The esthetic revolution has expanded beyond all expectations. The desire for a beautiful smile is more and more the primary reason patients seek dental care. But don’t make the mistake of thinking that smile design is just about straight, white front teeth.
There is a basic principle that must be understood if perfected smile design is to be achieved. That principle is that the anterior teeth must be in precise harmony with all aspects of masticatory system function. This requires four critical decisions:
1. The position and inclination of each anterior tooth.
2. The contour of each anterior tooth.
3. The relationship of the anterior teeth to the TMJs.
4. The relationship of the anterior teeth to the posterior teeth.
There are many different factors that influence these four decisions. So let’s try to sum up, in condensed form, some of the points in the decision process for restoring anterior teeth.
A MAJOR POINT TO REMEMBER
The position and contour of the anterior teeth are extremely important to the harmony and stability of the total masticatory system, including the masticatory musculature. This can only be understood in the context of the effect of posterior disclusion on the musculature.1 The anterior guidance plays the dominant role with help from the condylar path in separating the posterior teeth in all eccentric jaw movements.
All the teeth should contact with equal intensity when the condyles are seated in centric relation. But the moment the jaw moves in any direction from centric relation the posterior teeth should immediately separate. This separation shuts off more than two-thirds of the elevator muscles and reduces the forces on the anterior teeth during excursive movements of the mandible.
It also reduces the load on the TMJs and eliminates any chance of excessive wear or overload on the posterior teeth. Immediate posterior disclusion is one of the most important concepts of occlusion to understand. Note: There are some exceptions to a goal of posterior disclusion. Guidelines for treatment planning those exceptions can be found in Chapter 30, Functional Occlusion: From TMJ to Smile Design (Elsevier).
The principle of posterior disclusion clarifies why it is so important to develop a stable anterior guidance. Wear, mobility, or movement of the anterior teeth can reintroduce posterior interferences during jaw movements, resulting in muscle hyperactivity and overload of the posterior teeth and the TMJs. So long term stability of the anterior guidance is the key to long term stability of the rest of the occlusion.
DETERMINING THE ANTERIOR RELATIONSHIP
No guesswork is needed to determine the position and contour of the anterior teeth. Every anterior tooth has an ideal position and contour that fits into a precise set of lines that form a functional matrix.2
A full explanation of the functional matrix is not possible in the space allowed for this article but let’s examine some of the principles. Determination of the matrix requires decisions which, if done correctly, position the contours for each anterior tooth in perfect functional harmony. Since functional harmony is dependent on anatomic harmony this approach produces the most naturally beautiful esthetic result.
PRINCIPLE ONE… ESTABLISH STABLE ANTERIOR CONTACTS IN CENTRIC RELATION
If the anterior teeth don’t contact in centric relation, immediate posterior disclusion cannot be achieved. This puts posterior teeth in potential overload during jaw movements. That is why determination of CR is the starting point for functional smile design (Fig. 1).
If the anterior guidance is designed to function in harmony with jaw movements, and does its job without interference from posterior teeth (posterior disclusion), the result is a peaceful, coordinated neuromusculature (Fig. 2).
If posterior teeth interfere with any part of the anterior guidance pathways, it can result in:
1. Hyperactive incoordinated musculature (occluso-muscle pain).
2. Overload on posterior teeth.
3. Forward displacement of the mandible during closure, producing overload on anterior teeth.
4. Excessive wear, hypermobility, and/or tooth migration (unstable occlusion).
5. Sore or sensitive teeth.
PRINCIPLE TWO… ESTABLISH PRECISE INCISAL EDGE POSITIONS
Precise positioning of the upper incisal plane is rarely given the attention it deserves. Anterior teeth that interfere with the lip closure path, the neutral zone, or the envelope of function always result in compromised esthetics. The compromise is evident when teeth are too long or when incisal edges are too far forward. The horizontal positioning of the incisal plane is critical, not only for esthetics and phonetics, but also for long term stability.
Deciding on the exact position and contour of the incisal edges cannot occur until the precise contour of the labial surfaces is finalized (Fig. 4). That is why the sequence of steps in determining the functional matrix is so critical.
Determining the labial contours of the upper anterior teeth establishes their inclination and thus the horizontal position of the incisal edges, which should contact the inner vermillion border of the lower lip during gentle “F” sounds (Fig. 5). Observe many restored anterior teeth and it will be apparent how often this key requirement for esthetics is violated.
PRINCIPLE THREE… HARMONIZE THE ANTERIOR GUIDANCE
The refinement of the anterior guidance is greatly simplified once centric relation has been established as the starting point, and incisal edge positions have been refined as the end point. Remember that the job of the anterior guidance is to disclude all posterior teeth in all jaw excursions from centric relation. There are other factors to understand if predictable results are to be achieved routinely but the three principles cited here form an essential framework to build on.
Predictable anterior esthetics requires:
1. Correct labial contours.
2. Precise incisal edges.
3. Precise lingual contours.
None of these requirements requires even the slightest amount of guess work.
When anterior teeth are to be restored the determination of precise incisal edges, labial contours, and anterior guidance starts with a diagnostic wax-up. The wax-up on mounted casts is used to fabricate provisional restorations after the teeth are prepared. Experience has shown that even the most beautiful diagnostic wax-up almost always falls short of an ideally perfected smile that fulfills all requirements for function and most natural esthetics. It is only through refinement of the provisional restorations that perfection is achieved. An understanding of the functional matrix2 is the key to a step-by-step sequence for predictably accomplishing this goal. It is a learnable process that is well worth the effort.
Oral Health welcomes this original article.
REFERENCES
1.Williamson EH, Lundquist DO: Anterior Guidance: Its effect on anterior temporalis and masseter muscles. J. Prosthet Dent 39: 816-823, 1983.
2.Dawson PE, Functional Occlusion: From TMJ to Smile Design St. Louis, Missouri. 2007, Mosby, Inc/Elsevier.
