With the large variety of restorations that digital laboratories are now producing it’s essential to use best practices when performing the CAM operation. In this 3-part blog series, Razmig Tatoulian and Alex DeVos of the CAP/Zahn Support team will review step-by-step instructions for spruing the most common restorations, including screw-retained, Maryland bridges, inlay/onlays, and veneers.
Number of Sprus, Placement, and Positioning
We will begin with bringing in a regular crown in SUM3D. Usually it comes into the program with sprus automatically on the restorations, but these need to be adjusted because the software doesn’t know how to read the anatomy. For most types of units and almost every material all you need is one spru on buckle and lingual side, the only exception is bridges and molars if you are milling it in zirconia. When milling molars in any other materials such as PMMA or wax you can still get away with only using two sprus. For molars in zirconia, we will need a total of three sprus, making sure they are at the correct height. Remember not to position the spru too close to the margin or the top, placing the spru at the height of contour. If you place it too high there will be a small triangle of space hidden below the spru, which the mill would have a hard time reaching, making more work for you after it is milled out.
Spruing an Example Molar
In our example of a molar, we will have three sprus total. Making sure to add the two sprus near the corners of the crown, not too close to the cusp or the marginal ridge, and at the height of contour. You can make one of the sprus fully “cutable”. In SUM3D that means one of the sprus will be green, so it will be completely cut away at the end of being milled. The green spru should be on the side with the two sprus and should be the one that is slightly at an angle compared to the other sprus. The red sprus are going to be cut half way through. After that, we are finished spruing this restoration and ready to move on to the next.
This was the first of a three-part series on spruing best practices. Be on the look out for the additional blog posts coming soon or check out our on-demand webinar, Spruing 101: Best Practices By Restoration Type.
Note: Please note that the workflows discussed in this blog are based on Sum3D Dental and Roland DWX 51D. The approach and techniques discussed are based on our internal R&D, and can be used as rule of thumb for day-to-day operations. Techniques and approaches you will see in this post can also apply to different milling systems such as Amann Girrbach or imes.