All-ceramic crowns – Metal free ceramics
Thanks to advanced technology it is now possible to make a strong and lasting bridges without using a metal base.
These bridges, made entirely from ceramic (metal free crowns) on the front teeth fully compensate the natural aesthetic appearance of teeth, however, due to limitations of the material in terms of the elasticity of all-ceramic crowns, bridge can span the space of a single tooth, which means that the bridge can contain a maximum of three segments. For the side bridges, where the teeth have larger ranges we are using metal free crowns with zirconium bases. Zirconium is the white color and high purity material (1300MP). Zirconium was first used in space technology, and after years of testing has found its use in medicine in orthopedic surgery (femoral head in hip prosthesis). Numerous studies have shown that Zirconium has no damaging effect on the organism and that in contact with the soft tissues and the bone does not cause any adverse or allergic reactions.
Except for making the bridges, zirconium can be used for the production of the implant and for the Composite. The degree of tooth grinding for the placement of metal free crowns is far less than for the crowns with a metal frame, due to the fact that a high resistance to the forces of chewing is achieved with a thickness of only 0.4 mm. The edge of these crowns are perfectly polished so it have an excellent relation with the gum tissue. The surface of the metal-free crowns is resistant to acids, it does not have micro-cracks and thus impedes the accumulation of sediments, and consequently facilitates cleaning and prevents gum disease and periodontal tissue.
The advantages of using the ceramic crowns:
- the longevity
- the extreme strength
- the excellent biological compatibility
- the less conducted heat and metal cold
- the full metal-free construction
- no black edging along the edge of the gum tissue
- the high translucency
- the structure of zirconium can be individually painted according the color of the patient's teeth
The procedure of making the all-ceramic crowns:
By computer scanning of the plaster model (plaster cast model based on fingerprint taken by the doctor), a technician first models the structure in a special program and then carves it out of a zirconium block. That structure is then applied with the layers of the ceramic which gives a tooth the natural look. Thanks to its whiteness on which the ceramic layers are applied to, the Zirconium gives a vivid and natural color to the teeth.
Types of materials used for production of all-ceramic crowns
Zirconium is a very hard ceramics that is used as a strong base for construction of metal free ceramic superstructure. Zirconium that is used in dentistry is zirconium oxide, which is stabilized by the addition of yttrium oxide. Full name of zirconium used in dentistry is yttrium stabilized zirconium or YSZ.
Zirconium substructure crowns are usually projected on a digital model of the patient's mouth, which is obtained by using 3D digital scanning prints or patterns. Substructure is then reduced by zirconium blocks in soft pre-sintered condition. When cut, a pre-sintered zirconium sintered in a furnace where it shrinks by 20% and reaches full strength of about 850MP.
Dental technician can add a layer of esthetic ceramics on the cap in order to achieve the final color and shape of the teeth. Sometimes a monolithic crown can be made solely from zirconium ceramic without adding a layer of esthetic ceramics. These crowns look thick (compacted) with high resistance, with no transparency or fluorescence.
Alumina was introduced as a dental material in 1989 when it was melted and fused with the glass. Recently, the cap from alumina was constructed using a CAD / CAM techniques in which the cap that is too large decreases to a pre-sintered block Al2O3. The block is sintering and shrinking to appropriate size. In order to achieve a proper color and shape a feldspar ceramics can be placed on that alumina cap.