Investigating three methods of assessing the clinically relevant trueness of two intraoral scanners

Aims Intraoral scanners (IOS) are used for a wide range of treatments. Most IOSs produce data appropriate for local work, such as crowns, but evidence suggests that full-arch scans result in more erroneous scans, which may affect the fit of clinical appliances. There are no standardized methods for assessing the quality of IOSs. Though many studies have investigated the accuracy of scanners, one may find the reported values are difficult to interpret in a clinical context. Materials and methods This study investigated the trueness of two IOSs, using three metrics. The clinical value of each metric is discussed. A dentate model was scanned 10 times using two intraoral scanners. Three methods were used to assess the trueness of the scans against a scan produced in a laboratory scanner. Results The mean unsigned distance deviation between a laboratory scan and the Primescan scans was 0.016(±0.006)mm. The mean unsigned distance deviation between the laboratory scan and the Omnicam scans was 0.116(±0.01)mm. The arch width between molars was 55.44mm for the Solutionix scan. The arch width of the Primescan was 55.439(±0.075)mm, while the Omnicam reported 54.672(±0.065)mm. The mean proportion of the Primescan scans deviating beyond 0.1mm when compared against the Solutionix was 0.7(±2.0)%. The equivalent for the Omnicam was 42.1(±2.5)%. Conclusions All methods indicated significantly different results between the scanners. The Primescan produced truer scans than the Omnicam, regardless of measurement method. The intermolar-width and proportion beyond 0.1mm methods may give more clinically relevant insight into the trueness of scan data than current gold-standard methods

Assessment of All-Ceramic Dental Restorations Behavior by Development of Simulation-Based Experimental Methods

New dental materials are often introduced into the market and especially in the current practice, without a basic understanding of their clinical performance because long‐term controlled clinical trials are required, which are both time consuming and expensive. Ceramic materials are known for their relatively high fracture resistance and improved aesthetics, but brittleness remains a concern. The stressed areas of the materials are key factors for the failure analysis, and numerical simulations may play an important role in the understanding of the behavior of all‐ceramic restorations. Simulation‐based medicine and the development of complex computer models of biological structures are becoming ubiquitous for advancing biomedical engineering and clinical research. The studies have to be focused on the analysis of all‐ceramic restorations failures, investigating several parameters involved in the tooth structure–restoration complex, in order to improve clinical performances. The experiments have to be conducted and interpreted reported to the brittle behavior of ceramic systems. Varied simulation methods are promising to assess the biomechanical behavior of all‐ceramic systems, and first principal stress criterion is an alternative for ceramic materials investigations. The development of well‐designed experiments could be useful to help to predict the clinical behavior of these new all‐ceramic restorative techniques and materials

Adaptive Methods for Point Cloud and Mesh Processing

Point clouds and 3D meshes are widely used in numerous applications ranging from games to virtual reality to autonomous vehicles. This dissertation proposes several approaches for noise removal and calibration of noisy point cloud data and 3D mesh sharpening methods. Order statistic filters have been proven to be very successful in image processing and other domains as well. Different variations of order statistics filters originally proposed for image processing are extended to point cloud filtering in this dissertation. A brand-new adaptive vector median is proposed in this dissertation for removing noise and outliers from noisy point cloud data. The major contributions of this research lie in four aspects: 1) Four order statistic algorithms are extended, and one adaptive filtering method is proposed for the noisy point cloud with improved results such as preserving significant features. These methods are applied to standard models as well as synthetic models, and real scenes, 2) A hardware acceleration of the proposed method using Microsoft parallel pattern library for filtering point clouds is implemented using multicore processors, 3) A new method for aerial LIDAR data filtering is proposed. The objective is to develop a method to enable automatic extraction of ground points from aerial LIDAR data with minimal human intervention, and 4) A novel method for mesh color sharpening using the discrete Laplace-Beltrami operator is proposed. Median and order statistics-based filters are widely used in signal processing and image processing because they can easily remove outlier noise and preserve important features. This dissertation demonstrates a wide range of results with median filter, vector median filter, fuzzy vector median filter, adaptive mean, adaptive median, and adaptive vector median filter on point cloud data. The experiments show that large-scale noise is removed while preserving important features of the point cloud with reasonable computation time. Quantitative criteria (e.g., complexity, Hausdorff distance, and the root mean squared error (RMSE)), as well as qualitative criteria (e.g., the perceived visual quality of the processed point cloud), are employed to assess the performance of the filters in various cases corrupted by different noisy models. The adaptive vector median is further optimized for denoising or ground filtering aerial LIDAR data point cloud. The adaptive vector median is also accelerated on multi-core CPUs using Microsoft Parallel Patterns Library. In addition, this dissertation presents a new method for mesh color sharpening using the discrete Laplace-Beltrami operator, which is an approximation of second order derivatives on irregular 3D meshes. The one-ring neighborhood is utilized to compute the Laplace-Beltrami operator. The color for each vertex is updated by adding the Laplace-Beltrami operator of the vertex color weighted by a factor to its original value. Different discretizations of the Laplace-Beltrami operator have been proposed for geometrical processing of 3D meshes. This work utilizes several discretizations of the Laplace-Beltrami operator for sharpening 3D mesh colors and compares their performance. Experimental results demonstrated the effectiveness of the proposed algorithms

