A Dental Revolution? The intriguing effects of the profound social and dietary changes of the 18/19th centuries on the masticatory system

Developments in milling technology and an influx of new commodities from the 18th-19th centuries AD transformed the composition of the British diet, foreshadowing the soft hyper-nutritive diets of many 21st century populations. Jaw development is highly plastic and depends on the functional demands placed on the masticatory system, particularly during chewing. A reduction in jaw dimensions and an increase in poor occlusion among modern groups has, therefore, been attributed to the softer diet that emerged during the Industrial Revolution. Consequently, it has been hypothesised that underlying these changes are differences in masticatory behaviour when compared to pre-industrial groups. This thesis aims to test this hypothesis in order to assess whether a dental revolution, a radical transformation in masticatory behaviours, occurred in the Industrial Period. A method of 3D dental wear pattern analysis called Occlusal Fingerprint Analysis (OFA) was utilized to reconstruct masticatory behaviours from the wear facets of the molar teeth. Dental wear facets reflect the pathways of mandibular movement that occur during the chewing cycle. The facet patterns of the lower second molars of individuals from the Industrial period (n=104; 1700-1900AD) were compared to a pre-industrial sample dating to the Mediaeval and Early Post-Mediaeval periods (n=130; 1100-1700AD). Dynamic virtual simulations of the chewing stroke were also undertaken for a subset of individuals from each period (n=32). Significant differences in dental wear facet patterns between the two groups indicated that masticatory behaviours were altered in response to changing dietary composition; there was a shift to a more vertically directed chewing action as foods became softer and more heavily processed during the Industrial era. The research confirms the fundamental role food properties play in shaping mastication and, consequently, addresses the underlying mechanism responsible for the changes in occlusion and jaw morphology that have occurred over the past three centuries

Design of a mechatronic measurement system for surface fatigue of dental composites

PhD ThesisThis thesis focuses on the design and development of a rolling-ball mechatronic system for on-line testing and measurement of surface contact fatigue of dental composites, and is based on a technique initially developed at the Newcastle Dental School. The mechatronic system synergistically combines the mechanical/electronic hardware with a low-cost embedded digital signal controller (DSC microcontroller) hardware and software to monitor and measure in real-time surface wear due to contact fatigue. ISO/TS 14569-2.2001 standard specification for testing of dental materials was used for selecting appropriate test variables. The mechatronic system attempts to simulate the human oral environment with temperature and moisture being controlled. A closed-loop PI control algorithm combining both optical encoder pulse timing and counting methods is used to drive a dc brushless motor at speeds of 240 and 2040 rpm. A small (2mm diameter) ruby ball is mounted in a V-grooved mandrel which over time creates a circular orbital wear path in the dental composite material. One algorithm has been designed to acquire and process the on-line measurement of wear using a linear voltage differential transformer (LVDT), with another monitoring the fatigue cycling process. A graphical user interface (GUI) has also been designed and implemented on a laptop which is connected to the rig embedded controller. A kinematic model of the rolling ball constrained in a V-groove has been developed along with a finite element analysis of the surface deformation. This has been augmented by a comprehensive test programme, in dry, moisturized and elevated temperature (i.e. 37°C), using Synergy D6 specimens. Using ANOVA test, 70% reproducibility of fatigue track measurements was attained. A comparison of LVDT transducer and profilometer measurements indicated 5% consistence with each other. The insight gained from the testing programme sets a basis for an extensive programme to qualify and validate the measurement system basing on ISO/TS 14569-2.2001 specifications.The Tanzania Government: The University of Dar es Salaam

