In Ralev Dental clinic we have an innovative system for fabrication of crowns, bridges, inlays, onlays, overlays and endocrowns from pure ceramic in one single visit in the clinic withtout the need of a temporary crown and waiting the standart period of one week for the fabrication of the construction from the dental technicians. (read more…)
Dental crowns are two main types: whole crowns (jacket) and partial crowns ( endocrowns, inlays, onlays, overlays, as well as veneers) .
These complex names can be clarified easily to the patient according to the size of the damage to be restored.
Jacket crowns – these are the classic type of crowns, where the tooth is prepared under the form of a little tooth stump on which the crown is cemented. It covers it completely and restores the normal form, function and aesthetics. Jacket crowns are almost always used in the manufacture of dental bridges. With dental bridges at least two crowns are made on the adjacent teeth, to which the missing tooth is attached.Jacket crowns are made for teeth with a removed nerve and alive teeth. They are the universal, safest and most commonly used option for recovery of major damage of the teeth and restoration of missing teeth (construction of bridges).
Endocrowns – These are the crowns made for teeth with a removed nerve. They belong to the partial crowns, because the tooth is not prepared as with jacket crowns. In this type of crowns the healthy parts of the tooth are shaped appropriately to enable the made in the dental laboratory endocrown to adhere to the tooth.
Endocrowns have a specific shape, and reach deeply in the core of the tooth at their base. They are glued adhesively to the rest of the tooth and are not so invasive in nature.Overlays – These are semi-crowns, which are made for alive teeth and cover the entire chewing part of the tooth, but without reaching the gum and without grinding healthy parts of the tooth.
Inlays and onlays – These are the smallest prosthetic restorations. They are analogous to dental fillings and are used for tooth cavities and small damage of the teeth.
Veneers – they can be two main types – classical veneers (made on the outer visible surface of the front teeth) and occlusal veneers (made along the chewing surface of back teeth – premolars and molars). Classic veneers are used for aesthetic correction of the appearance of teeth, while occlusal veneers are used to lift the bite and correct abraded teeth.(Read more about classic veneers …).
Dental Bridges – They are complex devices used to restore missing tooth/teeth. They may be of various sizes – from a 3-part bridge (restoration of one missing tooth) to 16-part structures, restoring teeth of the entire jaw. Dental bridges can be several types:
Adhesive bridges – the missing tooth is fixed to the adjacent teeth by glass fiber and composite.
These are the main types of dental prosthetic restorations. They can be made of different materials and that is where the main difference between them is. .
Crowns, bridges and semi-crowns can be divided into two main types according to the material they are made of – metal-containing and metal-free.
Metal-containing crowns: metal crowns, metal and plastic crowns, cermet (metal-ceramic) crowns and bridges.
Metal and metal and plastic crowns are classic crowns and bridges used mainly in the past. They are rarely used today, because they have unaesthetic look with gray or golden colour.
Metal-ceramic crowns and bridges – until recently they were the most frequently used and distributed devices, used for the restoration of missing or damaged teeth. This is due to their structure. They are made of a metal base, which gives strength, and a ceramic coating, which ensures the aesthetic look and makes them difficult to distinguish from natural teeth. Metal-ceramic devices are affordable in Bulgaria.
The disadvantages of metal-ceramic crowns and bridges are:
• Availability of gray metal edge at the base of the crown, which reaches the gum or enters into it (in non-threshold crowns). The metal edge releases metal ions, which over time enter into the gum and change its colour – there is grayish discolouration of the gum under the crown.
• The metal ions may also be caused by oral galvanism – the saliva in the oral cavity is an electrolyte and when there are amalgam fillings, metal or metal-ceramic crowns in the mouth, made at different times, an exchange of ions may occur between them, which leads to mucosal damage and unpleasant sensations such as burning or metallic taste in the mouth.
• In some cases allergies to the metal alloy, used for making metal-ceramic crowns and bridges, develop.
