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

The impact of print orientation and graphene nanoplatelets on biaxial flexural strength and cytotoxicity of a 3D printable resin for occlusal splints

OBJECTIVES

3D printing found its way into various medical applications and could be particularly beneficial for dentistry. Currently, materials for 3D printing of occlusal splints lack mechanical strength compared to polymethyl methacrylate (PMMA) used for standard milling of occlusal splints. It is known that print orientation and graphene nanoplatelets (GNP) can increase biaxial strength in a variety of materials. Thus, the aim of this study was to assess if adjustment of print orientation and addition of GNP improve biaxial strength and if they affect cytotoxicity of a 3D printable resin for occlusal splints.

METHODS

Specimens were printed vertically and horizontally with a stereolithography (SLA) printer and multilayered GNP powder was added to the resin at different concentrations. Printed specimens were characterized by Raman spectroscopy, optical profilometer analysis and scanning electron microscopy. Biaxial strength was evaluated by biaxial flexural testing. Cytotoxicity of specimens on L929 and gingival stromal cells (GSC) was assessed by the toxdent test, the resazurin-based toxicity assay and live-dead staining.

RESULTS

Horizontally printed specimens showed significantly higher biaxial strength and lower deformation. GNP did not improve biaxial strength and material deformation of 3D-printed resins. None of the specimens were cytotoxic to L929 cells or GSC.

SIGNIFICANCE

Print orientation in SLA printing has a significant impact on biaxial strength and material deformation. 3D printable materials can reach comparable or even improved biaxial strength compared to PMMA when using the optimal print orientation while GNP has no beneficial effects on the biaxial strength of resins for 3D printing of occlusal splints.

Effect of postpolymerization time and atmosphere on surface properties and biofilm formation in additively manufactured resins for definitive restorations

OBJECTIVES

To investigate how postpolymerization time (PPT) and atmosphere (PPA) influence the surface properties, protein adsorption, and microbial adhesion of two types of additively manufactured (AM) resins used for definitive restorations.

METHODS

Two different types of commercially available AM resins for definitive restorations (UR and CR) were used to create disk-shaped specimens. These specimens were divided into eight groups based on resin type (UR and CR), PPT (standard or extended), and PPA (air or nitrogen). After postpolymerization, the surface roughness (Ra and Sa) and surface free energy (SFE) of all specimens were measured. The study also evaluated protein adsorption, microbial attachment, and cytotoxicity. A non-parametric factorial analysis of variance with post-hoc analyses was conducted, using a significance level (α) of 0.05.

RESULTS

The Ra and Sa values for CR were higher than those for UR, regardless of PPT or PPA (P < 0.05). For UR, SFE was higher with extended PPT compared to standard PPT. CR had higher SFE than UR under standard PPT. The interaction between PPT and PPA had a significant effect on protein adsorption (P < 0.05). When PPT was standard, nitrogen significantly increased protein adsorption compared to air. The interaction between resin type and PPA, and between resin type and PPT, significantly affected microbial adhesion (P < 0.05). The changes in PPT or PPA did not affect the cytotoxicity of either AM resin.

CONCLUSION

Surface properties, protein adsorption, and microbial attachment were influenced by the interactions among PPT, PPA, and resin type. These factors can have implications for resin-based definitive restorations.

CLINICAL SIGNIFICANCES

Clinicians should understand the impact of PPT and PPA on the surface properties of AM resins for definitive restorations, particularly regarding protein adsorption and microbial adhesion. Additionally, the type of AM resin (based on chemical composition) could affect its biological properties.

Accuracy, adaptation and margin quality of monolithic zirconia crowns fabricated by 3D printing versus subtractive manufacturing technique: A systematic review and meta-analysis of in vitro studies

OBJECTIVE

The purpose of this systematic review and meta-analysis was to evaluate the accuracy (trueness and precision), marginal and internal adaptation, and margin quality of zirconia crowns made by additive manufacturing compared to subtractive manufacturing technology.

METHODS

The investigation adhered to the PRISMA-ScR guidelines for systematic reviews and was registered at the Prospero database (n°CRD42023452927). Four electronic databases, including PubMed, Scopus, Embase, and Web of Science and manual search was conducted to find relevant studies published until September 2023. In vitro studies that assessed the trueness and precision, marginal and internal adaptation, and margin quality of printed crowns compared to milled ones were included. Studies on crowns over implants, pontics, temporary restorations, laminates, or exclusively experimental materials were excluded.

RESULTS

A total of 9 studies were included in the descriptive reporting and 7 for meta-analysis. The global meta-analysis of the trueness (P<0.74,I2=90 %) and the margin quality (P<0.61,I2=0 %) indicated no significant difference between the root mean square of printed and milled zirconia crowns. The subgroup analysis for the printing system showed a significant effect (P<0.01). The meta-analysis of the crown areas indicated no significant difference in most of the areas, except for the marginal (favoring milled crowns) and axial (favoring printed crowns) areas. For precision and adaptation, both methods showed a clinically acceptable level.

CONCLUSIONS

Additive manufacturing technology produces crowns with trueness and margin quality comparable to subtractive manufacturing. Both techniques have demonstrated the ability to produce crowns with precision levels, internal discrepancy, and marginal fit within clinically acceptable limits.

CLINICAL SIGNIFICANCE

3D printing emerges as a promising and potentially applicable alternative method for manufacturing zirconia crowns, as it shows trueness and margin quality comparable to restorations produced by the subtractive method.

Biocompatibility and customizability: Expanding possibilities with 3D printed guide cannulas

BACKGROUND

Intracerebral cannulation bypasses the blood-brain barrier, and is frequently used for targeted drug delivery to specific brain structures. Despite the availability of brain infusion kits and manual injections without cannulation, the traditional design of guide cannulas continues to be utilized in research. Several protocols describing guide cannula manufacture from stainless steel needles have been published previously.

NEW METHOD

We describe a method for producing the first fully plastic guide cannula intended for intracerebroventricular injections in mice using Dental Sand A1-A2 resin and digital light processing 3D printing.

RESULTS

The lack of resin neurotoxicity for primary rat cortical neuron cultures was shown. Histological evaluations performed 6 weeks after guide cannula implantation to C57/black mice show that plastic cannula are biocompatible. Microglial and astroglial reactions to plastic cannulas are reduced compared to lab-made stainless steel cannulas. Plastic cannulas are less prone to obstruction, and remained unobstructed over the course of 3 weeks of daily injections, while 50 % of stainless steel cannula became impassable by the 2 week mark.

COMPARISON WITH EXISTING METHODS

These are the first published cannulas intended for applications in mice which combine the presence of usable threads, allowing dummy cannula fixation, with a low profile and small footprint compared to commercially available cannulas.

CONCLUSIONS

Editable parametric and stl files for reproducing the cannulas presented in this manuscript are included. The method described in this paper is accessible to most laboratories, enabling near-perfect standardization in length combined with a high level of customizability.

Comparison of mechanical and surface properties of two 3D printed composite resins for definitive restoration

STATEMENT OF PROBLEM

Additive manufacturing (AM) technology is emerging as an innovative approach in the dental field. In recent years, manufacturers have introduced 3-dimensionally printed composite resins (3D-CRs) that are specifically designed for the AM of definitive prostheses; however, the mechanical and surface properties of these materials require investigation.

PURPOSE

The purpose of this in vitro study was to assess and compare the mechanical and surface properties of 2 commercially available 3D-CRs for definitive restoration after artificial aging.

MATERIAL AND METHODS

Saremco print Crowntec; Saremco Dental AG and Varseo Smile Crown Plus; Bego GmbH were printed with a layer thickness of 50 µm at a 90-degree angle. A total of 20 bar-shaped specimens (25×2×2 mm) were produced from each material to measure the flexural strength (σf) and elastic modulus (E) using a 3-point bend test, and 5 disk-shaped specimens (Ø15×3 mm) from each material were used to measure the surface microhardness using a microhardness test. Half of the specimens were tested under dry conditions, while the other half were immersed in distilled water for 30 days. Five disk-shaped specimens (Ø15×3 mm) from each material were used to evaluate surface roughness before and after undergoing toothbrushing simulations. Additionally, 5 disk-shaped specimens (Ø15×1 mm) were used to assess water sorption (wsp) and solubility (wsl) over 28 days. Statistical analyses were conducted using the Wilcoxon matched-pairs signed-rank test (1-tailed) with 90% power (α=.05).

