Resin tags formation by modified Renewal MI formulations in a carious dentine model.

Objectives: To determine which components in a new restorative material (Renewal MI) improve its ability to form resin tags within demineralized dentine. Methods: Varied components included polylysine (PLS), monocalcium phosphate (MCP), powder to liquid ratio (PLR), 4-methacryloyloxyethyl trimellitate anhydride (4META), and polypropylene glycol dimethacrylate (PPGDMA). Urethane dimethacrylate (UDMA), containing PPGDMA (24 wt%) and 4META (3 wt%), was mixed with glass filler with MCP (8 wt%) and PLS (5 wt%). PLR was 3:1 or 5:1. Reducing MCP and/or PLS to 4 and 2 wt% respectively or fully removing MCP, PLS, 4META or PPGDMA gave 16 formulations in total. Renewal MI, Z250 (with or without Scotchbond Universal adhesive) and Activa were used as commercial comparators. Collagen discs were obtained by totally demineralizing 2 mm thick, human, premolar, coronal dentine discs by immersion in formic acid (4M) for 48 h. The restorative materials were then applied on top (n = 3), before dissolving the collagen in sodium hypochlorite (15%). SEM/EDX was employed to determine resin tags length, composition, and surface coverage. Results: Tags were >400, 20 and 200 µm and covered 62, 55 and 39% of the adhesion interface for Renewal MI, Scotchbond and Activa, respectively. With experimental formulations, they were 200 and >400 µm long with high vs. low PLR and composed primarily of polymerized monomers. Percentages of the adhesion interface covered varied between 35 and 84%. Reducing PLS or MCP caused a decline in coverage that was linear with their concentrations. Reducing MCP had lesser effect when PLS or PLR were low. Removal of 4META caused a greater reduction in coverage than PPGDMA removal. Conclusion: PLS, MCP, 4META, PPGDMA and low PLR together enhance Renewal MI tags formation in, and thereby sealing of, demineralized dentine.

Evaluation of setting kinetics, mechanical strength, ion release, and cytotoxicity of high-strength glass ionomer cement contained elastomeric micelles.

BACKGROUND: Low mechanical properties are the main limitation of glass ionomer cements (GICs). The incorporation of elastomeric micelles is expected to enhance the strength of GICs without detrimentally affecting their physical properties and biocompatibility. This study compared the chemical and mechanical properties, as well as the cytotoxicity, of elastomeric micelles-containing glass ionomer cement (DeltaFil, DT) with commonly used materials, including EQUIA Forte Fil (EF), Fuji IX GP Extra (F9), and Ketac Molar (KT). METHOD: Powder particles of GICs were examined with SEM-EDX. Setting kinetics were assessed using ATR-FTIR. Biaxial flexural strength/modulus and Vickers surface microhardness were measured after immersion in water for 24 h and 4 weeks. The release of F, Al, Sr, and P in water over 8 weeks was analyzed using a fluoride-specific electrode and ICP-OES. The toxicity of the material extract on mouse fibroblasts was also evaluated. RESULTS: High fluoride levels in the powder were detected with EF and F9. DT demonstrated an initial delay followed by a faster acid reaction compared to other cements, suggesting an improved snap set. DT also exhibited superior flexural strength than other materials at both 24 h and 4 weeks but lower surface microhardness (p < 0.05). EF and F9 showed higher release of F, Al, and P than DT and KT. There was no statistically significant difference in fibroblast viability among the tested materials (p > 0.05). CONCLUSIONS: Elastomeric micelles-containing glass ionomer cement (DT) exhibited satisfactory mechanical properties and cytocompatibility compared with other materials. DT could, therefore, potentially be considered an alternative high-strength GIC for load-bearing restorations.

Drug development for major chronic health conditions-aligning with growing public health needs: Proceedings from a multistakeholder think tank.

