Outside~In Occlusal Design & the Sacrosanct Incisal Edge

“First figure out what you want it  to look like, then figure out how to make it fit.”

That is the current mantra of modern treatment planning in dentistry. It clarifies a methodology down to something so basic and easy to follow. The application & rationale certainly require a bit more explanation and exploration.

There is simple rationale for starting with the upper single central incisal edge in our treatment planning. The midline and incisal edge together are the cornerstone of the smile. From an aesthetic standpoint, if we start anywhere else, we risk loss of space, symmetry and starting the whole process over again. Eventually we may or will get there-maybe and with lots of effort and potential repeating of the process.

This has been exemplified through Dr. Frank Spear’s FGTP (Facially Generated Treatment Planning), more recently Dr. Christian Coachman’s DSD (Digital Smile Design) but really goes all the way back to the Hanau Quint and the fundamentals of denture setups.

This rationale however goes past aesthetics and can also facilitate efficiency in planning ‘fit’, while maintaining the aesthetics that we achieved in the ‘looks’ planning stage.

In general concept and application, this is the rationale and flow:

The maxillary incisal edge placement is designed in location through aesthetics and phonetics. In fact, phonetics becomes the first component of ‘fit.’ If we like the looks but the patient cannot talk, that really is fit issue that must lead to altering of that sacrosanct edge. It may only be a bevel or labial~lingual inclination. In some cases it may be length. After that has been accomplished-the melding of aesthetics and speech, any changes made to the maxillary incisal edge are at the expense of the aesthetic goal. Consider the edge placement at this point sacrosanct.

Next-we truly move to fit. Traditionally this has been the occluding contact of the lower incisal edge against the palatal surface of the maxillary central incisor. There are pitfalls in this approach that I will get to but let’s first explore a different approach-which is the outside~in approach to occlusal design & equilibration.

The second step involves matching the mandibular incisal edge to our desired maxillary incisal edge.  Porcelain is said to live and die on the incisal edges…and the transition to and from those edges. That is an issue of distribution of forces along a flat receiving area and the resistance encountered getting to and leaving that receiving area. So matching the lower incisal table to the existing maxillary table that we designed provides that distributed, axially loaded force (as much as possible) of parafunction.

From that edge to edge position, we move ‘outisde-in’ off of the incisal table and towards MIP. The next contact that we encounter/transition to is over the inciso~lingual edge of the maxillary central-also called the ‘leading edge.’ This is possibly the most overlooked occlusal contact area but arguably the most critical when we look at porcelain failure.  If that transition is not smooth or if the contact area in that transition is to concentrated on one small area, failure can and will occur. The leading edge then is matched to the  leading edge of the mandibular central incisor-which is the inciso~facial edge or bevel.  It has been my experience that spending time & attention to refining the tables to this edge transition will significantly reduce you porcelain chipping and fracture.

From that edge transition, we can continue the outide-in journey along the palatal surface of the maxillary central incisor and finally to the leading edge of the mandibular incisor defining the MIP occluding contact.

The maxillary incisal edge defines the mandibular incisal edge.

The mandibular & maxillary leading edges are defined and matched.

The transition between incisal tables & leading edges are refined.

The excursive  contacts are maintained outside-in which finally defines the MIP palatal contacts.

So-returning to the comment at the beginning of the blog about the pitfalls of starting ‘anywhere else’, lets talk about starting this process from the MIP contact or ‘inside out.’

The mandibular leading edge is matched to the MIP contact-sound good.

The mandibular leading edge defines and refine the excursive contacts as we move toward the maxillary incisal edge. Looking good.

The mandibular leading edge reaches and defines the maxillary leading edge-still seems to be working.

Then we get to the tables. As we transition to matching the mandibular table to the aesthetically defined maxillary edge, do they match. If not what do we do? Do we change the maxillary edge? Well-that could change our desired aesthetics. So-that would lead us to adjusting the mandibular table.  Does that adjustment affect the mandibular leading edge? If that is the case then all of the work we did in our inside-out excursions may or will need to be redone. Back and forth the process goes. Inefficiency.

Of course-there is also the possibility in the above scenario that we began with ‘fit’ and did not even set that maxillary edge first. Then we would be performing that inside-out occlusal design first then our incisal edge would either be compromised by the plane of the mandibular incisal edge. Or-we go through the whole inside-out process, then we set the maxillary incisal edge. Again-all of  other contacts  would likely need to be altered.

I hope that this helps clarify or at least shed some light on the advantages of an outside-in approach and the sacrosanct nature of the aesthetic maxillary incisal edge.

I would like to thank Dr.’s David Latz, Frank Graziano & Steve Ratcliff for sharing their knowledge, insights & passion with me on this subject back in the day at The Pankey Institute. It was truly a critical crux point in my journey.

As always, if you enjoyed this blog, please feel free to ask a question or post comment. Sharing this blog is also appreciated using the share buttons below.


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