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PHOTOPOLYMERIZED COMPOSITIONS AND LIGHT SOURCES FOR DENTAL PRACTICE (REVIEW)
Abstract
The review presents an analysis of articles published for the period 2005-2021. in top-rated publications devoted to the research results in the field of creating light-curing (photopolymerizable) compositions for use in dental practice. The information concerning the main ingredients of the compositions: di (meth) acrylate monomers, fillers, pigments, and photoinitiators is summarized. A comparative assessment of light sources, which determine the curing efficiency of materials of such a functional purpose, is presented. The results of a patent search, in the PatentScope database, are presented. For the period 2000-2021. have been identified 692 patents, which are related to the creation of dental photopolymer composites.
... ОБЗОРЫ Российский стоматологический журнал Том 26 (2) 2022 АКТУАЛЬНОСТЬ На сегодняшний день композиты являются тем реставрационным материалом, который используется в каждом стоматологическом кабинете [1,2]. Серебряная амальгама и неорганические цементы были заменены композитными материалами в качестве наиболее частых материалов прямой реставрации. ...
BACKGROUND: The article presents a review of the chemical aspects of the reaction of light polymerization of composites in dental practice. This reaction refers to free radical polymerization reactions, with photons as activators. In dentistry, composites are classified as chemically cured, light cured, doubly cured, and thermally cured. This depends on the origin of the activation energy of free radical polymerization of methacrylates. Chemically, dental composites are usually a mixture of four main components: an organic polymer matrix, an inorganic filler, an appret compound, a binder matrix and filler, and an initiatoraccelerator system. The radical polymerization process includes four main stages. The first stage is activation; in the case of light cured dental composites, it is photoactivation. In this case, a photoinitiator molecule is excited, for example, camphorquinone, which is widely used in the production of dental composite materials. If a free radical is formed, the polymerization process is similar for all composite materials based on a methacrylate organic matrix. The only difference is exactly how free radicals are formed and the rate of their formation. Under the influence of light quanta, the carbon atom of the ketone group of camphorquinone passes into an excited state, which allows the excited photoinitiator molecule to interact with two methacrylate molecules by a double bond. The double bond gives one electron to the excited camphorquinone molecule, and the second electron acts as a free radical agent; in other words, a macroradical is formeda monomer molecule that can attach other monomer molecules to itself.
The presented paper concerns current knowledge of commercial and alternative photoinitiator systems used in dentistry. It discusses alternative and commercial photoinitiators and focuses on mechanisms of polymerization process, in vitro measurement methods and factors influencing the degree of conversion and hardness of dental resins. PubMed, Academia.edu, Google Scholar, Elsevier, ResearchGate and Mendeley, analysis from 1985 to 2020 were searched electronically with appropriate keywords. Over 60 articles were chosen based on relevance to this review. Dental light-cured composites are the most common filling used in dentistry, but every photoinitiator system requires proper light-curing system with suitable spectrum of light. Alternation of photoinitiator might cause changing the values of biomechanical properties such as: degree of conversion, hardness, biocompatibility. This review contains comparison of biomechanical properties of dental composites including different photosensitizers among other: camphorquinone, phenanthrenequinone, benzophenone and 1-phenyl-1,2 propanedione, trimethylbenzoyl-diphenylphosphine oxide, benzoyl peroxide. The major aim of this article was to point out alternative photoinitiators which would compensate the disadvantages of camphorquinone such as: yellow staining or poor biocompatibility and also would have mechanical properties as satisfactory as camphorquinone. Research showed there is not an adequate photoinitiator which can be as sufficient as camphorquinone (CQ), but alternative photosensitizers like: benzoyl germanium or novel acylphosphine oxide photoinitiators used synergistically with CQ are able to improve aesthetic properties and degree of conversion of dental resin.
This study evaluated the physico-mechanical properties of experimental composite resins made with different resin matrix and light-curing units. Experimental composite groups were divided according to monomers (BisGMA + TEGDMA-BT and BisGMA + BisEMA + UDMA + TEGDMA-BBUT) and photoinitiator system (camphorquinone-CQ and 1-phenyl-1,2-propanedione-PPD). A quartz tungsten halogen (QTH) or light-emitting diode (LED) were used to light cure all materials. Knoop microhardness (n = 10) was determined using Knoop microhardness test. Compressive strength, diametral tensile strength, and Young modulus (n = 7) were obtained using a universal testing machine at crosshead speed of 1.0 mm/min. The data were submitted to a three-way ANOVA and the Tukey post-hoc test (α = 0.05). QTH presented the highest total irradiance values and similar total radiant exposure to LED. For the compressive strength test, BT-PPD light-cured with LED group showed the lowest mean value. BT-CQ light-cured with LED group exhibited the lowest diametral tensile strength results. The BBUT-composite resins presented lowest Young modulus values, with no statistical difference between light-curing units (QTH and LED) and photoinitiators system (CQ and PPD). Application of QTH or LED in BT-based composite resins with PPD photoinitiator generated suitable results regarding the physico-mechanical properties.
The photoinduced polymerization of monomers is currently an essential tool in various industries. The photopolymerization process plays an increasingly important role in biomedical applications. It is especially used in the production of dental composites. It also exhibits unique properties, such as a short time of polymerization of composites (up to a few seconds), low energy consumption, and spatial resolution (polymerization only in irradiated areas). This paper describes a short overview of the history and classification of different typical monomers and photoinitiating systems such as bimolecular photoinitiator system containing camphorquinone and aromatic amine, 1-phenyl-1,2-propanedione, phosphine derivatives, germanium derivatives, hexaarylbiimidazole derivatives, silane-based derivatives and thioxanthone derivatives used in the production of dental composites with their limitations and disadvantages. Moreover, this article represents the challenges faced when using the latest inventions in the field of dental materials, with a particular focus on photoinitiating systems based on iodonium salts. The beneficial properties of dental composites cured using initiation systems based on iodonium salts have been demonstrated.
In this study, novel urethane-dimethacrylate monomers were synthesized from 1,3-bis(1-isocyanato-1-methylethyl)benzene (MEBDI) and oligoethylene glycols monomethacrylates, containing one to three oxyethylene groups. They can potentially be utilized as matrices in dental restorative materials. The obtained monomers were used to prepare four new formulations. Two of them were solely composed of the MEBDI-based monomers. In a second pair, a monomer based on triethylene glycol monomethacrylate, used in 20 wt.%, was replaced with triethylene glycol dimethacrylate (TEGDMA), a reactive diluent typically used in dental materials. For comparison purposes, two formulations, using typical dental dimethacrylates (bisphenol A glycerolate dimethacrylate (Bis-GMA), urethane-dimethacrylate (UDMA) and TEGDMA) were prepared. The monomers and mixtures were tested for the viscosity and density. The homopolymers and copolymers, obtained via photopolymerization, were tested for the degree of conversion, polymerization shrinkage, water sorption and solubility, hardness, flexural strength and modulus. The newly developed formulations achieved promising physico-chemical and mechanical characteristics so as to be suitable for applications as dental composite matrices. A combination of the MEBDI-based urethane-dimethacrylates with TEGDMA resulted in copolymers with a high degree of conversion, low polymerization shrinkage, low water sorption and water solubility, and good mechanical properties. These parameters showed an improvement in relation to currently used dental formulations.
