After preparing all four axial walls of the crown preparation, look through the occlusal view and you can notice that the crown has a rather boxy shape. When viewed occlusally, a crown prep should have a round shape (no sharp axial walls) with even and obvious margins. Smooth the sharp corner by NOT isolating the bur on the sharp corner but moving the bur in wide directions of not more than 1.5mm wide until the corner is smoothed out. Still, you have to curve around that area to not make it flat.

Next, when you can check the taper of the walls, whether there are under tapered or undercut areas. Every aspect of the crown, should have a uniform taper. Just think that the crown has a uniform 3 dimensional shape with uniform tapered walls on whatever aspect you look at. To be sure, one trick is to grab your periodontal probe, place it close, touching the entire length of the wall. If there is a gap somewhere between the instrument and the wall, it means that the wall is uneven or has an undercut. Remove this by carefully gliding through, sweeping the entire wall in one direction that covers at least 1.5mm.

Next, place a small bevel on the non-functional cusp to get rid of sharp angles. Always make sure there are no sharp angles anywhere and round-off anything that feels sharp with your finger.

When finishing margins and walls, it is very important still to parallel your burs along the long axis of the tooth. Otherwise, you will definitely get an undercut somewhere that is very hard to undo if happens so. Though even your main objective is to finish the margins alone using burs, it is always best to consider the walls with it. Since margins and walls are made together, it is also proper to finish them together as well. Some may find it hard or be afraid that they may unnecessary reduce structures along the walls, an important key to always remember is a firm and stable hand rest and a light pressure along the walls.

Michael’s Video (Margins and Walls Posterior)

Michael’s Video (Cornered Walls)