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Objectives: The aim of this study was to quantify the blue light that passes through different incremental thicknesses of bulk fill in comparison to conventional resin-based composites (RBCs) and to relate it to the induced mechanical properties. Materials and methods: Seven bulk fill, five nanohybrid and two flowable RBCs were analysed. Specimens ( n = 5) of three incremental thicknesses (2, 4 and 6 mm) were cured from the top for 20 s, while at the bottom, a spectrometer monitored in real time the transmitted irradiance. Micro-mechanical properties (Vickers hardness, HV, and indentation modulus, E) were measured at the top and bottom after 24 h of storage in distilled water at 37 °C. Electron microscope images were taken for assessing the filler distribution and size. Results: Bulk fill RBCs (except SonicFill) were more translucent than conventional RBCs. Low-viscosity bulk fill materials showed the lowest mechanical properties. HV depends highly on the following parameters: material (η = 0.952), incremental thickness (0.826), filler volume (0.747), filler weight (0.746) and transmitted irradiance (0.491). The bottom-to-top HV ratio (HV) was higher than 80 % in all materials in 2- and 4-mm increments (except for Premise), whereas in 6-mm increments, this is valid only in four bulk fill materials (Venus Bulk Fill, SDR, x-tra fil, Tetric EvoCeram Bulk Fill). Conclusions: The depth of cure is dependent on the RBC's translucency. Low-viscosity bulk fill RBCs have lower mechanical properties than all other types of analysed materials. All bulk fill RBCs (except SonicFill) are more translucent for blue light than conventional RBCs. Significance: Although bulk fill RBCs are generally more translucent, the practitioner has to follow the manufacturer's recommendations on curing technique and maximum incremental thickness. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Objectives: This study aimed to evaluate whether sonic-activated resin-based composites (RBCs) used as repair materials might improve the repair bond strength of aged RBC substrates. Materials and methods: Five RBCs were repaired by themselves and by all other materials. The repair was applied with and without sonic activation, resulting in 50 material application technique combinations ( n = 15) and 750 specimens. The cohesive strength of the five materials was used as control ( n = 15). Substrates were aged for 8 weeks in distilled water at 37 °C, roughened, cleaned with phosphoric acid, and repaired by using a silane primer and an adhesive as intermediate agents. The repair bond strength was assessed in a shear test. The modulus of elasticity ( E) of the five RBCs was additionally evaluated in a three-point bending test. Results: Results were compared using one- and multiple-way analyses of variance and Tukey's honestly significant difference post hoc test ( α = 0.05), partial eta-square statistics, Pearson's correlation, and Weibull's analysis. No significant effect of sonic activation on the repair material was found in any material combination. The repair strength was 35.4-90.9 % of the cohesive strength of the original composites. E varied between 4.1 GPa (CLEARFIL MAJESTY Esthetic) and 9.7 GPa (CLEARFIL MAJESTY Posterior). The strongest influence on the shear bond strength was performed by E ( η = 0.167), whereas the effect of E was significant but low ( η = 0.098). None of these parameters influenced the reliability of the repaired specimens (the Weibull parameter, m). The fracture pattern was mainly cohesive (93.3 %) in the control group and predominantly adhesive (89.2 %) in the repaired specimens. Conclusions: Except for the material with the highest modulus of elasticity used as a substrate material, it was not detrimental to combine different RBCs in terms of repair. Clinical relevance: If a substrate material is unknown, the recommendation for repairing would be in favor of a material with a high modulus of elasticity. [ABSTRACT FROM AUTHOR]

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 = 0.83), followed by irradiation time ( η = 0.27), and depth ( η = 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 = 0.96; HV, η = 0.89; E, η = 0.86), followed by depth (HV, η = 0.63; E, η = 0.54) and material (HV, η = 0.40; E, η = 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 in Tetric EvoCeram® and 120.71 (6.24) N/mm 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. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this study was to investigate micromechanical properties of five dual-curing resin cements after different curing modes including light curing through glass ceramic materials. Materials and methods: Vickers hardness (VH) and indentation modulus ( Y) of Panavia F2.0, RelyX Unicem 2 Automix, SpeedCEM, BisCem, and BeautiCem SA were measured after 1 week of storage (37 °C, 100 % humidity). The resin cements were tested following self-curing or light curing with the second-generation light-emitting diode (LED) curing unit Elipar FreeLight 2 in Standard Mode (1,545 mW/cm) or with the third-generation LED curing unit VALO in High Power Mode (1,869 mW/cm) or in XtraPower Mode (3,505 mW/cm). Light curing was performed directly or through glass ceramic discs of 1.5 or 3 mm thickness of IPS Empress CAD or IPS e.max CAD. VH and Y were analysed with Kruskal-Wallis tests followed by pairwise Wilcoxon rank sum tests ( α = 0.05). Results: RelyX Unicem 2 Automix resulted in the highest VH and Y followed by BeautiCem SA, BisCem, SpeedCEM, and finally Panavia F2.0. Self-curing of RelyX Unicem 2 Automix and SpeedCEM lowered VH and Y compared to light curing whereas self-curing of Panavia F2.0, BisCem, and BeautiCem SA led to similar or significantly higher VH and Y compared to light curing. Generally, direct light curing resulted in similar or lower VH and Y compared to light curing through 1.5-mm-thick ceramic discs. Light curing through 3-mm-thick discs of IPS e.max CAD generally reduced VH and Y for all resin cements except SpeedCEM, which was the least affected by light curing through ceramic discs. Conclusions: The resin cements responded heterogeneously to changes in curing mode. The applied irradiances and light curing times adequately cured the resin cements even through 1.5-mm-thick ceramic discs. Clinical relevance: When light curing resin cements through thick glass ceramic restorations, clinicians should consider to prolong the light curing times even with LED curing units providing high irradiances. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this study was to examine the long-term effect of heat on the mechanical behaviour of conventional highly viscous glass ionomer cements. Besides, the effect of storage time was evaluated. Materials and methods: Five cements (ChemFil Rock, Riva Self Cure, Fuji IX GP Fast, Equia and Ketac Molar Aplicap) were evaluated using three different preparation methods: no heat application, application of heat by means of a LED curing unit for 20 and 60 s. Four hundred fifty bar-shaped specimens were produced, maintained in distilled water at 37 °C and tested after 1 week, 1 month and 3 months ( n = 10). The Vickers hardness, indentation modulus and creep were measured. In addition, the amount and size of the glass fillers and voids were examined using a light and a scanning electron microscope. Results: Fuji IX GP Fast showed the highest Vickers hardness, Ketac Molar Aplicap showed the highest indentation modulus and the best value of creep was measured for Riva Self Cure. Vickers hardness, modulus of elasticity and creep resistance increased most for ChemFil Rock and Equia up to 1-month storage. Conclusions: Heat application showed no effect on the mechanical behaviour of ChemFil Rock, Fuji IX GP Fast and Equia at all ageing time. The impact of storage duration was low. Clinical relevance: Considering the measured mechanical properties, there is no need of using heat when restoring teeth with glass ionomer cements. [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]

