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A Voice in the Area: Maxillary Central Incisor Labial Surface Shape by Dr. Chad Foster

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A Voice in the Area: Maxillary Central Incisor Labial Surface Shape

by Chad Foster, DDS, MS, editorial director

In the world of smile aesthetics, few variables are more important than the position and shape of the maxillary anterior teeth. More specifically, the maxillary central incisors are considered the dominant aesthetic teeth. If you were given a blank slate and challenged to build the perfect dentition, and if aesthetics within the face and smile frame were any priority, without a doubt your strategy would start with two teeth: the maxillary central incisors.

A variety of factors are at play in aesthetic appreciation of the shape and position of the maxillary incisors. An interesting one that I find isn’t often discussed is the shape of their labial surface, which can be a very important diagnostic finding in certain cases. Even patients with relatively low “dental IQ” will often have surprisingly strong opinions on the labiolingual inclination, or amount of “flaring,” of the maxillary incisors.

On a side note, it’s important to understand that the labiolingual inclination of the maxillary central incisors is related but independent of their bodily anteroposterior (A-P) position within the maxilla. When the labial surface shape of the maxillary central incisors is very flat, any small degree of positive inclination can give the appearance of teeth that are “too flared.” Likewise, when these teeth show a more convex labial surface, even at a normal inclination they can aesthetically appear a bit lingually inclined or “undertorqued.” Fig. 1 is a good contrast of these shapes.
Fig. 1
A Voice in the Area: Maxillary Central Incisor Labial Surface Shape

Case study
The 13-year-old boy in the case shown here (Figs. 2a–2c) is a good example of how maxillary central incisor shape can factor into a treatment plan. This patient’s maxillary central incisors are more convex in shape, and the more convex the shape, the more positive the inclination needs to be to position the lower two-thirds (flat) facial surface of this tooth perpendicular to the floor (or “Frankfort horizontal”). Generally speaking, this is what I consider aesthetically ideal for maxillary central incisors. Note in Figs. 3A and 3B that the U1’s incisal 2/3 crown inclination is significantly more lingually inclined than the ideal position described above.

 Figs. 2a-c
A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
A Voice in the Area: Maxillary Central Incisor Labial Surface Shape

Figs. 3a-b
A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
A Voice in the Area: Maxillary Central Incisor Labial Surface Shape


As I mentioned earlier, in treatment planning, if I had the ability to position one tooth and build the dentition around it, it would be the maxillary centrals. I don’t always have the ability to do this; often other limiting variables take priority. In this case, that would potentially be the crowding and periodontal tolerance in the mandibular arch.

In my opinion, based on the level of crowding, the shape of the upper incisors, their inclination and their A-P position within the patient’s face (see side smiling photo), the maxillary arch would ideally be treated non-extraction for my treatment goals. Just because the upper arch can be treated non-extraction does not always mean that it’s possible in the lower arch, however, and interarch coupling/occlusion needs to be an important consideration. Periodontal tolerance to non-extraction in the lower arch was my main concern in considering non-extraction treatment and surely the reason why many would choose to treat this case with extractions (which would definitely be a reasonable plan depending on treatment goals).

There were, however, several factors that made me consider not extracting in the mandibular arch. The lower arch shape was very narrow in the premolar area relative to the maxillary premolar area, which was quite wider. (The lower left first bicuspid is actually in Brodie bite.) Some degree of linguoversion in the mandibular posterior segment is normal, but this seemed in some degree of excess. Also, the pretreatment lower incisor position is fairly upright. I was prepared to possibly extract a lower incisor, depending on how the first six months went, and made the patient and parents aware of that.

Progress photos are shown in Figs. 4–7. Early on, I used light IPR multiple times because space was being made for the lower left lateral and lower left canine. Given the position of the maxillary central incisors within his smile and face, my aesthetic treatment goals involved increasing the labiolingual inclination but not bodily retracting them. Upper incisor brackets were flipped/inverted to allow an increase in inclination as alignment proceeded in early undersized round wires, while also limiting the end range of that inclination once in slightly undersized rectangular steel; 0.016-by-0.025- inch stainless steel was strategically chosen as the final wire to limit this in the flipped/ inverted setup.
Fig. 4 A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
Fig. 5 A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
Fig. 6 A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
Fig. 7 A Voice in the Area: Maxillary Central Incisor Labial Surface Shape


Extra-broad light nickel titanium wires were paired with a light open-coil spring that was activated very gradually and very slowly. An eyelet was eventually used on the lower left lateral incisor, which I love for lingually blocked-out teeth (great for low force).

The case finished in 20 months (Figs. 8–14). In my opinion, the A-P and labiolingual position (again, separate but related variables) of the maxillary incisors finished in an aesthetically ideal position within his face and smile frame. The posttreatment cephalometric X-ray shows that the lower incisors were proclined to couple with the maxillary incisor position, which was the anticipated compromise even with efforts to mitigate that effect. CBCT images taken before and after treatment (important in evaluating root-to-alveolar housing position) are also included here.
Fig. 8 A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
Fig. 9a A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
Fig. 9b A Voice in the Area: Maxillary Central Incisor Labial Surface Shape

Fig. 10a A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
Fig. 10b A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
Fig. 11a A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
Fig. 11b A Voice in the Area: Maxillary Central Incisor Labial Surface Shape

Fig. 12a A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
Fig. 12b A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
Fig. 13a A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
Fig. 13b A Voice in the Area: Maxillary Central Incisor Labial Surface Shape

Figs. 14a-e
A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
A Voice in the Area: Maxillary Central Incisor Labial Surface Shape

A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
A Voice in the Area: Maxillary Central Incisor Labial Surface Shape
A Voice in the Area: Maxillary Central Incisor Labial Surface Shape


Conclusion
The shape of the labial surface of the maxillary incisors is an important aesthetic diagnostic finding. If the shape of these teeth for this patient had been more flat instead of convex, it very likely would have tipped the scales in favor of extractions in both arches to meet my treatment goals.

No matter what your treatment, aesthetic or extraction preferences are, I hope that this little variable will be one that earns consideration from time to time in your thought process
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