A Multidisciplinary Approach for Treating Bilateral Congenitally Missing Lateral Incisors

The treatment of congenitally missing teeth (CMT) has long been a challenge for providers, especially when the edentulous areas are in the smile zone. Patients often may be self-conscious due to both functional and esthetic concerns. In these situations, a multidisciplinary approach may be necessary that includes a dental team of clinician(s) and laboratory technician(s) to provide a predictable definitive treatment with lasting results that will also meet the patient's esthetic expectations.

CMT occurs in up to 16.5% of the general population.¹ The incidence of congenitally missing maxillary lateral incisors is the most common presentation of all anterior CMT, and bilateral occurrence is more prevalent than unilateral. It is important to note that CMT has been found to be a genetic mutation of the homeobox MSX1, which has been shown to serve as a risk indicator for ovarian and colon cancer.^2-4 Clinicians may suggest to their patients with CMT that they obtain a genetic test to assess the associated risk.

In many presentations of CMT, a multidisciplinary approach to treatment may include combinations of orthodontics, removable partial dentures (RPDs), fixed partial dentures (FPDs), indirect adhesive restorations, and implant-supported restorations (ISRs).⁵

The patient was a 42-year-old woman who worked in the healthcare business. She had CMT at the No. 7 and 10 sites. She disliked the appearance of her central incisors and pointed canines and bicuspids, and was dissatisfied with the acrylic RPD she had worn for 26 years (Figure 1 and Figure 2). Her goal was to have a uniform and brighter smile.

The patient reported no current or past medical issues that might affect her care. She had been treated by the providing clinician for the previous 9 years. With CMT at the lateral incisors, the patient had been using the same acrylic RPD since her first orthodontic treatment, 26 years prior. Due to financial challenges, she had waited many years before seeking definitive treatment.

Periodontal: The patient had been consistent with her hygiene maintenance visits. She had stable and minimal periodontal pockets (<3) with no bleeding on probing. There was radiographic evidence of minor angular bone loss on molars, especially the mandibular second molars. A diagnosis of American Academy of Periodontology (AAP) stage 1, grade Awas determined.⁶

Risk: Low
Prognosis: Good

Biomechanical: Multiple, small to moderately sized restorations were present in the posterior teeth, all of which were clinically acceptable, with no caries detected.

Risk: Moderate
Prognosis: Good

Function: No temporomandibular joint (TMJ) pain or sounds were present, nor were there any joint or occlusal complaints noted on the patient's dental history. The patient's immobilization and loading tests were negative, and she had normal range of motion. Occlusal morphology was Angle class I. These criteria indicated a diagnosis of acceptable function.

Risk: Low
Prognosis: Good

Dentofacial: Gingival display was not extreme, but full gingival contours were visible above the No. 7 and 10 sites during a Duchenne smile. The patient said she was embarrassed by the acrylic RPD that she had been wearing. Due to her self-consciousness about the missing teeth, esthetic success would be paramount.

Risk: High
Prognosis: Poor

Several treatment options were presented to the patient, as follows:

Option 1: The first option comprised left and right side, two-unit, cantilevered FPDs retained by the maxillary canines with ovate pontics. This was a relatively conservative option, however it did not address the patient's complaint about the unappealing look of her central incisors and the sharp appearance of her canines and bicuspids. She, therefore, decided against this approach.

Option 2: This option entailed left and right side, three-unit, lithium-disilicate ceramic FPDs retained by the maxillary canines and central incisors with ovate pontics, and two laminate veneers on the first bicuspids. It was explained to the patient that the survival rate of an FPD over 10 years is 81.1%.⁷ She had concerns about the predicted survival rate and the potential total expense of this option over her lifetime and, thus, decided against it.

Option 3: The final option involved lithium-disilicate veneers on the maxillary left and right first bicuspids, canines, and central incisors with ISRs in place of the lateral incisors. The ISRs would be lithium-disilicate crowns cemented to custom zirconia abutments. The 15-year survival rate of ISRs has been reported to be up to 93.33%.⁸ The 10-year survival rate of facial veneers is 95.6%.⁹ These survival rates were very appealing to the patient; however, the central incisors and canines adjacent to the No. 7 and 10 sites converged and there was insufficient space for implants. A minimum implant-to-tooth distance of 1.5 mm is required for longevity and health of the ISR.¹⁰ Therefore, limited fixed orthodontics would be needed to create sufficient space for the ISR, which was discussed with the patient. She felt comfortable with and accepted this option for treatment.

