Multi-response optimisation analysis of material properties in dental restorative composites under the influence of thermal and thermomechanical stimuli - A 3D finite element study.

OBJECTIVES: Restored teeth undergo more damage than intact teeth. Therefore, the scientific investigation of their mechanical and physical behaviour under varying oral conditions is vital. The current study is to numerically investigate the stresses on a class-II mesio-occluso-distal (MOD) restored molar due to thermal and thermomechanical stimuli with varying input properties such as coefficient of thermal expansion and elastic properties. This is performed to optimise the dental restoration material, thereby reducing the stresses and failure of the restoration. METHODS: An upper molar was scanned using µ-CT for segmenting and modelling the enamel and dentine. A class-II MOD cavity was then prepared on the model, after which non-manifold meshing was generated. The coefficient of thermal expansion (CTE) and elastic modulus (E) properties of the restoration were varied from 20 × 10-6 °C-1 to 55 × 10-6 °C-1 and 5 GPa-20 GPa, respectively. After the material properties and boundary conditions were set for the finite element (FE) analysis, the thermal and thermomechanical loading analyses were performed to demonstrate the influence of input parameters on the stress. The maximum values of principal stresses on the restoration-enamel junction and the restoration were evaluated. The results were statistically processed using analysis of variance, response surface methodology (RSM) and optimisation analysis to estimate the most optimum inputs for minimising principal stresses. RESULTS: The study reveals that the location of principal stress occurs at the restoration-enamel junction (REJ) and the restoration changes based on the composite material value of E and CTE due to thermal and thermomechanical stimuli. The REJ showed higher principal stress than restoration during the application of both thermal and thermomechanical stimuli, making it more vulnerable to fracture and failure. Moreover, the study showed non-linear variations in the values and locations of principal stresses due to thermal and thermomechanical stimuli with the change in the property of the restoration composite used. Finally, this study derived an optimised restorative value for CTE and E due to the application of thermal and simultaneous thermal and mechanical stimuli. CONCLUSION: This study highlights the importance of choosing the suitable material properties of the restoration composite by dental clinicians to repair a large class MOD cavity. The findings from this study also suggest that the difference in the values of E and CTE in a dental restoration composite when compared with the enamel causes a lack of uniformity in mechanical and thermal properties, thereby forming stress concentrations at the interfaces. The study establishes two optimised CTE and E values for the MOD restoration composite as 25 × 10-6 °C-1 and 20 GPa and 37 × 10-6 °C-1 and 5 GPa, respectively.

A comparison of the effects of incremental and snowplow techniques on the mechanical properties of composite restorations.

BACKGROUND: Glass fibre-reinforced composite (GFRC) has the potential to enhance the mechanical properties of resin-based restorations. Nevertheless, the application technique can influence the cervical margin porosity, potentially reducing the mechanical strength of restorations. METHODS: In an in vitro setup, mould specimens underwent six different treatments to assess the effects of snowplow and incremental curing techniques on the properties of GFRC (EverX) and universal resin composite (Filtek). Mechanical properties, namely flexural strength (FS), compressive strength (CS) and Vickers hardness (VH), were evaluated following ISO 4049 standards. Data interpretation utilized the Kruskal-Wallis tests. RESULTS: No significant difference emerged across groups for FS. CS in the snowplow method with lesser EverX thickness (SnPl_1) was comparable with only EverX and Filtek (P > 0.05). The CS was reduced in the snowplow technique with greater EverX thickness (SnPl_2) (P < 0.05) and further decreased with the incremental method (P < 0.001). VH results showed that EverX Posterior was consistently softer than Filtek, with specific patterns of hardness variations among different application methods. CONCLUSIONS: Applying EverX and Filtek using the snowplow technique delivers superior CS and VH for restorations in contrast to the incremental method. Utilizing the snowplow approach in high-stress areas can make restorations more fracture-resistant.

Selection and ranking of dental restorative composite materials using hybrid Entropy-VIKOR method: An application of MCDM technique.

