Missing Lateral Incisor Agenesis: Aesthetic Challenges With Cuspids in the Lateral Positions

Dr. George Kirtley


Encountering a patient who has been treated orthodontically to rectify the absence of the maxillary lateral incisors presents a unique aesthetic and functional challenge. Maxillary lateral incisor agenesis (MLIA) is the most common congenitally missing-permanent-tooth condition in the maxillary anterior region and contributes to significant aesthetic compromise and potential functional instability. Statistically, 20% of all congenitally missing teeth are maxillary laterals, and females are affected more than males. In addition, agenesis of both maxillary lateral incisors is more common than agenesis of only one.

Options for treating this condition, when diagnosed early, are:

1. Space closure with the mesial repositioning of the canine and subsequent reshaping (enamelplasty) with possible direct restorative procedures involving resin bonding

2. Repositioning of the canine with aesthetic preparation and restoration involving crowning or veneering with ceramic

3. Maintenance of the cuspid in its ideal functional position and orthodontically creating the proper mesial/distal width space for subsequent implant placement or prosthetic replacement of the missing lateral with bridge design

All of the above are viable choices, depending upon the anatomical environment and aesthetic/functional expectations, along with the immediate and long-term management challenges of a growing patient.

A consequence of tooth mass loss (missing tooth/teeth) in the arch and movement of teeth to eliminate the space caused by that loss of mass can result in narrowing of the arch. This can have a dramatic impact on facial/dental aesthetics and functional stability.

The primary focus of this article pertains more to the aesthetic component. However, the position of the cuspid plays an important and significant functional role in maintaining the homeostasis of the stomatognathic system. Canine unilateral contact on the working side is critical to accomplish that. Therefore, the whole rehabilitation treatment, which will often require a multidisciplinary approach (ie, periodontic/orthodontic/restorative/prosthodontic), should aim to establish such lateral disocclusion whenever possible. If not, such as in the case example presented here, where the cuspid has been orthodontically moved into the lateral position, functional design should aim for group function.

The Challenges Found With Previously Treated Cases
On occasion, as aesthetic/restorative dentists, patients with MLIA will present who have previously had treatments done for the condition. In the author’s experience, these individuals are often displeased with these previous aesthetic restorative attempts. In these situations, clinicians will often face some pretty tough treatment challenges. Available treatment options may be limited due to the treatment choices that may have already been offered and done by the previous doctors. Any new treatment plan, if not carefully thought out, may then offer these patients the potential for less than desirable aesthetic and functional results as well.

The case presented here involves a patient who was previously restored with full-coverage metal-ceramic restorations. The aesthetic restorative effort fell short of its potential (Figures 1 to 5). The preoperative condition on this patient involved congenitally missing lateral incisors. Orthodontic treatment, which involved repositioning the cuspids into lateral positions, had been implemented and completed at an early age. Subsequent to this, the restorative dentist attempted to create the anatomical appearance of a lateral incisor. Whereas there may have been some improvement, aesthetic design failure was obvious.

Figure 1. Preoperative frontal close-up photo (1:1). Figure 2. Pre-op right lateral view (1:1).
Figure 3. Pre-op left lateral view. Figure 4. Pre-op natural smile (1:2).
Figure 5. Retracted frontal view (1:2) with parallel lines drawn. Figure 6. Frontal view (1:1) with lines at the gingival.
Figure 7. Pre-op full-face photo. Figure 8. Full-face view, with lines drawn on the face.

Evaluation of the pre-op condition revealed multiple concerns that affected both intraoral and extraoral aesthetics. Both the gingival architecture and anatomical tooth form contributed to the deficiencies exhibited in each of these realms. Keeping in mind the principle that the most harmonious relationship between 2 lines is when they are parallel, we can clearly see the visual discord this condition presents (Figure 5).

Considered individually, the gingival architecture surrounding the anterior teeth was in reverse balance (Figure 6). In other words, the gingival margin on the central incisors was lower than the lateral incisor, an offense of ideal smile design principles. This circumstance was created as a result of the cuspid being moved into the lateral position without consideration of the proper gingival margin relationship to the central incisor. The MLIA condition precipitated this treatment choice but, as stated previously, was inadequate in answering the optimal aesthetic desires of the patient and the vision of this dentist.

Extraorally, the imbalance of the gingival architecture detracted from the facial appearance in the lower one-third of the face. Visual tension was created by the reverse gingival position and appearance of a “gummy smile” and a lateral incisor/central incisor proportion discrepancy (Figures 7 and 8).

Another basic of proper smile design is inherent proportion of the central incisors to one another and to what surrounds them. Anatomical disharmony between all teeth in the upper arch (the smile zone in particular) and even the lower arch was evident. Given this, the condition of MLIA poses a multi-dimensional challenge requiring a multi-faceted approach to attain the aesthetic goal.

Germane to this discussion is the obvious anatomical difference between the lateral incisor and the cuspid and the challenge of making one appear ideally as the other. The differences in size, shape, and appearance between lateral incisors and canines is significant. Lateral incisors are incisiform, with smaller and flatter labial surfaces and broad, flat incisal edges, while the cuspids are more conical and pointed. The surrounding bone also presents a significant difference. Cuspids, being the cornerstones of the arch, display a prominent eminence, which is a graphic distinction from the adjacent teeth and their bone envelopment. This is perhaps the most significant challenge in creating “the look” of a true lateral incisor (Figures 9 to 13).