Objectives: This study aimed to evaluate the performance of accelerating procedures for bonding of orthodontic brackets in vitro by comparing different adhesives (etch-and-rinse, self-etch) and polymerization procedures (curing devices, time). The performance was characterized by three parameters: (1) the bond strength achieved, (2) the incidence of enamel damage, and (3) the extent of residual composite on the tooth. Materials and methods: Bracket bonding was performed on 500 extracted human teeth after application of either an etch-and-rinse adhesive or a one-step self-etch adhesive. Two different two-component self-etch adhesives (Clearfil SE and Transbond Plus) and two single-component self-etch adhesives (Ideal and iBond) were investigated after using different polymerization procedures (light-emitting diode for 10 or 20 s or plasma arc curing device for 3 or 6 s). The bond strength, incidence of enamel damage, and extent of residual composite on the tooth were measured. Results: Single-component self-etch adhesives gave the lowest bond strengths. No significant difference in bond strength could be detected between the two-component self-etch adhesives and the etch-and-rinse method. There was a 70.3 % risk for enamel damage at bond strengths above 12 MPa, but only 5 % risk below 12 MPa and no risk below 8.2 MPa. The risk of enamel damage increased by an odds ratio increment of 1.3 for each additional MPa above 8.2 MPa. Conclusion: Single-component self-etch adhesives showed the lowest bond strengths, caused limited enamel damage, and generally left less residual composite on the tooth. Clinical relevance: The nature of the adhesive greatly influences the resultant bond strength, the risk of enamel damage, and the extent of residual composite on the teeth. [ABSTRACT FROM AUTHOR]

Objectives: The study aims to measure and compare the effect of different exposure times and exposure distances on the degree of cure (DC) of light hardening resin based pit and fissure sealants. Methods: A representative selection of 13 commercial sealants brands was chosen. DC of each material (n = 6) was measured in real-time by Fourier transform infrared spectroscopy (FTIR) at three clinically relevant exposure times (10, 20, 40 s) and two fixed exposure distances (4 mm and 7 mm) between sample and light source. Data were analyzed by a multi-variant analysis and partial eta-squared statistic. Results: Factors ''material'', ''exposure time'' and ''exposure distance'' had a significant influence on the DC across all materials (ηp²= 0:927; 0:774 and 0.266 respectively) with ''material'' and ''exposure time'' showing the strongest effect (significance level α ≤ 0.05). In general, an increased exposure time and reduced exposure distance between sample and light source led to increased DC for all the materials. Conclusions: Degree of cure is influenced significantly by the brand of sealant and by exposure time. In some cases it is found that DC is also affected significantly by the exposure distance. Clinical significance: On the basis of this study, an exposure time of at least 20 s and a maximum exposure distance of 4 mm between curing unit and material surface is recommended. [ABSTRACT FROM AUTHOR]

Abstract: The objective of the study was to investigate the influence of long-term storage (up to 1year) and coating on the variation of micro-mechanical properties of four conventional restorative glass ionomer cements (GICs) within 3.5mm deep class I cavities. Four commercially available GICs (Riva Self Cure (SDI), ChemFil Rock (Dentsply), Fuji IX Fast and Fuji IX GP Extra/Equia (GC)) were applied to 100 teeth. In each tooth, two similar 3.5mm deep class I cavities were prepared and filled with the GICs, with and without resin coating. The samples were stored in artificial saliva at 37°C for 1week, 1month, 3months, 6months and 1year. The variation in mechanical properties (indentation modulus (E) and Vickers hardness (HV)) were determined in 100μm steps starting from the filling surface, through the intermediate layer in between dentine and GIC, and ending 100μm in dentin. HV and E were strongly influenced by the material (P <0.05, partial eta-squared ηP 2 =0.31 and 0.23) but less by aging duration (P <0.05, ηP 2 =0.02 and 0.12) and resin coating (P <0.05, ηP 2 =0.02 and 0.03). The depth of measurement (0–2mm) has no influence on HV (P =0.789). HV shows a gentle increase over the 1year storage period (P =0.002). A ∼300μm GIC zone at the areas close to dentin with weaker properties as those measured in dentin or GIC was identified in all fillings, irrespective of the presence of coating, and at all storage periods. The thickness of this zone is more strongly influenced by storage (P <0.05, ηP 2 =0.081) than by material type (P <0.05, ηP 2 =0.056), while coating showed no influence (P =0.869). Filler morphology and dimension were similar to upper parts of the GIC filling; however, the amount of low cations was higher. We concluded that the development of an intermediate layer in between dentine and GIC with lower mechanical properties might be responsible for the bond quality of GIC to dentine. Moreover, class I GIC restorations are unlikely to feature constant mechanical properties throughout the cavity, regardless of conditions such as aging and coating. [Copyright &y& Elsevier]

