Permeability of triamcinolone acetonide, released from mucoadhesive films, through a buccal mucosa-mimetic barrier: Permeapad™.

OBJECTIVES: The permeability of triamcinolone acetonide (TA), from bilayer mucoadhesive buccal films, through a biomimetic membrane, Permeapad™, was investigated employing Franz diffusion cell. The delivery systems composition and ethyl cellulose (EC) backing layer, on drug permeability, were assessed. METHODS: Three TA-loaded films were tested; hydroxypropyl methylcellulose (HPMC K4M; bilayer [F1] and monolayer), HPMC K4M/Polyvinylpyrrolidone (PVP): 90/10 [F2], and HPMC K15M film [F3]. All films contained propylene glycol (PG-plasticiser). TA solution alone was used as a control. TA permeability via a Permeapad™ barrier, simulating buccal mucosa, was assessed over 8 h using a Franz diffusion cell. TA permeated into the receptor compartment, released in the donor compartment, and located on/within the Permeapad™ barrier were analysed using UV-spectrophotometer. RESULTS: 45.7 % drug retention within the Permeapad™ barrier was delivered from F1 (highest). F1, F2, and F3 significantly improved the TA's permeability through Permeapad™, compared to TA solution alone (e.g., 8.5 % TA-solution, 21.5 %-F1), attributed to the synergy effect of HPMC and propylene glycol acting as penetration enhancers. F1 displayed a significant increase in drug permeability (receptor compartment; 21.5 %) compared to F3 (17.0 %). PVP significantly enhanced drug permeability (27.5 %). Impermeable EC backing layer controlled unidirectional drug release and reduced drug loss into the donor compartment (e.g., ∼28 % for monolayer film to ∼10 % for bilayer film, F1). SIGNIFICANCE: The mucoadhesive films demonstrated improved TA permeability via Permeapad™. The findings suggest that these bilayer mucoadhesive films, particularly F1, hold promise for the effective topical treatment of oral mucosa disorders, such as recurrent aphthous stomatitis and oral lichen planus.

Assessment of wear characteristics, longevity and stiffness of Essix-type retainers.

OBJECTIVE: To compare four commercially available Essix-type retainers in terms of longevity, wear characteristics, stiffness and their range of rigidity. MATERIALS AND METHODS: An in vitro study was conducted at Queen Mary University of London. Four groups of thermoplastic materials were included: Duran (PETG), Essix C + (Polypropylene), Vivera and Zendura (Polyurethane). A working typodont was fabricated to evaluate surface wear characteristics using a wear machine with a customized jig. Retainers were measured for tensile test, and water absorption was measured at five different time points up to 6 months after initial immersion in two different physical states and two different solutions. Hydrolytic degradation was also evaluated using FTIR spectroscopy. RESULTS: Essix C + was the most flexible retainer with Vivera the stiffest material. Zendura and Essix C + had the most surface wear (413 µm ± 80 and 652 µm ± 12, respectively) with absorption rates of up to 15 wt% in artificial saliva occurring with Zendura. Only Essix C + displayed signs of degradation following water absorption. CONCLUSIONS: All materials had characteristic levels of flexibility and were susceptible to water absorption. Duran 1.5 mm performed similarly to Vivera in relation to stiffness and wear properties. While Zendura and Vivera have similar chemical structures, they exhibited differences concerning wear resistance and water absorption. Further clinical research evaluating the clinical relevance of these laboratory findings is required. CLINICAL RELEVANCE: Characteristic patterns of wear and rigidity of four commercially available Essix-type retainers were observed. This information should help in the tailoring of retainer material on a case-by-case basis considering treatment-related factors and patient characteristics including parafunctional habits.

Impact of the superimposition reference area on intraoral scanning accuracy in a partially dentate maxilla.