RESULTS

The mean ±standard deviation flexural strength values were 123.4 ±8.7 MPa for Saremco print Crowntec and 109.9 ±15.8 MPa for Varseo Smile Crown Plus. After aging, these values were 97.5 ±15.2 MPa for Saremco print Crowntec and 94.2 ±11.7 MPa for Varseo Smile Crown Plus. The mean Vickers hardness values were 33.2 ±0.8 N/mm2 for Saremco print Crowntec and 31.5 ±0.6 N/mm2 for Varseo Smile Crown Plus. After aging, the mean values were 31.7 ±0.9 N/mm2 for Saremco print Crowntec and 29.6 ±1.0 N/mm2 for Varseo Smile Crown Plus. The mean modulus of elasticity was 4.2 ±0.3 GPa for Saremco print Crowntec and 3.82 ±0.2 GPa for Varseo Smile Crown Plus. After 21 days, the mean sorption values were 11.52 ±0.6 mg/mm3 for Saremco print Crowntec and 12.43 ±0.4 mg/mm3 for Varseo Smile Crown Plus. After 28 days, the mean solubility values were 1.36 ±0.4 mg/mm3 for Saremco print Crowntec and 0.98 ±0.3 mg/mm3 for Varseo Smile Crown Plus. Significant differences were found between the 2 3D-CRs in flexural strength in the dry state (P=.03), in Young modulus after 30 days of water immersion (P=.023), and in Vickers hardness in the dry state (P=.01) and after 30 days of water immersion (P=.018).

CONCLUSIONS

Both 3D-CRs provided good in vitro performance and the mechanical properties required for long-term clinical application. Artificial aging decreased the flexural strength of both 3D-CRs.

Effects of Printing Angle and Post-Curing Time on the Color and Translucency of 3D-Printed Temporary Restoration

In resins produced with a 3D printer, the printing parameters affect the properties of the restoration produced. This study examined the effect of the printing angle and post-curing time on the optical properties of temporary restorations. A total of 135 disk-shaped Formlabs temporary resins (10 × 2 mm) were produced at three different printing angles (0, 45, and 90 degrees) and post-cured for three different times (20, 40, and 60 min) (n = 15). Color and translucency measurements were taken for each group with a spectrophotometer (VITA Easyshade V). The ΔE values between printing angles and curing times influence each other. The highest color change was observed in the groups produced with a 90° printing angle. Considering the post-curing times, the highest color change was observed in the groups cured for 40 min. Increasing the curing time from 20 to 40 min decreases the translucency, whereas further increasing the curing time does not significantly affect the translucency. In terms of the impact on the translucency caused by the printing angles, 0° exhibited a lower translucency compared to other printing angles. During the 3D printing of temporary prostheses, both printing angles and post-curing times can affect their optical properties.

Effects of printing orientation and artificial ageing on martens hardness and indentation modulus of 3D printed restorative resin materials

BACKGROUND

Three-dimensional (3D) printing is increasingly used to fabricate dental restorations due to its enhanced precision, consistency and time and cost-saving advantages. The properties of 3D-printed resin materials can be influenced by the chosen printing orientation which can impact the mechanical characteristics of the final products.

PURPOSE

The objective of this study was to evaluate the influence of printing orientation and artificial ageing on the Martens hardness (HM) and indentation modulus (EIT) of 3D-printed definitive and temporary dental restorative resins.

METHODS

Disk specimens (20 mm diameter × 2 mm height) were additively manufactured in three printing orientations (0°, 45°, 90°) using five 3D-printable resins: VarseoSmile Crownplus (VCP), Crowntec (CT), Nextdent C&B MFH (ND), Dima C&B temp (DT), and GC temp print (GC). The specimens were printed using a DLP 3D-printer (ASIGA MAX UV), while LavaTM Ultimate (LU) and Telio CAD (TC) served as milled control materials. Martens hardness (HM) and indentation modulus (EIT) were tested both before and after storage in distilled water and artificial saliva for 1, 30, and 90 days at 37 °C.

RESULTS

90° printed specimens exhibited higher HM than the other orientations at certain time points, but no significant differences were observed in HM and EIT between orientations for all 3D-printed materials after 90 days of ageing in both aging media. LU milled control material exhibited the highest HM and EIT among the tested materials, while TC, the other milled control, showed similar values to the 3D printed resins. CT and VCP (definitive resins) and ND displayed higher Martens parameters compared to DT and GC (temporary resins). The hardness of the 3D-printed materials was significantly impacted by artificial ageing compared to the controls, with ND having the least hardness reduction percentage amongst all 3D-printed materials. The hardness reduction percentage in distilled water and artificial saliva was similar for all materials except for TC, where higher reduction was noted in artificial saliva.

SIGNIFICANCE

The used 3D printed resins cannot yet be considered viable alternatives to milled materials intended for definitive restorations but are preferable for use as temporary restorations.

Effects of postpolymerization conditions on the physical properties, cytotoxicity, and dimensional accuracy of a 3D printed dental restorative material

STATEMENT OF PROBLEM

Although the introduction of high-speed 3-dimensional (3D) printing technology has significantly reduced printing time, the time required for postpolymerization is a speed-determining step because of the long wait time. How postpolymerization conditions affect material properties is unclear.

PURPOSE

The purpose of this in vitro study was to assess the physical properties, accuracy, and biosafety of a 3D printed dental restorative material according to postpolymerization conditions.

MATERIAL AND METHODS

Specimens were prepared by 3D printing with a digital light processing 3D printer with 1 interim dental material (C&B MFH). All printed specimens underwent a postpolymerization process with 5 different postpolymerization devices and were designated as groups D1 (D102H), FO (Form Cure), LC (LC-3DPrintBox), ME (Medusa), and MP (MP100). The light intensity and temperature of each device were measured, and the Vickers hardness, flexural strength and modulus, degree of conversion (DC), cytotoxicity, and polymerization shrinkage were analyzed. Statistical analyses were conducted with 1-way analysis of variance, the Tukey post hoc test, and regression testing (α=.05). Scanning electron microscopy was used to assess the fracture surface characteristics of the specimens.

RESULTS

Light intensity was strongest with the ME device, and the temperature inside the device during postpolymerization showed the highest increase with the LC device and the lowest increase with the D1 device. The LC group specimens showed the highest mean Vickers hardness, and the MP group showed the lowest. The flexural strength was ≥100 MPa in all groups, with a flexural modulus ranging from 1.17 to 1.5 GPa. The DC results were similar to the physical properties test results. The D1, FO, LC, and ME groups all showed ≥70% cell viability, indicating no toxicity. The FO group showed the highest shrinkage rate of 0.52%.

CONCLUSIONS

When the light intensity was strong, the surface was sufficiently hard, and toxic substances were not eluted even after a short postpolymerization time, suggesting that light intensity modulation and time management can be used to improve the postpolymerization process.

Effect of nanomodified 3D printed photopolymerizable resin on flexural strength, color, and antimicrobial efficacy: An in vitro study

STATEMENT OF PROBLEM

Three-dimensional (3D) printing has become popular in dentistry, but studies on the influence of incorporating organic and inorganic nanofillers on 3D printed materials are lacking.

PURPOSE

The purpose of this in vitro study was to assess the flexural strength, color, and antimicrobial efficacy of 3D printed photopolymerizable resin upon adding titanium dioxide nanoparticles (TiO2 NPs) and silanized chitosan nanoparticles (sCS NPs).

MATERIAL AND METHODS

A stereolithographic material (VarseoSmile Crown plus; Bego) was used as a control group (VSC resin), and 3 nanocomposite resin groups were prepared by adding nanoparticles as follow: titanium dioxide group (VSC resin + 0.4% wt. TiO2 NPs), chitosan group (VSC resin + 0.4% wt. sCS NPs), and hybrid group (VSC resin + 0.2% wt. TiO2 NPs + 0.2% wt. sCS NPs). A total of 132 specimens were designed by using a free computer-aided design software program, printed, postpolymerized, and divided into 4 groups. The nanocomposite resins were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and Fourier-transform infrared spectroscopy (FTIR). Bar shaped specimens (n=44) were tested for 3-point flexural strength using a universal testing machine followed by the color measurement of disk-shaped specimens (n=44) with a spectrophotometer. Antimicrobial capacity was measured with Streptococcus mutans, and absorbance was measured using a microplate reader (n=44). Statistical assessments were made with 1-way ANOVA followed by the Tukey post hoc test with Bonferroni adjustment (α=.05).

RESULTS

The hybrid group recorded the highest mean value of flexural strength 135.51 MPa, showing a significant difference compared with that of the control group (P=.022). Regarding color, the mean ∆E00 for titanium was 1.18, for chitosan was 4.26, and for the hybrid group was 3.23 (P<.001). The optical density of the chitosan (2.42) was significantly higher than that of the titanium 1.36 (P=.007) and that of the control 1.63 (P=.042).

CONCLUSIONS

The incorporation of nanofillers resulted in an increase in flexural strength, but it adversely affected the color of nanocomposite resins. Antimicrobial efficacy was improved by incorporating titanium nanofillers.

