A Multidisciplinary Approach for Full-Mouth Rehabilitation in Oligodontia: A Clinical Report Open Access

Oligodontia is a rare dental condition defined by a congenital absence of 6 or more permanent teeth, excluding the third molars.¹  The esthetic and functional outcomes associated with genetic diseases significantly impact individuals' quality of life.²  The absence of teeth limits dentofacial growth, leading to insufficient alveolar bone development.³  Orthognathic surgery associated with bone grafts is sometimes required to correct severe skeleton discrepancies and to allow the placement of dental implants in a prosthetic corridor. The management of oligodontia requires a multidisciplinary approach and appropriate timing to ensure satisfactory long-term follow-up results.

We reported the case of a 17-year-old patient missing 18 permanent teeth followed since the age of 7 for nonsyndromic oligodontia. During her growth, she was rehabilitated with temporary removable partial dentures. The patient denied other medical-surgical history, and genetic assessment ruled out an associated syndrome. The patient presented with a short facial height and a class III skeletal malocclusion by maxillary retrognathia. The maxillary and mandible showed significant vertical and horizontal alveolar bone resorption. Eight persistent temporary teeth and only 10 permanent teeth were present (Figure 1), with extrusions of 11 and 21 due to the lack of mandibular incisors.

Orthognathic surgery was performed with LeFort I osteotomy advancement combined with maxillary and mandibular bone reconstruction. This bone reconstruction consisted of multiple 3D casts using parietal bone as the cortical part and the xenogeneic bone as the cancellous part (Figure 2a–d). Articulator-mounted diagnostic casts were used (setup) to design a surgical splint to simulate the surgical procedure. Starting from the initial setup and the patient's last removable prosthesis, a radiological guide was made using the double-scan technique to simulate the implant position according to the ideal prosthetic emergence. The radiological guide was then transformed into a surgical guide with both dental and mucosal support.

After 6 months of bone healing, 6 maxillary implants and 5 mandibular implants (Nobel BioCare Parallel CC, Nobel Biocare Services AG, Zurich, Switzerland) were placed under general anesthesia (Figure 3). The ablation of the osteosynthesis material of the cortical grafts and the avulsion of maxillary central incisors were performed during the same procedure. Those teeth could not be preserved due to an insufficient prosthetic height, even after the augmentation of the vertically dimension simulated. The second-step implant surgery was achieved under local anesthesia 4 months later, allowing the placement of multiunit abutments (MUAs) and mucosal adaptation. Due to the partial resorption of the bone graft and the proximity of the lower alveolar nerve, the implant in position 43/44 presented an exposure of an implant turn requiring the placement of the MUA abutment in a supragingival position, without esthetic or functional consequence with preserved stability over time (Figure 4a and b). After mucosal healing (15 days), a maxillo-mandibular polyether impression was made using the pick-up technique. Using screw-retained occlusion waxes, the occlusion plane, the vertical dimension, and the medial sagittal plane were identified, and the data were transmitted to the lab. In this way, the first basic esthetic and functional reference elements were obtained. Dynamic and static recordings were also transferred as photographs and videos. The vertical dimension was increased for esthetic reasons to balance the reduced lower facial height and functionally because of the insufficient prosthetic height available to insert 2 osteo-anchored prostheses. This augmentation resulted in 4 mm occlusions on the second molars and 10 mm occlusions on the first molars, making the conservation of the first molars impossible (Figure 5).

Temporary screw-retained polymethyl methacrylate (PMMA) prostheses were fitted 7 days later so that the functional and esthetic envelopes could be analyzed under real conditions (Figure 6; Figure 7a and b). On the second molars, semidirect onlays were made to recreate occlusal contacts and to maintain proprioception. After 15 days, depending on the patient's complaints, a few esthetic corrections were made. After 1 month, new polyether impressions were made to obtain an ideal mucosal profile at the postextraction sites. A cross-assembly was performed using temporary prostheses on the Artex articulator, which is a system for transferring craniofacial data. Similarly, the bipupillary line and medial sagittal plane were again recorded using the Ditramax system (Marseille, France). The final models were scanned in the laboratory with the temporary prostheses in place, and the occlusion was computed by scanning the final model.