An experimental fibre-reinforced dental resin composite

PhD ThesisFibre-reinforced dental resin composites (FRCs) have shown increased fracture resistance and tensile strength compared with particulate filled composites (PFC). However, clinically successful restorative materials require adequate bond strength and wear resistance along with high strength. An experimental FRC (ST) was developed and tested as a dentine replacement. It has randomly distributed E-glass fibres above their critical length of 0.5-1.6 mm. This work aimed to evaluate the possibility of using ST as a single restorative material by assessing its three-body wear resistance and surface contact fatigue. The polymerisation shrinkage, water sorption, and bond strength of ST were also assessed. Two commercially available materials; an FRC (Build It FR) and PFC (Z250) were used as comparators. ST showed significantly lower wear resistance and higher contact fatigue. No significant difference was found regarding polymerisation shrinkage but ST had significantly higher water sorption, lower shear bond strength (SBS) to human dentine. SBS of the interfacial layers within and between the dental resin composites was evaluated after 24 hours and 1 year of water storage in the absence of an oxygen inhibition layer. Build It/Z250 showed a significantly higher SBS at both time intervals. The presence of an oxygen inhibited layer increased the interfacial strength in all groups except ST/Z250. ST formulations were varied in resin/diluent (Bis-GMA/TEGDMA) ratios, filler loading and fibre lengths for development. Wear testing found changing the Bis-GMA/TEGDMA ratio from 60/40 to 70/30 decreased the wear resistance regardless of filler loading and fibre length. In summary, wear resistance of ST and its variants was insufficient to recommend its use as a single restorative material without a surface veneer of PFC. As a dentine replacement, ST was only comparable with Z250 and Build It in polymerisation shrinkage and SBS between composites in the absence of an oxygen inhibition layer

Oral processing of micro-aerated chocolates: a computational mechanics, rheological and tribological study

The emerging need to reduce the calorific value of foods, while simultaneously improving the consumer perception drives the quest for food structures that satisfy both criteria. Aiming to shed light on the influence that micro-aeration has on the breakdown of chocolate during the early stages of the oral processing, this study focuses on the investigation of the effect that micro-aeration has from a computational mechanics, rheological and tribological perspective. Firstly, several constitutive models are investigated and compared in both the explicit and implicit Finite Element (FE) frameworks and are calibrated using experimental results from mechanical testing conducted in a parallel PhD study. Afterwards, a non-local damage evolution law is presented providing mesh objectivity in both microscopic and macroscopic FE calculations. The constitutive model coupled with the non-local damage model, implemented in an ABAQUS VUMAT subroutine, is then applied in a micromechanical model for the prediction of the elastic, plastic, and fracture properties of micro-aerated chocolate using as input the properties of the non-aerated solid chocolate. Different boundary conditions are employed in both monodisperse and polydisperse dispersion of pores for the estimation of a representative volume element that is used for the estimation of the macroscopic properties. Overall, micro-aeration reduces the elastic, plastic and fracture properties of the chocolate, whereas the polydisperse dispersions provide a better estimation for the equivalent fracture strain at failure. The estimated values are applied in macroscopic FE simulations of the first bite, where the force-displacement FE results match the experimental data obtained by a replicate of the first bite model with 3D printed molar teeth. The forces needed for the fragmentation of chocolate reduce with micro-aeration level as shown from the experiments and validated by the FE simulations, whereas the in-vivo and in-vitro fragmentation studies show that micro-aerated chocolate breaks into more and smaller pieces. Furthermore, the effect of the micro-aeration on the rheological properties of the molten chocolate with and without the influence of artificial saliva is investigated. Micro-aeration increases viscosity values while the storage and loss moduli decrease. From a tribological perspective, a new bench test rig to measure friction in the simulated tongue-palate contact is developed. The test was applied to molten chocolate samples with and without artificial saliva. Friction was measured over the first few rubbing cycles, simulating mechanical degradation of chocolate in the tongue-palate region. The coefficient of friction increases with cocoa solids percentage and decreases with increasing micro-aeration level. The presence of artificial saliva in the contact reduced the friction for all chocolate samples, however, the relative ranking remained the same. Finally, the link between structure, material properties and sensory perception is given through a comparison with data from sensory tests. The current study can be used as a cost efficient tool for the investigation of new food structures that reduce the calorific value while enhancing the taste perception.Open Acces

