It can be an incredibly frustrating clinical situation, when you have been meticulous about preparing a posterior tooth, (most commonly a molar) for a crown and things aren’t predictable. Using your burs you created depth cuts to ensure adequate occlusal clearance. After the impression you allow your assistant to fabricate the temporary only to have them come get you. Why? Because the temp is thin or perforated on the occlusal. When you go back to check, and have the patient bite, sure enough the opposing tooth is touching your prep.

A common reason that this happens is because we just prepared away the patient’s first point of contact in centric relation. The lateral pterygoid muscle in coordination with the elevator muscles has a learned pattern of firing that bring the mandibular teeth into maximum intercuspal position. This “learned” position is programmed by the patient’s first point of contact when the condyles are seated. For some patients when we remove this contact, and therefore the message that was programming the muscles to locate MIP, they release quickly. When the muscles release and the condyles seat, the occlusion is now totally different than MIP was moments before.

One solution that I considered briefly was to no longer work on molars! Alas, not a great business strategy.

Removing this frustration is about understanding which patients are at risk. Identifying risk begins with the exam, whether we are discussing caries or occlusion. There are several key factors that alert me to this potential issue. I start by identifying the patient’s first point of contact and clarifying if it is on the tooth we are about to prepare. If I am going to prepare FPC away, then I look at the magnitude and direction of the patient’s slide, or the difference between this position and MIP. If the difference is small (1-2mm), then even if their condyle does seat the occlusal difference will not cause an issue for clearance. So large slides (3mm or greater) could cost approximately 1mm of clearance on the prepared tooth. Other factors include whether they have a history of occlusal changes or more than one MIP they can find.

Understanding the risk, still leaves us with the question of how to proceed. That is a longer conversation for another post. However, if we proceed as we would before, at least knowing the risk we can explain this to the patient ahead of time, and help them understand how we would manage it if it happens.

There are three critical components to the incisal edge anatomy of anterior teeth. Understanding the function and esthetics of the pitch and two bevels is essential to creating an ideal patient result.

How can a clinician re-create the full anatomic form of the tooth in ceramics and composite? 

In my last blog on this topic, I discussed the dimensions, characterization, esthetics, restorative approach and challenge of mimicking ‘pitch‘ esthetics. Now, I’ll delve into mastering the bevels to create superior restorative results. Combining an esthetic pitch with functional bevels will ensure a smooth composite or ceramic outcome.

Components of Incisal Edge Anatomy Function and Esthetics: Bevels

The two bevels can be found on alternately the labial and the lingual of the transition zone between the pitch and these surfaces. They are often called the leading edge and the trailing edge.

Bevels

Dimensions: The bevels on both sides have a variable width. They can be between less than a millimeter to multiple millimeters long.

Characterization: The bevels lengthen in patients who grind their teeth in an excursive pathway pattern. Patients who parafunction edge to edge might eliminate the bevel. This makes it easier to shear enamel off on the labial or lingual side of the tooth. It also could result in chipping the edge enamel.

Function: The bevel is a transition zone to create smooth functional movement passing from excursive movements onto the pitch. Intercuspal stops on lower incisors are often on or gingival to the bevel.

Whether you are finalizing an equilibration, the occlusion on composites, or ceramics, perfecting anterior guidance is all about both pitch and bevel surfaces. These critical components are a great example of marrying form and function in your technique.

What is your restorative approach for recreating incisal edge anatomy? We’d love to hear from you in the comments!