The aims of this study were to evaluate the physicochemical and mechanical properties, antimicrobial (AM) functionality, and cytotoxic potential of novel dental polymers containing quaternary ammonium and trimethoxysilyl functionalities (e.g., N-(2-(methacryloyloxy)ethyl)-N,N-dimethyl-3-(trimethoxysilyl)propan-1-aminium iodide (AMsil1) and N-(2-(methacryloyloxy)ethyl)-N,N-dimethyl-11-(trimethoxysilyl)undecan-1-aminium bromide (AMsil2)). AMsil1 or AMsil2 were incorporated into light-cured (camphorquinone + ethyl-4-N,N-dimethylamino benzoate) urethane dimethacrylate (UDMA)/polyethylene glycol-extended UDMA/ethyl 2-(hydroxymethyl)acrylate (EHMA) resins (hereafter, UPE resin) at 10 or 20 mass %. Cytotoxic potential was assessed by measuring viability and metabolic activity of immortalized mouse connective tissue and human gingival fibroblasts in direct contact with monomers. AMsil–UPE resins were evaluated for wettability by contact angle measurements and degree of vinyl conversion (DVC) by near infra-red spectroscopy analyses. Mechanical property evaluations entailed flexural strength (FS) and elastic modulus (E) testing of copolymer specimens. The AM properties were assessed using Streptococcus mutans (planktonic and biofilm forms) and Porphyromonas gingivalis biofilm. Neither AMsil exhibited significant toxicity in direct contact with cells at biologically relevant concentrations. Addition of AMsils made the UPE resin more hydrophilic. DVC values for the AMsil–UPE copolymers were 2–31% lower than that attained in the UPE resin control. The mechanical properties (FS and E) of AMsil–UPE specimens were reduced (11–57%) compared to the control. Compared to UPE resin, AMsil1–UPE and AMsil2–UPE (10% mass) copolymers reduced S. mutans biofilm 4.7- and 1.7-fold, respectively (p ≤ 0.005). Although not statistically different, P. gingivalis biofilm biomass on AMsil1–UPE and AM AMsil2–UPE copolymer disks were lower (71% and 85%, respectively) than that observed with a commercial AM dental material. In conclusion, the AM function of new monomers is not inundated by their toxicity towards cells. Despite the reduction in mechanical properties of the AMsil–UPE copolymers, AMsil2 is a good candidate for incorporation into multifunctional composites due to the favorable overall hydrophilicity of the resins and the satisfactory DVC values attained upon light polymerization of AMsil-containing UDMA/PEG-U/EHMA copolymers.
Material characterization by the determination of relationships between structure and properties at different scales is essential for contemporary material engineering. This review article provides a summary of such studies on dimethacrylate polymer networks. These polymers serve as photocuring organic matrices in the composite dental restorative materials. The polymer network structure was discussed from the perspective of the following three aspects: the chemical structure, molecular structure (characterized by the degree of conversion and crosslink density (chemical as well as physical)), and supramolecular structure (characterized by the microgel agglomerate dimensions). Instrumental techniques and methodologies currently used for the determination of particular structural parameters were summarized. The influence of those parameters as well as the role of hydrogen bonding on basic mechanical properties of dimethacrylate polymer networks were finally demonstrated. Mechanical strength, modulus of elasticity, hardness, and impact resistance were discussed. The issue of the relationship between chemical structure and water sorption was also addressed.
The aim of the present research was to study the percentage
water sorption and solubility of Esthet composite
resin based on an ethoxylated bisphenol A glycol dimethacrylate
(Bis–EMA) and Heliomolar composite resin based
on bisphenol A glycol dimethacrylate (Bis–GMA). Six specimens
were prepared for each material using aluminum disc 15
mm in diameter and 1 mm in thickness between two glass
slides; then they were light cured for 80 seconds on each side.
Percentage water sorption and solubility were measured after
one week and one month. The results showed that water sorption
after 1 week for Esthet composite and Heliomolar composite
were 0.433 and 1.12, respectively and solubility were
0.074 and 1.066, respectively; while water sorption after 1
month were 0.517 and 2.57, respectively and solubility were
0.176 and 2.689, respectively.
It could be concluded that the percentage sorption and
solubility of composite based on Bis–EMA were significantly
lower than that based on Bis–GMA.
This review article compiles the characteristics of resin based dental composites and an effort is made to point out their future perspectives. Recent research studies along with few earlier articles were studied to compile the synthesis schemes of commonly used monomers, their characteristics in terms of their physical, mechanical and polymerization process with selectivity towards the input parameters of polymerization process. This review covers surface modification processes of various filler particles using silanes, wear behaviour, antimicrobial behaviour along with its testing procedures to develop the fundamental knowledge of various characteristics of resin based composites. In the end of this review, possible areas of further interests are pointed out on the basis of literature review on resin based dental materials.
The aim of this work was to obtain an efficient protocol with a green, fast and facile way to synthesize TiO2 NPs and its application as fillers for enhancement of desired dental properties of light curing dental composites.
A comparative study comprised the fabrication of light curing restorative composite materials with incorporating different fillers with varying wt%, varying resin material composition, to determine optimal dental restoration by focusing on the physical properties of dental materials. It was observed that the as-prepared green synthesized TiO2 nanohybrid particles contributed to the improvement in physical properties, thus promoting the green and rapid synthesis of nanohybrid fillers. In addition, mechanical values for experimental cured resin materials with bare and surface modified fillers were obtained. The experimental light curing nanocomposites with 5 wt% (wt%) nanohybrid surface modified filler particles with BisGMA (60 wt%), TEGDMA (20 wt%) and UDMA (20 wt%) resin composition provided increased physical strength and durability with higher compressive stress 195.56 MPa and flexural stress 83.30 MPa. Furthermore, the dental property, such as polymerization shrinkage (PS) obtained from volumetric method was decreased up to 3.4% by the addition of nano-hybrid fillers. In addition to this, the biocompatible and antimicrobial nature of TiO2 and its aesthetics properties such as tooth-like color makes TiO2 favorable to use as fillers.
This study presents a green and facile method for the synthesis of TiO2 nanohybrid particles that can be successfully used as fillers in an experimental light curing resin matrix for enhancing its dental properties. This describes the potential of the green synthesized TiO2 nanohybrid particles to use as fillers in restorative dentistry.
The aim in this study was to evaluate the influence of different ratio of camphorquinone/tertiary amine concentration on the flexural strength (FS), elastic modulus (EM), degree of conversion (DC), yellowing (YL), water sorption (WS) and water solubility (WSL) of experimental composites. Thus, acrylate blends were prepared with different camphorquinone (CQ) and amine (DABE) concentrations and ratios by weight: (CQ/DABE%): 0.4/0.4% (C1), 0.4/0.8% (C2), 0.6/0.6% (C3), 0.6/1.2% (C4), 0.8/0.8% (C5), 0.8/1.6% (C6), 1.0/1.0% (C7), 1.0/2.0% (C8), 1.5/1.5% (C9), 1.5/3.0% (C10). For the FS and EM, rectangular specimens (7x2x1 mm, n=10) were photo-activated by single-peak LED for 20 s and tested at Instron (0.5 mm/min). Then, the same specimens were evaluated by FTIR for DC measurement. For YL, disks (5x2 mm, n=10) were prepared, light-cured for 20 s and evaluated in spectrophotometer using the b aspect of the CIEL*a*b* system. For WS and WSL, the volume of the samples was calculated (mm³). For WS and WSL, composites disks (5x0.5 mm, n=5) were prepared. After desiccation, the specimens were stored in distilled water for 7 days and again desiccated, in order to measure the WS and WSL. Data were submitted to one-way ANOVA and Tukey’s test (5%). The groups C8, C9 and C10 showed higher DC, EM and YL means, compared to other composites. Therefore, the FS and WS values were similar among all groups. Also, C1, C2 and C3 presented higher WSL in 7 days, compared to other composites. In general, higher concentrations of camphorquinone promoted higher physical-mechanical properties; however, inducing higher yellowing effect for the experimental composites
Contemporary dentistry literally cannot be performed without use of resin-based restorative materials. With the success of bonding resin materials to tooth structures, an even wider scope of clinical applications has arisen for these lines of products. Understanding of the basic events occurring in any dental polymerization mechanism, regardless of the mode of activating the process, will allow clinicians to both better appreciate the tremendous improvements that have been made over the years, and will also provide valuable information on differences among strategies manufacturers use to optimize product performance, as well as factors under the control of the clinician, whereby they can influence the longterm outcome of their restorative procedures.
