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| How we determine the best preparation for a crown? The safest preparation for the patient is the parallel preparation. This way you are equal far away from the nerve. Because the parallel prep may create undercuts the best preparation is considered 6° conical (3° each side). Everything more than 10° and approaching 20° or going over can damage the pulp (nerve) and coarse necessity of root canal treatment after crown is cemented. The following illustration will help you to understand the rationale for this. As conical you prepare to the right as closer you come to the nerve of the tooth with high possibility to damage the nerve
By the way we have burs 3° inclined, which allow us to achieve this goal automatically without any problems.
This consideration bring us to prepare the teeth as parallel as possible. See some of my preparation:
If you do not follow this rule may come to complication root canal treatment in the following case:
This Picture illustrate bad execution of root canal treatment and crown. It is almost certain this crown will not hold very long. The post is symbolic extremely short. Post should be extend for about 2/3 of the root to hold! Next picture illustrate the correct length of post:
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The last picture is the correct preparation.