STATEMENT OF PROBLEM: The alignment of 3-dimensional (3D) files involves selecting a reference area before performing a local best fit alignment during the digital scan superimposition and is essential for comparing digital scans. Scan alignment relies on both reference area location and the alignment algorithm. However, a consensus on the impact of different reference areas on intraoral scanning accuracy is lacking. PURPOSE: The purpose of this in vitro study was to assess the impact of 3 superimposition reference areas on the accuracy of 3 intraoral scanners for a partially dentate maxilla. MATERIAL AND METHODS: A Kennedy class II resin cast was scanned using 3 intraoral scanners (Primescan, TRIOS 3, and Emerald) outputting 30 digital scans (10 per scanner). Test scans from intraoral scanners were subsequently compared with a reference digital standard tessellation language file generated by a laboratory scanner with validated accuracy. The files were superimposed using best fit alignment for each intraoral scanner using 3 different superimposition reference areas (whole region of interest, palate, and all teeth). Accuracy was assessed by using a 3D analysis program (Geomagic Control X; 3D systems) for each scanner at 4 preselected areas. Test and reference scan differences were depicted on color maps and quantified via root mean square deviations. Differences were analyzed using regression analysis with the post hoc student t test and Bonferroni correction (α=.05). RESULTS: The TRIOS 3 and Emerald produced positive deviations in the palatal color maps, whereas Primescan produced more uniform color maps, regardless of the superimposition strategy used. Primescan exhibited the best accuracy (trueness and precision) in both palatal and bounded edentulous areas, regardless of the superimposition reference area. The TRIOS 3 recorded the highest distal extension trueness (ranging from 42.9±7.7 µm to 65 ±19.5 µm), and Primescan achieved the highest precision (ranging from 28.5 ±9.8 µm to 48.9 ±16.9 µm), regardless of the superimposition area. Emerald demonstrated the highest teeth trueness (ranging from 31.6 ±6.8 µm to 69.6 ±11.5 µm), while Primescan produced the highest precision (ranging from 17.9 ±6.1 µm to 30.7 ±9.2 µm), regardless of the reference area used. CONCLUSIONS: The chosen reference area for best fit alignment significantly influenced digital scan accuracy (P<.001). Primescan displayed the highest palatal and bounded edentulous area accuracy, with TRIOS 3 recording the highest distal extension trueness. Emerald recorded the highest teeth trueness and Primescan recorded the highest distal extension and tooth precision. All conclusions were independent of the superimposition strategy used.

Effect of Food-Simulating Liquids on the Leachability of Plasticizers from Dental Tissue Conditioners.

OBJECTIVE: Tissue conditioners are composed of poly(ethyl methacrylate) (PEMA) powder and plasticizer/ethanol mix liquid. Butyl phthalyl butyl glycolate (BPBG) plasticizer is commonly used in tissue conditioners, but the main concern with phthalate plasticizer is its leachability and biocompatibility, especially the estrogenic activity and cytotoxicity of phthalate. Therefore, acetyl tributyl citrate (ATBC) plasticizer has been introduced and formulated as plasticizer in tissue conditioner; however its leachability characteristics are still unknown. Furthermore, the effect of foodsimulating liquids toward leachability of BPBG and ATBC plasticizers has not been documented. The objective of this study was to compare the effect of food-simulating liquids on the leachability of plasticizers and hardness of two experimental tissue conditioners containing BPBG and ATBC plasticizers. MATERIALS AND METHODS: Ten experimental materials were prepared using PEMA polymer powder with 95% plasticizer (BPBG and ATBC) and 5% ethanol by volume, using powder to liquid ratio of 1.67:1, and the thickness was controlled at 3 mm. Shore A hardness value was measured after immersion in distilled water, artificial saliva, 25% ethanol/water mix, 3% citric acid, and coconut oil at 37°C. Measurements were taken at 2 hours and 1, 2, 3, 4, 7, 10, 14, 21, 28, 42, 56, and 84 days. Six readings were taken for each sample and hardness change was calculated and statistically analyzed using Wilcoxon signed-rank test. RESULTS: Increase in hardness value was noted for both plasticizers over time with the highest increase was when immersed in coconut oil. Shore A hardness value was significantly higher in ATBC after 84 days of immersion in all food-simulating liquids. The increase in hardness is due to plasticizer/ethanol leaching; however, as ethanol content was the same (5%), the hardness change is attributed to the leaching of plasticizers. CONCLUSION: Leaching of both plasticizers was highest in coconut oil indicating that tissue conditioners may have a shorter intraoral lifetime in patients eating high-fat diet.

Diagnosis of pathological speech with streamlined features for long short-term memory learning.