The objective of this investigation was to design the selection and ranking of dental restorative composite materials using hybrid Entropy-VIKOR as the MCDM method. Eleven performance defining attributes (PDAs) of dental composites were considered to investigate the best formulation among the dental composites. The weight criteria of various PDAs of the dental composite were calculated by the Entropy method: PDA-1(0.0527), PDA-2 (0.0113), PDA-3(0.1692), PDA-4(0.1291), PDA-5(0.0207), etc. The VIKOR method was employed to demonstrate the rank of dental composites. As per the VIKOR method, the first rank was obtained by DHZ6, the second rank was by DHZ8, the third rank was by DHZ4, the fourth rank was by DHZ2, and the lowest rank was by DHZ0. The Hybrid Entropy-VIKOR method holds significance in the biomedical realm due to its capability to effectively address complex decision-making scenarios. Its ability to account for multiple criteria, uncertainties, and compromise solutions makes it particularly useful for enhancing decision-making processes in the biomedical field, where selecting the most suitable options is critical for patient outcomes and healthcare advancements.

A low-shrinkage dental composite with epoxy-polyhedral oligomeric silsesquioxane.

Polymerization shrinkage and mechanical properties affect the service life of dental restorative composites. Polyhedral oligomeric silsesquioxanes (POSS) can be an efficient strategy to improve the shrinkage properties and mechanical properties simultaneously. In this work, epoxycyclohexyl POSS (E-POSS) was used to modify the Bis-GMA/TEGDMA dental resins. E-POSS were introduced into the acrylic resin system via ring-opening reaction, and a cationic/free radical hybrid system was obtained. Double bond conversion, glass transition temperature, heterogeneity, crosslink density of dental resins and volumetric shrinkage, water sorption/solubility, flexural strength/modulus of dental composites were investigated. As the introduction of E-POSS caused higher double bond conversion and lower crosslink density, the polymerization shrinkage was significantly reduced to 2.91% (p < 0.05) and the flexural strength increased to 117.19 MPa (p < 0.05) compared to the control sample (5.06%, 99.16 MPa, p<0.05). Lower water sorption and solubility were also observed in composites contained E-POSS (p < 0.05).

[Color measurements of composite materials for tooth restoration in standardized in vitro conditions]. / Izmerenie tsveta kompozitnykh materialov dlia restavratsii zubov v standartizovannykh usloviiakh in vitro.

A national standard GOST R 58165-2018 (ISO/TR 28642:2016) 'Dentistry - Guidance on colour measurement' has been developed based on the international document which establishes standardized conditions for carrying out laboratory methods of measuring color by visual and instrumental methods. In vitro tests of samples of FiltekTM Ultimate, FiltekTMZ250 and Premise on the acoustooptic color analyzer SPEKTRON-M (FGUP 'VNIIOFI', Russia) in accordance with the recommendations of the standard GOST R 58165-2018 (ISO/TR 28642:2016) allowed to determine the effect of the shelf life of paste composite materials on the aesthetic indicators: colour compatibility, colour stability after aging and degree of transparency. The greatest changes in color characteristics in the CIELAB system during the storage of pastes were noted for the Premise Kerr A2 Enamel and A3 dentin composites. The greatest color change after exposure in water at 37 ° C was established for FiltekTMZ250 A4 samples with a long shelf life of the composite resin, ΔE=3.92>2.7 (p=0.001), but the color resistance of samples of the same composite from a new batch after exposure in water corresponds to the requirements of the standard, ΔE=2,18<2,7 (p=0,001).

Characterization of spatial patterns of dental restorative nanocomposites.

The aim of this study was to provide important insights into the effects of four different dental polishing protocols (one single-step and one multi-step either followed or not by diamond paste polishing) on the 3D surface morphology of two representative dental resin-based nanocomposites (a nanofilled and a nanohybrid composite) by means of digital image analysis and processing techniques. The 3D surface morphology was investigated by atomic force microscopy. Segmentation, statistics of height distributions (described by statistical parameters, according to ISO 25178-2: 2012) and Minkowski functionals were applied to the images to characterize the spatial patterns of analyzed samples at micrometer scale. The nanofilled composite had significantly lower values of height parameters in comparison with nanohybrid one. Multi-step polishing protocol generated a statistically significant smoother finish for both tested materials, than one-step polishing protocol, even when it was followed by diamond paste polishing. Diamond paste polishing generated a statistically significant smoother surface of tested samples. This suite of surface analysis tools is important in the research and manufacture of these dental resin-based nanocomposites, where material surfaces have a key role in the functionality of objects.