Developing atom probe tomography for unique nanoscale insights into biomaterials

Bone provides structure and support for vertebrates, and it is the largest ion exchanger in the body to maintain homeostasis. Bone is a complex and heterogeneous composite material mainly composed of inorganic phases (mineral), organic phases (collagen, non-collagenous proteins), and water. Understanding the spatial structure and chemical composition of bone across different length scales is of great significance for elucidating its biomineralization mechanism, mechanical support, bone pathological treatment, and bone scaffold development. However, the simultaneous characterization of structure and chemical information of bone at the nanoscale presents many limitations, especially the exploration of 3D spatial structure and the mapping of low atomic mass elements. Among the many synthetic bone substitutes, bioactive glasses (BG) are an attractive candidate with applications in critical bone damage repair, as they stimulate biological responses that favor bone formation and angiogenesis. However, previously it has been difficult to develop an amorphous BG that combines a 3D porous structure with a strong biological activity because conventional BG easily crystallizes during processing. The crystallization of bioactive glass limits the dissolution rate of the material and therefore slows down the surface reactivity, leading to a decrease in scaffold bioactivity and bone regeneration capabilities. In recent years, a new amorphous 3D strontium-containing BG (pSrBG) scaffold was developed by adding strontium to increase the bioactivity of BG. Prior characterization of this material showed a scaffold with a near-perfect bone contact without fibrous tissue coverage, and that it supports nearly exclusively lamellar bone repair, similar to normal and functional bone. Besides, strontium was detected in new form bone and plasma after 21 days of transplantation in vivo, indicating that strontium successfully diffused as the material dissolved. However, due to the detection limits of conventional characterization techniques, it was not possible to specify the precise locality of released ions, and hence, it is not clear whether the locally achievable strontium concentration at the interface exceeds the medically acceptable range. Furthermore, the mechanism of Sr uptake into the bone and bone repair remains inconclusive. Atom probe tomography (APT) is a 3D microscopy characterization technique with a unique combination of high spatial and chemical resolution, which can be used to characterize this new type of biomaterial, animal bone, and the interface between material and bone. The work in this thesis presents the enabling preliminary development of APT techniques prior to this interface analysis. The synthetic bone material and porcine trabecular bone were investigated and characterised using APT. The challenges and corresponding countermeasures of biomaterials for APT sample preparation and experiments are outlined. The influence of various experimental parameters such as temperature, detection rate, laser pulse energy, and pulse frequency on the data quality by the LEAP-5000XR is explored and discussed. To this end, optimal operating conditions of APT were investigated and selected for two strontium-containing bioactive glass particles, the pSrBG scaffold, and porcine trabecular bone. The structure, including the spatial distribution of collagen and mineral phases, and their chemical composition were analyzed at the atomic level within the porcine trabecular bone. The challenges and limitations of APT in reconstruction analysis and quantitative chemical composition measurements of biomaterials are addressed. This study demonstrates that APT has the unique capacity to identify and characterize significant compositional variations in nanoscale volumes within individual bone phases that may provide new insights into the further development and demonstration of the potential of APT in exploring the spatial structure and chemical composition of bones. It also provides the basis for advancing knowledge in APT research at the interface of pSrBG and bone