BACKGROUND: Pathological speech diagnosis is crucial for identifying and treating various speech disorders. Accurate diagnosis aids in developing targeted intervention strategies, improving patients' communication abilities, and enhancing their overall quality of life. With the rising incidence of speech-related conditions globally, including oral health, the need for efficient and reliable diagnostic tools has become paramount, emphasizing the significance of advanced research in this field. METHODS: This paper introduces novel features for deep learning in the analysis of short voice signals. It proposes the incorporation of time-space and time-frequency features to accurately discern between two distinct groups: Individuals exhibiting normal vocal patterns and those manifesting pathological voice conditions. These advancements aim to enhance the precision and reliability of diagnostic procedures, paving the way for more targeted treatment approaches. RESULTS: Utilizing a publicly available voice database, this study carried out training and validation using long short-term memory (LSTM) networks learning on the combined features, along with a data balancing strategy. The proposed approach yielded promising performance metrics: 90% accuracy, 93% sensitivity, 87% specificity, 88% precision, an F1 score of 0.90, and an area under the receiver operating characteristic curve of 0.96. The results surpassed those obtained by the networks trained using wavelet-time scattering coefficients, as well as several algorithms trained with alternative feature types. CONCLUSIONS: The incorporation of time-frequency and time-space features extracted from short segments of voice signals for LSTM learning demonstrates significant promise as an AI tool for the diagnosis of speech pathology. The proposed approach has the potential to enhance the accuracy and allow for real-time pathological speech assessment, thereby facilitating more targeted and effective therapeutic interventions.

Features and networks of the mandible on computed tomography.

The mandible or lower jaw is the largest and hardest bone in the human facial skeleton. Fractures of the mandible are reported to be a common facial trauma in emergency medicine and gaining insights into mandibular morphology in different facial types can be helpful for trauma treatment. Furthermore, features of the mandible play an important role in forensics and anthropology for identifying gender and individuals. Thus, discovering hidden information of the mandible can benefit interdisciplinary research. Here, for the first time, a method of artificial intelligence-based nonlinear dynamics and network analysis are used for discovering dissimilar and similar radiographic features of mandibles between male and female subjects. Using a public dataset of 10 computed tomography scans of mandibles, the results suggest a difference in the distribution of spatial autocorrelation between genders, uniqueness in network topologies among individuals and shared values in recurrence quantification.

Comparison of the elastic recovery and strain-in-compression of commercial and novel vinyl polysiloxane impression materials incorporating a novel crosslinking agent and a surfactant.

This study aims to formulate experimental vinylpolysiloxane (VPS) impression materials and compare their elastic recovery and strain-in-compressions with three commercial VPS materials (Aquasil, Elite, and Extrude). Five experimental materials (Exp), two hydrophobic (Exp-I and II) and three hydrophilic (Exp-III, IV and V) were developed. Exp 1 contained vinyl-terminated poly-dimethyl siloxane and a conventional cross-linking agent (poly methylhydrosiloxane), while Exp- II contained a novel cross-linking agent that is tetra-functional dimethyl-silyl-ortho-silicate (TFDMSOS). Exp III-V (hydrophilic materials) were formulated by incorporating different concentrations of non-ionic surfactant (Rhodasurf CET-2) into Exp II formulation. Measurement of elastic recovery and strain-in-compression for commercial and experimental materials were performed according to ISO4823 standard using the calibrated mechanical testing machine (Tinius Olsen). One-way analysis of variance (one-way ANOVA) and Tukey's post-hoc (HSD) test were used for statistical analysis and a p-value of ≤ 0.05 was considered significant. Exp-I has statistically similar values to commercial VPS. The Exp-II showed the highest elastic recovery, while % elastic recovery was reduced with the addition of the non-ionic surfactant (Rhodasurf CET-2). The % reduction was directly related to the concentration of Rhodasurf CET-2. In addition, Exp II had significantly higher strain-in-compression values compared to Exp-I and commercial materials. These values were further increased with the addition of a non-ionic surfactant (Rhodasurf CET-2) was added (Exp-III, IV and V).

Triamcinolone acetonide release modelling from novel bilayer mucoadhesive films: an in vitro study.

