Anterior Tooth Form and Formation: A Systematic Approach
Maxillary anterior teeth have functional and esthetic components. Because of this esthetic value, there are countless theories, courses, and presentations to explain and teach the intricacies of maxillary anterior teeth. When we consider color, texture, rotations, spacing, and many more topics it is easy to get lost in the details. This post will not focus on the details. Before I focus on the details I ALWAYS follow this systematic approach for anterior tooth arrangement. Just like building a house, the framework or foundation must be constructed first. After the framework is completed, the details are then added to make each tooth unique. Following these exact steps on every case will save a tremendous amount of time and will also allow for the variability of nature. These steps are followed whether I do one unit or six. The same steps are used for wax-ups, temporaries, or definitive restorations, digital or analog. The goal is developing efficiency by following the same protocol time after time. This protocol allows the technician or dentist tremendous variability for adding the details after the foundation is completed.
1) When creating multiple anterior teeth, the starting points are always the midline and the labial incisal edge of the central incisors. The midline is determined by facial landmarks. A horizontal line can be drawn connecting the glabellum, apex of the nose, and the center of the chin. A second interpupillary line (fig.1) can be drawn which is perpendicular to the facial midline. The labial incisal edge of the central incisors will be parallel with the interpupillary line. The midline and labial incisal edge should be predetermined prior to the definitive restorations. If the dentist has done the temporaries a model of the correct midline and incisal edge position should be provided to the lab.
2) The contact points come next. As the contact areas move from the centrals to the canines they move cervically. (red line fig.2,3)
3) The next step is the most critical step, the lingual surface. Since all teeth exist within a masticatory system it is impossible to shape teeth without addressing how they interact with the antagonist tooth, or teeth. The incisal edge of the tooth is more accurately an incisal ridge2. The ridge consists of the labial incisal edge (red line in fig.4,5) and the lingual incisal edge (blue line in (fig.4,5). These two incisal edges form the boundaries of the incisal ridge. The lingual edge, which is often ignored, is the functional component that is dictated by the mandibular incisors and how a person chews. The labial edge is the esthetic incisal edge that is seen when a person speaks and smiles. The maxillary lingual incisal edge is the most critical part of the ridge with regard to function. The lingual edge cannot be ignored or placed arbitrarily without consideration of the mandibular incisors.
The location, or placement of the labial edge is mostly determined by facial esthetics and phonetics. This edge can be lengthened or moved as long as it does not affect function with the mandibular incisors, speech, and facial esthetics.
The incisal ridge is rarely symmetrical and the two edges are rarely parallel. (fig.4,5)
In short, the lingual function and contour are addressed prior to the labial contour.
4) The mesial line angle is created next. (black line fig.6) When viewed directly from the facial the central, lateral, and canines are divided in segments vertically (fig.3). The central is divided in thirds. The lateral and canine are divided in half. The mesial line angle of the central will start near the contact point and terminate in the cervical portion of the tooth at the mesial third of the tooth. This line angle should match the mesial line angle of the adjacent central incisor as closely as possible.
The lateral mesial line angle starts at or above the contact point and terminates in the cervical portion at the middle half of the tooth.
The mesial line angle of the canine starts above the contact point and angles towards the middle of the tooth.
5) The distal line angles come next (fig.7), always moving from the central to the canine. Whenever possible, the distance between these line angles should closely mimic the contralateral tooth. The width of the contralateral teeth is not always the same, but they can be optically matched more easily if the line angles match.
6) The cervical height of contour (white line fig. 8,9) closely follows the contour of the soft tissue (pink). This is why it is important to do this step with a soft tissue model, or solid model. The apex of the CEJ on the central incisor is at the distal third. The apex of the lateral and canine are at the middle of the tooth (red dots in fig.8).
8) The last step for the basic framework is the labial incisal edge. The shape of the labial edge (red line fig.10) can be highly variable as long as it is not in the pathway of the mandibular incisors during chewing. Typically, the labial edge of the centrals and the canines will follow the same line when viewed on a horizontal plane. In this case, the Kois Waxing Guide (fig.11) from Panadent is used to show how the central incisors and canines are on the same incisal plane.
When the framework is shown without teeth (fig.12) the basic shapes become apparent. From this point forward attention can be paid to filling in the lines, or connecting the dots. After the basic framework is completed the individual esthetics can be completed. The individual esthetics varies from person to person, but the basic framework is always the same and the same steps are always followed.
When the teeth are viewed facially the distal half of the canine is not in view (fig.13) or barely in view. The arch form can be broadened simply by making the distal half of the canine more in view.
Creating esthetic anterior tooth contours that function properly requires a tremendous amount of skill and knowledge. Tooth morphology, facial esthetics, soft tissue contour, and occlusion all play a role. When creating a framework it is important to not get locked in to a specific tooth form or design. The framework should follow the basic commonalities of teeth and allow room for the variability of details. Having a consistent repeatable protocol for the basic framework will save tremendous amounts of time.