Dental dimethacrylate-based nanohybrid composite Kalore GC: Kinetic study of its light-curing

AbstractObjectiveThis study investigated the light-curing kinetic of the novel dental dimethacrylate-based nanohybrid composite (Kalore GC). Its organic matrix consists of a high molecular weight monomer called DX 511 as well as the known dimethacrylate monomers bisphenol A ethyl dimethacrylate (Bis-EMA) and urethane dimethacrylate (UDMA).MethodsFour properties were measured: degree of conversion (DC), depth of curing (DOC), polymerization shrinkage (S) and glass transition temperature (Tg) versus curing time. These properties were measured by spectroscopic imaging in Attenuated Total Reflection (ATR-FT-IR), scrape test, density measurements and dynamic mechanical thermal analysis (DMTA), respectively.ResultsAfter 10s of light curing, the DC was 2.50%, DOC 1.86 mm and S 1.48%. The composite cured for 10s showed two Tg; 56.4 °C and 112.8 °C. At this stage, the maximum rate of polymerization was noticed. The curing, however, continued with much lower and decreased rate for up to 100s. There, a maximum DC of about 40% and a maximum DOC of about 3.5 mm were observed. Tg values were raised to 59.5 and 102.3 °C, respectively.ConclusionsWithin the condition of this study, the optimum curing time of Kalore GC seems to be 100 s. The composite light-cured up to 300 s showed two Tg, indicating that this compound still contained unreacted double bonds of C=C and macroradicals, which continued to cure upon heating in DMTA

Overviews on the Progress of Flowable Dental Polymeric Composites: Their Composition, Polymerization Process, Flowability and Radiopacity Aspects

A review article has been conducted including the main research results and comments referring to flowable dental polymeric materials. To begin with, the synthesis and composition of this category of composites is discussed, revealing the major components of the commercial products in terms of chemistry and proportion. Later, the polymerization characteristics are unfolded regarding the reaction time and rate, volumetric shrinkage and depth of cure for both photocurable and self-curable composites. To continue, some perspectives of the pre-treatment or accompanying processes that a clinician may follow to enhance the materials’ performance are described. Fluidity is certainly associated with the progress of polymerization and the in-depth conversion of monomers to a polymeric network. Last, the aspects of radiopacity and translucency are commented on, showing that all flowable polymeric composites satisfy the radiography rule, while the masking ability depends on the fillers’ properties and specimen thickness. The reviewing article is addressed to all field scientists and practitioners dealing with flowable dental composites studies or applications

Study of the dynamic thermomechanical properties and the elution of unreacted monomers of current nanohybrid and nanofill light-cured dental composites

