In case of teeth that are extensively affected by decay, with wide fillings, or of those that have been endodontically treated (having the nerve removed), the obturation (cavity filling) is no longer effective as the thin walls of the tooth don’t provide streangth anymore and there is the risk of fracture. Dental crowns are an excellent way of rehabilitating these teeth and, also, of yielding the necessary resistance.
Dental crowns are coatings which cover the tooth that has been prepared, restoring its initial shape and dimension. They cement on the naturally existent teeth and can be removed only by the professional dentist. A dental crown possesses an aesthetic role also, correcting the shape or position of the tooth on which it is applied.
Before applying a crown, the affected tooth must be treated by removing the eventual decays and by consolidating it with a cavity filling. If the nerve has been taken out some time beforehand, it’s recommended to do a retroalveolar radiography (on that precise tooth) to see how the tissue around the root has been healed. Moreover, if the tooth has got thin, weak walls it’s indicated for it to be strengthened with one or more fiberglass pivots, or with a corono-ridicular metal device (DCR), created in the lab. Once the ‘foundation’ is healthy, the next step is to cover the tooth with a crown that offers the necessary streangth for it to bear the mechanical requests to which it is permanently subjected during mastication and therefore it is protected of fracture risk.
The dental bridges treat missing teeth spaces. They functionally and aesthetically restore the missing of 1-3 teeth and they correspond to more crowns united. Marginal crowns can be attached tot the neighbour teeth , on one site and another of the edentulous space or can be assembled on two or more dental implants.
If the missing tooth is not replace, the neighbour teet have the tendency to rotate or migrate towards the empty space, with the result of an abnormal occlusion. The disequilibrium caused by the missing teeth can evolve towards gingival diseases and the dysfunction of the temporomandibular joint.
Fixed dental bridges cannot be taken out of the oral cavity, as can be done with the removable denture.
Benefits of the treatment with crowns or with dental bridges:
- Immediate results;
- Replace the missing teeth;
- Improve face physiognomy;
- Are invisible, undetectable among the other natural teeth;
- Easy and rapid to adapt to;
- The force of masticator muscles will be uniformly distributed on as many teeth as possible;
- Are biocompatible and do not render allergic reactions in the case of zirconium and ceramics usage;
- Are easy to maintain, just as natural teeth (by making use of the toothbrush, of an interdental brush and of dental floss);
- Are resistant in time;
Types of Dental Crowns and Dental Bridges
The most utilized in the current practice are:
- Acrylic crowns are temporary, provisional on a limited period of a few days or weeks;
- Composite Crowns: have low streangth, are still provisional;
- Ceramic Crowns: for a long term treatment.
The crowns can be made of porcelain (ceramics) on a metal or zirconium structure, or can be entirely ceramic.
The last generations of porcelain works on a zirconium structure or those entirely ceramic, are created to be invisible, undetectable among the other natural teeth. They are an excellent combination of endurance, biocompatibility and naturalness. They are well tolerated by the organism, do not yield allergic reactions nor colour the gum where it’s contacted by the crown (the metal gingival tattoo can appear at crowns on a metal base).
Dental crowns and bridges are individually fabricated for each patient, according to the clinical situation, the therapeutic necessities and the patient’s wishes, so as to achieve the result of a beautiful, natural smile that everybody desires.
It’s important to point out that the daily activities of patients are not affected by the temporary lack of one or more teeth until the crown is finalized, as a provisional acrylic crown is immediately fabricated.
The clinical and laboratory phases can last between 1-5 weeks, depending on complexity.
How to choose the type of dental crown?
These are the traditional option, currently used at the dental practice. They are made of a metal cape (the core), over which ceramics is added through burning in a special oven at high temperatures. The metal is completely covered by porcelain and it’s not visible on the exterior. The modern techniques use CAD-CAM technology and by means of a computer the metallic cape is realized through computerized milling, which eliminates human errors and assures intimate micronic adaptation.
The advantages of metalo-ceramic crown
- Increased endurance
- Good aesthetics;
- A wide variety of colours and pigments are available in order to copy the tooth’s natural colour;
- Accessible prices;
- Facile technology employed to attain them.
The disadvantages of metalo-ceramic crown:
- The aesthetics is not totally reached because of the metal supporting structure which blocks the light from passing through and doesn’t allow the attainment of the teeth’s natural translucence.
- The metal’s presence can give allergies, only gold being biocompatible. The rest of the dental alloys have got allergy risk through the presence of Cr, Co, Ni, etc.;
- Over time, there may appear the black colouring of the gum (metal tattoo) through a migration phenomenon of the metal ions from the inside of the crown, to the neighboring, gingival tissues. This problem brings a major aesthetic deficit and it’s difficult to solve. Even if the coating crown is changed with one without metal, the coloration remains.
- The phenomenon of electric file can appear if inside the mouth more types of metal alloys are used. The result is that a metal taste is enhanced, whereas the food taste is lost; also it is possible to appear black pigmentation of the lips, tongue, cheeks and gums.
