaw taken by alginate. A contemporary alternative to this method for dental impressions is intraoral scanning. There are numerous companies on the market that has their own equipment for digital dentistry, but the well-known is CEREC.
These scanners have the shape of bigger toothbrush and is able to make the most precise scans of the entire dental arch. Scans can be sent to a dental laboratory or can be connected to in-office milling and grinding units for further fabrication. Thanks to digital dentistry, entire process in the fabrication of a crown can be performed in 15-30 minutes, while the conventional methods might take days for complete restoration to be finished. Whatever method for production is applied, the final restoration is nearly the same. The only difference is the higher precision of digital dentistry. There are many different units for digital dental procedures. In our office, we use very modern Sirona CEREC Ac Bluecam, Sirona Cerec 3 and Sirona inLAB MCXL that provides the entire process of in-office production, from scanning dental arches to planning, fabrication, and cementation. You can read more about our dental laboratory at the following link here.
More detailed explanation regard entire side-chair, in-office production of crowns and bridges is given in the video on the YouTube channel of Tooth&Go Academy. You can see simplify version with the following graphic explanation of the entire procedure from tooth preparation to scanning and milling with all Sirona units used in our Clinic here.
Besides this full-digital procedures, there is also an alternative method for crown fabrication that include conventional methods in taking dental impression and production of a model of patients’ teeth that is scanned with Sirona inEOS X5 scanning unit.
The next steps include the design of future crown in Sirona software and its production in milling unit, for more precise fabrication than with conventional methods for production of ceramic fused to metal crowns. The detailed explanation of this process is available here.
There are a great number of materials that can be used for the crowns. From standard ceramic fused to metal crowns to full ceramics and zirconia. Modern dentistry sets full-ceramic so as zirconia as a golden standard for dental restorations. Zirconia is considered as the material of choice mostly for dental bridges with its great esthetical properties and high flexural strength. In our dental clinic, we use a few different types of zirconia blocs, from the company called DentalDirect. Zirconia is great material for full ceramic crowns but mostly for dental bridges. Another great solution, when talking about single crowns, is IPS e.max, which is lithium disilicate glass-ceramic material, usually indicated for full ceramic crowns, so as for veneers, inlays and onlays. Another type of material that we use for full ceramic crowns, but also for veneers and inlays is VITA Suprinity, a glass-ceramic reinforced with 10% zirconia dioxide that has great optical properties. VITABLOCS Mark II is feldspar ceramic, the most clinically tested one, and TriLuxe blocks, also a feldspar ceramic, with its special multichromatic properties, already integrated into the bloc, so they can imitate the full spectrum of different shades from tooth’s neck to its incisal edge.
After the crown is produced, it should be tried in the patient’s oral cavity for the last check-up and any additional changes or improvements. In this phase, patients can suggest all small changes in the shape of the crown so as the color or additional shading. When the both, patient and the dentist, are satisfied with the final product, the crown can be temporary cemented and the patient is free to go with an obligation to come back for check-ups every 6 months to 1 year.
When talking about the crowns, it is important to mention that besides single crowns that are replacing a missing structure of the existing tooth or just change its visual properties, there are also specially designed crowns for combined prosthodontics solutions.
These types of crowns are intended to retain the partial dentures and are made of a metal alloy whit specially designed seat for dentures while ceramic is fused to its outer surface for esthetical appearance. Besides these specific crowns, there are also crowns on implants. The difference in the fabrication of these crowns from the conventional crowns cemented on the prepared tooth is that impressions are taken over metal abutment, fixated to the implant. Except this, another difference is related to fixation of these crowns, since they can not only be cemented but also screw-retained to the implant.
What are Dental bridges?
When one or more teeth are missing, there are several options how this deficiency can be resolved. In most cases, the best solution includes implant placement. Other options include prosthodontics, fixed or removable. Fixed prosthodontics are, in fact, dental bridges. Like in real life, this also applies to dental bridges, there should be two “shores” that will hold both sides of a bridge, that will fill the space of missing teeth with new crowns, called pontics. This means that you need to have at least two stable teeth that will be used as the anchors, known as abutment teeth, for the new bridge. Sometimes, in cases where a greater number of teeth is missing, more teeth need to be included as anchors that will hold a dental bridge in a solid, stable place.
Planning dental bridges is a complex procedure that includes detailed clinical examination and analysis of radiographs. This procedure also includes the adequate discussion with patient’s wishes and expectation regarding their future look of the dental arch and more importantly its function.
The procedure for design and production of a dental bridge is very similar to one related to single crown production. A great advantage of modern dentistry is a digital dentistry with special software like Digital Smile Design (DSD) that can create the most harmonic individual smile for each patient.
With analysis conducted with such software, the future prosthodontics solutions can be visible in digital form for the patient and they can make suggestions for every step of the restoration even before the final decision is made. Teeth preparation is the first step in the production of dental bridges when all preparations of surrounding tissues are finished. Impressions of prepared teeth and soft tissues can be taken by conventional dental materials or with digital technologies, in the same manner previously described for single crowns. The same goes for the entire process of production and materials that can be used: ceramic fused to metal, zirconia and pressed ceramics.
It is important to understand that planning of prosthodontics therapy, whether it includes single crowns or more complex solutions that include implants and/or dental bridges, needs detailed analysis with your dentist in order to get a fully functioning and esthetical final result that will last for many years.