#DNotes Memo Concerning Tools for Dental Tooth Reduction

Most dentists are well aware of the documented requirements for tooth reduction in various situations. For example:

PFM: Incisal = 1.5 – 2.0 mm ; Facial = 1.5 – 2.0 mm ; Lingual = 0.5 – 1.0 mm

PFZ: Incisal = 1.5 – 2.0 mm ; Facial = 1.5 – 2.0 mm ; Lingual = 0.5 – 1.0 mm

FZ: Incisal = 1.5 – 2.0 mm ; Facial = 1.0 – 1.5 mm ; Lingual = 1.0 – 1.5mm 

e.Max: Incisal = 1.0 – 2.0 mm ; Facial = 0.5 – 1.0 mm ; Lingual = 1.0 mm

Yet a very large number of unaesthetic as well as weak dental restorations are ultimately caused by under-reduction, simply because the dentist is unaware how to measure! 

Very useful tools do exist to help the dentist know how much to reduce teeth in order to get both aesthetic and strong results? At Shanto, the most useful tool, we know of is the Flexible Clearance Guide – made by Belle de St.Claire, and sold locally by Patterson Dental. We use it in the lab all the time, but it is particularly useful chairside because it is flexible! 

When you use it, please note that you must be able to pull the Flexible Clearance Guide through WITHOUT RESISTANCE in order to know that you have at least as much clearance as what the guide indicates (0.5, 1.0, 1.5, 2.0, 2.5, or 3.0 mm)! 

Also, please note that there is an important difference between clearance and reduction!!! Clearance is the space created between the prepped tooth and the opposing. Reduction is how much you have reduced in relation to the planned shape of the restored tooth. For example on facial surfaces, clearance is irrelevant because there is no opposing dentition, but appropriate reduction is still important because you don’t want the facial of the restoration to be “sticking out” after the restoration is made. 

In addition, premolars and molars actually have occlusal surface areas that need reduction which has little or nothing to do with clearance – such as marginal ridges (where opposing cusps should not occlude), or situations where there is no opposing tooth (i.e. lots of clearance) but where measuring reduction is still important to get the correct restorative anatomy! 

Please remember that on its own in the mouth the Flexible Clearance Guide measures only (not reduction). In order to make accurate measurement of reduction (e.g. facial surfaces), you need to use the Flexible Clearance Guide in conjunction with another tool – a Reduction Guide – which can be a putty index of say the pre-op tooth or a wax-up! This is the reason you should ALWAYS use a Reduction Guide when you are prepping anterior teeth, because appropriate reduction of facial surfaces is of course super important and has nothing to do with clearance! Hence when you are planning to prep anterior teeth, should ALWAYS do a wax-up – even for singles! All wax-ups you send to Shanto, will always be returned to you with a Reduction Guide. 

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