PALS probing of photopolymerization shrinkage in densely packed acrylate-type dental restorative composites.

BACKGROUND: Using positron annihilation lifetime spectroscopy (PALS), microstructural changes in commercial dental restorative composites under light-curing polymerization were identified as a modification in mixed positron/Ps trapping, where the decay of positronium (Ps; the bound state of positrons and electrons) is caused by free-volume holes mainly in the polymer matrix, and positron trapping is defined by interfacial free-volume holes in a mixed filler-polymer environment. In loosely packed composites with a filler content of <70-75%, this process was related to the conversion of Ps-to-positron trapping. OBJECTIVES: To disclose such peculiarities in densely packed composites using the example of he commercially available acrylate-based composite ESTA-3® (ESTA Ltd., Kiev, Ukraine), which boasts a polymerization volumetric shrinkage of only 1.5%. MATERIAL AND METHODS: ESTA­3® was used as a commercially available acrylate-based dental restorative composite. A fast-fast coincidence system of 230­ps resolution based on 2 photomultiplier tubes coupled to a BaF2 detector and ORTEC® electronics was used to register lifetime spectra in normal-measurement statistics. The raw PAL spectra were treated using x3-x2-CDA (coupling decomposition algorithm). RESULTS: The annihilation process in the densely packed dental restorative composites (DRCs), as exemplified by the commercially available acrylate-based composite ESTA­3®, is identified as mixed positron/ Ps trapping, where o-Ps decay is caused by free-volume holes in the polymer matrix and interfacial filler-polymer regions, and free positron annihilation is defined by free-volume holes between filler particles. The most adequate model-independent estimation of the polymerization volumetric shrinkage can be done using averaged positron annihilation lifetime. A meaningful description of the transformations in Psand positron-trapping sites under light curing can be developed on the basis of a semiempirical model exploring x3­x2­CDA. There is a strong monolithization of agglomerated filler nanoparticles in these composites, caused by the photo-induced disappearing of positron traps at the cost of Ps-decaying holes. CONCLUSIONS: Governing the polymerization void-evolution process in densely packed DRC ESTA­3® occurs mainly in the filler sub-system as positron-to-Ps trapping conversion, which is the reason for the low corresponding volumetric shrinkage.

BisGMA analogues as monomers and diluents for dental restorative composite materials.

Current commercially available dental composite materials have certain limitations for their use, including high monomer viscosity and high polymerization shrinkage, resulting in residual stresses and interfacial gaps. This study focused on the chemical modification of resin monomer bisphenol A-glycidyl methacrylate (bisGMA), so as to reduce the viscosity and polymerization shrinkage. In this design, the hydroxyl groups of bisGMA were transformed into ester groups with various alkyl chain length and branching. The modified monomers showed promising properties including reduced viscosity, reduced polymerization shrinkage, increased hydrophobicity, increased degree of double bond conversion, and improved mechanical properties of the resulting dental resin composites. The structure/property relationships of the new monomers were investigated, and optimal monomer structures were identified for dental composites with improved properties.

Local viscoelastic response of direct and indirect dental restorative composites measured by AFM.

We investigated the viscoelastic response of direct and indirect dental restorative composites by the novel technique of AM-FM atomic force microscopy. We selected four composites for direct restorations (Adonis, Optifil, EPH, CME) and three composites for indirect restorations (Gradia, Estenia, Signum). Scanning electron microscopy with micro-analysis was also used to support the results. The mean storage modulus of all composites was in the range of 10.2-15.2 GPa. EPH was the stiffest (p<0.05 vs. all other composites but Adonis and Estenia), while no significant difference was observed between direct and indirect group (p≥0.05). For the loss tangent, Gradia had the highest value (~0.3), different (p<0.05) from Optifil (~0.01) and EPH (~0.04) despite the large coefficient of variation (24%), and the direct composites showed higher loss tangent (p<0.01) than the indirect composites. All composites exhibited minor contrast at the edge of fillers, showing that these are pre-polymerized, as confirmed by EDS.

Mechanical properties of polymer-infiltrated-ceramic (sodium aluminum silicate) composites for dental restoration.