Application of advanced surface patterning techniques to study cellular behavior

Surface manipulation for the fabrication of chemical or topographic micro- and nanopatterns, has been central to the evolution of in vitro biology research. A high variety of surface patterning methods have been implemented in a wide spectrum of applications, including fundamental cell biology studies, development of diagnostic tools, biosensors and drug delivery systems, as well as implant design. Surface engineering has increased our understanding of cell functions such as cell adhesion and cell-cell interaction mechanics, cell proliferation, cell spreading and migration. From a plethora of existing surface engineering techniques, we use standard microcontact printing methods followed by click chemistry to study the role of intercellular contacts in collective cancer cell migration. Cell dispersion from a confined area is fundamental in a number of biological processes, including cancer metastasis. To date, a quantitative understanding of the interplay of single cell motility, cell proliferation, and intercellular contacts remains elusive. In particular, the role of E- and N-Cadherin junctions, central components of intercellular contacts, is still controversial. Combining theoretical modeling with in vitro observations, we investigate the collective spreading behavior of colonies of human cancer cells (T24). The spreading of these colonies is driven by stochastic single-cell migration with frequent transient cell-cell contacts. We find that inhibition of E- and N-Cadherin junctions decreases colony spreading and average spreading velocities, without affecting the strength of correlations in spreading velocities of neighboring cells. Based on a biophysical simulation model for cell migration, we show that the behavioral changes upon disruption of these junctions can be explained by reduced repulsive excluded volume interactions between cells. This suggests that in cancer cell migration, cadherin-based intercellular contacts sharpen cell boundaries leading to repulsive rather than cohesive interactions between cells, thereby promoting efficient cell spreading during collective migration. Despite the remarkable progress in surface engineering technology and its applications, a combination of pattern properties such as stability, precision, specificity, high-throughput outcome and spatiotemporal control is highly desirable but challenging to achieve. Here, we introduce a versatile and high-throughput covalent photo-immobilization technique, comprising a light-dose dependent patterning step and a subsequent functionalization of the pattern via click chemistry. This two-step process is feasible on arbitrary surfaces and allows for generation of sustainable patterns and gradients. The method is validated in different biological systems by patterning adhesive ligands on cell repellent surfaces, thereby constraining the growth and migration of cells to the designated areas. We then implement a sequential photopatterning approach by adding a second switchable pattering step, allowing for spatiotemporal control over two distinct surface patterns. As a proof of concept, we reconstruct the dynamics of the tip/stalk cell switch during angiogenesis. Our results show that the spatiotemporal control provided by our “sequential photopatterning” system is essential for mimicking dynamic biological processes, and that our innovative approach has a great potential for further applications in cell science. In summary, this work introduces two novel and versatile paradigms of surface patterning for studying different aspects of cell behaviour in different cell types. The reliability of both setups is experimentally confirmed, providing new insight into the role of cell-cell contacts during collective cancer cell migration as well as the tip/stalk switch behaviour during angiogenesis