Objectives: The aim of this study was to measure the degree of conversion (DC) of five dual-curing resin cements after different curing modes with a second- and a third-generation light-emitting diode (LED) curing unit. Additionally, irradiance of both light curing units was measured at increasing distances and through discs of two glass ceramics for computer-aided design/manufacturing (CAD/CAM). Materials and methods: Irradiance and spectra of the Elipar FreeLight 2 (Standard Mode (SM)) and of the VALO light curing unit (High Power Mode (HPM) and Xtra Power Mode (XPM)) were measured with a MARC radiometer. Irradiance was measured at increasing distances (control) and through discs (1.5 to 6 mm thickness) of IPS Empress CAD and IPS e.max CAD. DC of Panavia F2.0, RelyX Unicem 2 Automix, SpeedCEM, BisCem, and BeautiCem SA was measured with an attenuated total reflectance–Fourier transform infrared spectrometer when self-cured (negative control) or light cured in SM for 40 s, HPM for 32 s, or XPM for 18 s. Light curing was performed directly (positive control) or through discs of either 1.5- or 3-mm thickness of IPS Empress CAD or IPS e.max CAD. DC was analysed with Kruskal–Wallis tests followed by pairwise Wilcoxon rank sum tests ( α = 0.05). Results: Maximum irradiances were 1,545 mW/cm 2 (SM), 2,179 mW/cm 2 (HPM), and 4,156 mW/cm 2 (XPM), and all irradiances decreased by >80 % through discs of 1.5 mm, ≥95 % through 3 mm, and up to >99 % through 6 mm. Generally, self-curing resulted in the lowest DC. For some cements, direct light curing did not result in higher DC compared to when light cured through ceramic discs. For other cements, light curing through ceramic discs of 3 mm generally reduced DC. Conclusions: Light curing was favourable for dual-curing cements. Some cements were more susceptible to variations in curing mode than others. Clinical relevance: When light curing a given cement, the higher irradiances of the third-generation LED curing unit resulted in similar DC compared to the second-generation one, though at shorter light curing times. [ABSTRACT FROM AUTHOR]

Objectives: To assess the effect of irradiation time and distance of the light tip on the micro-mechanical properties and polymerisation kinetics of two bulk-fill resin-based composites at simulated clinically relevant filling depth. Methods: Micro-mechanical properties (Vickers hardness (HV), depth of cure (DOC) and indentation modulus (E)) and polymerisation kinetics (real-time increase of degree of cure (DC)) of two bulk-fill resin-based composites (Tetric EvoCeram® Bulk Fill, Ivoclar Vivadent and x-tra base, Voco) were assessed at varying depth (0.1-6 mm in 100 mm steps for E andHV and 0.1,2,4 and 6 mm for DC), irradiation time (10,20 or 40 s, Elipar Freelight2) and distances from the light tip (0 and 7 mm). Curing unit's irradiance was monitored in 1 mm steps at distances up to 10 mm away from the light tip on a laboratory-grade spectrometer. Results: Multivariate analysis (a = 0.05), Student's t-test and Pearson correlation analysis were considered. The influence of material on the measured mechanical properties was significant (η² = 0.080 for E and 0.256 for HV), while the parameters irradiation time, distance from the light tip and depth emphasise a stronger influence on Tetric EvoCeram® Bulk Fill. The polymerisation kinetics could be described by an exponential sum function, distinguishing between the gel and the glass phase. The above mentioned parameters strongly influenced the start of polymerisation (gel phase), and were of less importance for the glass phase. Conclusions: Both materials enable at least 4 mm thick increments to be cured in one step under clinically relevant curing conditions. Clinical significance: The susceptibility to variation in irradiance was material dependent, thus properties measured under clinically simulated curing conditions might vary to a different extent from those measured under ideal curing conditions. [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: Recently, it has become possible to reconstruct complete occlusal surfaces using the biogeneric tooth model. This study aimed to mathematically assess and compare the morphologic agreement between original morphology and CAD-reconstructed, waxed-up and CAM partial crowns. Materials and methods: Thirty-nine intact first permanent molars (39 participants) were included. Impressions, bite registrations and three gypsum replicas were made. Preparations for CAD/CAM partial crowns were performed and scanned. The restorations were biogenerically reconstructed (CEREC® v3.80) and milled. Wax-ups of these preparations were scanned as well as the milled restorations and original teeth. Discrepancies were evaluated by matching the scans with the original morphologies (Match3D, output: volume/area, z difference) and by contact patterns. The discrepancies were compared between CAD-reconstructions and either wax-ups or milled restorations (paired t test, α = 0.025 for two multiple tests). Results: The mean differences between natural tooth morphology (triangular stabilisation 71.8 %) and biogeneric reconstructions, wax-ups and milled restorations (triangular stabilisation 87.2 %) were: 184 ± 36 μm (volume/area), 187 ± 41 μm ( z difference); 263 ± 40 μm (volume/area), 269 ± 45 μm ( z difference) and 182 ± 40 μm (volume/area), 184 ± 41 μm ( z difference). Differences associated with biogeneric reconstructions were significantly less than those of wax-ups (volume/area and z difference, p < 0.0001), but not significantly different than those of milled restorations ( p = 0.423 (volume/area), p = 0.110 ( z difference)). Conclusions: CAD software enables a closer reconstruction of teeth than do wax-ups, even when no cusps remain. The milling device is precise enough to transfer CAD into the final restoration. Clinical relevance: This study shows that state of the art CAD/CAM can effectively produce natural tooth morphology and may be ideal for fixed partial dentures. [ABSTRACT FROM AUTHOR]

Objectives: The effect of gloss and heat on the mechanical behaviour of a recently launched glass carbomer cement (GCP, GCP dental) was evaluated and compared with resin-modified glass ionomer cements (Fuji II LC, GC and Photac Fil Quick Aplicap, 3M ESPE). Methods: 120 bar-shaped specimens (n = 20) were produced, maintained in distilled water at 37 °C and tested after one week. The GCP specimens were cured with and without heat application and with and without gloss. The flexural strength and modulus of elasticity in flexural test as well as the micro-mechanical properties (Vickers Hardness, indentation modulus, creep) of the top and bottom surface were evaluated. The amount and size of the fillers, voids and cracks were compared using a light and a scanning electron microscope. Results: In the flexural test, the resin-modified glass ionomer cements performed significantly better than GCP. Fuji II LC and Photac Fil (Weibull parameter: 17.7 and 14.3) proved superior reliability in the flexural test compared to GCP (1.4-2.6). The highest Vickers Hardness and lowest creep were achieved by GCP, whereas Fuji II LC reached the highest indentation modulus. The results of this study proved that relationships exist between the compositions, microstructures and mechanical properties of the cements. Conclusions: Heat treatment and gloss application did not influence the mechanical properties of GCP. The mechanical properties were basically influenced by the type of cement and its microstructure. Clinical significance: Considering the measured mechanical properties, there is no need of using gloss or heat when restoring teeth with GCP. [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]