Investigating the impact of post-curing cycles on surface hardness and color stability in 3D printed resin crowns

This study evaluated the effect of different post-curing cycles on the Vickers hardness, color change, and translucency value of 3D printed methacrylic acid ester-based temporary and permanent crown resins. A total of 300 samples were printed in disk shape (ø:8 mm, thickness: 2 mm) using VarseoSmile Crown Plus (VSC) and VarseoSmile Temp (VST) materials from a 3D printer. These disks were divided into five subgroups (n = 30 each) based on flash-curing cycles (0, 750, 1500, 2250, and 3000). Surface hardness tests and color tests were conducted on both the green state and flash-cured groups. The data were analyzed using univariate analysis of variance (ANOVA). The hardness of 3D printed temporary and permanent crown resin increased with post-curing time. Compared to the post-curing cycle recommended by the manufacturer, no clinically significant color change (ΔE00 ≥ 2.25) was observed in any of the polymerized groups. It was determined that permanent crown material had a more translucent structure than temporary crown material. The interaction between material and post-curing had significant effects on surface hardness, color (ΔE00), and translucency of 3D printed methacrylic acid ester-based resins.

Influence of different printing orientations and post-polymerization time on the translucency of three-dimensional (3D) printed denture base resins

PURPOSE

To evaluate the effect of different printing orientations and post-polymerization time with thermal cycling on the translucency of 3D-printed denture base resins.

METHODS

Heat-polymerized (HP) acrylic resin specimens were fabricated and 3D-printed denture base materials (NextDent, ASIGA, FormLabs) were printed with different printing orientations (0, 45, 90 degrees) and subjected to different post-polymerization times (15-, 30-, 60-, and 90-min). All specimens were polished and immersed in distilled water for 1 day at 37°C. CIEDE2000 was used to measure the translucency parameters (TP00) before and after thermal cycling (5000 cycles) recording the color parameters (L*, a*, b*) against a black and white background using a spectrophotometer. k-factors ANOVA followed by post hoc Tukey's test (α = .05) was performed for statistical analysis.

RESULTS

The k-factors ANOVA test showed a significant effect of resin material, post-polymerization time, and printing orientation on translucency (p < 0.001). In comparison to HP, all 3D-printed resins showed lower translucency with all post-polymerization times and printing orientation (p < 0.001) except FormLabs resin (p > 0.05). For all 3D-printed resins, the translucency increased, with increasing the post-polymerization time (p < 0.001) and 60- and 90-min showed the highest translucency. For printing orientation, 90 and 45 degrees significantly showed high translucency in comparison to 0 degrees (p < 0.001). FormLabs showed significantly higher translucency when compared with NextDent and ASIGA per respective printing orientation and post-polymerization time. The translucency significantly decreased after thermal cycling for all tested resins (p < 0.001).

CONCLUSION

The findings of this study demonstrated that the translucency of 3D-printed resins is influenced by the printing orientation, post-polymerization time, and resin type. As a result, choosing a resin type, and printing orientation, with a longer post-polymerization time should be considered since it may improve the esthetic appearance of the 3D-printed resins.

Impact of Nanoparticle Addition on the Surface and Color Properties of Three-Dimensional (3D) Printed Polymer-Based Provisional Restorations

This study aimed to evaluate and compare the impact of additives such as ZrO2 and SiO2 nanoparticles (ZrO2NP or SiO2NP) on the hardness, surface roughness, and color stability of 3D printed provisional restorations. Two hundred samples in total were printed using 3D printed resins (ASIGA, and NextDent). Each resin was modified with ZrO2NPs or SiO2NPs in two different concentrations (0.5 wt% and 1 wt%), while one group was kept unmodified (n = 10). Disc-shaped (15 × 2.5 mm) samples were designed and printed in accordance with the manufacturer's recommendation. Printed discs were evaluated for color changes through parameters CIELAB 2000 system (ΔE00), hardness using Vickers hardness test, and surface roughness (Ra) using a noncontact profilometer. After calculating the means and standard deviations, a three-way ANOVA and Tukey post hoc test were performed at α = 0.05. The addition of ZrO2NPs or SiO2NPs to ASIGA and NextDent resins significantly increased the hardness at a given level of concentration (0.5% or 1%) in comparison with pure (p < 0.001), with no significant difference between the two modified groups per resin type (p > 0.05). The highest hardness value was detected in 1% ZrO2NPs with 29.67 ± 2.3. The addition of ZrO2NPs or SiO2NPs had no effect on the Ra (p > 0.05), with 1% ZrO2NPs showing the highest value 0.36 ± 0.04 µm with NextDent resin. ZrO2NPs induced higher color changes (∆E00), ranging from 4.1 to 5.8, while SiO2NPs showed lower values, ranging from 1.01 to 1.85, and the highest mean ∆E00 was observed in the 1% ZrO2NPs group and NextDent resin. The incorporation of ZrO2NPs and SiO2NPs in 3D printed provisional resins increased the hardness without affecting the surface roughness. The optical parameters were significantly affected by ZrO2NPs and less adversely affected by SiO2NPs. Consequently, care must be taken to choose a concentration that will improve the materials' mechanical performance without detracting from their esthetic value.

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.

Post-polymerization of three-dimensional printing resin using a dental light curing unit

Background/Purpose

In vat photopolymerization, post-polymerization of the three-dimensional (3D) printing resin is necessary to ensure the optimum physical properties of the printed objects. This study aimed to evaluate the potential use of a handheld polywave light-emitting diode (LED) dental light-curing unit (LCU) for post-polymerizing 3D printed resins by measuring the microhardness and biaxial flexural strength of the post-polymerized resin.

Material and methods

3D printed 1- and 2-mm-thick disks were irradiated with a dental LCU at 3200 mW/cm2. Post-polymerization was repeated either on one side from the top surface: two cycles (T2), four cycles (T4), and eight cycles (T8), or on both sides from the top and bottom surfaces: one cycle (T1B1), two cycles (T2B2), and four cycles (T4B4) for each side. The microhardness and biaxial strength of the disks were compared to those post-polymerized by a conventional desktop polymerizing unit (PC) and those without post-polymerization (NC).

Results

Microhardness of the disks varied between the top and bottom surfaces of the 1-mm and 2-mm-thick disks, depending on the post-polymerization methods. T8 and T4B4 produced comparable microhardness on the top surface to PC for both thicknesses. In contrast, PC, T2B2, and T4B4 exhibited the highest microhardness on the bottom surface. Except for NC, the 1-mm-thick disks had a higher biaxial flexural strength than the 2-mm-thick disks. T4B4 resulted in the highest biaxial flexural strength for both thicknesses, which was comparable to that of the desktop polymerizing unit.

Conclusion

The microhardness and biaxial flexural strengths of the post-polymerized 3D-printed disks increase with polymerization time. With sufficient polymerization from both sides, the polywave LCU has the potential to be a viable alternative to desktop polymerization units.

Characterization of Microstructure, Optical Properties, and Mechanical Behavior of a Temporary 3D Printing Resin: Impact of Post-Curing Time

The present study aimed to characterize the microstructure of a temporary 3D printing polymer-based composite material (Resilab Temp), evaluating its optical properties and mechanical behavior according to different post-curing times. For the analysis of the surface microstructure and establishment of the best printing pattern, samples in bar format following ISO 4049 (25 × 10 × 3 mm) were designed in CAD software (Rhinoceros 6.0), printed on a W3D printer (Wilcos), and light-cured in Anycubic Photon for different lengths of time (no post-curing, 16 min, 32 min, and 60 min). For the structural characterization, analyses were carried out using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The mechanical behavior of this polymer-based composite material was determined based on flexural strength tests and Knoop microhardness. Color and translucency analysis were performed using a spectrophotometer (VITA Easy Shade Advanced 4.0), which was then evaluated in CIELab, using gray, black, and white backgrounds. All analyses were performed immediately after making the samples and repeated after thermal aging over two thousand cycles (5-55 °C). The results obtained were statistically analyzed with a significance level of 5%. FT-IR analysis showed about a 46% degree of conversion on the surface and 37% in the center of the resin sample. The flexural strength was higher for the groups polymerized for 32 min and 1 h, while the Knoop microhardness did not show a statistical difference between the groups. Color and translucency analysis also did not show statistical differences between groups. According to all of the analyses carried out in this study, for the evaluated material, a post-polymerization time of 1 h should be suggested to improve the mechanical performance of 3D-printed devices.

Effect of thermal cycling on the flexural strength of 3-D printed, CAD/CAM milled and heat-polymerized denture base materials

BACKGROUND

This study compared the impact of thermal cycling on the flexural strength of denture-base materials produced through conventional and digital methods, using both subtractive and additive approaches.

