Evaluating oxygen shielding effect using glycerin or vacuum with varying temperature on 3D printed photopolymer in post-polymerization

Evaluation of Shear Bond Strengths of 3D Printed Materials for Permanent Restorations with Different Surface Treatments

The development of high-filled 3D printing resin necessitates a bonding protocol for dental indirect restorations to achieve optimal bond strength after cementation. This study evaluates shear bond strengths of high-filler 3D printed materials for permanent restorations with various surface treatments. Rodin Sculpture 1.0 (50% lithium disilicate fillers) and 2.0 Ceramic Nanohybrid (>60% zirconia and lithium disilicate fillers) were tested, with Aelite All-Purpose Body composite resin as control. Samples were prepared, post-cured, and sandblasted with alumina (25 µm). Surface roughness was analyzed using an optical profilometer. Two bonding protocols were compared. First, groups were treated with lithium disilicate silane (Porcelain Primer) or zirconia primer (Z-Prime Plus) or left untreated without a bonding agent. Beam-shaped resin cement (DuoLink Universal) specimens were bonded and stored in a 37 °C water bath. Second, additional sets of materials were coated with a bonding agent (All-Bond Universal), either followed by silane application or left untreated. These sets were then similarly stored alongside resin cement specimens. Shear bond tests were performed after 24 h. SEM images were taken after debonding. One-Way ANOVA and post hoc Duncan were performed for the statistical analysis. Rodin 1.0 exhibited increased adhesive failure with silane or zirconia primer coating, but significantly improved bond strengths with bonding agent application. Rodin 2.0 showed consistent bond strengths regardless of bonding agent application, but cohesive failure rates increased with bonding agent and filler coating. In all groups, except for Rodin 1.0 without bonding agent, silane coating increased cohesive failure rate. In conclusion, optimal shear bond strength for high-filler 3D printing materials can be achieved with silane coating and bonding agent application.

Digital manufacturing techniques and the in vitro biocompatibility of acrylic-based occlusal device materials

OBJECTIVES

Material chemistry and workflow variables associated with the fabrication of dental devices may affect the biocompatibility of the dental devices. The purpose of this study was to compare digital and conventional workflow procedures in the manufacturing of acrylic-based occlusal devices by assessing the cytotoxic potential of leakage products.

METHODS

Specimens were manufactured by 3D printing (stereolithography and digital light processing), milling, and autopolymerization. Print specimens were also subjected to different post-curing methods. To assess biocompatibility, a human tongue epithelial cell line was exposed to material-based extracts. Cell viability was measured by MTT assay while Western blot assessed the expression level of selected cytoprotective proteins.

RESULTS

Extracts from the Splint 2.0 material printed with DLP technology and post-cured with the Asiga Flash showed the clearest loss of cell viability. The milled and autopolymerized materials also showed a significant reduction in cell viability. However, by storing the autopolymerized material in dH2O for 12 h, no significant viability loss was observed. Increased levels of cytoprotective proteins were seen in cells exposed to extracts from the print materials and the autopolymerized material. Similarly to the effect on viability loss, storing the autopolymerized material in dH2O for 12 h reduced this effect.

CONCLUSIONS/CLINICAL RELEVANCE

Based on the biocompatibility assessments, clinical outcomes of acrylic-based occlusal device materials may be affected by the choice of manufacturing technique and workflow procedures.

Effects of surface glazing on the mechanical and biological properties of 3D printed permanent dental resin materials

Purpose This study aimed to determine the surface glazing effect on the mechanical and biological properties of three-dimensional printed dental permanent resins.Methods Specimens were prepared using Formlabs, Graphy Tera Harz permanent, and NextDent C&B temporary crown resins. Specimens were divided into three groups: samples with untreated surfaces, glazed surfaces, and sand-glazed surfaces. The flexural strength, Vickers hardness, color stability, and surface roughness of the samples were analyzed to identify their mechanical properties. Their cell viability and protein adsorption were analyzed to identify their biological properties.Results The flexural strength and Vickers hardness of the samples with sand glazed and glazed surfaces were significantly increased. The color change was higher for surface untreated samples than that for the samples with sand-glazed and glazed surfaces. The surface roughness of the samples with sand-glazed and glazed surfaces was low. The samples with sand-glazed and glazed surfaces have low protein adsorption ability and high cell viability.Conclusions Surface glazing increased the mechanical strength, color stability, and cell compatibility, while reducing the Ra and protein adsorption of 3D-printed dental resins. Thus, a glazed surface exhibited a positive effect on the mechanical and biological properties of 3D-printed resins.

Effect of post-curing conditions on surface characteristics, physico-mechanical properties, and cytotoxicity of a 3D-printed denture base polymer

OBJECTIVE

This study aims to investigate the influence of post-polymerization (post-curing) conditions on surface characteristics, flexural properties, water sorption and solubility, and cytotoxicity of additively manufactured denture base materials.