A dentofacial analyzer was used in conjunction with a laser line instrument designed for acquiring accurate spatial positioning to obtain a proper dentofacial relation for the diagnostic models to be mounted precisely to a dental articulator. The diagnostic models were articulated in maximum intercuspal position, as the patient's functional diagnosis was acceptable. No changes were needed at the incisal edge position or posterior occlusal plane position of the maxillary teeth.

With lips in repose, the anterior teeth exhibited desirable esthetics; the incisal edge of the patient's central incisors was 1.5 mm below the lip, and the canines were level with the lip.¹¹This position was replicated in the diagnostic wax-up and would be repeated in the final restorations.

Limited maxillary fixed orthodontics were placed for a period of 8 months. A pre-orthodontic cone-beam computed tomography (CBCT) scan (CS 9300, Carestream Dental, carestreamdental.com) showed the roots of the central incisors and canines converged toward each other (Figure 3). A minimum distance of 6.2 mm would be needed for placement of a tapered 3.2 mm x 10.5 mm implant (Legacy2^™ [3.2L2], Implant Direct, implantdirect.com). The pre-orthodontic scan (Figure 3) showed the space for No. 7 was 4.5 mm and the space for No. 10 was 4.6 mm.

During the orthodontic phase, the apices of the central incisors were tipped mesially and the apices of the canines were tipped distally to provide sufficient space for the implants. A 0.016-in nickel titanium (NiTi) archwire was used throughout treatment with open coil springs in the lateral incisor locations. Periodic periapical radiographs were taken to confirm the positions of the apices.

A final CBCT was taken when sufficient space was established, and the positions of the teeth were stabilized for an additional 3 months. The post-orthodontic CBCT image (Figure 4) showed 6.2 mm of space at the No. 7 site and 6.8 mm of space at the No. 10 site to accommodate the impending implants.

Digital imaging and communications in medicine (DICOM) image files from the final CBCT and standard tessellation language (STL) files from the intraoral scan (CEREC Omnicam, Dentsply Sirona, dentsplysirona.com) of the final models were merged using online surgical guide planning software (Passage [version 5.1.12], Anatomage, anatomage.com). A surgical guide was designed and printed for the two implants (Figure 5).

Conservative surgical flaps were made and osteotomies were created using the surgical guide to ensure accurate placement of the 3.2L2 implants (Figure 6). Then, a 0.016-in x 0.022-in NiTi archwire with closed coil springs was used passively for the 3-month integration period (Figure 7). During this time the patient wore the original RPD. Although the success rates of two-stage surgery and one-stage surgery are reported to be equal,¹² the clinician opted to use the two-stage approach to allow additional post-orthodontics stabilization time.

Palatal incisions at the palatal line angles of the central incisors and canines were made, and the tissue was flapped facially to create a thicker facial phenotype. Using a matrix from the diagnostic wax-up, screw-retained provisional crowns were made and placed on the 3.2L2 temporary plastic engaging abutments.

Over a 3-month period, the emergence profile was altered at the facial tissue surface of the provisional abutment to create an ideal gingival architecture. Properly contoured emergence profiles of the implant abutment are essential to provide optimal esthetic and stable gingival architecture.¹³

The fixed orthodontic appliance was removed (Figure 8), and teeth Nos. 5, 6, 8, 9, 11, and 12 were prepared for lithium-disilicate laminate restorations, with axial reduction averaging 0.5 mm to 0.75 mm. Custom impression coping transfer abutments were made from the existing provisional abutments/crowns. The custom fabricated provisional abutments were attached to the laboratory analogs and the tissue surfaces were impressed with bite registration material (Futar^®, Kettenbach, kettenbachusa.com). An example of the custom abutment transfer procedure from a different though similar case is shown in Figure 9 through Figure 12.

