Mike Skramstad When doing hybrid abutment crowns (screw retained), sprue position is not predictable. The sprue goes usually 90 degrees from the TiBase or Scanpost notch. IMO, I just don't care much about this because the sprue is easy to remove no matter where the sprue goes. However, if you want it to not affect your contact, then in general, place the notch on the mesial or distal.
Where it really matters (the sprue) is when you are doing hybrid abutment split restorations... and this is very unpredictable and depends not only on the implant placed, but also the overall general design and restorative situation.
So Let's look at a couple cases....
This is an Astra implant.
One piece (sprue 90 degrees off tibase)
Now, if you split it, it appears the sprue is about 10 degrees off the TiBase and the TiBase didn't rotate in the software.
If we look at another implant (again an astra) but on the other side (tooth #19), almost an exact scenerio happens... You begin to think that you can predict this a little bit. 90 degrees and 10 degrees.
Low let's try another implant system: Nobel Replace Select....
Here is the screw retained (again 90 degrees)
Here is the split (again 10 degrees)
Now Nobel Active:
Screw retained (again 90 degrees)
But now the split is not 10 degrees, it is even a little more than 90 degrees. BUT... the notch stays in the same place, which is good.
Now that's look at another problem:
Here is the initial tibase notch position on an Astra implant on #13.
If we do a screw retained crown, same 90 degrees and the implant notch is stable.
But watch what happens when you split the crown... The notch goes from the DB to the ML. Also, the split sprue is not 10 degrees away from the notch, it's more like 90 degrees.
Same concept happens on this implant:
Here, the notch stays in the same place, but the sprue is in a 90 degree position opposite to the non split case:
So, you can see.... when it really matters (split cases), it's unpredictable.
