Ceramics are man-made solid materials that are formed by nonmetallic and inorganic raw materials. They are chemically altered at high temperatures. The traditional porcelain is composed of three naturally occurring minerals: pure white clay, silica, and feldspar. The basic components of dental porcelain are just silica and feldspar. Additional components are aluminum oxide as well as pigments and opacifying agents, which are varied by the manufacturer depending on the intended application. Only denture teeth contain clay as the third basic component of traditional porcelain. All heat-processed dental porcelains contain small crystals (leucite and/or alumino-silicate crystals) that are embedded in a matrix that consists of silicate. The relative amount of crystals and glass depend on the formulation of the specifically manufactured porcelain. Leucite is a reaction product of potassium feldspar and glass. It influences the optical properties of dental porcelains, their strength, and their hardness. Until recently, all-porcelain restorations had to be used with caution because of the risk of fracture and their abrasive effect on the opposing teeth that contact them in occlusal function as well as parafunction. The fracture is caused by brittleness and generally attributed to the rapid and uninterrupted growth of cracks that usually begin at weak spots and flas of the dental ceramic. Aluminous oxide increase the strength of dental porcelains. However, crowns made with this type of porcelain fit poorly due to the shrinkage during heat processing in the dental lab. Therefore, these aluminous materials were fused to metal substrates to make them more stable and prevent crack propagation.
IPS E.max and IPS Empress are both dental veneer porcelains that are known for their durability and aesthetic appeal. They are made from a single blocks of lithium disilicate ceramics. Empress veneers are known for their aesthetic appeal and natural appearance. Even though they are not as strong as IPS E.max veneers by themselves, a meticulous bonding technique allows for an even distribution of chewing forces, which makes the difference in strength less important.
IPS E.max is known for its strength, durability, and ability to mimic the translucency of natural teeth. Emax is considered the gold standard in dental aesthetics and can be used to create full-contour restorations. It is the successor of IPS Empress. Emax 70% lithium disilicate is twice as strong as IPS Empress, which is only 60% lithiumm disilicate. IPS E.max has a structural strength of up to 400 MPa.
Metal bases lead to poor aesthetics due to the interference with the transmission of light through the porcelain and by creating discoloration directly caused by free metal ions. In addition, some patients may have allergic reactions or other sensitivities to metals. This was one of the motivating factors that led to the development of ceramic-only systems that are strong enough to not require any supportive metal core. Many porcelain systems are available now. Some are powder-slurry systems, such as Optec HSP, Duceram LFC), others are castable (e.g. Dicor), machinable (e.g. Cerec Vitablocks, Dicor MGC), infiltrated (e.g. In-Ceram), and pressable ceramics (e.g. IPS Empress, Authentic, and others).
IPS Empress is a glass ceramic that is created by heat-pressing of preformed ingots. The high shrinkage of leucite crystals creates compressive stress in the vitreous phase. It might be easier to look at it as a contractive tension that prevents the development of surface cracks. The randomly oriented leucite crystals are tightly packed, which also aids in the progression of tiny cracks. The combined effects of heat pressing, initial firing, and stain and glaze of the veneers adds a 50% increase in strength. This higher cohesive strength and fracture toughness allows for thicker areas of porcelain with a lesser risk of fracture. Unbonded glazed IPS Empress has a flexural strength of 215 MPa compared to 71 MPa of feldspatic porcelain, 114 MPa of Dicor, 167 MPa of Optec HSP, and 419 MPa of In-Ceram. IPS Empress is bonded to dentin with a resin cement after conditioning of the surfaces of both the restoration and the prepared tooth, as will be explained later in the description of the procedure. This further increases its fracture resistance significantly and reduces microleakage. The occlusal wear of IPS Empress is in the range of enamel due to its fine-grain structure. Heat-pressed glass-ceramic crowns high survival rates after several years in function. The relativ amounts of scattering and transmission of light depends on the chemical composition of the porcelain, the size and structure of the crystals, and the fabrication processes. The more light penetrates through the dental restoration, the more translucency is achieved, which might be comparable to natural teeth. This higher light penetration also preserves the natural pale-pink appearance of the gingival tissue that is next to the dental restorations.
IPS Empress Esthetic
IPS Empress pressed systems for all-ceramic dental restorations have been successfully used for more than 20 years. However, aesthetics and functional qualities of the original system has been subsequently improved..
One of the innovations is IPS Empress Esthetic. This system utilizes a stronger core porcelain that is created by the heat processing of ingots, a cutback technique, and the placement of a veneering porcelain that is baked against the core structure. This allows for the development of youthful and natural incisal translucency, mammellons, and Halo effect, in addition to the anatomical landmarks of youth, such as incisal notching.
The first step of the fabrication of porcelain veneers with this material is the design of a wax-up the form of which is integrated into oral and masticatory function. It integrates the "test results" of dental provisionals that are used by patients to verify how they tolerate possible changes in dental anotomy and function. These wax-ups are sprued, invested, and burnt out in an oven. Then the porcelain ingots for the veneers are pressed into the mold. After divesting, the porcelain veneer will have the exact form of the previous wax-up.
After minimum refinements, the freshly produced porcelain veneers would be ready to go into the patient's mouth. However, they would be just in one color. Therefore the incisal edge is removed to allow for the addition of different shades of veneering porcelain in layers. The first layer may be a porcelain wash paste that adds internal effects. The additional layers of porcelain lead to varying optical effects due to the use of different values. The use of translucent porcelains creates a three-dimensional effect, which makes even very bright porcelain veneers look natural, youthful, and playful.
Once all the layering with the veneering porcelains is completed, the veneers are heat processed again. The completed new teeth receive their final touch-ups by the lab technician and are glazed at their surface with a final heat treatment. The porcelain veneers are ready for delivery.