Objective: The study focused on a recently launched conventional glass ionomer cement (GIC) with a particular chemical formulation of both, filler and acrylic liquid, by analysing its mechanical behaviour in comparison to three conventional GICs. Furthermore, the effect of resin coating and storage conditions was evaluated. Materials and methods: Three commercially available GICs were chosen: Riva Self Cure (SDI), Fuji IX Fast (GC) and Fuji IX GP Extra/Equia (GC). Additionally a newly developed zinc-containing GIC-ChemFil Rock (Dentsply)-was tested. Mechanical properties were determined at macro- [flexural strength (FS) and modulus of elasticity ( E)] and micro-scale [Vickers hardness (VH) and indentation modulus ( E)] after storing coated and uncoated specimens in artificial saliva and distilled water for 7 and 30 days. Results: ChemFil Rock revealed the highest FS, but the lowest VH and E. The micro-mechanical properties of the analysed GICs did neither benefit from the new zinc formulation nor from resin coating. A resin coating is nevertheless a valuable support for GIC fillings, since it offers the absence of visible surface defects like crazing and voids, and thus, it led to significant improvements in flexural strength. This statement is also valid for ChemFil Rock, contrary to manufacture recommendation. The impact of storage agent and storage duration on the measured properties was low. Conclusions: The new development (ChemFil Rock) might represent a promising approach regarding longevity of GIC fillings in molar regions, due to the high flexural strength and the absence of visible surface defects like crazing and voids. Clinical relevance: All GICs should receive surface protection in order to perform their maximum in stability. [ABSTRACT FROM AUTHOR]

Objectives: The study analyzed the reparability and compatibility of light-curing resin-based composites (RBCs) of the categories 'microhybrid,' 'nanohybrid,' and 'packable.' Materials and methods: Six RBCs with different matrix and filler formulation-purely methacrylate-based composites (MBCs), ormocer-based composites (OBCs), and silorane-based composites (SBCs)-were used for the specimens. Every material was combined with itself and with the other five RBCs, resulting in a total of 36 combination groups ( n = 20). The specimens were polymerized, aged for 8 weeks in distilled water at 37 °C, and then repaired by means of a repair kit. Shear bond strength and fracture mode were measured after aging of the specimens, undergoing storage for 24 h in distilled water at 37 °C followed by thermocycling (5,000 cycles, 5-55 °C) and an additional 4-week storage in distilled water at 37 °C. Results: Data were statistically analyzed using ANOVA with TUKEY HSD post hoc test ( α = 0.05). On average, the OBC Admira reached the highest value as a substrate material (30.41 MPa), and the SBC Filtek Silorane reached the lowest value (8.14 MPa). Filtek Silorane was identified as the repair material with the highest bond strength value (28.70 MPa), while a packable composite reached the lowest bond strength value (15.55 MPa). The analysis of the break modes showed that adhesive breaks are typical when strength is at its lowest (6.27 MPa). A large number of cohesive fractures are conspicuous when identical materials are used for repair, except Filtek Silorane (2 % cohesive fractures). Conclusions: The study demonstrated that the effect of the different materials on bond strength varies strongly, depending on whether the material is used as filling or as repair material. Clinical relevance: It is generally advisable but not compulsory to combine identical RBCs. [ABSTRACT FROM AUTHOR]

Objectives: The aim of our study was to measure and compare degree of conversion (DC) as well as micro- (indentation modulus, E; Vickers hardness, HV) and macromechanical properties (flexural strength, σ; flexural modulus, E) of two recently launched bulk fill resin-based composites (RBCs): Surefil® SDR™ flow (SF) and Venus® bulk fill (VB). Materials and methods: DC ( n = 6) was investigated by Fourier transform infrared spectroscopy (FTIR) in clinical relevant filling depths (0.1, 2, and 4 mm; 6 mm bulk, 6 mm incremental) and irradiation times (10, 20, 40 s). Micro- ( n = 6) and macromechanical ( n = 20) properties were measured by an automatic microhardness indenter and a three-point bending test device after storing the specimens in distilled water for 24 h at 37°C. Furthermore, on the 6-mm bulk samples, the depth of cure was determined. A field emission scanning electron microscope was used to assess filler size. Results were evaluated using one-way analysis of variance, Tukey's honest significance test post hoc test, a multivariate analysis ( α = 0.05) and an independent t test. Weibull analysis was used to assess σ. Results: VB showed, in all depth, significant higher DC (VB, 62.4-67.4 %; SF, 57.1-61.9 %), but significant lower macro- (VB, E = 3.6 GPa; σ = 122.7 MPa; SF, E = 5.0 GPa; σ = 131.8 MPa) and micromechanical properties (VB, E = 7.3-8.8 GPa, HV = 40.7-46.5 N/mm²; SF, E = 10.6-12.2 GPa, HV = 55.1-61.1 N/mm²). Both RBCs showed high reliability (VB, m = 21.6; SF, m = 26.7) and a depth of cure of at least 6 mm at all polymerization times. The factor 'RBC' showed the strongest influence on the measured properties ( η = 0.35-0.80) followed by 'measuring depth' ( η = 0.10-0.46) and 'polymerization time' ( η = 0.03-0.12). Conclusions: Significant differences between both RBCs were found for DC, E, σ, and E at all irradiation times and measuring depths. Clinical relevance: Curing the RBCs in 4-mm bulks for 20 s can be recommended. [ABSTRACT FROM AUTHOR]