OBJECTIVES: Recurrent aphthous stomatitis (RAS) is a painful disorder that commonly appears as ulcers on the oral mucosa, lasting ∼two weeks (minor) to months (major and herpetiform). Current treatment often necessitates the use of topical steroids in the form of pastes, mouthwashes, or gels, but these forms are often ineffective due to inadequate drug contact time with the ulcers. In this study, the performance of novel bilayer mucoadhesive buccal films loaded with triamcinolone acetonide (TA) has been evaluated for targeted drug delivery. METHODS: Experimental mucoadhesive films of hydroxypropyl methylcellulose (HPMC), polyvinyl alcohol (PVA), and polyvinyl pyrrolidone (PVP) were prepared by the solvent casting method, and ethyl cellulose (EC) was applied as the backing layer. The films were characterized for their physical properties, including swelling index (SI), folding endurance, adhesion force with porcine buccal mucosa, residence time and in-vitro drug release. RESULTS: The data showed that the films were flexible with folding endurance> 300 times. With porcine buccal mucosa i) suitable adhesion forces were obtained (between 2.72 and 4.03 N), ii) residence times of> 24 h, and iii) surface pH between 6.8 and 7.1 indicating they would be non-irritant. All films released 100% TA over 6 h, but with varying profiles. The release of TA (over 6 h) from PVP-free films followed Fickian diffusion kinetics (diffusion-controlled release of drug), whereas the mechanism of release from PVP-containing films was found to be a superposition of diffusion-controlled and erosion-controlled release (anomalous). SIGNIFICANCE: The developed films hold great promise for potentially treating RAS and other oral conditions.

Perception of COVID-19 pandemic restrictions on dental researchers.

BACKGROUND/OBJECTIVES: Historical evidence shows a gender-based disproportionate effect of pandemics across different populations. In 2020, the coronavirus disease 2019 (COVID-19) pandemic began spreading its devastating effects worldwide. The goal of the present study was to investigate the effect of the COVID-19 pandemic on research productivity, work-life arrangements, and mental health of dental professionals worldwide with focus on gender differences. METHODS: A 38-item survey, concerning demographics, career stage, employer support, family structure, mental health, and relationships, was distributed to 7692 active members of the International Association for Dental Research. Bivariate associations between independent variables and the primary outcome variable were tested using Spearman's correlation test. A logistic regression model was used to assess the simultaneous, independent associations between each variable and researcher productivity. RESULTS: A total of 722 responses were obtained, indicating a 9.4% response rate. Higher productivity was reported by male respondents (p = 0.021), and by those in senior career stages (p = 0.001). Institutional support was associated with higher productivity (p < 0.0001). Lower productivity was reported by younger researchers (p = 0.003). Remote work negatively affected productivity (p < 0.0001) and female respondents reported working more hours, regardless of work location (p = 0.004). Poor mental health was associated with low productivity (p < 0.0001). CONCLUSIONS: Our results showed that the COVID-19 pandemic significantly affected dental professionals' perceived productivity and mental health around the globe. Younger individuals and women were disproportionally affected, and institutional support had a significant influence to mitigate effects of the pandemic for dental researchers.

Dimensional changes of commercial and novel polyvinyl siloxane impression materials following sodium hypochlorite disinfection.

BACKGROUND: Dental impressions are used to record anatomy of teeth and surrounding oral structures. Impression materials become contaminated with saliva and blood requiring disinfection, which may have negative impact on dimensional stability of materials. OBJECTIVE: Comparatively evaluate linear dimensional changes of synthesized Tetra-functional (dimethylsilyl) orthosilicate (TFDMOS) containing Polyvinylsiloxane (PVS) impressions following sodium hypochlorite disinfection. METHODS: Percentage dimensional changes of three commercial PVS (Elite HD Monophase, Extrude and Aquasil Ultra Monophase) and five experimental PVS impression materials were measured. Experimental material contained novel cross-linking agent (TFDMOS) and a non-ionic surfactant (Rhodasurf CET-2) that is Exp-A (without TFDMOS), Exp-B (with TFDMOS), Exp-C (TFDMOS+ 2% Rhodasurf CET-2), Exp-D (TFDMOS+ 2.5% Rhodasurf CET-2) Exp-E (TFDMOS+ 3% Rhodasurf CET-2). Samples were made using rectangular stainless-steel molds (40 × 10 × 3 mm3) and linear dimensional changes were measured using a calibrated travelling microscope at 10× magnification after immersion in distilled water (D.W) and 1% Sodium Hypochlorite solution at two different time intervals i.e., 30 min and 24 h. RESULTS: Samples immersed in 1% NaOCl showed significant (p < 0.05) dimensional changes after 30 min of immersion. Exp-E showed significantly greater dimensional changes than their control (Exp-A and Exp-B). In distilled water, there were no significant difference among the tested materials. Aquasil exhibited highest expansion (0.06%) in both solutions. At 24 h, among the commercial materials, Extrude had the greatest expansion followed by Aquasil and Elite in DW while Aquasil showed the greatest expansion followed by Extrude and Elite in NaOCl. CONCLUSION: Experimental PVS had linear dimensional changes within the ISO 4823; 2015 recommended range. However, extended immersion can negatively affect the linear dimensions.

