Photopolymerization Of Composites Research Articles

Effect of translucency and absorbance of composite on temperature change during photopolymerization.

This study investigated the effect of translucency and absorbance of conventional (FiltekTM-Z350-XT) and bulk-fill (Tetric®-N-Ceram) composites on temperature change during photopolymerization, using a non-contact infrared sensor. Three shades from each composite were selected to prepare disk-shaped specimens (n=3), which then photopolymerized with LED-light for 20 s. A second light exposure was performed on the photopolymerized specimens. The first peak temperature rise during composite photopolymerization (ΔTtotal), second peak temperature rise by the light (ΔTlight), and net peak temperature rise by composite curing heat (ΔTcomposite) were obtained from the temperature change vs. time curve. The changes in ΔTtotal and ΔTlight with varying the composite shade were greater than those in ΔTcomposite. The conventional composite showed higher ΔTtotal and ΔTlight than bulk-fill composite. ΔTtotal and ΔTlight increased as translucency parameter decreased, and absorbance increased. The potential risk for heat-induced pulpal damage should be considered when selecting a composite shade, especially for deep cavities.

Thermal Sensing of Photo-Activated Dental Resin Composites Using Infrared Thermography.

The goal of this study was to compare the pulp temperature increase during light curing of different composite thicknesses in deep class I cavities using two thermal sensing tools. Round occlusal class I cavities with a remaining dentin thickness (RDT) of 1 mm from the cavity floor were performed on 15 extracted sound molars. Samples were divided into three groups (n = 5). In group A, cavities were restored using the Filtek Z350 XT conventional composite through the incremental filling technique, whereas group B cavities were restored using the Filtek Bulk-Fill flowable composite through the bulk-fill technique. Specimens of the Filtek Bulk-Fill flowable composite using the incremental filling technique were used to restore cavities in group C. An infrared thermal camera (IRT; Flir, Wilsonville, OR, USA) and K-type thermocouple (Perfect Prime TC0520, New York, NY, USA) were used to measure the heat generated during composite photo-polymerization. There were no significant differences within the same group using either the thermocouple or IRT (p > 0.05). One-way ANOVA showed no significant differences between groups A and C (p > 0.05), whereas group B was significantly different from groups A and C with each sensing tool (p < 0.05). IRT and thermocouple heat readings were comparable. Based on the current findings, the bulk-fill technique resulted in the lowest heat generation among the groups. Therefore, increasing the light-curing time and the number of composite increments was directly correlated with increases in intra-pulpal temperature.

66 - Thermal analysis of composite photopolymerization with non-contact infrared sensor

66 - Thermal analysis of composite photopolymerization with non-contact infrared sensor

Real-time measurement of transmittance changes during photo-polymerization of conventional and bulk-fill composites.

This study investigated transmittance changes during photo-polymerization of composites in real-time. The transmittance changes of one conventional micro-hybrid, three conventional nano-hybrid, and four bulk-fill composites were measured before, during, and after photo-polymerization, and the maximum rate of transmittance change was compared with that of polymerization shrinkage. A significant difference in transmittance of composite between before and after photo-polymerization was observed. The transmittance of composites except for one bulk-fill composite increased during photo-polymerization. There was a correlation between the maximum rate of transmittance change and the maximum rate of polymerization shrinkage. The transmittance analysis of composites gives very important information to know for the final aesthetic restoration and allows to evaluate polymerization kinetics.

Relocation and reinforcement of the adhesive/composite interface with spontaneous amine-peroxide interfacial polymerization

ObjectivesThis study demonstrates a spontaneous redox polymerization process located at the adhesive-composite interface that precedes photocure of the composite with the intent to improve bonding. MethodsAn aromatic amine and benzoyl peroxide redox initiator system was partitioned between BAPO-photoinitiated BisGMA/HEMA adhesive and BisGMA/TEGDMA resin-composites. The composite was placed on the photocured adhesive layer with a brief delay before photopolymerization of the composite layer. Micro-tensile bond strength between the adhesive and composite was assessed in comparison with the non-redox active control materials. ResultsThe presence of amine or peroxide in these resins without the redox initiation contribution enhanced both the rate and the final conversion of the BAPO-based photopolymerizations. Control formulations using redox-only initiation showed active polymer formation starting at approximately 30 s when physical mixing of the redox components was involved; however, simply by waiting 60 s between composite placement and photocure provided adequate time for passive interfacial diffusion of benzoyl peroxide from the pre-cured adhesive into the overlaid aromatic amine-containing composite such that a sufficient degree of redox initiated interfacial polymerization occurred prior to the composite photocure. The result was a significant increase in the adhesive to composite micro-tensile bond strength with the failure site moved away from the mainly interfacial failure noted for the control. SignificanceThe stress-free autonomous pre-conversion of a redox-initiated thin film of composite that then provides a compositionally homogeneous interface for composite photopolymerization offers a means to enhance at least short-term bond strength between the adhesive and composite phases during restorative placement.

