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Zirconium dioxide: general comments

Zirconium dioxide is produced from the mineral zircon (ZrSiO4). The designations zircon and zirconium oxide are not correct as designations of the structural formula ZrO2. Zircon stands for the mineral zirconium silicate (ZrSiO4), which serves as the natural raw material for structural ceramics.

The correct designation for ZrO2 is: zirconium dioxide.

Additives are added to the initial powder:

  • Auxiliary materials (water, organic compounds) facilitate shaping into blanks and evaporate during pre-sintering.
  • Sintering additives remain in the material and influence the sintering behavior and the properties of the finished ceramic.
  • Among other things, zirconium dioxide from pritidenta contains hafnium oxide, yttrium oxide and aluminum oxide.

All frame materials age, and this also includes metals. Partially stabilized zirconium dioxide (opaque / translucent), however, exhibits good aging resistance: its strength does not fall below the 800 MPa required by DIN EN ISO 6872, even after a long wearing period. High and extra translucent, fully stabilized zirconium dioxide exhibits excellent aging resistance: no loss of strength was observed in scientific studies, even after a long period of wear.

Everything is radioactive, even the human body (6,000 Bq). A zirconium dioxide crown exhibits approx. 0.4 Bq, a PMF crown up to 2 Bq. The ceramic dental standard DIN EN ISO 6872 specifies upper limits; the proof of compliance is included in the respective technical documentation.

No, the hardness and surface quality are decisive. In the ideal case, monolithic full contour restorations made of zirconium dioxide are therefore polished – especially the areas with antagonist contact – and glazed additionally. For the glaze on the polished surfaces we recommend the use of lithium silicate spray (e.g. CeraFusion).

If correctly designed and fabricated, zirconium dioxide restorations are as durable as PMF crowns.

Chipping stands for flaking of the veneering ceramic, which can be caused by the following factors:

  • sharp edges of the frame material
  • strong blasting (= high blasting pressure) of the outer and inner surfaces
  • Non-compliance with the specified heating and cooling phase during the sintering process and the veneering process
  • Tensile stress in the veneering layer (due to differing layer thicknesses)
  • Frame design does not follow a reduced contour (= cusp support)
  • Veneering layer is too thick (>1.5 mm layer thickness)
  • Falling below the minimum frame wall thickness (<0.4 mm)
  • Too pronounced extra- or intraoral grinding of the final sintered restoration
  • Contraindicated processing
  • Differing thermal expansion behavior (CTE) between frame and veneering ceramic

Commonly, fractures are also sometimes referred to as chipping.

 

Various factors interact her

  • Perfect working basis on the model (preliminary work in the dental practice)
  • Precise scanning data
  • CAD parameters for crown design (spacer, margin contour, …)
  • Settings of the CAM system
  • Diameter and quality of the processing tools
  • Sintering process (firing program, bedding on pearls / occlusal pins...)
  • Always observe the processing instructions of the manufacturer!

During sintering, fine-grained ceramic or metallic materials are heated – often under increased pressure. To ensure that the workpiece retains its shape, the temperatures are kept below the melting point of the main component.

As a rule, shrinkage occurs as the particles of the starting material compress through diffusion processes and reduction of the specific surface area, and pore spaces are filled. Each bridge greater than approx. 4 units should be stabilized during sintering with an individual cross-connector appropriate to the material. Occlusal sintering supports ensure uniform horizontal and vertical material contraction.

Sintering gives the material its (almost) maximum density and thus its properties specified for dental prostheses.

If all the parameters of the sintering process are correct, the following reasons are possible for an undesirable change in shade/translucency:

  • Contamination in the furnace through foreign materials, e.g. residues of staining liquids > perform cleaning firing program with cleaning powder, replace sintering pearls.
  • Cross-contamination through contaminated milling cutters > do not use tools that have already been used for metals, acrylics or other materials during manual finishing.
  • Contamination through coolants/grinding additives > when wet grinding priti®multibloc ZrO2, use pure water, clean the tank beforehand, use second tank if necessary.
  • Varying wall thicknesses > particularly in the case of very translucent zirconium dioxide, the wall thickness has a major influence on the shade effect; the thicker the material, the darker or more color-intensive the effect.
  • Different stump shades > in the case of highly discolored stumps, one should use a more opaque material. This can even be used on metallic constructions without a color cover, for more translucent materials an opaquer or opaque luting material is required.
  • Additional staining> although pre-stained zirconium dioxide can theoretically be treated additionally with staining liquids, it is preferable to realize further characterization with glaze stains.

