Contemporary Planning Tools for Restoration of Congenitally Missing Maxillary Lateral Incisors

Congenitally missing maxillary lateral incisors have a high prevalence in the general adolescent population, as documented in the literature.¹ Usually, the treatment of choice is to open space for implants in the lateral incisor positions, place implants, and restore the two missing lateral incisors.² When the patient is too young for implants, the space can be maintained with resin-bonded fixed dental prostheses with excellent long-term success rates.³ An alternative approach is to close the spaces and convert canines into lateral incisors and canines into premolars prosthetically, which is also termed "canine substitution."⁴

When choosing between these two restorative options, several factors should be considered. First, if veneers are planned for the case, both treatments are feasible; if veneers are not planned, opening space is less invasive. Second, the time required to open the space versus the time required to close the space is a consideration. The patient will undoubtedly prefer the shorter treatment, assuming both options offer the same clinical potential. A third factor is the implant positions. The main difference clinically between the two aforementioned approaches is that one scenario will have implants placed in the lateral incisor positions, and the other (canine substitution) will have implants placed in premolar positions. In general, implants placed in the posterior tend to be a safer option in the long term.

The depicted patient presented to the authors' clinics with the request to change the compromised esthetic situation, predicated by the missing maxillary lateral incisors (Figure 1 through Figure 3). Because the roots were in a position that was more favorable to closing the spaces, and since the orthodontic treatment would serve as a pretreatment to veneers, it was decided to treat this situation with "canine substitution," that is, the spaces would be closed and the canines converted into lateral incisors, while implants would be placed more posteriorly.

Two major challenges present themselves in this scenario, however. The first is managing the spaces optimally to ensure there is adequate space for the future restorations. To address this challenge, the authors chose to overlap the orthodontic treatment with implant placement and restoration, with the logic being that closing a space can be done more precisely than opening a space. Implants were placed during the orthodontic treatment using surgical guides to ensure precise positioning in relation to the end goal. After osseointegration, the implants were loaded with provisional acrylic restorations with optimal crown dimensions. This allowed the orthodontist to use the implants in the last phase as anchorage to close the spaces very predictably (Figure 4 and Figure 5).

The other obvious challenge in a situation like this is the conversion of a canine, the largest anterior tooth, into a lateral incisor, the smallest anterior tooth. Converting the crown is not particularly difficult and is just a matter of guided preparation. The difficult part, however, is converting the root.

Two key procedures can be planned to achieve this goal, as was done in this case. First, the orthodontist places a negative torque on the canine root, with the intention of bringing it into a more palatal position during the orthodontic treatment, hiding it inside the bone, and flattening the canine fossa.

The second procedure involves managing the tooth profile. A canine has a bulky profile due to its large root, and a more delicate tapered profile is desired for the future lateral incisor. To achieve this, the authors reshaped both the crown and the root of the existing canine. This step in the process must be performed during the orthodontic treatment so that the resulting space from the reshaping can be closed (Figure 6).

Contemporary Treatment Planning

In contemporary treatment planning, the case is planned upfront and rendered to the patient for acceptance, then the dental team proceeds to execute the treatment with maximum predictability and trueness to the plan. Virtual tooth libraries are critical to achieving the aforementioned goals. With a digital workflow, monolithic restorations are the most predictable means of turning a virtual design into a successful clinical result. Monolithic restorations possess fewer optical characteristics when compared to their layered counterparts but can provide an advantage when using natural tooth morphologies in the design process due to the ability of CAD/CAM systems to accurately copy their shape.

The tooth morphology must be selected carefully in terms of proportions, line angle architecture, and surrounding tissues, keeping the desired end-result in mind so that the desired morphology may be preserved throughout the design process. This is done during the smile design phase. A web-based technology (Smilecloud, Smilecloud Biometrics, smilecloud.com) was used that combines artificial intelligence with algorithms and essentially couples a smile design software with a search engine of natural morphologies that is rendered in real-time allowing both the patient and the restorative team to visualize various potential outcomes and choose the desired tooth morphology (Figure 7).

These libraries can be downloaded as unique natural shape compositions that can be converted into a CAD design. Using the same library throughout the planning process is the key to predictability. This line of thought also highlights the need for proper selection of a library/composition in relation to the intraoral case-specific situation for a simple reason: tooth selection is indirectly proportional to the number of adjustments that will be required during the design process, hence the need to preserve the morphology of the library.

The output of the smile design process is a selected tooth library and its relation to the face. Position of the library is transferred into a 3D project using 3D software (Autodesk Meshmixer, Autodesk, Inc., meshmixer.com), and the library is placed on top of tissue, resulting in a motivational mock-up that can be further used to verify the accuracy of the transfer and validate the design with the patient. This also presents an opportunity for the clinician to convert a design into a visual experience for the patient by video recording the situation before and after creation of the motivational mock-up (Figure 8).

