Have you ever received a call from your lab telling you that they need more room to complete a case ideally? While it's a call we as restorative dentists never want to get, it is almost inevitable. However, over-reduction can also be undesirable as it compromises the patient's tooth. Today I would like to discuss some tips that can help you avoid both over-reduction and under-reduction.

As restorative dentists it's easy to fall into a trap when we think of tooth reduction and the given amount of room needed for our cases. We can too easily jump to the conclusion that the amount of room needed for the material being used is the amount of tooth structure that needs to be removed. While this can sometimes be the case, this logic only works if the tooth being prepared is the same size and in the same position and orientation of the desired final restoration.

If for instance you are preparing a central incisor that has been worn down 1.5mm and you plan to restore it with an incisal edge position that is 2.0mm more coronal to its current position, then you only need 0.5mm of reduction. In a case such as this, to reduce a full 2.0mm off the insical edge of the worn tooth, you would drastically over-reduce. Conversely if you are preparing a tooth that has super-erupted you will have to add the amount of super-eruption to get the true overall reduction needed; if not, you will under-reduce. These same principles can be applied to any tooth that is not of the same size and in the same orientation of the desired end restoration.

When the end goal is to correct the size and/or positioning of teeth through restorative means, I find it hugely beneficial to have a diagnostic wax-up completed for a couple of reasons. It confirms that my vision can actually be completed. Also, assuming that I can achieve the desired goal, I can then fabricate reduction guides based off of the wax-up to aid me in achieving the proper amount of reduction.

I hope you have found these tips helpful in thinking of room versus reduction when you prepare teeth. In future articles I will go deeper into preparation guides and specific techniques to help apply the general concept discussed here.

John R. Carson, DDS, PC, Spear Visiting Faculty. [ www.johnrcarsondds.com ]