Photopolymerizable Adhesives Based on Poly(Vinyl Butyral) Solutions in Methacrylic Monomers for Fireproof Glass Assemblies

Photopolymerization of compositions based on poly(vinyl butyral) solutions in a mixture of di-(1-methacryloxy-3-chloropropoxy-2-)methylphosphonate (FOM-II) and 2-hydroxypropylmethacrylate (HPMA) monomers is studied. The effectiveness of these compositions as photocurable adhesives for fireproof glass assemblies is evaluated. It is shown that the developed photopolymerizable adhesives can be recommended for fabrication of fireproof glass assemblies for building purposes due to their translucence, high adhesion to silicate glass (up to 30.5 MPa), and accordance with the EIW15 protection class according to the results of firing tests.

A New Phosphine for Efficient Free Radical Polymerization under Air.

A new phosphine is proposed as efficient coinitiator for camphorquinone (CQ)-based photoinitiating systems for the free radical polymerization of (meth)acrylates. Remarkably, this new co-initiator can exhibit two functionalities: a phosphine moiety to overcome oxygen inhibition and an iodonium salt moiety as counter cation to initiate the polymerization process. Excellent polymerization performances in the presence of CQ for the free radical polymerization of methacrylates under blue light are observed, and amine-free systems can be easily developed from the proposed structure. The photopolymerization of composites is also investigated in the presence of the new phosphine (without iodonium counter cation) and very interesting depth of cure can be obtained from the new developed photoinitiating system after only 20 s of irradiation with a blue light-emitting diode.

Comparison of temperature change of one-step self-etch adhesive and two-step self-etch adhesive during photo polymerization of composite restoration.

Objectives: To compare the mean temperature difference in one-step self-etch adhesive versus two-step-self etch adhesive during photo polymerization of composite. Study Design: Randomized control trial. Study Design: Was done at Department of Operative Dentistry Dr. Ishrat-ul-Ibad Khan Institute of Oral Health Sciences, Karachi. Period: From January 2017 to June 2017. Material &amp; Methods: A total of 92 human extracted maxillary and mandibulars third molar teeth were selected in this study. All discs were divided into two groups. 46 were treated with one-step self-etch adhesive and other 46 were treated with two-step self-etch adhesive. For both the study groups, the temperature was recorded at the start of procedure of photo polymerization and at the end of procedure. From the other side of the disc temperature was measured by non-contact infrared thermometer and recorded. Results: Male to female ratio 1.6:1. The age of the study population ranged from 20 years to 65 years, with mean age of the patients was 32.41±3.01 years. Pre and post mean and the standard deviation (SD) of temperature was 31.95±2.14 and 38.40±1.97 in One-step self-etch adhesive and 31.91±2.25 and 38.45±2.26 in two-step-self-etch adhesive group respectively. Mean change was 6.45 ± 0.78 in One-step self-etch adhesive and 6.45±0.74 in two-step-self-etch adhesive group. Mean difference was not statistically significant between groups (p=0.605). While within group comparison, mean temperature was significantly high in one-step self-etch adhesive and also in two-step-self-etch adhesive. Conclusion: It is concluded that dental practitioners should be aware of the risk of thermal insults to the pulp as a result of photo polymerization of resin-containing restorative materials, especially when caries-affected deep dentin is involved for longer periods.

