Abstract
To allow for implant placement in severe atrophic edentulous mandibles, distraction osteogenesis can be used to gain sufficient bone height. The efficacy of extra-osseous and intra-osseous devices is evaluated. In this retrospective study, 45 patients treated with an extra-osseous device (EOD) were compared with 43 patients treated with an intra-osseous device (IOD). From a statistical point of view, both patient groups were comparable for age and sex ratio. The IOD group gained more bone height (9.8 mm) than the EOD group (6.0 mm). A significantly higher degree of backward tilting of the device was observed in the EOD group (12.1°), compared with the IOD group (3.0°). There were also significantly more fractures of the basal bone segment and sensory disturbances of the chin area in the EOD group than in the IOD group. The IOD group scored significantly better on bone height gained, backward tilting of the device, occurrence of fractures, and postoperative sensory disturbances. Despite the fact that the mean preoperative bone height for the IOD group was substantially higher (18.6 mm) than for the EOD group (11.9 mm), it may be concluded that for augmentation procedures of the edentulous mandible, the IOD is more favourable.
To make implant placement possible in the extreme resorbed mandible, vertical distraction osteogenesis (VDO) has been introduced as a technique for bone generation. By first making a horizontal osteotomy in the interforaminal area, the upper segment is moved slowly upwards, allowing formation of bone tissue (callus) within the gap region. By using VDO, harvesting bone transplants can be avoided.
After 10 years of widespread application of VDO in the alveolar ridge, there is still significant disagreement about various treatment parameters, such as surgical technique, type of distraction device and minimal bone height necessary to perform the distraction . With respect to the type of device, two main philosophies have developed: the extra-osseous distractor (EOD) and the intra-osseous (endosseous) distractor (IOD) . There are only a few articles comparing EODs and IODs . In these studies, miscellaneous patient groups were included, with atrophied alveolar ridges in the maxilla or mandible, in fully as well as partially edentulous situations.
An EOD mainly consists of a frame with a spindle, which is fixed with plates and screws on the buccal aspect of the bone. EODs are capable of transporting the osteotomized bone segment, irrespective of whether teeth are present or not . An IOD, generally, has a pin-like configuration, that perforates the osteotomized segment that is to be distracted . This limits its use to only the fully or partially edentulous alveolar process. Modifications have been introduced, in which the IOD itself can be used secondarily as a dental implant .
Materials and methods
All fully edentulous patients who were treated at two clinics with a VDO device to enlarge the available bone volume to allow for implant placement were included in this study. At the Paracelsus Medical School, Salzburg, Austria, patients underwent osteodistraction with an IOD (Endo-Distraction Krenkel ® , Mondeal ® , Tuttlingen, Germany: Fig. 1 ) and at the Gelderse Vallei Hospital, Ede, the Netherlands, patients underwent osteodistraction with an EOD (Mondeal Vertical Distraction ® device Mondeal ® , Tuttlingen, Germany; Fig. 2 ). Both groups were surveyed retrospectively. Data were collected on sex, age at operation, preoperative and postoperative bone height, bone height gained, tilting of the distraction device and complications such as fractures, anchorage loss and sensory disturbances.
Surgical technique
For both distractor types, installation was performed under general anaesthesia. First, a horizontal incision was made on the vestibular surface of the lower lip to expose the alveolar process according to a modified Edlan method. A mucoperiostal flap was reflected only on the vestibular side, leaving the periosteum in place on the alveolar crest. The lingual mucosa remained attached to the bone, thereby ensuring that the bone segment to be distracted obtained its blood supply via both the lingual and crestal side. The mental nerves were always identified on both sides.
The EOD device was fixed using the 12-hole base-plate (length 56 mm, thickness 2 mm) at the lower border with titanium screws (length 9 mm, diameter 1.2 mm), and the 6-hole upper plate (length 32 mm, thickness 2 mm) at the top of the residual mandible with 5 mm screws (diameter 1.2 mm). A horizontal osteotomy was performed in between the two plates using a reciprocal saw. Care was taken to restrict the osteotomy to the interforaminal area. To facilitate mobilization of the upper segment, the distractor was removed temporarily. After remounting the distractor, the wound was closed in layers, taking care to keep the adjustment screw visible ( Fig. 3 ).