A natural, patient-customized fluorescence is best achieved using a fluorescent glaze or veneering material. On the one hand the addition of fluorescent additives to zirconium dioxide leads to a considerable reduction in translucency, on the other hand, this cannot achieve the intensity of the natural fluorescence of teeth.

It is recommended to compare flexural strength, translucency and indication spectrum.


priti®multidisc ZrO2 / priti®multibloc ZrO2: General

priti®multidisc ZrO2 multicolor is available in the three translucency grades High Translucent (HT), Extra Translucent (ET) and Translucent (T) – each in 7 or 8 shade categories, which allow the reproduction of all VITA shades.

priti®multibloc ZrO2 multicolor is available in the translucency grade High Translucent (HT) – in 3 shade categories which allow reproducing 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 monolithically full contour crowns and bridges (max. 3 units) for the anterior and posterior region

Extra Translucent (ET) / Translucent (T): partial crowns, monolithic full contour and partially or fully veneered crowns and bridges (up to 16 units) as well as individual abutments for the anterior and posterior region on natural abutments and implants

Opaque (O): partially or fully veneered crowns and bridges (up to 16 units) as well as individual abutments for the anterior and posterior region on natural abutments and implants

Each shade category stands for a specific shade range, which is covered by the color gradient integrated in the blank. Depending on the position of the construction on the gradient, in other words, further up or down on the blank, the basic shade of the restoration is lighter or darker.
pritidenta shade category VITA classical® A1-D4 shadesVITA System 3D Master®
A lightA1 – A32M1, 1M2, 2R1.5, 2M2, 3M2
A darkA3,5 – A43R2.5, 5M3, 4L2.5
B lightB1 – B22L1.5
B darkB3 – B43L2.5, 3M3
C lightC1 – C23M1, 3L1.5
C darkC3 – C44L1, 5M1, 5M2
D lightD2 – D44R1.5, 4R2.5, 3R1.5, 4M1, 4M2, 4M3
priti bleach0M1, 0M2, 0M3, 1M1

priti®MPguide ZrO2 High Translucent and priti®MPguide ZrO2 Extra Translucent are shade guides to determine the tooth shade according to the pritidenta shade categories. The shade sample strips are simply matched to the patient's tooth; the shade category and the required position in the round blank (top / middle / bottom) are indicated on each sample.

The software MPT – Multicolor Positioning Tool offers a simulation of the color effect after sintering. The construction can be moved within the virtual round blank and the software shows how the finished restoration would look in color depending on its position.

Single crowns in the anterior region: 0.4 mm
Single crowns in the posterior region and for all bridge abutments: 0.6 mm


priti®multidisc ZrO2 / priti®multibloc ZrO2: Processing

The materials priti®multidisc ZrO2 monochrome and multicolor in the translucency grades Opaque, Translucent and Extra Translucent are Class 5 dental ceramics with a flexural strength of well over 800 MPa. According to DIN EN ISO 6872, they are therefore suitable for monolithic bridges and veneered bridges with four or more units. There is no limitation regarding the span and distribution of the bridge abutments; as a matter of principle, the static and physiological load limits must be observed. pritidenta recommends:

  • max. one terminal bridge pontic
  • max. two pontics in the posterior region
  • Adaptation of wall thicknesses and connector cross-sections for extreme spans

The blank holder is inserted straight and lengthwise into the blank holder of the machine via the locking device, then the grub screw can be tightened with a torque wrench – on Dentsply Sirona systems it engages audibly. For a correct fit, the block should only be fixated at the front end with the finger during fixation.

  • The blank holder is centered on the horizontal plane, but slightly offset downwards on the vertical plane; this may have to be compensated for in the CAM software.
  • The shade gradient from light to dark leads from the top to the bottom in the block; the top side of the block is indicated by the imprint. If necessary, the alignment of the block in the machine blank holder must be adapted to the alignment in the CAM software.

