Influence of Post-Curing in Nitrogen-Saturated Condition on the Degree of Conversion and Color Stability of 3D-Printed Resin Crowns

Post-curing is the process of applying extra light to complete the polymerization process of 3D printing. The mechanical properties of light-cured three-dimensional (3D) printed resin can be improved by decreasing the oxygen concentrations during post-curing, and nitrogen-saturated post-curing has been applied for this purpose. This study aimed to evaluate and compare the color stability of 3D-printed resin crowns that were post-cured in both normal air and nitrogen-saturated conditions. Crowns were fabricated with a 3D printer and post-cured in normal air (control group; air) or nitrogen-saturated conditions (experimental group; nitrogen). The specimens in each group were subdivided into four subgroups, each exposed to different discoloration agents: distilled water, coffee, wine, and curry. Post-immersion color changes were measured using a digital spectrophotometer and analyzed using repeated-measures ANOVA. Fourier transform infrared (FT-IR) spectroscopy evaluated the degree of conversion of resin over immersion times for both post-curing conditions. Upon comparing the effects of post-curing conditions, a significant difference between the control and experimental groups in terms of immersion time in the wine and curry subgroups was found. FT-IR analysis showed a significant difference in the degree of conversion between the air and nitrogen groups from 10 to 300 s. These findings suggest that nitrogen-saturated post-curing can potentially enhance the conversion rate of 3D-printed resin crowns, thereby improving their color stability.

Effect of Surface Polishing on Physical Properties of an Occlusal Splint Material for Additive Manufacturing under Protection Gas Post-Curing Condition

The aim of this study was to evaluate the effect of surface polishing as well as the post-curing atmospheres (air and nitrogen gas) on the physical properties of an occlusal splint material for additive manufacturing. Flexural strength, flexural modulus, Vickers hardness number (VHN), degree of carbon double bond conversion (DC), water sorption (W_SP), and water solubility (W_SL) were evaluated. Surface polishing significantly affected the evaluated properties. Regardless of the post-curing atmosphere, flexural strength, flexural modulus, VHN, and DC showed significantly higher values for the polished specimens when compared with the unpolished ones, while W_SP and W_SL were significantly lower for the polished specimens. Unpolished specimens post-cured at nitrogen gas showed significantly higher VHN and DC values. However, the effect of the post-curing at a nitrogen gas atmosphere was non-significant in polished specimens. The current results suggested that surface polishing plays a role in the physical properties of the evaluated occlusal splint material and can enhance all the evaluated properties regardless of the post-curing atmosphere. Meanwhile, the post-curing at a nitrogen gas atmosphere can enhance the VHN and DC but its effect is confined only to the surface layers, which can be removed during surface polishing.

Separating Curing and Temperature Effects on the Temperature Coefficient of Resistance for a Single-Walled Carbon Nanotube Nanocomposite

The temperature coefficient of resistance (TCR) determines the electrical performance of materials in electronics. For a carbon nanotube (CNT) nanocomposite, change of resistivity with temperature depends on changes in CNT intrinsic conductivity, tunnelling thresholds and distances, matrix' coefficient of thermal expansion, and other factors. In our study, we add one more influencing factor-the degree of cure. Complexities of the curing process cause difficulties to predict, or even measure, the curing state of the polymer matrix while uncertainty in the degree of cure influences TCR measurements leading to biased values. Here we study the influence of the cure state on the TCR of a single-walled CNT/epoxy polymer nanocomposite. For the given degree of cure, TCR measurements are conducted in the temperature range 25-100 °C, followed by the next 24 h of post-curing and a new cycle of measurements, 8 cycles in total. We find that contrary to industry practice to expect a high degree of cure after 3 h at 130 °C, the curing process is far from reaching the steady state of the material and continues at least for the next 72 h at 120 °C, as we observe by changes in the material electrical resistivity. If TCR measurements are conducted in this period, we find them significantly influenced by the post-curing process continuing in parallel, leading in particular to non-monotonic temperature dependence and the appearance of negative values. The unbiased TCR values we observe only when the material reaches the steady state are no longer influenced by the heat input. The dependence becomes steady, monotonically increasing from near zero value at room temperature to 0.001 1/°C at 100 °C.

