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01 Nov 2010 | Australasian Dental Practice

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core3dcentres delivers IPS e.max CAD from Australia's only Ivoclar Vivadent validated milling centre

Core3dcentres has become the first and so far only milling centre to deliver Ivoclar Vivadent validated IPS e.max CAD restorations to Australia after going through a stringent validation process with Ivoclar Vivadent to achieve this high standard.

The move marks another milestone in dental technology as the shift in the manufacturing of crowns and bridges from lost wax techniques towards CAD/CAM processes continues.

In this regard, CAD/CAM has made the use of monolithic restorations possible. Monolithic restorations are crowns made from a single, solid piece of material which does not rely on a bond between porcelain and a substructure. The resulting restoration is much stronger and more durable.

The industry has seen materials such as translucent zirconia used to manufacture these types of restorations with outstanding fit, marginal integrity and strength, but they can appear too opaque to be used in the aesthetic zone. However, thanks to improvements in materials science technologies, Ivoclar Vivadent now offers a lithium disilicate product that allows for the manufacture of milled monolithic crowns with outstanding aesthetics and translucency as well. This innovative new product is the IPS e.max CAD block.

IPS e.max CAD is a lithium disilicate glass-ceramic block for use with CAD/CAM manufacturing processes. It is engineered using an innovative process which provides outstanding qualities for dental applications.

The block is first manufactured using a continuous process glass technology known as a pressure casting. This process uses optimized parameters which removes any defects (such as porosity and gathering of pigments) in the block. This "blue" pre crystallized transitional state is the result of the microstructure of the glass-ceramic where a buildup of lithium metasilicate crystals (Li2SiO3) form - giving the block its moderately strong properties and good edge stability (Figure 1). This relatively soft intermediary state has strength of about 140MPa which means it can be easily milled in an efficient and accurate manner which minimises the risk of crack propagation. This blue transitional state also allows for manual adjustments to be made to the crown or cut backs for further layering of porcelain where indicated.

Following the milling process, the restorations are tempered at 850 degrees celsius and reach their fully crystallized state. During this process, the lithium metasilicate crystals are transformed into lithium disilicate crystals (Li2SO2O5) which results in the high strength of the final restoration (360 MPa) and the desired aesthetic properties (Figure 2).

IPS emax CAD blocks are available in three levels of translucency:

* Low Translucency (LT) blocks are used to fabricate full contour partial and full crowns. These ingots allow slight discolouration of underlying teeth to be hidden. LT blocks come in 16 A-D shades and 4 bleach BL shades.

* High Translucency (HT) blocks are used to fabricate minimally-invasive full contour restorations. The colour of these restorations can be enhanced by the underlying dentine showing through the translucent material. HT blocks come in 16 A-D shades and 4 bleach BL shades.

* Medium Opacity (MO) blocks are used to fabricate frameworks that are placed on heavily discouloured preparations. They are then veneered with IPS e.max ceram and come in 5 group shades (MO 0 - MO 4)

The success of each case is heavily reliant on the clinician informing the laboratory of the underlying dentine (stump) shade that the restoration will be placed upon. It is only with this information that the correct block choice can be made. For the cementation of IPS e.max restorations you can choose between proven adhesives and conventional cementation materials depending on the indication at hand. Crowns and bridges can be cemented using adhesive, self adhesive and conventional methods. Inlays and veneers are cemented adhesively as usual.

There is a wide variance in the quality of CAD crowns produced today depending on the type of machine that is used to mill the restoration. Marginal integrity can vary greatly along with fit, surface texture and aesthetics. The only way to ensure the products are manufactured to the highest standards is to use a validated milling centre. core3dcentres has recently gone through a stringent validation process with Ivoclar Vivadent using the DMG Ultrasonic 20 mill. This ensures that all produced restorations are stress free, durable, have maximum strength, are highly aesthetic and comply with Ivoclar Vivadent's strict certification standards.

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