Distraction Osteogenesis in Implantology for Ridge Augmentation-A Systematic Review

The purpose of this systematic review was to evaluate distraction osteogenesis for ridge augmentation in implant dentistry and also to present the associated advantages and limitations. A Medline and manual search was conducted to identify clinical studies concerning distraction osteogenesis in implant dentistry published between 1998 to 2012. 52 articles were assessed. The articles included evaluated the type of distractor used, augmentation achieved and the success and survival rate of implant placed in the augmented site. It was seen that when comparing methods of regeneration, a decreased treatment time is seen in cases of distraction osteogenesis. The reason for this lies in the fact that within 12 weeks the distraction segments are formed and there is a increase noted in the height of the alveolar bone, from 5 to 15 mm as well as an implant survival rate of 95.7%. It can be concluded that distraction osteogenesis is a relatively simple, effective and reliable technique for alveolar ridge reconstruction in contemporary implant dentistry. It can be considered versatile owing to its simplicity, possibility of avoiding bone grafts, infections and blood transfusions. The fact that graft and membrane exposure or inadequate tissue coverage do not pose complications, makes this an effective method of bone augmentation in implantology.

D e n ta l Impl a n ts a n d Dentu

Introduction
The field of implant dentistry is dynamic. A major contraindication to the placement of dental implants is inadequate volume and integrity of bone at the chosen site. In patients who have decreased bone dimensions or bone of inferior quality in the mandible, augmentation bone grafts are essential before the placement of implants. As a result of periodontitis, extractions and trauma of the craniofacial region, sometimes there is atrophy of the alveolar ridge [1]. Placement of implants may be prevented by inadequate bone dimensions unless the deficient areas have bone grafts placed or the inferior alveolar nerve repositioned [2]. In order to correct bone, it is important to carry out autogenous onlay bone grafts, guided bone regeneration, alloplastic augmentation and alveolar split grafting [3][4][5][6][7][8]. Each of these have their respective pros and cons. Sometimes they do not guarantee the desired bone regeneration, specially in cases of large bone defects and therefore, there is a need for a secondary donor site. There are however some problems associated with this. These include graft rejection as well as donor site morbidity. Nerve repositioning may result in paresthesia from nerve manipulation. Although vast research has been done and documented on the concept of guided bone regeneration, the provision of adequate space for this regeneration seems difficult in cases of such large bone volume [5,6,9]. Unfortunately, none of the above methods provide reliable or predictable results. They all require a greater waiting time between surgeries to increase the ridge and the placement of the implant. Distraction osteogenesis (DO), described by Codivilla, is a biological process that stimulates the formation of new bone following the gradual separation of two bone segments previously joined together [10]. Illizarov carried forward this concept, and is credited with having defined and established the biological bases for the clinical use of osteogenesis distraction in the management of different bone deformities [11][12][13]. It was Block et al. who employed these principles experimentally following which they were the first to publish studies on the using alveolar distraction osteogenesis (ADO) in animals in 1996 [14]. In cases of ridge deficiencies in the maxillary arches, Chin et al. reported the use of ADO as a treatment option [15].
The ADO is a technique allowing augmentation of alveolar ridge height along with the formation of new bone. It also includes obtaining a significant increase in the surrounding soft tissues, thereby offering a predictable result, with low morbidity and infection rates and a significantly shorter waiting period for rehabilitation with implants (10 weeks) in comparison with the traditionally used methods [16][17][18][19]. The widespread use of distraction osteogenesis owes its success to the fact that it is versatile, simple, and there is simultaneous augmentation of the soft tissue with bone, and the possibility of avoiding bone grafts, infections, blood transfusions, and inter-maxillary fixation. It does not carry the unnecessary weight of complications of graft and membrane exposure or inadequate tissue coverage, therefore making the distraction procedure an ideal technique for bone augmentation in implantology.

