zirconia powder
HiPer®-DENT-Z Dental Blanks
Information for Dental Laboratories
HiPer®-DENT-Z Dental Blanks are pre-sintered zirconia workpieces for the manufacture of aesthetic and mechanical robust dental restorations. Hereafter we provide some information regarding the use of HiPer®-DENT-Z Dental Blanks to facilitate your work. The given information does not replace the instructions for use delivered with each product but provides additional explanation.
Material Properties: Zirconia
In dentistry the most common zirconia variety used is yttria-partially stabilized zirconia. This material is characterized by a solid solution of yttrium ions in the zirconia lattice. Yttrium ions put up resistance to the naturally occurring phase transformation during cooling from sinter temperature to room temperature, thus restraining – stabilizing – the tetragonal high temperature phase and preventing the zirconia lattice to “switch” to the monoclinic low temperature phase.
Zirconia stabilized this way shows very high fracture toughness, due to significant reduction of crack propagation speed by transforming zirconia crystallites. This phenomenon is called transformation-toughening and determines the high mechanical strengh of Yttria-stabilized zirconia
The mechanical strength of a restoration depends also on milling parameters, the sintering regimen and the number of veneering cycles. Therefore, mechanical strength values achieved in dental laboratories usually range below the values given by many Dental Blank manufacturers because these values were acquired under ideal conditions with specifically treated test specimens. Values given for HiPer®-DENT-Z are verified with different specimen dimensions and testing regimes and can be achieved in a dental laboratory.
Restoration Design
The design of crowns, bridges, cantilever bridges, telescopic crowns e. g. must take the material properties into consideration. For ceramic materials like zirconia minimum wall thickness and connector cross-sections are mandatory (see instructions for use delivered with the product). Restoration construction should be conducted in a fashion that allows for a veneer thickness similar to the wall thickness of the framework.
Milled Dental Blank
Processing HiPer®-DENT-Z Dental Blanks on Machining Centers
Pre-sintered Dental Blanks possess a limited mechanical strength and require careful handling. Mounting of Dental Blanks in the machining center should be done by using the largest possible contact area between Blank and retainer to avoid induction of cracks. The same rationale applies for the holding forces which should be kept as low as possible. Ideally suitable torque values are determined and used. Dust and chippings have to be removed from fixtures.
Please keep in mind, that your milling tools will be dulled with increasing service life and therefore induce increasing forces on the Dental Blank. Checking the cutting condition of your milling tool on a regular basis is strongly recommended. Best practice would be the microscopic assessment of cutting edges or tool coating and determination of change criteria.
Processing of Dental Blanks applying dull tools or unsuited machining parameters may result in false dimensions or damages, sometimes only detectable after sintering or veneering. Typical indicators for blunt tools are chips, cracks and shiny patches, often visible not until sintering.
Dismount the finished restoration from the Dental Blank carefully and blow off dust and adherent particles with oil-free compressed air for perfect veneer adherence.
Advice: The milled restoration should be sintered as soon as possible to avoid adsorption of humidity.
3-Unit Framework from HiPer®-DENT-Z Zirconia
Sintering Your Piece of Work
The sintering step is crucial for restoration quality. Best possible densification of the still porous framework can only be achieved if certain prerequisites are satisfied:
- The restoration has to be sintered according to the compulsory program and the employed kiln reaches the demanded temperature at the product position
This prerequisite should be verified periodically by measuring with a second calibrated thermo couple. Depending on the age of the heating elements, shielding of the framework, kiln load or position of the thermo couple the effectice temperature at the product position can deviate from the control reading.
- Multi-unit frameworks have to be sintered uniformly to avoid shrinkage-derived deformation or structural tensions
This prerequisite can be achieved by central positioning of the framework – heating elements are located at equal distance – and shielding with suitable kiln furniture. The latter prevents the framework to be exposed to direct radiation from glowing heating elements. Sometimes the sintering program needs to be adjusted for ensuring complete through heating.
- Frameworks need to be protected from „hot spots“ and/or heating element discharge for prevention of local overheating or contamination, respectively
Examination of the kiln heating units on aregular basis helps fulfill this prerequisite. If your heating elements feature local glowing areas – hot spots – even at very low power input they should be exchanged or your work pieces should be protected by shielding with appropriate kiln furniture. Aged heating elements from molybdenum disilicide or silicon carbide may produce discharge which sometimes leads to discoloration and/or shiny plaques on your framework.
Veneering of HiPer®-DENT-Z Frameworks
Standard procedures for veneering of restorations from HiPer®-DENT-Z zirconia. Veneering ceramics must have a proper thermal expansion coefficient (see instructions for use delivered with the product) and must wet zirconia.
Pretreatment of the sintered framework is usually not necessary if particulate contamination from the milling procedure has been removed adequately. Nevertheless sandblasting with appropriate sandblasting media (e. g. alumina 110 µm) is possible.
As opposed to the latter clean firing of a sintered framework is counterproductive. Firing schedules for veneering ceramics should provide sufficient soaking time and prevention of thermal shocks during cooling. Early opening of the kiln might cause cracks. The same applies for exposure of a hot veneered framework to cold air or water.
Finishing of sintered and veneered frameworks
Finishing processes are only acceptable if suitable and sharp diamond tools are used and sufficient water cooling is present. Sharp edges have to be avoided. Wall thickness should not fall below 0,4 mm (see instructions for use delivered with the product). For after-sintering smoothing of the framework surface, only very fine-grained diamond tools are acceptable. Veneered frameworks must be treated according to the instructions of the veneering ceramic supplier.
If you have any further questions, do not hesitate to contact us.
Order information concerning our products you will find on our internet homepage www.hiper-medical.de
Please regard the instructions for use delivered with HiPer®-DENT-Z Dental Blanks!
