Prosthetic Rehabilitation of Edentulous Ridges Following Alveolar Distraction Osteogenesis: Clinical Report of Three Cases

After tooth loss caused by any variety of reasons, alveolar ridge bone height and width deficiencies limit the use of endosseous dental implants. To reconstruct a full-thickness alveolar defect, autogenous onlay bone grafts traditionally have been performed.1 However, autogenous bone graft has the risk of donor-site problems with the harvesting of the bone graft and graft resorption.2,3 Guided bone regeneration has also been presented as a reliable solution for correcting atrophic ridges,4 but this technique may result in unpredictable bone formation or infection from membrane exposure.5 To overcome the problems associated with these techniques, distraction osteogenesis has evolved as a promising procedure for alveolar ridge augmentation before implant placement.1 

Distraction osteogenesis was originally created for orthopedic purposes to increase the length of long bones and was later applied to the maxillofacial region to correct severe malformations.4,6 The technique relies on stretching the bones to achieve lengthening, to generate new bone, and to correct deformities in height and width.2,7 This process also aims to bring the bone to the exact position needed for subsequent prosthodontic treatment. This is particularly important for cases in which an implant-supported fixed prosthetic denture is planned and oral implants need to be precisely installed into the desired position.7 

The purpose of this clinical report is to present the clinical experience in treating defects of edentulous ridges by means of intraoral vertical distraction osteogenesis followed by placement of endosseous implants in the distracted areas.

This clinical report included three female patients (mean age of 55 years) with alveolar defects caused by periodontal disease or resulting from traumatic tooth loss and subsequent atrophy of the alveolar ridge (Figures 1a and b, 2a and b, 3a and b). Seventy-year-old patient 1 was referred to our clinic with a complaint of loose and ill-fitting complete mandibular dentures. Patient 2, a 55-year-old with a removable partial denture in the mandible and a complete denture in the maxilla, was referred to the clinic because of her concerns about her appearance, speech, and difficulty in chewing. Patient 3, a 52-year-old, was referred to the clinic with a complaint of loose and ill-fitting complete maxillary and mandibular dentures.

Informed consent was obtained from each patient before they participated in the study. The patients underwent alveolar ridge distraction using intraoral extraosseous devices (Table). There was no relevant systemic history for the patients. Distraction was performed in the mandible of all patients. In patient 1, segmental atrophy was located at the anterior region (incisor region). In the other 2 patients, segmental atrophy was located at the posterior parts of the mandible (premolar-molar regions) (Table).

The surgical procedures were performed under local anesthesia in all patients. The vestibular bone was exposed by a horizontal paracrestal incision, preserving the crestal and oral soft tissues for blood supply of the latter bone segment. Lateral release incision allowed for buccal mucoperiosteal flap elevation providing access to the prospective osteotomy site. Careful subperiosteal dissection was performed to obtain adequate visibility of underlying bone but to preserve the lingual or palatal pedicle after the osteotomy was performed. The outline of the osteotomy was marked with a fissure bur before adaptation of the distractor, and the distraction vector was slightly directed to the vestibular aspect. The osteotomy was performed using a reciprocating saw, and the transport segment was finally mobilized with an osteotome. After the bone segments were mobilized, the distractor was then applied, fixed, and temporarily activated to test for movement of the distracted segment. Subsequently, the distracted segment was repositioned to its initial position and then the surgical incision was sutured with 4/0 silk sutures, leaving part of the distractor passing through the incision.

The patients were given postoperative instructions to maintain a liquid or pureed diet for 1 month and to progress to a soft diet after that. Antibiotics were prescribed for a maximum of 10 days (clindamycin 3 × 600 mg), twice a day. The patients were also provided with an analgesic to be used on an as-needed basis. Chlorhexidine gluconate 0.12% mouth rinse 15 mL twice daily was used for 2 weeks postoperatively.

Standard panoramic radiographs were performed at the first postoperative days (Figures 1c, 2c, and 3c). After the latency period (7 days) for initial healing, the distractors were activated by turning the screw of the rods at a rate of 1 mm/d in 2 activations for 10 days. The distraction device was left in position for a 12-week consolidation period. At the end of this period, the rod and plates were removed under local anesthetic. Soft-tissue closure was once again done in a similar manner (Figures 2d and 3d).

In patients 2 and 3, the distraction regenerate was well ossified and stable. The healing period proceeded without complications. The patients reported no pain or discomfort and tolerated the procedure well. However, in patient 1, lingual tipping of the distraction vector in the anterior mandible occurred during the distraction phase. Then, 5 weeks later, a subsequent osteotomy of the newly formed bone and transport segment was performed, and they were fixed in a labial position with plates and screws.

