Brief Description of the End Product
Medical Product Registration Certificate No. РЗН 2018/6961
Mechanical properties of the workpieces:
Density of the unsintered material: min. 2.75 g/cm3
Density after sintering: min. 6.02 g/cm3
Open porosity: 0%
Vickers hardness: (HV10) min. 1300 MPa
Ultimate bending strength (4-points): 1400 ±72.3 MPa
E modulus: 200.5 ± 2.2 GPa
Ultimate strength (cracking resistance): 5.36 ±0.16 MPa m1/2
Thermal expansion coefficient (25 - 500 C): (9.9 ±0.2) x10ˉ⁶ 1/K
Description of ZrO2 Powder Workpiece Types:
ZrO2 powder workpieces without color shades as per VITA scale
ZrO2 powder workpieces with color shades as per VITA scale
As a rule, multilayered (ML)с workpieces consists of four layers with color shades as per the VITA scale and smooth gradients from transparent-white to dark-brown shades.
E.g.: a ML A Light (A1 – A3,5) workpiece consists of four layers with A1 - A2 - А3 - A3.5 color shades that are situated in the same sequence throughout the workpiece height. The first layer and the last one occupy 35% of the workpiece height, the intermediate ones, 15% each. The components giving the workpiece such shades are powders and additives based on Zpex Smile - supertranslucent materials. I.e., actually these layers are A1HT (High Translusency) - A2HT - A3HT - A3.5HT. The workpieces designated ML A Dark (A1-A3.5) are also four-layer but each layer consists of powders and additives based on Zpex - translucent materials designated with letter T (Translucency): A1T - A2T - A3T - A3.5T.
The workpiece marking and the company logotype are applied on the side of the top (the lightest) layer. For convenience of milling machine operators, the bottom side (the darkest layer) is marked with a color point.
The starting material for the production of workpieces is yttrium-stabilized nanodisperse zirconium dioxide powder made by TOSOH company (Japan).
At the first stage, the powder in a standard package is brought to the powder preparation area where it is weighed on an analytical scale and put into special containers for feeding into the axial press measuring hoppers.
On this area, various types of powders are mixed in order to obtain the standard 16 shades in workpieces. Mixing is carried out on a programmable bench according to a technology developed on the basic of the TOSOH company's recommendations.
Then the powder undergoes axial pressing on a special axial press according to a program developed for this kind of powder mixture. The obtained workpieces are moved semi-automatically by a linear manipulator to the preliminary control workplace.
At the preliminary control stage, the workpieces undergo weight parameters measurement and visual control for absence of crack and mechanical damages. Non-defective items are vacuumed in a special film, put on special pallet and moved on stacker carts to the isostatic pressing area.
After isostatic pressing, the workpieces undergo presinterization in special programmable ceramic ovens. Presinterized workpieces are machined on a CNC turning and milling center.
Then the workpieces are brought to the final control area where comprehensive control of output parameters is performed using special optical equipment and those parameters are recorded for every individual batch. It takes into account the type, grade and batch of the starting material, the mixture composition and preparation method, presinterization temperature and other parameters that are recorded in an inspection certificate that is stored in a digital form and on a hardcopy for 15 years, the useful life of the final product (a dental restoration).
The workpieces that passed the final control are marked on a special printer that applies in solvent ink the manufacturer's logotype, the workpiece physical dimensions and type, the source material batch number and the manufacture date, as well as a special parameter: material volumetric shrinkage coefficient that must be taken into account during subsequent milling of dental restoration according to the CAD/CAM technology. The volumetric shrinkage coefficient is calculated on the grounds of the results of processing the linear parameters of a reference sample having a special shape that is cut out of one workpiece of every batch. The workpiece undergoes a burning cycle up to the tetragonal form of the zirconium dioxide powder sintering in a special laboratory oven according to a preset program and then it is measured with a micrometer.
The marked workpieces are packed in special individual and group packages and handed over to the storage area. Then they are shipped to the consumers through the order picking area.