METHODS

The tested specimens were additively manufactured using digital light processing and classified into different post-curing condition groups: submerged in water (WAT), submerged in glycerin (GLY), and air exposure (AIR). An uncured specimen (UNC) was used as a control. The surface topography and roughness were observed. The flexural strength and modulus were determined via a three-point bending test. The water sorption and solubility were subsequently tested. Finally, an extract test was performed to assess cytotoxicity.

RESULTS

Different post-curing conditions had no significant effects on the surface topography and roughness (Sa value). Various post-curing conditions also had no significant effects on the flexural strength. Notably, the flexural modulus of the WAT group (2671.80 ± 139.42 MPa) was significantly higher than the AIR group (2197.47 ± 197.93 MPa, p = 0.0103). After different post-curing conditions, the water sorption and solubility of the specimens met the ISO standards. Finally, all post-curing conditions effectively reduced cytotoxic effects.

SIGNIFICANCES

Post-curing with different oxygen levels improved flexural properties, and flexural modulus significantly increased after the specimens were submerged in water. In addition, water sorption and solubility, and cytocompatibility were optimized by post-curing, irrespective of the post-curing conditions. Therefore, the water-submerged conditions optimized the flexural modulus of the 3D-printed denture base materials.

Influence of different post-processing methods on the dimensional accuracy of 3D-printed photopolymers for dental crown applications - A systematic review

OBJECTIVES

To perform a systematic review that provides an overview of the current literature on the influence of different post-processing methods on the accuracy of additive-manufactured (3D-printed) photopolymer crown materials, and whether more research is needed.

MATERIALS AND METHODS

The search used three online databases, Ovid (MEDLINE), Scopus and Web of Science which were screen for publications that involved assessing dimensional accuracy in post-processing of 3D printed dental crown materials. Publications that were literature reviews, abstracts, written in a language different from English, or publications that did not assess dimensional accuracy were excluded.

RESULTS

The included articles were published between 1995 and 2023. After the removal of duplicates using Endnote, 135 studies remained for further screening, 13 were selected for full-text analysis, and 7 studies were included in the systematic review. A total of 7 articles were examined and categorised based on several factors, such as the type of material, number of specimens per group, print layer thickness, print angle of specimens, 3D printer used, properties of the specimens studied, and the method of analysing the accuracy of the specimens.

CONCLUSION

It was found that post-processing washing times outside the prescribed instruction for use (IFU) may have an impact on the physical and biocompatibility characteristics of the material. Studies focusing on inert mediums during post-processing require more detailed investigation. The use of different post-curing conditions does not significantly affect the materials dimensional accuracy.

Influence of Post-Processing on the Degree of Conversion and Mechanical Properties of 3D-Printed Polyurethane Aligners

BACKGROUND

This study explores how different post-processing methods affect the mechanical properties and degree of conversion of 3d-printed polyurethane aligners made from Tera Harz TC-85 resin.

METHODS

Using Fourier-transform infrared (FTIR) spectroscopy, the degree of conversion of liquid resin and post-processed materials was analyzed. This investigation focused on the effects of various post-curing environments (nitrogen vs. air) and rinsing protocols (centrifuge, ethanol, isopropanol, and isopropanol + water). The assessed mechanical properties were flexural modulus and hardness.

RESULTS

The degree of conversion showed no significant variance across different groups, though the polymerization environment influenced the results, accounting for 24.0% of the variance. The flexural modulus varied considerably, depending on both the rinsing protocol and the polymerization environment. The standard protocol (centrifugation followed by nitrogen polymerization) exhibited the highest flexural modulus of 1881.22 MPa. Hardness testing revealed significant differences, with isopropanol treatments showing increased resistance to wear in comparison to the centrifuge and ethanol rinse treatments.

CONCLUSIONS

This study conclusively demonstrates the adverse effects of oxygen on the polymerization process, underscoring the critical need for an oxygen-free environment to optimize material properties. Notably, the ethanol rinse followed by nitrogen polymerization protocol emerged as a viable alternative to the conventional centrifuge plus nitrogen method.

Influence of postpolymerization time and atmosphere on the mechanical properties, degree of conversion, and cytotoxicity of denture bases produced by digital light processing

STATEMENT OF PROBLEM

Studies on the effects of postprocessing conditions on the physical properties, degree of conversion (DC), and biocompatibility of denture bases produced by digital light processing are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the effects of the atmosphere during postpolymerization and of postpolymerization time on the flexural strength, Vickers hardness, DC, cytotoxicity, and residual monomer content of denture bases.

MATERIAL AND METHODS

Six different groups of bar- and disk-shaped specimens from the denture base resin were produced, considering 2 different atmospheres (air and nitrogen) and 3 different postpolymerization times (5, 10, and 20 minutes). To determine the physical properties, the flexural strength and Vickers hardness were measured. Fourier transform infrared spectrometry was used to calculate DC. Cytotoxicity was assessed from the effect on human gingival fibroblasts. The residual monomer content was determined by using high-performance liquid chromatography. Based on the normality test by the Shapiro-Wilk method, a nonparametric factorial analysis of variances was conducted (α=.05).