The impression copings were then coupled with the new tissue impression and analog. This allowed flowable composite material to be added into the tissue impression and onto the transfer abutments, reproducing the exact emergence profile of the provisionals. Approximately 1 mm of facial free gingiva at the implant sites was removed to provide optimal gingival architecture. This procedure was performed with an all-tissue dental laser with a MZ6 tip in gingivectomy mode (Waterlase iPlus^® 2.0, Biolase, biolase.com) (Figure 13). No hemorrhaging occurred. The final pocket depth at the facial aspect was 2 mm.

All models were mounted to the articulator using a dentofacial analyzer system that is designed to enable an accurate transfer of maxillary and mandibular positions from the patient to the articulator. This allows the laboratory technician and clinician to optimally work together. The implant abutments were made according to the transferred impression coping abutments as described above.

The abutment designs were then sent to a digital outsourcing center for milling in zirconia (ArgenZ^™, Argen, argen.com) with titanium bases. Crowns and veneers were designed according to the provisional model, milled in wax, invested, pressed, and finished in lithium disilicate. Medium translucent (MT) ingots, OM3 shade, were used as prescribed by the clinician. MT ingots were chosen to partially mask the A2 prepared tooth stump shade.

Rubber dam was utilized in delivery of the restorations. In order to properly clean the teeth for optimum bond strength, the teeth were air-abraded at 40 psi using 27-µm aluminum oxide.¹⁴ The zirconia custom abutments were torqued to 35 Ncm. This was repeated after 10 minutes for ideal preload.¹⁵

The intaglio surfaces of the lithium-disilicate veneers were treated with 35% hydrofluoric acid-etch for 20 seconds, steam cleaned, and silanated with a universal priming agent (Monobond Plus^®, Ivoclar Vivadent, ivoclarvivadent.com). Retraction cords (00 size) (Ultrapak^™, Ultradent Products, Inc, ultradent.com) with hemostatic gel (ViscoStat^™ Clear, Ultradent Products, Inc) were placed around all the teeth (Nos. 5, 6, 8, 9, 11, and 12) and abutments (Nos. 7 and 10) (Figure 14). Teflon tape was also used to isolate adjacent teeth during the seating of the veneers. A semi-gel etchant (Uni-Etch^® w/ BAC, BISCO, bisco.com) was placed on all prepared teeth for 15 seconds and then rinsed for 10 seconds. A universal adhesive (All-Bond Universal^®, BISCO) was scrubbed onto the teeth for 20 seconds.¹⁶

Each veneer was placed using a veneer placement handpiece (LumiGrip^®, DentMat, denmat.com) (Figure 15), which helped simplify and improve the accuracy of the procedure. A light-cure translucent shade veneer cement (RelyX^™ Veneer Cement, 3M Oral Care, 3m.com) was used as the adhesive cement. A 1-second cure with a curing light (Valo^™, Ultradent Products, Inc) was done to tack the veneers in place, allowing for quick cleanup before the final setting of the cement. Then, 20-second cure cycles were performed from the facial and lingual directions to ensure complete cement polymerization. A 2-week postoperative check was done to ensure all tissues were healthy, and a nightguard was provided.

The final result was as planned and the patient was extremely pleased with the outcome, especially her new smile (Figure 16 and Figure 17). Total treatment time was 18 months. Figure 18 and Figure 19 show the patient's full-face smile from 9 years before treatment and post-treatment, respectively.

It is important for clinicians to comprehensively recognize and appreciate the variable complexity of the treatment of CMT cases. Thus, many times utilizing a multidisciplinary approach is necessary for successful outcomes. When multiple providers are involved, however, the financial obligations and scheduling becomes more complex for patients. Therefore, it is incumbent on the restorative dentist to take the lead in determining the final outcome prior to treatment and to ensure frequent, close communication with all of the providers. Finally, such complex cases require a high level of trust between the providing clinicians and the patient, who must be totally committed to the treatment in order for a successful and desirable outcome to be achieved.

Peter Young, DDS
Assistant Professor, Division of General Dentistry, School of Dentistry, Loma Linda University, Loma Linda, California; Mentor, Kois Center, Seattle, Washington; Private Practice, Arcadia, California; Master, Academy of General Dentistry

Claudio Bucceri, CDT
Owner and Master Technician, Swiss Dental & Technical Art, Inc., Seattle, Washington; Clinical Instructor, Kois Center, Seattle, Washington