METHODS

In total, 60 rectangular specimens were fabricated with specific dimensions for flexural strength tests. The dimensions were set according to the International Organization for Standardization (ISO) guideline 20795-1:2013 as 64 × 10 × 3.3 ± 0.2 mm. Specimens from each material group were divided into two subgroups (thermal cycled or nonthermal cycled, n = 10/group). We used distinct methods to produce three different denture-base materials: Ivobase (IB), which is a computer-aided-design/computer-aided-manufacturing-type milled pre-polymerized polymethyl methacrylate resin disc; Formlabs (FL), a 3D-printed denture-base resin; and Meliodent (MD), a conventional heat-polymerized acrylic. Flexural strength tests were performed on half of the samples without a thermal-cycle procedure, and the other half were tested after a thermal cycle. The data were analyzed using a two-way analysis of variance and a post hoc Tukey test (α = 0.05).

RESULTS

Based on the results of flexural-strength testing, the ranking was as follows: FL > IB > MD. The effect of thermal aging was statistically significant for the FL and IB bases, but not for the MD base.

CONCLUSIONS

Digitally produced denture bases exhibited superior flexural strength compared with conventionally manufactured bases. Although thermal cycling reduced flexural strength in all groups, the decrease was not statistically significant in the heat-polymerized acrylic group.

The Impact of Technology Teaching in the Dental Predoctoral Curriculum on Students' Perception of Digital Dentistry

The goal was to assess dental students' perception of digital technologies after participating in a CAD/CAM exercise for scanning, designing, and manufacturing computer-aided provisional fixed dental restorations. A survey was conducted among second- (pre-D2 and post-D2), first- (D1, negative control), third-, and fourth-year dental students (D3 and D4, positive controls). Only OSU College of Dentistry students who completed the activity and completed the surveys were included. Seven questions were rated, which evaluated changes in knowledge, skill, interest, the importance of technology availability in an office, patients' perception of technology, the importance of having the technology, and the expected frequency of clinics utilizing the technology. Statistical analysis was performed with a significance level of 0.05. A total of 74 pre-D2 and 77 post-D2 questionnaires were completed. Additionally, 63 D1, 43 D3, and 39 D4 participants responded to the survey. Significant differences were found for "knowledge" and "skill" between the pre-D2 and post-D2 and pre-D2 and control groups (p < 0.001). There was a significant difference between the post-D2 participants and all the controls in terms of "interest" (p = 0.0127) and preference for in-practice technology availability (p < 0.05). There were significant results between the post-D2 participants and all the controls regarding the importance of technology availability in an office (p < 0.001) and the expected frequency of clinics utilizing the technology (p = 0.01). No significance was found for "value of technology to patients" and "the importance of having the technology". The presence of technology in practice and in educational academic environments significantly improved students' interest and perception of their knowledge and skill.

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 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.

Biaxial Flexural Strength of Printed Splint Materials

One therapeutical alternative in the treatment of functional disorders is the use of printed oral splints. The mechanical properties of these materials are highly essential to their clinical effectiveness, and their performance may vary depending on factors such as cleaning, post-polymerization, or their orientation during construction. The objective of this in vitro investigation is to evaluate the effectiveness of the selected materials in terms of their biaxial flexural strength in relation to the criteria listed above. Splint materials were used in the printing of 720 discs. The printing process was carried out in different orientations in relation to the building platform. Either an automatic or manual cleaning process was performed on the samples. For post-polymerization, either an LED or Xenon light was utilized. A piston-on-three-ball test was used to measure the biaxial flexural strength (BFS) of the materials after they were stored in water for either 24 h or 60 days. The homogeneity of the data was controlled by employing the Levene method, and the differences between the groups were analyzed using the ANOVA and Bonferroni methods. After being stored for twenty-four hours, the mean BFS ranged anywhere from 79 MPa to 157 MPa. Following a period of sixty hours, the BFS exhibited a substantial drop and revealed values that ranged from 72 to 127 MPa. There was no significant difference that could be identified between the materials or between the various cleaning processes. The results of post-polymerization showed that the LED light produced higher means than the Xenon light did. In terms of position, the mean values varied greatly, with 0°'s mean value being 101 MPa, 45°'s mean value being 102 MPa, and 90°'s mean value being 115 MPa. The use of a build orientation of 90° and post-polymerization with LED light resulted in significantly increased biaxial flexural strength. According to this study, this design should be implemented in order to ensure that splint materials have the highest possible strength.

Effect of Different Post-Curing Methods on the Degree of Conversion of 3D-Printed Resin for Models in Dentistry

The aim was to investigate the effects of different post-curing units on the chemical properties (degree of conversion) of 3D-printed resins for producing models in dentistry. The goal is to determine whether less-expensive post-curing units can be a viable alternative to the manufacturer's recommended units. Forty-five samples were fabricated with an LCD printer (Phrozen Sonic Mini, Phrozen 3D, Hsinchu City, Taiwan) using MSLA Dental Modeling Resin (Apply Lab Work, Torrance, CA, USA). These samples were divided randomly into four different groups for post-curing using four distinct curing units: Phrozen Cure V2 (Phrozen 3D, Hsinchu City, Taiwan), a commercial acrylic nail UV LED curing unit (SUNUV, Shenzhen, China), a homemade curing unit created from a readily available UV LED light produced (Shenzhen, China), and the Triad® 2000™ tungsten halogen light source (Dentsply Sirona, York, PA, USA). The degree of conversion was measured with FTIR spectroscopy using a Nicolet 6700 FTIR Spectrometer (Thermo Fisher Scientific, Waltham, MA, USA). Phrozen Cure V2 had the highest overall mean degree of conversion (69.6% with a 45 min curing time). The Triad® 2000 VLC Curing Unit had the lowest mean degree of conversion value at the 15 min interval (66.2%) and the lowest mean degree of conversion at the 45 min interval with the homemade curing unit (68.2%). The type of light-curing unit did not yield statistically significant differences in the degree of conversion values. There was a statistically significant difference in the degree of conversion values between the 15 min and 45 min curing intervals. When comparing individual light-curing units, there was a statistically significant difference in the degree of conversion for the post-curing units between the 15 min and 45 min curing time (p = 0.029).

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.

Fracture toughness, work of fracture, flexural strength and elastic modulus of 3D-printed denture base resins in two measurement environments after artificial aging

OBJECTIVES

To investigate the fracture toughness (KIC), work of fracture (WOF), flexural strength (FS) and elastic modulus (E) of four additively manufactured denture base resins in two different measurement environments after artificial aging.

METHODS

Rectangular specimens in two different dimensions (n = 480) were 3D-printed with four denture base resins: Denture 3D+ (DEN; NextDent), Fotodent Denture (FOT; Dreve ProDiMed), Freeprint Denture (FRE; Detax), V-Print dentbase (VPR; VOCO)). KIC, WOF, FS and E were measured after (1) water-storage (37 °C; KIC = 7 d; FS = 50 h); (2) water-storage + hydrothermal-aging (20 min, 0.2 MPa, 134 °C); (3) water storage + thermocycling (10,000 cycles, 5/55 °C) in two measurement environments (i) air-23 °C and (ii) water-37 °C. For FS, fracture types were classified, and relative frequencies determined. Univariate ANOVA, Kruskal-Wallis, Mann-Whitney U, and Spearman's correlation were calculated (p < 0.05, SPSS V.27.0). Weibull modulus (m) was calculated using the maximum likelihood estimation method.

RESULTS

DEN showed the highest KIC (5/6 groups), WOF and highest corresponding m (1/6 groups), while FRE presented the highest FS (2/6 groups) and E values. Hydrothermal-aging and thermocycling reduced KIC and WOF, FS and E, and the number of FS fracture pieces. For 6/8 groups, hydrothermal aging resulted in lower FS than thermocycling. Measurement in air-23 °C led to higher FS for 7/12 groups and a more brittle fracture behavior. A positive correlation between KIC and FS was observed.

SIGNIFICANCE

With measurements in air-23 °C resulting in higher FS than reported in water-37 °C, the measurement environment should be adapted to the clinical situation to allow valid predictions on the mechanical behavior of denture base resins when in situ.

Evaluation of photopolymer resins for dental prosthetics fabricated via the stereolithography process at different polymerization temperatures-Part I: Conversion rate and mechanical properties

STATEMENT OF PROBLEM

Improvement in the mechanical properties of 3-dimensional (3D) printed dental prostheses is necessary to prevent wear caused by an antagonist or fracture. However, how different printing temperatures affect their mechanical properties is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the mechanical properties of 3D printed parts fabricated at different printing temperatures.