Opaque materials are more suited for this than the more translucent materials. And although our zirconium dioxide offers very stable margins, chipping must be expected at extremely high processing speeds. Good results are achieved with the following settings:

Processing stepRoughing
Occlusal/cavity
Roughing / finishing
Occlusal / cavity + residual material
Processing toolRoughing cutter Roughing / finishing cutter
Parameters:
Speed (n)19,000-23,000 rpm 23,000-27,000 rpm
Feed velocity (Vf)1,200-1,500 mm/min 800-1,200 mm/min
Allowance0,15 mm0,15 mm
Path distance1,00 mm0,20 mm
Cutting depth1,00 mm0,50 mm

1. Separation of the object from the blank
2. Straightening of the connector attachment points
3. Cleaning of milling dust
4. Correct positioning for sintering on sintering plate / sintering pearls

After the CAM process: cleaning / removal by suction (clean brush / no compressed air to avoid contamination by foreign particles).

After sintering: cleaning / removal by blasting (50 µm corundum blasting material, max. 1 bar pressure, 10 mm distance, 5 sec blasting time/unit)

Any programmable open furnace designed for high temperature sintering (up to 1,600 °C) is suitable.

The actual temperature in the furnace chamber during sintering can be measured very accurately with "PTC rings" (e.g. from Schupp) and the temperature value can be corrected in the sintering program if necessary. In addition, process control can be performed by adding PTC rings at regular intervals to the sintering process.

Recommended procedure:

  • Use ring type MTH 1,340 °C – 1,520 °C - available from www.schupp-ceramics.com
  • Insert the ring when standard sintering (always use the same position in the sintering bowl or sintering furnace, best to make a note of this)
  • Remove the ring and measure it with a suitable measuring instrument (also note a position on the rings for all future measurements)
  • Check measured values after correction using "Ring temperature correction curve" in the respective "Temperature-Table for PTCR" and, if necessary, adjust the final temperature in 10 °C increments

 

 

Option 1: standard sintering at 1,450 °C (heating and cooling rate of 10 °C/min, dwell time 2 h)
Option 2: speed sintering at 1,500 °C (heating rate of 10 °C/min, cooling rate of 40 °C/min, dwell time 30 min)

Single-tooth restorations and bridges with a maximum of 3 units can be sintered together. To avoid stress in the bridge restorations, long-term cooling down to 400 °C should always be performed and the material should then be slowly cooled down further on the firing tray.

Attention: ceramics generally have low thermal conductivity – if they cool down too quickly, stresses arise in the workpiece and this can later lead to cracks and fissures in the veneering layer or the frame.

Steady uniform cooling of the frame and veneering ceramic as well as a stable, balanced support of the restoration during sintering are important. Firing trays / pins should be metal-free. The following firing parameters are recommended:

Type of procedureHeating/cooling rateLong-term cooling cooling all firing cyclesRemoval of workpiece from furnace
Full contourreducednecessary (400 °C – 200 °C)100 °C
partial contour/framereducednecessary (400 °C – 200 °C)100 °C

After every veneering and glaze firing
1. Careful removal of the firing tray from the furnace chamber
2. Placement of the firing tray on a refractory surface, protected against strong temperature fluctuations (e.g. draught)
3. Complete cooling of the restoration to room temperature (duration approx. 20 min, depending on size and volume)

Yes > 50 µm-corundum blasting material, max. 1 bar pressure, 10 mm distance, 5 seconds blasting time / unit.

We recommend diamond abrasives and water cooling. Alternatively, there are zirconium dioxide grinders from various manufacturers that operate without cooling. However, shape-specific changes should be made before sintering wherever possible.


priti®multidisc ZrO2 / priti®multibloc ZrO2: finishing and fixation

Option 1: Polishing – also with diamond polishing paste
Option 2: Glaze and painting technique – preferred by us because polish produces an extremely smooth, often unnatural looking surface. Any stain and glaze material approved for zirconium dioxide can be used.

All techniques of full and partial veneering, including cut back, can be applied without restriction with any ceramic material that is matched to the CTE of zirconium dioxide. Please follow the processing instructions of the veneering ceramic manufacturer as a matter of principle, e.g. regarding liner, firing parameters, etc.

By blasting the inner surfaces/cavities with 50 µm corundum blasting material, max. 1 bar pressure, approx. 10 mm distance and approx. 5 sec blasting time/unit.

Phosphate cement or glass ionomer cement can be used. Alternatively, (self-)adhesive fixation is possible. For translucent materials, tooth-colored luting materials are recommended. Temporary luting is not recommended.

If the restorations are tried-in on the patient in any manner, the inner surfaces/cavities should be blasted again with 50 µm corundum blasting material, max. 1 bar pressure, approx. 10 mm distance and approx. 5 sec blasting time/unit to avoid any contamination of the surface and thus ensure maximum bonding with the luting material.