Intracoronal stress transfer through enamel following RBC photopolymerisation:A synchrotron X-ray study

Objectives: To measure the spatial distribution of crystallographic strain in tooth enamel induced by the photo-polymerisation of a dimethacrylate resin based composite cavity restoration. Methods: Six sound first premolar teeth, allocated into two groups (n = 3), were prepared with mesio-occlusal distal cavities. The enamel was machined at the point of maximum convexity on the outer tooth to create a vertical fin of thickness 100 μm and 0.5 mm depth to allow for synchrotron X-ray diffraction measurements. 2D diffraction patterns were used to determine crystallite orientation and quantify changes in the hydroxyapatite crystal lattice parameters, before and after photo-polymerisation of a composite material placed in the cavity, to calculate strain in the respective axis. The composite was photo-polymerised with either relatively high (1200 mW cm−2, group 1) or low (480 mW cm−2, group 2) irradiances using LED or quartz halogen light sources, respectively. A paired t-test was used to determine significant differences in strain between irradiance protocols at ɑ = 0.001. Results: Photo-polymerisation of the composite in the adjacent cavity induced significant changes in both the crystallographic c and a axes of the enamel measurement area. However the magnitude of strain was low with ∼0.1% difference before and after composite photo-polymerisation. Strain in enamel was not uniformly distributed and varied spatially as a function of crystallite orientation. Increased alignment of crystallites perpendicular to the cavity wall was associated with higher c axis strain. Additionally, strain was significantly greater in the c (p < 0.001) and a axis (p < 0.001) when using a high irradiance photo-polymerisation protocol. Significance: Although cuspal deflection is routinely measured to indirectly assess the ‘global’ effect of composite shrinkage on the tooth-restoration complex, here we show that absolute strains generated in enamel are low, indicating strain relief mechanisms may be operative. The use of low irradiance protocols for photo-polymerisation resulted in reduced strain

Disruption of enamel crystal formation quantified by synchrotron microdiffraction

AbstractObjectivesTo understand the pathology of the ultrastructure of enamel affected by systemic disorders which disrupt enamel tissue formation in order to give insight into the precise mechanisms of matrix-mediated biomineralization in dental enamel in health and disease.MethodsTwo-dimensional synchrotron X-ray diffraction has been utilized as a sophisticated and useful technique to spatially quantify preferred orientation in mineralized healthy deciduous dental enamel, and the disrupted crystallite organization in enamel affected by a systemic disease affecting bone and dental mineralization (mucopolysaccharidosis Type IVA and Type II are used as examples). The lattice spacing of the hydroxyapatite phase, the crystallite size and aspect ratio, and the quantified preferred orientation of crystallites across whole intact tooth sections, have been determined using synchrotron microdiffraction.ResultsSignificant differences in mineral crystallite orientation distribution of affected enamel have been observed compared to healthy mineralized tissue. The gradation of enamel crystal orientation seen in healthy tissue is absent in the affected enamel, indicating a continual disruption in the crystallite alignment during mineral formation.ConclusionsThis state of the art technique has the potential to provide a unique insight into the mechanisms leading to deranged enamel formation in a wide range of disease states.Clinical relevanceCharacterising crystal orientation patterns and geometry in health and following disruption can be a powerful tool in advancing our overall understanding of mechanisms leading to the tissue phenotypes seen clinically. Findings can be used to inform the appropriate dental management of these tissues and/or to investigate the influence of therapeutic interventions or external stressors which may impact on amelogenesis

Elastin-Like Protein, with Statherin Derived Peptide, Controls Fluorapatite Formation and Morphology

Life Science Initiative, QMUL. The work was additionally supported by the European Research Council Starting Grant (STROFUNSCAFF) and the Marie Curie Career Integration Grant (BIOMORPH). The authors would like to acknowledge Dr. Carol Crean and Dr. Rachida Bance-Soualhi (Department of Chemistry, University of Surrey) for their help with acquiring the Raman spectroscopy data, funded by EPSRC (grant number EP/M022749/1). KS gratefully acknowledges Dr. Sherif El-Sharkawy for intellectual input and Gastón Agustín Primo for help with FTIR deconvolution, alongside other group members of the Mata, MHAtriCell and DPSU groups

Temperature dependent crystallization of amorphous Y67Fe33 studied using kinetic small angle neutron scattering

Temperature-resolved small angle neutron scattering (SANS) has been used to study the nucleation, growth kinetics and crystallite morphology in the Y–Fe system. Crystallization from amorphous Y67Fe33 to the YFe2 Laves phase via a novel ‘YFe’ intermediate phase has been followed to completion as a function of temperature from 180 to 500 ◦C. The SANS results agree well with published kinetic neutron diffraction data. Below 390 ◦C, diffraction data suggest that SANS arises solely from the contrast between crystalline Y and the Fe-rich amorphous matrix. Between 390 and 410 ◦C all temperature variables are seen to form a sharp peak. This suggests that critical scattering occurs at Tc ≈ 400 ◦C. This critical scattering implies that full crystallization of Y67Fe33 occurs over a very narrow (∼20 ◦C) temperature range

Time-resolved neutron studies of metallic phase formation

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Intensity versus azimuthal angle taken from a typical (002) Bragg reflection of an enamel diffraction pattern.

<p>Pronounced peaks highlight a high degree of texture in this sample. Both peaks have been fitted to a Gaussian plus baseline (red and green lines respectively).</p

SEM images of enamel from the surface of a) artificially demineralized b) artificially remineralized c) naturally carious (surface) and d) healthy region.

<p>The inset to d) shows the bulk of the carious region ∼150 µm from the surface.</p