Comparison of the Hardness of Novel Experimental Vinyl Poly Siloxane (VPS) Impression Materials with Commercially Available Ones.

PURPOSE: To determine the hardness and Young's moduli of both commercial and experimental vinyl poly siloxane (VPS). METHODS: The purpose of this study was to develop a medium-bodied experimental (Exp-I, II, III, IV, and V) VPS impression materials and to analyse their effects on hardness and Young's modulus and compare them with three commercial VPS materials (Aquasil, Elite, and Extrude) using Shore A hardness tester. Measurements were recorded after 1, 24, 72, and 168 hours of mixing. The results were analysed with one-way ANOVA and post hoc Tukey's test using the SPSS PASW statistical 22 software. RESULTS: Commercial and experimental vinyl polysiloxane exhibited higher Shore A hardness values with time (i.e., 1 hour after mixing, 24 hours after mixing, 72 hours after mixing, and 1 week after mixing). All Comml and Exp VPS demonstrated a significant increase (ANOVA, p < 0.05) in hardness at increasing time points. Generally, all commercial VPS exhibited significantly higher values for Shore A hardness compared to all Exp formulations. For commercial products, Elt M presented significantly highest values at all-time points followed by Aq M then Extr M. Exp-I was significantly harder than all other Exp VPS at all-time points. Young's modulus values were directly related to Shore A hardness; materials with higher Shore A hardness values had higher Young's moduli. CONCLUSION: Continued polymerisation of elastomeric impression materials results in increased hardness over time. Hardness, Young's moduli, and rigidity of the set commercial and experimental VPS materials were within the required limits. Shore A hardness and Young's moduli were directly proportional to each other, and commercial and experimental materials had enough rigidity to contain the stone during pouring.

The effect of layered double hydroxide on fluoride release and recharge from a commercial and an experimental resin varnish.

OBJECTIVES: Layered Double Hydroxide (LDH) is capable of fluoride anion exchange and release. This study investigated the effects of incorporating ZnAl-LDH in commercial and experimental dental varnishes, on fluoride release and re-release after charging in NaF. METHODS: Five discs of each material (commercial ClinproXT varnish and experimental light cured resin varnish), with and without 9%ZnAl-LDH were immersed and agitated in deionised water (DW) at 37 °C. A fluoride ion selective electrode measured fluoride release in DW daily over two-weeks. At 3, 6, 9 and 12 days the discs were recharged in 15 ml 0.05 M NaF solution (37 °C) for five minutes followed by immersion in DW. Energy dispersive X-ray spectra (EDS), weight changes and SEMs were performed on discs, before and after each cycle. RESULTS: Evidence of ZnAl-LDH was confirmed by the presence of peaks for zinc and aluminium in EDS spectra. Cumulative fluoride and mean fluoride released between Clinpro, Clinpro + LDH and resin were significantly different (ANOVA, Tukey's HSD post-hoc test, p < 0.001) except between the resin and resin + LDH. Mean fluoride concentrations differed significantly after every recharge between Clinpro, Clinpro + LDH and resin, but not between the resin and resin + LDH (p < 0.01). The weights and SEMs of the experimental resins +/-LDH, appeared to be stable whilst the weights of Clinpro samples +/-LDH, fluctuated and fragmented. SIGNIFICANCE: ClinproXT and experimental resin containing ZnAl-LDH recharged with fluoride did not significantly increase fluoride release compared to the unmodified materials. However, all LDH-F incorporated materials demonstrated fluoride recharging properties which appear beneficial to dentistry and thus further work is required to improve these properties.