The use of a free-radical polymerization inhibitor, butylhydroxytoluene (BHT), and a common photo-initiator, camphorquinone (CQ), to reduce polymerization stress in dental composite was investigated in this study. Samples were prepared by mixing Bis-GMA, UDMA, and TEGDMA at a 1:1:1 ratio (wt%), and silanized borosilicate glass fillers at 70 wt% were added to form the composite. Sixteen groups of resin composite were prepared using combinations of four CQ (0.1%, 0.5%, 1.0%, and 1.5%) and four BHT (0.0%, 0.5%, 1.0%, and 1.5%) concentrations. For each group, six properties were tested, including flexural strength (FS), flexural modulus (FM), degree of conversion (DC), contraction stress (CS), stress rate, and gel point (GP). The effects of CQ and BHT combinations on each of these properties were evaluated using two-way analysis of variance (ANOVA) and Fisher's Protected Least Significant Differences test at the 5% significance level. Groups with low CQ and BHT showed moderate values for FS, FM, and CS with a 70% DC. Increasing the BHT concentration caused a decrease in CS and DC with an increase in GP values. Increasing the CQ content led to a steady increase in values for FS and FM. High CQ and BHT combinations showed the most promising values for mechanical properties with low stress values.
Dental resin composite cements were prepared with simply mixing method of Part A and Part B. The material components in Part A were composed of Bis-GMA, TEDGMA, 4-META, SiO2 nanopowders and BPO. The components in Part B were Bis-GMA, TEDGMA, 4-META, SiO2 nanopowders and 2,2¢-(4-methylphenylimino) diethanol. Before using SiO2 nano-filler in the formulation of Part A and Part B, it had to be coated with methacryloxypropyltrimethoxysilane (MPS) which served as a silane coupling agent. Therefore, the optimum amount of MPS (1, 1.2, 1.5 and 2%) and SiO2 nano-filler (20, 27.27 and 33.33 wt%) used to fabricate the composites were investigated. The homogeneous mixture of Part A and Part B at mass fraction of 1:1 was formed into the bar shape with dimension of 25 mm x 2.0 mm x 2.0 mm and then cured under light source for 20 s. Then flexural strength was measured using the universal testing machine. Depth of cure was tested using mould which was perforated in cylindrical shape of 6 mm in depth and of 4 mm in diameter. The result showed that composite with 27.27 wt% of salinized SiO2 nanopowders by 1.5% of MPS showed the highest flexural strength of 65 MPa and depth of cure of more than 5 mm which were accepted according to ISO 4049. This study could be concluded that using a proper amount of MPS to silanize SiO2 nanopowders and using an optimum amount of SiO2 nanopowders significantly improved the flexural strength of dental resin composite cements.
Unlabelled:
The aim of this study was to evaluate the effect of low shrinkage monomers on physicochemical properties of dental resin composites. Two low shrinkage resin composites: one with a crosslink branching monomer (Kalore, GC Corp) and a novel monomer (Venus Diamond, Heraeus Kulzer) were compared to a conventional resin composite formulation (Filtek Z250, 3M/ESPE). The volumetric shrinkage was evaluated by µCT analysis (n=5) and the physicochemical properties by degree of C=C conversion (DC), flexural strength (FS) and Young's modulus (YM) (n=10). All samples were light cured by a LED device (Radii, SDI) with 16 J/cm2. The results were analysed by one-way ANOVA and Tukey test for multiple comparisons (α=0.05). No statistical difference was found between µCT shrinkage values to Kalore (1.8%) and Venus Diamond (1.7%) (p≥0.05); Z250 presented statistical highest shrinkage value (2.0%). Kalore presented higher statistical DC (60.8%) than Venus Diamond (49.5%) and Z250 (49.6%). No statistical difference was found between FS or YM properties to Venus Diamond and Z250; Kalore presented statistical lowest FS and YM properties (p≥0.05).
Conclusion:
Using novel monomers seem to reduce polymerization shrinkage without affecting the physicochemical properties evaluated of resin composites rather than using crosslink branching monomers.
Objectives: To evaluate the effect of photoinitiators and reducing agents on cure efficiency and color stability of resin-based composites using different LED wavelengths.
Methods: Model resin-based composites were associated with diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) or camphorquinone (CQ) associated with 2-(dimethylamino)ethyl methacrylate (DMAEMA), ethyl 4-(dimethyamino)benzoate (EDMAB) or 4-(N,N-dimethylamino)phenethyl alcohol (DMPOH). A narrow (Smartlite, Dentisply) and a broad spectrum (Bluephase G2, Ivoclar Vivadent) LEDs were used for photo-activation (20J/cm2). Fourier transform infrared spectroscopy (FT-IR) was used to evaluate the cure efficiency for each composite, and CIELab parameters to evaluated color stability (ΔE00) after aging. The UV-vis absorption spectrophotometric analysis of each photoinitiator and reducing agent was determined. Data were analyzed using two-way ANOVA and Tukey’s test for multiple comparisons (α=0.05).
Results: Higher cure efficiency was found for type-I photoinitiators photo-activated with a broad spectrum light, and for CQ-systems with a narrow band spectrum light, except when combined with an aliphatic amine (DMAEMA). Also, when combined with aromatic amines (EDMAB and DMPOH), similar cure efficiency with both wavelength LEDs was found. TPO had no cure efficiency when light-cured exclusively with a blue narrowband spectrum. CQ-systems presented higher color stability than type-I photoinitiators, especially when combined with DMPOH.
Conclusions: After aging, CQ-based composites became more yellow and BAPO and TPO lighter and less yellow. However, CQ-systems presented higher color stability than type-I photoinitiators, as BAPO- and TPO-, despite their higher cure efficiency when photo-activated with corresponding wavelength range.
Clinical Significance: Color matching is initially important, but color change over time will be one of the major reasons for replacing esthetic restorations; despite the less yellowing of these alternative photoinitiators, camphorquinone presented higher color stability.
The characteristics of Ethoxylated-BisGMA (E-GMA) composite were investigated to find out its possibility as an alternative to Bis-GMA. Even though Bis-GMA has been most commonly used as a major matrix for the restorative composites, Bis-GMA has an inherent problem of huge viscosity. In this study, the properties of E-GMA composite were investigated and compared with those of Bis-GMA composite. The E-GMA composite exhibited much better physical-chemical properties than Bis-GMA/TEGDMA (70wt%/30wt%) composite; for example, deeper depth of cure, higher degree-of-conversion (DC), lower polymerization shrinkage, and lower water sorption. From these experimental results, it might be suggested that E-GMA could be used as a promising alternative to the most widely used material of Bis-GMA.
The viscosity of the initial monomer mixture and the chemical structure of the monomers are both important variables in the kinetic behavior of resin composites. This paper aims to determine the effect of opaque mineral fillers and monomer ratios on the shrinkage strain-rate and time at maximum shrinkage strain (Smax) rate, of experimental composites based on (BisGMA/TEGDMA) monomers. Polymerization shrinkage and the degree of conversion (DC) of resin composites are closely related manifestations of the same process. The proportionality of these two properties was also investigated by studying the variation of the ratio: (total shrinkage strain/degree of conversion): (Smax/DC), as a function of mineral filler contents and monomer ratios.
Resin composites were prepared by mixing different monomer ratios of (BisGMA/TEGDMA) with camphoroquinone and dimethyl aminoethyl methacrylate (DMAEMA) as photo-initiator system. Five different radiopacifying filler agents: La2O3, BaO, BaSO4,·SrO and ZrO2 at various volume fractions ranging from 0 to 80 wt.% were added. The samples were cured at ca. 550 mW/cm2. The shrinkage strain-rate, was calculated from the derivative of shrinkage strain using numerical differentiation. The shrinkage strain was measured by the bonded-disk technique at room temperature. Degree of conversion was calculated using FTIR/ATR spectroscopy.
The results revealed that the fraction of opaque filler had no significant effect on the shrinkage strain-rate and on the time at maximum shrinkage strain-rate but these two parameters are closely related to the monomer ratios and viscosity of the organic matrix. The results have confirmed the proportionality of the shrinkage strain and DC and showed that the filler contents and monomer ratios would not affect this proportionality.