Figures 9 to 11. Lateral incisor illustrations.
Figures 12 and 13. Cuspid illustrations.

Given this distinct anatomical difference and, as in this case, that the cuspid is in the lateral position, one cannot make a cuspid “look” like a lateral incisor without consideration of soft- and hard-tissue alteration. A pre-op evaluation—periodontally, radiographically, and in conjunction with a periodontic specialist—was imperative for correct treatment planning. Procedurally, this was addressed through flap elevation, revealing the true picture of osseous presence or lack thereof. Where there is bone, we can alter it. Where there is not, we cannot (at least in this circumstance). Decreasing clinical crown length on the existing cuspid/lateral and increasing clinical crown length on the central incisors, at the same time, presented a technical challenge. Being able to create clinical crown length regarding the central incisors was attainable through osseous resection/contouring followed by gingivectomy to the proper level, maintaining biologic width (Figure 14). Gingival position regarding the cuspid (in lateral position) required coronally repositioning the flap and flattening the cuspid eminence (Figures 15 and 16). The plasty of the eminence allowed for an emergence contour that better mimics that of a lateral incisor. Furthermore, preparation of the coronal aspect of the cuspid by narrowing it mesial-distally allowed for the design of an aesthetic restoration that adhered more ideally to that of a true lateral incisor dimension.

Figures 14 to 16. Surgical photos.

The Importance of Material Selection and Proper Placement
The importance of proper ceramic selection in aesthetic restorative cases such as this is critical. Feldspathic porcelain, lithium disilicate, and zirconia each have their own specific characteristics. Proper choice of material is contingent upon the need for strength, preparation design, and visual/aesthetic characteristics. In cases in which there is minimal preparation, feldspathic porcelain may be of consideration. In cases such as this one featured, in which previous restorations have been placed and significant preparation is present, pressed ceramics or even zirconia may be considered. In this case, the decision was to use a pressed lithium disilicate all-ceramic (IPS e.max [Ivoclar Vivadent]) due to its strength (500 MPa) and natural high-end aesthetics in the smile zone.

Figure 17. Postoperative frontal view (1:1). Figure 18. Post-op right lateral view.
Figure 19. Post-op left lateral view.
Figure 20. Post-op full-arch view.

Decisions made to ensure the proper placement of the ceramic units also demand close scrutiny. Whenever possible, it is best to use a composite luting resin cement with lithium disilicate. In this case, there was a combination of veneers and full-coverage ceramic crowns in the upper arch. Of course, this is dependent upon the light source being able to adequately reach the ceramic/tooth interface to initiate and completely cure the resin cement. So, the different types of restorations demanded a different technique in placement: light-cured cement for the veneers and a dual-cured cement for the full crowns.

All tooth surfaces where veneers were to be placed were cleaned and debrided using a microetcher (Etchmaster Disposable Air Abrasion System [Groman Dental]). The intaglio surfaces of the ceramic veneers were cleaned with phosphoric acid, rinsed, dried, silanated (Bis-Silane [BISCO Dental Products]), and layered with a thin coat of Porcelain Bonding Resin (BISCO Dental Products). Then a self-etching/self-priming universal bonding agent (All-Bond Universal Adhesive [BISCO Dental Products]) was applied to the teeth, and the veneers were luted using a light-cured resin cement (RelyX Veneer Cement [3M]). Since the ceramic thickness was substantial with the full-coverage units in this case, a dual-cure, self-adhesive composite luting resin (RelyX Unicem 2 [3M]) was chosen to ensure a complete depth of cure and predictable bond strength.

We can see how dramatically the smile zone is impacted when disproportion is exhibited as in the condition of MLIA. Even without any formal dental training, the lay public (ie, patients), when viewing someone’s smile or their own, can surmise when a problem exists and when something is not visually pleasing. Visual tension is the harbinger of aesthetic need, usually combined with an underlying functional concern. Moving a tooth into a position that is foreign to its normal place alters the functional and aesthetic dynamic. If consideration of repositioning or not repositioning a cuspid can be addressed in advance of treatment, then the clinician will most often make the best choice. However, when this is done without considering those choices, compromise and limitations will abound. It is this compromise that challenges us and stimulates our creativity to answer the functional and aesthetic demands. This is what delineates cosmetics from functional aesthetics and allows the opportunity to more fully impact the end result (Figures 17 to 20).

Treating MLIA requires the joint work of a multidisciplinary team that, after evaluating all aspects of oral health (facial aesthetics, dental aesthetics, occlusion, function, and periodontal parameters), decides to adopt a treatment plan that provides the most biological, cost-effective, and long-term treatment outcome.

Dr. Kirtley has accredited status in the American Academy of Cosmetic Dentistry. He teaches at New York University as a visiting lecturer in aesthetics and is a senior clinical instructor for the Aesthetic Advantage Hands-on Aesthetic Continuum in New York; London, United Kingdom; and Palm Beach, Fla. He lectures internationally on smile design, aesthetics, marketing the aesthetically driven practice, and complex rehabilitation cases. He can be reached at george@smilesbygeorge.com.

Disclosure: Dr. Kirtley reports no disclosures.

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