Objective: Clinical data indicate an increased trend in material fracture as reason for failure in composite restorations, questioning whether modern resin-based composites (RBCs) are able to fulfil the rising aesthetical demands and to provide at the same time a sufficient mechanical stability also in larger cavities. Nano-hybrid RBCs are promoted as materials with improved mechanical properties. The aim of this study was to analyse differences in mechanical properties within and between modern flowable and non-flowable nano-hybrid and micro-hybrid RBCs by measuring mechanical properties at macro- and micro-scale. Methods: Thirty-four RBCs with traditional and new monomer formulation or photo-polymerization initiator technology-15 nano-hybrid, nine micro-hybrid and ten flowable-were therefore considered. Flexural strength, flexural modulus (E), indentation modulus, Vickers hardness (HV) and creep were measured after the samples had been stored in water for 24 h at 37°C. Differences within the materials as well as within material categories were statistically analysed using one-way ANOVA with Tukey HSD post hoc test ( α = 0.05) as well as partial eta-square statistics. Results: The category of micro- and nano-hybrid RBCs performed in all properties superior compared to the flowable RBCs. The former two categories differ significantly only with regard to three parameters, with nano-hybrid RBCs showing higher HV respectively lower E and filler weight. The micro-mechanical parameters proved to be more sensitive to differences in filler amount and RBCs type than the macro-mechanical properties. Clinical relevance: Only few differences were found between nano-hybrid and micro-hybrid RBCs as a material category and thus, from laboratory tests, no clear advantages in the mechanical stability in stress-bearing areas of nano-hybrid RBCs are expected clinically. Similar is valid for materials with new monomer formulation or photo-polymerization initiator technology. However, several of the measured nano-hybrid RBCs showed consistently higher mechanical properties than the mean values of the micro-hybrid RBCs. [ABSTRACT FROM AUTHOR]

Objectives: This study evaluates the dentin infiltration ability of various types of adhesives and compares four classes of adhesive systems with regard to this property. The infiltration is determined quantitatively, characterized as tag length and ratio of infiltration, and qualitatively, characterized as homogeneity, regularity, and continuity of the resin tags. Materials and methods: Flat dentin surfaces from 140 halves of caries-free molars were bonded with four classes of adhesive systems. The adhesives ( n = 20) were labeled with rhodamine B isothiocyanate and applied on the occlusal dentin following the manufacturer's recommendations and were subsequently light cured, 20 s. Then a 2-mm thick composite layer was applied and light cured, 20 s. The specimens were stored in distilled water at 37°C, 24 h. Two slices were sectioned mesio-distally from each sample and were investigated with a confocal laser scanning microscope. The measurements were done at 0.5, 1.5, and 2.5 mm from the enamel-dentin junction. The data were analyzed by using analysis of variance and the general linear model. Results: The class of adhesive, the composition, and the dentin position were significant factors affecting the investigated parameters. The use of etch and rinse adhesives in comparison to self-etch adhesives provided the formation of longer, more homogeneous, very regularly distributed but mostly fractured tags. Conclusions: A comparison of adhesives confirmed that etch and rinse systems remain better in bond infiltration. Clinical relevance: While the importance of tags formation on bonding is still controversially discussed, adhesive systems with a high ratio of infiltration might better protect the tooth against microorganism contamination. [ABSTRACT FROM AUTHOR]

Objectives: Nanohybrid resin-based composites (RBCs) containing new types of matrix monomers such as dimer acid-based dimethacrylate or tricyclodecane-urethane are assumed to show decreased water uptake and therefore better resistance to hydrolytic degradation than RBCs using bisphenol A diglycidyl methacrylate (BisGMA) due to their hydropobic nature. Our study aimed to analyze the effect of aging on six nanohybrid RBCs, of which two are using these new types of monomers, with regard to differences in the mechanical properties of the materials. Materials and methods: Diametral tensile strength (DTS), Vickers hardness (HV), and creep were measured. Mechanical tests were performed after storing samples for 24 h in distilled water, as well as after aging (thermocycling for 5,000 cycles at 5-55°C and storage for 4 weeks either in distilled water, artificial saliva, or ethanol). Results: The effect of aging on all test parameters was lower than the effect of the material. This information was provided by a general linear model, showing higher partial η values for the influence factor material than for the factor aging. The influence of aging on the micromechanical properties HV and creep was proven to be more sensitive than on the macromechanical property (DTS). This was also illustrated by lower η values for the variable aging for DTS. An increase of the creep of all materials was observed after storage in alcohol. Conclusions: The use of new types of monomers could not be shown to be a significant advantage to the other examined materials containing BisGMA. Clinical relevance: Nanohybrid composites can be recommended as universal filling materials, whether based on new or conventional monomers. [ABSTRACT FROM AUTHOR]

Objectives: This study's purpose was to evaluate the depth of cure (DOC) and the variation of mechanical properties with depth of two nano-hybrid resin-based composites (RBCs) containing a novel monomer composition based on dimer-acid derivatives (h-Da) or rather tricyclodecane-urethane structure (TCD-urethane) compared to three conventionally formulated nano-hybrid RBCs based on hardness-profile measurements. Materials and methods: Specimens were produced through different layering techniques (bulk, incremental) and curing times (10, 20, and 40 s). Mechanical properties (Vickers hardness (HV), modulus of elasticity (E)) were evaluated every 100 μm longitudinally throughout the bisected samples using an automatic micro-hardness indenter. DOC was determined as the depth at which the 80% hardness cutoff value in relation to the surface hardness was reached. Results were compared using one- and multiple-way ANOVA, Tukey HSD post-hoc test ( α = 0.05) and partial eta-squared statistic. Results: Increasing curing time resulted in a significant increase in DOC. Generally, the novel-formulated materials showed higher DOC values. 'Curing time' and 'material' showed the strongest effect on DOC. Starting in 4 mm depth, significantly higher HV and E was reached for incremental compared to bulk-curing technique. Values in 0.1 and 2 mm depth (bulk, incremental) as well as in 4 mm depth (incremental) were independent from curing time, while in greater depths, values generally increased with curing time. 'Filling technique' and 'material' performed the strongest influence on mechanical properties. Conclusions: Within the limits of this study, the novel-formulated RBCs showed better performance concerning DOC compared to conventional materials. Clinical relevance: For cavities deeper than 3 mm, all tested materials should be placed incrementally to ensure adequate polymerization. In large cavities (≥6 mm), the lowest increment should be cured at least 40 s. The novel-formulated RBCs might be cured in comparatively bigger increments. [ABSTRACT FROM AUTHOR]

