In the last lesson, I talked about how to create the right connector thickness. Today’s lesson is closely related to the last lesson. It is about how to create embrasures.
After zirconia milling, we usually trim the result as contouring. The problem is why should we trim it? It is because the zirconia result is not the same as the design, especially the embrasures.
As you know, there are several types of embrasures. For example, there are buccal embrasures, lingual embrasures, occlusal embrasures, and cervical embrasures.
The Role and Importance of Embrasures
The embrasure provides a spillway for food to escape during chewing process and a way for water and saliva. Eventually, these protect the gingiva. Insufficient embrasure spaces may result periodontitis or gum recession. Also, since the embrasure is a space between teeth, it plays an aesthetic role to make the teeth look separate. Therefore, we cannot give up these important roles of the embrasure.
We make some space for the zirconia bridge embrasures by hand trimming after milling. However, the connector thickness getting thinner than 12 or 15mm² which we secure for sufficient thickness. To solve this problem, we need to create the embrasure space without hand trimming. What I am going to talk about today is how to create the embrasure while designing.
How to Design the Perfect Embrasures
Here is a posterior teeth case. In the case of anterior teeth, your design can be reproduced through 90 degree milling, so the best way is to use 90 degree milling. This is a three-unit bridge case which does not require the 90 degree milling since it is a posterior teeth. I will create the buccal embrasures with it. This is the Connectors stage.
Like the previous lesson, I set 12 or 15mm² for the connector thickness and then move on to the FREE tab to design the connector shape.
I am sure that most of you finish your work at this point. If you finish like this, the embrasure space seems to be well designed, but the actual milling result is all blocked up.
It is because milling tools cannot get into the embrasure space. Always consider whether you are designing suitable for milling. Even though I have designed well, the final embrasure space would be blocked up if the tool cannot get into the space. I need to make a room for the smallest milling tool that I am using.
Let’s go to the Expert mode and trim the shape little bit.
Move on to the ADAPT tab and the Approx. tab. There is the Disk cutter option.
Place the disk cutters at the right position.
Have a close look at the pass and then open the space for the tool as big as the tool could fit in. Set as about 0.5mm for a 0.6mm tool and 0.2 or 0.3mm for a 0.3mm tool.
I set it as 0.5mm and cut intersections.
It seems little big, but 0.5mm thickness is opened between the teeth by clicking the OK button.
I need to design the space as a connector. Not too unnaturally opened, design the right shape. I will have the ideal embrasure result with this design after milling.
Now, I’m going to compare the results of the well-designed embrasure like I have done so far and without the design. I am opening hyperVIEW to compare the results of the cases with enough tool space and without tool space. You can find out the milling result in advance. Click Result and Calculate to see the approximate shape of the results.
The calculation is done.
The case on the left does not have sufficient embrasure space. The one on the right has sufficient embrasure space. The milling results show the difference in this way. In the case on the left, it looks like the embrasure is all blocked up, and in the case on the right, it looks like it is open widely.
From the buccal side, the embrasure is naturally formed on the left case, it is not formed at all and blocked up on the right case. I can check the milling accuracy as well.
I see that the embrasure is almost same as my design by setting the milling result to transparent. However with this case, it is milled with blocked up embrasures. Can you see the difference between the two data in the circles above?
As you see, there is a big difference between reserving the embrasure space and not. Once you reserve sufficient embrasure space like today’s lesson, you do not have to trim the milling result with your hands. You will keep the best connector thickness as you design. Today, we have talked about how to design the embrasure without hand trimming. Thank you for reading my lesson.