Influence of Viscosity of Compositions Based on Dimethacrylate Esters on Kinetics of Their Photopolymerization Initiated by 9,10-Phenanthrenequinone

The kinetics of photopolymerization of compositions based on dimethacrylic oligomers in which the viscosity was varied from 3.1 to 376.7 cSt was investigated (initiator 9,10-phenanthrenequinone) under the influence of visible light. Triethyleneglycol dimethacrylate and dimethacrylates OCM-2 and MDPh-2 were used, as well as solvents methanol and butanol-1. The dependences of the viscosity of dimethacrylate–alcohol compositions on the concentration of components were determined. It was shown that the photoreduction rate of 9,10-phenanthrenequinone in dimethacrylate OCM-2 decreases with the alcohol and acetonitrile addition. It was found that, at the initial stages of the reaction, the dependence of the reduced photopolymerization rate on the initial viscosity of the compositions is described by a saturation curve with the plateau at a viscosity of 80 cSt or more.

Investigating the limits of resin-based luting composite photopolymerization through various thicknesses of indirect restorative materials

ObjectiveTo determine the limitations of using light-curable resin-based luting composites (RBLCs) to bond indirect ceramic/resin-composite restorations by measuring light transmittance through indirect restorative materials and the resulting degree of conversion (DC) of the luting-composites placed underneath. MethodsVarious thicknesses (0–4mm) and shades of LAVA Zirconia and LAVA Ultimate were prepared and used as light curing filters. A commercial, light curable RBLC, RelyX Veneer (control) was compared with four experimental RBLCs of the following composition: TEGDMA/BisGMA (50/50 or 30/70wt%, respectively); camphorquinone/amine (0.2/0.8wt%) or Lucirin-TPO (0.42wt%); microfillers (55wt%) and nanofillers (10wt%). RBLCs covered with the LAVA filter were light-cured for 40s, either with the dual-peak BluephaseG2 or an experimental device emitting either in the blue or violet visible band. The samples were analyzed by Raman spectroscopy to determine DC. Light transmittance through the filters was measured using a common spectroscopy technique. ResultsAll the factors studied significantly influenced DC (p<0.05). RBLCs with increased TEGDMA content exhibited higher DC. Only small differences were observed comparing DC without filters and filters ≤1mm (p>0.05). For thicknesses ≥2mm, significant reductions in DC were observed (p<0.05). Transmittance values revealed higher filter absorption at 400nm than 470nm. A minimal threshold of irradiance measured through the filters that maintained optimal DC following 40s irradiation was identified for each RBLC formulation, and ranged between 250–500mW/cm2. SignificanceThis work confirmed that optimal photopolymerization of RBLCs through indirect restorative materials (≤4mm) and irradiation time of 40s is possible, but only in some specific conditions. The determination of such conditions is likely to be key to clinical success, and all the factors need to be optimized accordingly.

Effect of Viscosity of Dimethacrylate Ester-Based Compositions on the Kinetics of Their Photopolymerization in Presence of o-Quinone Photoinitiators

The kinetics of photopolymerization of compositions based on dimethacrylate oligomers with viscosities ranging from 1.5 to 376.7 cSt under the action of visible light (9,10-phenanthrenquinone and a mixture of 3,6-di-tert-butyl-1,2-benzoquinone with N,N-dimethylcyclohexylamine as initiators) is studied. Dimethacrylates of poly(ethylene glycols) with the number of ethoxy fragments of n = 1–4 and 8, dimethacrylates of OKM-2 and MDF-2 trademarks, and solvents (benzene, acetonitrile, and dinonyl ester of phthalic acid) are used. At the initial stages of the reaction, the dependence of the reduced rate of photopolymerization of such compositions on their initial viscosity is described by a curve attaining a plateau at a viscosity of 100 cSt or above. The dependences of viscosity of all dimethacrylates on temperature ranging from –10 to +80°С are determined, the effective activation energies of monomer viscous flow are calculated, and the temperature dependences of the number of molecules in associates for each of the oligomers are ascertained. At Т = 20°С, the number of molecules in the associates of poly(ethylene glycol) dimethacrylates with n = 1–4 does not exceed 10, for n = 8 the number of molecules in the associates is ∼102, and for dimethacrylates of OKM-2 and MDF-2 trademarks this value is above 104.

