When looking at the proximal view:
- Tapering of the buccal and lingual walls
- Bi-planar labial reduction of anteriors and premolar
Aside from the tapering of the buccal and lingual walls, the bi-planar labial reduction needs to put on a lot of focus here.
Two-plane Reduction
When you look at the incisors on the mesial or distal view, the labial surface has a curve. Since crown preparation needs to preserve the anatomy of the crown while creating space for the bulk of the material, our prep should also have this curve as well. To simplify things this curve can be divided into two parts: Gingival half and Incisal half. While thinking that this curve has two parts, these are actually coherent to each other with a smooth transition in between. Also the difference of both angles should not be that great. Otherwise, your prep will have an awful angle on the labial surface looking as if it is a beak of a bird (which we obviously do not want!).
Video here
Tapering of Buccal and Lingual Walls
Most often overlooked feature when looking at the proximal view is that the buccal and lingual walls should be tapering towards the line of draw as well. To be specific for the anterior teeth, the gingival portion of the labial surface and the lingual wall (cingulum) should converge towards the line of draw. It is important to perceive the crown as if in a 3 dimensional shape (like a cone). Thus in whatever aspects you look at, the axial walls should have a uniform taper, each pair of opposing walls should all converge towards the line of draw.