Distraction osteogenesis is a useful technique that could form new bone between bony surfaces that are gradually pulled apart without the need for bone grafting.
Few reports have described the use of distraction osteogenesis in reconstructing segmental bony defects. Ilizarov and colleagues 1–3 were the first to describe this technique in the management of osteomyelitis of the lower extremities. Constantino et al. 4 tried the same principles of mandibular reconstruction by the application of the distraction osteogenesis transport disc technique in segmental bony defect in the mandible in six animals.
Herford 5 presented the first use of intraoral plate-guided distractor in four patients with segmental mandibular defect ranging from 4 to 7 cm.
The effects of rate and frequency were discussed by Ilizarov’s experimental work. He recommended a rate of 1 mm/day to achieve successful distraction. His experiment on dog tibia with a rate of 0.5 mm led to premature union, whereas a faster rate of 2 mm/day resulted in significant incidence of nonunion 5,6.
Recently, Cheung et al. 7 demonstrated that different bone morphogenetic proteins were expressed at different rates of mandibular distraction osteogenesis using rabbit models.
King et al. 6 studied the effect of the distraction rate and the consolidation period on bone density after mandibular osteodistraction in rats. They compared distracted sides with control nondistracted sides. There results suggested that rapid distraction caused significant loss of bone density.
The adjunctive application of electric current to the rapidly distracted bone may have a positive effect on the regenerate formed and could be used to decrease the total treatment time by increasing the distraction rate.
The discovery of electromechanical properties of the bone in the last 20 years led to the hypothesis that bone formation is dependent on its electromechanical potentials 8.
Piezoelectricity of a material is its property to generate voltage when stressed or deformed. This is considered as the direct form of piezoelectricity. The mechanical deformity that takes place when electric current is applied is known as indirect or converse piezoelectricity 9,10.
It has been established that piezoelectricity is a naturally occurring phenomenon in the human body such as in bone, cartilage, tendon, dentin, and other connective tissues. This could produce electric charge when stimulated 8,11.
The strength of the piezoelectric effect was correlated to the known capacities of the tissues to undergo adaptive remodelling. This could explain alveolar bone remodelling induced by orthodontic appliances 10.
The effect of electrical stimulation on osteoblastic cells had been investigated in several in-vitro studies 12–16.
Hagiwara and Bell 17 reported a significant increase in new bone formation during gradual distraction of a mandibular rabbit.
A leading research paper has been published by El-Hakim et al. 18, studying the effect of electric current stimulation on mandibular distraction of goats. There results suggested that direct electric current stimulation displayed a synergistic action with mandibular distraction in goats.
There are no available clinical studies to correlate the effect of electrical current application with mandibular distraction.
The purpose of this study was to evaluate the effect of electric current stimulation on the distracted bone formed by the transport disc distraction device in the reconstruction of human mandibular defects.
Materials and methods
This study was conducted on two groups of patients who required reconstruction of their mandibular defects after segmental resection of ameloblastomas. Reconstruction was attempted using an intraoral segment transfer device (KLS Martin Group, Tuttlingen, Germany), which has a 0.6-mm titanium mesh to allow its bending and adaptation on the bony segment and stump. Our target was to achieve 5 cm of bone regenerate in the horizontal direction. The device was fixed directly to the bony stump and to the transport disc after shaping and pending the meshes to the required mandibular shape. Four to five pairs of screws were used to fix to the upper and lower meshes with the segment transport disc and the mandibular stump (Fig. 1). Activation was carried out through a transcoetaneous rod.
Patients of the two groups were selected blindly. Intraoral vestibular incision was performed. Sharp and blunt dissection to remove fibrosis along the planned distractor zone was performed to create a bed for the distractor arm and the transport disc to move along.
The device meshes were fixed primarily to the basal bone of the mandible and to the planned transport disc after making the primary cut for the transport disc. The transport disc was designed to be at a distance between 1 and 1.5 cm according to the availability of the remaining bone and the location of the remaining bony mandible. Instead of the short and thin microscrews of 1.5 mm diameter, longer and wider miniscrews of a larger diameter of 2 mm were used.