Composite Photopolymerization: Temperature Increase According To Light Source And Dentin Thickness

Composite Photopolymerization: Temperature Increase According To Light Source And Dentin Thickness

Spatio-temporal analysis of shrinkage vectors during photo-polymerization of composite

ObjectivesThe purpose of this study was to validate a new method to investigate the polymerization shrinkage vectors of composite during light curing and to evaluate the overall utility and significance of the technique. MethodsAn optical instrument was developed to measure the location and direction of the polymerization shrinkage strain vectors of dental composite during light curing using a particle tracking method with computer vision. The measurement system consisted of a CCD color camera, a lens and a filter, and software for multi-particle tracking. A universal hybrid composite (Z250, 3M ESPE, St. Paul MN, USA) was molded into thin disk-shaped specimens (un-bonded and bonded) or filled into a cavity within a tooth slab (bonded). The composite surface was coated with fluorescent particles prior to light curing. The images of the fluorescent particles were stored at 2 frames/s for 10min, and the movements of the particles on the composite surface were tracked with computer vision during curing. The polymerization shrinkage strain vectors as a function of time and location were analyzed. The volume shrinkage of the composite was also measured for comparison. ResultsThe linear and volume shrinkage of the composite at 10min were 0.75 (0.12)% and 2.26 (0.18)%, respectively. The polymerization shrinkage vectors were directed toward the center of the specimen and were isotropic in all directions when the composite was allowed to shrinkage freely without bonding. In contrast, the shrinkage vectors were directed toward the bonding surface and were anisotropic when the composite was bonded to a fixed wall. The regional displacement vectors of composite in a tooth cavity were dependent on the location, depth and time. SignificanceThe new instrument was able to measure the regional linear shrinkage strain vectors over an entire surface of a composite specimen as a function of time and location. Therefore, this instrument can be used to characterize the shrinkage behaviors for a wide range of commercial and experimental visible-light-cure materials in relation to the composition, boundary condition and cavity geometry.

Synthesis of new copolymers 4,4’-sulfinylbisphenol derivative with N-vinyl-2-pyrrolidone - photopolymerization and thermo-mechanical studies

AbstractSynthesis, structure and characterization of the new sulfur monomer sulfinylbis[benzene-4,1-diyl(oxy-2-hydroxypropane-3,1-diylmethacrylate)] (SO.DM) and its photopolymerization with N-vinyl-2-pyrrolidone (NVP) are presented. SO.DM was obtained in the three-step reaction. In the first step, 4,4’- sulfinylbisphenol from 4-[(4-hydroxyphenyl)thio]phenol was obtained. In the second step the epoxy compound was synthesized. It was obtained in the reaction of 4,4’- sulfinylbisphenol with 2-(chloromethyl)oxirane in the two phases liquid/liquid system including organic and aqueous phases. In the third step, ring opening of the obtained diglycidyl ether was carried out with the use of methacrylic acid in the presence of triethylbenzylammonium chloride (TEBAC) as a catalyst. Structures of new compounds were confirmed by spectroscopic methods (FT-IR, 1H and 13CNMR and DIP-MS). Photopolymerization of compositions containing different ratios of the monomers (SO.DM and NVP) and an initiator (Irgacure 651) was carried out. The following properties (before and after curing) were determined: density, polymerization shrinkage, glass transition temperature, Young’s modulus, hardness, tensile strength. Moreover, dynamic-mechanical and thermal properties were studied.

Relationships between conversion, temperature and optical properties during composite photopolymerization

Optical properties of composite restoratives, both cured and uncured, are of obvious importance in a procedure reliant on photoactivation, since they may affect light transmission and therefore materials conversion upon which mechanical properties and ultimate clinical performance are dependent. The objective of the present study was to evaluate simultaneous, real-time conversion, and the development of the temperature and optical properties. The dimethacrylate resin (Bis-GMA/TEGDMA 70/30 mass%) was prepared at three filler loading (0, 35 or 70 mass%: no fill, low and high fill, respectively) combined with three initiator concentrations (CQ/EDMAB: 0/0, 0.2/0.8 or 1.0/1.6 mass%). Specimens were exposed to either low (50 mW cm −2) or high (500 mW cm −2) irradiance. Simultaneous conversion (near-IR peak area), temperature (thermocouple) and visible light transmission (UV–vis spectroscopy) measurements were conducted throughout the polymerization process. The refractive index of the resin rises linearly with conversion ( r 2 = 0.976), producing a refractive index match between resin/filler at approximately 58% conversion in these materials. The percentage increase in light transmission during conversion was greater for increasing filler levels. Higher CQ content led to maximum light transmission at slightly higher levels of conversion (60–65% and 50–55% for the high and low filled materials, respectively). The broad distribution of filler concentrations allows for the clinically relevant generalization that highly filled composites not only jeopardize absolute light transmission, conversion and depth of cure, but also demonstrate the complex interrelationship that exists between materials, processing conditions and the optical properties of dental composites.