Treatment results of the distraction osteogenesis were evaluated by means of panoramic radiographs. The distance between the upper edge of the lower plate and the alveolar crest was measured after the distractor was inserted and at the end of the distraction period. The difference in the two heights revealed the vertical distracted bone gain. The distance between the inferior margin of the mandible and the alveolar crest was assessed so that alterations in bone height could also be observed after distractor removal. The difference between the bone height immediately after distraction and final bone height at the end of consolidation period represented the bone relapse.8 

The mean gain in the vertical height of bone obtained immediately after the distraction procedure was 8.1 mm. However, all patients had bone relapse after the consolidation period (mean bone relapse  =  1.83 mm or 22.6%). After the distraction period, vertical bone gains of 6.3 mm, 6.4 mm, and 6.1 mm were recorded for patients 1, 2, and 3, respectively (Table).

Based on the prosthodontic planning, radiographic splints with tooth setup were made. The treatment plan consisted of establishing a correct vertical dimension with a fixed implant. The patients were given a detailed explanation concerning the present state, procedures, and alternative treatment plans, and then informed consent was obtained from the patients.

In patient 1, treatment with mandibular implant-supported overdenture prosthesis retained with ball attachments was planned. Thus, 2 implants spaced 12 to 16 mm apart (edge to edge) were placed in the lateral region to the distracted anterior mandible. Previously, the patient had needed a vestibuloplasty with a cutaneous soft-tissue graft before loading the implant to obtain adequate vestibular depth and keratinized tissue around the implants. The abutment connection was delayed for 6 months after placement of the implant.

In patient 2, fixed mandibular reconstruction with 6 implants (second molar, first premolar, canine) with 3 independent fixed partial dentures (right molar to right premolar, right canine to left canine, left molar to left premolar) was planned. Similarly, in patient 3 fixed mandibular reconstruction with 6 implants (second molar, second premolar, canine) and 3 independent fixed partial dentures (right molar to right premolar, right canine to left canine, left molar to left premolar) was planned. In patients 2 and 3, fixed maxillary reconstruction with 8 implants (second molar, first premolar, canine, and central incisor) and 4 independent fixed partial dentures (molar to premolar, canine to central incisor, bilaterally) was also planned.

The surgeon used a custom surgical guide to help place the implants. The marginal bone of the implants was evaluated by periapical radiographs. Furthermore, each radiograph was calibrated using the known width of the coronal cylinders of the implants. In total, 6 implants were inserted in the distracted areas. In addition, 8 implants were inserted in the maxilla of both patients. The implants were submerged and uncovered 4 months later for healing screws and abutments to be inserted.

In patient 1, an implant-retained removable prosthesis with ball attachments to the mandible and a complete denture to the maxilla were planned (Figure 1d). After removal of the cover screws (ITI, Straumann, Basel, Switzerland), impression copings (ITI) with appropriate diameters were placed. The impression of the alveolar mucosa was made with a zinc oxide eugenol impression paste (Cavex, Cavex Holland BV, Haarlem, Netherlands). After the dentures were fabricated, ball attachments were connected to the fixtures in the mouth. Retentive components were then placed on the abutment and undercuts were blocked out. Venting holes were prepared in the overdenture for expressing excess acrylic resin. Upon removal of the denture, irregularities and voids in the intaglio surface of the denture around the attachments were filled in with additional acrylic resin (Vertex, Vertex-Dental BV, Zeist, The Netherlands). Excess acrylic resin was removed; the complete dentures were polished and inserted in the maxilla and mandible.

In patient 2, extractions of the existing mandibular canines were planned because of mobility and occlusion plane problems. After these teeth were extracted, a fixed prosthetic denture in the form of a full-arch bridge was planned for both jaws. In patient 3, the decision was also made to fabricate a cement-retained fixed partial denture for both jaws. After the placement of impression copings, definitive impressions of the maxillary and mandibular implants were made using transfer copings and a polyether impression material (Impregum, 3M Espe, Seefeld, Germany). The impression copings were fixed onto the abutment analogs. Cement-retained prostheses were then completed on abutment-level models from a base metal alloy (Master-Tec, Ivoclar Vivadent AG, Schaan, Liechtenstein) and porcelain (VITA VM 13, VITA Zahnfabrik, Bad Säckingen, Germany) and cemented to the abutments.

Routine clinical assessments were made 1, 2, 6, and 12 months after prosthetic loading and then annually with visual and radiographic examinations. Criteria for success included the following: effective placement and primary stability of the planned implant, stability of the implant (lack of mobility), absence of pain or any subjective sensation at each visit, lack of peri-implant infection with suppuration, and lack of continuous radiolucency around the implant.9 Routine radiographs consisted of panoramic radiographs taken preoperatively (Figures 1a, 2a, and 3a), after the distraction osteogenesis (Figures 1b, 2b, and 3b) and placement of implants (Figure 3e), at the time of prosthetic loading (Figures 1e and 2e), and annually thereafter until the end of follow-up. The initial appearance of the patients (Figures 1b, 2b, and 3b), the intraoperative view after distraction osteogenesis (Figures 1d, 2d, and 3d) and final outcome of the prosthodontic treatment are shown in Figures 1f, 2f, and 3f.

