Darin O'Bryan, D.D.S. One of the most common questions we get on the forums is how to correct the short abutment proposals that occur regularly for doctors. There is at least a case a week that gets posted with an abutment that looks like this:
As can be seen the abutment is extremely short. This is in addition to the problem of the TiBase sticking up past the abutment. There is too much facial wall of the restoration and not enough of the lingual wall. This problem all stems from the restoration insertion axis.
What happened in this case and in the other cases that we see is the insertion axis is positioned to lingual. The red means it is past the 20 degrees that is possible in creation of an off angle abutment. However, even if the red was not showing, the abutment would still be too short. When positioning the restoration axis, you want to line up parallel to the long axis of the other teeth in the anterior segment.
The way I have found to explain this is to position the axis the same as if there was a tooth there that was prepared for a crown. So in the above screen shot, it is easy to visualize a crown preparation within the white area surrounding the restoration axis dot. When this is done, the abutment that is proposed at the split looks much better.
The abutment is now much better proportioned with long axial walls for better retention. The TiBase will stick above this abutment no matter how you design it but this is easily remedied by following the steps outlined in this blog.
