Search

The real-time polymerization of light-curable experimental resin composites filled with amorphous calcium phosphate (ACP) was monitored. Experimental composites were based on a 2,2-bis[4-(2-ethoxy-3-methacryloyloxy propoxy)phenyl]propane (Bis-EMA)/triethyleneglycol dimethacrylate (TEGDMA)/2-hydroxyethyl methacrylate (HEMA) resin photoactivated by a camphorquinone/tertiary amine system. Four ACP composites were prepared, containing 40 wt% ACP and 0/10 wt% reinforcing fillers (barium glass and silica). Additionally, two control composites were prepared which contained only reinforcing fillers (40-50 wt%). The degree of conversion (DC) was monitored in real time using a Fourier-transform infrared (FTIR) spectrometer with an attenuated total reflectance accessory. During the light curing (1,219 mW cm -2 ) for either 20 or 40 s, infrared spectra were collected from the bottom of 2-mm-thick composite specimens at the rate of two spectra per second over 5 min. When cured for 40 s, the ACP composites attained a high DC (89.1%-92.4%), while the DC of control composites was significantly lower (53.5%-68.4%). All materials showed a lower DC for the shorter curing time (20 s) and various extents of 5-min postcure polymerization: 12.9%-21.5% for the ACP composites and 2.7%-5.2% for the control composites. The control composites reached the maximum reaction rate much earlier (4.1-4.3 s) and at lower DC (9.9%-10.4%) than did the ACP composites (17.4-22.0 s and 43.5%-49.3%, respectively)., (© 2018 Eur J Oral Sci.)

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 1219 mW/cm 2 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., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Objectives: to determine the mode of light transmission and its impact on the polymerisation kinetic in modern bulk-fill resin-based composites (B-RBC)., Materials and Methods: Four low-viscosity methacrylate-based and one high-viscosity ormocer-based B-RBCs were considered. One material was available in three different shades that were all analyzed. Polymerization kinetic and light transmittance were assessed in 2 and 4mm specimen depths. Incident and transmitted irradiance and radiant exposure were measured in real-time on a laboratory-grade spectrometer., Results: A progressive enhanced light transmittance during polymerisation was identified in all materials except for TetricEvoFlow BulkFill, which became progressively opaque in all shades. One-way ANOVA and multivariate analysis (α=0.05) were performed. The parameter material has a significant (p<0.001) effect on DC (η P 2 =0.856) and light transmittance parameters (irradiance, η P 2 =0.965; radiant exposure, η P >0.95), differentiating between the gel- and the glass-phase and revealing a faster initiation of polymerization and a slower transition into the glass-phase by lowering the filler volume. Depth retarded the transition into the glass-phase, but did not alter DC measured 300s post-irradiation. Moderate inverse correlation was identified among DC and filler volume% (-0.646) or filler weight% (-0.403), while no correlation among DC and light transmittance (p=0.141; 0.125). The maximal rate of carbon-carbon double bond conversion varied within the analyzed materials but was independent from specimen's depths.2 =0.956); specimen depth influences only transmittance (η P 2 =0.978; 0.980). DC variation in time was best described by an exponential sum function (R 2 >0.95), differentiating between the gel- and the glass-phase and revealing a faster initiation of polymerization and a slower transition into the glass-phase by lowering the filler volume. Depth retarded the transition into the glass-phase, but did not alter DC measured 300s post-irradiation. Moderate inverse correlation was identified among DC and filler volume% (-0.646) or filler weight% (-0.403), while no correlation among DC and light transmittance (p=0.141; 0.125). The maximal rate of carbon-carbon double bond conversion varied within the analyzed materials but was independent from specimen's depths., Conclusions: Light transmission changes during polymerization do not alter polymerization kinetics in modern B-RBCs. DC 300s post-irradiation was maintained with depth, while light was attenuated, the faster the more translucent the material was. DC and quality of curing cannot be related to light transmittance in B-RBCs., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Objectives: The study aims to characterise a low and high viscosity giomer bulk fill resin restorative with established low and high viscosity resin-based composite (RBC) restoratives at simulated clinical relevant specimen depths., Methods: The irradiance of a light curing unit (Bluephase 20i) was measured on a laboratory-grade spectrometer at distances up to 10mm from the light tip (in 1mm increments). Polymerization kinetics (real-time decrease of CC double bond and degree of cure, DC) and micro-mechanical properties (Vickers hardness/HV; Depth of cure/DOC; Indentation modulus/E) were assessed at varying specimen depths (0.1-6mm in 100μm steps for E, DOC and HV and 0.1, 2, 4 and 6mm for DC) for a 20s irradiation., Results: One and two-way ANOVA (α=0.05) were performed. The parameter material has a significant (p<0.001) effect on DC (ηP(2)=0.839), HV (ηP(2)=0.683), and E (ηP(2)=0.536), whereas the specimen depth influenced only DC (ηP(2)=0.584) but not HV (p=0.093) or E (p=0.133). The polymerisation kinetic could be described by an exponential sum function, distinguishing between the gel and the glass phase. The hardness drop out was lower than 20%, indicated a depth of cure of 6mm for all materials., Conclusions: The low and high viscosity giomer bulk-fill restoratives fulfil the requirements of bulk-fill placement, since under the analysed irradiation conditions an adequate depth of cure of >4mm was identified. Variation of DC with specimen depth was low, with little variation at specimen depths of <4mm. The micro-mechanical properties of the giomer materials were higher compared with the conventional RBC materials., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Objectives: This study aimed to describe the polymerization process and to quantify the parameters of influence in two bulk-fill resin-based composites by comparing two real-time methods: the Fourier transform infrared (FTIR) spectroscopy and the visible light transmission spectrometry., Materials and Methods: The degree of conversion (DC) was recorded in real time for 5 min using the attenuated total reflectance FTIR spectroscopy (n = 6) on the lower surface of 2, 4, and 6 mm thick samples irradiated for 20 s. The variation in irradiance was recorded during material irradiation at the bottom of the samples (n = 5). Results were statistically analyzed using one-way and multiple-way ANOVAs with Tukey HSD post hoc test (α = 0.05), partial eta-squared statistics, and Pearson correlation., Results: No significant difference was found in DC in any materials as a function of incremental thickness, whereas the irradiance passing the specimens differed consistently within both analyzed increments and materials. These data could be described by the superposition of two exponential functions, the first being attributed to the gel phase and the second to the glass phase, resulting in an exponential sum function. DC data were able to calculate the end of the gel phase and the beginning of the glass phase, whereas irradiance measurements were able to detect only the last phase. The polymerization kinetics in the glass phase was less material-dependent as in the gel phase., Conclusions: The irradiance measurements were more sensitive to variation in thickness, meaning that translucency is continuing to change as a function of thickness at a higher extent than DC., Clinical Relevance: Knowing the impact of the modulation factors describing the calculated sum exponential function allows the manipulation of the polymerization process at different stages to tailor material properties.