Learning about tooth removal with robot technology

Deze PhD-thesis richt zich op een fundamenteel onderzoek van de extractieleer en maakt daarbij gebruik van robottechnologie. Het onderzoek omvat zes inhoudelijke hoofdstukken, waarin verschillende aspecten van dit onderwerp worden behandeld. Het tweede hoofdstuk analyseert de literatuur over robottechnologie in de tandheelkunde en wijst op de matige kwaliteit van beschikbare literatuur, zeker als het op klinische toepassingen aankomt. Hoofdstuk 3 biedt een overzicht van robotsystemen in alle deelgebieden van de tandheelkunde sinds 1985. Hoofdstuk 4 introduceert een meetopstelling om krachten en bewegingen bij tandextracties nauwkeurig vast te leggen, terwijl hoofdstuk 5 de resultaten van een serie experimenten voor wat betreft krachten en momenten weergeeft. Hoofdstuk 6 beschrijft het bewegingsbereik en de snelheden tijdens tandheelkundige extracties, zoals gemeten met een robotarm. Hoofdstuk 7 beschrijft de ontwikkeling en eigenschappen van een classificatiemodel voor extracties op basis van kracht- en bewegingsgegevens. De conclusie benadrukt de toenemende interesse in robotinitiatieven in de tandheelkunde, de behoefte aan wetenschappelijke validatie van de toegevoegde waarde daarvan en het potentieel van robottechnologie om ons fundamentele begrip van de extractieleer te vergroten. De studies benadrukken het belang van gegevensverzameling, analyse en samenwerking tussen verschillende disciplines om ons fundamentele begrip van extracties te verbeteren, met een focus op tandheelkundig onderwijs en uiteindelijk de patiëntenzorg

Determination of the Transverse Horizontal Axis and Interocclusal Registration Using a Novel Optical Technique

Motivation: Dental treatments sometimes require the recording and reproduction of the patient’s transverse horizontal axis (THA). This is the axis about which the mandible will rotate, when the condyles are fully seated in their glenoid fossae. However, methods for recording this axis are rarely used in general practice, due to expense and perceived lack of efficacy. Problem Statement: A simplified method for accurately recording the THA, and interocclusal records (IORs), is needed for general dentistry. Approach: An optical 3D scanning method is proposed to kinematically record the THA. A simulation determines the required hardware specifications to build the scanner at minimal cost. The ability to record the hinge axis of a dental articulator is explored. High quality interocclusal optical records are essential, and these are investigated in subsequent experiments. Areas for improvements are identified and efforts are made to enhance the system speed and calibration. Results: Simulation results indicated that all 6 upper and lower anterior teeth, including 2mm of gingivae should be captured, with an accuracy of 50µm. The THA on a dental articulator could be located with a radial accuracy of 2.65±1.01mm. The repeatability (precision) of IORs showed a standard deviation of 22µm anteriorly, and a mean of 43µm posteriorly in vitro. The accuracy (trueness and precision) of the IORs was -15±22µm anteriorly, and up to -93±121µm posteriorly in vitro. A faster scanning protocol enabled in vivo testing. 29 IORs of a single subject took <2s to perform. The registrations showed a repeatability of 31µm anteriorly and 70µm posteriorly. A novel calibration process produced significantly reduced stereo reprojection errors compared to traditional methods (0.22 vs 0.27 pixels), offering a potential future system enhancement. Conclusions: The proposed method shows potential to improve the speed, accuracy and simplicity with which the THA, and interocclusal registration, can be recorded. Further developments have been suggested prior to embarking on clinical trials

Cranial form evolution and functional adaptations to diet among papionins : a comparative study combining quantitative genetics, geometric morphometrics, and finite element analysis

This thesis aims to study the evolution of cranial form and its biomechanical adaptation to the function of feeding in papionins, a group of primates with well-established phylogeny, large variations in cranial form, and well known ecologies and diets. The thesis firstly tests the hypothesis of evolutionary divergence of papionin cranial forms by random genetic drift with a quantitative genetic model (previously tested for acceptable type I error rates); if rejected, different cranial forms should reflect adaptations to the particular biomechanical demands of different diets. To study those adaptations, hypotheses about the cranial biomechanical performance under biting loads are then formulated in terms of the diet of each papionin species and tested using 3D finite element models and geometric morphometrics. Large scale deformations and cranial form are assessed using landmarks distributed over the cranium, and local strain distributions are assessed visually. Lastly, the association between cranial form, biomechanical parameters and diet among papionin species is tested using partial least squares. Results show that papionin cranial forms did not diverge by random genetic drift alone and thus adaptation must have occurred. When testing for biomechanical adaptation to biting, there are differences in cranial deformations between durophagous and graminivorous species, each with particular adaptations in the cranium that are thus apparent in cranial strains and deformations. Another striking result is that male and female crania of a single species (eating the same foods) deform similarly, albeit having different forms. The cranium of the phylogenetic outgroup Macaca deforms differently from all other papionins, but generally cranial deformations do not follow the phylogenetic relationship among papionins. Finally, a statistically significant association is found between cranial form and cranial deformations, and between diet and cranial form. Bite force and deformations show a less clear association with diet