Polymer composite materials for dental restorations are a modern, highly interesting, research field. They consist of two main phases, the polymeric network produced by a mixture of dimethacrylates such as Bis-GMA, Bis-EMA, UDMA or TEGDMA, and the inorganic filler load, mainly SiO2 and other silicates. The division into nanofilled composites and nanohybrids is based on the particle size distribution of reinforcing filler. The researchers internationally have proposed some liquids as food/beverages or oral simulators, and their use allows us to rapidly examine the wear caused to the materials, along with other processes that may occur, such as sorption and elution of substances. Undoubtedly, the physicochemical and mechanical properties of the materials are strongly influenced by the presence of solvents/solutions simulators. Five modern, commercially available, products are the subject of this research, namely Filtek™ Supreme XT Body (3M ESPE), Filtek™ Supreme XT Translucent (3M ESPE), Grandio® (Voco GmbH), Protofill- nano (Association of Dentists, Thessaloniki) and Tetric EvoCeram® (Ivoclar Vivadent AG), which present different ingredients and characteristics. The technique of photopolymerisation (λ= 410-500 nm) is applied to cure the samples; their curing time was investigated by FT-IR and established in 60 s. Wearing and ageing liquids for those materials included H2O, artificial saliva SAGF® and 75%v/v EtOH/H2O. The time exposure periods ranged from one day up to three months. Dynamic Thermomechanical Analysis (DMTA) is suitable for such materials experiments, which exhibit viscoelastic behaviour while mimic the cyclic masticatory loads the restorations receive within the mouth. Thus, all the composites exhibited two Tg (the glass transition temperature is an important feature), when the measurements were made after short immersion intervals, and one Tg for longer ageing time. It has been concluded that the amount of the inorganic portion in a polymer composite affects the mechanical properties, which are enhanced with increased presence. The influence of warmer liquid environment-stay results in post-polymerisation of the material in short-time exposure and plasticization in long term; the effect of the ethanol solution is particularly burdensome for the materials. High Pressure Liquid Chromatography (HPLC) detects the unreacted monomers or hydrolysis reactions’ derivatives formed during extraction in the above-mentioned media. The application and validation of the appropriate analytical method may quantify the ingredients eluted. From the foregoing monomers, which polymerize due to structural differences in different degrees, the interest accumulates on bisphenol derivatives. Their extraction is enhanced in aqueous and ethanol mediums. Not only the portion of polymer content, but also the size of the dimethacrylates, seem to affect the elution of unchanged monomers in simulating liquids, into oral cavity and human organism by extension.Τα σύνθετα πολυμερικά υλικά οδοντιατρικών αποκαταστάσεων αποτελούν ένα σύγχρονο και πολύ ενδιαφέρον πεδίο έρευνας. Αποτελούνται από δυο κύριες φάσεις, την οργανική μήτρα, (συμπολυμερή των Bis-GMA, Bis-EMA, UDMA ή TEGDMA) και την ανόργανη ενισχυτική φάση που είναι κυρίως SiO2 ή/και άλλες ανόργανες ενώσεις. Χαρακτηρίζονται ως νανοσύνθετα ή νανοϋβριδικά ανάλογα με την κοκκομετρική κατανομή των σωματιδίων του ανόργανου μέρους τους. Τα οδοντιατρικά σύνθετα πολυμερικά υλικά λειτουργούν στη στοματική κοιλότητα και υφίστανται την επίδραση του σάλιου, νερού και διαφόρων υπολειμμάτων τροφών/ποτών. Για την επίδραση αυτών, στην αντοχή των σύνθετων, έχει προταθεί η παραμονή τους σε ορισμένα υγρά που προσομοιάζουν τα στοματικά. Στην παρούσα Διατριβή μελετήθηκαν με Δυναμική Θερμομηχανική Ανάλυση (DMTA) και Υγρή Χρωματογραφία Υψηλής Πίεσης (HPLC) πέντε σύγχρονα εμπορικά προϊόντα• και συγκεκριμένα τα Filtek™ Supreme XT Body (3M ESPE), Filtek™ Supreme XT Translucent (3M ESPE), Grandio® (Voco GmbH), Protofill-nano (Συνεταιρισμός Οδοντιάτρων Θεσσαλονίκης) και Tetric EvoCeram® (Ivoclar Vivadent AG), τα οποία παρουσιάζουν διαφορετική σύσταση. Αρχικά μελετήθηκε η κινητική του φωτοπολυμερισμού των υλικών με την τεχνική της Φασματοσκοπίας Υπερύθρου (FT-IR) με σκοπό να βρεθεί ο βέλτιστος χρόνος φωτοπολυμερισμού, που προσδιορίστηκε ότι είναι για όλα τα δείγματα 60 s. Ο φωτοπολυμερισμός έγινε με ειδική συσκευή που διαθέτει λυχνία αλογόνου και εκπέμπει στο ορατό φως (λ=410-500 nm). Ως μέσα γήρανσης των υλικών χρησιμοποιήθηκαν το Η2Ο, τεχνητό σάλιο SAGF® και 75% v/v EtOH/H2O. Τα δείγματα παρέμειναν στα υγρά από μια ημέρα έως και τρεις μήνες πριν την ανάλυση τους με DMTΑ και HPLC. Στην DMTA τα σύνθετα υλικά έδειξαν δύο θερμοκρασίες υαλώδους μετάβασης (Tg) όταν τα δείγματα παρέμειναν σε κάποιο υγρό για μικρό χρονικό διάστημα, ενώ έδειξαν ένα Tg για μεγαλύτερο χρονικό διάστημα. Διαπιστώθηκε ότι η ποσότητα της ανόργανης φάσης σε ένα σύνθετο πολυμερικό υλικό επηρεάζει τις μηχανικές ιδιότητες, οι οποίες ενισχύονται με την αύξηση του ποσοστού της. Το θερμό περιβάλλον φαίνεται να προκαλεί μεταπολυμερισμό βραχυπρόθεσμα και το υγρό γήρανσης πλαστικοποίηση μακροπρόθεσμα. Τη μεγαλύτερη επίδραση στα υλικά παρατηρήθηκε ότι έχει το διάλυμα αιθανόλης/νερού. Η HPLC ανιχνεύει τα αναλλοίωτα (ελεύθερα) μονομερή που δεν αντέδρασαν ή προϊόντα διάσπασης της πολυμερικής μήτρας που σχηματίζονται κατά την παραμονή των υλικών στα υγρά γήρανσης. Με την εφαρμογή και επικύρωση της ανάλογης αναλυτικής μεθόδου είναι εφικτή η ποσοτικοποίηση των συγκεντρώσεων των ενώσεων αυτών. Από τα προαναφερθέντα μονομερή, τα οποία λόγω δομικών διαφορών πολυμερίζονται σε διαφορετικό βαθμό, ενδιαφέρον συγκεντρώνουν τα δισφαινολικά παράγωγα. Η εκχύλισή τους ενισχύεται στο αιθανολικό περιβάλλον