Objective: The objective of this study was to evaluate the effect of irradiation time and specimens thickness on the polymerization kinetic and variation in micro-mechanical properties of two commercial resin-based composites (RBCs) based on radical amplified photopolymerization (RAP) technology™, and to compare them with four camphorquinone (CQ)/amine-based RBCs., Materials and Methods: The materials were analysed by assessing the polymerization kinetic and the degree of cure (DC) at 0.1 mm and 2 mm depth during 5 minutes after photoinitiation, after curing for 10 s, 20 s and 40 s (Elipar Freelight2). The variation in micro-mechanical properties (Vickers hardness (HV), indentation modulus (E), and depth of cure (DOC)) was assessed in 100 μm steps on 6-mm-high specimens irradiated as above and stored in the water for 24 h at 37 °C., Results: The results were statistically compared using one-way ANOVA with Tukey HSD post hoc test (α = 0.05) and a general linear model. The parameter material exerted the strongest effect on DC (partial eta-squared η p (2) = 0.83), followed by irradiation time (η p (2) = 0.27), and depth (η p (2) = 0.09). The polymerization kinetic, well described by an exponential sum function, showed in all materials a faster decrease in carbon-carbon double bonds at 0.1 mm than at 2 mm depth. The materials based on RAP achieved the highest DC values and a faster polymerization at both depths. The irradiation time exerted the strongest effect on the mechanical properties (DOC, η p (2) = 0.96; HV, η p (2) = 0.89; E, η p (2) = 0.86), followed by depth (HV, η p (2) = 0.63; E, η p (2) = 0.54) and material (HV, η p (2) = 0.40; E, η p (2) = 0.67). At the most favorable curing conditions (40 s, surface), the mechanical properties of the analyzed materials varied between 11.38 (0.80) GPa in Estelite® Sigma Quick and 20.80 (1.42) GPa in Estelite® Posterior for E, and between 74.33 (3.56) N/mm(2) in Tetric EvoCeram® and 120.71 (6.24) N/mm(2) in Estelite® Posterior for HV., Conclusions: RAP-initiated material demonstrated a higher increase in DOC with prolonged irradiation time than the analyzed CQ/amine based materials., Clinical Relevance: An irradiation time of 20 s is also recommended for RAP-initiated RBCs.

In the chronology of polymer-based composite materials, flowable bulk-fill composites represent the most recent development. They enable a significant reduction in treatment time by being applied in larger increments of 4 to 5 mm. The aim of the investigation was to assess the polymerization quality and mechanical performance of a new formulation that has just entered the market and was still in experimental formulation at the time of the investigation, and to compare these results in the context of clinically established materials of the same category. Adequate curing in increments of up to 4 mm could be confirmed both by profiling the elastoplastic material behavior of large increments in 100 µm steps and by real-time assessment of the degree of conversion and the associated polymerization kinetic. A slightly lower amount of filler in the experimental material was associated with slightly lower hardness and elastic modulus parameters, but the creep was similar and the elastic and total indentation work was higher. The kinetic parameters were assigned to the specific characteristics of each tested material. The mechanical macroscopic strength, evaluated in a three-point bending test and supplemented by a reliability analysis, met or exceeded the standards and values measured in clinically established materials, which for all materials is related to the higher flexibility of the beams during testing, while the modulus of elasticity was low. The low elastic modulus of all flowable bulk-fill materials must be taken into account when deciding the clinical indication of this material category. [ABSTRACT FROM AUTHOR]

Reversible addition–fragmentation chain transfer (RAFT)-mediated polymerization has been implemented in commercially available bulk-fill dental composites, with the idea of either optimizing polymerization at depth, while providing sufficient opacity, or reducing exposure time. The elastoplastic and viscoelastic behavior of the materials pursuing both ideas are described comparatively in connection with the microstructure of the materials and artificial aging. A 3-point bending test was followed by reliability and fractographical analyses. The elastoplastic and viscoelastic behavior was monitored with an instrumented indentation test equipped with a DMA-module at various frequencies (0.5–5 Hz). Data reveal that the similarity in filler loading is reflected in similar elastic moduli. Increased strength was offset by higher plasticity and creep and was related to microstructure. Aging showed a significantly stronger influence on material behavior than differences in composition. The elastoplastic parameters of both materials deteriorate as a result of aging, but to a material-specific extent. Aging has a strong influence on elastic material behavior, but very little on viscous material behavior. The parameter that is most sensitive to aging is damping behavior. Detailed laboratory characterization indicates comparable in vitro behavior with clinically successful materials. [ABSTRACT FROM AUTHOR]

