As you all know, there are two types of abutments. Stock abutments which are designed and sold by implant manufacturers, and custom abutments which are made by dental technicians according to patients’ cases. Abutments can be divided into two types as like this.
Roles and Advantages of Custom Abutment
Since the custom abutment is manufactured according to the shape of the prosthesis, mechanical complications or screw loosening appear significantly less. In addition, it shows a very high success rate even with the posterior teeth where high masticatory force is applied.
The correct abutment design and the importance of CAM system that reproduces the design.
However, in order to achieve these results, the correct custom abutment design is essential. Even if the custom abutment is precisely designed using a CAD system, it is difficult to guarantee success if a CAM system cannot support it.
The limitation of the 4-axis milled abutment
The reason why the CAM system does not perfectly reproduce the design of the custom abutment is because it is made with 4-axis milling. Most 5-axis milling machines use only 4 axes when milling the custom abutment.
For this reason, even if the margin line of the abutment is beautifully designed along the gingiva line, the milled abutment is sometimes separated from the gingiva.
If the chamber or the shoulder of the margin line is designed to ensure the thickness of the prosthesis, it may not always be possible to ensure it after milling.
This is the limit of a 4-axis milling machine.
Also, it is difficult to secure the thickness of the prosthesis since the undercut on the occlusal side cannot be milled at all and the occlusal surface must be re-trimmed by hand to secure the thickness of the prosthesis.
The 5-axis milled abutment with a case
However, if this abutment is milled with 5 axes, these problems can be solved easily and simply. This is because the shape and the thickness of the margin, and even the shape of the occlusal surface can be reproduced perfectly. This is directly related to the success of the implant.
The difference between the 4-axis milled abutment and the 5-axis milled abutment.
Now, I will explain how different between the 4-axis milled abutment and the 5-axis milled abutment with a case. I designed an abutment and milled it in 4 axes and 5 axes. Let’s scan these abutments to see how different these are.
The data above is the CAD data that I designed. Let’s go to Expert mode, select the Gingiva type, and load the data for 4-axis milling.
I will begin Align Meshes.
As you can see, the occlusal surface is very different.
The chamber part, which is the distal part, is likely undercut because it has not been milled. As you can see, there is a huge difference. Then, let’s load the data for 5-axis milling this time for comparison. I select the Gingiva type as well and load the data for 5-axis milling.
You can see that the occlusal surface and the margin are reproduced very precisely. Let’s check the data at the same time.