Effects of Post-Curing Light Intensity on the Mechanical Properties and Three-Dimensional Printing Accuracy of Interim Dental Material

This study evaluated the effects of the light intensity of curing and the post-curing duration on the mechanical properties and accuracy of the interim dental material. After designing the specimen, 3D printing was performed, and the light intensity was divided into groups G20, G60, G80, and G120 (corresponding to 1.4−1.6, 2.2−3.0, 3.8−4.4, and 6.4−7.0 mW/cm2, respectively), with no post-curing or 5, 10, or 20 min of post-curing being performed. The flexural properties, Vickers microhardness, degree of conversion (DC), and 3D accuracy were then evaluated. The flexural properties and Vickers microhardness showed a sharp increase at the beginning of the post-curing and then tended to increase gradually as the light intensity and post-curing time increased (p < 0.001). On the other hand, there was no significant difference between groups in the accuracy analysis of a 3D-printed three-unit bridge. These results indicate that the light intensity of the post-curing equipment influences the final mechanical properties of 3D-printed resin and that post-curing can be made more efficient by optimizing the light intensity and post-curing time.

Comparative Evaluation of Surface Roughness and Hardness of 3D Printed Resins

The effect of printing parameters on the surface characteristics of three-dimensional (3D)-printed denture base resins (DBRs) is neglected. Therefore, this study investigated the effect of printing orientation and post-curing time on the surface roughness and hardness. One conventional heat-polymerized (HP) resin and two 3D-printing resins (NextDent (ND) and ASIGA (AS)) were used to fabricate a total of 250-disc (10 × 2.5 mm) specimens. ND and AS specimens were printed with different orientations (0-, 45-, and 90-degree) and each orientation group was subjected to four post-curing times (30, 60, 90, 120 min). Printed specimens were thermo-cycled (10,000 cycles) followed by the measuring of surface roughness (Profilometer (Ra)) and hardness (a Vickers hardness (VH)). ANOVA and post hoc tests were used for data analysis (α = 0.05) at significant levels. AS and ND showed no significant changes in Ra when compared with HP (p ˃ 0.05), except the 45-degree orientation (AS/90 min and AS/120 min) significantly increased surface roughness (p ˂ 0.001). There was no significant difference in Ra with different orientations and post-curing time for both materials AS and ND (p ˃ 0.05). Compared with HP, 3D-printed DBRs showed low VH values (p ˂ 0.001). For AS, 90-degree orientation showed a significant decrease in VH at 60, 90, and 120 min when compared with 0- and 45-degree orientation (p ˂ 0.001), while ND showed no significant difference in VH with different printing orientations (p ˃ 0.05). The VH of AS and ND improved when increasing post-curing time to 120 min (p ˂ 0.001), and the printing orientations and post-curing time did not affect the Ra of 3D-printed DBRs.

Effect of printing orientation and post-curing time on the flexural strength of 3D-printed resins

PURPOSE

To evaluate the effect of printing orientation combined with different post-curing times on the flexural strength of 3D-printed resins.

MATERIALS AND METHODS

A total of 480 rectangular specimens with the dimensions of 64×10×3.3 mm were designed and fabricated from two 3D printed acrylic resins and one heat-polymerized resin (HP). 3D-printed groups were divided into 3 groups according to printing orientations (0-, 45-, 90-degree); each group was subdivided into 4 groups according to post-curing time (30, 60, 90, 120 min.). All specimens were subjected to thermal cycling (10,000 cycles) before testing flexural strength. Fractured surfaces were examined under scanning electron microscope (SEM). ANOVA and Tukey's post hoc test were used for data analysis (α = 0.05).

RESULTS

The result of this study showed that the highest flexural strength values of 3D-printed resin (NextDent, and ASIGA) were in 0-degree groups. Also, the flexural strength values increased when post-curing time was increased regardless of the printing orientation and the highest flexural strength was recorded at 120 min post-curing time in all orientations. SEM analysis showed rougher surface with irregular lamellae which represented a ductile fracture confirming that high energy is required for crack propagation and these features markedly increased as post-curing time increased.

CONCLUSION

The results showed that the 0-degree orientation groups showed higher flexural strength compared to other groups. Similarly, with increased post-curing time, the flexural strength increased. This article is protected by copyright. All rights reserved.