Characteristics of experimental resin-modified glass-ionomer cements, containing alternate monomers to HEMA.

OBJECTIVE: Resin-modified glass ionomer cements (RMGICs) present several advantages (e.g. fluoride release), but their reported cytotoxicity has been associated with hydroxyethyl methacrylate (HEMA) monomer release. Therefore, different monomers were tested for use in RMGICs in order to improve their biocompatibility and reduce monomer release. METHODS: Eight experimental liquid compositions were prepared replacing different percentages of HEMA (conventional monomer used in commercial RMGICs) with hydroxypropyl-methacrylate (HPM) and/or tetrahydrofurfuryl-methacrylate (THFM), which are known to have better biocompatibility. Moreover, two commercial materials (Fuji-Plus and RelyX) and two compositions, based on these (home), were included as controls. Monomer release of all materials (commercial, home and experimental) were tested using high-performance liquid chromatography (HPLC) methods after immersing discs in deionized-water (DW) or ethanol:DW. Cytotoxicity of the materials extracts was tested on normal human oral fibroblast line (NHOF-1) using 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay. RESULTS: Three experimental materials containing THFM (F3, R3 and R4) showed less or similar monomer release compared to corresponding commercial products. Furthermore, two experimental materials (F3 and F4) showed similar effects on NHOF-1 cells compared to the negative control medium. SIGNIFICANCE: The lower monomer release and higher cell viability of some experimental THFM compositions are encouraging. THFM partially replacing HEMA is potentially a suitable alternative for producing biocompatible RMGICs.

Improved water absorption behaviour of experimental hydrophilic vinyl polysiloxane (VPS) impression materials incorporating a crosslinking agent and a novel surfactant.

OBJECTIVES: To study the effects of incorporating a further crosslinking agent and a novel surfactant on the water absorption behaviour of experimental VPS impression materials. METHODS: Part 1: The water uptake behaviour of Aquasil-Ultra-Monophase (AqM) was studied gravimetrically in three media (DW, 1%NaOCl and Perform ID), at 23 °C and 37 °C, over a period of one and four-months (n = 5) to gain information on long-term immersion. Part 2: Five experimental materials were formulated: Exp-I and II as hydrophobic and Exp-III-V as hydrophilic, containing an additional cross-linking agent (TFDMSOS) and Rhodasurf CET-2 surfactant. Their water uptake and desorption (both at 23 °C) properties (gravemetrically), solubility, pH and diffusion coefficient (DC) data were compared with three commercial, hydrophilic VPS impression materials, over seven days (n = 5). The results were analysed statistically. RESULTS: Part 1: Significant differences in water absorbed by AqM were observed in the three media at 23 °C. Aq M had a significantly higher uptake in 2% Perform ID, than in DW and NaOCl. At 37 °C, over four-months the uptake profiles were more enhanced and differed. Part 2: All Exp and commercial materials significantly increased in weight in both media (DW and 1% NaOCl at 23 °C), with differing uptake profiles and non-reached equilibrium. Exp-VPS absorbed significantly less water than commercial-VPS. Desorption of all VPS from both parts was faster than absorption, followed Fickian diffusion kinetics and reached equilibrium within 1-3 days. Desorption DCs for Exp-VPS were higher than commercial materials (10-10 versus 10-11 m2 s-1). The solubility was higher in 1% NaOCl compared to DW. The pH of DW after immersion of samples significantly increased compared to 1% NaOCl. SIGNIFICANCE: The incorporation of novel cross-linking agent, TFDMSOS and non-ionic surfactant, Rhodasurf CET-2, (ethoxylated-cetyl-oleyl alcohol) improved the dimensional stability of hydrophilic Exp-VPS in DW and 1% NaOCl. These materials merit further research in producing accurate casts of the patient's anatomy following disinfection.

Novel fluoride rechargeable dental composites containing MgAl and CaAl layered double hydroxide (LDH).