Composite Photopolymerization with Diode Laser

Under clinical conditions, the time needed for the proper light curing of luting composites or the multi-incremental buildup of a large restoration with halogen curing units is quite extensive. Due to the development of high power curing devices, such as argon lasers and plasma arc lights and, in order to decrease curing time, halogen and LED devices have developed a high intensity polymerization mode. This study compared the degree of conversion using Fourier Transform Infrared Spectroscopy (FT-IR) of two composite materials: Tetric Ceram and Tetric EvoCeram polymerized with three polymerization modes (high, low and soft mode) of a Bluephase 16i LED curing unit and blue diode laser intensity of 50 mW on the output of the laser beam and 35 mW/cm2 on the resin composite sample. Descriptive statistic, t-test, ANOVA, Pearson Correlation and Tukey Post hoc tests were used for statistical analyses. The results show a higher degree of conversion for the polymerization of composite samples with all photopolymerization modes of the LED curing unit. However, there is no significant difference in the degree of conversion between the LED unit and 50-second polymerization with the blue diode laser. Tetric EvoCeram shows a lower degree of conversion regardless of the polymerization mode (or light source) used.

Forming lattices of microlenses by the method of dosed photopolymerization of UV-hardened optical composites

This paper discusses two processes for forming microstructures, based on selective photopolymerization of a composite and the volume-reduction effect of a composite when it undergoes photopolymerization. Both processes belong to the group of grey-scale lithography methods and make it possible to accurately form the surface of microlenses when the optical density distribution of a photomask over the radius of the microlens is given.

Use of near-IR to monitor the influence of external heating on dental composite photopolymerization

Objectives: This study was conducted to determine the effect of modest external heating on the photopolymerization kinetics and conversion of commercial dental composite restorative materials. Methods: A transmission-mode, real-time near-infrared spectroscopic technique was used to monitor the photopolymerization process in the composite materials at various temperatures between 23 and 70 °C. Several light curing units, differing in spectral output and power densities were compared at the different cure temperatures. Several significantly different commercial composites were compared for their response. Results: Regardless of the curing light or composite material used, photopolymerization at a moderate curing temperature of 54.5 °C resulted in significantly higher immediate and final conversion values compared with room temperature photocuring. Contrary to the room temperature cured materials, at the elevated cure temperature the extent of post-cure was minor and different curing lights produced very uniform conversion values within a given material. The time required to reach a given level of conversion, established as full conversion with the room temperature cure, was reduced typically by 80–90% using the elevated curing conditions. Complementary kinetic studies confirmed the effect of cure temperature on increasing the polymerization rate in dental composites as significant. Significance: Increasing the temperature of composite resin within potentially biologically compatible limits can significantly influences resin polymerization. These increased rates and conversion could lead to improved properties of composite restorative materials.

Distribution of the degree of conversion over the thickness of the polymer layer on photopolymerization of composites

The kinetic character of the charge in the degree of conversion in different portions of the layer of the polymer formed during photopolymerization of photopolymerized liquid composites has been elucidated. The ATR method has experimentally demonstrated the constancy of the degree of conversion (40–45%) during photopolymerization in a moving (deep in the liquid photopolymerized composite frontal to UV radiation) polymer layer at the polymer-liquid photopolymerized composite interface.

IR-spectroscopic study of the process of photopolymerization of polyvinyl compounds

The process of the change of the degree of photochemical transformation of compositions by UV irradiation in depth according to the thickness of the formed polymer was studied by the method of multiple total internal reflection in the infrared range. In layered photo-polymerization of compositions based on polyvinyl compounds, a considerable gradient of the degree of photocuring into the depth of the polymer is observed. It was shown that the mean conversion in the total layer of the polymer is equal to 85±5%), whereas at the interface between polymer-photopolymerizing composition it varies in the range 40–45%. For unidirectional irradiation under conditions securing reflection of UV radiation, the formation of the polymer proceeded as the result of the motion of two interfaces between polymer-photopolymerizable compositions, moving with different velocities in opposite directions.