In group 1, six adult patients were asked to wear a custom-made electric stimulator device. The custom-made electrical stimulator device was fabricated with microtransistors and resistors in a circuit with a 9-V battery to produce a direct current of 10 μA continuously (Fig. 2).
The device was attached at points through which the distracted zone was enclosed. Patients were asked to wear the device continuously for a minimum of 12 h/day. The device was used throughout the latency, activation, and consolidation periods (Fig. 3).
In the second group, which served as the control, four patients were included with the same parameters. No electric stimulator device was used.
The distraction process was started after a latency period of 7 days, an activation of 2 mm/day was carried out and followed by a consolidation period of 7 weeks, which was more than double the activation period for all of our cases.
Methods of evaluating the effect of the electric stimulation included clinical, radiographic, an ultrasound assessments, and bone density measurements of the distraction zone on the digital panoramic radiographs were analysed using the Grey scale analyser software (Digora for windows application version 1.51 soredex, finndent, Tuusula, Finland) on the digital radiographs. As all patients were adults, standardization of the kV to 27 and µA to 10 was achieved. The distracted area bone density was compared with the bone density of the control during early activation, late activation, early consolidation, late consolidation, and 12 months postoperatively.
Data obtained were tabulated and analysed by an IBM computer using statistical program for social science version 12 (IBM Co., USA). Bone densities were measured at three points on the cranial, the central, and the caudal border on the distracted bone gap. Anatomical structures such as the inferior dental canal and teeth roots were avoided.
Computed tomographic (CT) examination was carried out at the end of the distraction to confirm bone maturation. The bone density (quantitative CT value in Hounsfield units) was evaluated in both axial and coronal cuts. In each cut, three points were calculated, two in the margins and one at the centre. The mean was recorded, tabulated, and analysed statistically (Fig. 4).
The resected segment was reconstructed varying between 50 and 70 mm. In all cases, there were no available functional proximal segments.
The technique combining a transport disc distractor and an electric stimulator was well tolerated by all patients.
In case the transport disc had a tooth moving with it, reduction of the occlusal table of that tooth had been carried out during the activation period to maintain adequate occlusion without interference.
None of the cases required a hospital stay for more than 24 h after surgery.
The fast rate of distraction of 2 mm once daily did not give the patients agonizing pain during the activation process although discomfort was a common experience.
Infection occurred around the rod of the devices in about half of the patients in the electric stimulation group, but was not severe to cease the distraction process. The infection was treated with Sulbactam/Ampicillin given orally. In the control group, infection occurred in all the patients included; the distraction process had to be slowed to 1 mm daily in two cases and had to be ceased for the other two. Unfortunately, a scar was formed around the distractor activation arm in all cases, which was not disfiguring and faded away during the follow-up period. Dehiscence was noticed in three patients at the end of the activation process; patients were instructed to increase oral hygiene measures by chlorhexidine mouth wash.
No facial nerve damage occurred in all cases. The distraction process had to be ceased in one patient in the electric stimulation group because of stoppage of the transport disc movement and loosening of the screw. Another patient of the same group reported a hypersensitive feeling at the distribution of the mental nerve.
The distance achieved was more in the electric stimulation group. The control group encountered a lot of complications as expected from previous literature; without adding a bone stimulant, we could not maintain a 2 mm rate throughout the distraction period because of infection and early stoppage of the device.
The regenerated bones were of good length and shape to correct the aesthetic and functional problems (Fig. 5). Gross examination of the distracted bone at the time of device removal revealed new bone formation that could not be differentiated from the native bone.
The distracted bone formed in all cases was found to be stable at the end of the distraction process with no mobility, which indicates clinical union.
Gross examination of the distracted bone at the time of device removal revealed new bone formation, which could not be differentiated from the native bone.
The results obtained by comparing bone density measurements of the electric-stimulated distracted bone and the control during different phases of distraction showed that there were no statistically significant difference between the two groups at the early activation and the late activation periods. The bone density of the electric stimulation group increased more by the end of the consolidation phase than the control group.
