Abstract
Extensive resorption of the mandible increases the interarch space and rehabilitation with traditional dentures is often unsatisfactory due to the superficialization of intraoral muscles. A study of 19 patients who underwent augmentation of an atrophic mandible using a bilateral two-step osteotomy and interpositional bone graft technique is presented. Three horizontal bone cuts (one in the intraforamina and two in the molar region) were made and jointed together by two short vertical bone cuts mesialy to the mental nerve. The cranial fragment was lifted and the iliac bone graft was interposed recreating the correct intermaxillary relationship. A broad vascular pedicle was maintained during surgery, ensuring nutrition from the lingual side, essential to reduce resorption of the bone graft and cranial fragment. 141 Biomet 3i Osseotite ® implants were placed. Patients were rehabilitated with a full-arch implant-supported fixed prosthesis or an implant-supported overdenture. This clinical study describes the resorption process over a 4 year follow-up. 3 of 19 suffered from persistent neurosensitive disturbances. In conclusion, bilateral two-step osteotomy in association with interpositional bone graft is a reliable surgical means to recreate the anatomical morphology of the mandible.
Dental rehabilitation of completely mandibular edentulous patients with dental implants has become common over the last few decades. There is a close relationship between the teeth and the alveolar process. Wolff’s law states that ‘bone remodels in relation to the forces applied’. Every time the function of bone is modified, a change occurs in its internal architecture and external configuration. According to Misch, the lack of teeth and therefore stimulation to the alveolar bone causes a decrease in trabeculae and bone density with loss of width and height. Edentulous alveolar ridges go through a resorption pattern accelerated by inflammatory local processes and conventional mandibular dentures. This is the case for a substantial number of patients in whom the resorption has progressed to Class VI . Advanced resorption increases the interarch space and obliges the use of short fixtures with a high risk of overloading them.
Several techniques for reconstructing the atrophic edentulous mandible have been used with variable results . There is agreement that on-lay bone grafts placed to gain vertical height undergo extensive bone resorption compared with those used to reconstruct the alveolar bone in the palatal–buccal or lingual–buccal dimension . Vermeeren et al. report unfavourable results of mandibular on-lay grafts, attributable to severe bone resorption that occurred after bone grafting and peri-implant bone resorption after implant placement and prosthetic loading. It has been reported that calvarial bone graft had minimal bone resorption even when 2 or 3 layers of bone graft were laid between the mental foramina; dental implants were placed to support overdentures .
The sandwich osteotomy technique for augmenting an atrophic mandible between the mental foramina is reliable with stable results . The authors propose a modified sandwich technique with a horizontal intraforamina osteotomy and two other horizontal osteotomies posterior to the mental nerve with interposed autogenous corticocancellous iliac bone grafts. The authors have focused on the possibility of recreating mandibular alveolar bone in the horizontal and vertical dimension to place implants in the ideal position with the correct length.
Material and Methods
19 patients (12 women, 7 men) with severely atrophic mandibles were selected for augmentation surgery. They ranged in age from 48 to 68 years old (average 58.8 years). Preoperative imaging included conventional panoramic radiographs, plaster models and photographs. The resorption process involved the symphyseal bone and the portion of the mandible distal to the mental nerve. Patients with less than 5 mm between the mandibular canal and the alveolar crest were excluded from the study ( Figs. 1 and 2 ). The presence of medical conditions that could jeopardize treatment with implants was an exclusion criterion.
Surgical Technique
Fully informed consent was obtained from all patients prior to treatment. For all of the operations general anesthetics were administered via nasotracheal intubation.
A mucoperiosteal incision was made extending from the retromolar area buccal to the crest of the ridge to the opposite site. The mucoperiosteum was elevated and the mental nerves were identified. Great care was taken not to exposure the lingual side. A broad vascular pedicle was maintained ensuring nutrition from the lingual side.
A horizontal intraforamina osteotomy was performed maintaining a safe margin from the mental nerves. A further two bone cuts were made parallel to the cranial border of mandibular canal and their length was related to the implant plan. The three bone cuts were jointed by two other vertical bone cuts just mesial to the mental foramen, giving the shape of a bilateral two-step osteotomy ( Fig. 3 A-C) . The cranial fragment became free to move due to two vertical or slightly distally angulated bone cuts in the molar region. All the bone cuts were made with an oscillating bur to minimize the width of the cut and the quantity of bone lost during the operation.
The last part of the osteotomy was made with chisel and hammer to preserve the integrity of the vascular pedicle on the lingual side. The cranial fragment was lifted and placed directly above the caudal fragment ( Fig. 4 A , B). A cortical-cancellous bone graft was harvested from the anterior portion of the iliac crest and shaped to fit between the mandible and the cranial fragment. The interposed graft was able to sustain the cranial fragment but titanium osteosynthesis screws and plates were used to obtain stability ( Fig. 4 C). The mucoperiosteal flap was repositioned and closed with 3.0 Vicryl mattress sutures. Intravenous antibiotic therapy was given 1 h before the operation (2 g of piperacillin and 0.25 g of tazobactam) and was then continued intramuscularly twice a day for 5 days. Vestibuloplasty was performed on 18 of 19 patients about 7 weeks after the first surgery. The patients were asked to not wear dentures for the first 3 postoperative months . Fig. 5 shows a postoperative orthopantomogram (OPT).
