Optical Coherence Tomography (OCT) is an imaging technique that uses near infra-red light to non-invasively form cross-sectional images of specimens, in a similar way to ultrasound and RADAR. A number of research groups have used OCT to study natural and artificial carious lesions and to some extent erosive lesions. For this, a variety of in vitro models have been used. However, the exact mechanism by which these demineralised enamel lesions affect the OCT measurements is not fully understood. This remains a barrier to its adoption as both an analytical laboratory tool and a widespread technique in clinical dentistry. Therefore, the aim of this thesis was to develop an understanding of how different demineralised enamel lesions manifest in OCT measurements. This is necessary for the technique to become useful as an in vivo clinical measurement and imaging system. Consequently, this study was carried out in a controlled laboratory environment for which a novel specimen holder was designed. This mitigated against specimen movement and maintained specimen hydration, which can be a source of uncertainty in the measurements. A custom-built OCT microscope was used for this work, which enabled automation of experiments and continuous time-lapse OCT imaging over time periods of hours to several days. This enabled bovine enamel demineralisation dynamics to be captured during in vitro caries and erosion formation. The stability of the system also enabled direct comparison between the OCT measurements of the optical properties of different demineralisation models. To achieve these measurements, the OCT system was carefully characterised and compared to established profilometry measurements. Interestingly, this revealed that the experimental protocol used to obtain lesions for profilometry was not to be representative of the lesions formed and measured by OCT. This is an important point when interpreting OCT data in light of other techniques. A novel method of analysis was developed that uses longitudinal OCT image correlation to quantify early stage surface softening during erosion. By using OCT volumetric data, this technique was able to measure sub-resolution changes at the specimen surface. Early results also indicate sensitivity to remineralisation. This thesis shows that OCT is sensitive to different demineralisation models produced and measured under controlled conditions. New method of handling the data can observe changes not previously seen in OCT. However, further work is still required to understand the underlying physical changes that lead to this sensitivity in OCT.

The utilisation of 3D digitisation and visualisation has grown considerably since 2008 and is becoming an increasingly useful tool for the digital documentation and metric analysis of archaeological artefacts and skeletal remains. It provides public access to rare and fragile specimens of palaeontological and palaeopathological importance whilst reducing the physical impact on these remains. Research in engineering and computer vision provides some insight into the impact of surface properties such as colour, specularity, reflectance and shape on the quality of the recorded 3D image, but within the archaeological and palaeontological disciplines comparable work has not yet been developed. If archaeology and anthropology are to provide long term reliable data from archaeological and palaeontological specimens in a way that doesn’t require repeated re-digitisation, we need to understand the impacts that the taphonomic histories of such samples have on our ability to 3D record them. Understanding the relationship of these taphonomic histories and the surface and optical properties will promote informed choices about the suitability of recording techniques. This thesis considers the taphonomic processes that affect the preservation of bone over archaeological, forensic and palaeontological timescales and the effect this has on the quality of 3D digital models. The digital refit of fragmentary bone samples is considered in relation to the effect of taphonomic alterations to bone. Conclusions regarding the key taphonomic factors and 3D digital model quality are drawn and areas of further work are identified.

The utilisation of 3D digitisation and visualisation has grown considerably since 2008 and is becoming an increasingly useful tool for the digital documentation and metric analysis of archaeological artefacts and skeletal remains. It provides public access to rare and fragile specimens of palaeontological and palaeopathological importance whilst reducing the physical impact on these remains. Research in engineering and computer vision provides some insight into the impact of surface properties such as colour, specularity, reflectance and shape on the quality of the recorded 3D image, but within the archaeological and palaeontological disciplines comparable work has not yet been developed. If archaeology and anthropology are to provide long term reliable data from archaeological and palaeontological specimens in a way that doesn’t require repeated re-digitisation, we need to understand the impacts that the taphonomic histories of such samples have on our ability to 3D record them. Understanding the relationship of these taphonomic histories and the surface and optical properties will promote informed choices about the suitability of recording techniques. This thesis considers the taphonomic processes that affect the preservation of bone over archaeological, forensic and palaeontological timescales and the effect this has on the quality of 3D digital models. The digital refit of fragmentary bone samples is considered in relation to the effect of taphonomic alterations to bone. Conclusions regarding the key taphonomic factors and 3D digital model quality are drawn and areas of further work are identified. / Arts and Humanities Research Council