A pulpotomy is the therapy for management of pulp exposures due to caries in symptom-free primary molars. The aim was to longitudinally compare the relative effectiveness of the Er:YAG laser, calcium hydroxide and ferric sulphate techniques with dilute formocresol in retaining symptom-free molars. Two hundred primary molars in 107 healthy children were included and randomly allocated to one technique. The treated teeth were blindly reevaluated after 6, 12, 18, 24 and 36 months. Descriptive data analysis and logistic regression analysis accounting for multiple observations per patient by generalised estimating equation were used. Additionally, various influences including tooth type, upper and lower jaws, type of anaesthesia, operator and the final restoration on treatment success were evaluated (Wald chi-square test). After 36 months, the following total (considering clinical and clinically symptom-free radiographic failures) and clinical success rates were determined (in percent): Formocresol 72 (92), laser 73 (89), calcium hydroxide 46 (75), ferric sulphate 76 (97). No significant differences were detected between formocresol and any other technique after 36 months. However, the odds ratio of failure appeared to be three times higher for calcium hydroxide than for formocresol. No significant differences in total success rates were seen regarding the aforementioned influencing clinical parameters. The correct diagnosis of the pulpal status, bleeding control and the specific technique are highly important for long-term success of pulpotomies in primary molars. According to the presented long-term data, pulpotomies using ferric sulphate revealed the best treatment outcome among the used techniques, while calcium hydroxide resulted in the lowest success rates after 3 years. Therefore, we can recommend ferric sulphate for easy and successful treatment of primary molars with caries-exposed pulps. [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]

The ability of a restorative material to withstand fracture is of crucial importance especially in stress-bearing area. Therefore, the study aims to analyse the fracture toughness of a large number of dental restorative materials categories. The fracture toughness ( K) of 69 restorative materials belonging to ten materials categories-micro-hybrid, nanofilled, microfilled, packable, ormocer-based, and flowable resin-based composites (RBC), compomers and flowable compomers, as well as glass ionomer cements (GIC) and resin-modified GIC was measured by means of the single-edge notched-beam method after storing the samples ( n = 8) for 24 h in distilled water. Data were analyzed with the one-way analysis of variance (ANOVA) followed by the Tukey's test and partial eta-squared statistics ( p < 0.05). Large variations between the tested materials within a material category were found. The lowest fracture toughness was reached in the GIC group, followed by the microfilled RBCs, resin-modified GIC, and flowable compomers, which do not differ significantly among each other as a material group. The ormocer-based, packable, and micro-hybrid RBCs performed statistically similar, reaching the highest fracture toughness values. Between the two categories of flowables-composites and compomers-no differences were measured. The correlation between K and filler volume (0.34) and respective filler weight (0.40) was low. K increased with the volume fraction of fillers until a critical value of 57%, following with a plateau, with constant values until ca. 65% volume fraction. Above this value, K decreased slightly. Due to the very large variability of the fracture toughness within a material type, the selection of a suitable restorative material should have not been done with respect to a specific material category, especially in stress-bearing areas, but by considering the individual measured material properties. [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]

Abstract: Objectives: Dimer acid based metacrylates and TCD-urethane are promoted as new monomers of nano-hybrid resin based composites as alternatives for the conventional BisGMA. Investigations of this study focused on the mechanical and the storage behavior of nano-hybrid resin based composites (RBCs) composed of these new types of monomers in comparison to RBCs using BisGMA. Methods: Flexural strength and modulus were determined in a three-point-bending test. Additionally, the modulus of elasticity was measured on microscopic scale (E micro) using an automatic microhardness indenter. Tests were performed on samples after 24h storage in distilled water, as well as after thermocycling and storing the materials for four weeks in either distilled water, artificial saliva or ethanol. Results: The six measured materials showed a pronounced decrease of flexural strength, flexural modulus and E micro after four weeks storage in alcohol. Results after four weeks storage in water and saliva could not be proven to be significantly different. The most sensitive factor of influence on all test parameters was the material. Significance: Nano-hybrid composites with new or conventional monomers performed similar in regard to the mechanical properties and the behavior of the materials after aging. [Copyright &y& Elsevier]

The aim of this study was to assess the performance of light-cured luting resin after curing under the ceramic restoration in comparison to dual-cured luting resin, by evaluating the micromechanical properties. Two hundred seventy thin luting composite films of ca. 170 μm in thickness were prepared by using two light-cured luting resins (Variolink Veneer, Ivoclar Vivadent; RelyX Veneer, 3M ESPE) and a dual-cured luting resin (Variolink II, Ivoclar Vivadent). The composites were cured by using a LED-unit (Bluephase®, Ivoclar Vivadent) with three different curing times (10, 20, and 30 s) under two ceramics (IPS e.max Press, Ivoclar Vivadent; IPS Empress® CAD, Ivoclar Vivadent) of different thicknesses (0, 0.75, and 2 mm). Forty-five groups were included, each containing six thin films. The samples were stored after curing for 24 h at 37°C by maintaining moisture conditions with distilled water. Micromechanical properties of the composites were measured with an automatic microhardness indenter (Fisherscope H100C, Germany). For each sample, ten indentations were made, thus totalizing 60 measurements per group. Micromechanical properties of the luting resins were statistically analyzed (SPSS 17.0). Significant differences were observed between the micromechanical properties of the luting resins ( p < 0.05). Variolink II showed the highest values in modulus of elasticity ( E = 11 ± 0.5)* and Vickers hardness (HV = 48.2 ± 3.2)* and the lowest values in creep (Cr = 4.3 ± 0.1)* and elastic-plastic deformation (We/Wtot = 38.6 ± 0.7)* followed by RelyX Veneer ( E = 6.9 ± 0.3, HV = 33 ± 2.5, Cr = 4.6 ± 0.2, We/Wtot = 41.8 ± 1.0)* and Variolink Veneer ( E = 4.4 ± 0.4, HV = 20.1 ± 2.6, Cr = 5 ± 0.2, We/Wtot = 43.7 ± 1.3)*. Dual-cured luting resin expressed higher values in the micro-mechanical properties compared to the light-cured luting resins. The effect of luting resin type on the micromechanical properties of the luting resins was higher than the effect of curing time, ceramic type and ceramic thickness respectively (*The values of reference without ceramics for 30 s curing time). [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]