Surgical Technique
Fully informed consent was obtained from all patients prior to treatment. For all of the operations general anesthetics were administered via nasotracheal intubation.
A mucoperiosteal incision was made extending from the retromolar area buccal to the crest of the ridge to the opposite site. The mucoperiosteum was elevated and the mental nerves were identified. Great care was taken not to exposure the lingual side. A broad vascular pedicle was maintained ensuring nutrition from the lingual side.
A horizontal intraforamina osteotomy was performed maintaining a safe margin from the mental nerves. A further two bone cuts were made parallel to the cranial border of mandibular canal and their length was related to the implant plan. The three bone cuts were jointed by two other vertical bone cuts just mesial to the mental foramen, giving the shape of a bilateral two-step osteotomy ( Fig. 3 A-C) . The cranial fragment became free to move due to two vertical or slightly distally angulated bone cuts in the molar region. All the bone cuts were made with an oscillating bur to minimize the width of the cut and the quantity of bone lost during the operation.
The last part of the osteotomy was made with chisel and hammer to preserve the integrity of the vascular pedicle on the lingual side. The cranial fragment was lifted and placed directly above the caudal fragment ( Fig. 4 A , B). A cortical-cancellous bone graft was harvested from the anterior portion of the iliac crest and shaped to fit between the mandible and the cranial fragment. The interposed graft was able to sustain the cranial fragment but titanium osteosynthesis screws and plates were used to obtain stability ( Fig. 4 C). The mucoperiosteal flap was repositioned and closed with 3.0 Vicryl mattress sutures. Intravenous antibiotic therapy was given 1 h before the operation (2 g of piperacillin and 0.25 g of tazobactam) and was then continued intramuscularly twice a day for 5 days. Vestibuloplasty was performed on 18 of 19 patients about 7 weeks after the first surgery. The patients were asked to not wear dentures for the first 3 postoperative months . Fig. 5 shows a postoperative orthopantomogram (OPT).
Radiographic Evaluation of Bone-level Changes
Radiographs were taken before surgery and postoperatively and at intervals of 3, 6, 12, 24 and 48 months. All the OPTs were taken with the same digital orthopantomograph with standardized magnification. Measurements were taken with imaging software directly on the digital OPT. Three bilateral reference lines where chosen; one just over the foramen and the other 2 distally to the mental foramen at 8 and 16 mm ( Fig. 3 B). The distance from the alveolar ridge to the cranial line of the inferior alveolar nerve was calculated. The symphyseal area was calculated with three reference lines; one on the sagital plane and the other two lines right and left 10 mm distally to it ( Fig. 3 C). It was possible to quantify changes of height. The observation periods ranged from 2 to 4 years, with a mean of 3.8 years. All measurements were taken with a minimum distance of 1 mm from the implants. This study does not focus on the peri-implant bone resorption.
Implant Procedure and Implant Survival Rates
Second stage surgery was performed 4 months later and osteosynthesis devices were removed while osseointegrated implants were placed in a routine fashion ( Fig. 6 A-C) . All patients received Biomet 3i Osseotite ® implants (West Palm Beach, FL, USA). Survival rate implants were considered those characterized by: absence of persistent pain; absence of perimplant infection with suppuration; absence of mobility; absence of continuous peri-implant radiolucency; perimplant bone resorption present in the first year but reduced in the following years .
Statistical Analysis
The Kruskal–Wallis test was used to determine whether there was a statistically significant difference in the resorption pattern of the symphyseal area and the three bilateral reference lines shown in Fig. 3 B (at the mental foramen (D), 8 mm distally to the foramen (E) and 16 mm distally to the foramen (F)).
Results
The clinical results of this procedure were satisfactory. This bilateral two-step osteotomy changed the contour of the mandible. The augmented ridges appeared to be firm in all cases. The mucoperiosteum on the lingual side was stretched, but remained attached to the alveolar crest even during the surgery. The cranial fragment of the osteotomy rotated posteriorly; this inconvenience was also described by Jensen et al. The authors noticed a change in the slope of the mandible but it did not affect the placement of the implants in symphyseal bone.
In 3 patients, presenting extreme atrophy during lifting of the osteotomized segment, a fracture of the cranial segment occurred. These intra-operative complications always occurred on the thinner part of the cranial fragment of the osteotomy. It was still possible to complete mandibular reconstruction and prosthetic treatment.
The mean hospitalization was 4 days (range 3–6 days). The healing process was problematic in 3 patients due to the development of small sequestrums, which were removed under local anaesthesia. 7 screws were removed before the implant stage surgery. Postoperative recovery after implant placement was uneventful in all patients.
During the follow-up period, one patient dropped out of the study 2 years after surgical augmentation of the atrophic mandible. The dental implants of this patient were placed and loaded but he did not attend recall visits.
The anterior vertical mandibular height increased and the correct intermaxillary relationship was recreated. The gain of vertical bone at 3 months was on average 11 mm (SD ± 1, minimum 8.7 mm and maximum 12.7 mm). The resorptive process was active during the first 6 months and continued at a slower pace thereafter. At 6 months, 11% was reabsorbed and at 4 years 8 mm of the 11 mm were still present giving stability to implants ( Table 1 ). 73 implants were placed in the symphyseal area and the survival rate at the end of the observation period was 96%. Three implant failures occurred within 1 year of loading.