The global pharmaceutical industry portfolio is skewed towards cancer and rare diseases due to more predictable development pathways and financial incentives. In contrast, drug development for major chronic health conditions that are responsible for a large part of mortality and disability worldwide is stalled. To examine the processes of novel drug development for common chronic health conditions, a multistakeholder Think Tank meeting, including thought leaders from academia, clinical practice, non-profit healthcare organizations, the pharmaceutical industry, the Food and Drug Administration (FDA), payors as well as investors, was convened in July 2022. Herein, we summarize the proceedings of this meeting, including an overview of the current state of drug development for chronic health conditions and key barriers that were identified. Six major action items were formulated to accelerate drug development for chronic diseases, with a focus on improving the efficiency of clinical trials and rapid implementation of evidence into clinical practice.

Creating Equitable and Inclusive Clinical Trials for Multiple Myeloma.

Black and Latino/Hispanic populations are disproportionately impacted by multiple myeloma (MM) in the United States and are underrepresented in many clinical trials. The Multiple Myeloma Research Foundation sponsored a 1-day workshop of 46 experts spanning the ecosystem of MM research and care, including government, academia, nonprofits, pharma/biotech, community partners, and retail pharmacy. Specific, tangible steps to overcome the well-documented barriers to improving the diversity and inclusivity of clinical trials were discussed, including broadening inclusion/exclusion criteria, reducing the financial and other burdens of trial participants, selecting diverse study sites, including implicit bias training, and taking steps to empower patients.

Assessment of physical/mechanical properties and cytotoxicity of dual-cured resin cements containing Sr-bioactive glass nanoparticles and calcium phosphate.

The aim was to develop dual-cured resin cements containing Sr-bioactive glass nanoparticles (Sr-BGNPs; 5 or 10 wt%) and monocalcium phosphate monohydrate (MCPM; 3 or 6 wt%). Effects of additives on degree of monomer conversion (DC), biaxial flexural strength/modulus, shear bond strength (SBS), mass/volume change, color stability, ion release, and cytotoxicity were examined. Controls included material without reactive fillers and Panavia SA Plus (PV). Experimental cements showed higher DC than PV regardless of light activation (p<0.05). Mean SBS and color stability were comparable between experimental cements and PV. Cell viability upon the exposure to sample extracts of experimental cements was 80%-92%. High additive concentrations led to lower strength and modulus than PV (p<0.05). The additives increased mass change, reduced color stability, and promoted ion release. The experimental resin cements demonstrated acceptable mechanical/chemical properties and cytotoxicity. The additives reduced the strength but provided ion release, a desirable action to prevent recurrent caries.

Modifying dental composites to formulate novel methacrylate-based bone cements with improved polymerisation kinetics, and mechanical properties.

OBJECTIVES: The aim was to develop bone composites with similar working times, faster polymerisation and higher final conversion in comparison to Cortoss™. Additionally, low shrinkage/heat generation and improved short and longer-term mechanical properties are desirable. METHODS: Four urethane dimethacrylate based composites were prepared using tri-ethylene-glycol dimethacrylate (TEGDMA) or polypropylene dimethacrylate (PPGDMA) diluent and 0 or 20 wt% fibres in the glass filler particles. FTIR was used to determine reaction kinetics, final degrees of conversions, and polymerisation shrinkage/heat generation at 37 °C. Biaxial flexural strength, Young's modulus and compressive strength were evaluated after 1 or 30 days in water. RESULTS: Experimental materials all had similar inhibition times to Cortoss™ (140 s) but subsequent maximum polymerisation rate was more than doubled. Average experimental composite final conversion (76%) was higher than that of Cortoss™ (58%) but with less heat generation and shrinkage. Replacement of TEGDMA by PPGDMA gave higher polymerisation rates and conversions while reducing shrinkage. Early and aged flexural strengths of Cortoss™ were 93 and 45 MPa respectively. Corresponding compressive strengths were 164 and 99 MPa. Early and lagged experimental composite flexural strengths were 164-186 and 240-274 MPa whilst compressive strengths were 240-274 MPa and 226-261 MPa. Young's modulus for Cortoss™ was 3.3 and 2.2 GPa at 1 day and 1 month. Experimental material values were 3.4-4.8 and 3.0-4.1 GPa, respectively. PPGDMA and fibres marginally reduced strength but caused greater reduction in modulus. Fibres also made the composites quasi-ductile instead of brittle. SIGNIFICANCE: The improved setting and higher strengths of the experimental materials compared to Cortoss™, could reduce monomer leakage from the injection site and material fracture, respectively. Lowering modulus may reduce stress shielding whilst quasi-ductile properties may improve fracture tolerance. The modified dental composites could therefore be a promising approach for future bone cements.