MATERIAL AND METHODS

Photopolymer specimens were fabricated at 3 different temperatures (room temperature, 50 °C, and 70 °C) using a stereolithography 3D printer. After rinsing to remove the residual monomer, the specimens were divided into 2 groups: with or without postprocessing. The viscosity of the photopolymerization resin was measured while the temperature was increased. Furthermore, the double-bond conversion (DBC) of the printed part was evaluated (n=3). Mechanical properties were investigated via dynamic mechanical analysis (n=1) and tensile testing (n=5). Statistical comparisons were performed via 1-way analysis of variance, followed by the Tukey honestly significant difference test (α=.05).

RESULTS

The DBC rates of the green condition group increased from 66.67% to 86.33% with increasing temperature. In addition, these specimens exhibited improved mechanical properties and reduced residual monomer levels.

CONCLUSIONS

Specimens fabricated at a temperature of 70 °C exhibited mechanical properties suitable for clinical application.

Effects of post-polymerization conditions on color properties, surface roughness, and flexural strength of 3D-printed permanent resin material after thermal aging

PURPOSE

To evaluate the color, surface properties, and flexural strength of 3D-printed permanent crown resin subjected to different post-polymerization conditions after artificial aging.

MATERIALS AND METHODS

Ninety (10 × 2 mm) disc-shaped specimens were printed by using permanent crown resin with SLA technology. Specimens were divided into nine different groups, subject to post-polymerization conditions at three different times (15, 20, and 30 min) and three different temperatures (40, 60, and 80°C) (n = 10). Color and surface roughness measurements were repeated pre-post thermal aging (5.000 cycles, 5-55°C) and a flexural strength test was carried out. Data were analyzed with Shapiro-Wilk, Kruskal-Wallis, ANOVA, Tukey HSD, and Dunn tests (α < 0.05).

RESULTS

ΔE00  values showed results below the acceptable color threshold, except for the 30 min 40°C group (ΔE00 <1.8). No difference was found between the relative translucency parameter and surface roughness values of the 20 min 60°C group recommended by the manufacturer and the other groups. A significant difference was found between the flexural strength values of the groups (p < 0.001).

CONCLUSIONS

The color properties, surface topography, and mechanical properties of the printed permanent crown material were affected by different post-polymerization conditions: polymerized at different times and temperatures. Although the flexural strength and color change values showed promising results, more studies are required to evaluate its suitability for clinical use.

Comparison of the Cytotoxic Effect of 3D-Printed Resins, Resin-based CAD/CAM blocks and Composite Resin

Background

This study investigated the cytotoxic effects of 3D-printed permanent resins, resin-based CAD/CAM blocks and composite resin on human gingival fibroblast (HGF-1) and mouse fibroblast (L929) cell line.

Material and Methods

3D-printed permanent resins (Crowntec and Permanent Crown), resin-based CAD/CAM blocks (Vita Enamic and Brilliant Crios) and composite resin (Clearfill Majesty Posterior) were used in the study. Samples were prepared from the planned materials and kept in DMEM according to ISO 10993-12:2021 standard (3 cm2/ml). The cytotoxic effect of the materials on HGF-1 and L929 cells was examined by MTT test at the end of 24 and 72 h. Two-way analysis of variance test (ANOVA) was used to analyze cell viability data.

Results

3D-printed permanent resins, resin-based CAD/CAM blocks and composite resin extracts showed similar cell viability on HGF-1 and L929 cells at the end of 24 h (p>0.05). Resin-based CAD/CAM block (Vita Enamic) produced the highest cell viability on HGF-1 and L929 cells at the end of 72 h (p<0.05). Cell viability values of samples produced in 3D printers with different printing properties did not differ significantly (p>0.05).

Conclusions

3D-printed permanent restoration resins showed similar cell viability on HGF-1 and L929 cells to resin-based CAD/CAM blocks and composite resin. Key words:3D-printed resin, CAD/CAM block, Composite resin, Cytotoxicity, Human Gingival Fibroblast.

Effects of storage and toothbrush simulation on Martens hardness of CAD/CAM, hand-cast, thermoforming, and 3D-printed splint materials

OBJECTIVES

To investigate Martens hardness parameters of splint materials after storage in liquids and toothbrush simulation.

MATERIALS AND METHODS

Ten specimens per material and group were fabricated (hand-cast CAST, thermoformed TF, CAD/CAM-milled CAM, 3D-printed PS, PL, PK, PV), stored in air, water, coffee, red wine, and cleaning tablets and investigated after fabrication, 24 h, 2- and 4-week storage or toothbrushing. Martens hardness (HM), indentation hardness (HIT), indentation modulus (EIT), the elastic part of indentation work (ηIT), and indentation creep (CIT) were calculated (ISO 14577-1).

STATISTICS

ANOVA, Bonferroni post hoc test, between-subjects effects, Pearson correlation (α = 0.05).

RESULTS

HM varied between 30.8 N/mm2 for PS (water 4 weeks) and 164.0 N/mm2 for CAM (toothbrush). HIT values between 34.9 N/mm2 for PS (water 4 weeks) and 238.9 N/mm2 for CAM (toothbrush) were found. EIT varied between 4.3 kN/mm2 for CAM (toothbrush) and 1.8 kN/mm2 for PK (water 2 weeks). ηIT was found to vary between 16.9% for PS (water 4 weeks) and 42.8% for PL (toothbrush). CIT varied between 2.5% for PL (toothbrush) and 11.4% for PS (water 4 weeks). The highest impact was identified for the material (p ≤ 0.001).

CONCLUSIONS

Storage and toothbrushing influenced Martens parameters. The properties of splints can be influenced by the choice of materials, based on different elastic and viscoelastic parameters. High HM and EIT and low CIT might be beneficial for splint applications.

CLINICAL RELEVANCE

Martens parameters HM, EIT, and CIT might help to evaluate clinically relevant splint properties such as hardness, elasticity, and creep.

Influence of the postpolymerization type and time on the flexural strength and dimensional stability of 3D printed interim resins

STATEMENT OF PROBLEM

The mechanical strength of 3-dimensionally (3D) printed interim resins is unclear but influenced by printing parameters. Evidence regarding standardization of the postpolymerization type and time for 3D printed interim resins is sparse.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of postpolymerization type and time on flexural strength and dimensional stability of 3D printed resins for interim restorations.

MATERIAL AND METHODS

A total of 288 bars were 3D printed (Form 2; Formlabs, stereolithography-SLA, 50 µm, 30 degrees), (25×2×2 mm; International Organization for Standardization-ISO 4049:2019) abraded and randomly divided into 9 groups (n=30) according to postpolymerization (Ultraviolet device-UV; Microwave with water-MWA; Microwave without water-MW) and time (15, 20, and 30 minutes for UV; and 5, 8, and 10 minutes for MW and MWA). Each bar was then measured with digital calipers at 11 points for length, thickness, and width before and after postpolymerization to analyze dimensional stability. The flexural strength was then measured (σ; 980.6 N, 1 mm/minute) and the fractured surfaces were analyzed with scanning electron microscopy. The σ (MPa) data were evaluated by using a 2-way analysis of variance (ANOVA) and the Tukey honestly significant difference (HSD) pairwise comparisons test (α=.05). Dimensional stability data (mm) were analyzed by using the Kruskal-Wallis test and Dwass-Steel-Critchlow-Fligner multiple comparisons. The Weibull analysis was performed with σ data.

RESULTS

The 2-way ANOVA revealed that all factors and their interaction were significant for σ (P<.001). The UV groups presented the highest σ values, being statistically higher than all MW and MWA groups. The Weibull analysis revealed that postpolymerization UV groups found the highest values regarding the characteristic strength, although the MW 8-minute group (13.71) found the highest value for the Weibull modulus. Furthermore, the Kruskal-Wallis test revealed that only the postpolymerization factor was significant for dimensional stability (P<.001). The postpolymerization microwave groups found greater expansion variations at all times, with the MW 8-minute group (0.78 ±0.54) presenting the greatest variation in dimensional stability.

CONCLUSIONS

UV was determined to be the most suitable type of postpolymerization for interim printed resin among the postpolymerization methods, regardless of the application time. The postpolymerization MW groups found greater variations in dimensional stability.

Effect of different surface treatments on the retention force of additively manufactured interim implant-supported crowns

PURPOSE

To compare the effect of different pre-cementation surface treatments and bonding protocols on the retention force of additively manufactured (AM) implant-supported interim crowns.

