The biocompatibility and the in vivo degradation of poly(L-lactide), (PLLA)- based materials has prompted much interest in the development of these materials into scaffolds for tissue engineering applications. PLLA-based polymers have been available for use in craniomaxillofacial surgery since 1991. Usually, a plate or sheet of the polymer is placed in or over a defect in the bone. Ideally the bone will use the polymer as a support to repair the defect and as the polymer degrades, the bone will continually remodel, so that the loss of mass and mechanical strength of the polymer correlates with the increase in the mass and strength of the new bone. However, this is an ideal situation, and is not always observed in practice. The aim of this work is to develop PLLA-based materials that should encourage bone growth onto the material and allow control over the rate of degradation. PLLA-co-succinic anhydride networks were synthesised and the mineralisation and degradation of these materials were evaluated in vitro. The synthesis of these networks, involved the polymerisation of 4-arm star PLLA polymers, which were coupled through their end groups with succinic anhydride. The low molecular weight star PLLA polymers were synthesised using calcium hydride and pentaerythritol as initiator and co-initiator respectively. Calcium hydride was preferred to stannous octoate in this study as there is concern over the release of tin-containing when the polymer is implanted. As only very limited studies have been directed into the polymerisation and resulting polymers formed using calcium hydride, this was a major focus of the study. The identification of hydrogen in the reaction tubes was evidence that calcium alkoxide, formed from the reaction of pentaerythritol and calcium hydride, is the actual initiating species for the ring opening polymerisation. In situ FT-Raman spectroscopy was used as a tool to monitor the reaction process and was found to be a convenient and reliable method for obtaining information about the polymerisation kinetics. Analysis of the FTRaman kinetic curves, along with analysis of products by GPC, polarimetry and NMR spectroscopy showed that the polymerisation was 'quasi-living' depending on the ratio of pentaerythritol and calcium hydride in the system. Furthermore, both the degree of transesterification and racemisation of polymers synthesised in optimised reactions were low. The PLLA-co-succinic anhydride networks were synthesised by coupling of hydroxyl-terminated PLLA star polymers with succinic anhydride (one-pot reaction) and by coupling hydroxyl-terminated PLLA stars with succinic anhydride-terminated PLLA star polymers (two-pot reaction), using a carbodiimide, EDC to mediate the esterification. The one-pot reaction produced polymers with high gel fractions and high conversion of functional groups in the gel, whereas the gel fraction and conversion of functional groups was lower in the two-pot reaction. For the networks synthesised in the one-pot reaction, the molecular weight between crosslinks was controlled by the length of the PLLA polymer arms. The networks synthesised were characterised by FTIR-ATR spectroscopy, SEM, contact angle and by swelling. The extent of mineralisation of the PLLA-co-succinic anhydride networks in simulated body fluid (SBF) after 14 days was greater than the mineral deposition on the high molecular weight PLLA reference polymer. The degradation of the networks was carried out under accelerated conditions in 0.1 M NaOH at 37 degrees Celsius. All networks degraded much more slowly than the high molecular weight linear PLLA reference sample. The rate of degradation was found to be dependent on the crystallinity of the polymer chains, with the more crystalline networks degrading at a faster rate, while the location of the degradation, surface or bulk, was controlled by the crosslink density, showing that the degradation is 'tuneable'.

Introduction: As fractures of the supraorbital region are far less common than midfacial or orbital fractures, a study was initiated to investigate whether fist blows could lead to fractures similar to those often seen in the midface. Methods: A detailed skull model and an impactor resembling a fist were created and a fist blow to the supraorbital region was simulated. A transient finite element analysis was carried out to calculate von Mises stresses, peak force, and impact time. Results: Within the contact zone of skull and impactor critical stress values could be seen which lay at the lower yield border for potential fractures. A second much lower stress zone was depicted in the anterior-medial orbital roof. Conclusions: In this simulation a fist punch, which could generate distinct fractures in the midface and naso-ethmoid-orbital region, would only reach the limits of a small fracture in the supraorbital region. The reason is seen in the strong bony architecture. Much higher forces are needed to create severe trauma in the upper face which is supported by clinical findings. Finite element analysis is the method of choice to investigate the impact of trauma on the human skeleton.