The choice to use a full-ceramic osteo-anchored bridge was made. The framework was machined from a ZirkonZahn Prettau 2 Dispersive block (Gais, South Tyrol, Italy), sintered at 1600°C and radiologically controlled. A cut back was performed on the 6 anterior mandibular and maxillary teeth, and the posterior sectors were defined. The zirconia framework (Figure 8a and b) was then used to try to stabilize the occlusion and to ensure that prophylactic cleaning would be possible. The main issue with the initial framework was the “balcons” on the apical part of the 6 anterior teeth on both the maxillary and mandibular sides, which made it impossible to use interdental brushes. Sintered ceramics were then tested to check the esthetics and color in situ (Figure 9). A feeling of “square teeth” emerged, and the embrasures did not seem sufficiently open or sufficiently textured; hence, the whole arch seemed too flat and had a difference in color between the front and rear teeth. The laboratory made the requested modifications, and perfect esthetic and functional harmony was achieved when the final model was put in the patient's mouth (Figure 10). During a 5-year biannual follow-up, no peri-implantitis or prosthetic fractures were found. A stable marginal bone resorption without symptoms is observed in position of 15, 13, and 23 explained by the strong masticatory forces exerced in this area (Figure 11).

This case report described the oligodontia management, with the difficulties encountered during the realization steps:

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  the osseous time with the choice of the bone grafting technic allowing to a 3D reconstruction in 1 surgical step;

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  the timing of implant rehabilitation at the end of growth, without evolution of the alveolar processes;

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  the conservation of natural teeth for proprioception;

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  the prosthetic part with the PMMA intermediate prostheses;

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  the complications encountered after the case.

The surgical part includes the LeFort I osteotomy advancement with simultaneous parietal and xenogenic bone grafting to improve the interarch relationships in patients with severe skeletal discrepancy (combined or not with a mandibular bilateral sagittal split osteotomy) and to increase the bone volume in the same time, allowing future implant placement.⁴  Due to the lack of tooth germs, the alveolar bone did not grow normally; thus, bone and soft tissue were insufficient for prosthodontic treatment. In the study of Hartlev et al,⁵  almost all the patients with oligodontia required orthodontic treatment and bone augmentation.

In cases of extreme atrophy of the maxilla and mandible with horizontal and vertical bone defects, the objective is to benefit from a substantial donor site allowing 3D reconstruction of cortical and cancellous bone in order to ensure the long-term success of the implants.⁶  Parietal bone harvesting is a reliable technique in these indications and is associated with significantly lower resorption rates than iliac bone harvesting and results in more bone growth than when intraoral donor sites are used.⁷  To augment the bone volume obtained, the parietal grafts are appositioned at distance of the natural bone and the created space is filled with xenogenic bone to limit the resorption of the grafts. A 1-stage procedure could also be proposed for patients with severe maxillary atrophy and total maxillary edentulism with simultaneous dental implantation and orthognathic surgery. However, a higher risk of implant failure was reported with this procedure.⁸ 

The timing of implant rehabilitation, for teenagers, remains controversial and needs to be discussed with the patient and his or her family. Implant placement is often performed after the end of the patient's growth due to the risk of dental germ damage and skeletal dimension modifications, with high anterior variation. According to the literature, the end of growth varies between 14 and 15 years of age in females and 17 and 18 years of age in males, with high interindividual variability; but these age ranges are highly debated.⁸  Additionally, as osseointegrated implants behave like ankylosed teeth, their evolution does not follow the alveolar processes of adjacent teeth during growth. This growth decreases after 20 years, but remains present. This can lead to infraposition functionally and esthetically failure for the implant therapy.⁹  Some authors thus advise not to offer implant therapy before the age of 20–25, which leads to significant social and behavioral problems in patients.¹⁰  When doubt remains regarding the end of growth, individual skeletal maturity should be assessed prior to implant placement. Implant placement during growth is generally not recommended due to the risk of dental germ damage and skeletal dimension modifications, with high anterior variation.