While it is reasonably well known that certain dental procedures increase the temperature of the tooth's surface, of greater interest is their potential damaging effect on the pulp and tooth-supporting tissues. Previous studies have investigated the responses of the pulp, periodontal ligament, and alveolar bone to thermal irritation and the temperature at which thermal damage is initiated. There are also many in vitro studies that have measured the temperature increase of the pulp and tooth-supporting tissues during restorative and endodontic procedures. This review article provides an overview of studies measuring temperature increases in tooth structures during several restorative and endodontic procedures, and proposes clinical guidelines for reducing potential thermal hazards to the pulp and supporting tissues.
The organic phase of resin composites is constituted by dimethacrylate resins, the most common monomers being the bisphenol A diglycidildimethacrylate (BisGMA), its ethoxylated version (BisEMA), triethylene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA). This study compared the homopolymers formed from the monomers used in restorative dental composites in terms of their degree of conversion (DC) and reaction kinetics (by near infra-red spectroscopy, n=3), mechanical properties (flexural modulus and strength in three point-bending, FM and FS, respectively, n=15), water sorption and solubility (WS and SL, respectively - ISO 4049, n=5). Materials were made photopolymerizable by the addition of camphoroquinone/dimethylamine ethyl methacrylate. TEGDMA showed the highest DC, followed by BisEMA, UDMA and BisGMA, both at 10 min and at 24h (p<0.001). UDMA showed the highest rate of polymerization, followed by TEGDMA, BisEMA and BisGMA (H0=13.254, p<0.001). UDMA and TEGDMA presented similar FM, significantly higher (p<0.001) than BisEMA and BisGMA, which in turn present statistically similar values (p>0.001). For FS, UDMA presented the highest value (p<0.001), followed by TEGDMA, then by BisEMA and BisGMA, which were statistically similar (p>0.001). BisGMA showed the highest WS, and TEGDMA and BisEMA the lowest. UDMA was statistically similar to all (H0=16.074, p<0.001). TEGDMA presented the highest SL, followed by UDMA, BisGMA and BisEMA (p<0.001). The tested homopolymers presented different behaviors in terms of polymerization kinetics, flexural properties, water sorption and solubility. Therefore, the use of copolymers is justified in order to obtain high DC and mechanical properties, as well as good resistance to water degradation.
The purpose of this study was to compare the inorganic content and morphology of one nanofilled and one nanohybrid composite with one universal microhybrid composite. The Vickers hardness, degree of conversion and scanning electron microscope of the materials light-cured using LED unit were also investigated. One nanofilled (Filtek™ Supreme XT), one nanohybrid (TPH®(3)) and one universal microhybrid (Filtek™ Z-250) composite resins at color A(2) were used in this study. The samples were made in a metallic mould (4 mm in diameter and 2 mm in thickness). Their filler weight content was measured by thermogravimetric analysis (TG). The morphology of the filler particles was determined using scanning electron microscope equipped with a field emission gun (SEM-FEG). Vickers hardness and degree of conversion using FT-IR spectroscopy were measured. Filtek™ Z-250 (microhybrid) composite resin shows higher degree of conversion and hardness than those of Filtek™ Supreme XT (nanofilled) and TPH®(3) (nanohybrid) composites, respectively. The TPH(3)® (nanohybrid) composite exhibits by far the lowest mechanical property. Nanofilled composite resins show mechanical properties at least as good as those of universal hybrids and could thus be used for the same clinical indications as well as for anterior restorations due to their high aesthetic properties.
Objectives
The objective was to investigate the mechanical properties, fluoride release and apatite formation of resin based dental composites based on a fluoride containing Bioactive Glass (BG) with and without a silylating agent.
Methods
A SiO2–P2O5–CaO–SrO–Na2O–CaF2 BG was synthesized by the melt quench route. This glass and a commercially available inert glass (IG) were incorporated into a light cured BisGMA-TEGMA resin. The composite resins were then evaluated in terms of their ability to form apatite by Fourier Transform Infrared spectroscopy (FTIR) and by scanning electron microscopy (SEM) following immersion in artificial saliva at pH 4 (AS4) and pH 7 (AS7). The experiments were performed with and without silylation of the BG. The compressive strength and flexural strength were determined after 1, 28 and 84 days of immersion in the AS4 and AS7 immersion media.
Results
The FTIR spectra of the BG composites exhibited split bands at approximately 560 and 600 cm⁻¹ corresponding to a apatite formation in the surface or on the surface under all immersion conditions. SEM showed the presence of a reacted layer of glass particles in the composite surface and the presence of a surface layer of apatite in AS7.
The compressive strength and flexural strength were significantly higher for the silylated BG composites. The strengths of both silylated and non silylated BG composites and IG composites decreased upon immersion.
Significance
BG composites exhibit reduced strengths upon immersion but still exhibit strengths comparable to existing composites after 84 days of immersion.
SYLOID® 244 has never been applied as a filler in composites with potential dental application. Therefore, the aim of research was to apply this silica in its unmodified and diazonium salt-modified forms in different mass ratios as fillers in light-cured methacrylic composites. The effectiveness of modification process was confirmed with the use of Raman spectroscopy. Methacrylic composites with the modified and unmodified SYLOID® 244, as well as unfilled resin as a control group were prepared. Their basic physicochemical properties, such as depth of cure, mass stability during incubation in saline, flexural and compressive strengths were examined. A positive effect of SYLOID® 244 modification on the properties of the examined composites was also demonstrated. The obtained results proved the high applicability of SYLOID® 244 as a filler in composites with potential dental applications.
Objectives:
To investigate the polymerization kinetics and the degree of conversion (DC) of experimental resin composites with varying amount of bioactive glass 45S5 (BG).
Methods:
Experimental resin composites based on a photo-curable Bis-GMA/TEGDMA resin system were prepared. The composite series contained 0, 5, 10, 20, and 40 wt% of BG and reinforcing fillers up to the total filler amount of 70 wt%. Composite specimens were light cured with 1,219 mW/cm2 for 20 or 40 s and their DC was monitored during 5 min at the data collection rate of 2 s-1 using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR).
Results:
The 5-min DC values for experimental composites were in the range of 42.4-55.9% and 47.3-57.9% for curing times of 20 and 40 s, respectively. The differences in the 5-min DC between curing times of 20 s or 40 s became more pronounced in materials with higher BG amount. Within both curing times, a decreasing trend of the 5-min DC values was observed with the increasing percentage of BG fillers. The maximum polymerization rate also decreased consistently with the increasing BG amount.
Conclusions:
Unsilanized BG fillers showed a dose-dependent inhibitory effect on polymerization rate and the DC. Extending the curing time from 20 to 40 s showed a limited potential to improve the DC of composites with higher BG amount.
Significance:
The observed inhibitory effect of BG fillers on the polymerization of resin composites may have a negative influence on mechanical properties and biocompatibility.
In this study, the effect of varying different weight fraction of silane-treated nanosilica (0-15 wt%) on the wear behavior of Bisphenol-A glycidyl methacrylate/tri-ethylene glycol dimethacrylate–based dental composite was analyzed. Fourier transform infrared spectroscopy, transmission electron microscope, and thermo-gravimetric analysis were used to characterize silane-treated filler. The in vitro wear tests were performed up to 20 000 cycles using dental wear simulator. Four different working conditions were discussed including 2-body wear in distilled water and artificial saliva as well as 3-body wear in slurry of poppy seed mixed in distilled water and poppy seed mixed in artificial saliva. The results suggested that composites with increased in nanosilica fillers exhibited lower wear volume and smoother worn surface in all working mediums. In 2-body abrasive wear, the wear rate in distilled water was 10.05% more than that in artificial saliva condition. However, in 3-body abrasive wear, the wear rate in slurry of poppy seed mixed in artificial saliva was 15.96% more than that in the medium of poppy seed mixed in distilled water condition. Also, the 2-body abrasive wear rate was 56% and 22% more than the 3-body abrasive wear rate in the slurry of distilled water and artificial saliva condition, respectively.
