Structures of riboswitch RNA reaction states by mix-and-inject XFEL serial crystallography.

Riboswitches are structural RNA elements that are generally located in the 5' untranslated region of messenger RNA. During regulation of gene expression, ligand binding to the aptamer domain of a riboswitch triggers a signal to the downstream expression platform. A complete understanding of the structural basis of this mechanism requires the ability to study structural changes over time. Here we use femtosecond X-ray free electron laser (XFEL) pulses to obtain structural measurements from crystals so small that diffusion of a ligand can be timed to initiate a reaction before diffraction. We demonstrate this approach by determining four structures of the adenine riboswitch aptamer domain during the course of a reaction, involving two unbound apo structures, one ligand-bound intermediate, and the final ligand-bound conformation. These structures support a reaction mechanism model with at least four states and illustrate the structural basis of signal transmission. The three-way junction and the P1 switch helix of the two apo conformers are notably different from those in the ligand-bound conformation. Our time-resolved crystallographic measurements with a 10-second delay captured the structure of an intermediate with changes in the binding pocket that accommodate the ligand. With at least a 10-minute delay, the RNA molecules were fully converted to the ligand-bound state, in which the substantial conformational changes resulted in conversion of the space group. Such notable changes in crystallo highlight the important opportunities that micro- and nanocrystals may offer in these and similar time-resolved diffraction studies. Together, these results demonstrate the potential of 'mix-and-inject' time-resolved serial crystallography to study biochemically important interactions between biomacromolecules and ligands, including those that involve large conformational changes.

Near-Infrared Spectroscopy Reveals Brain Hypoxia and Cerebrovascular Dysregulation in Primary Biliary Cholangitis.

BACKGROUND AND AIMS: Primary biliary cholangitis (PBC) is an autoimmune cholestatic liver disease linked to symptoms including fatigue and altered mood/cognition, indicating that chronic liver inflammation associated with PBC can impact brain function. We employed near-infrared spectroscopy (NIRS), a noninvasive neuroimaging technique, to determine whether patients with PBC exhibit reduced cerebral oxygen saturation (StO2 ) and altered patterns of microvascular cerebral blood perfusion and whether these alterations were associated with clinical phenotype. This observational case-control study was conducted at a tertiary hospital clinic (University of Calgary Liver Unit). APPROACH AND RESULTS: Thirteen female patients with noncirrhotic PBC, seven female patients with cirrhotic PBC, and 11 healthy female controls were recruited by physician referral and word of mouth, respectively. NIRS was used to measure cerebral hemoglobin and oxygen saturation. A wavelet phase coherence method was used to estimate the coherent frequency coupling of temporal changes in cerebral hemodynamics. The PBC group demonstrated significantly reduced cerebral StO2 (P = 0.01, d = 0.84), indicating cerebral hypoxia, significantly increased cerebral deoxygenated hemoglobin concentration (P < 0.01, d = 0.86), and significantly reduced hemodynamic coherence in the low-frequency band (0.08-0.15 Hz) for oxygenated hemoglobin concentration (P = 0.02, d = 0.99) and total hemoglobin (tHb) concentration (P = 0.02, d = 0.50), indicating alterations in cerebrovascular activity. Complete biochemical response to ursodeoxycholic acid (UDCA) therapy in early patients with PBC was associated with increased cerebral tHb concentration and decreased hemodynamic coherence. CONCLUSIONS: Using NIRS, patients with PBC were found to have hypoxia, increased cerebral hemoglobin concentration, and altered cerebrovascular activity, which were reversed in part in UDCA responders. In addition, symptoms and quality-of-life measures did not correlate with brain hypoxia or cerebrovascular dysregulation in patients with PBC.

Resequencing and signatures of selection scan in two Siberian native sheep breeds point to candidate genetic variants for adaptation and economically important traits.

Russian sheep breeds represent an important economic asset by providing meat and wool, whilst being adapted to extreme climates. By resequencing two Russian breeds from Siberia: Tuva (n = 20) and Baikal (n = 20); and comparing them with a European (UK) sheep outgroup (n = 14), 41 million variants were called, and signatures of selection were identified. High-frequency missense mutations on top of selection peaks were found in genes related to immunity (LOC101109746) in the Baikal breed and wool traits (IDUA), cell differentiation (GLIS1) and fat deposition (AADACL3) in the Tuva breed. In addition, genes found under selection owing to haplotype frequency changes were related to wool traits (DSC2), parasite resistance (CLCA1), insulin receptor pathway (SOCS6) and DNA repair (DDB2) in the Baikal breed, and vision (GPR179) in the Tuva breed. Our results present candidate genes and SNPs for future selection programmes, which are necessary to maintain and increase socioeconomic gain from Siberian breeds.

