How to Ensure Adequate Mandibular Reduction Without a Guide

If you’ve done enough All-On-X cases you know that quite possibly the worst, gut wrenching feeling you can get is realizing post operatively that reduction was inadequate. 

This leads to a host of problems such as a thin prosthetic prone to fracture, having to unnecessarily open VDO, lip incompetence, and the dreaded visible transition line of the prosthesis. 

I have written an article you can access here, on “The Best Way to Confirm Your  Alveolar Reduction is On Point” for both the maxilla and mandible. 

This assumes of course the reduction is planned. Which, let’s be clear, it always should be planned pre-operatively. Preferably, by the restorative provider who will manage the prosthetic.

However, there are times when the following scenarios may occur: 

• You have carried out the pre-op planned reduction measurements, but intra-operatively things seem off and the pre-op VDO is not accurate with the intra-op VDO.

• You have received a patient as a referral from a restorative provider who should have completed a pre-op assessment of smile line, VDO etc but they forgot to include reduction numbers. 

• You have spent a lot of time and money creating a digital reduction guide…and now the guide doesn’t seem to fit intra-operatively. 

In these scenarios, as sweat starts to show through your surgeon’s cap, you try to keep your cool. You’re wondering how in the heck you’re going to ensure you have enough reduction for this case without reduction numbers or your fancy guide… 

Thankfully for you, the mandible has provided all surgeons a pre-made, built in, free mandibular reduction guide. And get this…it’s even applicable to edentulous cases! 

You can relax and dry off your surgeon’s cap as you set aside your $1000 reduction guide that doesn’t fit very well. 

As you gaze back upon the mandible you see an amazingly clear reduction line, seeming to almost pop out at you…the external oblique ridge. It’s always been there staring at you. How did you not notice??

I felt this way too. It had always been there for me…waiting to guide me. But early on, somehow I overlooked it. Finally I gave in and let it lead me. The external oblique ridge hasn’t steered me wrong since. 

Now, I simply take a sterilized #2 pencil and draw a line along the external oblique ridge. I then extend this pencil line, at that same height, anteriorly along the mandible. I proceed to complete my reduction to this pencil line – essentially an extension of the external oblique ridge.

This has been adequate reduction in literally every case I have done since initiating this protocol. For reference, I have been using this method since 2022 (approximately 800 arches as of this posting).

The beautiful thing about using the external oblique ridge as a guide is that it eliminates the most problematic area – the posterior mandible. It ensures adequate reduction in this frequently under reduced anatomic region. 

For those of you feeling like you may lose your way as you wander toward the anterior mandible, don’t fret. Here, take your reduction to the bottom of the central incisor socket and this will be adequate virtually every time. 

The video below is my drawn reduction line along the external oblique ridge extending to the bottom of the mandibular central incisor socket. The perio probe is used to highlight the 15mm (or more) of planned reduction from the incisal edge of the second pre-molars and central incisor that this technique provides.