A more-and-more-accepted alternative to the time-consuming and technique-sensitive, classic, incremental-layering technique of resin-based composites (RBCs) is their placement in large increments. The so-called bulk-fill RBCs had to be modified for a higher polymerization depth and already have a 20-year history behind them. From the initial simple mechanisms of increasing the depth of cure by increasing their translucency, bulk-fill RBCs have evolved into complex materials with novel polymerization mechanisms and bioactive properties. However, since the materials are intended to replace the tooth structure, they must be comparable in mechanical behavior to the substance they replace. The study compares already established bulk-fill RBCs with newer, less-studied materials and establishes their relationship to dentin with regard to basic material properties such as hardness and indentation modulus. Instrumented indentation testing enables a direct comparison of tooth and material substrates and provides clinically relevant information. The results underline the strong dependence of the measured properties on the amount of filler in contrast to the small influence of the material classes into which they are classified. The main difference of RBCs compared to dentin is a comparable hardness but a much lower indentation modulus, emphasizing further development potential. [ABSTRACT FROM AUTHOR]

The study aims to characterize various LED light curing units (LED-LCU) in order to determine the tolerance threshold for varying the polymerization conditions. Two violet-blue and two blue LED-LCUs were analyzed by using a laboratory-grade spectrophotometer system. Fifty-five curing conditions were simulated in each LED-LCU by varying the position (centered and with an offset of 3-mm to the left, right, lower and upper direction) and the exposure distance (0 mm to 10 mm in 1-mm steps). Irradiance decreased with increasing exposure distance, while the effect of the LCU position was significant and LCU-specific. Only one LED-LCU enables the irradiance threshold of 1,000 mW/cm2 to be achieved in all positions up to an exposure distance of 4 mm. LCUs with a more homogeneous light beam profile more easily tolerate deviations from the ideal curing conditions. The study enables dentists to identify the limits of modern LED-LCUs and to estimate potential deviations from ideal curing conditions for clinically relevant situations. [ABSTRACT FROM AUTHOR]

Copyright of Quintessenz der Zahntechnik is the property of Quintessenz Verlags GmbH and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Dental bulk-fill restorations with resin-composites (RBC) are increasing in popularity, but doubts concerning insufficient curing in depth still disconcert clinicians. An alternative might be offered by modern dual-cured RBCs, which additionally provide bioactive properties. This study assessed the impact of additional light-curing on polymerization kinetics, the degree of conversion (DC) and mechanical properties of a novel, dual-cured RBC with alkaline fillers. Since the bioactivity of a material often implies a release of compounds, the mechanical stability in simulated clinical environments was also evaluated. Polymerization kinetics and DC were assessed at 2- and 4-mm specimen depths in real-time up to one hour (n = 6). Incident and transmitted irradiance and radiant exposure were recorded at 2- and 4-mm depths. Micro-mechanical profiles (n = 6) were assessed in 100-µm steps along 6-mm deep specimens at 24 h post-polymerization. Flexural strength and modulus (n = 10) were determined up to three months of immersion in neutral (6.8) and acidic (4) pH conditions. DC variation in time was best described by a sigmoidal function (R2 > 0.98), revealing a retarded (3.4 ± 0.4 min) initiation in C=C double bond conversion in self-cured versus dual-cured specimens. The setting reaction kinetic was identical at 2- and 4-mm depths for the self-cure mode. For the dual-cure mode, polymerization initiated at 2-mm depth instantly with light-irradiation, while being retarded (0.8 min) at 4-mm depth. The material behaves similarly, irrespective of curing mode or depth, later than 11 min after mixing. Flexural strength and modulus was comparable to regular RBCs and maintained up to three months in both neutral and acidic conditions. Additional light-curing initially accelerates the polymerization kinetic and might help shorten the restauration procedure by hardening the material on demand, however with no effect on the final properties. [ABSTRACT FROM AUTHOR]

Objective: This study aimed to evaluate the amount of light (360-540 nm) passing through shaded zirconia with respect to material thickness, exposure distance, and different curing modes. Methods: The specimens were divided into groups according to thickness as follows: 0.5, 1, 1.5, 2, 2.5, and 3 mm. Thirty-five zirconia and seven glass-ceramic (control group) specimens were fabricated for each group (N = 252). Zirconia was divided into five subgroups (n = 7) and stained to the following shades: CL1, CL2, CL3, and CL4. One zirconia group remained unstained (CL0). Irradiance passing through the different specimens was measured using a violet-blue LED curing unit in three curing modes (Xtra-power, high-power, and standard-power mode) with a fibre-optic USB4000 spectrometer. Irradiance was measured at varying exposure distances, ranging from direct contact of the curing unit with the surface to a distance of 7 mm from the surface, increasing in 1 mm steps. Data were analyzed using a multivariate analysis and linear mixed models ( p < 0.05). Results: The control group, the glass-ceramics, transmitted the highest irradiance values, followed by CL0 (unshaded zirconia), CL1 (~A1/B1), CL2 (~A3/A3.5/A4/B3/B4), and CL3 (~A3.5/B3/B4/C3/D3), respectively. The highest transmitted irradiance was measured at a specimen thickness of 0.5 mm for all materials, decreasing exponentially with increased ceramic thickness. Within one type of ceramic, one thickness, and one polymerization mode, a decrease in transmitted irradiance with increased exposure distance could be observed only at a distance of 3 mm and above. Conclusions: Unshaded zirconia was significantly less translucent compared with the glassceramic, but the translucency decreased slower with material thickness. The Beer-Lambert law describes well the decrease of transmitted irradiance with an increase of the specimens' thickness for all materials. Except for dark ceramics, this would allow for calculating the transmitted irradiance through any material thickness and any initial irradiance. Clinical significance: The amount of light passing through ceramics is an important aspect for an adhesive cementation, since many dual-cured luting materials reveal a high sensitivity to additional occurrence of blue light. For restorations thicker than 1.5 mm in light-shaded zirconia and 0.5 mm in darker-shaded zirconia the use of less-light-sensitive dual-cured cements are recommended. [ABSTRACT FROM AUTHOR]