- By the gum’s retraction, which appears through a natural process as the years go by, the metal edge of the crown can be noticed and it looks like a black line. This inconvenience can be eliminated by using cermet-metalo ceramic with a ceramic verge (1 mm of the cape’s metal is removed at the gum’s level and instead of it a special ceramics with high firmness is added).
To this tipe of crowns the ceramic id added over a zirconium core. Zirconium is a chemical element of the metals’ group and it is used in dentistry under the form of zirconium oxide due to its qualities: streanght, biocompatibility, white colour.
The zirconium cape is obtained through CAD-CAM computerized milling of a zirconium oxide block.
The advantages of ceramic crowns on zirconium supporting structure:
- The major advantage is the high aesthetics. The crowns are invisible, undetectable among the other natural teeth. The metal, which is black, is eliminated and it is no longer necessary for the technician to use an opaque ceramics to mask the metal. Zirconium is white, lets the light pass through it and also allows the attainment of crowns with translucence similar to the natural tooth;
- Zirconium is tough and has increased endurance;
- Zirconium and ceramics are biocompatible, don’t react with the organism, do not give allergies, do not colour the gum in black;
- High precision and adaptation through the computerized processing techniques.
The disadvantages of crowns on zirconium supporting structure:
- The high costs;
- Having to turn to a specialized laboratory to manufacture them.
How to choose between all ceramic crowns and those on zirconium supporting structure?
In making the choice there must be considered:
- The colour of the natural tooth that needs to be covered. If it is darker than normally due to nerve removal, previous metallic fillings or if it has a metal DCR, then it’s better to choose the option with the zirconium supporting structure which will mask the black colour of the remains. The integral ceramics is more translucentand lets the colour of the underneth tooth to be seen.
- The area in which the tooth that needs reconstruction is. Basically, for the frontal part it is better to choose the integral ceramics because the light falls directly on the tooth and the translucence of the crown it is important to estehetics; also the mastication force is reduced. However, modern materials have progressed so much that today, all ceramic crowns can be attained on the sides, too.
All Ceramic Crowns
Integral ceramic crowns do not use metal or zirconium capes, but are totally made of ceramics. They are realized through pressing, milling or burning and they reproduce the natural shades of the teeth perfectly, also their translucence and texture is attained to the smallest details. They are the most aesthetic of all types of crowns, practically invisible among the natural teeth. They allow the light to pass through them; precisely as the natural tooth does (the zirconium blocks a small part of the light).
There is a great diversity of materials and techniques for obtaining integral ceramic crowns. In a decreasing order of the aesthetic gain achieved they are:
- Feldspathic ceramic crowns: they are obtained through successive burning of ceramic layers on platinum foil or on a model of refractory mass. They are the most aesthetic ones, of a distinguished naturalness;
- Crowns attained through pressing on a pressed ceramic nucleus. In order for them to last, successive layers of ceramics are burned. They have a very good aesthetics.
- Crowns obtained through computerized CAD-CAM milling: have the advantage of being rapid, are made in the dental practice in one visit only. The computer carves the crown in a ceramic block, which afterwards can be painted to imitate the neighboring tooth. It is recommended to be applied to the teeth from the back, as the aesthetics is modest.
The advantages of integral ceramic crowns:
- They are the most aesthetic dental crowns;
- They are biocompatible;
- They have increased streangth if they are fixed correctly through an adhesive technique. Their cementing is special, with the aid of several materials, not just the actual cement: phosphoric acid, hydrofluoric acid, silane, bonding, cement-based composit chosen to imitate the tooth’s colour. Being correctly cemented, the integral, ceramic crown performs a chemical connection with the tooth’s structure, becoming a whole. The risk of fracture is minimal.
The disadvantages of integral, ceramic crowns:
- The high costs;
- The pretentious cementing technique;
- The necessity of a modern laboratory, specialized in high estehetics;
- Bridges cannot be made, only single crowns;
- Cannot be performed on dark coloured teeth.
The durability of dental crowns over time:
All types of ceramic crowns, regardless of the material they are made of, have increased streangth and do not break in case of normal mastication. There are a multitude of ceramic producing firms on the market, with varied prices, different aesthetic qualities and distinct endurance. The price of a dental crown will reflect the quality of the material used, the capability and competence of the laboratory and of the dentist.
Under the conditions of respecting the correct realization indications and techniques, the longevity of these dental works is very good.
The studies published in relevant literature claim that there is a very good longevity of these restorations, the approximate lifetime being between 8 and 12 years.
If you have got prosthetic works (crowns, bridges) you must respect a few rules, which will prolong your tooth’s life:
- Do not break hard foods between the teeth: nut shells, bones, etc.
- Do not open bottles or other objects with your teeth; avoid biting hard fruit and use a knife to cut them instead;
- If you have bruxism (teeth clenching and grinding during the night) wear a mouth guard for protection;
- Daily hygiene must be impeccable regarding both the natural teeth and the crowns. Floss every night and use interdental toothbrushes, according to what the dentist recommends;
- Do not forget about professional cleaning (scaling, brushing, and airflow). It is recommended once every six months, or more often if needed, given your gums’ condition and given the efficiency of individual brushing.