The IOD device was inserted in the middle of the symphyseal area. After drilling a hole in both the cranial and basal segments, the distraction rod was guided through the basal bone segment into the soft tissues of the submandibular chin area. The upper segment was fixed to the upper part of the device, thus moving upwards when activating the rod by turning it to the left. After closing the wound, only the top of the device was visible ( Fig. 4 ).
In both techniques, perioperative antibiotics were administered as well as chlorhexidine mouth washes. Because of the changing contour and the presence of the top of the distractor device in the oral cavity, the lower dentures could not be worn during the distraction period.
After a 7-day latency period, activation of the distraction device was initiated. The EOD was activated at 0.5 mm a day; the IOD device was activated at from 0.25 mm at the beginning up to three to four times 0.25 mm a day. A consolidation period of 10–12 weeks followed the distraction period, after which, the distractor was removed and, in the same session, the endosseous implants were installed. Four months later, prosthetic rehabilitation was performed. Patients treated with an EOD received two per-mucosal implants to allow for a bar- or ball-retained overdenture. In patients treated with an IOD, four implants were placed to support individual milled bars with dorsal elongations, onto which a removable bridge was positioned.
Lateral cephalometric tracings
For each patient, lateral cephalometric radiographs were compared, taken preoperatively and postoperatively, as at the end of the distraction period. By making tracings, measurements were performed using the Frankfurter horizontal plane as a reference. Perpendicularly, an auxiliary line was constructed. Subsequently, another line, tangent to the top and the bottom of the alveolar process, was drawn at right angles to this auxiliary line ( Fig. 5 ). As such, the bone height at the mandibular symphysis could be measured using an electronic digital calliper (ETC industrial ® ETC Europe).
To calculate the angle of the lingual movement of the upper segment, an extra auxiliary line running through the heart of the distractor device was drawn. The difference in angles, as measured before and after active distraction, served as an indication of the backward tilting of the upper segment ( Fig. 6 ).
Statistics
Student’s t -test for equality of means was used to elucidate differences in age, preoperative and postoperative bone height, increase in bone height and tilting between the IOD and the EOD group.
Results
Eighty-eight edentulous patients with mandibular atrophy were treated by VDO. From 1998 to 2005, at the Department of Oral and Maxillofacial Surgery of the Hospital Gelderse Vallei (Ede, the Netherlands), 45 edentulous patients (4 males and 41 females, aged 36–77 years, mean age 63 years) underwent VDO of the edentulous mandible. In the same time period, at the Paracelsus Medical School, Salzburg, Austria, the edentulous mandibles of 43 patients (5 males and 43 females, aged 37–76 years, mean age 59 years) were distracted using an IOD.
No significant diversity between both groups, with respect to sex and age, was seen ( Table 1 ).
| Extra-osseous device | Intra-osseous device | |
|---|---|---|
| N | 45 | 43 |
| Gender | Male 4, female 41 | Male 5, female 38 |
| Age variation | 36< >77 | 37< >76 |
| Extra-osseous device | Intra-osseous device | p -Value | |||
|---|---|---|---|---|---|
| Mean | Standard deviation | Means | Standard deviation | ||
| Mean age at operation | 62.6 years | 8.7 years | 58.9 years | 10.2 years | 0.076 |
| Bone height pre-operative | 11.9 mm | 2.1 mm | 18.6 mm | 4.5 mm | 0.000 * |
| Bone height post-operative | 17.9 mm | 2.4 mm | 27.8 mm | 3.6 mm | 0.000 * |
| Increase bone height | 6.0 mm | 1.7 mm | 9.2 mm | 4.13 mm | 0.000 * |
| Tilting | 12.1° | 5.43° | 3.0° | 0.5° | 0.000 * |
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