Pressable ceramics have become a top choice of many clinicians because of their ability to create such esthetically pleasing restorations. With our Z4 Investment and Disposable Plungers being great choices for improving pressing results, we've had an opportunity to help many dental laboratories troubleshoot different types of problems.
Many of the newer all-ceramic materials can be tricky to use at first and users must often make adjustments to "dial in" their results. With that in mind we thought we would share a few of the problems and solutions we commonly see.
1. Use the leveling cap when you pour up the ring to make sure that the top is as flat as possible. To get rid of the "nub" left behind by the leveling cap just use a plaster knife to gently remove it. Remember the top of the ring will be the base when you are pressing, so even a slight angle can lead to split rings or short presses.
2. Large rings require additional bench set time, and with our Z4 Investment we want the rings to be mostly cool and dry before placing them in the burnout furnace. It's a good idea to pop the investment out of the ring after about 30 minutes and let them sit for an additional 10 - 15 minutes. This is especially true for 200 gram rings and 300 gram rings, since it takes that larger mass longer to fully set.
3. Once you remove the investment from the ring and take the base and cap off you do not need to scrape the top of the ring to "allow the gasses to escape". While the whole theory seems kind of like rubbish to us, maybe it was necessary 50 years ago and maybe these other companies are selling investments that were developed 50 years ago - but with Z4 it is not needed.
The reason we strongly advise against scraping rings is because of the way the process is often carried out. Typically we see an old model trimmer wheel or a piece of sand paper on the bench, and techs take the ring, turn it over and aggressively grind it on the wheel or paper. We've also seen some labs take the ring and trim the top with a model trimmer. In all of these cases the grinding can cause micro-fractures and lead to rings that will split. In the case of a wet model trimmer, reintroducing water to the ring can cause the top to blow off in the burnout furnace.
4. If you are still using Alox plungers our advise is to switch to disposable plungers. With Vacalon Disposable Plungers you get a clean plunger every time you press. With Alox plungers you have to manually clean them, and even after the chemicals and blasting you can't be guaranteed all of the material has been removed, possibly resulting in in contamination. Furthermore, repeated cleanings can cause Alox plungers to become deformed and distorted, leading to cracked rings.
5. The burnout furnace and the pressing furnace both play key roles in the pressing process, and can make or break the results. The most important thing about the burnout furnace is the accuracy of the temperature. We've seen burnout furnaces run anywhere from 200°F over to 200°F under their displayed temperature.
We also see many problems related to the pressing furnaces, and one of the major issues is using older standard pressing furnaces to try to press lithium disilicate materials such as e.Max® Press. While it is entirely possibly to use these older furnaces, getting things dialed in can require a lot of trial and error. Most furnace manufacturers have specific instructions for pressing lithium disilicate, and often times making these changes will help improve results.
The best option is using a newer furnace designed with lithium disilicate in mind, as they much more intelligent and offer more features. We've seen labs spend countless hours and waste expensive ingots only to come to the realization that their 15 year old furnace simply isn't cut out for the task.
These are just a few of the things that can help avoid unexpected results and reduce wasted time. In the end it is about getting your set up dialed in and eliminating the variables. Once you have removed the variables, as long as you keep things consistent you should achieve consistent results.
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