Orthodontic Considerations in Restorative Management of Hypodontia Patients With Endosseous Implants
The use of implant-supported restorations in patients with hypodontia remains challenging and requires a multistage treatment that begins in late mixed dentition and continues into late adolescence. The aim of this article is to review the role of orthodontics in endosseous implant rehabilitation of patients with hypodontia. The MEDLINE, Web of Science, Scopus, Cochrane databases, and necessary scientific textbooks were searched for relevant studies and reviews, and as far as possible, they were only included if they had been cited at least once in the literature. Dental implants are susceptible to overloading as the periodontal ligament is absent and the proprioceptive nerve endings are either lacking or very limited. Patients with hypodontia may present with skeletal features such as short and retrognathic maxilla, prognathic mandible, and shorter lower anterior facial height, and they sometimes need orthognathic correction as part of their overall treatment. Dental problems vary and include bimaxillary retroclination of incisors, spacing, centerline discrepancies, microdontia, hypoplastic enamels, ankylosis of the retained primary teeth, overeruptions, and volume deficiencies of alveolar ridges. The challenges mentioned, as well as bone volume deficiencies, compromise the successful placement of implants. Orthodontic strategies and techniques, such as uprighting mechanics, extrusion/intrusion, delayed space opening, and orthodontic implant site-switching, can be used to create, preserve, or augment the implant site. After orthodontic site development, the final planned position of the teeth should be maintained with a rigid bonded retainer; overlooking this stage may compromise the implant site and require orthodontic retreatment.
Figure 1. Oligodontia, including agenesis of maxillary permanent canines and primary retained maxillary canines (arrows), is displayed. The patient was sent for medical examination as a mild form of ectodermal dysplasia was suspected. Figure 2. Panoramic radiograph of the patient seen in Figure 1. The following teeth were absent: 4, 6, 7, 10, 11, 20, 23, 29. Figure 3. Agenesis of the left maxillary and mandibular second premolars and the retained infraoccluded left mandibular primary molar (arrow) are shown. Nearly, 55% of retained primary mandibular second molars show signs of infraocclusion,43 but only 2.5%–8.3% of retained primary molars are severely infraoccluded (positioned below the gingival margin of the adjacent teeth).44 Figure 4. The maxilla grows in a downward and forward direction. The transverse growth of the maxilla occurs primarily because of growth at the midpalatal suture. This is greater posteriorly than anteriorly. After the age of 6–7 years, the transverse growth of the mandible in the incisor region is minimal.54 Implants placed in the anterior mandible after the age of 11 years had a relatively stable position, not constraining the transverse growth.139–142 However, the horizontal and vertical growth of the mandible continues through adolescence and early adulthood. With a Class III tendency and further horizontal growth of the mandible there may be a need for replacing implants or changing the abutments in the future. Figure 5. Agenesis of the mandibular left second premolar is shown. The size of the second retained primary mandibular molar is larger (9.5 mm) than that of the adjacent premolar (7.5–8 mm).87
A thin maxillary buccal cortical bone (a,b) (arrows) is a common occurrence101 and associated with a detrimental bone loss after placing an implant. A recent study107 revealed that the crestal labial soft tissue thickness and implant's labial bone thickness were highly associated in the anterior maxillary region. If immediate loading is the treatment of choice, atraumatic extractions and implant site preparations (c) (eg, piezoelectric systems), as well as placement of implants more palatally (d), help avoid complications.
The patient in Figure 6 showed signs of periodontal bone loss around maxillary central incisors (a,b) and it was decided to perform socket preservation in those areas (c) and implants placed in tooth number 6, 7, and 10 areas instead.
Figure 8. Overeruption of opposing teeth or drift of adjacent teeth into the edentulous space is a common problem associated with patients with hypodontia. For a 4 mm diameter implant, a minimum mesiodistal space of 8 mm is required for implant placement. The fixed appliances may be used for uprighting and space opening. Mini-implants can be used with fixed appliances to intrude the overerupted teeth, open up space mesiodistally, and upright the tilted teeth adjacent to edentulous space. Figure 9. Overeruption of right maxillary first and second permanent molars into the opposing mandibular edentulous area can be seen. Mini-implants, in combination with selective alveolar corticotomies113 or osteotomies,114,115 may be used to intrude the overerupted molars. Figure 10. A patient with retained maxillary primary canines (arrows) and congenitally absent maxillary lateral incisors. If replacements of maxillary lateral incisors with implants are planned, the distalization of the maxillary canines can be done after the age of 13 years or near the end of skeletal growth.131 This approach may preserve the buccolingual bone volume in the maxillary lateral incisor regions. Figure 11. The orthodontic implant site-switching technique uses tooth movement to generate new bone. (A) A first premolar is pushed distally into the second premolar position, where bone volume deficiency exists. (B) New bone is generated in the first premolar position and can be used for implant placement, obviating the need for bone grafting.
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