Objectives: The aim of our study was to analyse whether the irradiation time and/or the modulation of irradiation time influence the degree of conversion (DC) and the amount of elutable substances from modern nano-hybrid resin-based composites (RBCs). Materials and methods: The DC was recorded in real time for 5 min by means of attenuated total reflectance-Fourier transform infrared spectroscopy ( n = 5) on the lower surface of 2-mm-thick samples irradiated with continuous and modulated irradiation times for 20 s and 40 s. The modulated times comprise a short polymerisation (2 s or 5 s) followed by a rest period of 1 min and an additional polymerisation to complete 20 s and 40 s of polymerisation (2 s + 18 s, 5 s + 15 s, 2 s + 38 s and 5 s + 35 s). After storing the specimens in ethanol/water for 7 days at 37 °C, the eluates were analysed by gas chromatography-mass spectrometry. Results were statistically analyzed using a one-way ANOVA analysis ( α = 0.05). Results: The effect of irradiation time on DC is similar in all three analyzed materials, showing a significant increase in DC by increasing irradiation time from 20 s to 40 s, while the DC is not influenced within one irradiation time (20 s or 40 s) by the modulation of time. Conclusions: The type and amount of eluates are strongly dependent from the material and the irradiation protocol. Clinical relevance: An interrupt irradiation of RBCs is clinically feasible, reducing in general the amount of elutable substances at similar DC as the corresponding continuous polymerisation. [ABSTRACT FROM AUTHOR]

This study investigated the effects of aging and irrathation time on the macro- and micro-mechanical properties of a highly translucent nanohybrid composite (IPS Empress Direct, Trans Opal shade, Ivoclar Vivadent). Flexural strength, flexural modulus, indentation modulus, Vickers hardness, and creep were measured after being irradiated with different durations (5, 10, 20, and 40 s) and aged under different conditions (24 h at 37°C in water; 5,000 times of thermocycling between 5°C and 55°C followed by 4-week storage in artificial sahva or alcohol). Rate of cure was also measured for these four irradiation times at composite specimen surface and at 2 mm depth. Effects of aging and irradiation time were statistically analyzed using one-way ANOVA with Tukey's HSD post hoc test (a=0.05), partial eta-squared statistic, and Weibull analysis. Alcohol aging significantly reduced the mechanical properties. Aging in saliva produced a positive effect on micro-mechanical properties. Irrathation time should be at least 20 s to yield favorable mechanical properties. [ABSTRACT FROM AUTHOR]

Objective: The aim of this study was to investigate the effect of polymerisation and ageing on the incremental bond strength (IBS) and fracture mechanics of experimental and commercial, well established ormocer-based materials. Methods: An experimental dimethacrylate-diluent-free ormocer was compared with two commercial products (Admira (VOCO); Ceram X Duo (Dentsply)). For Ceram X Duo, the strength between dentin shades (DD) and between dentin and enamel shades (DE) was measured. In order to simulate clinical conditions, when a direct access to the composite surface is impeded, the curing unit was applied at different distances (1, 3 or 6 mm) from the sample's surface. IBS was measured after the samples were stored in distilled water (24 h/37 °C) and after ageing (5,000 cycles between 5 and 55 °C followed by storage (28 days/37 °C) in distilled water). Additionally, the degree of cure (DC) was measured in a thin film (~50 μm). A multivariate analysis, an additional one-way ANOVA with Tukey HSD post hoc test (α = 0.05), an independent t test (α = 0.05), and Weibull statistics were used to assess the results. Results: After 24 h, the values for IBS were statistically the same. Differences revealed after ageing, whereby the experimental material achieved the significant highest and Admira the lowest results. By evaluating after 24 h and after ageing, the experimental material obtained the smallest Weibull modulus 'm'. The predominant breaking mechanism is cohesive, even though the number decreases in favour for the mixture and adhesive fractures after ageing. Clear differences arose with regard to DC. The experimental material reached considerably lower values (31.9-33.2 %) unlike Ceram X Duo (45.6-48.3 %) and Admira (52.9-58.8 %). Conclusions: The IBS and the DC are far more dependent on the parameter filler volume percent and material than on the polymerisation distance. Clinical significance: A dimethacrylate-diluent-free ormocer matrix offers a better stability opposite ageing but achieves a lower DC and reliability. [ABSTRACT FROM AUTHOR]

