The reconstruction of critical-size bone defects following tumour resection or bone loss due to trauma is topical today and relates to the complexity of the treatment involved and poor healing outcomes. In bone bioengineering, the current trends are to explore novel methods of repairing these defects by using various bone substitutes. Various graft materials have been used for the restoration of these defects. A graft ideally needs to promote osteogenesis, osteoinduction and osteoconduction. The aim of this investigation was to assess the histological, radiographic and mechanical properties of the tissue regenerate following the application of tricalcium phosphate (TCP) scaffolding and recombinant human bone morphogenetic protein 7 (rhBMP-7) for the reconstruction of a critical-size osteoperiosteal mandibular continuity defect in the rabbit model. Highly purified and freeze dried recombinant human BMP-7 was used. It was produced by Chinese hamster ovary cells in culture and purified from the culture media. All the TCP samples had a porosity of 80% and average pore size of 100 – 500µm. For the rhBMP-7 loaded scaffolds; rhBMP-7 was reconstituted according to a recommended specification and 400ng were loaded by adsorption into the TCP scaffolds. Nine adult New Zealand white rabbits (3.0-4.0kg) were used for the planned study. In each case a unilateral osteoperiosteal mandibular body critical-size defect was created. In six cases the critical-size defect was filled with the rhBMP-7 on the TCP scaffolding, and in three cases the TCP was used alone. Assessments were made with plain radiographs at 0, 4, 8, and 12 weeks follow-up. Three months post-operatively the animals were sacrificed, the mandibles removed and the surgical sites were assessed with cone beam CT radiography, tested mechanically and analysed histologically. More bone regeneration was seen radiographically and histologically within the mandibles that received rhBMP-7 in the TCP, with evidence of both woven and lamellar bone formation. Union was obtained at the surgical site with no cartilage formation. The regenerated bone was confined to the area that had received the scaffold, with no calcification of the surrounding soft tissues. The TCP was also resorbed more completely in this experimental group. Very little bone was formed in the cases where the defect was filled with TCP alone. The mechanical properties of the regenerate in the group that received the rhBMP-7 and TCP were also significantly superior to those of the cases that received TCP alone. Histologically the overall mean of the percentage regenerated bone volume in the rhBMP-7 and TCP cases was 29.41% ± 6.25, while that for the TCP alone cases was 6.35% ± 3.08. The difference between the groups was statistically significant (p = 0.014). Mechanically the failure moments for the TCP alone cases were found to be very low (0-48mNm) while those for the rhBMP-7 and TCP cases were higher but there was considerable variation between the cases (55-2115mNm). Some of the cases in this group achieved failure moments comparable to normal untreated bone. In conclusion TCP scaffolding and rhBMP-7 can be used successfully for the reconstruction of critical-size mandibular defects in the rabbit model and TCP loaded with rhBMP-7 was significantly superior in its capacity for bone regeneration histologically when compared to TCP alone. The resultant bony regenerate could also at times have mechanical properties similar to those of natural bone. But due to the variability of the mechanical properties further investigations are required before clinical application.

Ultrasonic cutting has existed in surgery since the 1950s. However, it was not until the end of the 20th century that advances in ultrasonic tool design, transduction and control allowed commercially viable ultrasonic cutting devices to enter the market. Ultrasonic surgical devices, like those in other power ultrasonic applications such as drilling and welding, require devices to be driven at high power to ensure sufficient output motion is produced to fulfil the application it is designed to perform. With the advent of novel surgical techniques surgeons require tuned ultrasonic tools which can reduce invasiveness while giving access to increasingly difficult to reach surgical sites. To fulfil the requirements of novel surgical procedures new tuned tools need to be designed. Meanwhile, it is well documented that power ultrasonic devices, whilst driven at high power, are inherently nonlinear and, if no attempt is made to understand and subsequently control these behaviours, it is likely that these devices will suffer from poor performance or even failure. The behaviour of the commercial ultrasonic transducer used in bone surgery (Piezosurgery® Device) is dynamically characterised through finite element and experimental methods whilst operating in conjunction with a variety of tuned inserts. Finite element analysis was used to predict modal parameters as well as stress levels within the tuned devices whilst operating at elevated amplitudes of vibration, while experimental modal analysis validated predicted resonant frequencies and mode shapes between 0-80kHz. To investigate the behaviour of tuned devices at elevated vibrational amplitudes near resonance, responses were measured whilst the device was excited via the burst sine sweep method. In an attempt to provide an understanding of the effects that geometry, material selection and wavelength of tuned assemblies have on the behaviour of an ultrasonic device, tuned inserts consisting of a simple rod horn design were characterised alongside more complex cutting inserts which are used in maxillofacial and craniofacial surgery. From these results the aim will be to develop guidelines for design of tuned inserts. Meanwhile, Langevin transducers, commonly known as sandwich or stack transducers, in their most basic form generally consist of four parts; a front mass, a back mass, a piezoceramic stack and a stud or bolt holding the parts together under a compressive pre-load. It is traditionally proposed that the piezoceramic stack is positioned at or close to the vibrational nodal point of the longitudinal mode, however, this also corresponds with the position of highest dynamic stress. It is also well documented that piezoceramic materials possess a low linear stress threshold, therefore this research, in part, investigates whether locating the piezoceramic stack away from a position of intrinsic high stress will affect the behaviour of the device. Through experimental characterisation it has been observed that the tuned devices under investigation exhibited; resonant frequency shifts, jump amplitudes, hysteretic behaviour as well as autoparametric vibration. The source of these behaviours have been found to stem from device geometry, but also from heating within the piezoceramic elements as well as joints with different joining torques.