Role of implant configurations supporting three-unit fixed partial denture on mandibular bone response: biological-data-based finite element study.

Implant-supported fixed partial denture with cantilever extension can transfer the excessive load to the bone around implants and stress/strain concentration potentially leading to bone resorption. This study investigated the effects of implant configurations supporting three-unit fixed partial denture (FPD) on the stress and strain distribution in the peri-implant bone by combining clinically measured time-dependent loading data and finite element (FE) analysis. A 3-dimensional mandibular model was constructed based on computed tomography (CT) images. Four different configurations of implants supporting 3-unit FPDs, namely three implant-supported FPD, conventional three-unit bridge FPD, distal cantilever FPD and mesial cantilever FPD, were modelled. The FPDs were virtually inserted to the molar area in the mandibular FE models. The FPDs were loaded according to time-dependent in vivo-measured 3-dimensional loading data during chewing. The von Mises stress (VMS) and equivalent strain (EQS) in peri-implant bone regions were evaluated as mechanical stimuli. During the chewing cycles, the regions near implant necks and bottom apexes experienced high VMS and EQS than the middle regions in all implant-supported FPD configurations. Higher VMS and EQS values were also observed at the implant neck region adjacent to the cantilever extension in the cantilevered configurations. The patient-specific dynamic loading data and CT-based reconstruction of full 3D mandibular allowed us to model the biomechanical responses more realistically. The results provided data for clinical assessment of implant configuration to improve longevity and reliability of the implant-supported FPD restoration.

Bone metabolism induced by denture insertion in positron emission tomography.

18F-fluoride positron emission tomography (PET) can identify subtle functional variation prior to the major structural change detectable by X-ray. This study aims to investigate the mechanobiological bone reaction around the abutment tooth and in the residual ridge, induced by insertion of removable partial denture (RPD) within two different groups of patients: patients without denture experience (Group 1) and patients with denture experience before (Group 2), using 18F-fluoride PET imaging technique. 18F-fluoride PET/computerised tomography (CT) scan was performed to examine the bone metabolic change in mandible before and after the RPD treatment. Region of interests (ROIs) were placed in alveolar bone around abutment tooth and in residual bone beneath the RPD. Standardised uptake value (SUV), reflecting the accumulation of 18F-fluoride, was measured for each ROI. In all subjects of Group 1, SUVs after insertion were higher than before in both alveolar bone and residual bone, while there was less significant change in SUV in subjects of Group 2. This study demonstrated using longitudinal 18F-fluoride PET scans to effectively examine the bone metabolic change in mandible induced by occlusal loading after RPD insertion. Using this technique, within the six subjects in this study, it was shown that bone metabolism around abutment tooth and residual ridge increased after RPD insertion in case of first-time denture user, while there was no big change in the patient with experience of denture before. This study revealed the effectiveness of applying PET to evaluate bone metabolic activity as mechanobiological reaction.

Microstructural analysis of Co-Cr dental alloy at the metal-porcelain interface: a pilot study.

OBJECTIVE: The purpose of the study was to observe whether conventional porcelain firings had an effect on the underlying microstructure of cobalt-chromium alloys used in porcelain-fused-to-metal systems. METHODS: One as cast (non-veneered) and two porcelain veneered Co-Cr specimens layered with and without tungsten(W)-metal conditioner were manufactured and analysed. Electron backscatter diffraction was used to determine the crystal structures and grain size across the porcelain-fused-to-metal interface. RESULTS: No difference was found in the microstructure of the alloy in both with and without W-metal conditioner. For the porcelain fired specimens, disparately sized granular structures were observed adjacent to the metal-porcelain interfaces compared to the bulk of the metal. Ellipsoid shaped grains at the alloy surface ranged between 1-11 µm in diameter and averaged 2.70 µm (SD: 2.17 µm) for the specimen layered with W-metal conditioner and 2.86 µm (SD: 1.85 µm) for the specimen layered without W-metal conditioner. Grains located in the bulk were > 200 µm with dendritic-like features. The depth of the fine grain structure adjacent to the surface had an average depth of 15 µm. The crystal structure of the surface layer was found to be predominantly hexagonal close-packed whereas the underlying bulk was a mixture of both face-centered cubic and hexagonal close-packed phases. For the as cast specimen, similar large grains of over 200 µm was observed but exhibited no dendritic like features. In addition, no fine grains were observed at the surface region of the as cast alloy. CONCLUSION: Conventional porcelain firings altered the interfacial and bulk microstructure of the alloy while the presence of the W-metal conditioner had no influence on the underlying alloy microstructure.