3D-Printed vs. Heat-Polymerizing and Autopolymerizing Denture Base Acrylic Resins

The aim of this work was to investigate the effect of two post-curing methods on the mechanical properties of a 3D-printed denture base material. Additionally, to compare the mechanical properties of that 3D-printed material with those of conventional autopolymerizing and a heat-cured denture base material. A resin for 3D-printing denture base (Imprimo^®), a heat-polymerizing acrylic resin (Paladon^® 65), and an autopolymerizing acrylic resin (Palapress^®) were investigated. Flexural strength, elastic modulus, fracture toughness, work of fracture, water sorption, and water solubility were evaluated. The 3D-printed test specimens were post-cured using two different units (Imprimo Cure^® and Form Cure^®). The tests were carried out after both dry and 30 days water storage. Data were collected and statistically analyzed. Resin type had a significant effect on the flexural strength, elastic modulus, fracture toughness, and work of fracture (p < 0.001). The flexural strength and elastic modulus for the heat-cured polymer were significantly the highest among all investigated groups regardless of the storage condition (p < 0.001). The fracture toughness and work of fracture of the 3D-printed material were significantly the lowest (p < 0.001). The heat-cured polymer had the lowest significant water solubility (p < 0.001). The post-curing method had an impact on the flexural strength of the investigated 3D-printed denture base material. The flexural strength, elastic modulus, fracture toughness, work of fracture of the 3D-printed material were inferior to those of the heat-cured one. Increased post-curing temperature may enhance the flexural properties of resin monomers used for 3D-printing dental appliances.

Additive Manufacturing for Automotive Applications: Mechanical and Weathering Durability of Vat Photopolymerization Materials

In this study, the effect of the post-curing process as well as the long-term weathering behavior were studied for three different three-dimensional printable, pigmented (black), nonstabilized, ultraviolet (UV) cure resin formulations (A and B being thiol-ene chemistry, and C being acrylate chemistry). To study the effect of the post-cure process, the printed parts were post-cured using one of five different processes: no post-cure, UV-only, heat-only, UV+heat, and electron beam (EB) post-curing. Bulk tensile properties and nanohardness were measured for each of the systems and post-cure conditions. For weathering studies, the parts were post-cured using the recommended UV-only process and exposed using the ASTM D7869 exterior weathering protocol. The results show that the post-cure process had a significant effect on the final mechanical properties of the resins and was dependent on the underlying resin chemistry. Thermal post-curing was not as effective as UV curing for Resin C compared with the two other resins, which could both undergo thermal polymerization. In addition, Resin B showed the smallest change in mechanical properties before and after post-curing, regardless of the type of post-curing process. EB post-curing, even at very low dosages, that is, from 0.05 to 1 Mrad, resulted in considerable post-cure cross-linking to the point of embrittlement and a significant drop in percent elongation at break for dosages above 0.5 Mrad. Although Resins A and C outperformed Resin B in photooxidation performance, all three resins demonstrated that promising results considering no hindered amine light stabilizers were used in the formulations.

A Hydrophobic Derivative of Ciprofloxacin as a New Photoinitiator of Two-Photon Polymerization: Synthesis and Usage for the Formation of Biocompatible Polylactide-Based 3D Scaffolds

A hydrophobic derivative of ciprofloxacin, hexanoylated ciprofloxacin (CPF-hex), has been used as a photoinitiator (PI) for two-photon polymerization (2PP) for the first time. We present, here, the synthesis of CPF-hex and its application for 2PP of methacrylate-terminated star-shaped poly (D,L-lactide), as well a systematic study on the optical, physicochemical and mechanical properties of the photocurable resin and prepared three-dimensional scaffolds. CPF-hex exhibited good solubility in the photocurable resin, high absorption at the two-photon wavelength and a low fluorescence quantum yield = 0.079. Structuring tests showed a relatively broad processing window and revealed the efficiency of CPF-hex as a 2PP PI. The prepared three-dimensional scaffolds showed good thermal stability; thermal decomposition was observed only at 314 °C. In addition, they demonstrated an increase in Young's modulus after the UV post-curing (from 336 ± 79 MPa to 564 ± 183 MPa, which is close to those of a cancellous (trabecular) bone). Moreover, using CPF-hex as a 2PP PI did not compromise the scaffolds' low cytotoxicity, thus they are suitable for potential application in bone tissue regeneration.

