Zirconium dioxide: General
The principal raw material is the mineral zirconium (ZrSiO4). The basic powder is combined with various additives: Excipients (water, organic compounds) make it more workable when shaping the round blanks and evaporate before the sintering process. Sinter additives remain in the material and affect the sintering process and the characteristics of the finished ceramic material. Zirconium dioxide from pritidenta contains hafnium oxide, yttrium oxide and aluminum oxide and other substances.
All framework materials age, even metals. However, partially-stabilized zirconium dioxide (opaque/translucent) has high resistance to aging: Even after long periods of degradation, its strength does not fall below the 800 MPa level required by the Medical Devices Act (MPG). High Translucence, fully-stabilized zirconium dioxide has very high resistance to aging: Even after long periods of degradation, no loss of strength was detected in scientific studies.
Everything is radioactive, even the human body (6,000 Bq). A crown made of zirconium dioxide has approx. 0.4 Bq, a PFM crown up to 2 Bq. There are upper limits specified in the MPG; compliance certification is available in the CE registration documentation for each product.
No, the key factors are hardness and surface finish. So monolithic, fully anatomical restorations made of zirconium dioxide should ideally be given high gloss polishing and glazed.
Zirconium dioxide restorations are as durable as PFM crowns provided that the design and finish are correct.
Chipping occurs when material from the ceramic veneer is chipped off. This may be due to CTE deviations, irregularities in the veneer thickness, etc. Chipping is sometimes used colloquially to refer to fractures.
A number of different factors are at play here:
- Ideal working basis (preliminary work at the dental practice)
- Accurate scan data
- CAD parameters
- CAM system settings
- Diameter and quality of machining tools
- Sinter process (firing program, positioning on beads/occlusal pins...)
- Material > always follow the manufacturer’s instructions!
During sintering fine-grained ceramic or metal materials are heated, often under high pressure. To ensure the workpiece retains its shape, temperatures are kept below the melting point of the main component.
The framework will generally shrink here since the powder particles are compacted by diffusion and contraction of the specific surface, and pore spaces are filled in. Each bridge with around 4 pontics or more should be stabilized during sintering with an individual cross connector customized to the mass of material. Occlusal sintering pins ensure the material contracts evenly across the horizontal and vertical planes.
Sintering reduces the material (almost) to its maximum density as required for dental prostheses.
If all parameters for the sintering process are correct, the following could be the reason for unwanted changes in color and translucency:
- Contamination with foreign materials in the furnace such as residues of dye liquids > cleaning firing with cleaning powder, replace sintering beads
- Cross-contamination from milling machine > During manual finishing avoid tools previously used for metals, plastics or other materials.
- Contamination by coolants/grinding additives > For wet grinding of priti®multibloc ZrO2 use purified water and clean the tank before use; use a 2nd tank if necessary.
- Variations in wall thicknesses > Particularly in highly translucent zirconium dioxide materials, the wall thickness of the restoration is a crucial factor in determining the color. Color intensity increases (darkens) as wall thickness increases.
- Different stump colors > Where stumps are highly discolored, an opaque material should preferably be selected which can be used even on metal structures with no colored covering layer; an opaquer or opaque fixing material is required for more translucent materials.
- Additional coloring > Pre-colored zirconium dioxide can theoretically be treated additionally with dye liquids but it is better to use glaze paint stains to individualize the restoration.
For practically-minded dental technicians, we recommend comparing flexural strength, translucency and the list of indications.
priti®multidisc ZrO2 / priti®multibloc ZrO2: General
priti®multidisc ZrO2 monochrome is available in the four translucencies: High Translucent (HT), Extra Translucent (ET; from February 2018), Translucent (T) and Opaque (O) – all in white and all 16 VITA classical A1-D4 shades.
priti®multidisc ZrO2 multicolor is available in the three translucencies: High Translucent (HT), Extra Translucent (ET) and Translucent (T) – in 7/8 color categories respectively, which can be used to reproduce all VITA shades.
priti®multibloc ZrO2 multicolor is available in High Translucent (HT) – in 3 color categories, which can be used to reproduce the VITA classical A1-B2 shades.
High Translucent (HT) = 49 %
Extra Translucent (ET) = 45 %
Translucent (T) = 40 %
Opaque (O) = 35 %
High Translucent (HT): Inlays, onlays, veneers, partial crowns, anatomically reduced and monolithic, fully anatomical crowns and bridges (up to three pontics) for anterior and lateral areas
Extra Translucent (ET) / Translucent (T): Partial crowns, monolithic, fully anatomical and partially or fully veneered crowns and bridges (up to 16 pontics) and custom anterior and lateral suprastructures on natural abutment teeth and implants
Opaque (O): Partially or fully veneered crowns and bridges (up to 16 pontics) and custom anterior and lateral suprastructures on natural abutment teeth and implants
|pritidenta color category||VITA classical shades (A1-D4)|
|A light||A1 – A3||A dark||A3,5 – A4|
|B light||B1 – B2|
|B light||B1 – B2|
|B dark||B3 – B4|
|C light||C1 – C2|
|C dark||C3 – C4|
|D light||D2 – D4|
The priti®MPguide ZrO2 High Translucent is a color guide you can use to determine the tooth color that matches pritidenta’s colors. The shade sample sticks are simply matched with the tooth; each sample states the shade and the position required in the round blank (top/middle/bottom).