Contralateral Nodal Relapse in Well-lateralised Oral Cavity Cancers Treated Uniformly with Ipsilateral Surgery and Adjuvant Radiotherapy With or Without Concurrent Chemotherapy: a Retrospective Study.

AIMS: To evaluate the incidence and pattern of contralateral nodal relapse (CLNR), contralateral nodal relapse-free survival (CLNRFS) and risk factors predicting CLNR in well-lateralised oral cavity cancers (OCC) treated with unilateral surgery and adjuvant ipsilateral radiotherapy with or without concurrent chemotherapy. MATERIALS AND METHODS: Consecutive patients of well-lateralised OCC treated between 2012 and 2017 were included. The primary endpoint was incidence of CLNR and CLNRFS. Univariable and multivariable analyses were carried out to identify potential factors predicting CLNR. RESULTS: Of the 208 eligible patients, 21 (10%) developed isolated CLNR at a median follow-up of 45 months. The incidence of CLNR was 21.3% in node-positive patients. CLNR was most common at level IB (61.9%) followed by level II. The 5-year CLNRFS and overall survival were 82.5% and 57.7%, respectively. Any positive ipsilateral lymph node (P = 0.001), two or more positive lymph nodes (P < 0.001), involvement of ipsilateral level IB (P = 0.002) or level II lymph node (P < 0.001), presence of extranodal extension (P < 0.001), lymphatic invasion (P = 0.015) and perineural invasion (P = 0.021) were significant factors for CLNR on univariable analysis. The presence of two or more positive lymph nodes (P < 0.001) was an independent prognostic factor for CLNR on multivariable analysis. CLNR increased significantly with each increasing lymph node number beyond two compared with node-negative patients. CONCLUSION: The overall incidence of isolated CLNR is low in well-lateralised OCC. Patients with two or more positive lymph nodes have a higher risk of CLNR and may be considered for elective treatment of contralateral neck.

X-ray microdiffraction, TEM characterization and texture analysis of human dentin and enamel.

Human tooth is a complex bioceramic composite, which consists of enamel, dentin and the interface, the dentin-enamel junction (DEJ). The crystal properties and ultrastructure of the inorganic phase through the thickness of healthy human molar teeth were investigated using X-ray microdiffraction (µXRD), electron diffraction and transmission electron microscopy (TEM) techniques. The XRD data were analysed using the Le Bail profile fitting approach. The size and the texture of the crystallites forming enamel and dentin in the crown part of teeth were measured using both techniques and then compared. Results showed that the thickness of dentin crystallites was found to decrease towards the DEJ, whereas the thickness of the enamel crystallites increased from the DEJ towards the outer layers. It was demonstrated that enamel exhibited an increase of texture in 002 lattice planes from the DEJ towards the outer layers. Texture was also detected in 102 lattice planes. The texture effect in 002 planes at the scale of less than 1 µm was also demonstrated in dentin. The variation of lattice parameters as a function of the position within the thickness of dentin and enamel was also observed. The values of the nonuniform microstrain in the dentin and enamel crystallites were from 1.40 × 10(-6) % to 4.44 × 10(-5) %. The good correlation between XRD and TEM indicated that µXRD is a useful technique to study crystallography and microstructure of heterogeneous enamel and dentin. The observed gradient characteristics of texture and crystallite size in enamel and dentin maybe an evolutionary outcome to resist wear and fracture, thereby contributing to the excellent mechanical properties of teeth.

Identifying the source of bullet wipe: a randomised blind trial.

