Vertical Mandibular Alveolar Bone Distraction and Dental Implant Placement: A Case Report

Tooth loss secondary to trauma or periodontal disease or as a result of congenital alterations produces a loss of alveolar ridge height and width. In such cases, esthetic and functional implant-supported rehabilitation requires the use of techniques designed to augment the atrophic alveolar ridge.1 Guided bone regeneration and particulate, or en bloc, grafting are among the traditional techniques used to achieve such augmentation. However, bone distraction offers an alternative approach for the management of large-bone defects.2^,3 Distraction osteogenesis has some advantages. In effect, no additional surgery involving a harvesting procedure is needed, there is no limit to lengthening, and simultaneous lengthening of the surrounding soft tissues occurs.1 

A case is presented in which a large vertical bone defect in the anterior mandibular zone was corrected via vertical alveolar bone distraction. A total of 6 dental implants were placed, 3 in the distracted segment, which allowed for complete implant-supported restoration of the mandible.

A 44-year-old woman with a hepatitis C virus infection and a history of facial trauma in childhood (ie, loss of the right eye, several teeth, and part of the anterior mandibular ridge) presented for implant-supported mandibular rehabilitation. Clinical intraoral examination revealed significant anterior mandibular bone and vestibular atrophy (Figure 1). There was approximately 6 cm of mesiodistal alveolar deficiency and 2 cm of vertical deficiency. The patient had a fixed prosthesis replacing her anterior maxillary teeth. Orthopantomography (Figure 2) and computerized axial tomography confirmed the presence of adequate alveolar bone for osteogenesis distraction of the anterior mandible.

The surgical procedure was completed using local anesthesia (2% articaine with adrenaline 1:100 000). A full-thickness, trapezoidal flap was reflected from 3.5 to 4.6. A rounded drill was used to mark the bone between the mental foramina for distraction. A divergent rhomboid osteotomy of the vestibular cortical and spongy components was then performed with tungsten carbide discs, fracturing the lingual cortical layer with a mallet and chisel. The Lead System (Stryker Leibinger, Freiburg, Germany) was used for distraction. After bone-fragment mobilizing, a drill was used to prepare the distractor bed in the distraction fragment and remaining bone. Because the bone segment was longer than 2 cm, 2 distractor screws were positioned with their respective plates. The distractor screw traversed both plates through one of their orifices, and these were affixed to the bone by osteosynthesis screws. The base plate was positioned in the lower zone with fixation to the mandibular bone, while the distractor plate was affixed in the upper zone and to the mobile-bone fragment (Figures 3 and 4). Continuous, simple, triple-zero silk sutures were placed (Figure 5). Amoxicillin was prescribed (750 mg 3 times a day for 7 days), along with ibuprofen 600 mg during 4 days and 0.2% chlorhexidine rinses. The stitches were removed after 7 days.

After 12 days, distraction of the alveolar segment was started at a rate of 1 mm daily (ie, a single turn of the screw daily). In the first 3 days, the patient reported to the clinic for distraction and then continued the process at home with following clinic visits. Following the 15 days of activation, the resulting bone augmentation was evaluated (Figure 6).

During the distraction-consolidation period, an anteroinferior vestibuloplasty was carried out to increase the vestibular depth. Under local anesthesia (2% articaine with adrenalin 1:100 000), an incision was made in the alveolar crest from canine to canine. A partial-thickness flap was raised to the vestibular fundus, where suturing to the periosteum was carried out. The exposed zone was covered with Surgicel.

The implants were placed 12 weeks after the completion of distraction. We first positioned 6 Defcon TSA implants (Impladent, Sentmenat, Barcelona, Spain) with Avantblast surfacing to prevent collapse of the distracted bone fragment. The remaining teeth were then extracted and the distraction screws were removed. The dimensions of the implants and the Ostell values obtained at the time of surgery are shown in Table 1. All implants were left submerged.

Second-stage surgery was performed 2 months later and, after healing of the mucosa (1 month later), the cemented, fixed prosthesis was placed and yielded an acceptable esthetic outcome and good radiologic adjustment (Figures 7 through 9). The clinical and radiologic control 24 months later showed good implant and soft tissue conditions (Figure 10).

Extensive bone defects in the anterior mandible complicate the location and angulation for dental implanting. The patient in this report presented with a large vertical bone defect of the anteroinferior alveolar ridge that was treated with alveolar bone distraction. This technique facilitates bone and soft tissue proliferation through distraction or stretching of pre-existing native bone. No donor-site surgery is required, and there is no limit to elongation. Distraction increases soft tissues (ie, skin, mucosa, blood vessels, muscle, nerves) as well as bone,4 and there is a lesser tendency toward bone resorption.5 The disadvantages of distraction are the prolonged period of distraction5 and the need for maintaining strict control of segment bone direction during distraction.4 The success rates of implant placed in distracted alveolar bone ranges from 85% to 97%.6,7 

According to Ley and Cranin,2 the success of alveolar bone distraction depends on a series of factors, including: (1) osteogenic tissue preservation, (2) stabilization of the distractor screws and plates, (3) an adequate latency period, (4) an appropriate rhythm and rate during the distraction period, and (5) observation of the required consolidation period. It is essential to preserve the blood supply to the distracted segments. An incision on the crest with reflection of a full-thickness buccal flap was used to preserve the soft tissue supply to the bone segment. Stabilization of the distractor elements is essential for correct bone-block movement. We used 2 distractors according to Garcia-Garcia et al,8 who recommend this approach when bone blocks are longer than 2 cm in length. The latency, activation rate, duration of activation, and consolidation period in alveolar bone distraction vary according to different authors (Table 2).5,7,9–11 Distraction was started 12 days after surgery at a rate of 1 mm daily.

An important treatment decision is the timing of implant placement. Block et al12 found that the space between the base bone and distracted bone block was filled within 6 to 8 weeks. The main characteristic of this new bone was the presence of mature lamellar bone and osteoblasts, which indicated active bone formation. According to Degidi et al,13 the optimum moment for implant placement is 10 to 16 weeks after the active phase of distraction has been completed. In this case, the implants were placed after 12 weeks of consolidation.

According to Chin,14 the implants should be left submerged for 5 months, with prosthesis placement after second-step surgery. However, at present, new implant surfaces make it possible to shorten the treatment times required for implant-supported prosthetic rehabilitation. Dedigi et al13 combined alveolar bone distraction with immediate loading and obtained satisfactory results after 12 months of follow up. In this case, implant loading was started early (90 days after placement), thereby shortening the treatment time and improving patient comfort.