The mean bone density measurement by CT of the distracted electric stimulation group at the end of the distraction process was 779±201, whereas that of the control side was 720±150. There were statistically significant differences between them.
Application of electric field proved to induce physical forces that regulate connective tissue function, promoting maturation and calcification of the extracellular matrix 19. The stimulant effect of the electric current on the distracted mandibular bone was investigated only on animal models 17,18. One of the major problems with distraction osteogenesis is the lengthy process required to achieve a successful outcome. Patients with a large segmental mandibular defect would benefit from cutting down the lengthy time needed to achieve newly formed bone with segment transfer distractor devices.
The present study tested the effect of electric stimulation on rapidly distracted bone segments. The distraction rate was at a constant of 2 mm/day, which shortened the treatment time without affecting the biomechanical stability of the regenerate. Bone densities of electrically stimulated distracted bones at the 1-year follow-up were more than those of controls. As lengthening proceeded, the bony densities of the regenerate first decreased, reaching minimum values; then the bone density started to increase to reach its maximum values by the end of the consolidation period 20. The present study had similar results although bone densities of the regenerate increased to values above the control and maintained its value at the 1-year follow-up. This was supported by other reports that showed that the cut end of a bone had a tendency to be denser than the nonoperated control 2,21,22. It might be the effect of the applied electric current that stimulates the whole distracted gap rather than the cut end only. The bone density measurement in this study showed increased densities of the calcified lengthened bone stimulated by electric application. The bone densities obtained were above that of the control at the end of the distraction process in both digital imaging analysis and CT measurement. In the present study, using electric stimulation, early maturation of the distracted bone was evident. New bone formation shadow was noticed around 4 weeks of consolidation as radio-opaque spots. By 7 weeks of consolidation, bone bridging could be seen, indicating the positive effect of electric current application on bone formation and bone healing. Bone densities of the distracted bone at the 1-year follow-up were more than that of the control.
The application of electric current was well tolerated by the patients presented in this study.
Bone electrical potential changes with the force applied. Bone cuts alter the bone electrical potential; these play an important role in healing, bone growth, and remodelling 23.
The mechanisms by which such a stimulant effect could accelerate bone maturation were unclear. Several explanations have been described. It was thought that electrochemical products were produced due to the effect of electric current applied and these products favoured bone formation 24,25. One of the major roles might be attributed to the OH radical 15, and the associated reduction in partial oxygen tension PO2 or the increase in the medium PH with the associated vascularization that might favour new bone formation 26. These biproducts would lead to depolarization of the transmembrane potential of the bone cells opening its calcium channels 15.
Enlargement of calcium gates would occur and more calcium would be incorporated into the cells 27. The increased of the intracellular calcium ions in the cytoplasm would come from the free extracellular calcium and from calcium stores at the endoplasmic reticulum that was triggered by the open calcium gates 16.
This increase in the calcium content would increase bone mineralization and activate cell proliferation by various mechanisms 27. The electric potential might control cell nutrition and proliferation, which could affect the orientation of both the internal and the external callus macromolecules 28. The electric field produced might enhance the enzymatic activities of the bone formed 29. The DNA and the cyclic AMP systems of osteoblasts were activated 14. Osteoplastic vascular endothelial growth factors were markedly upregulated by the applied electric current, and bone morphogenetic proteins and alkaline phosphatase activity of bone cells were significantly increased 11. Transforming growth factor β1 and messenger RNA in the osteoplastic cells increased 30.
Research showed that chondrocytes were more differentiated than pluripotent cells and the expression of proteoglycan and type II collagen were increased by the applied electric current. The collagen fibres produced were oriented in a spatial manner. This structure could enhance its calcification 18. Adjunctive application of electric current with a segment transfer distraction device plays a positive role in enhancing bone formation during distraction osteogenesis and would allow a faster rate of distraction (Fig. 6).
Conflicts of interest
There are no conflicts of interest.
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