OBJECTIVE: This study aims to incorporate 2:1 MgAl and 2:1 CaAl layered double hydroxides (LDHs) in experimental dental-composites to render them fluoride rechargeable. The effect of LDH on fluoride absorption and release, and their physico-mechanical properties are investigated. METHODS: 2:1 CaAl and 2:1 MgAl LDH-composite discs prepared with 0, 10 and 30wt% LDH were charged with fluoride (48h) and transferred to deionized water (DW)/artificial saliva (AS). Fluoride release/re-release was measured every 24h (ion-selective electrodes) with DW/AS replaced daily, and samples re-charged (5min) with fluoride every 2 days. Five absorption-release cycles were conducted over 10 days. CaAl and MgAl LDH rod-shaped specimens (dry and hydrated; 0, 10 and 30wt%) were studied for flexural strength and modulus. CaAl and MgAl LDH-composite discs (0, 10, 30 and 45wt% LDH) were prepared to study water uptake (over 7 weeks), water desorption (3 weeks), diffusion coefficients, solubility and cation release (ICP-OES). RESULTS: CaAl LDH and MgAl LDH-composites significantly increased the amount of fluoride released in both media (P<0.05). In AS, the mean release after every recharge was greater for MgAl LDH-composites compared to CaAl LDH-composites (P<0.05). After every recharge, the fluoride release was greater than the previous release cycle (P<0.05) for all LDH-composites. Physico-mechanical properties of the LDH-composites demonstrated similar values to those reported in literature. The solubility and cation release showed a linear increase with LDH loading. SIGNIFICANCE: LDH-composites repeatedly absorbed/released fluoride and maintained desired physico-mechanical properties. A sustained low-level fluoride release with LDH-composites could lead to a potential breakthrough in preventing early stage carious-lesions.

Polymerization shrinkage kinetics and degree of conversion of commercial and experimental resin modified glass ionomer luting cements (RMGICs).

OBJECTIVES: Tetrahydrofurfuryl-methacrylate (THFM) and hydroxypropyl-methacrylate (HPM) were used to partially or fully replace HEMA in experimental RMGICs. The experimental materials were compared with home and commercial products in terms of degree of conversion, polymerization shrinkage and exotherm. METHODS: Two commercial RMGICs used were Fuji-Plus (FP, GC, Japan) and RelyX-Luting (RX, 3M-ESPE, USA). Two additional in-house liquids were prepared based on the commercial materials liquids. Eight experimental liquid compositions (F1, F2, F3 and F4 based on Fuji-Plus; R1, R2, R3 and R4 based on RelyX-Luting) were prepared replacing 100% HEMA with HPM in F1 and R1 or 70%/30% HPM/THFM in F2 and R2. 50% HEMA was replaced with THFM in F3 and R3 compared to 30% in F4 and R4. All liquids were mixed with the corresponding commercial powder. Degree of conversion was determined using Fourier-transform infrared spectroscopy (FT-IR). Polymerization shrinkage and exotherm were measured using the bonded-disk method. RESULTS: Compositions containing HPM (F1 and R1) showed lower degree of conversion compared to experimental compositions containing THFM, home and commercial materials (p<0.0001). FP-commercial showed significantly higher polymerization shrinkage and exotherm compared to all other materials in both groups (p<0.0001). FP-commercial showed higher degree of polymerization shrinkage and exotherm at 5min compared to all materials due to the incorporation of an additional cross-linker (glycerol-dimethacrylate). In general, compositions containing THFM, presented polymerization shrinkage and degree of conversion values similar to their corresponding commercial products. SIGNIFICANCE: THFM monomer showed promising results and could be potentially useful in the development of new RMGICs with improved properties.

Layered Double Hydroxide Fluoride Release in Dental Applications: A Systematic Review.

This systematic review appraises studies conducted with layered double hydroxides (LDHs) for fluoride release in dentistry. LDH has been used as antacids, water purification in removing excess fluoride in drinking water and drug delivery. It has great potential for controlled fluoride release in dentistry, e.g., varnishes, fissure sealants and muco-adhesive strips, etc. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement was followed with two reviewers performing a literature search using four databases: PubMed, Web of Science, Science Direct and Ovid Medline with no date restrictions. Studies including any LDH for ion/drug release in dentistry were included, while assessing the application of LDH and the value of the methodology, e.g., ion release protocol and the LDH production process. Results: A total of 258 articles were identified and four met the inclusion criteria. Based on two in vitro studies and one clinical study, LDH was previously studied in dental materials, such as dental composites and buccal muco-adhesive strips for fluoride release, with the latter studied in a clinical environment. The fourth study analysed LDH powder alone (without being incorporated into dental materials). It demonstrated fluoride release and the uptake of volatile sulphur compounds (VSC), which may reduce halitosis (malodour). Conclusion: LDHs incorporated in dental materials have been previously evaluated for fluoride release and proven to be clinically safe. LDHs have the potential to sustain a controlled release of fluoride (or other cariostatic ions) in the oral environment to prevent caries. However, further analyses of LDH compositions, and clinical research investigating any other cariostatic effects, are required.

