The Importance of Perspective in Incisal and Occlusal Assessments

The most fundamental element in planning and treatment is to level the incisal and occlusal planes relative to a correct head posture. Accurate assessment and communication of the pre-operative scenario is essential to resolve any problems. In this article, I will address the importance of perspective when making incisal and occlusal assessments.

Orthodontics, orthognathic surgery, periodontal procedures, complete denture prosthodontics, and restorative therapies all use horizon as the standard reference. Once the incisal plane is level, the gingival heights can be adjusted accordingly, and the maxillary midline can be made perpendicular to this horizontal plane.

Why is this so important? Because successful design of the occlusal scheme provides a result that is more esthetically pleasing. To accomplish this, you must have an accurate means of transferring the existing condition of the patient to the articulator, generally using an esthetically corrected facebow. 

What Do We Mean by “Level” in Incisal and Occlusal Assessments?

To achieve the most ideal esthetic and functional outcome for the patient, the goal in virtually all dental therapies is to level the incisal and occlusal planes to horizon based on the corrected head posture. This can raise the question: what is level? Is it perfectly level to horizon or is there a slight curve to the incisal plane? Does the incisal plane “follow the curve of the lower lip?”

I believe the concept of “level” is dictated by the perspective of our view of the plane. If our eyes are in alignment with the maxillary occlusal plane, the incisal plane will be “level” with horizon (Figure 1).

 

From an occlusal view, the maxillary arch is curved canine to canine; the incisal plane is truly a plane, not a line. When evaluating a patient—or, more challengingly, a photograph, which is two-dimensional—it can be easy to think a line drawn “canine cusp tip to canine cusp tip” establishes the incisal line. If your view is parallel to the occlusal plane, a flat line can be drawn from cusp tip to cusp tip, negating the fact that the arch is curved anteriorly. Once you incorporate the slope of the occlusal plane, anterior to posterior, relative to the correct head posture and true horizontal, a curved line canine to canine will become apparent. This curve will be exaggerated if your clinical assessment is from too high a position or if the photograph is taken from high and shooting downward (Figure 2).

 

Be sure to communicate this information to all relevant members of the dental team. And I strongly recommend that the procedures needed to capture this information are completed during the initial diagnosis and treatment planning phase, and again during the provisionalization stage if indirect restorations will be fabricated.

In the laboratory, a facebow transfer is used to mount the maxillary cast. Freehand mounting can lead to an error in the occlusal plane and midline if a cant exists because, unless told otherwise, the technician will assume the planes are level. I recommend sending a photograph of the facebow to the lab with your restorative case to provide the technician with verification of the accuracy of the transfer. 

The primary objective in essentially all cases is to “level” the incisal and occlusal assessments and–as I hope I have shown here—perspective is a crucial element in getting it right.

Robert Winter, D.D.S., is a member of Spear Resident Faculty.