The effect of varying monocalcium phosphate and polylysine levels on dental composite properties.

OBJECTIVES: The aim was to quantify effects of polylysine (PLS, 2 or 5 wt%) and monocalcium phosphate (MCP, 4 or 8 wt%) on properties of dental composites. METHODS: Light-activated, lower surface polymerisation kinetics versus sample depth (1-4 mm) of 4 formulations were quantified using ATR-FTIR. Water sorption and solubility (at 1 week) were assessed following ISO/4049. PLS release (over 1 month) and biaxial flexural strength (over 6 months) of fully-cured, water-immersed, 1 mm thick discs were determined. Surface mineral precipitation, following immersion in simulated body fluid (SBF), was assessed by SEM. Z250 was used as a conventional composite comparator. RESULTS: With 40s light exposure, increasing depth (from 1 to 4 mm) led to enhanced delay before polymerisation (from 3 to 17s) and decreased final conversion (72-66%) irrespective of PLS and MCP level. Increasing PLS and MCP raised solubility (4-13 µg/mm3). Water sorption (between 32 and 55 µg/mm3) and final PLS release (8-13% of disc content) were raised primarily by increasing PLS. Higher PLS also reduced strength. Strength reached minimum values (69-94 MPa) at 3 months. Surface mineral deposition was enhanced by increased MCP. For Z250, polymerisation delays (3-6s) and final conversions (55-54%) at 1-4 mm depth, solubility (0 µg/mm3), water sorption (16 µg/mm3) and strength (180 MPa) were all significantly different. CONCLUSION: Delay time increased whilst final conversion decreased with thicker samples. Higher PLS enhances its percentage release, but lower level is required to keep water sorption, solubility and mechanical properties within ISO 4049 recommendations. Doubling MCP raises solubility and enhances minerals reprecipitation with minimal mechanical property compromise.

Assessment of Mechanical/Chemical Properties and Cytotoxicity of Resin-Modified Glass Ionomer Cements Containing Sr/F-Bioactive Glass Nanoparticles and Methacrylate Functionalized Polyacids.

This study prepared low-toxicity, elemental-releasing resin-modified glass ionomer cements (RMGICs). The effect of 2-hydroxyethyl methacrylate (HEMA, 0 or 5 wt%) and Sr/F-bioactive glass nanoparticles (Sr/F-BGNPs, 5 or 10 wt%) on chemical/mechanical properties and cytotoxicity were examined. Commercial RMGIC (Vitrebond, VB) and calcium silicate cement (Theracal LC, TC) were used as comparisons. Adding HEMA and increasing Sr/F-BGNPs concentration decreased monomer conversion and enhanced elemental release but without significant effect on cytotoxicity. Rising Sr/F-BGNPs reduced the strength of the materials. The degree of monomer conversion of VB (96%) was much higher than that of the experimental RMGICs (21-51%) and TC (28%). The highest biaxial flexural strength of experimental materials (31 MPa) was significantly lower than VB (46 MPa) (p < 0.01) but higher than TC (24 MPa). The RMGICs with 5 wt% HEMA showed higher cumulative fluoride release (137 ppm) than VB (88 ppm) (p < 0.01). Unlike VB, all experimental RMGICs showed Ca, P, and Sr release. Cell viability in the presence of extracts from experimental RMGICs (89-98%) and TC (93%) was significantly higher than for VB (4%). Experimental RMGICs showed desirable physical/mechanical properties with lower toxicity than the commercial material.

ICAM-1-mediated osteoblast-T lymphocyte direct interaction increases mineralization through TGF-ß1 suppression.