Materials and Methods
Studies to be included in this structured review had to fulfil the following inclusion criteria:

Discussion
The data related to the long-term survival rate of implants in the lower jaws post distraction osteogenesis in partially edentulous patients is limited. In a study by Enisdilis et al. survival rate of 95.7% after a mean follow-up of 39.4 months (range 4.8-58.3 months) post-implantation was observed which is comparable to the survival rate of 100% reported by Chiapasco et al. [22,25]. The results of the investigation by Froum et al. documented a similar implant success rate (90.9%) [26]. In case of the maxilla, a survival rate of 90.4% was reported by Jensen et al. with at least 3 years follow-up postrestoration after a vertical distraction of 3-15 mm (mean 6.5 mm) [23]. Even though there was an adequate bone production, ensuring a high longterm implant survival rate in this series, 75.7% of patients suffered complications. In the literature, the total percentage of complications ranges from 0% to 100% [27]. No statistical difference was observed in success rates between implants placed in autogenous bone grafted sites v/s distracted bone sites. However when comparing bone grafting neovascularity with distraction regenerate has neovascularity it is seen that the latter is more resistant to infection than is the case with bone grafting.
Elo et al. displayed as much success in autogenous bone grafting as distraction osteogenesis in preprosthetic alveolar bone augmentation procedure [28]. Chiapasco et al. reported a better long term prognosis, when comparing GBR to DO as far as bone gain maintenance and peri-implant bone resorption after prosthetic loading are concerned. Though survival rates of implants are the same between DO and GBR groups, the success rates of implants differ significantly. Since it is possible to achieve more vertical gain with DO, it is more commonly indicated than GBR. Results from this multicenter prospective study seem to demonstrate that DO can be an effective and reliable surgical No restrictions were placed concerning the study design. Randomized and non-randomized clinical trials, cohort studies, case control studies and case reports were included in the review (Figure 1). A Medline search was performed to identify clinical articles published between the dates 1998 to 2012. The following search terms were used: distraction osteogenesis and implants, alveolar distractions osteogenesis and implants, alveolar distraction and implants. In addition the manual search of the journals from 1992 to 2012 was performed. The review looks on certain key aspects of distraction osteogenesis in implant dentistry that will be helpful in deciding whether to employ distraction osteogenesis for augmentation of bone before implant placement. Thus, the data obtained from each article (52 articles were reviewed) was divided into 2 (Tables 1 and 2).

Results
Distraction osteogenesis for the correction of deficits of edentulous ridges seems to be a reliable method for overcoming the problems connected with bone grafting and GBR. The following advantages can be anticipated with intraoral distraction osteogenesis: i) Provides the opportunity to obtain a natural formation of bone between the distracted segment and basal bone in a relatively short time span.
ii) Eliminates the need to harvest bone, with consequent shortening of operating times and reduction in morbidity.
iii) Soft tissues can follow elongation of the underlying bone. iv) Can be frequently performed under local anaesthesia on an outpatient basis and postoperative recovery is favourable.
v) The regenerated bone seems to resist resorption.
vi) The newly generated bone seems to be able to withstand the functional demands of implant supported prostheses [14]. Distraction osteogenesis can produce a gain in alveolar bone height from 5 to15 mm in edentulous segments of the mandible and mean values from 5   2 DID devices loosened. 9/10 patients-satisfied with their facial asymmetry, the one who was not had 2 DIDs during the follow up period.

months
The vertical distance between the implants, as measured from the centre of the abutments averaged 9.05 ± 1.01 mm after the initial 10 days of distraction, and 8.85 ± 1.05 mm after 10 weeks of healing. From 6 to 10 weeks, and until sacrifice at 12 months after loading, the radiographic density of the bone between the distracted segment and the remaining corpus of the mandible increased. Histologically the cortices were intact and continuous across the distraction gap.
2 Oda et al. [37] 12 implants Greater integration between the implant and the distracted segment-12 weeks after distraction than at 8 weeks. The distraction implants were loaded by prosthetic superstructures 4 to 6 months after distraction For 5% of the implants, pathologic probing depth of more than 3 mm and sulcus bleeding were registered prior to prosthetic treatment. These observations decreased during the next 9 months. Periotest values were normal before the start of prosthetic treatment. There was a decrease in the Periotest values, thus an increase in implant stability, during the following 9 months 5 Watzek et al [18] 11 Nobel Biocare, Göteborg, Sweden, regular platform, length 10 to 15 mm).