Carbon Fiber Electrode Arrays for Cortical and Peripheral Neural Interfaces

Neural interfaces create a connection between neural structures in the body and external electronic devices. Brain-machine interfaces and bioelectric medicine therapies rely on the seamless integration of neural interfaces with the brain, nerves, or spinal cord. However, conventional neural interfaces cannot meet the demands of high channel count, signal fidelity, and signal longevity that these applications require. I investigated the damage resulting from conventional Utah arrays after multiple years of implantation in the cortex of a non-human primate as a possible explanation for these limitations. The neuron density around the electrode shanks was compared to the neuron density of nearby healthy tissue, finding a 73% loss in density around the electrodes. The explanted arrays were imaged and characterized for degradation. Coating cracks, tip breakage, and parylene cracks were the most common degradation type. A significantly higher number of tip breakage and coating crack occurrences were found on the edges of the arrays as compared to the middle. In this work, I made clear the need for a minimally damaging alternative to the Utah electrode array. Neural interfaces composed of carbon fiber electrodes, with a diameter of 6.8 microns, could enable a seamless integration with the body. Previous work resulted in an array of individuated carbon fiber electrodes that reliably recorded high signal-to-noise ratio neural signals from the brain for months. However, the carbon fiber arrays were limited by only 30% of the electrodes recording neural signals, despite inducing minimal inflammation. Additionally, it was relatively unknown if carbon fibers would make suitable long-term peripheral neural interfaces. Here, I illustrate the potential of carbon fiber electrodes to meet the needs of a variety of neural applications. First, I optimized state-of-the-art carbon fiber electrodes to reliably record single unit electrophysiology from the brain. By analyzing the previous manufacturing process, the cause of the low recording yield of the carbon fiber arrays was identified as the consistency of the electrode tip. A novel laser cutting technique was developed to produce a consistent carbon fiber tip geometry, resulting in a near tripling of recording yield of high amplitude chronic neural signals. The longevity of the carbon fiber arrays was also addressed. The conventional polymer coating was compared against platinum iridium coating and an oxygen plasma treatment, both of which outperformed the polymer coating. In this work, I customized carbon fiber electrodes for reliable, long-term neural recording. Secondly, I translated the carbon fiber technology from the brain to the periphery in an architecture appropriate for chronic implantation. The insertion of carbon fibers into the stiffer structures in the periphery is enabled by sharpening the carbon fibers. The sharpening process combines a butane flame to sharpen the fibers with a water bath to protect the base of the array. Sharpened carbon fiber arrays recorded electrophysiology from the rat vagus nerve and feline dorsal root ganglia, both structures being important targets for bioelectric medicine therapies. The durability of carbon fibers was also displayed when partially embedded carbon fibers in medical-grade silicone withstood thousands of repeated bends without fracture. This work showed that carbon fibers have the electrical and structural properties necessary for chronic application. Overall, this work highlights the vast potential of carbon fiber electrodes. Through this thesis, future brain-machine interfaces and bioelectric medicine therapies may utilize arrays of sub-cellular electrodes such as carbon fibers in medical applications.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169982/1/elissajw_1.pd

Assessment of Phantom Dosimetry and Image Quality of Accuitomo 170 and MiniCAT Cone-Beam Computed Tomography

Introduction: Escalating use of cone-beam computed tomography contributes to a burgeoning public health issue regarding the amount of ionizing radiation associated with diagnostic imaging delivered to the population, especially children. Methods: Effective doses were calculated and compared from optically stimulated dosimeter measurements and a previously validated protocol using anthropomorphic adult and child phantoms scanned with the Accuitomo 170 (J. Morita, Japan) and MiniCAT (Xoran Technologies, Ann Arbor, MI) CBCT machines. Results: Average child phantom doses (440 and 117 µSv) were 60% and 56% greater than the adult doses from the Accuitomo 170 and MiniCAT units respectively. Thyroid dose, particularly to the child, had a significant contribution to the overall dose. Conclusion: Effective dose for the two units increased as FOV increased. The child dose, especially the thyroid, increased when compared to the adult phantom. Child protocols and the smallest FOV helps reduce the child's effective dose.Master of Scienc

Design, Fabrication and Validation of a CMOS-MEMS Kelvin Probe Force Microscope

The Kelvin Probe Force Microscope is a type of scanning probe instrument that is used to discern the different work functions of a sample. A sharp probe at the end of a cantilever is lowered onto a substrate where electrostatic forces, caused by the difference in work function cause the cantilever to oscillate at the modulated frequency. Using this instrument, high resolution images can be obtained, mapping the surface electronic characteristics. However, developments of this instrument have generally been limited to obtaining higher resolution images as well as reducing noise in the output, limiting the widespread appeal of this expensive instrument. There exist many applications where extremely cheap, low footprint and easy-to-use Kelvin Probe Force Microscopes would be beneficial. In order to cheaply produce this microscope in batch, a post-processed CMOS-MEMS device is utilized. The polysilicon resistors act as a strain gauge such that a conventional optical system will not have to be employed. The ability to use integrated bimorph actuators on chip allow for movement of the cantilever without the employment of large piezoelectric stages with creep effects. Embedded electronics can be fabricated with the CMOS process alongside the MEMS device, allowing full integration of an on board amplifier and read out system. In general, a large table top system can be minimized onto the size of a <1 mm2 area, a microcontroller and a computer. In this work, a Kelvin Probe Force Microscope is designed, fabricated and validated. A MEMS device was designed following similar characteristics of a generic cantilever beam. The stiffness, length, resonant frequency, and other tip characteristics can be mimicked with careful design. The resultant designs were fabricated using a CMOS-MEMS process. In order to obtain a sharper tip with modified characteristics, various methods were employed; such as gallium-aluminum alloy tip formation as well as electroless plating onto the tip of the device. Finally, the resultant device is tested against a sample. It was seen that the MEMS device followed similar characteristics of the conventional microscope itself, validating the equations that define the method. Bimorph actuators were tested to show movement, allowing the integration of the cantilever with the XYZ-stage. Work function changes are observed while scanning different materials. It is shown throughout the course of this thesis, that a true Kelvin Probe Force Microscope can be designed, fabricated and validated using CMOS-MEMS technology.1 yea