Modulation of osteoblast functions by T lymphocytes is important in inflammation-associated mineralized tissue diseases. The study aimed to determine whether direct interaction between these two cell types affects osteoblast functions and mineralization. The results showed that direct contact between the two cell types was evident by scanning electron microscopy and transmission electron microscopy. Under osteogenic induction, higher hydroxyapatite precipitation was observed in cocultures with direct contact with T lymphocytes compared with that by osteoblasts cultured alone. Cocultures without direct cell contact caused a decrease in mineralization. Direct cell contact also upregulated intercellular adhesion molecule (ICAM)-1 and simultaneously downregulated transforming growth factor (TGF)-ß1 in osteoblasts. However, the downregulation of TGF-ß1 was reversed by ICAM-1 blocking. Exogenously added TGF-ß1 in cocultures with direct cell contact suppressed mineralization. In conclusion, studies are consistent with ICAM-1-mediated direct contact between osteoblasts and T lymphocytes increasing mineralization via downregulation of TGF-ß1 in osteoblasts in vitro. This suggests a possible unexpected, but crucial, role of T lymphocytes in enhancing matrix mineralization during the repair process in vivo. The study identifies ICAM-1/TGF-ß1 as possible novel therapeutic targets for the treatment and prevention of inflammation-associated mineralized tissue diseases.

Effects of Novel Dental Composites on Streptococcus mutans Biofilms.

With the phase-out of amalgam and the increase in minimally invasive dentistry, there is a growing need for high-strength composite materials that can kill residual bacteria and promote tooth remineralization. This study quantifies how antibacterial polylysine (PLS) and re-mineralizing monocalcium phosphate monohydrate (MCPM) affect Streptococcus mutans biofilms and the strength of dental composites. For antibacterial studies, the MCPM-PLS filler percentages were 0-0, 8-4, 12-6, and 16-8 wt% of the composite filler phase. Composite discs were immersed in 0.1% sucrose-supplemented broth containing Streptococcus mutans (UA159) and incubated in an anaerobic chamber for 48 h. Surface biomass was determined by crystal violet (CV) staining. Growth medium pH was measured at 24 and 48 h. Biofilm bacterial viability (CFU), exo-polysaccharide (water-soluble glucan (WSG) and water-insoluble glucan (WIG)), and extracellular DNA (eDNA) were quantified. This was by serial dilution plate counting, phenol-sulfuric acid microassay, and fluorometry, respectively. The biaxial flexural strengths were determined after water immersion for 1 week, 1 month, and 1 year. The MCPM-PLS wt% were 8-4, 8-8, 16-4 and 16-8. The normalized biomass, WSG, and WIG showed a linear decline of 66%, 64%, and 55%, respectively, as the PLS level increased up to 8%. The surrounding media pH (4.6) was all similar. A decrease in bacterial numbers with the 12-6 formula and a significant reduction with 16-8 compared to the 0-0 formulation was observed. The eDNA concentrations in biofilms formed on 12-6 and 16-8 formulations were significantly less than the 0-0 control and 8-4 formulations. Doubling MCPM and PLS caused a 14 and 19% reduction in strength in 1 week, respectively. Average results were lower at 1 month and 1 year but affected less upon doubling MCPM and PLS levels. Moreover, a 4% PLS may help to reduce total biomass and glucan levels in biofilms on the above composites. Higher levels are required to reduce eDNA and provide bactericidal action, but these can decrease early strength.

Assessment of Physical/Mechanical Performance of Dental Resin Sealants Containing Sr-Bioactive Glass Nanoparticles and Calcium Phosphate.

