Most often when we think about the labial surface as having 2 planes, we tend to overdo it and rather make two distinct planes with an angle in between. This is a very common mistake. The labial surface should not look like a bird’s beak when viewed mesiodistally!

Since you have been taught about the classical approach, we really recommend this approach more because you will less likely to have that weird angle. You have to think that these two planes should have a good transition from gingival to incisal. In order for us not to make the labial surface with an awkward angle, we reduce the gingival 2/3 first, then the incisal 1/3 after. In this way, as we reduce the incisal half, we can connect it with the gingival half, creating a very smooth transition with it.

Gingival 2/3

When reducing the gingival portion, there will be a lot of things that are possible to be getting messed up with if you are not very careful with the bur angulation. You may end up getting an undercut or an over-tapered wall. There two reference that you can base your angle on:

1. Check the general angulation of the gingival portion of the labial surface. Do not be distracted by the angulation of the cingulum near the gum line, this is not the right angle. Just look at the POINT where the curvature cingulum transitions to the labial surface and FROM there go towards incisally. Place your bur on this surface and check for its general angulation of this slope. This will be the right angle.
2. The gingival surface is nearly parallel to the long axis of the tooth. This principle lies to the fact that the gingival half of the crown influences the actual path of draw of the crown. When your bur is kept parallel to the axis, then your path of draw should be perfect as well, creating less chance of making undercuts.

When doing the depth grooves for the gingival 2/3, it is normal for it to be extended all the way towards the incisal edge, especially if your depth grooves are deep (1.5mm deep). So it is also normal for the gingival reduction to be extended towards the incisal portion as well. When connecting all of these grooves, always remember to smooth everything out until there are no noticeable bumps and the whole surface is an even plane.

Incisal 1/3

Up to this point, the incisal 1/3 of the crown has been reduced too. However, this section of the crown needs to be reduced again because we want to have a bi-planar reduction, right? This area must have its own reduction to allow for an adequate space for the crown material.

However, since much of the original tooth structure has been reduced, our reference now would be the adjacent tooth. So place your bur on the incisal 1/3 of the adjacent tooth and get the general angulation.

You may not place depth grooves for this step, and by using your obtained angulation, reduce the incisal 1/3 on the get go. After, go ahead and smoothen the angle between the gingival and incisal portion. The angulation between these two slopes are not great but when using a perio probe to compare them, it is actually evident.

Insert Michael’s video