OBJECTIVE: To assess the usefulness of scanning electron microscopy and energy dispersive x-ray spectroscopy in matching bullet wipe to the bullet. HYPOTHESIS: Bullet wipe can be used to match a bullet type to a crime scene.

Risk factors for injury in Olympic-style competition taekwondo: a systematic review.

AIM: The aim of this review was to systematically collate and qualitatively evaluate the epidemiologic data on risk factors related to injuries in taekwondo athletes. METHODS: Electronic searches of relevant literature were carried out in the AusportMed, CINAHL, PubMed, Scopus, and SPORTDiscus databases. A study was included if: 1) it was a prospective experimental or observational investigation; 2) it contained data on Olympic-style taekwondo athletes; and 3) it contained data on risk factors for injuries. All eligible studies were assessed by two independent reviewers. RESULTS: Sixteen studies were deemed eligible for inclusion, of which a total of nine unique data sets were identified. Six potential risk factors were found to have been prospectively investigated to date, of which only three were shown to be associated with the occurrence of injury. The available data indicated that competing in heavier weight divisions was associated with increased overall injury incidence rates. In addition, adolescent athletes and athletes lacking blocking skills were both found to be associated with increased occurrence of concussion injuries. CONCLUSION: There is a paucity of identified risk factors for injury in taekwondo. Future epidemiologic research should consider a wider range of potential risk factors, in particular modifiable risk factors, and translate ascertained factors into practical preventive efforts.

Gunshot induced indirect femoral fracture: mechanism of injury and fracture morphology.

INTRODUCTION: Indirect ballistic fractures occur when a projectile passes close to, but not contacting, the bone. The mechanism of how these fractures occur is not yet proven, but recently the acoustic shockwave has been excluded as a cause. The objective of this study is to determine whether the expanding temporary cavity, the collapse of this cavity or its oscillation causes these fractures. In addition, we describe the fracture morphology and biomechanical causes of this injury. METHOD: 40 fresh deer femora were strain gauged and embedded in ballistic gelatin before being shot with four different projectiles with varying distances off the bone. Pressure recordings, chronographs and radar allowed assessment of local pressures and energy transfer. High-speed video allowed the temporal relationship between the temporary cavity and fracture formation to be analysed, while sample dissection allowed the fracture morphology to be described. RESULTS: The fractures produced were consistently wedge-shaped and caused by the expansion of the temporary cavity, flexing the bone beyond its yield point, causing tension failure on the cortex opposite the expanding temporary cavity and a compression wedge on the side of the cavity. Local pressure was not predictive of fracture formation but the energy transfer to the gelatin block was predictive. CONCLUSIONS: Indirect fractures are caused by the expansion of the temporary cavity and relate to the proximity of this cavity to the bone. Fractures occur from flexion of the bone and classically display wedge-shaped fracture patterns with the apex of the wedge pointing away from the expanding cavity.

Challenges in the Sustainability of Brachytherapy Service in Contemporary Radiotherapy.

Brachytherapy has a long history of delivering a highly conformal radiation dose to the target volume with sparing of adjacent normal tissue and has an irreplaceable role in certain cancers, such as cervical and prostate cancers. There have been futile attempts to replace brachytherapy with other radiation techniques. Despite that there are multifaceted challenges in preserving this dying art, from establishment, to a trained workforce, to maintenance of the equipment and source replacement costs. Here we focus on the challenges to access brachytherapy, the availability and distribution of care across the globe and appropriate training leading to proper implementation of the procedure. Brachytherapy holds a significant place in the treatment armamentarium of most common cancers, such as cervical, prostate, head and neck and skin cancers. However, there is an uneven distribution of brachytherapy facilities, not only across the globe, but also at a national level, with a larger proportion of facilities concentrated in certain regions, more so in low and low-middle income countries. The regions with the highest incidence of cervical cancer have the least access to brachytherapy facilities. Attempts to bridge the gap are essential and should be focused on uniform distribution and access to care, improving training of the workforce through specialised training programmes, reducing the cost of care, planning to reduce the recurring cost, generating evidence and research guidelines, renewing interest in brachytherapy through rebranding, use of social media and building an attainable long-term roadmap.

Non-surgical organ preservation in laryngeal and hypopharyngeal cancers: an audit from the clinic.