The study evaluated the effect of ozone application on the composite-to-composite bond. Three hundred and twenty cylindrical composite specimens were divided into two groups: group 1 was subjected to a 60 s ozone application, whereas group 2 remained untreated. Four subgroups were obtained from each group according to the intermediate repair agent: an adhesive, a silane, silane/adhesive combination, or flowable composite. Repair composite cylinders were built-up. The composite repair strength was tested after 24 h and after thermocycling with a shear test. Additionally, 4 mm × 4 mm × 2 mm composite specimens were prepared and stored 24 h in deionized water. Half of the specimens were subjected to ozone application and the other served as control. The elastic modulus (E) and the Vicker's hardness (VH) of the composite surfaces were tested immediately and after thermocycling. Significant differences among the experimental groups were detected ( p < 0.001). The composite repair strength was affected by the pretreatment and by the intermediate agent, whereas, the thermocycling was not significant. The partial eta-squared statistics showed that the intermediate agent was the main factor affecting the composite repair strength, whereas the pretreatment played a minor role. No differences were observed between ozone and control groups when the same intermediate agent and the same aging conditions were applied. Repairing with flowable composite tended to achieve higher bond strengths (20.7 and 26.5 MPa in ozone and control groups, respectively, after 24 h). The use of silane coupling agent showed the lowest composite repair strengths. Ozone did not affect E and VH ( p > 0.05) and the thermocycling affected only E ( p < 0.05). In conclusion, the application of ozone does not impair the composite-to-composite bond. [ABSTRACT FROM AUTHOR]

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]

Purpose: To evaluate the effect of gasiform ozone on the repair strength of ormocer-based and silorane-based composites. Methods: 160 cavities were created in methacrylate cylinders. Half of the cavities were filled with a silorane- based composite, whereas the other half was filled with an ormocer-based composite. After storage (1 week, deionized water, 37°C) the specimens of each restorative material were divided into two main experimental groups: in Group 1 the specimens were subjected to a 60-second ozone gas application; in Group 2 no pretreatment was performed (control). The corresponding adhesive of each restorative material was applied as the intermediate repair agent in both groups. Repair cylinders were then built up with the homologous material. Half of the specimens in each group were subjected to thermocycling (5,000 cycles, 5°C-55°C, dwell time 30 seconds, transfer time 5 seconds) prior to testing, whereas the other specimens were immediately tested. The repair strength was assessed with a shear test. The two-way ANOVA with pretfeatment and thermocycling as the main factors was used to analyze the shear bond strength data within each restorative material. Results: The pretreatment, the thermocycling and their interaction did not significantly affect the repair strength of either tested materials (P> 0.05). The ozone treatment did not significantly affect the repair strength. The silorane-based composite showed lower repair strengths compared to those of the ormocer-based composite. The immediate repair strengths in the ozone-treated and control groups were respectively, 28.1(13.8) MPa and 28.8(8.8) MPa for the silorane-based composite and 31.5(9.3) MPa and 35.6(10.6) MPa for the ormocer-based composite. After thermocycling, the repair strengths in the ozone-treated and control groups were 27.7(9.7) MPa and 29.5(11.1) MPa for the silorane-based composite and 31.4(6.0) MPa and 34.2(4.5) MPa for the ormocer-based composite. Mixed failures occurred most frequently in all experimental groups. In conclusion, ozone did not affect the repair strength of the tested silorane-based and ormocer-based composites. [ABSTRACT FROM AUTHOR]

Adhesives and lining/base materials should relieve the stresses concentrated at the tooth/restoration interface. The study aimed at comparing the mechanical properties of eight adhesives and six glass-ionomer cements (GICs). The adhesives were applied on dentin disks, whereas 2 mm × 3 mm × 2 mm GICs specimens were prepared in a teflon mold. Vicker’s hardness (VH), elastic modulus ( E), creep (Cr) and elastic work (We/Wtot) were measured with a micro hardness indenter. One-way ANOVA and Tukey’s test were used to compare the mechanical properties within each materials’ type and among the materials’ classes. Enamel and dentin were used as references. Significant differences were detected within each materials’ type and among the materials’ classes and enamel and dentin. GICs were superior to adhesives in VH and E and showed a VH similar to dentin. GICs presented mechanical properties more similar to enamel and dentin than adhesives. [ABSTRACT FROM AUTHOR]

Since a direct comparison of composites efficacy in clinical studies is very difficult, our study aimed to analyse in laboratory tests under standardised and simulated clinical conditions a large variety of commercial composite materials belonging to eight different materials categories. Thus, 72 hybrid, nano-hybrid, micro-filled, packable, ormocer-based and flowable composites, compomers and flowable compomers were compared in terms of their mechanical behaviour. Flexural strength (FS), flexural modulus (FM), diametric tensile (DTS) and compressive strength (CS) were measured after the samples had been stored in water for 24 h at 37°C. Results were statistically analysed using one-way ANOVA with Tukey HSD post hoc test ( α = 0.05) as well as partial η2 statistics. Large varieties between the tested materials within the same material category were found. The hybrid, nano-hybrid, packable and ormocer-based composites do not differ significantly among each other as a material type, reaching the highest FS values. Nano-hybrid composites are characterised by a good FS, the best DTS but a low FM. The lowest mechanical properties achieved the micro-filled hybrids. The flowable composites and compomers showed for all properties comparable result. Both flowable material categories do not differ significantly from the micro-filled composites for the most mechanical properties, showing only a higher DTS. The filler volume was shown to have the highest influence on the measured properties, inducing a maximum FS and FM at a level of 60%, whereas such dependence was not measured for DTS or CS. The influence of the type of material on the mechanical properties was significant but very low, showing the strongest influence on the CS. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: Cationic ring-opening monomers with a reduced shrinkage stress – silorane – are being used as matrix resins for recently introduced dental composites. Since shrinkage and mechanical properties are generally opposite properties, our study aimed to analyze the mechanical behavior of the silorane-based composite in comparison to six homologous clinical successful methacrylate-based composites. Methods: Mechanical properties were determined at macro- (strength and modulus of elasticity), micro- (hardness, modulus of elasticity and creep) and nano-scale (nano-dynamic-mechanical parameters: complex, storage, loss modulus and tan δ) after storing the materials for 24h in distilled water as well as after aging (thermocycling and storing for 4 weeks in water, saliva or alcohol). Results: The strongest influence on the mechanical properties at macroscopic scale was exerted by the storage media although the influence of the material was also significant. At micro- and nano-scale, the material itself influenced the mechanical properties stronger than the storage. By comparing the four storage conditions, a multivariate analysis revealed a significant decrease in all measured mechanical properties by storing for 4 weeks in water, saliva or alcohol, when compared to the 24h storage. The strongest effect was exerted through the alcohol storage, whereas the effect of storing for 4 weeks in water or saliva was comparable. The nano-composites were more degraded by a 4-week storage in water and saliva than the micro-hydrids, whereas the effect of storing in alcohol was material depended. The tested silorane-based composite revealed good mechanical properties. The material was very stable in all applied solvents and more reliable by storing in alcohol solutions than the measured methacrylate-based composites. Significance: From the point of view of the mechanical properties measured at macro-, micro- and nano-scale, the silorane-based composite was comparable to clinically successful methacrylate-based composite materials, encouraging the clinical use of the new composite material. [Copyright &y& Elsevier]