Objectives: This study aimed to determine the degree of conversion (DC) of two nano-hybrid resin-based composites (RBCs) with novel monomer composition based on dimer acid derivates (hydrogenated dimer acid) and tricyclodecane-urethane structure compared to three nano-hybrid materials containing conventional matrices. DC was evaluated at 0.1, 2, and 6 mm depth at varying irradiation times (10, 20, and 40 s) and layering techniques (bulk and incremental). Materials and methods: DC was measured in real time by a Fourier transform infrared spectroscopy (FTIR) spectrometer with attenuated total reflectance accessory. The FTIR spectra were recorded on the bottom of the samples in real time for 5 min from photoinitiation. Results were compared using one- and multiple-way ANOVA, Tukey's HSD post hoc test ( α = 0.05), and partial eta-squared statistic. Results: After 5 min of measurement, DC showed no significant difference by varying cure time for specimens of 0.1 mm thickness. At 2 mm depth, the DC significantly increased after a cure time of 20 s compared to 10 s, remaining equal after 40 s of irradiation. At 6 mm depth, bulk curing showed significantly lower DC compared to incremental curing for all polymerization times. Specimen geometry revealed a strong effect on DC ( η = 0.90) followed by curing time ( η = 0.39). Conclusions: The RBCs containing the dimer acid and tricyclodecane-urethane structure showed a relatively low decrease of DC with increasing incremental thickness compared to the conventionally formulated materials. The former reached the highest DC among the tested materials. Clinical relevance: For the tested RBCs, increments of 2 mm and irradiation time of at least 20 s may be recommended for clinical practice. The two materials containing novel monomer composition might be applied for enlarged increments because of the low decrease of DC they demonstrated for 6-mm increments. [ABSTRACT FROM AUTHOR]

Light supplying to luting resin cements is impeded in several clinical situations, causing us to question whether materials can properly be cured to achieve adequately (or adequate) mechanical properties. The aim of this study was therefore to analyse the effect of light on the micro-mechanical properties of eight popular dual-cured self-adhesive resin cements by comparing them with two conventional, also dual-cured, resin cements. Four different curing procedures were applied: auto-polymerisation (dark curing) and light curing (LED unit, Freelight 2, 20 s) by applying the unit directly on the samples' surface, at a distance of 5 and 10 mm. Twenty minutes after curing, the samples were stored for 1 week at 37°C in a water-saturated atmosphere. The micro-mechanical properties-Vickers hardness, modulus of elasticity, creep and elastic/plastic deformation-were measured. Data were analysed with multivariate ANOVA followed by Tukey's test and partial eta-squared statistics ( p < 0.05). A very strong influence of the material as well as filler volume and weight on the micro-mechanical properties was measured, whereas the influence of the curing procedure and type of cement-conventional or self-adhesive-was generally low. The influence of light on the polymerisation process was material dependent, with four different behaviour patterns to be distinguished. As a material category, significantly higher micro-mechanical properties were measured for the conventional compared to the self-adhesive resin cements, although this difference was low. Within the self-adhesive resin cements group, the variation in micro-mechanical properties was high. The selection of suitable resin cements should be done by considering, besides its adhesive properties, its micro-mechanical properties and curing behaviour also. [ABSTRACT FROM AUTHOR]

High bond strengths are required in order to avoid bracket failure during treatment while brackets should be removable. In addition, chair time should be kept at a minimum. Therefore, the aim of this study was to investigate any differences in bracket's bond strength to enamel by reducing the polymerization time and the steps of bonding procedure. Five hundred teeth were randomly allocated into 20 groups. The groups were established considering the investigated curing units (quartz-tungsten-halogen (QTH) and light-emitting diode (LED), each with two different polymerization times) and the used bonding agents (Clearfil SE Bond, Transbond Plus, Ideal1, iBond, and Transbond XT Primer following acid etching). The brackets were debonded using a shear-peel load and used to calculate the bond strength. The location of adhesive failure was registered by using the modified adhesive remnant index (ARI). The influence of the parameters curing unit, curing time, and bonding agent as well as their interaction products on bond strength showed that the bonding agent influenced the bond strength most followed by curing time. The parameter curing unit as well as all the generated interaction products of it showed a lower impact. Regarding the ARI, the bonding agent exhibited also the highest influence. Using a LED resulted in comparable bond strengths as the QTH curing device also at shorter exposure times. Additionally, the two-component self-etching primers showed similar bond strengths compared to the acid-etching method. Chair time can be reduced by using two-component self-etching primers and LED without decrease of bond strength. [ABSTRACT FROM AUTHOR]

Recent reports claim that modern light-emitting diode (LED) curing units improve curing efficiency by increasing the units' irradiance. In this context also, short polymerisation times up to 5 s are proposed. The aim of this study was to examine whether there are differences in the curing efficiency of modern LED curing units by assessing their effect on two different composite materials and by varying the irradiation time. A nano- and a micro-hybrid resin-based composite (RBC) were polymerised for 5, 10 and 20 s with three commercial and a Prototype LED unit (Elipar™ S10). Cylindrical specimens (6 mm in depth, 4 mm in diameter) were prepared in three increments, each 2-mm thick, and were consecutively cured. Degree of cure was measured for 20 min in real time at the bottom of the samples, starting with the photoinitiation. The micro-mechanical properties (modulus of elasticity, E and Vickers hardness, HV) were measured as a function of depth, in 100-μm steps, on the above described samples stored in distilled water for 24 h at 37°C. Data were analysed with multivariate ANOVA followed by Tukey's test, t test and partial eta-squared statistics. In descending order of the strength of their effect, the type of RBC, depth, polymerisation time and curing unit were significant factors affecting the micro-mechanical parameters ( p < 0.05). The degree of cure at 6-mm depth was less but significantly influenced by the curing unit and curing time and was independent from the type of RBC. A 5-s irradiation time is not recommended for these units. Whereas a 5-s irradiation is acceptable at the sample's surface, a minimum of 20 s of irradiation is necessary for an adequate polymerisation 2 mm beyond the surface. [ABSTRACT FROM AUTHOR]