The aim of this study was to assess the chemical/mechanical properties of ion-releasing dental sealants containing strontium-bioactive glass nanoparticles (Sr-BGNPs) and monocalcium phosphate monohydrate (MCPM). Two experimental sealants, TS1 (10 wt% Sr-BGNPs and 2 wt% MCPM) and TS2 (5 wt% Sr-BGNPs and 4 wt% MCPM), were prepared. Commercial controls were ClinproXT (CP) and BeautiSealant (BT). The monomer conversion (DC) was tested using ATR−FTIR (n = 5). The biaxial flexural strength (BFS) and modulus (BFM) were determined (n = 5) following 24 h and 7 days of immersion in water. The Vickers surface microhardness (SH) after 1 day in acetic acid (conc) versus water was tested (n = 5). The bulk and surface calcium phosphate precipitation in simulated body fluid was examined under SEM-EDX. The ion release at 4 weeks was analyzed using ICP-MS (n = 5). The DC after 40 s of light exposure of TS1 (43%) and TS2 (46%) was significantly lower than that of CP (58%) and BT (61%) (p < 0.05). The average BFS of TS1 (103 MPa), TS2 (123 MPa), and BT (94 MPa) were lower than that of CP (173 MPa). The average BFM and SH of TS1 (2.2 GPa, 19 VHN) and TS2 (2.0 GPa, 16 VHN) were higher than that of CP (1.6 GPa, 11 VHN) and BT (1.3 GPa, 12 VHN). TS1 showed higher Ca, P, and Sr release than TS2. Bulk calcium phosphate precipitation was detected on TS1 and TS2 suggesting some ion exchange. In conclusion, the DC of experimental sealants was lower than that of commercial materials, but their mechanical properties were within the acceptable ranges. The released ions may support remineralizing actions.

Impact of Dentine Pretreatment with Matrix Metalloproteinase Inhibitors on Bond Strength of Coronal Composite Restorations: A Systematic Review and Meta-analysis of In Vitro Studies.

OBJECTIVES: Matrix metalloproteinase (MMP) enzymes participate in collagen matrix degradation, including in dentine, potentially compromising bond strength. Therefore, MMP inhibitors have been hypothesized to improve restoration bond strength and stability. This systematic review aimed to evaluate the influence of different MMP inhibitors applied as dentine surface pretreatments on the immediate (24 hours) and longer term (months) bond strength of direct coronal composite restorations. MATERIALS AND METHODS: This systematic literature review followed the Preferred Reporting Items for Systematic Review and Meta-analyses (PRISMA) statement. A systematic literature search of three databases (Ovid MEDLINE, Ovid Embase, and Google Scholar) was conducted independently by two reviewers from inception to April 2022. An adapted quality assessment tool was independently applied by two reviewers for risk of bias assessment. STATISTICAL ANALYSIS: RevMan v5.4 software was used for meta-analyses. A random-effects model was used to generate mean differences with 95% confidence intervals for treatment and control comparisons. The Q-test and I2 -test were used to test for heterogeneity. The proportion of total variance across studies attributable to heterogeneity rather than chance was calculated. Overall effects were tested using the Z-test, while subgroup differences were tested using Chi-squared tests. RESULTS: Of 934 studies, 64 studies were included in the systematic review and 42 in the meta-analysis. Thirty-one MMP inhibitors were reported, three of which were included in the meta-analysis: 2% chlorhexidine (CHX), 0.3 M carbodiimide (EDC), and 0.1% riboflavin (RIBO). Pretreatment with 2% CHX for 30 and 60 seconds did not significantly improve bond strength compared with controls either immediately or after long-term ageing. However, pretreatment with 0.3 M EDC and 0.1% RIBO (but not CHX) significantly improved bond strength compared with control groups both immediately and over time. Most studies showed a medium risk of bias. CONCLUSIONS: These in vitro findings pave the way for rationale clinical trialing of dentine surface pretreatment with MMP inhibitors to improve clinical outcomes.

Incorporation of MMP inhibitors into dental adhesive systems and bond strength of coronal composite restorations: A systematic review and meta-analysis of in vitro studies.

