When looking at the buccal/Lingual View, these are the things that you need to look out for:
- Tapering of Proximal Walls
- Interproximal Margins
Tapering of Walls
Before, a parallel wall is the ideal because in this manner the crown is less likely to be dislodged when an oblique (or sideways) and lifting force is applied on the crown. However, creating this nearly parallel wall also creates more chance of errors (i.e. undercuts). So research say that a preparation could have an optimal taper just to prevent us from creating undercuts but it would still have enough retention for the crown. The optimal taper actually varies a lot but a simple guideline could be followed: Tapering should be visible, not to be exaggerated but just enough that is evident.
Depending on which tooth we are working on, the acceptable degree of taper varies a lot. For example, when we are doing long crowns such as the anteriors, it is ok to taper more a bit but when on the posteriors with shorter crowns, tapering should not be exaggerated but still evident.
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The tapering of the walls also corresponds to the long axis of the the tooth. This principle should be taken into fact that your bur needs to follow the long axis of tooth. This is done especially on the lower molars because the angulation is tilted lingually. Remember when you had your practice on Class II of lower molars, you have to keep your bur angulation slightly lingual? You also need to apply that principle when reducing the axial walls of a lower molar. Since the tooth is lingually inclined, your walls should follow on suit so that you will create even reductions on all walls. Refer to this video on how to carefully analyze a tooth’s angulation and effectively replicate that on your bur angulation.
Refer to this video on how to make perfectly tapered walls on a lower molar tooth!
Axial Reductions and Margins
Not everyone knows that both of these features need to be done right at the same time. Most would like to do it separately, for instance, if they want to make the make margins defined, or just make it alone, they always focus only on the margin itself and while doing so they loose track of the angulation of the bur, creating a very huge undercut near the margin. The correct way of doing this is that you have to always retrieve the bur angle that you have done before, making sure that the whole surface of the bur touches the wall. And then, you may proceed on making the margins and walls at the same time.
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Interproximal Margins
Adequate clearance from the adjacent tooth is very important as well as making the interproximal margins as low, 0.5 to 1mm above the gingival margin. More often seen mistake is that there is a lump of enamel here. This area should be smooth, even and continuous. To check, run the tip of the explorer on this area.
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Lingual Segment
Common mistake is especially when working on an anterior tooth is that the lingual wall (or the cingulum) gets a little small or become nothing at all. Remember that we need this wall because it helps with the retention of the crown.
Also, the taper of the lingual wall needs to correspond with the gingival portion of the labial wall. That both of these walls are converging incisally. When done properly, this will create a very good line of draw for the crown.
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