Traditional and adhesive cementation
A rough surface gives greater adhesion both with traditional and adhesive cementation.
It is useful to sand the surfaces with aluminium oxide, 110nm, 3-4 bar.
Traditional cementation
No particular conditioning is necessary.
Use
- Zinc-phosphate cement
-
Glass-ionomer cement
e.g. Dyract cem plus, Dentsply, Costanza, Vivaglass Cem
Adhesive cementation
This does not mordant.
In order to clean the internal part before cementation sand the surface with 110nm aluminium oxide at 1 bar.
Use type Panavia21, PanaviaF cements.
Cold isostatic pressing is a process in which the powder/granulate is pressed uniformly in all directions.
The granulate is placed in a flexible rubber mould. Once full, the mould is immersed in a not compressible liquid which transmits the pressure (up to 4000 bar ) uniformly in all points and in all directions.
Benefits:
- equal compression ratios (hydrostatic) give highly homogeneous density of the green (not sintered) product in both the axial and radial direction
- the same uniform shrinkage and mechanical resistance throughout the product
- higher mechanical and chemical resistance than an axially pressed product
Disadvantages:
- high production costs
- low automation
Zirconia granulate, with almost zero humidity, is placed in the Widia (tungsten carbide) mould in a precise quantity; the mould is a tank with fix quantity of raw material and movable to increase homogeneity of densification of the products. The powders are compacted through application of pressure in a single direction, using a mobile piston. During pressing, the raw material granulate therefore runs along routes varying in length: shorter in the centre of the product and longer in the peripheral zones. Pressing may vary due to friction of the granules against each other and the granulate against the walls of the mould. This could lead to lower compacting in the so-called neutral compression zone of the product and therefore not uniform distribution of density and shrinkage of the product. Optimisation of the process reduces the differences in shrinkage of the semi-processed product in the different directions.
Advantages:
- high productivity
- high level of automation
- inexpensive
Disadvantages:
- products with relatively simple shape and limited height
- densification and therefore porosity is not uniform, due to not uniform compacting of the powder
Zirconia is obtained using chemical processes or through Zirconium Silicate and Baddeleyite electrofusion. The quality of the granulate considerably influences porosity and possible defects in the sintered product:
- the size of the grains has an effect on performance of the material (nanometric dimensions of the crystals guarantee high mechanical resistance and high resistance to chemical agents)
- distribution of the grains, on the other hand, may influence hydrothermal stability of the sintered material.
- distribution of the additives influences the porosity and therefore translucence of the material.
Medical applications need high-quality Zirconia purified with a controlled production process. The method used is hydrolysis of Zirconium sand, following purification with chlorhydric acid and subsequent calcination. CO.N.CE.P.T. uses Japanese powders produced with this method
      
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Albums
Warning!
This processing may alter the biological, chemical, physical and mechanical properties of the Zirconia products.
A possible overheating of the surface of the prosthetic structure may lead to a transformation of the structure from tetragonal (high resistance) to monoclinic (low resistance value) and to a greater wear of the diamond wheels.
- in case of small grinding operations on the sintered product, the temperature during grinding for all the ZYTTRIA elements must be lower than 70°C
- cool the Zirconia structure with a jet of water during the grinding phase
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Tooth with mass lower than 1g.
Tooth with mass up to 3g.
Tooth with mass higher than 3g. The maximum temperature time may be reduced to 1 hour, depending on the thickness of the prosthetic structure. Certain sintering cycles may be completed in 8 /12 hours, but this depends on the geometry of the prosthetic structure to be sintered. The laboratory must optimise the cycle on the basis of the product to be sintered to avoid distortions and cracks.
Temperature specifications However, sintering temperatures have the following tolerance:
The sintering range for the ZYTTRIA Z401 WHITE and ZYTTRIA Z COLOR is between 1450°/1480°C and 1500°/1530°C for the ZYTTRIA Z402 EXTRA-TRASLUCENT. General recommendations
Sintering of Zirconia depends on the type of powder used. Due to the low thermal conductivity of Zirconia, the thermal gradient (or temperature increase and decrease speed) depends on the mass of the structure to be sintered. Besides mass, sintering speed also depends upon the shape of the cap, bridge or crown to be sintered. The tooth with the highest mass determines the firing cycle speed. |
Pre-sintered Zirconia is porous (48%) and absorbs processing water or dyeing liquids on the basis of the milling and immersion time.
Warning!
Zirconia products must be properly dried before being placed in the sintering kiln. The product may be dried after wet processing or dyeing with a fan heater at a temperature between 80° and 100 °C, for a time which varies depending on the thickness of the dental prosthesis. Drying time ranges from 30 minutes to 2 hours.
An infrared lamp may also be used. Alternatively, the product may be dried in the sintering kiln in the one-step drying cycle at 150°C for at least 30 minutes.
The measurements of the final dental prosthesis must be known before milling the pre-sintered components.
Some machines use the multiplication (enlargement) coefficient, while others use shrinkage.
If the MULTIPLICATION COEFFICIENT method (enlargement coefficient) is used, each final measurement must be multiplied by this coefficient, specified for each lot.
If PERCENTAGE SHRINKAGE is used, the formula is:
[(pre-sint. - sint.) / (pre-sint.)]*100
(shrinkage of the pre-sintered product during sintering referred to the initial measurements of the pre-sintered product).
If this method is used, each measurement of the final prosthesis must therefore be multiplied by the following value:
100 /(100 – percentage shrinkage), specified for each lot.
The results obtained following one of the two methods indicate the dimensions which the pre-sintered prosthesis must have before being fired in the oven.
These values are based on the experience of CO.N.CE.P.T. following various tests conducted considering machinability, density of the “green” (unsintered) product and final density.
Minimum element thickness
The values indicated are references for the technician in preparation of the prosthetic elements. However, designing of the prosthetic element is the responsibility of the dentist and the dental technician, who must check the sizing of the prosthetic structure case by case.
The wall strength should be at least
ANTERIOR TEETH
- incisal/occlusal thickness 0.7mm
- circular thickness 0.5mm
POSTERIOR TEETH
- occlusal thickness = 1.5 mm – circular thickness = 0.5mm
ABUTMENT crowns for bridge framework with 2 pontics
- incisal/occlusal thickness =1mm
- circular thickness = 0.7mm
The connector surface should be at least
Anterior bridge
- with 1 pontic= 7mm 2
- with 2 pontics = 9mm2
Posterior Bridge
- with 1 pontic = 9mm2
- with 2 pontic= 12mm”
Pre-sintered ZYTTRIA® may be milled using the most common Cad/Cam systems or with manual pantographs.
In order to avoid possible breakages and/or any stress on the product being processed, consult the machine manual to select the most appropriate milling and revolution speed.
Program the milling machine considering the final dimensions of the structure (see Shrinkage Calculation).
Process the component with the tungsten carbide or diamond-point mill according to the manufacturer’s instructions of the system used.
Warning!
Pre-sintered products must not come into contact with liquids (water, oil) or creams during milling and during the other processing phases. Milling may be performed in a humid environment, provided that the block is completely dry before sintering.