One major challenge implant surgeons are often faced with is large edentulous area which has insufficient bone volume for the purpose of implant placement. There are several methods have been used to augment the defected sites most common guided tissue regeneration (GTR), and autogenous bone particulate, or block graft, but these methods have several major disadvantages in GTR has limited ability when it comes to generate adequate bone height predictability, and the complication of membrane exposure, and possibility of infection of the site, or graft loss. In other hand autogenous bone grafting has predictable results, but might cause a major discomfort for the patient at the donor site also has high cost. So, a different method has been developed by using distraction devices, which has acceptable increase in bone volume for the implant surgeon for the correction of severe defect, and possible implant placement in the future. A case report is presented describing the use of alveolar distraction to augment a vertically deficient of alveolar ridge at the mandible anterior after implants failure at mandible lateral incisors.
History of Distraction Osteogenesis
Gravel Ilizarov was a Russian orthopedic surgeon is considered to be the father of distraction osteogenesis (DO) in the 1940s and 1950s. Professor Ilizarov was able to illustrate that a long bone could be cut and stretched if only the appropriate device and protocol could be established. In 1988, Professor Ilizarov presented his work in US and in 1992 McCarthy reported first cases in mandible. In 1992, McCarthy, Schreiber and Karp applied this concept to treat hemifacial microsomia by distracting the mandible. In 1996, Block, Chang and Crawford described the first alveolar distraction in dogs and in the same year, Chin and Toth applied alveolar distraction to humans.
Ilizarov’s work is based on the well-known law of tension-stress, the principle whereby gradual traction on living tissues can, under certain condition, stimulate the regeneration and active growth of those tissues i.e., tension forces stimulate histogenesis.
Implications of Distraction Osteogenesis
The first advantage of distraction osteogenesis is that it has more potential to regenerate bone compared to bone grafting.
Secondly, distraction osteogenesis does not require a second surgical site for the donor site, which reduces discomfort, treatment time, and the cost of the procedure.
Thirdly, distraction osteogenesis creates a vital bone of excellent quality for the placement of implants, which is not always the case with autogenous or allogeneic bone grafting.
Finally, the greatest advantage of distraction osteogenesis for mandibular augmentation may not be related to bone, but soft tissues which are lengthened together with the bone tissue.
Limitations of Distraction Osteogenesis
The downside of distraction osteogenesis is that there must be a minimum quantity of bone about 5 mm of the transport and anchorage segment is a must to have adequate strength to withstand force of mobilization and transport.
In addition, expansion occurs only in the direction of transport (Vector). The patient must also cooperate with the activation process.
Indication of Distraction Osteogenesis
In alveolar distraction the main indication is the vertical augmentation of the ridge with or without soft-tissue deficiency. DO has an advantage over other techniques such as guided bone regeneration and onlay bone grafting in that it can predictably generate more than 5 mm of alveolar height. 2,3 In addition, the mucosa also develops with increase of vestibular height. Thus the technique is useful in either optimization of esthetic looks in the anterior or increasing the volume of bone before implant takes place in the posterior. Both distraction osteogenesis and onlay bone grafting are applied in the event that traumatic defects occur in complex multidimensional alveolar and mucosal deficiencies. There may be less bone available to distract in extremely atrophic areas. This requires onlay bone graft to be done first and then the grafted area can be vertically distracted after 16 weeks healing. However, in cases of mild to moderate horizontal atrophy, distraction osteogenesis can be done first, followed by onlay bone grafting, or guided tissue regeneration.
Materials and Method
The purpose of this patient report is to use a clinical case to demonstrate the preoperative planning, surgical technique, treatment protocol, and application of alveolar ridge augmentation with the distraction device in partially edentulous ridges for improvement of esthetic areas, after failed implants. A 47-year-old female patient complained she felt pain because of her lower implants that were done in private clinic about 18 months ago. Her medical history was found to be noncontributory to her present complaint because she has no known drug allergies and neither was she on any kind of medication. The patient drinks only occasionally but has no history of tobacco use. Intra- oral examination revealed severe destruction of soft and hard tissue around the mandible lateral incisors implants (Fig.1and 2). Radiographic findings showed severe bone lost almost to the apex of the two implants at mandible lateral incisors (Fig. 3 to 5). Based on the clinical examination, it was determined that the patient’s implants had to be removed first, and then reconstructed with
alveolar DO to gain vertical height. Clinical features of this case included severe alveolar bone and soft tissue deficiency.
Failed Implant Removal
Alveolar Distraction Technique
It is a four steps technique involving
a) Full thickness flap to expose the alveolar defect.
b) Latency period 7 to 10 days. (The latency period is the time from surgery until distraction is activated).
c) Distraction, during which bone is transported incrementally at the rate close to 1 mm/day.
d) Time for consolidation, typically 2 months, before the device removed.
The entire Alveolar distraction process takes 2-3 months from the time of initial surgery to the time when devices are removed, and possible implants placement.
The distraction/postoperative protocol typically include the following phases: a latency period, device activation, a consolidation period (Figure. 24).
This latency period is typically 5 to 7 days long. Factors that may affect the duration of the latency period include the age of the patient, the extent of tissue trauma created during surgery, and the healing rate for the patient.
Following the latency period, the device is activated; this is done with the ratchet wrench and adapter, screwdriver handle, and straight driver, or with a temporary activation tool. The pitch on the threaded distraction rod is 0.4 mm, so one complete turn equals this vertical distance. Typically, patients are distracted one or two turns (0.4 to 0.8 mm) on a daily basis until the desired amount of vertical distraction has been achieved. Because a clinician can evaluate using only tactile feedback generated by the device, it is recommended that the clinician activate the device in the dental office. Distraction results in vertical elevation of the transport segment, which enlarges the regeneration chamber. Because the chamber is surrounded by vital bone on four sides and by periosteum on two sides.
When the desired height of the alveolar crest is achieved, distraction ends and consolidation begins. The threaded rod is left in place for the duration of consolidation, which lasts about 12 weeks; longer consolidation periods may improve results by limiting the amount of relapse. During this time, bony union occurs across osteotomy margins (the vertical osteotomy cut lines and in the distraction zone), and the gingiva expands to the new alveolar bone volume 3,7.
According to this classification in table 1 9, the present case has both horizontal and vertical defects and the defect is larger than 7 mm. Therefore, it is a class III ridge defect.
The key to success in distraction osteogenesis is careful, precise, well planned surgery with care taken to preserve the vitality of the transported segment, educate and follow patients and maintain precise vector control of the regenerating tissue.
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by Dr. Ali Alajmi