Aside from under reducing tooth structure, one of the biggest mistake of doing crown preparation is an under tapered crown. it is advocated that an ideal taper should be around 3 to 4 degrees on each wall (6 to 8 degrees when combined). This taper will ensure no undercuts for easy insertion of the crown and avoiding too much distortion of the impression material. This taper is kept minimal because too much of it will decrease the retention form of the crown.

Before, a parallel shaped bur can be used to reduce the axial walls of the crown. However, it is very difficult to achieve a tapered wall using these burs because you have to be very mindful of your bur angulation. You have to manually taper your bur to achieve a taper wall. So this leads to increase margin of errors such as undercuts and unequal reduction of walls.

To prevent such operator errors, manufacturers nowadays make burs with a tapered shaped to make it easier for us to achieve a tapered wall. So, all we have to do is just keep our burs parallel to the long axis of the tooth and the bur will do the tapering for us. So doing a taper is all simplified, it just that you need to make your bur parallel to the long axis of the tooth. Let me ask you a question, so in making any axial wall, what angle does your bur need to be at?

It needs to be always parallel to the long axis of the clinical crown. So with that, we only have to keep in mind of is the depth or the amount of reduction that we have to make; that reduction will depend on what type of crown you are doing.

In the bench test, it is a must that you have an evident slight taper all through out the aspects of the crown. Think of your crown as a 3 dimensional shape, when you shift the crown looking at in the buccal, lingual, mesial or distal aspects, the axial walls should have a taper or it is slightly converging towards the occlusal/incisal area. Be sure to meet this requirement before submitting your crowns for checking!

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