Effects of Post-Curing Time on the Mechanical and Color Properties of Three-Dimensional Printed Crown and Bridge Materials

Three-dimensional (3D) printing is increasingly being utilized in the dental field. After fabricating a prosthesis using a 3D printed resin, a post-curing process is required to improve its mechanical properties, but there has been insufficient research on the optimal post-curing conditions. We used various 3D printed crown and bridge materials in this study, and evaluated the changes in their properties according to post-curing time by evaluating the flexural strength, Weibull modulus, Vickers hardness, color change, degree of conversion, and biocompatibility. The obtained results confirmed that the strength of the 3D printed resin increased when it was post-cured for 60–90 min. The Vickers hardness, the degree of conversion, and biocompatibility of the 3D printed resins increased significantly around the beginning of the post-curing time, and then increased more gradually as the post-curing time increased further. It was observed that the color tone also changed as the post-curing time increased, with some groups showing a ΔE₀₀ value of ≥ 2.25, which can be recognized clinically. This study has confirmed that, after the printing process of a 3D printed resin was completed, a sufficient post-curing time of at least 60 min is required to improve the overall clinical performance of the produced material.

Optimization of the Curing and Post-Curing Conditions for the Manufacturing of Partially Bio-Based Epoxy Resins with Improved Toughness

This research deals with the influence of different curing and post-curing temperatures on the mechanical and thermomechanical properties as well as the gel time of an epoxy resin prepared by the reaction of diglycidyl ether of bisphenol A (DGEBA) with an amine hardener and a reactive diluent derived from plants at 31 wt %. The highest performance was obtained for the resins cured at moderate-to-high temperatures, that is, 80 ° C and 90 ° C , which additionally showed a significant reduction in the gel time. This effect was ascribed to the formation of a stronger polymer network by an extended cross-linking process of the polymer chains during the resin manufacturing. Furthermore, post-curing at either 125 ° C &nbsp; or 150 ° C yielded thermosets with higher mechanical strength and, more interestingly, improved toughness, particularly for the samples previously cured at moderate temperatures. In particular, the partially bio-based epoxy resin cured at 80 ° C and post-cured at 150 ° C for 1 h and 30 min, respectively, showed the most balanced performance due to the formation of a more homogeneous cross-linked structure.

3D-printed material for temporary restorations: impact of print layer thickness and post-curing method on degree of conversion

AIM

The purpose of this investigation was to evaluate the impact of print layer thickness and post-curing method on the degree of conversion (DC) of a three-dimensional (3D) print material for temporary restorations.

MATERIALS AND METHODS

120 specimens of the resin material NextDent C&B were additively manufactured in three different print layer thicknesses (25 µm, 50 µm, and 100 µm) using a DLP printer, and post-cured by either Labolight DUO (LL), Otoflash G171 (OF), LC-3DPrint Box (PB) or PCU LED (PCU). Each subgroup contained 10 specimens. Raman spectra were measured for the liquid state of the resin (n = 10), directly after printing (Rprint) and after post-curing (Rcured). DC and ΔDC were calculated. The data were statistically analyzed using the Kolmogorov-Smirnov test, the general linear model analysis together with partial eta-squared (ηP²), Kruskal-Wallis, and Mann-Whitney U tests (P < 0.05).

RESULT

Specimens post-cured by OF showed the highest ΔDC, followed by specimens post-cured by PB, PCU, and LL (P < 0.001). Post-curing by PB, PCU, and LL resulted in the same ΔDC value range (P = 0.076 to 0.209). The print layer thicknesses of 100 µm and 50 µm (P = 0.931) showed higher ΔDC than the print layer thickness of 25 µm (P < 0.001).

CONCLUSION

The choice of the post-curing method has a high impact on the DC of the tested 3D print material followed by the specific print layer thickness. Overall, specimens post-cured by OF showed the highest DC and ΔDC values. Brands Technology Duration Wavelength Manufacturer LC-3DPrint Box (PB) Ultraviolet light (UV) 30 min Range 315 to 550 nm, peaks at approximately 360 and 435 nm NextDent (Soesterberg, Netherlands) Otoflash G171 (OF) Flashlight, nitrogen atmosphere Two processes of 2000 flashes Range 300 to 700 nm, peaks at approximately 480 and 530 nm NK Optik (Baierbrunn, Germany) Labolight DUO (LL) Light-emitting diode (LED) Two processes of 3 min Range 380 to 510 nm, peaks at approximately 395 and 475 nm GC Europe (Leuven, Belgium) PCU LED (PCU) Light-emitting diode (LED), vacuum 5 min Peaks at approximately 410 nm Dreve (Unna, Germany).