BACKGROUND: There is increasing concern regarding efficacy of organ preservation protocol in laryngeal and hypopharyngeal cancers. METHOD: This study retrospectively assessed disease-related and functional outcomes of 191 patients with non-metastatic laryngeal or hypopharyngeal squamous cell carcinoma treated with curative intent (radiotherapy with or without chemotherapy). RESULTS: Seventy-six patients (39.8 per cent) had a primary cancer in the larynx, and 115 patients (60.2 per cent) had a primary cancer in the hypopharynx. The median follow up was 39 months. The 3-year time to progression, overall survival, local control and laryngectomy free survival was 56.2 per cent, 76.3 per cent, 73.2 per cent and 67.2 per cent, respectively. At the time of analysis, 83 patients (43.5 per cent) were alive and disease free at their last follow up and did not require tube feeding or tracheostomy. The laryngo-oesophageal dysfunction-free survival was 61 per cent at 3 years. CONCLUSION: Organ conservation protocols remain the standard of treatment in appropriately selected patients with laryngeal and hypopharyngeal cancers.

Tooth wear and wear investigations in dentistry.

Tooth wear has been recognised as a major problem in dentistry. Epidemiological studies have reported an increasing prevalence of tooth wear and general dental practitioners see a greater number of patients seeking treatment with worn dentition. Although the dental literature contains numerous publications related to management and rehabilitation of tooth wear of varying aetiologies, our understanding of the aetiology and pathogenesis of tooth wear is still limited. The wear behaviour of dental biomaterials has also been extensively researched to improve our understanding of the underlying mechanisms and for the development of restorative materials with good wear resistance. The complex nature of tooth wear indicates challenges for conducting in vitro and in vivo wear investigations and a clear correlation between in vitro and in vivo data has not been established. The objective was to critically review the peer reviewed English-language literature pertaining to prevalence and aetiology of tooth wear and wear investigations in dentistry identified through a Medline search engine combined with hand-searching of the relevant literature, covering the period between 1960 and 2011.

Concurrent Cetuximab-based bioradiotherapy versus Cisplatin-based Chemoradiotherapy in the Definitive Management of Favourable Biology Human Papillomavirus-associated Oropharyngeal Squamous Cell Carcinoma: Systematic Review and Meta-analysis.

Replacing cisplatin with cetuximab concurrently during radiotherapy has been one of the strategies of treatment de-escalation in human papillomavirus (HPV)-associated oropharyngeal squamous cell carcinoma (OPSCC). However, until recently, there were limited data on the efficacy and safety of such an approach. A systematic search of the literature was carried out to identify prospective randomised controlled trials comparing definitive cisplatin-based chemoradiotherapy (CT-RT) versus cetuximab-based bioradiotherapy (BRT) in HPV-positive OPSCC. Overall survival and locoregional control were primary outcomes of interest; rates of acute and late toxicities (≥grade 3) were secondary end points. Outcome data were aggregated using a random-effects model as per Cochrane methodology including risk of bias assessment and expressed as hazard ratio or risk ratio as appropriate with respective 95% confidence intervals. Data from five randomised controlled trials involving 1560 patients with HPV-positive OPSCC were aggregated in the meta-analysis. Cetuximab-based BRT was associated with a significantly increased risk of death (hazard ratio = 2.83, 95% confidence interval 1.22-6.57; P = 0.02) and locoregional relapse (hazard ratio = 2.78, 95% confidence interval 1.77-4.39; P < 0.0001) compared with cisplatin-based CT-RT. Cisplatin was associated with higher rates of acute ≥grade 3 toxicity in terms of acute kidney injury, dry mouth, febrile neutropenia, hearing impairment, nausea and vomiting, whereas dermatitis and acneiform rash were more common with cetuximab. There were no significant differences in overall rates of late ≥grade 3 toxicity (risk ratio = 0.63, 95% confidence interval = 0.36-1.10; P = 0.10). In conclusion, there is moderate-certainty evidence that cetuximab-based BRT leads to inferior efficacy outcomes compared with cisplatin-based CT-RT in the definitive curative-intent management of HPV-associated OPSCC.

Post-cricoid and Upper Oesophagus Cancers Treated with Organ Preservation Using Intensity-modulated Image-guided Radiotherapy: a Phase II Prospective Study of Outcomes, Toxicity and Quality of Life.