Defining the Effect of a Polymeric Compatibilizer on the Properties of Random Polypropylene/Glass Fibre Composites

Random polypropylene composites reinforced with short glass fibres have been successfully fabricated by melt-mixing. Polypropylene grafted with maleic anhydride (PP-g-MA) was added to the composites, which was expected to act as a compatibilizer and greatly limit the negative effects known to arise from the feeble polymer matrix/glass fibre interfaces. The effect of compatibilizer concentration on the structural, mechanical and thermal behaviour of the composites has been investigated. The results revealed an improvement of the glass fibre/matrix interaction upon the addition of the compatibilizer, which resulted in enhancing the overall material stiffness and the ability of the matrix to store energy. In particular, the lowering of the glass transition and the investigation of the fracture surfaces of the composites confirmed the improved PPR/fibre adhesion. Examination of the tensile elongation indicated the improvement of the Young’s modulus and yield strength with the addition of PP-g-MA, while the storage modulus was also shown to be significantly increased. These results confirmed the versatility and efficiency of the approach presented in this work to improve the thermomechanical properties and sustainability of PPR and promote its usage in industrial applications and commercial manufacturing

Fluorosilane Water-Repellent Coating for the Protection of Marble, Wood and Other Materials

The preservation of cultural heritage monuments and artifacts requires the development of methods to produce water-repellent materials, which can offer protection against the effects of atmospheric water. Fluorosilanes are a very promising class of materials, as they act as precursors for the formation of low surface energy polymer networks. 1H,1H,2H,2H-perfluorooctyl-triethoxysilane is applied on marble, wood and the surfaces of other materials, such as glass, silicon wafer, brass, paper and silk. According to the measurements of static water contact angles, it is reported that superhydrophobicity and enhanced hydrophobicity are achieved on the surfaces of coated marble and wood, respectively. Hydrophobicity and hydrophilicity were observed on the treated surfaces of the other materials. More important, water repellency is achieved on any hydrophobic or superhydrophobic surface, as revealed by the very low sliding angles of water drops. The study is accompanied by colorimetric measurements to evaluate the effects of the treatment on the aesthetic appearances of the investigated materials. Finally, the capillary absorption test and a durability test are applied on treated wood and marble, respectively

Polymerisation Kinetics on FT-IR and Colorimetric Changes under UV Irradiation for a Commercial Polycyanoacrylate Adhesive, Addressed to Glass Restoration

