Continuous mandibular distraction osteogenesis using superelastic shape memory alloy (SMA)

Abstract

Distraction osteogenesis is a well-established method of endogenous tissue engineering. It is a biological process of bone neo-formation between segments subjected to tension. The concept of this study was to investigate the distraction osteogenesis with a device capable of creating a permanent and constant force during the whole process as if a very large number of small elongations were applied constantly. The mechanical testing of the device used to produce the constant force and the in vivo analysis of the bone growth after it was implanted in rabbits are presented on this work. The device consists of a NiTi coil spring, superelastic at body temperature, in order to have a stress plateau during the austenitic retransformation during the unloading. The in vivo analysis was made on six female rabbits of 12 months old. A segmental mandibulectomy at the horizontal arm of the mandible and a corticotomy at 5mm distant from the gap were made. Next, following a latency period of five days, the SMA springs were implanted to induce the bone neo-formation. The displacement at the unloading plateau shows that it is necessary to have longer springs or to use several (available commercially) in series in order to fulfil the requirements of a human distraction. The temperature variations induced changes in the spring force. However, when the temperature returns to 37 degrees C the distraction force recovers near the initial level and does so completely when the distraction process continues. For the in vivo study, all six rabbits successfully completed the distraction. The radiographies showed the gap as distraction advanced. A continuity in the newly formed bone with similar transversal and horizontal dimensions than the original bone can be observed on the histologies. In conclusion, the application of a constant force on distraction osteogenesis, using SMA springs, may be a successful alternative to the conventional gradual distraction.

Biomechanical Configurations of Mandibular Transport Distraction Osteogenesis Devices

“…The relationship with the cutaneous tissues MBT devices can be internal, 9,[14][15][16][17][18][19][20][21]24,25,27,31,42 if the bulk of the device is buried beneath the cutaneous tissues, or external, 1,8,22,23,26,[28][29][30]32,[43][44][45] if the device uses transcutaneous pins to attach to the bone (Fig. 4).…”

“…5): power screw, 1,8,9,15,[17][18][19][20][21][22][23]26,[28][29][30][31][32]42,45,54 spring, 24,25,55 traction wire, 14,16 hydraulic, 27 and rack and pinion. 2,56 The power screw activation system, also called screw lead activation system, translates torque into linear force to be used to distract the mandibular bone by matching an external helical threaded screw with either a negative or female threaded nut with the same thread form (Fig.…”

“…It is unique in that it does not have an activation arm, because the external energy is stored within a preformed superelastic shape memory alloy (SMA) that allows the system to deliver a continuous force directly on the callus without external activation. 24,25 However, the first activation of the spring, after the latency period, requires an operative process to release the activation mechanism. 64 Spring activation mechanisms can be either a uniform coiled wire 24,35,65 or a bent wire with different conformations.…”

“…7 Bone transport distraction osteogenesis is used for the reconstruction of segmental defects by means of the incremental movement of one (bifocal distraction) (Fig. 2B1), [14][15][16][17][18][19][20][21][22][23][24][25][26][27] two (trifocal distraction) (Fig. 2B2), 9,[28][29][30][31][32] or three (quadrifocal distraction) (Fig.…”

Biomedical Applications of Shape Memory Alloys

“…The presence of parts made by SMA exploiting pseudoelasticity allows the device to apply lighter (with respect to the forces generated by an arch completely in steel) and constant forces. Pseudoelastic behavior is also exploited for producing orthodontic distractors [22] (Figure 8(b)), which are used for solving the problem of teeth overcrowding in the mandible district: after a mandibular symphyseal distraction osteogenesis, the device is applied in order to produce an expansion of the mandible. Also in this case the use of SMA assures tensile forces nearer to the physiological values and constant in time.…”