In 2007, the low shrinkage silorane-based composites with a completely new resin chemistry were introduced. As for the case of composite repair, the question of whether this new material class can be repaired with the same methods like dimethacrylate-based composites arises. The ability of a silorane-based composite (SBC) to be repaired was therefore examined in a shear-bond test. Specimens of SBC were polymerised, water-stored at 37°C for 1 week and then repaired with fresh dimethacrylate-based composite (MBC) or SBC material by using several intermediate agents (IMA). The shear-bond strength was then measured after an additional water storage of 1 week. As IMA, we tested an experimental silorane-flowable composite, two dimethacrylate-based flowable composites, a filled silorane system adhesive bond and a conventional unfilled adhesive, a silane in addition to an adhesive as well as a repair kit. Additionally, repairs of MBC with dimethacrylate-based flowable composite were prepared. Specimens of MBC and SBC bonded to dentine with the corresponding adhesives were used as a reference. The repairs of MBC with the flowable composite resin Tetric Evo Flow exhibited the highest mean repair bond strength value (42.2 MPa). For repair of SBC, the highest shear-bond strengths were measured for repairs using a silane additionally to a dimethacrylate-based adhesive resin, followed by repairs with the experimental silorane-based flowable composite resin Hermes Flow as IMA. SBC can be repaired in combination with a MBC; then a silane coupling agent plus a dimethacrylate-based IMA should be used. A silorane flowable as IMA is the best choice when SBC is to be repaired with SBC. [ABSTRACT FROM AUTHOR]

Abstract: Objective: Monomer development for a reduced shrinkage of composite materials still challenges the modern research. The purpose of this study was to analyse the shrinkage behavior of an innovative composite material for dental restorations based on a resin system that is claimed to control polymerization kinetics having incorporated a photoactive group within the resin. Methods: Shrinkage stress development within the first 300s after photoinitiation, gel point as well as micro-mechanical properties (Vickers hardness HV, modulus of elasticity E, creep Cr and elastic–plastic indentation work W e/W tot) were evaluated (n =10). The experimental flowable resin-based composite (RBC) was measured in comparison to regular methacrylate-based micro- (Esthet X Flow) and nano-hybrid flowable RBCs (Filtek Supreme Plus Flow). Additionally, the high viscosity counterparts of the two regular flowable methacryate-based composites (Esthet X Plus and Filtek Supreme Plus) as well as a low shrinkage silorane-based micro-hybrid composite (Filtek Silorane) were considered. The curing time was 20s (LED unit Freelight2, 3M-ESPE, 1226mW/cm2). Results: The experimental material achieved the significantly lowest contraction stress (1.1±.01MPa) followed by the silorane-based composite (3.6±.03MPa), whereas the highest stress values were induced in the regular methacrylate-based flowable composites EsthetX Flow (5.3±.3MPa) and Filtek Supreme Flow (6.5±.3MPa). In view of gel point, the best values were obtained for the experimental flowable composite (3.1±.1s) and Filtek Silorane (3.2±.3s), which did not differ significant from each others, whereas EsthetX Plus and Filtek Supreme Plus did also not differ significantly, inducing the shortest gel point. The experimental flowable material achieved also the lowest shrinkage-rate (maximum at 0.1MPa/s). For all analysed materials, no significant difference in the micro-mechanical properties between top and bottom were found when measured on 2mm thick increments 24h after polymerization. The categories of flowable materials performed in the measured micro-mechanical properties significantly inferior when compared to the hybrid-composites, showing lower HV and E and predominantly higher creep and plastic deformation. Within the flowable RBCs, the experimental material achieved the lowest Vickers hardness, the highest modulus of elasticity, the highest creep and showed the significantly lowest elastic deformation. Significance: The experimental flowable composite revealed the lowest shrinkage stress and shrinkage-rate values in comparison to regular methacrylate composites but intermediate micro-mechanical properties. Being at the same time more rigid (higher modulus of elasticity) and more plastic (low W e/W tot and high creep values) as the regular flowable materials, its effect on interfacial stress build-up cannot be easily predicted. [Copyright &y& Elsevier]

Shrinkage stress, degree of cure and mechanical properties are contradicting properties, forcing to a compromise between an adequate curing and low stress at the interface tooth-restoration. The purpose of this study was to quantify this relations for a micro-hybrid composite, by analysing in real time the development of degree of cure at depths of 2 and 6 mm, shrinkage stress and curing time until gelation, as well as the variation of micro-mechanical properties with depth, after curing with 13 regimes of one halogen and two light-emitting diode (LED) curing units. A nano-dynamic mechanical test was additionally performed on selected regimes (Ramp, Pulse and Fast Cure) of the same curing unit. The present study showed that the soft-start polymerization concept is still valid for less deep cavities (2 mm), even by curing with high-power LED curing units, since a soft-cure polymerization resulted in a delayed gel point and a lower shrinkage stress, keeping simultaneously the degree of cure and mechanical properties constant. At 6 mm depth, curing with soft-start regimes resulted in a significant decrease in degree of cure, although this decrease was less than 10%, while the mechanical properties were maintained. [ABSTRACT FROM AUTHOR]