Bone formation and bone healing were studied in the mandible, tibia and skull bones in adult, healthy and estrogen deficient rabbits implanted with different bone substitutes. In the first study an evaluation of the differences in bone regeneration in and around solid (Alveograf *) and porous hydroxyapatite (Interpore 200*) was undertaken. The implant material was placed into experimentally made bone defects and in half of the defects hydroxyapatite was mixed with a fibrin sealant (Tisseel *). The material alone or mixed with Tisseel was also placed subperiostally in the mandible. The observation time was six month. No difference in bone regeneration was found between solid or porous hydroxyapatite granulas and the addition of Tisseel* did not seem to disturb the bone healing process. The implant material placed subperiostally did not induce bone formation nor did it provoke any bone resorption. The addition of Tisseel made the implant material much easier to handle and retain in the tissue during surgery. Bone healing around hydroxyapatite implants was also evaluated in the second study. Experimental cavities in the mandible and tibia were filled with hydroxyapatite in granules or blocks (Interpore 200*) but now with or without autolyzed, antigen-extracted, allogeneic bone (AAA). Also in this study Tisseel* was used to facilitate the handling of the material. All cavities implanted with AAA-bone, regardless of the combination with hydroxyapatite or Tisseel, demonstrated excessive bone formation resembling exostosis formation. Thus, hydroxyapatite, both as granules and blocks, can be successfully combined with AAA bone utilizing the bone inductive capacity of AAA bone. The same model was used to study the healing in ovariectomized animals in the third study. Bone cavities were implanted with or without AAA bone and left to heal. The results indicate that the osteoinductive capacity of AAA bone is in operation also in animals deprived of a normal estrogen production. The effect of using AAA bone prior to implant insertion was studied in paper four. The bone-implant contact was significant higher when AAA bone had been used. The implant stability did not seem to be affected. In paper five defects were made in skull and tibial bone in estrogen deficient animals. The deficiency of estrogen was confirmed through blood analysis, the decrease in the weight of uterus and bone mineral density. The whole body scanning with DEXA showed that the ovariectomized animals developed osteopenia. Various degree of bone formation was seen in the defects due to the influence of the bone inductive substance AAA bone. The studies indicate that a conductive material like hydroxyapatite in granules or blocks could be useful in oral reconstructive surgery. The combination with AAA bone enhanced the bone formation in calvarial and tibial bone in healthy and estrogen deficient animals. Tisseel* could be used to facilitate handling and retention of the material in the intended position during the healing process without negative effects.