• Another feature of metal-ceramic crowns is cementing them. It is made with cements that bind only macro mechanically to the crown and the tooth, which under certain circumstances can lead to detachment of the crown.
• The metal base of the metal-ceramic crowns does not transmit light as natural teeth do, and with bright light, there is gray shade in the middle of the crown that reduces the aesthetics (darkening of the crown).
• For metal-ceramic crowns and bridges, the strength of the relationship between the ceramics and metal base is about 70 MPa and in some cases the ceramics can fracture. All these drawbacks are avoided in metal-free crowns.
Metal-free (ceramic and zirconium) crowns and bridges – Porcelain (IPS e.max, Lava TM, Alumina) and zirconia crowns with ceramic coating.
With the advancement of technology and development of new materials, a replacement to the metal base in the metal-ceramic crowns has been found in order to avoid its weaknesses. This material meets three key conditions: an extremely thin layer (0.3 mm in thickness) of the base; the thin base does not deform in the implementation of masticatory forces, and the third condition is that it has the same colour of the teeth. The material that fulfills all three conditions is the mineral zircon. In dentistry its compound – zirconium dioxide (ZrO2) – is used.
Its advantages are:
• Its colour is similar to the colour of natural teeth which ensures high aesthetics.
• It is the hardest material used in dentistry – hardness of about 1000 – 1200 MPa and it is virtually indestructible, even in patients with nocturnal clenching of the teeth.
• It does not give gray discolouration of the gums as the metal in the metal-ceramic devices, does not cause allergies, does not lead to galvanism, does not retain dental plaque, and does not discolour.
However, “the downside of zirconium” is its opacity. (*Natural teeth are made of two layers – enamel and dentine. The enamel, the surface layer, is transparent (clear) to a great extent. The dentine is located under the enamel and it is opaque, and it is the dentine that in reality gives the colour of the teeth. This configuration of the enamel and dentine leads to the natural colour and appearance of the tooth.)
The colour of the zirconia crowns and bridges match the colour of natural teeth, but it is opaque, which results in that the teeth look “artificial”. This effect is very popular and sought after among celebrities in the US. Because of this drawback, the zirconia crowns are used mostly in back teeth, which provide exceptional strength and high aesthetics.
The problem regarding the transparency of the zirconia crowns and bridges is resolved through using the zirconium as a basis (similar to the metal in the metal-ceramic crowns) and ceramics on top.
These are the so-called zirconium – ceramic restorations.
They combine the extremely high strength of the zirconium skeleton with the high aesthetics of the ceramic coating, which makes artificial teeth virtually indistinguishable from natural, while at the same time all the disadvantages of the metal-ceramic devices have been eliminated.
The strength of zirconium allows the production of large bridges of up to 16 teeth – which is the maximum for a jaw. Zirconia – ceramic devices are the best possible choice for prosthetic restoration in the rear sections of the teeth and for missing teeth, because the zirconium skeleton is strong enough to withstand the load during chewing, and the ceramic coating gives perfect aesthetics.
In summary, it can be said that zirconia – ceramic crowns and bridges are similar to metal-ceramic ones, with the only difference that the metal base is replaced with zirconium and all its flaws except one are eliminated – adhesive cementation.
Both zirconium and metal adhere to the tooth stump only macro mechanically through the cement, due to which the strength of the bonding is insufficient and these materials are only suitable for recovery of jacket (whole) crowns and bridges.
Surveys and research of a material that has the qualities of the natural tooth tissue (• sufficient strength – to withstand masticatory forces (• very high aesthetics – look completely natural and no different from natural teeth in colour, tint, transparency and translucency) and simultaneously adheres firmly to the patient’s teeth, led to the discovery and deployment in dentistry of the so-called lithium-disilicate ceramics (porcelain) – IPS e.max ceramics.
These are called crowns of pure ceramics.
IPS e.max ceramics represents inherently press ceramics. There are two varieties – compressed blocks from which the crown is cut by a special CAD/CAM machine and the other option is in powder form, which is mixed with liquid and then is applied layer by layer and treated in a special furnace.