The MPT – Multicolor Positioning Tool software simulates the color effect of the round blanks after sintering. It can be moved around inside the virtual round blank and the software shows what color the finished restoration would be for each position.
In the anterior tooth area: 0.4 mm
In the lateral tooth area and where bridge abutments are involved: 0.6 mm
priti®multidisc ZrO2 / priti®multibloc ZrO2: Machining
The block holder is pushed straight into the block holding device on the machine longitudinally over the locking mechanism. The grub screw can then be tightened using a torque wrench, with an audible click on Dentsply Sirona systems. Manually seat and secure the block on the front side only using light finger force.
- The block holder is centered on the horizontal plane but slightly below-center on the vertical plane; you may need to compensate for this in the CAM software.
- The color gradient from light to dark goes from top to bottom in the block; the stamped letters indicate the top of the block. The alignment of the block in the machine block holders may need to be changed to the alignment in the CAM software.
Opaque materials are more suitable here than more translucent materials. Our zirconium dioxide has high edge stability but cracks are possible at extremely high machining speeds. Good results are achieved with the following settings:
|Tool diameter||2,5 mm||1,0 mm||Parameter:||↓||↓|
|Spindle speed||20.000-22.000 rpm||20.000-22.000 rpm|
|Feed||1.200-1.500 mm/min||1.000-1.300 mm/min|
|Infeed Speed||1.000 mm/min||700 mm/min|
|Allowance||0,15 mm||0,15 mm|
|Tool path distance||1,00 mm||0,20 mm|
|Step down/step over||1,00 mm||0,50 mm|
1. Detach the object from the blank
2. Straighten the connection point
3. Clean out the mill dust
4. Place correctly on sinter plate/sintering beads
After the CAM process: Clean/remove by vacuuming (clean brush/avoid compressed air to prevent contamination by foreign particles)
After sintering: Clean/remove by blasting (50µ Corundum, max. 1 bar pressure, 10mm distance, 5s blasting time per unit).
Any programmable open furnace is suitable provided it is designed for high temperature sintering (up to 1,600°C).
Option 1: Standard sintering at 1,450°C. (Heating and cooling rate 10°C/min, hold time 2 hours)
Option 2: Rapid sintering at 1,500 °C (Heating rate 10°C/min, cooling rate 40 °C/min, hold time 30 min)
Single tooth restorations and bridges can be sintered together. To avoid tensions arising within bridges, longterm cooling should be applied up to 400 °C and the material then allowed to cool slowly on the firing tray.
Caution: Ceramics generally have low thermal conductivity: if they cool down too rapidly, tensions occur in the workpiece that could subsequently cause cracks and fissures in the veneer or framework.
It’s important to ensure the framework and the ceramic veneer cool down at an equal rate and that the restoration is supported in a stable, balanced way during sintering. Firing trays/firing pins should not contain any metal. The following firing parameters are recommended:
|Design type||Heating rate/Cooling rate||Long-term cooling following all firing cycles||Workpiece oven removal|
|Fully anatomical||Reduced||required (400 °C – 200 °C)||100 °C||Partially anatomical/framework||Reduced||required (400 °C – 200 °C)||100 °C|
Following each veneer/glaze firing:
1. Carefully remove the firing tray from the firing chamber
2. Place the firing tray on a fireproof base protected against severe fluctuations in temperature (such as drafts).
3. Allow restoration to cool down completely to room temperature (approx. 20 minutes depending on size and volume)
Yes > 50µ Corundum, max. 1 bar pressure, 10 mm distance, 5s blasting time per unit.
We recommended working with water-cooled diamond-tipped machining tools. Alternatively, various companies offer dedicated zirconium dioxide machining tools that do not require additional cooling. As far as possible, however, modifications affecting shaping should be made prior to sintering.
priti®multidisc ZrO2 / priti®multibloc ZrO2: Finalizing and fixing
Option 1: Polishing - preferably using a diamond polishing paste
Option 2: Glazing and painting - we prefer this because polishing produces an extremely smooth and often unnatural-looking surface. Any stain and glaze permitted for zirconium dioxide may be used.
All full or partial veneering methods can be used without restriction, including cutback, with any ceramic mapped to the CTE of zirconium dioxide. Please follow the instructions provided by the ceramic veneer manufacturer, for example in relation to liners, firing parameters, etc.
Phosphate cement or glass ionomer cement may be used. Alternatively, you can use self-adhesive fixing material. Tooth-colored fixing materials are recommended when using translucent materials. Temporary fixing is not recommended.