Alveolar distraction osteogenesis has been considered as an alternative to many other surgical techniques, such as bone augmentation for implant-supported oral rehabilitation of atrophic jaws, alloplastic graft augmentation, and guided bone regeneration.2,4,8,10,11 Moreover, this technique offers some advantages because it avoids donor-site morbidity and provides predictable gain of hard and soft tissues. Further advantages are the low infection rate and decreased bone resorption. Moreover, this technique allows the use of complementary regeneration techniques when the outcome is not completely satisfactory.10 Because of these advantages of the alveolar distraction osteogenesis, the technique was chosen for this clinical report.

Alveolar distraction osteogenesis also provides a short bone-consolidation period before implantation.12 Previous studies reported a mean time of 6 to 8 months after guided bone regeneration, which is much longer than the time required after distraction osteogenesis.12,13 Various consolidation times have been reported for distraction osteogenesis, but 3 to 4 months is typically adequate for maturation of the distraction regenerate.1 Similarly, in the patients in the present case report, the consolidation period after alveolar distraction was 3 months on average. The advantages of distraction osteogenesis have been confirmed by the present clinical report.

A number of complications that could arise with the distraction process include resorption of the transport segment, difficulty in completing the osteotomy on the lingual side, excessive length of the threaded rod, bone fracture, device failure, tipping of the transport segment, perforation of the mucosa by the transport segment, and inadequate length of distraction.10,14 Relapse and long-term results in alveolar distraction have been reported in several clinical studies.15,16 The bone relapse occurs because of scar-tissue contraction after distraction. A consolidation period of 3 months is generally accepted to be sufficient to avoid most of the relapse due to scar contraction.16 A previous study by Ettl and colleagues8 reported a mean vertical bone gain of 6.4 mm and an average bone relapse of 1.8 mm (21.1%) after a consolidation period of 18 weeks. Furthermore, in another study, the mean bone gain of 6.5 mm and an average bone relapse of 1.6 mm (25%) after a consolidation period of 8–10 weeks have been recorded.17 In accordance with the previous studies, in the present clinical report, after a consolidation period of 12 weeks, a mean bone gain of 6.3 mm and an average bone relapse of 1.8 mm (22.6%) were recorded. The bone relapse could be partly attributed to smoothing of the alveolar crest prior to insertion of the implants. Eventually, adjustment of the distraction protocol to include overcorrection of 15–25% may compensate the bone relapse during the consolidation period of the distracted alveolar bone.8,18 

Another complication that has frequently been encountered after distraction osteogenesis is the displacement of the transport segment. In a previous study by Ettl and colleagues,8 33 complications were observed in 36 patients. In 15 patients (4 maxilla and 11 mandible), oral displacement of the transport segment occurred, and corrective osteotomy of the distracted bone segment and vestibular augmentation were performed. Accordingly, in the present clinical report, in patient 1, the vector of distraction was lingually oriented, resulting in the regenerated bone being positioned lingually. To place the implants in the right position, an additional corrective osteotomy was performed. An incorrect vector of distraction could be explained by the tension caused by surrounding cheek and tongue muscles, together with the traction of the periosteum.8,19 Moreover, the soft-tissue complication that resulted in a reduced vestibular sulcus might be the result of inadequate fixed gingiva formation after surgical procedure. Therefore, a full-thickness vestibular incision in the lower vestibule might be useful to prevent these complications.

A variety of intraosseous and extraosseous devices are available for alveolar distraction osteogenesis.20 A previous study by Wolvius and colleagues18 indicated that the solution for optimal vector management is the bidirectional extraosseous alveolar distractor. The extraosseous devices in the cases presented here allowed good stability of both the device and the bone segment during the distraction and consolidation periods. Furthermore, the distraction rates were 1 mm/d, performed in 2 activations for 10 days. A previous study by Walker20 indicated that the greater the frequency of activation, the more favorable the distraction regenerate. The distraction rate for the patient presented in that study was also 1 mm/d, performed in 3 activations.

A major esthetic concern with alveolar distraction osteogenesis is obtaining a predictable position of the transosteal portion of the implant in relation to the newly generated bone ridge crest.21 However, in the present clinical report, alveolar distraction processes were performed in the posterior part of the mandible in patients 2 and 3. As esthetics is of less concern in the mandible, no esthetic complications occurred in either case. In addition, in patient 1, satisfactory results from esthetic and functional standpoints were acquired via implant-supported removable prosthesis.

The decision about when distraction osteogenesis can be performed should be based on the severity of alveolar bone loss. Furthermore, complications like oral displacement of the transport vector and inadequate soft-tissue extensions after distraction may arise. Therefore, long-term evaluation of a large number of patients will be necessary to evaluate the efficacy of this treatment protocol.

This clinical report has documented the creation of adequate height and volume of bone for rehabilitation of the patients with endosseous implant-supported dental restorations. Although distraction osteogenesis seems to be a promising method for mandibular reconstruction, it has some limitations. Bone relapse, displacement of the transport segment, and soft-tissue complications may occur after distraction osteogenesis. Thus, the potential complications and the traction by muscle forces on the floor of the mouth have to be considered carefully. Moreover, further research with more patients is needed to demonstrate a generalized trend.