Introduction: As fractures of the supraorbital region are far less common than midfacial or orbital fractures, a study was initiated to investigate whether fist blows could lead to fractures similar to those often seen in the midface. Methods: A detailed skull model and an impactor resembling a fist were created and a fist blow to the supraorbital region was simulated. A transient finite element analysis was carried out to calculate von Mises stresses, peak force, and impact time. Results: Within the contact zone of skull and impactor critical stress values could be seen which lay at the lower yield border for potential fractures. A second much lower stress zone was depicted in the anterior-medial orbital roof. Conclusions: In this simulation a fist punch, which could generate distinct fractures in the midface and naso-ethmoid-orbital region, would only reach the limits of a small fracture in the supraorbital region. The reason is seen in the strong bony architecture. Much higher forces are needed to create severe trauma in the upper face which is supported by clinical findings. Finite element analysis is the method of choice to investigate the impact of trauma on the human skeleton.:Background; Methods; Rersults; Discussion; Results; Consent

In the field of craniomaxillofacial (CMF) surgery, surgical planning is an important and necessary procedure due to the complex nature of the craniofacial skeleton. Computed tomography (CT) has brought about a revolution in virtual diagnosis, surgical planning and simulation, and evaluation of treatment outcomes. It provides high-quality 3D image and model of skull for Computer-aided surgical planning system (CSPS). During the planning process, one of the essential steps is to reestablish the dental occlusion. In the first project, a new approach is presented to automatically and efficiently reestablish dental occlusion. It includes two steps. The first step is to initially position the models based on dental curves and a point matching technique. The second step is to reposition the models to the final desired occlusion based on iterative surface-based minimum distance mapping with collision constraints. With linearization of rotation matrix, the alignment is modeled by solving quadratic programming. The simulation was completed on 12 sets of digital dental models. Two sets of dental models were partially edentulous, and another two sets have first premolar extractions for orthodontic treatment. Two validation methods were applied to the articulated models. The results show that using the proposed method, the dental models can be successfully articulated with a small degree of deviations from the occlusion achieved with the gold-standard method. Low contrast resolution in CBCT image has become its major limitation in building skull model. Intensive hand-segmentation is required to reconstruct the skull model. Thin bone images are particularly affected by this limitation. In the second project, a novel segmentation approach is presented based on wavelet active shape model (WASM) for a particular interest in the outer surface of the anterior wall of maxilla. 19 CBCT datasets are used to conduct two experiments. This model-based segmentation approach is validated and compared with three different segmentation approaches. The results show that the performance of this model-based segmentation approach is better than those of the other approaches. It can achieve 0.25 +/- 0.2mm of surface error distance from the ground truth of the bone surface. Field of view (FOV) can be reduced in order to reduce unnecessary radiation dose in CBCT. This ROI imaging is common in most of the dentomaxillofacial imaging and orthodontic practices. However, a truncation effect is created due to the truncation of projection images and becomes one of the limitation in CBCT. In the third project, a method for small region of interest (ROI) imaging and reconstruction of the image of ROI in CBCT and two experiments for measurement of dosage are presented. The first experiment shows at least 60% and 70% of radiation dose can be reduced. It also demonstrates that the image quality was still acceptable with little variation of gray by using the traditional truncation correction approach for ROI imaging. The second experiment demonstrates that the images reconstructed by CBCT reconstruction algorithms without truncation correction can be degraded to unacceptable image quality.

Additive manufacturing (AM) has enabled the possibility for the hospitals to become their own implant producers developing implants that are tailored to patient’s anatomy. Despite the enormous potential of custom-made implants there are challenges that complicate the implementation of them into clinical practice. The aim of this research is to (1) identify the main driving forces and barriers for the delivery of custom-made implants; (2) explore staff stakeholder views and practices related to the implementation of AM in surgery for the development of custom-made implants; (3) formulate recommendations on how to cope with the implementation challenges. The research method was an explorative qualitative study consisted of a literature review on the challenges of custom-made implants in clinical applications coupled with the collection and inductive analysis of empirical data. The empirical study was based on ten semi-structured interviews conducted among both domestic and international hospital managers medical doctors and research engineers. The consolidated framework for implementation research (CFIR) was utilized for data collection. Using the five domains of CFIR, the following results were obtained: (1) Characteristics of individuals: Most research participants indicated a positive attitude towards the innovation expressing self-efficacy to its use; (2) Intervention characteristics: Custom-made implants were perceived to have a relative advantage in surgical practice due to their high degree of observability and geometrical adaptability providing increased surgical quality, perfect patient fit and better understanding of pathologies. However, high implementation costs, low degree of trialability and high degree of complexity in the development process were regarded as drawbacks of the innovation; (3) Outer setting: the regulatory uncertainty and lack of reimbursement limit the accessibility of custom-made implants to low income populations; (4) Inner setting: scarcity of resources, staff resistance to change, insufficient management support, communication difficulties, limited access to educational materials and training opportunities as well as lack of time and innovative capacity were regarded by the majority of participants as implementation barriers; (5) Process: central for the success of implementation is the need for a coherent implementation plan and evaluation process as well as the engagement of key stakeholders such as hospital managers, payers, regulatory and implementation advisors. This dissertation proffers a deeper understanding of the implementation issues related to custom-made implants and offers preliminary recommendations on how to cope with implementation impediments through the use of Rogers diffusion of innovation coupled with concepts from the field of organizational change and innovation management including Clayton’s disruptive innovation.