Purpose: To systematically review in vitro studies that incorporated MMP inhibitors into adhesive systems in terms of the effect on immediate and aged bond strength of dental composite to dentine. Materials and methods: Independently, two reviewers conducted an electronic search in three databases (MEDLINE, EMBASE, and Google Scholar) following the Preferred Reporting Items for Systematic Review and Meta-Analyses Protocols (PRISMA-P), up to 6 March 2022. Results: The search resulted in 894 papers, 33 of which were eligible to be included in the review; of those, 13 fulfilled the meta-analysis eligibility criteria. Nineteen inhibitors were used among the studies, and those included in the meta-analysis were 2%, 0.2% chlorhexidine (CHX), 5 µM GM1489, and 0.5%, 1% benzalkonium chloride (BAC). In the meta-analysis, while above inhibitors showed no adverse effect on bond strength, 0.2% CHX and 5 µM GM1489 caused a significant increase in immediate and 12-months bond strength. All other inhibitors resulted in a significant increase in bond strength at six months of ageing. Conclusions: Incorporation of MMP inhibitors into the adhesive system has no unfavourable effect on immediate bond strength but a favourable effect on longer-term bond strength. Additionally, inhibitors other than CHX could have similar or better effects on bond strength.

Renewal MI Dental Composite Etch and Seal Properties.

This study's aim was to assess whether the Renewal MI composite can self-etch enamel, seal sound cavities, and stabilize demineralized dentine. Etching was assessed using scanning electron microscopy (SEM). Cavity sealing was quantified using the ISO-11405 dye microleakage test. Demineralized dentine stabilization was evaluated by visualizing resin tag formation, enzyme activity and mineral precipitation at the adhesion interface. Renewal MI provided a mild etching of sound enamel in comparison with 37% phosphoric acid. It provided a comparable seal of sound cavities to Z250/Scotchbond Universal adhesive and a superior seal to Activa, Fuji IX and Fuji II LC. With demineralized dentine, Renewal MI formed 300-400 µm resin tags covering 63% of the adhesion interface compared with 55 and 39% for Z250/Scotchbond and Activa. Fuji IX and Fuji II LC formed no resin tags. A higher tag percentage correlated with lower surface enzyme activity. Unlike Activa and Fuji II LC, Renewal MI promoted mineral precipitation from simulated body fluid, occluding adjacent dentinal tubules within 6 months. These novel etching and sealing properties may facilitate Renewal MI's application in minimally invasive dentistry.

Determination of Dental Adhesive Composition throughout Solvent Drying and Polymerization Using ATR-FTIR Spectroscopy.

The of this study aim was to develop a rapid method to determine the chemical composition, solvent evaporation rates, and polymerization kinetics of dental adhesives. Single-component, acetone-containing adhesives One-Step (OS; Bisco, Anaheim, CA, USA), Optibond Universal (OU; Kerr, Brea, CA, USA), and G-Bond (GB; GC, Tokyo, Japan) were studied. Filler levels were determined gravimetrically. Monomers and solvents were quantified by comparing their pure Attenuated Total Reflectance-Fourier Transform Infra-Red (ATR-FTIR) spectra, summed in different ratios, with those of the adhesives. Spectral changes at 37 °C, throughout passive evaporation for 5 min, then polymerisation initiated by 20 s, and blue light emitting diode (LED) (600 mW/cm2) exposure (n = 3) were determined. Evaporation and polymerisation extent versus time and final changes were calculated using acetone (1360 cm-1) and methacrylate (1320 cm-1) peaks. OS, OU, and GB filler contents were 0, 9.6, and 5.3%. FTIR suggested OS and OU were Bis-GMA based, GB was urethane dimethacrylate (UDMA) based, and that each had a different diluent and acidic monomers and possible UDMA/acetone interactions. Furthermore, initial acetone percentages were all 40-50%. After 5 min drying, they were 0% for OS and OU but 10% for GB. Whilst OS had no water, that in OU declined from 18 to 10% and in GB from 25 to 20% upon drying. Evaporation extents were 50% of final levels at 23, 25, and 113 s for OS, OU, and GB, respectively. Polymerisation extents were all 50 and 80% of final levels before 10 and at 20 s of light exposure, respectively. Final monomer polymerisation levels were 68, 69, and 88% for OS, OU, and GB, respectively. An appreciation of initial and final adhesive chemistry is important for understanding the properties. The rates of evaporation and polymerisation provide indications of relative required drying and light cure times. UDMA/acetone interactions might explain the considerably greater drying time of GB.