OBJECTIVE: To fabricate indirect restorative composites for CAD/CAM applications and evaluate the mechanical properties. METHODS: Polymer-infiltrated-ceramic composites were prepared through infiltrating polymer into partially sintered sodium aluminum silicate ceramic blocks and curing. The corresponding samples were fabricated according to standard ISO-4049 using for mechanical properties measurement. The flexural strength and fracture toughness were measured using a mechanical property testing machine. The Vickers hardness and elastic modulus were calculated from the results of nano-indentation. The microstructures were investigated using secondary electron detector. The density of the porous ceramic blocks was obtained through TG-DTA. The conversion degrees were calculated from the results of mid-infrared spectroscopy. RESULTS: The obtained polymer infiltrated composites have a maximum flexural strength value of 214±6.5MPa, Vickers hardness of 1.76-2.30GPa, elastic modulus of 22.63-27.31GPa, fracture toughness of 1.76-2.35MPam1/2 and brittleness index of 0.75-1.32µm-1/2. These results were compared with those of commercial CAD/CAM blocks. Our results suggest that these materials with good mechanical properties are comparable to two commercial CAD/CAM blocks. CONCLUSION: The sintering temperature could dramatically influence the mechanical properties. CLINICAL SIGNIFICANCE: Restorative composites with superior mechanical properties were produced. These materials mimic the properties of natural dentin and could be a promising candidate for CAD/CAM applications.

Light-cured dimethacrylate dental restorative composites under a prism of annihilating positrons.

BACKGROUND: Breakthrough resolutions in current biopolymer engineering rely on reliable diagnostics of atomic-deficient spaces over the finest sub-nanometer length scales. One such diagnostic is positron annihilation lifetime spectroscopy, which probes space-time continuum relationships for the interaction between electrons and their antiparticle (positrons) in structural entities like free-volume defects, vacancies, vacancy-like clusters, interfacial voids and pores, etc. OBJECTIVES: This paper is intended to highlight the possibilities of positron annihilation lifetime spectroscopy as an informative instrumentation tool to parameterize free-volume evolution in light-cured dimethacrylate dental restorative composites exemplified by Charisma® (Heraeus Kulzer GmbH, Hanau, Germany) and Dipol® (Oksomat-AN Ltd, Kyiv, Ukraine). MATERIAL AND METHODS: The subjects of the study were the commercially available dimethacrylate-type dental restorative composites Charisma® and Dipol®. The analysis used a fast-fast coincidence system of 230 ps resolution based on 2 photomultiplier tubes coupled to BaF2 scintillator detectors and ORTEC® (ORTEC, Oak Ridge, USA) electronics to register lifetime spectra in normal-measurement statistics evolving ~1 million coincidences. RESULTS: The annihilation process in both composites is identified as mixed positron-Ps (positronium) trapping, where ortho-Ps decaying is caused entirely by free-volume holes in the polymer matrix, and the 2nd component is defined mainly by interfacial free-volume holes between filler nanoparticles and the surrounding polymer. The most appropriate model-independent estimation of photopolymerization volumetric shrinkage in dental restorative composites can be done using averaged positron annihilation lifetime. Partiallyconstrained x4-term analysis of lifetime spectra is less efficient, giving greater scatter of variance with an additional artifact of fixed shortest lifetime allowing unresolved mixing in the 2nd component. A meaningful phenomenological description of transformations in Ps and positron-trapping sites under light curing, which occurs more efficiently in Charisma® than in Dipol® nanocomposites, can be developed at the basis of a semi-empirical model exploring a x3-x2-coupling decomposition algorithm. CONCLUSIONS: A deep understanding of void-evolution processes in dimethacrylate dental composites employing positron annihilation lifetime spectroscopy makes it possible to diagnose, characterize and engineer novel biomaterials for advanced use in medical practice.

Wear behavior of light-cured resin composites with bimodal silica nanostructures as fillers.