However, as these conditions do not apply to cases of oligodontia or anodontia, early implant placement could be proposed in these patients. This approach was approved by the French recommendations in 2006. The Haute Autorité de la Sauté (HAS) recommended the placement of at least 2 dental implants and at most 4 in the mandibular region for children suffering from oligodontia, over the age of 6, before the end of the growth, only after failure or intolerance of conventional prostheses.¹¹ 

Conservation of the remaining natural teeth should always be considered to preserve proprioception and to limit the psychological impact linked to the loss of the teeth. However, tooth extraction should be performed when major changes in the vertical dimension are required for prosthetic rehabilitation, which was the case for this patient. The therapeutic compromise was to remove the first molars and maxillary central incisors, which could not be retained after increasing the vertical dimension. Planning and adaptation were essential before and during treatment to anticipate the choice of prosthetic material according to the prosthetic height that can be used.

The prosthetic management of these global rehabilitations should go through a provisional screw-retained restoration in PMMA, based on functional and esthetic information from the conventional preimplant removable prosthesis in order to make the results of the definitive restorations more predictable.¹²  Moreover, temporary PMMA restoration was performed to determine the amount of vertical dimension augmentation needed. This material offers good results with high resistance to fracture and low porosity and is suitable for prophylaxis and cleaning. The biological integration of PMMA is allowed because no monomer is released, which differs from the outcome of conventional resins.^12,13 

A full-ceramic osteo-anchored bridge was chosen instead of a Brånemark prosthesis due to the lack of prosthetic height. Indeed, the Brånemark system could be used when the available prosthetic height was over 15 mm to respect the minimum thickness of the materials. We also decided to keep the possibility of cut-back and stratification on the anterior teeth to render the final restoration more natural with better transmission of light. The “all-ceramic” concept also has better biological features with the suppression of metallic components and better prophylaxis due to a diminution of bacterial attachment.¹⁴  Moreover, the patient's smile line did not require an additional resin part to recreate a new esthetic gingival margin.¹⁵  Prettau Zirconia was chosen for the final restauration because of its translucency and high flexural strength (1300 MPa)¹⁶  with the possibility of a natural color gradient. Furthermore, this material has almost no abrasion after over 3 million cycles of mastication (equal to 10 years in vivo) and no decrease in flexural strength according to a 10-year follow-up study.¹⁷ 

Regarding the potential difficulties encountered in these complex cases, in the retrospective study by Attia et al,¹⁸  the functional and esthetic outcomes of dental implants in patients with hypodontia were evaluated according to the success criteria of Albrektsson implants. Of the 155 dental implants placed, 18 implants did not meet Albrektsson's criteria, and 2 implants were removed. This low success rate, compared with the rate usually encountered in “conventional” implantology, is explained by the risk of resorption of the various bone grafts performed, leading to the placement of the implants in a less favorable condition (in number and in position).¹⁹  In our case, the 5-year panoramic X ray showed localized maxillary resorption in the premolar/molar area. This is explained by the stronger masticatory forces applied in this area and the use of parietal bone, which can be resorbed in a few years.^20,21 

Management of severe oligodontia is a life-long process, beginning with early removable temporary protheses before the age of 5 years and ending with the implant-supported rehabilitation in adulthood. It involves many competences in dentistry and requires rigorous organization and communication between specialties.

After treatment, esthetics, masticatory function, and phonatory function, as well as the psychological status of the patient, were significantly improved. The successful management of this treatment was possible thanks to good coordination among the different specialists involved. The surgical challenge was to realize early implant placement with a 1-step surgery for the bone grafts at the same time of the LeFort I osteotomy. The prosthetic challenge was to increase the vertical dimension of occlusion while maintaining proprioception via the natural teeth and allowing the use of predictable materials in the long term. This case reinforces the need for multidisciplinary management to anticipate complications and to inform patients of therapeutic alternatives and difficulties they may encounter.

The authors thank Andrew Jannetta for translation.