Varying 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) level improves polymerisation kinetics and flexural strength in self-adhesive, remineralising composites.

OBJECTIVES: To assess the influence of systematically varying concentrations of 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) versus 3% 4-META on the polymerisation kinetics and shrinkage, biaxial flexural strength (BFS) and modulus of remineralising composites. METHODS: Composites were prepared by adding poly(propylene glycol) dimethacrylate (24 wt%), camphorquinone (1 wt%) and MDP (0%, 5%, 10%, 15% and 20 wt%) or 4-META (3%) to urethane dimethacrylate. These were mixed with glass fillers containing 8 wt% monocalcium phosphate and 4 wt% polylysine (powder-liquid ratio of 3:1). Continuous spectral changes, following 20 s light exposure (37 °C), were assessed with an ATR-FTIR to monitor polymerisation kinetics (n = 3). Final extrapolated conversions (DC,max) were employed to calculate polymerisation shrinkage. BFS and modulus of 24-h dry stored disc specimens (10 × 1 mm; n = 10) were determined using a ball-on-ring jig setup. RESULTS: Maximum rate of polymerisation and DC,max increased linearly from 2.5 to 3.5% s-1 and 67 to 83%, respectively, upon increasing MDP from 0 to 20 wt%. Values with 3% 4-META were 2.6% s-1 and 78%. Shrinkage was 3.8 ± 0.3% for all formulations. Raising 4-META or MDP from 0 to 3 versus 5%, respectively, increased strength from 106 to 145 versus 136 MPa. A decreasing trend with higher MDP concentrations was noted. Elastic modulus showed no specific trend upon MDP increase. SIGNIFICANCE: Whilst final conversion levels were enhanced by 3% 4-META or >5% MDP, trends did not correlate with strength. Peak strengths with 3% 4-META or 5% MDP may therefore be due to acidic monomers providing linkage between the hydrophilic, non-silane treated particles and the polymer matrix.

Methacrylate peak determination and selection recommendations using ATR-FTIR to investigate polymerisation of dental methacrylate mixtures.

Investigation of polymerisation kinetics using ATR-FTIR systems is common in many dental studies. However, peak selection methods to calculate monomer-polymer conversion can vary, consequently affecting final results. Thus, the aim of this study is to experimentally confirm which method is less prone to systematic errors. Three commercial restorative materials were tested-Vertise Flow (VF), Constic and Activa Bioactive Restorative Kids. Firstly, Attenuated Total Reflectance Fourier Transform Infra-Red (ATR-FTIR) (Spectrum One, Perkin-Elmer, UK) spectra of monomers were acquired-10-methacryloyloxy decyl dihydrogen phosphate (10-MDP), bisphenol-A glycidyl dimethacrylate (Bis-GMA), 2-hydroxyethyl methacrylate (HEMA), triethyelene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA) to investigate proportionality of methacrylate peak heights versus concentration. Spectral changes upon light exposure of 2 mm discs of the restorative materials (irradiated for 20 s, LED curing unit 1100-1330 mW/cm2) were assessed to study polymerisation kinetics (n = 3), with continuous acquisition of spectra, before, during and after light exposure. Peak differences and degrees of conversion (DC %) were calculated using 1320/1336, 1320/1350 and 1636/1648 cm-1 as reaction/reference peaks. Inferential statistics included a MANOVA and within-subjects repeated measures ANOVA design (5% significance level). Proportionality of methacrylate peak height to concentration was confirmed, with the 1320/1352 cm-1 peak combination showing the lowest coefficient of variation (8%). Difference spectra of the polymerisation reaction showed noise interference around the 1500-1800 cm-1 region. Across the different materials, DC % results are highly dependent upon peak selection (p<0.001), with higher variability associated to the 1636 cm-1. Significant differences in the materials were only detected when the 1320 cm-1 peak was used (p<0.05). Within the same materials, methods were significantly different for Constic and Activa (p<0.05). It is possible to conclude that the 1320 cm-1 peak is more adequate to assess polymerisation of methacrylates and is therefore recommended.