To enhance wear behavior of resin composites, bimodal silica nanostructures including silica nanoparticles and silica nanoclusters were prepared and proposed as fillers. The silica nanoclusters, a combination of individually dispersed silica nanoparticles and their agglomerations, with size distribution of 0.07-2.70 µm, were fabricated by the coupling reaction between amino and epoxy functionalized silica nanoparticles, which were obtained by the surface modification of silica nanoparticles (~70 nm) using 3-aminopropyl triethoxysilane (APTES) and 3-glycidoxypropyl trimethoxysilane (GPS) as coupling agents, respectively. Silica nanoparticles and nanoclusters were then silanized with 3-methacryloxypropyl trimethoxysilane (γ-MPS) to prepare composites by mixing with bisphenol A glycerolate dimethacrylate (Bis-GMA) and tri (ethylene glycol) dimethacrylate (TEGDMA). Experimental composites with various filler compositions were prepared and their wear behaviors were assessed in this work. The results suggested that composites with increasing addition of silica nanoparticles in co-fillers possessed lower wear volume and smoother worn surface. Particularly, the composite 53:17 with the optimum weight ratio of silica nanoparticles and silica nanoclusters presented the excellent wear behavior with respect to that of the commercial Esthet-X, although the smallest wear volume was achieved by Z350 XT. The introduction of bimodal silica nanostructures as fillers might provide a new sight for the design of resin composites with significantly improved wear resistance.

Efeito das dimensões dos corpos de prova na resistência à flexão de compósitos restauradores / Effect of specimen size on flexural strength of restorative composites

O objetivo deste estudo foi avaliar, em relação à norma ISO, o efeito da redução das dimensões dos corpos de prova na resistência à flexão, em três pontos, dos compósitos restauradores de nanopartículas (Filtek Supreme - 3M ESPE) e micro-híbrido (Filtek Z-250 - 3M ESPE). Foram confeccionados 40 corpos de prova para cada material com asseguintes dimensões de comprimento, largura e espessura (n = 10): 1) 20 × 2 × 2 mm (ISO 4049); 2) 10 × 2 × 1 mm; 3) 10 × 1 × 1 mm; 4) 8 × 0,8 × 0,8 mm. Os compósitos foram inseridos em único incremento em matrizes metálicas bipartidas, correspondentes a cada dimensão avaliada, e fotoativados. Os corpos de prova foram armazenados a 37 ± 1 °C, em ambiente seco e protegido de luz, durante 7 dias. Posteriormente, foi realizado o ensaio de resistência à flexão, em três pontos, usando o equipamento MTS 810, com célula de carga de 10 kN e velocidade de 0,5 mm/min. Os resultados mostraram variabilidade significativa para as dimensões avaliadas (p = 0,00), com valores, em relação à norma ISO (116,700 MPa), estatisticamente superiores para os corpos de prova de 10 × 1 × 1 mm (142,530 MPa), semelhantes para os de 10 × 2 × 1 mm (115,815 MPa) e inferiores para os de 8 × 0,8 × 0,8 mm (86,650 MPa).Houve igualdade estatística (p = 0,08) para os compósitos estudados (Filtek Supreme, 125,270 MPa; Filtek Z-250, 108,130 MPa). Corpos de prova de 10 × 2 × 1 mm proporcionaram, com menor consumo de material, energia e tempo, valores de resistência à flexão equivalentes àqueles obtidos nas dimensões preconizadas pela norma ISO 4049.

The aim of this study was to evaluate the influence of specimen size, in comparison with the ISO Standard, on the three point flexural strength of resin composite restorative materials Filtek Supreme and Filtek Z-250. Fortyspecimens were fabricated for each material with the following length, width and thickness measurements (n = 10): 1) 20 × 2 × 2 mm (ISO 4049); 2) 10 × 2 × 1 mm; 3) 10 × 1 × 1 mm; 4) 8 × 0.8 × 0.8 mm. The composites were inserted in a single increment into two-piece metal device and light-polymerized. The specimens were dry stored at 37 ± 1 °C and protected from light for 7 days. After this period, flexural strength was measured by three-point flexure test using MTS 810 equipment, with a load cell of 10 kN at a speed of 0.5 mm/min. For the evaluated sizes, the results showed significant variability (p = 0.00) with values when compared with the ISO Standard (116.700 MPa), being statistically higher for the test specimens measuring 10 × 1 × 1 mm (142.530 MPa), similar for those of 10 × 2 × 1 mm (115.815 MPa) and lower for those of 8 × 0.8 × 0.8 mm (86.650 MPa). There was statistical equality (p = 0.08) for the studied composites (Filtek Supreme, 125.270 MPa; Filtek Z-250, 108.130 MPa). Specimens measuring 10 × 2 × 1 mm provided flexural strength values equivalent to those obtained in the sizes recommended by the ISO 4049 standard, with lower consumption of material, energy and time.

