PFZ...what is it?
Jerry Ragle, CDT
Porcelain fused to zirconia is now old school....
When zirconia first hit the market in 2009, with the introduction of BruxZir, it soon revolutionized the industry. It was strong, cheap, and pure white. The only way to shade it was dipping the milled restoration is colors, like dipping easter eggs in food coloring.... so much fun. As with everything, materials evolve, thankfully. The dipping process was tedious and burnt up every 6 months or so the $700 heating coils inside the sintering furnace due to the burn off residue from the liquid, but it worked, that’s all we had.
Then came a long pre-colored zirconia. That got rid of dipping, to a certain degree, but instead of dipping, we painted the incisal and gingival due to the monochromatic look. Then Multi-layered zirconia’s came to market, but strength became a factor. The more translucency in the shade the weaker the material. So early ML was great for anterior, but not so good for posterior, unless the joints were low in the puck. Today, we have not only multi-layered and translucency, we also have 1200 Mpa of strength from top to bottom, thus eliminating the need for PFZ which isn’t strong to begin with.
Keep in mind that PFZ stands for Porcelain Fused to Zirconia… It looked better than a PFM, but as a PFM the coping material is only as strong as the thickness of the coping, and you still need space for the felspathic porcelain that needs added which is weak. Don’t get me wrong, PFM was the one and only throughout my career and as long as proper anatomical thickness was maintained, meaning even support for the final porcelain, it worked, as did PFZ. Clinically there were fractures but very few by comparison to the number of crowns and or bridges being done.
Today multi-layered high-strength zirconia has replaced for the most part PFM and definitely PFZ. The main reason is the digital process. Not many technicians today know how to “stack” porcelain. I actually hate the word “stack” because one was pretty talented to layer 15 shades of powder with a brush and then barely touch it to complete the finish contour, back in the day.
An early technique to incorporate the digital process was to split design the coping and ceramic top. Metal was SLM (selective laser melting) and the top was wax printed and then ceramic pressed. Tedious technique. Today given the improvements of materials, software and mills, restorations are digitally designed and milled using a monolithic material as the material of choice.
Strength wise, zirconia is strong, it’s monolithic as mentioned unlike PFM and PFZ, but there are those cases where it simply doesn’t work, and a PFM is still in order. It’s quite rare, but long spans in the posterior with little vertical where a joint can’t be 4mm x 4mm minimum, the patient will most likely fracture the zirconia. Also, if zirconia is ground on and you see a spark, keep in mind you just set up a micro fracture.. It may not fracture today but it will when the patient is drinking a glass of milk, we have all heard it.
So, there you have it, for more information on Zirconia strength see the article What We Have Learned.