Dental crowns are classified according to the material used to make them, and, to a less degree, according to how they are made. These days, all crowns used in dentistry are either ceramic or metal-ceramic. These two makes differ in that one is completely ceramic, and the other has a metal core, comprising 50% of mass. The reason for even having two types of crowns for the same job is that metal is cheap, hard-wearing and easily fused with ceramic, reducing the fabrication cost by half when compared to pure ceramic crowns.
Metals used in making crowns are chromium, molybdenum and palladium. Non-metal crowns are made of zirconium, more specifically zirconium-dioxide (ZrO2), which is a type of sturdy ceramic material not to be confused with mineral zircon, which is used to make jewellery. Here, we mean a type of zirconium oxide which is not used only when making false teeth, but also to manufacture such materials as artificial diamonds or other ones requiring great durability. There is an option of making dental crowns out of gold and titanium alloy, which is practically all but gone from dentistry due to a high cost.
Crowns can be handmade, fabricated in a lab, or by the CEREC machine which we have at our clinic. Laboratory is preferred when we need to make smaller or bigger crown bridges, whereas we use CEREC machine if we need to make a piece of prosthetics swiftly; for example, a crown can be made in less than 30 minutes, which means that a patient will come with a damaged tooth and leave with a brand new crown within one visit. The benefit of using the CEREC machine or other 3D systems is that a crown is created according to a 3D scan, guaranteeing maximum accuracy.
At Cvejanović Clinic, the most predominant crown type used is zirconium, where ceramic is applied over zirconium caps, ensuring longevity and excellent appearance. At times we may use monolithic crowns made out of one piece zirconium, but these crowns are heavy and may resonate when they are in contact with the teeth from the other jaw. In our country there is almost no demand for pressed ceramic crowns, which are considered to be the most beautiful and brightest type, but are fragile because they do not have zirconium base, and are mostly popular in the USA, where they put emphasis on a dazzling smile. Another option is zirconium with ceramic put only on the front side, which is similar to our solution with spherically applied ceramic around the cap. Although this option is possible at our clinic, we do not use it, since there are no obvious benefits to this procedure.
Although metal-ceramic dental crowns are still present in dentistry, non-metal crowns have revolutionized the field. Only with the advent of non-metal crowns has it been made possible to have artificial pieces which are esthetically on par with healthy and well-shaped natural teeth. Metal-ceramic crowns refract light differently compared to natural teeth or ceramic crowns, and they are also a different shade of white. The cause of this effect is their grey metal core, and it is the most visible towards the tooth root, where metal is the closest to the surface, making a tooth dimmer. This is, however, primarily visible under intense light, and sometimes it does not even manifest itself.
Benefits of ceramic crowns
Another important advantage of non-metal crowns is complete bio-compatibility and preservation of tooth substance. Unlike metal which can produce allergic reactions, receding gums and the change in their colour, non-metal zirconium dental crowns cause no reactions in soft tissue, nor allergic reactions. In metal-ceramic crowns, the metal may come through in the collar region, resulting in a need to pull the gums over it in order to hide the metal edge. However, this may present a long-term problem in that the metal will gradually cause the gums to recede further, and the metal edge might, in time, become visible again. This last argument is the most important one when discussing an option to try and afford ceramic crowns.
It is worth mentioning that ceramic crowns require less contouring of tooth substance. Metal-ceramic dental crowns require recontouring of 1.5mm-2mm, whereas non-metal crowns only go as deep as 0.5mm-1mm. There is also an advantage when choosing the colour, because zirconium can achieve virtually any desired shade, meaning that if the chosen colour of the porcelain caps is A1, then the zirconium base may come in A1 shade as well.
Patients tend to say that the adaptation period for dental caps with metal ceramic crowns is longer and harder, that the feeling is different, and that the colour shade is somewhat different as well, whereas they get used to non-metal crowns in a matter of days. This may be ascribed to the fact that, unlike metal, zirconium is biocompatible. The metal in metal-ceramic dental crowns may cause galvanic currents in the mouth, severe irritation of soft tissue or gums, and sometimes allergic reaction in soft tissue. Using metal crowns will eventually cause receding gums and bone degeneration, as well as foreign body reactions in soft tissue. However, receding gums are also caused by natural processes, so we cannot say that metal crowns are a sole culprit.