Avaliação da resistência de união ao microcisalhamento entre compósitos restauradores e cimentos resinosos / Microshear bond strength between restorative composites and resin cements

Introdução e objetivo: As técnicas de cimentação adesiva têm sido largamente utilizadas nas restaurações dentárias. O objetivo deste estudo foi avaliar a resistência de união ao microcisalhamento entre compósitos restauradores e cimentos resinosos. Material e métodos: Vinte blocos de compósitos foram preparados até a obtenção de superfícies planas, que foram abrasionadas com lixa de carbeto de silício número 600. As amostras foram aleatoriamente divididas em quatro grupos (n=15), de acordo com os grupos experimentais: 1) bloco de Z250 + Single Bond + cilindro de RelyX ARC; 2) bloco de Z250 + Single Bond + cilindro de Panavia F; 3) bloco de Clearfil AP-X + adesivo do Clearfil SE Bond + cilindro de RelyX ARC; 4) bloco de Clearfil AP-X + adesivo do Clearfil SE Bond + cilindro de Panavia F. Os sistemas adesivos e os cimentos resinosos foram aplicados de acordo com os grupos experimentais, usando uma matriz do tipo Tygon. Os corpos-de-prova foram armazenados em água destilada 37±2ºC por 24 h. A resistência de união foi determinada por meio da máquina universal de ensaios Instron, a uma velocidade de 0,5 mm/min. Resultados: Os resultados obtidos em MPa (DP) foram analisados estatisticamente (ANOVA e teste de Tukey – p < 0,05) e mostraram os seguintes resultados: 1) 39,76 (5,34); 2) 45,01 (8,53); 3) 46,39 (9,22); 4) 45,78 (9,06). Não houve diferença estatisticamente significativa entre os grupos 1 e 2 e entre os grupos 3 e 4. Todavia houve diferença estatística entre os grupos 1 e 3. Conclusão: Quando a base de Clearfil AP-X foi utilizada com o adesivo do Clearfil SE Bond ou o cimento resinoso RelyX ARC, os valores médios de resistência de união ao microcisalhamento foram maiores. Os resultados sugerem que em reconstruções morfológicas dentárias, quando for aplicado o cimento resinoso, o uso de um adesivo hidrófobo sobre o compósito restaurador é necessário.

Introduction and objective: The techniques of adhesive cementation have been widely used in dental restoration. The purpose of this study was to evaluate the microshear bond strength between restorative composites and resin cements. Material and methods: Twenty composites blocks were prepared in order to obtain a flat surface, using 600-grid sandpaper. The samples were randomly divided in four groups (n=15) according to the experimental groups: [1] Z250 block + Single Bond + cylinder of RelyX ARC; [2] Z250 block + Single Bond + cylinder of Panavia F; [3] Clearfil AP-X block + Clearfil SE Bond adhesive + cylinder of RelyX ARC; [4] Clearfil AP-X block + Clearfil SE Bond adhesive + cylinder of Panavia F. The adhesive systems and the resin cements were applied according to the experimental groups, using a Tygon matrix. The samples were stored in distilled water at 37±2ºC for 24 hours. Microshear bond strengths were determined using an apparatus attached to an Instron universal testing machine at a crosshead speed of 0.5 mm/minute. Results: The results obtained in MPa (SD) were statistically analyzed (ANOVA and Tukey test, p<0.05), and showed the following results: [1] 39.76 (5.34); [2] 45.01 (8.53); [3] 46.39 (9.22); [4] 45.78 (9.06). There was no statistically significant difference between groups [1] and [2]; and between groups [3] and [4]. However, there was statistically significant difference between groups [1] and [3]. Conclusion: When Clearfil AP-X block was used with Clearfil SE Bond adhesive or RelyX resin cement, the microshear bond strength values were higher. The results suggest that in the union of the resin cements to the restorative composites, hydrophobic adhesives are necessary.