Abstract: Objective: The purpose of this study was to evaluate a nano-filled dental composite, with varying cure irradiation-time, in terms of the spatial distribution of dynamic-mechanical properties determined at nanometre scale and the resultant distinction between filler, matrix and inter-phase regions. Materials and methods: Specimen groups (n =5) of the composite Filtek Supreme XT were cured in 2mm deep molds for 5, 10, 20 and 40s, and stored for 24h in distilled water at 37°C. Properties were measured at 2mm depth, on the lower specimen surfaces. Nano-dynamic-mechanical parameters (complex, storage and loss modulus, tan δ) were determined at an array of 65,000 locations in a 5μm×5μm area. Micro-mechanical properties (hardness, modulus of elasticity, creep and elastic/plastic deformation) were also measured and additionally the real-time degree of cure, by ATR-FTIR, for 10min after photo-initiation and after storage. Results: The spatial distribution of nano-dynamic-mechanical properties varied significantly enabling four distinguishable matrix, filler-cluster and inter-phase regions to be identified. Proceeding from matrix to filler-cluster locations, complex-moduli increased linearly and loss-factors decreased linearly, consistent with visco-elastic composite theory. Curing time strongly affected all measured properties at 2mm depth. The organic matrix was shown to be inhomogeneous for all curing times. By increasing cure-time, the proportion of less well polymerized area decreased from 37.7 to 1.1%, resulting in a more homogeneous organic matrix. Significance: The experimentally observed graduated transition, in complex modulus and related dynamic-mechanical properties, across the matrix – inter-phases – filler-cluster regions is conducive to low internal stresses, in contrast to the abrupt modulus transitions anticipated or observed in many other particulate composite structures. The identification of these phase-regions provides a realistic basis for accurate nano- and micro-mechanical computational modelling. [Copyright &y& Elsevier]

Bioactive collagen crosslinkers propose to render the dentin hybrid layer less perceptive to hydrolytic challenge. This study aims to evaluate whether bond strength of dental resin composite to dentin benefits from riboflavin (RB)-sensitized crosslinking when used in a clinically applicable protocol. A total of 300 human dentin specimens were prepared consistent with the requirements for a macro-shear bond test. RB was applied on dentin, either incorporated in the primer (RBp) of a two-step self-etch adhesive or as an aqueous solution (RBs) before applying the adhesive, and blue light from a commercial polymerization device was used for RB photoactivation. Bonding protocol executed according to the manufacturer's information served as control. Groups (n = 20) were tested after 1 week, 1 month, 3 months, 6 months or 1 year immersion times (37 °C, distilled water). The different application methods of RB significantly influenced bond strength (p < 0.001) with a medium impact (η2p = 0.119). After 1 year immersion, post hoc analysis identified a significant advantage for RB groups compared to RBp (p = 0.018), which is attributed to a pH-/solvent-dependent efficiency of RB-sensitized crosslinking, stressing the importance of formulation adjustments. We developed an application protocol for RB-sensitized crosslinking with emphasis on clinical applicability to test its performance against a gold-standard adhesive, and are confident that, with a few adjustments to the application solution, RB-sensitized crosslinking can improve the longevity of adhesive restorations in clinics. [ABSTRACT FROM AUTHOR]

The aim of the study was to offer a comparative perspective on the mechanical and viscoelastic behavior of currently developed materials for simplified restoration concepts. These materials have not yet been clearly assigned whether they are complex hybrids of already known material categories or new material classes. A dual-cured, bulk-fill, bioactive resin-based composite (alkasite), a resin-modified glass ionomer cements (RM-GIC) with novel polymerizable acid polymers, and a glass ionomer cement (GIC) with improved adaptation to an acidic environment were compared with regard to their macro-mechanical parameters (3-point bending test, 3-PBT), fracture mechanism, quasi-static and viscoelastic behaviour (instrumented indentation test, IIT), morphology and structural appearance of the filler system (SEM analysis). The influence of surface finishing was quantified on the outcome of the 3-PBT, while the influence of aging and frequency was monitored on the outcome of the IIT. One and multiple-way analysis of variance (ANOVA) with Tukey honestly significant difference (HSD) post-hoc tests (α = 0.05) and Weibull analysis were applied. Surface finishing strongly influenced the outcome of the 3-PBT for RM-GIC and GIC but not of the alkasite. The highest material reliability (Weibull parameter m) was found with the alkasite, irrespective of the curing mode. Ground specimens showed decrease reliability, except for the alkasite in the light-cured mode. The predominant failure mode originated from sub-surface defects (52.5%), followed by corner (25%), edge (18.1%), and crack arrest (4.4%). The effect of the parameter material on the quasi-static outcome of the IIT was highest on elastic/plastic parameters (p < 0.001; e.g. elastic indentation work, η P 2 = 0.875), was moderate on the Martens Hardness (η P 2 = 0.420), and was low on the Vickers hardness (η P 2 = 0.218). The viscoelastic parameters, in particular the loss factor (tan δ) allow a clear documentation of the ongoing acid-base setting reaction during aging of one month, which was more pronounced in the GIC than in the RM-GIC. The decrease in tan δ with aging for GIC and RM-GIC reflects the maturation process and increased brittleness, while the increase in tan δ with aging reflects the polymer plasticization in the polymer-based alkasite. The mechanical and viscoelastic behavior depending on surface refinement, aging and frequency clearly allow to classify the currently developed materials for simplified restoration concepts into known material categories such as RBCs (alkasite), RM-GIC or GIC. [ABSTRACT FROM AUTHOR]