weeks 7 months
Computed tomograms obtained preand postoperatively showed consistent ossification of the osteotomized and distracted areas 12 weeks after the placement of implants, thin lamellar bone rose horizontally from the transport segment towards the surface of the implant. Twenty-four weeks after their placement, the implants were fully embedded in mature lamellar bone, and direct bone contact with the implant surface could be seen.
9 Gaggl et al. [51] After a radiographic estimate of the success of distraction the distraction insert was exchanged for the permanent implant head. In 2 patients a further conventional implant was inserted after a delay of 4-6 weeks. The distraction implants and conventional implants were allowed to heal for 4 months before prosthetic treatment started The mean peri-implant probing depth was 1.8 mm before start of the prosthetic treatment and decreased to 1.2 mm 12 months after implant loading. No implants were then lost. 25 Perry et al. [38] Sand blasted large grit acid etched solid screw type 4.1 x 12 mm.

weeks after consolidation
The mean BIC (±SD) for implants placed in the distracted sites was 54.7% ± 14.6%; for the onlay grafted sites 53.8% ± 11.8%; and for the control sites 51.2% ± 14.4%.
. 26 Saulacic et al. [41] 33 ITI (Straumann, Waldenburg, Switzerland) and 10 Frialoc (Frialit, Friaburg, Germany) The mean of bone relapse following consolidation period was 1.57 ± 1.82 mm at the mesial and 1.79 ± 1.68 mm at the distal aspects of implants After a consolidation period of 3 to 4 months the implant was left in the bone, The mean period from the first operation to the start of dental implant loading was 6.3 months.
3-year Cumulative survival rate of the dental implants was 93.75%.
BIC, Bone Implant contact; DI, Distraction implant; SD, Standard deviation. alternative to correct vertical deficits of edentulous ridges resulting from atrophy, trauma, congenital malformation, and the resection of benign or malignant tumors [29]. These results have been confirmed by other studies [23,30]. Regenerated bone seems to withstand the biomechanical demands of implant loading well. By taking periapical radiographs from time to time it is possible to assess the subsequent increase in bone density, 3 to 4 years after prosthetic loading. These encouraging results have been confirmed by other studies from the histologic and histomorphometric perspectives [31][32][33].
The histological analysis revealed that the new bone formed interconnected bone trabeculae that were oriented at an angle to the cut bone surface that was created through osteotomy. Furthermore, the new bone in the distraction region consisted of woven bone reinforced by parallel-fibered bone. With regards to the rate of distraction Ragheobar et al. waited for 5 days before initiation of distraction and used a rate of distraction of 1mm/day, which worked well [31]. A rate of distraction that allows for lengthening with bone formation and a proper soft tissue response is one that is said to be optimum. If too rapid, non-union will occur, whereas if it is too slow, there may be premature union. A continuous rhythm of distraction is thought to be ideal, wherein lengthening of approximately 1mm a day is noted [14]. A 3-week consolidation period before implant placement offers an immature bone that starts to form columns from the borders of the distracted area.
Histological studies carried out in humans, have proved the presence of bone trabecula parallel to the distraction vector and support the criterion that an 8-week consolidation period is enough for implant placement [32]. At the end of a 3-month consolidation period, the cumulative success rate of dental implants was 100% in human models [34,35]. In his series, Bilbao et al. with the same consolidation period, high primary stability was obtained only slightly lower than that achieved in native bone [36]. A human histologic study performed by Zaffe et al. showed that bone formation finished 60 days after the end of the distraction and decreased with longer times; early implant insertion was suggested to avoid bone loss due to mechanical unloading [32]. Placing an implant after 3 weeks of completion of distraction does not hamper bone regeneration. The implants osseointegrated in the augmented ridge, and the integration between implants and regenerated bone was better at 12 weeks after distraction than at 8 weeks after distraction [37].
In contrast Perry et al. concluded that integration of implants placed into augmented sites was equal to that of the control sites, and there was no difference in integration between the grafted and distracted sites [38]. With regards to peri-implant bone resorption alveolar bone distraction exhibited a mean peri-implant bone loss of 1.9 mm/year, together with high survival rates following prosthetic loading hence in alveolar DO, an overcorrection with 1 to 3 mm is suggested [39][40][41]. Wolvius et al. reported resorption rate of around 20% using a rigid extraosseous device [42]. Bone resorption does not depend only upon the use of a rigid or a semirigid distractor device. This was substantiated by Saulacic et al. described who described bone relapse of 26-29% with the use of an intraosseous semirigid distractor [41]. However a long-term implant survival rate for oral rehabilitation was noticed [43].The use of sinus lifting along with alveolar distraction for pre-implant reconstruction has also been seen. This brought about the limitations. Hence DO can be considered as a dependable option to augment complex alveolar ridge defects.

