Post-Processing is one of the most important steps in achieving a successful 3D printed dental model or appliance, and can easily be executed in a brief amount of time. When following the instructions for printing an intraoral appliance, the results are cleaner, smoother, more precise, and definitely safer for the patient. The products, tools, and equipment needed are often already being used in most dental laboratories or dental practices. To make the process more efficient, some manufacturers carry specialized equipment to clean and light-cure the printed devices.
Once the digital part has been completed and the print is successful, the analog task is condensed to basically three easy-to-follow procedures. The first step is the cleaning process, the second is the polymerization of the resin and the third is the polishing procedure.
Removing the printed structure from the Build Platform
An important recommendation in safely removing the printed patterns is to always wear gloves to avoid any uncured resin residue to stick to the operator’s skin. Uncured resin is toxic.
With the assistance of a tool like a metal chisel knife or plastic spatula, tap on the supports by placing the knife underneath the sprues, at the junction between the platform and the print, and scrape off the structure from the Build Platform. Placing a clean tray or paper towel on the working bench insures that the structures drop on a clean surface when detached from the build platform. Some of the sprues can be easily removed by hand or with the help of pliers. Remember that the units are still sticky and the structures at this point are prone to attract dust. Keeping the surrounding area clean is very important.
Cleaning the printed structure
Place the units in a container filled with 91% Isopropyl Alcohol (available at any drug store). With the help of a timer, set the container in an ultrasonic unit for five minutes. The vibration and alcohol will allow for about 90% of the excess resin residue to come off the structure. This procedure is what we normally call the “Dirty Bath”. A second container filled with 91% IPA is necessary for the “Clean Bath” procedure. The container is placed in the ultrasonic unit for another five minutes to conclude the cleansing of the resin.
Another way to do this is to immerse the Build Platform with the structures still attached to the plate into a container previously filled with 91% Isopropyl Alcohol, and use the vibration of an ultrasonic unit for five minutes. Repeat the procedure for a second bath, then detach the structures with a metal chisel knife or plastic spatula. This is also an accepted alternative to clean the printed units.
A great example of a unit that employs a similar process is the VeriWHIRL. The unit uses the same alcohol in two baths, but cleans with an oscillating, multi-speed stirrer every 60 seconds using a tornado-like vortex.
After the cleansing process, the structures must be completely dried with an oil-free air compressor or by simply placing them on a paper towel to air dry effectively. This is a perfect time for inspecting the structure.
Light Curing 3D Prints
Before light-curing the printed structures, make sure to follow the manufacturer’s instructions for the specific resin and indication. For instance, a model requires a polymerization process different than that of a temporary crown or denture teeth. In addition, the directions for the curing unit must be followed to successfully polymerize the resin.
Some curing chambers are programmed with a timer and some must be set by the amount of light flashes. Furthermore, there are units that can be used with nitrogen to prevent oxygen inhibition at the surface of the structures. Some units do not require the use of nitrogen nor a glycerin substance. These units are easier to use, more efficient, programmable with the required curing time with the additional advantages of being more affordable and suitable for both laboratories and dental practices. A great example of this is the VeriLUX Curing Unit by Whip Mix. Once the curing step is concluded, allow the units to cool before removing the remaining supports with plyers. Cut them as close as possible to the structure.
Finishing and Polishing
The finishing and polishing of the printed objects are determined by the type of structure being worked on. Polishing and finishing a denture is slightly different than that of a temporary crown. In all cases, it is very important to remove the dimples from the surface and smooth the rough area where the supports were connected using a coarse fiber wheel mounted on a mandrel and powered by a handpiece set at about 10,000 rpm. Continue to smooth the appliance with a fine fiber wheel to remove any scratches. Using a lathe with pumice helps remove the micro-scratches of a splint and denture base. To give it a final gloss, the best product to use is a polishing wheel with polishing compound. Proceed to clean the appliance and make sure to remove any debris or residue from the polishing paste in the intaglio area.
Some printed objects require a slightly different method for post-processing, but in general, if we follow the resin’s and equipment’s IFU (Instructions For Use), and develop an effective polishing technique, the process will result in a functional and attractive printed object. My recommendation is to research products and equipment that will facilitate the process of post-production.