Tetrabenzoylgermane 1 and various substituted tetrabenzoylgermanes 2–7 were investigated as visible light (VL) photoinitiators (PIs) for dental dimethacrylate resins and dimethacrylate-based composites. The tetrabenzoylgermanes 1–7 show a very strong VL absorption between 400 and 450 nm. Substituents on the benzoyl chromophore strongly influence their properties such as melting point, solubility, absorption behavior, or PI reactivity. A good photobleaching behavior and a very high reactivity as VL PI was found in photo-differential scanning calorimeter experiments for selected tetrabenzoylgermanes. Composite pastes containing only ∼0.1 wt % of Ge-PI exhibited a sufficient photocuring due to the high PI-reactivity of the tetraacylgermanes. Among the investigated germane PIs, tetrakis(2-methylbenzoyl)germane 2 shows the best performance as VL PI for restorative composites and enables the composites to be photocured using an LED with an emission maximum of 500 nm. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46115.
Objective:
This study evaluated the effects of filler type and the addition of thio-urethane oligomers on light-transmission, polymerization kinetics and depth of cure of resin composites.
Methods:
BisGMA:UDMA:TEGMA (5:3:2wt%) were mixed with 0 (control) or 20wt% thio-urethane. Fillers with various sizes and refractive indices were included and refractive index (RI) measured. Unfilled resins were used as controls. The RIs of materials were measured before and after polymerization. The irradiance reaching the bottom of 3-mm thick specimens was measured during the polymerization. Degree of conversion to a depth of 5mm was mapped. An optical bench was used to simultaneously follow conversion and light transmission.
Results:
The addition of thio-urethane increased the RI for all composites. As expected, RI also increased with conversion for all materials. The one exception was for the material filled with OX-50, in which the RI of the composite decreased with conversion. In this case, the irradiance at the bottom of the 3mm specimen was also the lowest among all groups. The addition of thio-urethanes had only minimal effect on light transmission within a filler type, but led to increased conversion in depth for all groups. The filler type itself had a greater effect on light transmission, and that correlated well with the degree of conversion.
Significance:
The effect of the thio-urethane addition on degree of conversion in depth was dependent on filler type. The additive can be tailored to improve the RI match with the filler to optimize light transmission in dental composites.
Restorative composites have evolved significantly since they were first introduced in the early 1960s, with most of the development concentrating on the filler technology. This has led to improved mechanical properties, notably wear resistance, and has expanded the use of composites to larger posterior restorations. On the organic matrix side, concerns over the polymerization stress and the potential damage to the bonded interface have dominated research in the past 20 y, with many “low-shrinkage” composites being launched commercially. The lack of clinical correlation between the use of these materials and improved restoration outcomes has shifted the focus more recently to improving materials’ resistance to degradation in the oral environment, caused by aqueous solvents and salivary enzymes, as well as biofilm development. Antimicrobial and ester-free monomers have been developed in the recent past, and evidence is mounting for their potential benefit. This article reviews literature on the newest materials currently on the market and provides an outlook for the future developments needed to improve restoration longevity past the average 10 y.
This paper is the second in a two-part series on the topic of LED light-curing units (LCUs). This part discusses LCU selection, cross infection and decontamination, maintenance, the blue-light hazard, and some possible future developments for LCUs. The article focusses on the practical aspects of the subject from the clinician's perspective. Scientific aspects are dealt with in the cited literature.
Light curing is a critical step in the restorative process when using light-activated resin-based composites, but it is frequently not given the attention it deserves. The selection of a reliable light curing unit (LCU) that meets the practitioner's needs is an important equipment purchase. Using an inappropriate LCU may seriously compromise the quality of care without the practitioner realising their mistake until years later. The importance of the subject is reflected by the rapidly increasing use of light-cured composites and the decline in the use of amalgam. Many changes have occurred in the equipment and materials available for making light-cured restorations in the last twenty years. This article is part of a two-part series that will describe those changes and recommend guidelines for the selection, use, and maintenance of light emitting diode light-curing units (LED LCUs). This paper (Part 1) discusses terminology, clinical studies, the development of LCUs in dentistry, the aims of light-curing, and the need to deliver an adequate amount of energy. The interaction between light source and material is briefly described to demonstrate the complex nature of the resin photopolymerisation process.
Objective:
Bioactive glass (BAG) has been suggested as a possible additive for dental restorative materials because of its antimicrobial effect and potential for promoting apatite formation in body fluids. The purpose of this study was to investigate the effects of bacterial biofilm on the change of colorimetric value and translucency of novel BAG-containing composites having different initial surface roughness.
Methods:
Composites with 72wt% total filler load were prepared by replacing 15% of the silanized Sr glass with BAG (65 mol % Si; 4% P; 31% Ca), BAG-F (61% Si; 31% Ca; 4% P; 3% F; 1% B), or silanized silica. Light-cured discs of 2-mm thickness (n=10/group) were divided into 4 different surface roughness subgroups produced by wet polishing with 600 and then up to 1200, 2400, or 4000 grit SiC. CIE L*a*b* were measured and the color difference and translucency parameter (TP) were calculated before and after incubating in media with or without a Streptococcus mutans (UA 159) biofilm for 2 wks (no agitation). Results were analyzed using ANOVA/Tukey's test (α=0.05).
Results:
All the color differences for BAG and BAG-F composite showed significant decreases with bacterial biofilm compared to media-only. The mean TP (SD) of BAG and BAG-F composite before aging [10.0 (2.8) and 8.5 (1.4)] was higher than that of the control composite [4.9 (0.8)], while the change in TP with aging was greater compared to the control with or without bacteria. BAG-F composites with the smoothest surfaces showed a greater decrease in TP under bacterial biofilm compared to the BAG composite.
Significance:
Highly polished dental composites containing bioactive glass additives may become slightly rougher and show reduced translucency when exposed to bacterial biofilms, but do not discolor any more than control composites that do not contain the BAG.
There are concerns that dental materials based on bis-phenol-A-glycidylmethacrylate (bis-GMA) may be hazardous. Alternative monomers such as 1,6-hexanediol dimethacrylate (HDDMA) is under research. This research aimed to determine the effect of resin matrix compositions on the biomechanical properties of E-glass fiber-reinforced composite (FRC) using bis-phenol-A-glycidylmethacrylate (bis-GMA), methylmethacrylate (MMA), 1,6-hexanediol dimethacrylate (HDDMA), camphorquinone (CQ) and N,N-cyanoethyl methylaniline (CEMA). The ratios of the resin matrices (weight %) were 78.4 % bis-GMA + 19.6 % MMA + 1 % CQ + 1 % CEMA (control-group), 78.4 % HDDMA + 19.6 % MMA + 1 % CQ + 1 % CEMA (EXP1-group) and 49 % HDDMA + 49 % MMA + 1 % CQ + 1 % CEMA (EXP2- group). E-glass fibers were embedded in matrix and light-cured for 3 × 40 s. Three-point bending (2 × 2 × 25) mm and Vicker's hardness (2 × 2 × 5) mm were examined (n = 6) by a universal testing machine (Torsee's UTM, Japan) and a micro-hardness tester (MTX70 Matsuzawa, Japan). The data were analyzed by ANOVA. Bending measurement revealed the mean value of control-group (674.1 ± 9.9) MPa was higher than EXP1-group (638.1 ± 8.6) MPa and EXP2-group (448.3 ± 7.8) MPa. The ANOVA showed significant difference in bending values among the groups (p < 0.05). Hardness measurement proved EXP1-group mean value (179.1 ± 2.5) VHN was higher than control-group (181.5 ± 11.5) VHN and EXP2-group (168.2 ± 7.9) VHN. The ANOVA proved there was significant difference (p < 0.05) in hardness values. In conclusion, a resin matrix system based on HDDMA-MMA (EXP1-group) showed comparable flexural strength and hardness properties to bis-GMA-MMA (control-group) system.