The aim of the study was to determine the effects of ultra-fast (3 s) light-curing on the viscoelastic behaviour at clinically relevant frequencies, and cell toxicity, in a resin-based composite (RBC) with reversible addition-fragmentation-chain transfer (RAFT) mediated polymerization. Three different protocols were used to cure cylindrical samples (height = 4 mm, ϴ = 5 mm), including ultra-fast (3s) cure with high radiant emittance, 10 s and 20 s cure with moderate radiant emittance. The properties of the light curing device were evaluated in all curing protocols by spectrophotometry up to an exposure distance of 10 mm. The light transmission through the samples was determined in real-time with the same spectrophotometer. Absorbance was calculated as a function of wavelength. The quasi-static (indentation hardness/H IT , indentation modulus/E IT) and viscoelastic (storage modulus/E′, loss modulus/E″, loss factor/tan δ) material behavior was determined in an instrumented indentation test with a DMA (Dynamic Mechanical Analysis) module for 10 frequencies (0.5–5 Hz) by profiling the center of the samples in 330 μm steps from top to bottom. Cellular toxicity on human gingival fibroblast (HGF-1) was assessed using a WST-1 colorimetric assay after incubation time of up to 3 months. One and multiple-way analysis of variance (ANOVA) with Tukey honestly significant difference (HSD) post-hoc tests (α = 0.05) were applied. The irradiance transmitted through a 4 mm high sample was less than 7% of the incident irradiance, and the absorbance was similar for all curing protocols, showing a decrease with wavelength. Similar quasi-static and viscoelastic parameters were observed regardless of the curing protocol. H IT increased slightly and E IT , E′, E″ and tan δ decreased with frequency. Occasionally, slightly higher confidence intervals were observed for the ultra-fast curing group, which were related to a potential accumulation of stress. The curing protocol had no effect on cell viability (p = 0.326) but the eluate age (p < 0.001, η P 2 = 0.879) did. None of the groups showed cell toxicity at any point in time with respect to the corresponding negative control. The ultra-fast curing with high irradiance induced no cell toxicity and an equivalent viscoelastic behavior as with conventional curing protocols in a RAFT-modified RBC. [ABSTRACT FROM AUTHOR]

Purpose: To analyze the curing behavior and the curing quality of a nano-hybrid composite material (Tetric EvoCeram) in relation to degree of cure, variation of hardness with depth and polymerization depth. Methods: The composite was evaluated after polymerizing the material with 13 different curing regimens of two LED devices and one halogen curing unit by assessing in real time the degree of cure at depths of 2 and 6 mm, the variation of hardness with depth and the polymerization depth. The sample preparation simulated the clinical incremental technique as well as a bulk fill procedure. Results: No correlation was found for the tested curing regimens between polymerization depth and surface hardness respectively between surface hardness and radiant exposure, whereas the polymerization depth was strongly dependent on polymerization time and radiant exposure. It can be therefore concluded that the surface hardness is not a reliable indicator of the quality of curing. The degree of cure was strongly influenced by depth and curing time, whereas the influence of the curing regimen and of the interaction products between these three factors was low. The higher effect on the variation of the Vickers hardness, measured 24 hours after polymerization, was exercised also by the depth, followed by curing regimen and curing time. [ABSTRACT FROM AUTHOR]

Summary: Objective: The present study determined the influence of polymerization shrinkage of eight commercially available hybrid, micro-filled and nano composites (Z100 and Filtek Supreme, 3M-ESPE; Charisma and Durafill, Heraeus Kulzer; Tetric and InTen-S, Ivoclar Vivadent; Enamel plus HFO, GDF; Palfique Estelite Low Flow, Tokuyama) placed in large class 1 cavities on the bond strength to dentin. Methods: Polymerization shrinkage was recorded for 300s at room temperature with a Stress–Strain-Analyzer (C FACTOR=0.3). The maximum contraction stresses after 300s, the time until gelation (t 0.5N) and the coefficient of near linear fit of contraction force/time (gradient) were analysed. For the evaluation of the micro-tensile-bond-strength (μ-TBS), hourglass shape samples obtained from a total of 32 no carious extracted human third and second molars, randomly divided into 8 groups, were used. Micro tensile bond strengths were determined by computing the ratio of maximum load by the adhesion area of the hourglass shape. In order to analyze the quality of the polymerization within fillings, hardness profiles of a surface cut thought the middle of the restored tooth and along the tooth axis were made. Further, the modulus of elasticity, determined in a three-point-bending test, as well as the variation of the modulus of elasticity and of the hardness within a filling were considered. The statistical analyses were conducted by ANOVA (α=0.05) and post-hoc Tukey''s test. Results: A significant correlation between polymerization shrinkage and μ-TBS was found (Pearson; −0.44). The correlation between modulus of elasticity in bending test and shrinkage stress (Pearson; 0.77), coefficient of near linear fit m (Pearson; 0.72), time until gelation (Pearson; −0.52) and micro-tensile-bond-strength (Pearson; −0.45) was also significant. A high polymerization tension and modulus of elasticity negatively affected the adhesion of the composite to the tooth hard substance. Further, the number of samples lost during the slice cutting and the hourglass shape preparation was found to correlate highly significantly with the shrinkage stress (Pearson; 0.97), coefficient of near linear fit m (Pearson; 0.94) and modulus of elasticity (Pearson; 0.82). All materials showed sufficient polymerization within the filling in comparison to the filling surface, the hardness at the bottom of the filling was greater than 80% of the maximum hardness value. The modulus of elasticity was not considerably reduced within the filling. Significance: High contraction stress and modulus of elasticity, fast development of contraction force and an early start of stress build-up of materials placed in restrictive cavities cause tension in the material with a possible subsequent distortion of the bond to the tooth structure. A low modulus of elasticity is not necessarily associated with high bond strength. However, it causes a more uniform stress distribution at the restorative composite-tooth interface. This is also evident in a reduced sample loss during the different stages of sample preparation. [Copyright &y& Elsevier]

The purpose of this study was to analyze the curing behavior of a nanocomposite by assessing in real time the degree of cure at depths of 2 mm and 6 mm. The variation of hardness with depth, shrinkage stress, and curing time until gelation with 16 curing regimes was further investigated using one halogen and three LED curing units. In the present study, it was shown that the soft-start polymerization concept is still valid, even with high-power LED curing units. A soft cure polymerization resulted in reduced shrinkage stress while simultaneously keeping the degree of cure and mechanical properties constant. For all tested curing unit types, a short polymerization duration (10 seconds) was insufficient to cure the nanocomposite in deeper layers-since the variation of hardness with depth showed a discontinuity between the layers, thus accounting for a decreased hardness of up to 30%. [ABSTRACT FROM AUTHOR]