AIMS: To prospectively examine the outcomes, toxicity and quality of life (QoL) of patients with post-cricoid and upper oesophagus (PCUE) cancers treated with an organ-preservation approach of (chemo)-radiotherapy using intensity-modulated image-guided radiotherapy (IM-IGRT). MATERIALS AND METHODS: This phase II prospective study was conducted at a tertiary cancer centre from February 2017 to January 2020. Forty patients with squamous cell carcinoma of PCUE of stage T1-3, N0-2, M0 were accrued. Gross exolaryngeal extension/dysfunctional larynx were major exclusion criteria. Patients received 63-66 Gy in once-daily fractions using volumetric modulated arc therapy with daily IGRT. Outcome measures included disease-related outcomes, patterns of failure, Radiation Therapy Oncology Group toxicities, feeding tube dependency and QoL. RESULTS: The median follow-up was 22 months. Twenty-six (87.5%) patients had locoregionally advanced disease and 34 (85%) patients received (chemo)-radiotherapy. A complete response was observed in 26 (65%) patients. The 2-year locoregional control, event-free survival and cause-specific survival were 59.6%, 40.2% and 44.8%, respectively. The volume of primary tumour (GTVPvol) exceeding 28 cm3 had inferior overall survival (P = 0.005) on univariate analysis. Multivariable analysis showed GTVPvol and positron emission tomography-computed tomography maximum standardised uptake value to be independently predictive for event-free and overall survival. A feeding tube requirement at presentation was seen in 11 (27.5%) patients, whereas long-term feeding tube dependency at 6 months was seen in 10 (37%) patients. For QoL, a statistical improvement in pain, appetite loss and swallowing was observed over time. CONCLUSION: Although the outcomes of PCUE cancers remain dismal, the use of state of the art diagnostic modalities, careful case selection and modern radiotherapy techniques improved outcomes as compared with before in this exclusive analysis of PCUE cancers.

Autoantibodies to GW bodies and other autoantigens in primary biliary cirrhosis.

Autoantibodies to intracellular targets in mitochondria and nuclei are serological hallmarks of primary biliary cirrhosis (PBC). One of the most recently identified cellular targets of PBC autoantibodies is a novel cytoplasmic structure referred to as GW bodies [GWB, G (glycine) W (tryptophan)-containing bodies (GWB)]. GWB are indentified as discrete cytoplasmic domains that are involved in mRNA processing via the RNA interference (RNAi) pathway. Key components of GWB include the proteins GW182, Ago2, RNA-associated protein 55 (RAP55) and Ge-1/Hedls. The primary objective was to study the frequency and clinical association of antibodies directed to GWB components, in 109 PBC patients. Autoantibodies to mitochondrial antigen-pyruvate dehydrogenase complex (M2), branched-chain 2-oxo-acid dehydrogenase complex and 2-oxo glutarate dehydrogenase complex (3E-BPO), gp210, sp100, promyelocytic leukaemia cell antigen (PML) and liver kidney microsomal-1 antigen (LKM-1) were detected by a line immunoassay and antibodies to GWB (GW182, RAP55, Ge-1, GW2, GW3) and glutamate receptor interacting protein (GRIP)-associated protein-1 (GRASP-1), by an addressable laser bead immunoassay (ALBIA). The most common GWB autoantigen targets were: RAP55-28%, GW182-12%, GW2-2% and antibodies to GRASP-1-17%. By comparison, the frequency of reactivity to established PBC autoantigens was: gp210, 27%; sp100, 27% and PML, 17%. None of the autoantibodies were associated with differences in Mayo risk score or liver decompensation. This study is the first study to show that antibodies to RAP55, GW182 and GRASP-1 are the most common GWB targets in PBC.

Fluoride release, recharge and mechanical property stability of various fluoride-containing resin composites.