Objectives:
This study investigated the effects of bacterial biofilm on the surface properties of novel bioactive glass (BAG)-containing composites of different initial surface roughness.
Methods:
BAG (65mol% Si; 4% P; 31% Ca) and BAG-F (61% Si; 31% Ca; 4% P; 3% F; 1% B) were synthesized by the sol-gel method and micronized (size ∼0.1-10μm). Composites with 72wt% total filler load were prepared by replacing 15% of the silanized Sr glass with BAG, BAG-F, or silanized silica. Specimens (n=10/group) were light-cured and divided into 4 subgroups of different surface roughness by wet polishing with 600 and then up to 1200, 2400, or 4000 grit SiC. Surface roughness (SR), gloss, and Knoop microhardness were measured before and after incubating in media with or without a Streptococcus mutans (UA 159) biofilm for 2 weeks. Results were analyzed with ANOVA/Tukey's test (α=0.05).
Results:
The SR of the BAG-containing composites with the smoothest surfaces (2400/4000 grit) increased in media or bacteria; the SR of the roughest composites (600 grit) decreased. The gloss of the smoothest BAG-containing composites decreased in bacteria and media-only, but more in media-alone. The microhardness of all of the composites decreased with exposure to media or bacteria, with BAG-containing composites affected more than the control.
Significance:
Exposure to bacterial biofilm and its media produced enhanced roughness and reduced gloss and surface microhardness of highly polished dental composites containing a bioactive glass additive, which could affect further biofilm formation, as well as the esthetics, of restorations made from such a material.
The dependence of the depth of cure (DOC) and degree of conversion (DC) on the depth of experimental and commercial materials were determined according to ISO 4049 procedure and with the use of Raman spectroscopy, respectively. Moreover, an attempt was made to find the correlation between the DOC and DC and the depth of the material. The hypothesis was that curing time recommended by the manufacturers is appropriate for curing both commercial and experimental materials to achieve comparable values of the examined properties. The impact of the filler characteristic was clearly observed. The longer curing time provides a deeper curing (DOC values) and higher reaction rate (DC); however, the dependence between the DC values and DOC values was not visible. Instead, a logarithmic trend in the relation of the DOC and curing time was clearly observed. The results of this study suggest that the experimental materials give some hope for potential clinical applications and should be further investigated. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42812.
For improved interstudy reproducibility, reduced risk of premature failures, and ultimately better patient care, researchers and dentists need to know how to accurately characterize the electromagnetic radiation (light) they are delivering to the resins they are using. The output from a light-curing unit (LCU) is commonly characterized by its irradiance. If this value is measured at the light tip, it describes the radiant exitance from the surface of the light tip, and not the irradiance received by the specimen. The value quoted also reflects only an averaged value over the total measurement area and does not represent the irradiance that the resin specimen is receiving locally or at a different moment in time. Recent evidence has reported that the spectral emission and radiant exitance beam profiles from LCUs can be highly inhomogeneous. This can cause nonuniform temperature changes and uneven photopolymerization within the resin restoration. The spectral radiant power can be very different between different brands of LCUs, and the use of irradiance values derived from dental radiometers to describe the output from an LCU for research purposes is discouraged. Manufacturers should provide more information about the light output from the LCU and the absorption spectrum of their resin-based composite (RBC). Ideally, future assessments and research publications should include the following information about the curing light: 1) radiant power output throughout the exposure cycle and the spectral radiant power as a function of wavelength, 2) analysis of the light beam profile and spectral emission across the light beam, and 3) measurement and reporting of the light the RBC specimen received as well as the output measured at the light tip.
© International & American Associations for Dental Research 2015.
This in vivo study evaluated pulp temperature (PT) rise in human premolars during exposure to a light curing unit (LCU) using selected exposure modes (EMs).
After local Ethics Committee approval, intact first upper premolars, requiring extraction for orthodontic reasons, from 8 volunteers, received infiltrative and intraligamental anesthesia. The teeth (n=15) were isolated using rubber dam and a minute pulp exposure was attained. A sterile probe from a wireless, NIST-traceable, temperature acquisition system was inserted directly into the coronal pulp chamber, and real time PT (°C) was continuously monitored while the buccal surface was exposed to polywave light from a LED LCU (Bluephase 20i, Ivoclar Vivadent) using selected EMs allowing a 7-min span between each exposure: 10-s either in low (10-s/L) or high (10-s/H); 5-s-turbo (5-s/T); and 60-s-high (60-s/H) intensities. Peak PT values and PT increases from baseline (ΔT) after exposure were subjected to one-way, repeated measures ANOVAs, and Bonferroni's post hoc tests (α=0.05). Linear regression analysis was performed to establish the relationship between applied radiant exposure and ΔT.
All EMs produced higher peak PT than the baseline temperature (p<0.001). The 60-s/H mode generated the highest peak PT and ΔT (p<0.001), with some teeth exhibiting ΔT higher than 5.5°C. A significant, positive relationship between applied radiant exposure and ΔT (r(2)=0.916; p<0.001) was noted.
Exposing intact, in vivo anesthetized human upper premolars to a polywave LED LCU increases PT, and depending on EM and the tooth, PT increase can be higher than the critical ΔT, thought to be associated with pulpal necrosis.
Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
Network homo- and copolymers were prepared by photo- and thermal radical polymerizations of urethane dimethacrylate bearing photo-initiating Irgacure unit (IrDM) at the same molecule, and their thermal, optical, and mechanical properties were investigated. In the photopolymerization, the resulting IrDM homopolymer indicated the highest glass transition temperature and thermal stability among homo- and copolymers of IrDM and MMA studied. In particular, IrDM homopolymer has the excellent environmental stability, and the coloration of IrDM copolymers and poly(MMA) observed by, heating seems to arise from the additional reactions of free initiator fragment and monomer remained unreacted in the system. For optical properties, all their polymers represented high transparency and refractive index (RI), but the mechanical properties much depended on the contents of IrDM unit in the copolymer. In the thermal copolymerization of IrDM and MMA using benzoyl peroxide (BPO) as an initiator, the resulting copolymers have still a photo-initiating unit at the bridge in the network structure, and post photo-irradiation to the polymer changed the mechanical performances. In addition, the copolymers of IrDM with 2-hydroxy methacrylate and acrylic acid (AA) were also prepared and their unique functionalities were investigated.
In the past 10 years, many new components were synthesized and evaluated for an application in enamel–dentin adhesives and direct composite restoratives. New bisacrylamide cross-linkers with improved hydrolytic stability and new strongly acidic polymerizable phosphonic acids and dihydrogen phosphates, as well as novel photoinitator systems, in combination with the implementation of novel application devices, have significantly improved the performance of the current enamel–dentin adhesives. The currently used resins for direct composite restoratives are mainly based on methacrylate chemistry to this day. A continuous improvement of the properties of current composites was achieved with the use of new tailor-made methacrylate cross-linkers, new additives, and photoinitiators as well as tailor-made fillers. Nowadays, dental adhesives and methacrylate-based direct restorative materials have found wide-spread acceptance. Nevertheless, future developments in the field of dental adhesives and direct composite restoratives will focus on improving durability and biocompatibility as well as the development of materials with a broader application spectrum and of smart adhesives or composites. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
To survey the recent literature from the late 1980s to recent years in order to assess the relationship between resin degradation, catalyzed by biological factors, and clinical failure outcomes such as marginal breakdown.
The literature shows that degradation occurs in many manufacturers' products despite varied vinyl acrylate compositions. The authors examine salivary enzyme activity and their ability to degrade the polymeric matrix of resin composites and adhesives, as well as oral microorganisms that can promote demineralization of the tooth surface at the marginal interface. A survey of recent research relating matrix metalloproteinase (MMPs) to the degradation of the exposed collagen at the dentin adhesive interface is also discussed in the context of marginal breakdown.
The literature provides strong support that together, the above factors can breakdown the marginal interface and limit the longevity of resin composite restorations. The authors have found that the field's current understanding of resin biodegradation in the oral cavity is just beginning to grasp the role of bacteria and enzymes in the failure of resin-based restorations.