The effects of cross-linking agent and surfactant on the tear strength of novel vinyl polysiloxane impression materials.

OBJECTIVES: To formulate experimental hydrophobic and hydrophilic vinyl polysiloxane (VPS) impression materials ab initio, comprising a novel cross-linking agent, tetra-functional (dimethylsilyl) orthosilicate (TFDMSOS), and a non-ionic surfactant, Rhodasurf CET-2 (ethoxylatedcetyl-oleyl alcohol), and to investigate their effects on tear strength (TS). METHODS: Five experimental formulations (Exp I-V) were prepared and compared with three medium bodied commercial VPS impression materials (Aq M, Elt M, Extr M). Tear test was performed on trouser test specimens (n=12 per material), at four time points (immediately, 24, 72 and 168 hours after setting). FTIR spectroscopy was used for identifying functional bonds and cross-linking. The results were analysed with one-way ANOVA, two-way ANOVA and post hoc Tukey's test using the SPSS PASW statistical 22 software. RESULTS: The material with novel cross-linking agent (Exp II) had significantly higher TSs at all-time points compared to Exp I (control; p˂0.05). Materials incorporating both TFDMSOS and surfactant (Exp III, IV and V), had further significantly increased TS at all-time points, which were concentration dependent. Extr M had a significantly lower TS (immediately after setting and at 24 hours) compared to all Exp and other commercial materials, with the exception of Elt M (difference not significant). The TSs of Exp II-V, after 72 and 168 hours, were significantly higher for than all commercial products and Exp I. FTIR spectra showed the consumption of Si-H groups indicating crosslinking had taken place with the addition of TFDMSOS and surfactant which contributed to an increase in the TS. SIGNIFICANCE: TFDMSOS cross-linking agent increased the TS of Exp II significantly at all-time points compared to the control. Novel surfactant further significantly increased TS, and it was also concentration dependent. Exp VPS with improved TS have been developed, addressing one of the drawbacks of commercial VPS materials.

Development of a novel bioactive glass for air-abrasion to selectively remove orthodontic adhesives.

OBJECTIVES: To develop a novel, bioactive glass for removing residual orthodontic adhesive via air-abrasion, following bracket debonding, and to evaluate its effectiveness against a proprietary bioactive glass 45S5(Sylc™)-air-abrasion, and a slow-speed tungsten carbide (TC) bur. MATERIALS AND METHODS: Three glasses were prepared and their bioactivity was proved. One novel glass (QMAT3) was selected due to its appropriate hardness, lower than that of enamel/45S5(Sylc™). Sixty extracted human premolars were randomly assigned to adhesive removal using: (a) QMAT3-air-abrasion, (b) 45S5(Sylc™)-air-abrasion, and (c) TC bur, which were further subdivided (n = 10) based on the adhesive used (Transbond XT™ or Fuji Ortho LC™). Enamel roughness was assessed using scanning electron microscopy (SEM) and non-contact profilometry before bracket bonding, after removing residual adhesive following bracket debonding and after polishing. RESULTS: QMAT3 formed apatite faster (6 h) than 45S5(Sylc™) (24 h) in Tris solution. QMAT3-air-abrasion gave the lowest enamel roughness (Ra) after removing the adhesives. SEM images showed a pitted, roughened enamel surface in the TC bur group and to a lesser extent with 45S5(Sylc™), while a virtually smooth surface without any damage was observed in the QMAT3-air-abrasion group. The time taken for adhesive removal with QMAT3 was comparable to 45S5(Sylc™) but was twice as long with the TC bur. CONCLUSIONS: QMAT3-air-abrasion is a promising technique for selective removal of adhesives without inducing tangible enamel damage. CLINICAL RELEVANCE: A novel bioactive glass has been developed as an alternative to the use of TC burs for orthodontic adhesive removal.