AIM: To determine the fluoride release and recharge of three fluoride-containing resin composites when aged in deionized water (pH 6.5) and lactic acid (pH 4.0) and to assess mechanical properties of these composites following aging. METHODS: Three fluoride-containing resin composites were analyzed in this study; a new giomer material named Beautifil II, Gradia Direct X, and Tetric EvoCeram. A glass ionomer cement, Fuji IX Extra, was also analyzed for comparison. Specimens were fabricated for two test groups: group 1 included 10 disc specimens initially aged 43 days in deionized water (five specimens) and lactic acid (five specimens). The fluoride release from these specimens was measured using a fluoride-specific electrode on nine specific test days during the aging period. Following 49 days of aging, each specimen was recharged in 5000 ppm neutral sodium fluoride solution for 5 minutes. Specimen recharge was then repeated on a weekly basis for 3 weeks. The subsequent fluoride rerelease was measured at 1, 3, and 7 days after each recharge episode. Group 2 included six disc specimens aged for 3 months in deionized water (three specimens) and lactic acid (three specimens). The hardness and elastic modulus of each specimen was measured using nano-indentation at intervals of 24 hours, 1 month, and 3 months after fabrication. Two-way factorial analysis of variance (ANOVA) and post-hoc (Tukey) testing was used to assess the influence of storage media (two levels) and composite type (three levels) on the fluoride release, fluoride rerelease, hardness, and elastic modulus of the assessed materials. The level of significance was set at p=0.05. RESULTS: All three composites demonstrated fluoride release and recharge when aged in both deionized water and lactic acid. The cumulative fluoride released from Beautifil II into both media was substantially greater than the fluoride released from Gradia Direct X and Tetric EvoCeram after 43 days aging and was significantly (p<0.05, ANOVA, Tukey test) greater during several analysis periods. Beautifil II demonstrated the greatest recharge ability of the three composites over the 3-week recharge period in both media. Fuji IX Extra demonstrated a significantly (p<0.05) greater fluoride release and recharge compared with the three resin composites. The elastic modulus and hardness of the three composites did not decrease significantly (p<0.05) with fluoride release or fluid uptake over the 3-month aging period, in either media. CONCLUSION: The three composites in the present study demonstrated fluoride release (Beautiful II > Gradia Direct X > Tetric EvoCeram) and fluoride recharge (Beautiful II > Gradia Direct X > Tetric EvoCeram). This capability raises the possibility of fluoride-containing composites exhibiting a lower incidence of recurrent caries than non fluoride­containing composites. The mechanical properties of each composite did not diminish with aging and fluoride release over the testing period.

Structure and compositional characteristics of caniniform dental enamel in the tuatara Sphenodon punctatus (Lepidosauria: Rhynchocephalia).

OBJECTIVE: The evolution of dental tissues in relation to tooth function is poorly understood in non-mammalian vertebrates. We studied the dentition of Sphenodon punctatus, the sole remaining member of the order Rhynchocephalia in this light. METHODS: We examined 6 anterior maxillary caniniform teeth from adult Sphenodon by scanning electron microscopy, nano-indentation and Raman spectroscopy. RESULTS: The elastic modulus (E) for tuatara enamel was 73.17 (sd, 3.25) GPa and 19.52 +/- 0.76 Gpa for dentine. Hardness (H) values for enamel and dentine were 4.00 (sd, 0.22) and 0.63 +/- 0.02 Gpa respectively. The enamel was thin (100 gm or less), prismless and consisted of grouped parallel crystallites. Incremental lines occurred at intervals of about 0.5 to 1 rm. There were tubular structures along the enamel dentine junction running from the dentine into the inner enamel, at different angles. These were widened at their base with a smooth, possibly inorganic lining. Enamel elastic modulus and hardness were lower than those for mammals. CONCLUSIONS: The presence of enamel tubules in the basal part of the enamel along the EDJ remains speculative, with possible functions being added enamel/dentinal adhesion or a role in mechanosensation.

Indentation of the cornea: A Bi-layer contact problem.

Histological observations of the cornea have identified the presence of multiple layers with differing thickness and function. The composition of the cornea consists primarily of collagen fibrils held together with proteoglycans but with an aqueous interstitial component being dominant. Indentation provides a means to quantify the spatial variation of the mechanical properties of the cornea, however the role of the different layers on the indentation response has barely been addressed. In addition, the response of the fluid content and its displacement during indentation has not been adequately considered. In this study indentation of the cornea with a relatively large spherical tipped indenter (R = 500 µm) is considered. It was observed that the initial phase of loading did not fit a classic Hertz elastic response but showed an initial steeper slope that gradually declines with increasing force and displacement. A relatively simple approach is developed that initially considers the cornea as a poro-elastic bi-layer contact problem, that is the presence of an outer thin stiffer Bowman's layer overlaying the thicker less stiff stroma.