Summary: Objective: The present study determined the influence of different light curing regimes (four light-emitting diode (LED) units (Freelight 1 and 2, 3M-ESPE; e-light, GC; Bluephase (prototype), Ivoclar Vivadent), two quartz–tungsten–halogen (QTH) lights (Astralis 10, Ivoclar Vivadent; Swiss Master Light, EMS) and one plasma-light curing unit (Easy Cure, DMDS)) on the curing behavior of a resin-based composite material (InTen-S, Ivoclar Vivadent). Methods: Polymerization shrinkage was induced by light curing the tested material with 14 different regimes of the curing units mentioned above. The contraction stress was recorded for 300s at room temperature with a Stress–Strain-Analyzer (c FACTOR=0.3). The maximum contraction stresses after 300s, the time until gelation (t 0.5N), and the coefficient of near linear fit of contraction force/time (gradient) were analyzed. The statistical analysis was conducted using ANOVA (α=0.05) and Tukey''s post hoc test. Results: The five tested regimes of the LED unit e-light revealed the lowest statistically significantly maximum contraction stress followed by the low intensity LED unit Freelight 1 and the plasma curing unit Easy Cure. The high intensity LED unit Freelight 2 exhibited a significantly higher contraction stress compared to Freelight 1. No significant differences between the standard and exponential modes within these curing units were found. No significant differences were found between the LED unit Freelight 2 and the pulse program of the halogen light curing unit Astralis 10. The highest polymerization stresses were observed for the high energy curing units, either QTH (Swiss Master Light and Astralis 10) or LED (Bluephase). Significance: Fast contraction force development, high contraction stress and an early start of stress build-up cause tension in the material with possible subsequent distortion of the bond to the tooth structure. The lowest polymerization stress was observed for the low energy LED lamps, while the plasma unit and the high energy QTH and LED curing units produced two to three times higher stress. [Copyright &y& Elsevier]

Objectives: The aim of this study was to assess the effect of different resin cement shades on the opacity and color difference of ceramics and to determine the polymerization efficiency of the resin cement at different shades after curing through ceramics. Methods: Two different ceramics (IPS e.max Press and IPS Empress1CAD, Ivoclar Vivadent) were used for this study. A light-cured veneer luting resin (Variolink Veneer, Ivoclar Vivadent) in four different shades of HV+1, HV+3, LV-1, and LV-3 was used for the colorimetric measurements. The color and spectral reflectance of the ceramics were measured according to the CIELab color scale relative to the standard illuminant D65 on a reflection spectrophotometer (ColorEye7000A, USA). Color differences (DE values) and the contrast ratios (CR) of the different groups of samples were calculated. In order to analyse the polymerization efficiency of the resin cements, the micromechanical properties of the resins were measured with an automatic microhardness indenter (Fisherscope H100C, Germany). The results were analysed using one-way ANOVA and Tukey's HSD post hoc tests (SPSS 18.0). Results: The one-way ANOVA test showed that the values of ΔE and CR of the different specimen groups were significantly different ( p < 0.05). Group 1 (20.7 ± 0.5) (IPS-CAD without resin cement) exhibited the highest and group 10 (14.8 ± 0.5) (e.max:HV+3) exhibited the lowest ΔE value. Significant differences in the micromechanical properties were identified among the tested resin cements in different shades ( p < 0.05). Conclusions: Resin cement shade is an important factor for the opacity of a restoration. Furthermore, the resin shade affects the micromechanical properties of the underlying resin cement. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: This study''s purpose was to measure and compare the degree of conversion (DC) and the amount of elutable substances from modern resin-based composites (RBCs) as function of polymerization time. One nano-hybrid RBC based on tricyclodecane-(TCD)-urethane (Venus® Diamond) and two conventionally formulated RBCs (TetricEvo Ceram®, Filtek™ Supreme XTE) were considered. Method: DC (n =5) was investigated in real time for 5min by Fourier transform infrared spectroscopy (ATR-FTIR) in a filling depth of 2mm at varied irradiation times (5, 10, 20, 40s). After storing the specimens in ethanol/water for 7 d at 37°C the eluates were analyzed by gas chromatography/mass spectrometry. Results were statistically analyzed using a multivariate analysis (α =0.05) an independent t-test (p <0.05) and a Pearson correlation analysis. Results: In all groups increasing curing time resulted in a significant increase in DC. For TetricEvo Ceram® a high significant inverse correlation was found between DC and the amount of eluted camphorquinone (CQ, Pearson correlation coefficient=−0.88), ethylene glycol dimethacrylate (EGDMA, −0.73), 4-N,N-dimethylaminobenzoic acid ethylester (DMABEE, −0.87), triethylene glycol dimethacrylate (TEGDMA, −0.68), Tinuvin P (−0.71) and bisphenol-A-polyetheylene glycol dimethacrylate (BisEMA, −0.84). Unexpectedly DC and the amount of eluted methyl acrylate (MAA) correlated directly (0.72). In the specimens of Venus® Diamond a significant inverse correlation was found between DC and the amount of eluted CQ (−0.69) and TEGDMA (−0.50), whereas in the specimen of Filtek™ Supreme XTE DC correlated with CQ (−0.96), EGDMA (−0.70), DMABEE (−0.87), TEGDMA (−0.92) and MAA (−0.92). Significance: This study demonstrated a strong inverse correlation between DC and elutable substances in RBCs. Both evaluation methods emphasis the importance of an adequate polymerization (20, 40s), since short curing-times (5, 10s) resulted in lower DC and higher amount of eluted substances with toxic potential. [Copyright &y& Elsevier]