MATERIAL AND METHODS

A total of 50 AM interim crowns (Temporary CB resin) were cemented on implant abutments. Five groups (n = 10) were established based on the different surface pre-treatments performed in the intaglio surface of the specimens: no surface pre-treatment (Group C or control), air-abraded with 50-μm aluminium oxide particles (Group AP), air-abraded with 50-μm aluminium oxide particles followed by the application of silane (Group AMP), silane (Group MP), and air-abraded with 30 μm silica-coated aluminum oxide particles followed by the application of silane (Group CMP). Each specimen was cemented into an implant abutment using a composite resin cement (Rely X Unicem2). Afterward, the specimens underwent retention testing with a Universal Instron machine. Pull-off forces (N) and modes of failure were registered. Statistical analysis was performed using Mann-Whitney U tests with Bonferroni corrections for multiple tests (α = 0.05).

RESULTS

The median retention force values were 233.27 ±79.28 N for Group Control, 398.59 ±68.59 N for Group MP, 303.21 ±116.80 N for Group AMP, 349.31 ±167.73 N for Group CMP, and 219.85 ± 55.88 N for Group AP. The pull-off forces were significantly greater for Group MP, while the differences between the remaining groups were not statistically significant (P > 0.05). Group AP showed the lowest retention force values among all the groups. Failure modes after the pull-off testing were predominantly adhesive and substrate failure of the AM interim material.

CONCLUSIONS

The surface treatment of the intaglio AM crown tested significantly influenced the retention force values measured. Pre-treatment with an MDP-containing silane improved the retentive force values computed, whereas pre-treatment with 50-μm Al2 O3 air-particle abrasion alone is not recommended prior to cementation on a titanium-based implant abutment.

Evaluating the conversion degree of interim restorative materials produced by different 3-dimensional printer technologies

STATEMENT OF PROBLEM

Three-dimensional (3D) printers are a relatively new technology, but the degree of conversion (DC) of the resin specimens produced by using this method is currently unknown. However, the DC of resin interim restorative materials is critical for their biocompatibility and physical properties.

PURPOSE

The purpose of this in vitro study was to evaluate the DC of interim restorative materials produced by using different 3D printer technologies and compare them with conventionally manufactured polymethyl methacrylate.

MATERIAL AND METHODS

Stereolithography, digital light processing, and liquid crystal display 3D printers were used as experimental groups, and a conventional (C) method was used as the control. Five different 3D printers (DWS Systems, Formlabs [FL], Asiga, Mega, and Vega) were included. The 3D printed specimens were designed in a rectangular prism geometry (10×4×2.5 mm) by using a computer-aided design software program (Materialise 3-matic) and printed with a layer thickness of 50 µm in the horizontal direction (n=15). Fourier transform infrared spectroscopy (FT-IR) spectra were measured in 3 steps: the liquid state of the resins, after washing with 99% isopropanol, and after final polymerization. For the C method, FT-IR spectra were assessed in 2 steps: immediately after mixing the liquid and powder and after polymerization. Statistical analysis of the data was performed with 1-way ANOVA followed by the post hoc Tukey honestly significant difference (HSD) test (α=.05).

RESULTS

There was no statistically significant difference in DC values between the 3D printed groups (P>.05). There was a statistically significant difference only between FL and the C in terms of DC (P=.042).

CONCLUSIONS

Three-dimensionally printed interim resin materials found comparable results with those of the C group. The DC was not affected by different 3D printing technologies.

Optical behavior of 3D-printed dental restorative resins: Influence of thickness and printing angle

OBJECTIVES

To evaluate the influence of thickness and printing angle on the optical properties of 3D-printed dental restorative resins.

METHODS

Four 3D printing resin systems were evaluated: DFT-Detax Freeprint Temp; FP- Formlabs Permanent Crown; FP- Formlabs Temporary CB; and GCT- GC Temporary-. Samples from each material were printed at 0° and 90°, and polished up to 0.5, 1.0, 1.5 and 2.0 mm thickness. Scattering (S), absorption (K) and albedo (a) coefficients, transmittance (T%), light reflectivity (RI) and infinite optical thickness (X∞) were calculated using Kubelka-Munk's model. Data were statistically analyzed using Kruskal-Wallis¸ Mann-Whitney tests, and VAF coefficient.

RESULTS

The spectral distribution on S, K, T%, RI,X∞ were wavelength dependent. Although the spectral behaviors were similar for all the specimens evaluated, the values of S, K, T% andX∞ presented significant differences between specimen thicknesses for all the materials used and for both printing orientations. Values for S and K increased, and T% and X∞ decreased. Significant differences between 0° and 90° were found for RI values at 0.5 and 1.0 mm thick samples, for S and K at 2.0 mm, for X∞ at 0.5 and 1.0 mm for DFT, and at 0.5 mm for FT.

CONCLUSIONS

Optical properties of 3D-printed restorative resins vary between thicknesses, and could be affected by the building orientation. Therefore, these factors should be considered in order to improve the biomimetic potential of 3D-printed dental restorative resins.

CLINICAL SIGNIFICANCE

Understanding the optical behavior of the 3D-printed restorative resins is essential to optimize their clinical performance.

Evaluation of flexible three-dimensionally printed occlusal splint materials: An in vitro study

OBJECTIVE

To evaluate and compare the mechanical properties, water sorption, water solubility, and degree of double bond conversion of three different commercially available three-dimensional (3D) printing resins used for the fabrication of flexible occlusal splints.

METHODS

A digital printer was used to generate specimens from the evaluated splint materials (KeySplint Soft, IMPRIMO LC Splint flex, and V-Print splint comfort). The specimens were equally divided and tested either dry or after water storage at 37 °C for 30 days. A three-point bending test was used to assess flexural strength, elastic modulus, and fracture toughness. A two-body wear test was performed using a dual-axis chewing simulator. Water sorption and water solubility were measured after 30 days. The degree of double bond conversion was determined by FTIR-spectrometry. All data for the evaluated properties were collected and statistically analyzed.

RESULTS

Both material and storage conditions had a significant effect on the flexural strength (P < 0.001), elastic modulus (P < 0.001), fracture toughness (P < 0.001), and wear (P < 0.001). The highest water sorption was noticed with IMPRIMO LC Splint flex (1.9 ± 0.0 %), while V-Print splint comfort displayed the lowest water solubility (0.2 ± 0.0 %). For the degree of conversion, it was statistically non-significant among the different materials (P = 0.087).

SIGNIFICANCE

Different flexible 3D-printed splints available in the market displayed variations in the evaluated properties and clinicians should consider these differences when choosing occlusal device materials. Among the tested flexible splint materials, KeySplint Soft had the greatest flexural strength, elastic modulus, fracture toughness, wear resistance, and degree of conversion. It also showed the lowest water sorption.

The effect of aging on the mechanical properties of 3-dimensional printed biocompatible resin materials used in dental applications: An in vitro study

INTRODUCTION

The mechanical properties of biocompatible printable resin materials in an intraoral environment is still being investigated. This study aimed to assess the effect of the aging process on the mechanical properties of resin samples produced by stereolithography appearance (SLA) and digital light processing (DLP) 3-dimensional printer systems.

METHODS

The cylindrical sample (4.00 × 20.00 mm) was designed by software, and the data were transformed into digital format. A DLP printer (n = 40) and an SLA printer (n = 40) carried out the printing process. The aging procedure was applied to 20 samples from each group using a thermocycling device. After the aging procedure, the samples were placed in the universal testing device for the 3-point bending test.

RESULTS

This study showed that the aging procedure decreased maximum load, bending stress, and Young's modulus values and increased maximum deflection values of the DLP group (P <0.01). However, no statistical difference was detected in the parameters compared with the SLA group except for the maximum deflection values. Furthermore, statistically significant differences were found between maximum deflection and Young's module values of SLA and DLP control and study groups (P <0.05).

CONCLUSIONS

This in vitro study revealed that the biocompatible printable resin materials produced by DLP and SLA printers had the mechanical strength to resist the values resembling the physiological occlusal forces even after the aging procedure and could produce intraoral appliances.

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.

Trueness, Flexural Strength, and Surface Properties of Various Three-Dimensional (3D) Printed Interim Restorative Materials after Accelerated Aging

Various 3D printing systems for interim fixed dental restorations are commercially available. This study aimed to evaluate the physical and mechanical properties of 3D printed resins used for interim restorations fabricated using various 3D printing systems and printing angulations after accelerated aging. Three different interim restorative materials were provided and printed using their specific 3D printing systems (A: NextDent; B: Asiga; C: Nova3D), and the testing specimens from each system were printed at two building angles: (1) 0° and (2) 90°. The six groups were A1, A2, B1, B2, C1, and C2, with sixteen specimens per group. Half of the specimens in each group (N = 8) were subjected to accelerated aging, including simulated brushing and thermocycling. Three-point bending, surface roughness, and Vickers microhardness tests were performed. Two-way ANOVA and Fisher's multiple tests were used for statistical analyses. The most accurate systems were found in groups C1 and C2 for length, A1 and B1 for width, and A1 and C1 for height. The specimen trueness only changed after aging for groups B1, B2, and C1. The flexural strength of the A2 group (151 ± 7 MPa) before aging was higher than that of the other groups, and the strength decreased after aging only for groups A1 and A2. The flexural strength, microhardness, and surface roughness of the 3D printed interim resins after aging varied depending on the material, system used, and printing angle.