This study evaluates a commercial polycyanoacrylate adhesive of medium viscosity regarding its suitability for the restoration of glass objects of cultural heritage in a museum environment (exhibition/storage). Loctite® Super Attak was investigated in terms of (a) its polymerisation rate and degree of conversion, using Infrared Spectroscopy FT-IR by monitoring the change of the C=C peak vs. C=O peak and (b) the alteration of the colour parameters of its films after its submission to UVC irradiation for several time intervals. It was confirmed that within 6 h, a thin-layered adhesive film acquires 80–85% of its polymerization in ambient conditions, while the reaction continues for up to 12–18 h in the conditions examined. The progress of the reaction is slower when the adhesive is in a protected environment. On the other hand, the effect of UVC rays on the glue is destructive and oxidative, provoking a yellow shade/colour from the first hours of exposure. The intensity of the yellowness becomes higher after 6 h of exposure, showing shifts in the absorption peaks of C–O/C=O groups of the initial IR spectrum and the augmentation of –OH absorptions. It was concluded that the adhesive is suitable for glass restoration, especially for instant, rapid, applications, under mild conditions of maintenance and exposure

Development of Bio-Composites with Enhanced Antioxidant Activity Based on Poly(lactic acid) with Thymol, Carvacrol, Limonene, or Cinnamaldehyde for Active Food Packaging

The new trend in food packaging films is to use biodegradable or bio-based polymers, such as poly(lactic acid), PLA with additives such as thymol, carvacrol, limonene or cinnamaldehyde coming from natural resources (i.e., thyme, oregano, citrus fruits and cinnamon) in order to extent foodstuff shelf-life and improve consumers’ safety. Single, triple and quadruple blends of these active compounds in PLA were prepared and studied using the solvent-casting technique. The successful incorporation of the active ingredients into the polymer matrix was verified by FTIR spectroscopy. XRD and DSC data revealed that the crystallinity of PLA was not significantly affected. However, the Tg of the polymer decreased, verifying the plasticization effect of all additives. Multicomponent mixtures resulted in more intense plasticization. Cinnamaldehyde was found to play a catalytic role in the thermal degradation of PLA shifting curves to slightly lower temperatures. Release of thymol or carvacrol from the composites takes place at low rates at temperatures below 100 °C. A combined diffusion-model was found to simulate the experimental release profiles very well. Higher antioxidant activity was noticed when carvacrol was added, followed by thymol and then cinnamaldehyde and limonene. From the triple-component composites, higher antioxidant activity measured in the materials with thymol, carvacrol and cinnamaldehyde

Zirconia Nanoparticles as Reinforcing Agents for Contemporary Dental Luting Cements: Physicochemical Properties and Shear Bond Strength to Monolithic Zirconia

Nanofillers in resin materials can improve their mechanical and physicochemical properties. The present work investigated the effects of zirconia nanoparticles (NPs) as fillers in commercial dental luting cements. Two dual-cured self-adhesive composites and one resin modified glass ionomer (RMGI) luting cement were employed. Film thickness (FT), flexural strength (FS), water sorption (Wsp), and shear bond strength (SBS) to monolithic zirconia were evaluated according to ISO 16506:2017 and ISO 9917-2:2017, whereas polymerization progress was evaluated with FTIR. Photopolymerization resulted in double the values of DC%. The addition of 1% wt NPs does not significantly influence polymerization, however, greater amounts do not promote crosslinking. The sorption behavior and the mechanical performance of the composites were not affected, while the film thickness increased in all luting agents, within the acceptable limits. Thermocycling (TC) resulted in a deteriorating effect on all composites. The addition of NPs significantly improved the mechanical properties of the RMGI cement only, without negatively affecting the other cements. Adhesive primer increased the initial SBS significantly, however after TC, its application was only beneficial for RMGI. The MDP containing luting cement showed higher SBS compared to the RMGI and 4-META luting agents. Future commercial adhesives containing zirconia nanoparticles could provide cements with improved mechanical properties