Knowledge of these biodegradation processes is pertinent to areas where innovative strategies in the chemistry of restorative materials are anticipated to enhance the longevity of resin composites.
This work was aimed at the study by dynamic mechanical analysis (DMA) of dental composites consisted of a Bis-GMA/TEGDMA (50/50 wt/wt matrix and silica nanoparticles (Aerosil OX50) as filler, silanized with various silanes. The silanes used were 3-[(1,3(2)-dimethacryloyloxypropyl)-2 (3)-oxycarbonylamidol propyltriethoxy-silane (UDMS), 3-methacryloxypropyl-trimethoxysilane (MPS), octyltrimethoxysilane (OTMS), blends of UDMS/OTMS (50/50 wt/wt), or MPS/OTMS (50/50 wt/wt). The total amount of silane was kept constant at 10%, by weight fraction relative to the filler weight. The silanized nanoparticles were mixed with the dimethacrylate matrix (60%) filler by weight fraction). The composites were light cured and tested by DMA for the determination of storage modulus (E'), loss modulus (E ''), tangent delta (tan delta), and glass transition temperature (T(g)). Measurements were performed in samples immediately after curing and samples stored in water at 37 degrees C for 1, 7, 30, or 120 days. OTMS-composite in which OTMS does not form covalent bond with the dimethacrylate matrix showed lower elastic modulus both in dry and wet conditions. The ability of bifunctional UDMS for crosslinking was found not to increase the elastic behavior of the composite, as it was expected, compared with that of MPS-composite, because of the high amount of the silane used. After immersion in water the elastic modulus of OTMS-composite remained constant, while that of the other composites increased after I day and then remained constant Lip to 120 days. (c) 2008 Wiley Periodicals, Inc.
This study investigated power density and relevant information related to light-curing units used in private dental offices in Changchun City, China. The power density of 196 light-curing units used in private dental offices in Changchun City was measured using a simple random sampling method. Relevant information included the brand, type, years of operation, frequency of use, model numbers and types of light guide, resin buildup on the light guides, damage caused by the light guides, required maintenance of the curing lights, and ratio of the unit and chair number. There were 132 quartz tungsten halogen (QTH) units and 64 light-emitting diode units. The power density range was defined as 0-1,730 mW/cm(2). The mean power density was 453.1 mW/cm(2). The mean years of operation of the light-curing units were 3.96. The majority of dentists never tested the power density of the light-curing units and a considerable number of light guide surfaces showed resin buildup and damage. In Changchun City, the majority of light-curing units were QTH. Some units needed to be replaced due to aging. The majority of dentists were not aware that the light-curing units require periodic testing and maintenance. The data herein indicate the importance of periodic testing of the power density of light-curing units and timely replacement of the components and then guarantee the quality of medical services and their benefits to patients.
Objectives:
Light cured materials are increasingly used in orthodontic clinical practice and concurrent with developments in materials have been developments in light curing unit technology. In recent years the irradiances of these units have increased. The aim of this study was to determine the safe exposure times to both direct and reflected light.
Methods:
The weighted irradiance and safe exposure times of 11 dental curing lights (1 plasma arc, 2 halogen and 8 LED lights) were determined at 6 distances (2-60 cm) from the light guide tip using a spectroradiometer. In addition, using the single most powerful light, the same two parameters were determined for reflected light. This was done at a distance of 10 cm from the reflected light, but during simulated bonding of 8 different orthodontic brackets of three material types, namely stainless steel, ceramic and composite.
Results:
The results indicate that the LED Fusion lamp had the highest weighted irradiance and the shortest safe exposure time. With this light the maximum safe exposure time without additional eye protection for the patient (at 10 cm), the operator (at 30 cm) and the assistant (at 60 cm) ranged from 2.5 min, 22.1 min and 88.8 min respectively. This indicates a relatively low short term risk during normal operation of dental curing lights. For reflected light at a distance of 10 cm the risk was even lower, but was affected by the material and shape of the orthodontic bracket under test.
Significance:
The short term risks associated with the use of dental curing lights, halogen, LED or plasma, appear to be low, particularly if as is the case adequate safety precautions are employed. The same is true for reflected light from orthodontic brackets during bonding. What is still unclear is the potential long term ocular effects of prolonged exposure to the blue light generated from dental curing lights.
Objectives:
The majority of modern resin-based oral restorative biomaterials are cured via photopolymerization processes. A variety of light sources are available for this light curing of dental materials, such as composites or fissure sealants. Quartz-tungsten-halogen (QTH) light curing units (LCUs) have dominated light curing of dental materials for decades and are now almost entirely replaced by modern light emitting diode light curing units (LED LCUs). Exactly 50 years ago, visible LEDs were invented. Nevertheless, it was not before the 1990s that LEDs were seriously considered by scientists or manufactures of commercial LCUs as light sources to photopolymerize dental composites and other dental materials. The objective of this review paper is to give an overview of the scientific development and state-of-the-art of LED photopolymerization of oral biomaterials.
Methods:
The materials science of LED LCU devices and dental materials photopolymerized with LED LCU, as well as advantages and limits of LED photopolymerization of oral biomaterials, are discussed. This is mainly based on a review of the most frequently cited scientific papers in international peer reviewed journals. The developments of commercial LED LCUs as well as aspects of their clinical use are considered in this review.
Results:
The development of LED LCUs has progressed in steps and was made possible by (i) the invention of visible light emitting diodes 50 years ago; (ii) the introduction of high brightness blue light emitting GaN LEDs in 1994; and (iii) the creation of the first blue LED LCUs for the photopolymerization of oral biomaterials. The proof of concept of LED LCUs had to be demonstrated by the satisfactory performance of resin based restorative dental materials photopolymerized by these devices, before LED photopolymerization was generally accepted. Hallmarks of LED LCUs include a unique light emission spectrum, high curing efficiency, long life, low energy consumption and compact device form factor.
Significance:
By understanding the physical principles of LEDs, the development of LED LCUs, their strengths and limitations and the specific benefits of LED photopolymerization will be better appreciated.
Objectives:
This work aims to review the key factors affecting the polymerization efficiency of light-activated resin-based composites. The different properties and methods used to evaluate polymerization efficiency will also be critically appraised with focus on the developments in dental photopolymer technology and how recent advances have attempted to improve the shortcomings of contemporary resin composites.
Methods:
Apart from the classical literature on the subject, the review focused in particular on papers published since 2009. The literature research was performed in Scopus with the terms "dental resin OR dimethacrylate". The list was screened and all papers relevant to the objectives of this work were included.
Results:
Though new monomer technologies have been developed and some of them already introduced to the dental market, dimethacrylate-based composites still currently represent the vast majority of commercially available materials for direct restoration. The photopolymerization of resin-based composites has been the subject of numerous publications, which have highlighted the major impact of the setting process on material properties and quality of the final restoration. Many factors affect the polymerization efficiency, be they intrinsic; photoinitiator type and concentration, viscosity (co-monomer composition and ratio, filler content) and optical properties, or extrinsic; light type and spectrum, irradiation parameters (radiant energy, time and irradiance), curing modes, temperature and light guide tip positioning.
Significance:
: This review further highlights the apparent need for a more informative approach by manufacturers to relay appropriate information in order for dentists to optimize material properties of resin composites used in daily practice.
