Is Prettau Zirconia too hard and abrasive?
In dentistry abrasion (Latin: abrasio = to scratch off) means the loss of tooth substance due to friction. Enamel and dentin are part of the so-called ‘hard’ tooth structure. Abrasion in this context translates into wear or attrition.
As we know from nature, elephants starve to death at the age of 50 – 60 years because their dentition at that stage is too abraded to process food.
Sintered Prettau Zirconia, owing to its own special material composition, displays incredible density and smoothness. Therefore the material does not cause any wear on natural dentition.
I illustrate this phenomenon by practical example: Rub wood against a smooth glass pane and nothing will happen but, rub wood against wood and it will splinter. As two materials of the same kind meet (tooth against tooth) natural dentition will inevitably wear also. However, when natural tooth meets smooth zirconia (like wood against glass) no abrasion occurs. The abrasive nature of any material is determined by its degree of surface polish and inherent density. The ”softer” enamel will glide over polished, much harder zirconia without wear.
By contrast veneer porcelain (or even metal) will cause wear on natural dentition due to its highly porous structure which acts like sandpaper.
Veneer porcelain is 1000 times more abrasive compared to polished Prettau Zirconia.
Our experiences with zirconia vindicate our view: Zirconia causes practically no abrasion to natural dentition.
In the past we have observed the facts in our own environment and currently they are being tested scientifi cally in several universities. In general terms we can say this: The harder and smoother a material the less the wear it causes under friction. Wear results in abrasion.
Prettau Zirconia – no extra load on the mandible joints
It would be wrong to assume the positive characteristics mentioned in the previous chapter (no abrasion) should cause negative effects on the joints because of hardness. Ceramic (veneered) restorations, implant borne or cemented, are inherently hard but have never been proven to cause joint problems. The joints’ surfaces are “padded” by the disc which acts as a shock absorber. The hardness of a restoration bears no influence on the joint load.
Imagine a pair of pliers: It makes no difference to the actual load on the pliers’ hinge whether its prongs are coated with rubber, metal, ceramic, or zirconia. The load on the hinge remains the same; just as a load on the mandible joint is stable. The average ‘bite force’ of the human jaw closing is approx. 5 kg – unlike, and incomparable to,
the sudden impact force of a slamming door.
Prettau Zirconia – the application
Design and mill your (full anatomical contour) frame as usual but use the special Prettau Liquids for pre-sinter colouring. A technician’s expertise in layering ceramic is helpful in getting a handle on this particular colouring technique. Occlusal surfaces are no longer painstakingly built in veneer porcelain but copy-milled from the fullcontour
mock-up frame. The frame is then fi red in a sinter furnace following a specific program designed for Prettau material. The fl exural strength of Prettau Zirconia lays 10% below regular zirconia but this shortfall is more than compensated for by the extra frame dimension (full contour!): No need to maintain space for veneer porcelain! Therefore actual flexural strength increases by up to 200%.
Prettau Zirconia is available in seven blank sizes and two different thicknesses (16 mm and 22 mm).