The fabrication of nanogap electrodes using nanoskiving

Het doel van dit onderzoek is om een beschrijving te geven van een simpele fabricagemethode om moleculaire tunnelingkoppelingen te bouwen. We hebben een methode ontwikkeld om electroden te fabriceren met daartussen een spleet in de range van nanometers, daarbij gebruik makend van “nanoskiving”, een vorm van lithografie. Deze krachtige, nieuwe techniek maakt het mogelijk om de beperkingen die er zijn in het veld van de moleculaire electronica te omzeilen. Nu kunnen we electroden fabriceren waarbij we controle hebben over de grootte van de nanospleet; bovendien kunnen we nu hele series electroden produceren. We hebben laten zien dat deze tunnelingapparaatjes gefabriceerd kunnen worden met een snelheid van één per seconde, terwijl er tegelijkertijd controle is over alle dimensies van de gefabriceerde electroden. Met behulp van deze bottom-up benadering zijn zogenaamde “SAM-templated addressable nanogap (STAN; SAM = zelf-assemblerende monolagen) electroden gefabriceerd. De spleetgrootte van sub-3 nanometer wordt bepaald door de moleculen die fungeren als matrijs voor de spleet. Omdat we alkaandithiolen gebruiken als matrijs voor de nanospleet kunnen we een resolutie halen op het Angströmniveau, de grootte van een C-C binding. Bovendien kunnen we door de hoge aspectratio van de STANs deze direct adresseren en verbinden met sondes voor hun elektrische karakterisatie. Wij geloven dat onze simpele, snelle en goedkope techniek een veelbelovende aanpak is die ons in staat stelt om apparaatjes op aanvraag te fabriceren om de tunnelingstroom te meten van willekeurige moleculen of SAMs. Verder kan de constructie van tunnelingkoppelingen uit willekeurige moleculen bereikt worden door de uitwisseling van dithiolen in de nanospleet met dithiolen in oplossing. Het inbouwen van willekeurige, symmetrische dithiolen in de STANs door middel van uitwisseling voorziet in een hoge doorvoer en generaliseerbare methode welke leidt tot een platform voor de meting van moleculen met een verscheidenheid aan electrodematerialen

Hybrid materials for meniscus replacement in the knee

The meniscus is cartilage that not only prevents the bones in knee joints to grind together but acts as a joint stabiliser. Many athletes and older people suffer from meniscus tears and degeneration. Meniscal tear treatments have been through meniscal suture or by partial meniscectomy (removal). These treatments may cause changes in loading or decreased contact area and increased contact stress. Consequently, the ultimate result is a total meniscectomy that potentially leads to osteoarthritis (OA). These current surgical strategies have lower success rates in younger patients. There are no successful artificial meniscus replacement devices for young patients, therefore, new materials for meniscus replacement are required. Here, the aim was to develop a novel biomimetic meniscus device made of a silica/polytetrahydrofuran (SiO2/polyTHF) inorganic/organic hybrid material. The device is biomimetic in terms of its structural design, mechanical properties, and integration with the host tissue. The device should delay onset of OA. The hybrid has unique properties in that is a bouncy material which has comparable mechanical properties to knee cartilage. Two pot hybrid synthesis was used to synthesise the SiO2/polyTHF hybrid and casting mould was developed based on the shrinkage factor of the hybrid. The hybrid synthesis modifications were conducted by controlling compositions and drying processes. Biological fixation of the hybrid meniscus was achieved by titanium anchors with gyroid porous architecture which can provide initial mechanical fixation and secondary biological fixation on the tibia. The architecture was designed using Solidworks and Rhinoceros software and printed by the Additive Manufacturing technique of selective laser melting (SLM). Mechanical testing of the device included compression, cyclic loading, shear strength and long-term 90 days in-vitro mechanical testing, tribology against living bovine 2 cartilage, and cell studies. The results suggest that combination of hybrid and Ti gyroid has potential to be meniscus implant due to comparable mechanical properties, low friction coefficient, and non-cytotoxicity.Open Acces