When converting a 2D project (smile design) into a 3D project, three key dimensions, all of which are naturally in the third, or sagittal, axis, must be managed: the emergence profile, static occlusion, and dynamic occlusion. A logical approach and sequence is used to manage the conversion. First, the team manages the emergence profile while simultaneously migrating the library into its ideal position, before managing the occlusion. To do this precisely, the technician uses a CBCT to attain an extra layer of information. This helps ensure that the library is placed in relation to the existing tooth structure and allows a highly precise planning of a realistic-looking emergence profile. The technician will perform a virtual crown lengthening procedure and design a tissue reduction guide (Figure 9 and Figure 10).

The next step is to functionalize the static and dynamic occlusion. To do this, an extra layer of information is needed: patient-specific dynamics. Modjaw (modjaw.com) is a technology that is used for this purpose. This technology utilizes a special camera and sensors mounted on the patient and is essentially an all-in-one facebow, condilograph, and pure patient dynamic recorder (Figure 11 and Figure 12). In the present case, the existing static position was recorded as the clinicians aimed to preserve the occlusion following the orthodontic treatment, which was planned and executed in centric relation. All the functional movements were also recorded, including protrusion, laterotrusion, phonetics, and chewing patterns, which are all needed during the design process (Figure 13).

A stable static occlusion has to be ensured first while trying to achieve stable contacts and as many cusp-fossa scenarios as possible. This step was rather trivial in this case since there were only a few implant-supported crowns that required the establishment of new occlusal contacts. Then, all of the patient's dynamics have to be simulated, ensuring that there are no interferences. A key aspect that needs verifying is whether the palatal cusps of the premolars, which will be converted into canines, require reduction or not.

The final design established during this process serves as a reference for the dentist when performing the clinical steps. A silicone index is manufactured from the printed model of the design to serve as a preparation guide.

The Restorations

The treatment follows the exact same sequence as the planning. The soft tissue was managed first, using a tissue guide that was fabricated during the planning stage (Figure 14). Low-frequency electrosurgery is preferred over the use of a scalpel blade, which cannot be properly handled in the small windows of the guide, and the use of low frequency reduces the amount of necrotized tissue. Low-frequency electrosurgery is highly predictable and allows precise copying of the zenith soft-tissue architecture of the design.

After the tissue reduction, the bone was adjusted with an ultrasonic non-coarse diamond tip to re-establish the proper biologic width. Retraction cords impregnated with aluminum sulphate and astringent were then placed in the newly created sulcus to ensure good homeostasis and fluid control (Figure 15). Tooth preparations were carried out using the silicone matrix from the final design.

No interocclusal record was taken because the preparation scan was aligned with the design project, which already contained both static and dynamic occlusion data. Acrylic restorations were used to guide the healing and verify the established esthetic and functional parameters before the definitive restorations were fabricated. These provisional restorations were primed and bonded with a spot-etch technique. Upon verification of the tooth shapes and morphologies, the same digital files were used to mill the definitive restorations from a ceramic material (IPS Empress^® CAD Multi, Ivoclar Vivadent, ivoclarvivadent.com). Minimal surface stain and glaze was applied. Restorations were then bonded under rubber dam following common resin bonding procedures for silica-based ceramics through hydrofluoric acid-etching and silanization and a total-etch technique on the teeth (Figure 16). The implant restorations were fabricated as zirconia-Empress^® screw-retained hybrids, as the authors typically use the same veneering materials for all of their patients. Figure 17 through Figure 19 depict the postoperative situation.

Current technologies allow more and more complex patient scenarios to be accurately planned, facilitating a multidisciplinary, integrated, and predictable approach. Libraries, specifically natural tooth morphology libraries, are key for high-end esthetics with monolithic CAD/CAM restorations. Careful planning of the cases enables the manufacturing of surgical and restorative guides, the use of which further increases predictability while reducing chairtime.

Florin Cofar, DDS
Co-founder, Smilecloud.com; Private Practice specializing in esthetic rehabilitations, Timisoara, Romania

Venceslav Stankov, DDS
Private Practice specializing in maxillofacial surgery and implantology, Plodiv, Bulgaria

Johnny Barbur, DDS
Private Practice specializing in orthodontics and temporomandibular joint disorders, Cluj-Napoca, Romania

Adrian Argint, DDS
Private Practice specializing in restorative and general dentistry, Timisoara, Romania

Ioana Popp, CDT
Master ceramist and digital technician specializing in complex restorative cases, Timisoara, Romania

Lucian Ciu, CDT
Digital technician specializing in restorative cases, Timisoara, Romania

Eric Van Dooren, DDS
Private Practice specializing in periodontics, implantology, and prosthodontics, Antwerp, Belgium