Conclusion
Distraction osteogenesis is an effective surgical procedure to treat vertical horizontal alveolar ridge deficiencies. By the various studies reviewed it can be concluded that is a reliable technique without any major complication and has a better long term prognosis and stability, especially after implant placement than conventional guided bone regeneration and bone transplantation techniques. In complex bony defects prior to implant placement excellent predictable ridge augmentation can be achieved which is very difficult with other conventional modalities. It can produce a gain in alveolar bone height from 5 to15 mm with the survival rate of implants ranging from 95.7-100% and success rate 94.2-98%. To conclude alveolar distraction osteogenesis is a relatively simple, effective and reliable technique for alveolar ridge reconstruction in contemporary implant dentistry. a change in the contour of a severely atrophic resorbed maxillary alveolus, thereby regenerating adequate bone on both the alveolar side and inside the maxillary sinus. This along with simultaneous sinus lifting proves to be a useful technique for patients with a severely atrophic maxilla requiring dental implant rehabilitation [44].

Complications
Chiapasco et al. concluded that despite very promising results, some limits were related to DO. First, inclination of the distracted bone segment, probably the result of traction of the palatal mucosa or of the muscles of the floor of the mouth which was successfully corrected by means of orthodontic appliances. Second, it is possible that there may be an insufficient dimension of the neocallus in the distracted region during the time of placing the implant. This may lead to a partial exposure of the implant threads in the region of distracted neogenerated tissue because of insufficient bone volume which has to be corrected by grafting the area with autogenous bone to cover the exposed implant threads. Third, the distraction device limits the application of the technique to composite vertical and horizontal defects. Adequate vertical osteotomies must be made in order to prevent interferences in the movement of the osteotomized segment. This may compromise the final result. Finally, minimal residual bone height of the atrophic area is needed to avoid the risk of alveolar damage, violation of the floor of the nose or the maxillary sinus, or mandibular fracture.
The authors arbitrarily chose a minimum bone height of approximately 5 mm to obtain a bone segment with enough volume to be stabilized by the distraction plate and microscrews with no risk of violation of the floor of the nose, the maxillary sinus mucosa, or the alveolar nerve. Moreover, vertically atrophied mandibles with less than 5 mm of bone height present a relevant risk of fracture during or after the performance of the osteotomy. 22 Fractures of basal bone and transport segment, breakage of distractor, and severe mechanical problems leading to abortion of treatment have also been described [27].Bone formation defects post distraction osteogenesis were usually chanced upon at the time of distractor explantation. These require supplementary corrective augmentation procedures in 11 of 45 distraction sites in a study [45].
Three-quarters of patients suffered complications requiring supplementary treatment measures were reported by Enisdilis et al. Distraction implantation to distractor removal was the case of fourfifths of complications that occurred. These figures undermine the theory that distraction osteogenesis is not an uncomplicated procedure [25]. However, dental implants were safely inserted into distracted areas in most instances and long-term survival of loaded implants was satisfactory. Often-mentioned soft tissue complications are dehiscences and failed lengthening of the fixed gingiva, resulting in a reduced vestibular sulcus Soft tissue dehiscences more frequently occur by the use of extraosseous devices which demand a larger covering mucoperiosteal flap and enforce the tension caused by surrounding cheek and tongue muscles [25,41]. According to Ettl et al. missing soft tissue extension may be more common with distraction of mandibular bone [46]. Kanno et al. said if a vertical alveolar DO is planned within 6 months of surgery such as for tooth extraction or alveolar trauma there should be sufficient over correction to compensate for a bone relapse of upto50% [47]. As concluded by Predjik et al. patients suffering from severe mandibular atrophy that were treated either with conventional augmentation techniques or VDO prove to be more susceptible to various complications wherein a majority of these complications occurred in the first year [48]. As with any surgical procedure there are a few limitations associated with DO, but the advantages outweigh