RESULTS

A significant interaction was detected between the atmosphere and postpolymerization time for hardness (P<.001) but no interaction for strength, DC, or cytotoxicity (P=.826, P=.786, and P=.563, respectively). Hardness was significantly affected by the postpolymerization time in the groups with the nitrogen atmosphere (P<.001). DC was significantly affected by the atmosphere (P=.012), whereas strength and cytotoxicity were not (P=.500 and P=.299, respectively). Cytotoxicity was significantly affected by the postpolymerization time (P<.001), but strength and DC were not (P=.482 and P=.167, respectively). Residual monomers were not detected after ≥10-minute postpolymerization time.

CONCLUSIONS

The atmosphere significantly affected hardness and DC, whereas the postpolymerization time significantly affected hardness, DC, cytotoxicity, and residual monomer content. Denture bases produced in a nitrogen atmosphere and with the 10-minute postpolymerization time showed sufficient hardness, DC, and no cytotoxicity.

Effect of 3D printing system and post-curing atmosphere on micro- and nano-wear of additive-manufactured occlusal splint materials

Although additive manufacturing has been widely applied for occlusal splint (OS) fabrication, it is still unclear whether 3D printing system and post-curing atmosphere would play a role in the wear resistance of additive-manufactured OS. Therefore, the aim of this study was to evaluate the effect of 3D printing system (liquid crystal display (LCD) and digital light processing (DLP)) and post-curing atmosphere (air and nitrogen gas (N₂)) on the wear resistance of hard and soft OS materials for additive-manufactured OSs (KeySplint® Hard and Soft). The evaluated properties were microwear (by two-body wear test) and nano-wear resistances (by nanoindentation wear test) as well as flexural strength and flexural modulus (by three-point bending test), surface microhardness (by Vickers hardness test), and nanoscale elastic modulus (reduced elastic modulus) and nano surface hardness (by nanoindentation test). For the hard material, the surface microhardness, microwear resistance, reduced elastic modulus, nano surface hardness, and nano-wear resistance were significantly affected by the printing system (p < 0.05), while all the evaluated properties except flexural modulus were significantly affected by the post-curing atmosphere (p < 0.05). Meanwhile, both the printing system and post-curing atmosphere significantly affected all the evaluated properties (p < 0.05). The specimens additive-manufactured by DLP printer tended to show higher wear resistance in the hard material groups and lower wear resistance in the soft material groups when compared to those by LCD printer. The post-curing at N₂ atmosphere significantly enhanced the microwear resistance of hard material groups additive-manufactured by the DLP printer (p < 0.05) and soft material groups additive-manufactured by the LCD printer (p < 0.01), while it significantly enhanced the nano-wear resistance of both hard and soft material groups regardless of the printing system (p < 0.01). It can be concluded that 3D printing system and post-curing atmosphere affect the micro- and nano-wear resistance of tested additively manufactured OS materials. In addition, it can be also concluded that the optical printing system providing higher wear resistance depends on the material type, and using nitrogen gas as a protection gas during post-curing enhances the wear resistance of tested materials.

Evaluation of the color stability of 3D printed resin according to the oxygen inhibition effect and temperature difference in the post-polymerization process

The aim of this study was to determine the color stability of 3D printed resin according to the post-curing conditions (polymerization conditions and temperature). Specimens were post-polymerized under different conditions of oxygen inhibition, such as on glycerin immersion (GLY), medium-low vacuum environment (VA), and oxygen contact (CON, the control group), and temperature (35 °C, 60 °C, and 80 °C). The degree of conversion (DC), water sorption (Wsp) and solubility (Wsl), surface roughness (Ra) were measured. Additionally, surface free energy (SFE), pH values of colorants were measured. Grape juice (grape), coffee, and curry were used as the colorants, and distilled water (DW) was used as a control. And the color value was measured before and after immersion using a spectrophotometer. Then, Calculated the color change. For statistical methods, The Shapiro-Wilk test performed to check for normality revealed that the data presented a normal distribution (p>0.05). ΔE values were analyzed using three-way ANOVA. DC, Wsp, Wsl, SFE, and Ra were analyzed using two-way ANOVA. To confirm the linear correlation, Pearson's correlation coefficient was determined. The threshold for significance (p) was set at 0.05 (95% confidence interval) for all tests. DC was the highest at 80 °C in the GLY group (95.08 ± 4.88%). And Wsl decreased with increasing temperature, and was lowest at 80 °C in the GLY group (0.46 ± 0.30 um/mm3). After the colorants were immersed for 30 days, as the temperature increased, ΔE decreased in the GLY group but not in the VA and CON groups, and was the lowest at 80 °C in the GLY group: (DW, 0.95 ± 0.45 [mean± SD]; grape, 6.45± 0.69; coffee, 4.50± 0.56; curry, 9.37± 1.40). There was also a significant inverse relation between DC and ΔE. A significant inverse relation was found between Wsl and DC, and a significant positive correlation was found between Wsl and ΔE. Wsp, SFE, and Ra did not affect color stability. In the post-polymerization process, increasing the temperature and GLY were effective in reducing ΔE, which was lowest at 80 °C in the GLY group. It was also observed that a complex mechanism between the DC, Wsl of 3D printed resin affects ΔE of the resin.