Effect of build orientation in gloss, roughness and color of 3D-printed resins for provisional indirect restorations

OBJECTIVES

The purpose of this study was to evaluate the effect of build orientation of 3D-printed provisional resins (3DRs) on gloss (Gs), surface roughness (Sa), maximum profile valley depth (Rv), and color difference (∆E00).

METHODS

PMMA CAD/CAM blocks (Vita Temp/Vita) were sectioned and served as a Control. Four 3DRs (Cosmos-SLA/Yller, Cosmos-DLP/Yller, PriZma-Bioprov/Makertech, Nanolab/Wilcos) were obtained as discs (15-mm diameter, 2.5-mm thickness) in three orientations (0°, 45°, and 90°) using different 3D printers (Form 2/Formlabs, P30/Straumann, Hunter/Flashforge, W3D/Wilcos, respectively). Samples were then cleaned with isopropyl alcohol prior to post-curing in specific post-curing units. Half of the samples' surface was covered with an adhesive tape and submitted to 10,000 toothbrushing (TB) cycles. The Gs and Sa at the brushed and not brushed surfaces were evaluated with a glossmeter (Novo-curve) and a laser confocal microscope (OLS5000) (n = 10), which also obtained the Rv and 3D representative images of the interface between not brushed and brushed surfaces. Electron microscopy images of the surface of some samples was also performed (n = 3). On another set of samples (n = 5), the coordinates of luminosity and color were obtained with a spectrophotometer (Easyshade V) at baseline and after 16.7 h and 200 h of UVB aging, to calculate the ∆E00 using CIEDE:2000 formula. Additionally, 3DRs photoinitiators were identified using a minispectrometer (USB2000 +) (n = 5). Data of Gs and Sa were submitted to three-way-, Rv to two-way-, and ∆E00 to mixed-ANOVA tests, followed by Tukey's test (α = 0.05). For all variables, results from experimental groups were compared to control using Dunnett's test (α = 0.05). Student's t-test was used to compare the control at different TB cycles (Gs, Sa) or aging periods (∆E00) (α = 0.05).

RESULTS

Build orientation of 3DRs did not influence any of the variables studied. The 10,000 TB cycles resulted in a decrease in Gs and increase in Sa for all resins tested. The control showed higher Gs after 10,000 TB cycles than Cosmos-SLA and Nanolab resins. Compared to all 3DRs, Control presented lower ∆E00 after 200 h of UVB aging. All 3DRs presented higher ∆E00 than the clinically acceptable after 200 h of UVB aging. Lucirin® TPO was identified in all 3DRs, although PriZma might also present other photoinitiators and Nanolab might present Irgacure 369.

SIGNIFICANCE

Alterations in build orientation are very useful and frequently performed in the day-today of 3D-printing, thus its effect in the optical properties and in the topography of 3D-printed restorations is very relevant. For the evaluated 3D-printed provisional resins, build orientation did not influence any of the variables studied (Gs, Sa, Rv, and ∆E00), even after toothbrushing cycles and UVB aging.

Effects of washing solution temperature on the biocompatibility and mechanical properties of 3D-Printed dental resin material

The use of digital manufacturing, particularly additive manufacturing using three-dimensional (3D) printing, is expanding in the field of dentistry. 3D-printed resin appliances must undergo an essential process, post-washing, to remove residual monomers; however, the effect of the washing solution temperature on the biocompatibility and mechanical properties remains unclear. Therefore, we processed 3D-printed resin samples under different post-washing temperatures (without temperature control (N/T), 30 °C, 40 °C, and 50 °C) for different durations (5, 10, 15, 30, and 60 min) and evaluated the degree of conversion rate, cell viability, flexural strength, and Vickers hardness. Increasing the washing solution temperature significantly improved the degree of conversion rate and cell viability. Conversely, increasing the solution temperature and time decreased the flexural strength and microhardness. This study confirmed that the washing temperature and time influence the mechanical and biological properties of the 3D-printed resin. Washing 3D-printed resin at 30 °C for 30 min was most efficient to maintain optimal biocompatibility and minimize changes of mechanical properties.

Evaluation of Prosthetic Outcomes and Patient Satisfaction With 3D-Printed Implant-Supported Fixed Prosthesis

OBJECTIVES

The objectives of this study were to quantify the number and type of prosthetic complications associated with 3D-printed implant-supported fixed prostheses (3DISFP) and to evaluate patient satisfaction and oral health-related quality of life over a four-month period.

METHODS

 Fifteen edentulous patients who underwent implant therapy were included in the study. Each patient received a 3D-printed prosthesis using OnX dental resin. Prosthetic complications were documented, and data from the 14-item Oral Health Impact Profile (OHIP) questionnaire were collected at two time points: at enrollment and during a four-month recall.

RESULTS

During the four-month evaluation period, a total of nine complications were recorded, with three classified as catastrophic failures. Statistical analysis revealed statistically significant differences in OHIP scores between the preoperative and postoperative assessments (p<0.001).

CONCLUSION

Within the limitations of this study, it can be concluded that utilizing 3D-printed prostheses with OnX resin represents a viable alternative for long-term implant-supported temporaries. The patients experienced a significant improvement in their oral health-related quality of life. These results suggest that 3D printing technology, combined with the use of OnX resin, holds promise in providing satisfactory clinical outcomes and enhanced patient satisfaction. However, it is important to acknowledge the limitations of this study, and further research is warranted to validate these findings and explore the long-term performance and durability of 3D-printed implant-supported fixed prostheses. This study contributes to the growing body of evidence supporting the effectiveness of 3D printing technology in implant dentistry. The results highlight the potential of 3DISFP with OnX resin to improve oral health-related quality of life in edentulous patients. Continued advancements in 3D printing materials and techniques will likely expand the utilization of these prostheses, ultimately benefiting patients in need of implant-supported restorations.

Mechanical Properties of Three-Dimensional Printed Provisional Resin Materials for Crown and Fixed Dental Prosthesis: A Systematic Review

The emergence of digital dentistry has led to the introduction of various three-dimensional (3D) printing materials in the market, specifically for provisional fixed restoration. This study aimed to undertake a systematic review of the published literature on the Mechanical Properties of 3D- Printed Provisional Resin Materials for crown and fixed dental prosthesis (FDP). The electronic database on PubMed/Medline was searched for relevant studies. The search retrieved articles that were published from January 2011 to March 2023. The established focus question was: "Do provisional 3D-printed materials have better mechanical properties than conventional or milled provisional materials?". The systematically extracted data included the researcher's name(s), publication year, evaluation method, number of samples, types of materials, and study outcome. A total of 19 studies were included in this systematic review. These studies examined different aspects of the mechanical properties of 3D-printed provisional materials. Flexural Strength and Microhardness were the frequently used mechanical testing. Furthermore, 3D-printed provisional restorations showed higher hardness, smoother surfaces, less wear volume loss, and higher wear resistance compared to either milled or conventional, or both. 3D-printed provisional resin materials appear to be a promising option for fabricating provisional crowns and FDPs.

Effects of Surface Preparation Methods on the Color Stability of 3D-Printed Dental Restorations

BACKGROUND

Color stability is a crucial performance parameter for dental restorations, and limited research exists on how surface preparation methods affect it. The purpose of this study was to test the color stability of three resins intended for 3D printing, which can be used to make dentures or crowns in A2 and A3 colors.

MATERIALS AND METHODS

Samples were prepared in the form of incisors; the first group was not subjected to any treatment after curing and washing with alcohol, the second was covered with light-curing varnish, and the third was polished in a standard way. Then, the samples were placed in solutions of coffee, red wine, and distilled water and stored in the laboratory. After 14, 30, and 60 days, color changes were measured (presented as Delta E) compared to material stored in the dark.

RESULTS

The greatest changes were observed for samples that were not polished, then were placed in red wine dilutions (ΔE = 18.19 ± 0.16). Regarding the samples covered with varnish, during storage, some parts detached, and the dyes penetrated inside.

CONCLUSIONS

3D-printed material should be polished as thoroughly as possible to limit the adhesion of dyes from food to their surface. Applying varnish may be a temporary solution.

Effect of various printing parameters on the accuracy (trueness and precision) of 3D-printed partial denture framework

OBJECTIVES

To measure and compare the accuracy of 3D-printed materials used for RPD production to improve workflow and eliminate errors in manufacturing.

