We call this the “rule of the sprue.” We always place the sprue on the largest and most bulky portion of the ceramic for milling. We even do this if the sprue goes on a contact. Why? Well, we’ve all seen something chip during milling. It comes with the territory for milling ceramic. We see very few failures of milling when the first part of the restoration has the most intricate, or thin, areas. This will leave the largest portion as the last to mill. This helps support the 3D shape of the restoration as it goes through this process.
Many will place the sprue for “convenience,” and that is OK, but the one time it should’ve been placed at the bulkiest position, but wasn’t, will be at the most INCONVIENENT time!
Our SRS instrument, the Sprue Removal System, is spectacular with removing sprues of any kind, except green state zirconia. You can find them HERE.