Trabecular bone is a porous composite material which consists of a mineral phase (mainly hydroxyapatite), organic phase (mostly type I collagen) and water assembled into a complex, hierarchical structure. In biomechanical modelling, its mechanical response to loads is generally assumed to be instantaneous, i.e. it is treated as a time-independent material. It is, however, recognised that the response of trabecular bone to loads is time-dependent. Study of this time-dependent behaviour is important in several contexts such as: to understand energy dissipation ability of bone; to understand the age-related non-traumatic fractures; to predict implant loosening due to cyclic loading; to understand progressive vertebral deformity; and for pre-clinical evaluation of total joint replacement. To investigate time-dependent behaviour, bovine trabecular bone samples were subjected to compressive loading, creep, unloading and recovery at multiple load levels (corresponding to apparent strain of 2,000-25,000 με). The results show that: the time-dependent behaviour of trabecular bone comprises of both recoverable and irrecoverable strains; the strain response is nonlinearly related to applied load levels; and the response is associated with bone volume fraction. It was found that bone with low porosity demonstrates elastic stiffening followed by elastic softening, while elastic softening is demonstrated by porous bone at relatively low loads. Linear, nonlinear viscoelastic and nonlinear viscoelastic-viscoplastic constitutive models were developed to predict trabecular bone's time-dependent behaviour. Nonlinear viscoelastic constitutive model was found to predict the recovery behaviour well, while nonlinear viscoelastic-viscoplastic model predicts the full creep-recovery behaviour reasonably well. Depending on the requirements all these models can be used to incorporate time-dependent behaviour in finite element models. To evaluate the contribution of the key constituents of trabecular bone and its microstructure, tests were conducted on demineralised and deproteinised samples. Reversed cyclic loading experiments (tension to compression) were conducted on demineralised trabecular bone samples. It was found that demineralised bone exhibits asymmetric mechanical response - elastic stiffening in tension and softening in compression. This tension to compression transition was found to be smooth. Tensile multiple-load-creep-unload-recovery experiments on demineralised trabecular samples show irrecoverable strain (or residual strain) even at the low stress levels. Demineralised trabecular bone samples demonstrate elastic stiffening with increasing load levels in tension, and their time-dependent behaviour is nonlinear with respect to applied loads . Nonlinear viscoelastic constitutive model was developed which can predict its recovery behaviour well. Experiments on deproteinised samples showed that their modulus and strength are reasonably well related to bone volume fraction. The study considers an application of time-dependent behaviour of trabecular bone. Time-dependent properties are assigned to trabecular bone in a bone-screw system, in which the screw is subjected to cyclic loading. It is found that separation between bone and the screw at the interface can increase with increasing number of cycles which can accentuate loosening. The relative larger deformation occurs when this system to be loaded at the higher loading frequency. The deformation at the bone-screw interface is related to trabecular bone's bone volume fraction; screws in a more porous bone are at a higher risk of loosening.

<p>Bone formation and bone healing were studied in the mandible, tibia and skull bones in adult, healthy and estrogen deficient rabbits implanted with different bone substitutes. </p><p>In the first study an evaluation of the differences in bone regeneration in and around solid (Alveograf *) and porous hydroxyapatite (Interpore 200*) was undertaken. The implant material was placed into experimentally made bone defects and in half of the defects hydroxyapatite was mixed with a fibrin sealant (Tisseel *). The material alone or mixed with Tisseel was also placed subperiostally in the mandible. The observation time was six month. No difference in bone regeneration was found between solid or porous hydroxyapatite granulas and the addition of Tisseel* did not seem to disturb the bone healing process. The implant material placed subperiostally did not induce bone formation nor did it provoke any bone resorption. The addition of Tisseel made the implant material much easier to handle and retain in the tissue during surgery.</p><p>Bone healing around hydroxyapatite implants was also evaluated in the second study. Experimental cavities in the mandible and tibia were filled with hydroxyapatite in granules or blocks (Interpore 200*) but now with or without autolyzed, antigen-extracted, allogeneic bone (AAA). Also in this study Tisseel* was used to facilitate the handling of the material. All cavities implanted with AAA-bone, regardless of the combination with hydroxyapatite or Tisseel, demonstrated excessive bone formation resembling exostosis formation. Thus, hydroxyapatite, both as granules and blocks, can be successfully combined with AAA bone utilizing the bone inductive capacity of AAA bone.</p><p>The same model was used to study the healing in ovariectomized animals in the third study. Bone cavities were implanted with or without AAA bone and left to heal. The results indicate that the osteoinductive capacity of AAA bone is in operation also in animals deprived of a normal estrogen production.</p><p>The effect of using AAA bone prior to implant insertion was studied in paper four. The bone-implant contact was significant higher when AAA bone had been used. The implant stability did not seem to be affected.</p><p>In paper five defects were made in skull and tibial bone in estrogen deficient animals. The deficiency of estrogen was confirmed through blood analysis, the decrease in the weight of uterus and bone mineral density. The whole body scanning with DEXA showed that the ovariectomized animals developed osteopenia. Various degree of bone formation was seen in the defects due to the influence of the bone inductive substance AAA bone. </p><p>The studies indicate that a conductive material like hydroxyapatite in granules or blocks could be useful in oral reconstructive surgery. The combination with AAA bone enhanced the bone formation in calvarial and tibial bone in healthy and estrogen deficient animals. Tisseel* could be used to facilitate handling and retention of the material in the intended position during the healing process without negative effects. </p>