Lithium-disilicate ceramics meets all the requirements for materials in dentistry and is close to the qualities of natural teeth.
It provides optimum aesthetics – there are different degrees of transparency, which gives a natural and “alive” appearance of the teeth. In addition, the colour can be modified with special paints and thus, restorations undistinguishable from natural teeth are achieved in patients with non-standard colour. Spots and cracks, specific to the teeth of an individual, can be ‘drawn’ on crowns and veneers of IPS e.max ceramics, thus fully mimicking natural teeth.
Lithium – disilicate ceramics has sufficient strength – elasticity is about 400 MPa in comparison to the metal ceramic which is about 70 MPa, and zirconium crowns – 1000 MPa. Therefore, all kinds of single crowns can be made, as well as three-part bridges in the area of the front teeth without the need to have a metal or zirconium as a base of the crown.
The third and most important advantage of the crowns of pure ceramics (IPS e.max) is the possibility of adhesive cementation. The inner surface of the crown and the tooth stump are treated with special substances, which prepare the surfaces for bonding to the cement. Thus, a high strength bond is achieved between the tooth stump, the cement and the crown.
Besides the standard crowns and bridges, these qualities of the pure ceramics (IPS e.max) allow the production of micro invasive ceramic dental restorations – – endocrowns, inlays, onlays, veneers and overlays.
Endocrowns – They are inherently a micro invasive alternative to standard jacket crowns. In teeth with removed nerves, where a small part of the natural tooth remains, placing of a post in the root canal and construction of a tooth stump are required. After appropriate preparation, a jacket crown is placed. The natural tooth is grinded simultaneously from two sides – from within (to remove the nerve) and outside (to achieve the conical shape of the tooth stump). After the root canals are treated and filled, a post and a tooth stump are not necessary with endocrowns and the remaining healthy parts of the tooth are smoothened appropriately to maintain the natural tooth. An impression is taken of the appropriately prepared tooth and either in the dental laboratory, or with the help of CAD/CAM, an endocrown is made of pure ceramics (IPS e.max). It is stuck inside the tooth by adhesive cementing to its walls, and the space, in which the nerve was located, is used as an additional retention chamber. Hence, their specific name – endocrowns – because they are stuck inside the pulp chamber. The endocrowns are micro invasive – they aim to retain the natural tooth without grinding.
Their aesthetics and strength are similar to that of the jacket crowns. Another advantage is that even after time or if there is a problem with the tooth or the endocrown, a standard crown can be made, which is not possible vice versa.
Inlays, onlays, overlays– Unlike endocrowns, inlays, onlays and overlays are made for alive teeth. The difference between the three is only the size of damage that is being restored with them. They are an alternative, not only to the crown, but to the photopolymer fillings, making them superior in strength and aesthetics. (Read more about inlays …)
In conclusion, the lithium- disilicate ceramics (pure ceramics) and the zirconia devices possess qualities as close as possible to those of natural teeth, with practically no serious drawbacks and have already replaced the metal-ceramics as the main material for making crowns and bridges worldwide.
Crowns and bridges made of them have a very high strength, optimal aesthetics and reliable bonding, but in addition are also micro invasive.
The choice of what kind of a crown or bridge is best in order to restore a dental defect is made by the dentist and is recommended for the patient, whom is provided with an option for a different type of device.
This is not the case when selecting the material from which the device is to be made. A major factor for Bulgaria is the financial side of the issue, and due to higher prices of the materials and sophisticated technology of manufacturing, the cost of these devices is two to three times higher than that of metal-ceramic crowns and bridges.
However, the price should not be leading in the choice of material for making crowns and bridges. This is because these devices stay in the mouth for over 10 years, and their production is a planned procedure which can be done months ahead.
The choice of porcelain or zirconia crowns is a right solution and long-term investment in the health and beauty of person’s smile.