This work was aimed at the study by dynamic mechanical analysis (DMA) of dental composites consisted of a Bis-GMA/TEGDMA (50/50 wt/wt) matrix and silica nanoparticles (Aerosil OX50) as filler, silanized with various silanes. The silanes used were 3-[(1,3(2)-dimethacryloyloxypropyl)-2 (3)-oxycarbonylamido] propyltriethoxy-silane (UDMS), 3-methacryloxypropyl-trimethoxysilane (MPS), octyltrimethoxysilane (OTMS), blends of UDMS/OTMS (50/50 wt/wt), or MPS/OTMS (50/50 wt/wt). The total amount of silane was kept constant at 10% by weight fraction relative to the filler weight. The silanized nanoparticles were mixed with the dimethacrylate matrix (60% filler by weight fraction). The composites were light cured and tested by DMA for the determination of storage modulus (E′), loss modulus (E″), tangent delta (tan δ), and glass transition temperature (Tg). Measurements were performed in samples immediately after curing and samples stored in water at 37°C for 1, 7, 30, or 120 days. OTMS-composite in which OTMS does not form covalent bond with the dimethacrylate matrix showed lower elastic modulus both in dry and wet conditions. The ability of bifunctional UDMS for crosslinking was found not to increase the elastic behavior of the composite, as it was expected, compared with that of MPS-composite, because of the high amount of the silane used. After immersion in water the elastic modulus of OTMS-composite remained constant, while that of the other composites increased after 1 day and then remained constant up to 120 days. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Methacrylate-functionalized silsesquioxanes (SSQO) were synthesized by the hydrolytic condensation of 3-(methacryloxypropyl)
trimethoxysilane (MPTMS) using dimethacrylate monomers as reactive solvent. Resins containing about 40wt% SSQO displayed
a modest increase in viscosity compared with the unmodified methacrylate monomer. This is attributed to a dilution of the
reacting medium, which discourages bimolecular reactions that lead to the generation of high-molar mass oligomers and, consequently,
prevents undesired increases of viscosity. Substitution of monomer with SSQO reduced the volumetric shrinkage during photopolymerization.
The amount of leachable monomer detected in formulations containing SSQO was markedly reduced. This indicates that the unreacted
monomer exists mainly as pendant chains instead of free leachable monomer. The presence of different proportions of SSQO in
the methacrylate monomer resulted in no apparent change in the flexural modulus and in a modest decrease in the compressive
yield stress of the polymerized materials. From results presented in this research, it emerges that methacrylate monomers
modified with SSQO are attractive for applications that require reduced volumetric shrinkage and long storage periods, such
as light-cured dental restorative composites.
To demonstrate that determination of the depth of cure of resin-based composites needs to take into account the depth at which the transition between glassy and rubbery states of the resin matrix occurs.
A commercially available nano-hybrid composite (Grandio) in a thick layer was light cured from one side for 10 or 40 s. Samples were analyzed by Vickers indentation, Raman spectroscopy, atomic force microscopy, electron paramagnetic imaging and differential scanning calorimetry to measure the evolution of the following properties with depth: microhardness, degree of conversion, elastic modulus of the resin matrix, trapped free radical concentration and glass transition temperature. These measurements were compared to the composite thickness remaining after scraping off the uncured, soft composite.
There was a progressive decrease in the degree of conversion and microhardness with depth as both properties still exhibited 80% of their upper surface values at 4 and 3.8 mm, respectively, for 10 s samples, and 5.6 and 4.8 mm, respectively, for 40 s samples. In contrast, there was a rapid decrease in elastic modulus at around 2.4 mm for the 10 s samples and 3.0 mm for the 40 s samples. A similar decrease was observed for concentrations of propagating radicals at 2 mm, but not for concentrations of allylic radicals, which decreased progressively. Whereas the upper composite layers presented a glass transition temperature - for 10 s, 55°C (±4) at 1 mm, 56.3°C (±2.3) at 2 mm; for 40 s, 62.3°C (±0.6) at 1 mm, 62°C (±1) at 2 mm, 62°C (±1.7) at 3 mm - the deeper layers did not display any glass transition. The thickness remaining after scraping off the soft composite was 7.01 (±0.07 mm) for 10 s samples and 9.48 (±0.22 mm) for 40 s samples.
Appropriate methods show that the organic matrix of resin-based composite shifts from a glassy to a gel state at a certain depth. Hence, we propose a new definition for the "depth of cure" as the depth at which the resin matrix switches from a glassy to a rubbery state. Properties currently used to evaluate depth of cure (microhardness, degree of conversion or scraping methods) fail to detect this transition, which results in overestimation of the depth of cure.
The study evaluates properties of an experimental dental composite consisting of a porous thermally sintered nano-silica as filler. The properties are compared with those of an experimental composite containing micro fillers and a commercially available nano-composite, Filtek Supreme(®) Translucent. Different models are used to predict the elastic modulus and strength of the composites.
Nano-silica with primary particles of 12 nm was thermally sintered to form nanoporous filer particles. The experimental composites were prepared by incorporating 70 wt.% of the fillers into a mixture of Bis-GMA and TEGDMA as matrix phase. Having added photoinitiator system the composites were inserted into the test molds and light-cured. The microfiller containing composites were also prepared using micron size glass fillers. Degree of conversion (DC%) of the composites was measured using FTIR spectroscopy. Diametral tensile strength (DTS), flexural strength, flexural modulus and fracture toughness were measured. SEM was utilized to study the cross section of the fractured specimens. The surface topography of the specimens was investigated using atomic force microscopy (AFM). The specific surface area of the sintered nano silica was measured using BET method. The data were analyzed and compared by ANOVA and Tukey HSD tests (significance level=0.05).
The results showed improvements in flexural modulus and fracture toughness of the composites containing sintered filler. AFM revealed a lower surface roughness for sintered silica containing composites. No significant difference was observed between DTS, DC%, and flexural strength of the sintered nanofiller composite and the Filtek Supreme(®). The results also showed that the modulus of the composite with sintered filler was higher than the model prediction.
The thermally sintered nano-porous silica fillers significantly enhanced the mechanical properties of dental composites introducing a new approach to develop materials with improved properties.
Light polymerizable tooth colored restorative materials are most widely preferred for advantages such as esthetics, improved physical properties and operator's control over the working time. Since the introduction of these light polymerizable restorative materials, there has been a concern about the depth of appropriate cure throughout the restoration. Photopolymerization of the composite is of fundamental importance because adequate polymerization is a crucial factor for optimization of the physical and mechanical properties and clinical results of the composite material. Inadequate polymerization results in greater deterioration at the margins of the restoration, decreased bond strength between the tooth and the restoration, greater cytotoxicity, and reduced hardness. Therefore, the dentist must use a light curing unit that delivers adequate and sufficient energy to optimize composite polymerization. Varying light intensity affects the degree of conversion of monomer to polymer and depth of cure.
The purpose of this work was the study of the effect of the amount of a urethane dimethacrylate silane (UDMS) coupling agent on physical properties of dental light-cured resin nanocomposites based on Bis-GMA/TEGDMA (50/50 wt/wt) matrix and Aerosil OX50 as filler.
Silica nanoparticles (Aerosil OX 50) used as filler were silanized with 5 different amounts of UDMS 1.0, 2.5, 5.0, 7.5 and 10 wt% relative to silica. The silanizated silica nanoparticles were identified by FT-IR spectroscopy and thermogravimetric analysis (TGA). Then the silanized nanoparticles (60 wt%) were mixed with a Bis-GMA/TEGDMA (50/50 wt/wt) matrix. Degree of conversion of light cured composites was determined by FT-IR analysis. The static flexural strength and flexural modulus were measured using a three-point bending set up. The dynamic thermomechanical properties were determined by DMA analyzer. Measurements were taken in samples stored, immediately after curing, in water at 37°C for 24 h. Sorption, solubility and volumetric change were determined after storage of composites in water or ethanol/water of 75 vol% for 30 days. Thermogravimetric analysis of composites was performed in nitrogen atmosphere from 50 to 800°C.
Almost all of used amount of silane remained chemically bounded on the surface of silica particles, forming a layer around them, which have dense accumulation of methacrylate groups. No significant statistic difference was found to exist between the degree of conversion values of composites with different silane contents. The composite with the lowest amount of UDMS (1.0 wt%) showed the lower flexural strength value, the higher static and dynamic elastic modulus values and the higher sorbed liquid value and solubility.
The optimum concentration of UDMS seems to be that of 2.5 wt%. Higher concentrations of UDMS did not improve the properties of composites.