METHODS

A partially edentulous maxilla (Kennedy Class III, modification 1) was prepared and designed with proximal plates, rest seats and clasps in one first premolar, one canine and two second molars. A total of 540 3D printed RPD frameworks were 3D printed with three different types of resin (DentaCAST (Asiga, Australia), SuperCAST (Asiga, Australia) and NextDent (3D Systems, Netherlands)). To evaluate the trueness of the printing materials, they were printed with three types of layer thickness: 50 μm, 75 μm and 100 μm, using two types of build angles: 0° and 45° and three types of plate locations: side, middle and corner. After production, all specimens were scanned and superimposed with a control sample that was digitally designed. Using the initial alignment and best-fit alignment method, the root mean square error (RMSE) was calculated. To capture region specific discrepancy, 10 points of XYZ internal discrepancy within RPDs were measured and Euclidean error was calculated. Data was statistically analysed using Shapiro-Wilk and Kruskal-Wallis tests, one-way ANOVA and T-test (SPSS Version 29) and MATLAB (R2022b).

RESULTS

Optimal results were found using 45°, middle of the build plate and layer thicknesses of 100 μm (115 ± 19 μm, DentaCAST), 75 μm (143 ± 14 μm, NextDent), 50 μm (98 ± 35 μm, SuperCAST), which were clinically acceptable. Results were statistically significant when comparing layer thickness in each testing group (p < 0.001). Layer thickness was a primary parameter in the determination of print accuracy among all materials (p < 0.001). Higher discrepancies and failures were observed in 0° prints. No statistically significant difference was found in material usage between build angles or layer thickness (p > 0.005).

CONCLUSIONS

All three 3D printing materials exhibited clinically acceptable RMSE results with a build angle of 45° with a printing layer thickness of 50 μm for SuperCAST, 75 μm NextDent and 100 μm for DentaCAST. The highest discrepancies were mostly found in posterior clasps, while the lowest discrepancy was found in palatal straps. Despite unoptimized spacing of prints, frameworks configured to print in the middle of the build plate result in the least printing failures.

Comparison of the color stability and surface roughness of 3-unit provisional fixed partial dentures fabricated by milling, conventional and different 3D printing fabrication techniques

OBJECTIVES

To compare the color stability and surface roughness of 3-unit provisional fixed partial dentures (FPDs) fabricated by milling, conventional, and different 3D printing fabrication techniques.

METHODS

A total sample of 160, 3-unit FPDs were subdivided into four groups; subtractive milled resin (SM), two 3D printed resins (Stereolithography; SLA and Digital Light Processing; DLP) and conventional self-cured polymethyl methacrylate resin (CM). Surface roughness (Ra) was assessed twice; at baseline (Ra1) and after artificial tooth brushing (Ra2). Color of the samples was measured after immersion in four different solutions (cola, coffee, black tea and distilled water) at three time intervals (1, 7 and 30 days). Comparisons of the Ra and the color change (∆E₀₀) were done using one-way ANOVA followed by multiple pairwise comparisons using Bonferroni adjusted significance level. Comparisons of the Ra at two stages (Ra1 and Ra2) were done using paired t-test. Univariate linear regression was performed followed by multivariable regression to assess the association between ∆E₀₀ and different factors (materials, solution, and time). Significance was set at P value <0.05.

RESULTS

The highest change in Ra following artificial tooth brushing was reported in the CM group, while the lowest change was reported in the SM group, with a significant difference between both groups (P<0.001). SM group had significantly lower ∆E₀₀ than the CM group followed by 3D printed SLA and DLP groups (P<0.001). Storage in coffee for 30 days showed the highest ∆E₀₀ values (P<0.001).

CONCLUSIONS

SM resin showed the least surface roughness and color change followed by 3D printed SLA resin. The difference in printing technology affected the tested properties with improved readings of 3D printed SLA resin.

CLINICAL SIGNIFICANCE

Milled provisional FPDs showed higher surface smoothness and color stability than those fabricated by SLA printing technology, but with no significant difference between both groups. Therefore, SLA printed resins can be an adequate substitute to milled resins in the fabrication of provisional FPDs to overcome the high expenses of milled provisional FPDs.

Fracture Load of 3D-Printed Interim Three-Unit Fixed Dental Prostheses: Impact of Printing Orientation and Post-Curing Time

The fracture resistance of 3-unit interim fixed dental prostheses (IFDPs) fabricated using digital light processing (DLP) additive technology with different printing parameters is neglected. Therefore, this study investigates the effect of different printing orientations and different post-curing times on the fracture resistance of 3-unit IFDPs fabricated from two three-dimensional (3D) printed resins, NextDent, C&B (CB), ASIGA, and DentaTOOTH. A 3-unit dye was scanned, and an IFDP was designed. A total of 300 specimens (150/materials, n = 10) were printed and divided into three groups according to printing orientations (0°, 45°, 90°) per material. Each orientation was subdivided into five groups (n = 10) considering the post-curing time (green state as control, 30, 60, 90, and 120 min). All specimens underwent thermocycling (5000 cycles). Each specimen was fitted onto the die and loaded until fracture using a universal testing machine with a loading rate of 1 m/min. Data were analyzed using ANOVA and post hoc Tukey test (α = 0.05). The result showed that printing orientation had a significant effect on the fracture load for both ASIGA and NextDent materials (p < 0.05). The highest fracture load was recorded with 45° orientation, followed by 0° orientation and 90° orientation showed the lowest values per respective post-curing time. Post-curing time increased the fracture load (p < 0.05). Post-curing time had a positive effect on the fracture load. As the post-curing time increased, the fracture resistance load increased (p < 0.05), with 90 and 120 min showing the highest fracture load. The 0° and 45° printing orientations have a high fracture load for 3D-printed IFDPs, and an increased post-curing time is recommended.

Effect of Different Vat Polymerization Techniques on Mechanical and Biological Properties of 3D-Printed Denture Base

Three-dimensional printing is increasingly applied in dentistry to fabricate denture bases. Several 3D-printing technologies and materials are available to fabricate denture bases, but there is data scarcity on the effect of printability, mechanical, and biological properties of the 3D-printed denture base upon fabricating with different vat polymerization techniques. In this study, the NextDent denture base resin was printed with the stereolithography (SLA), digital light processing (DLP), and light-crystal display (LCD) technique and underwent the same post-processing procedure. The mechanical and biological properties of the denture bases were characterized in terms of flexural strength and modulus, fracture toughness, water sorption and solubility, and fungal adhesion. One-way ANOVA and Tukey’s post hoc were used to statistically analyze the data. The results showed that the greatest flexural strength was exhibited by the SLA (150.8±7.93 MPa), followed by the DLP and LCD. Water sorption and solubility of the DLP are significantly higher than other groups (31.51±0.92 μgmm3) and 5.32±0.61 μgmm3, respectively. Subsequently, the most fungal adhesion was found in SLA (221.94±65.80 CFU/mL). This study confirmed that the NextDent denture base resin designed for DLP can be printed with different vat polymerization techniques. All of the tested groups met the ISO requirement aside from the water solubility, and the SLA exhibited the greatest mechanical strength.

Influence of the Printing Orientation on Parallelism, Distance, and Wall Thickness of Adjacent Cylinders of 3D-Printed Surgical Guides

This in-vitro study aimed to evaluate the influence of the printing orientation on parallelism, distance, and thickness between adjacent cylinders of 3D-printed surgical guides. CAD software was used to design a surgical guide with two adjacent parallel cylinders (reference); the design was saved as standard tessellation software (STL) and 63 samples were printed using three different orientations (0, 45, and 90 degrees). A metrology digital microscope was used to measure the distance, the angle and the thickness of the guides cylinders. Afterwards, the printed guides were scanned and cloud comparison software was used to compare STL files from the printed guides against the reference CAD model. One-way analysis of variance and Tukey test were used for multiple comparisons between groups and significance was p < 0.05. The printing orientation affected the distance between cylinders, the parallelism and the wall thickness. In addition, there were global deviations in all printing orientations. Printing with 90 degrees orientation produced almost-parallel cylinders but walls thicker than the reference model; all the cylinders converged toward the coronal but printing at 0 degrees produced the closest distance to the reference value. Within the limitations of this experimental in-vitro study it can be concluded that all the printing orientations influence the angle, the distance, and the thickness between adjacent cylinders of a surgical guide. Printing at 90 degrees produces the best global correspondence with the master model.

The influence of printing angle on color and translucency of 3D printed resins for dental restorations

OBJECTIVES

To evaluate the influence of printing orientation on color and translucency of 3D printing restorative resins.

METHODS

Four 3D printing resin systems in the available shades (DFT-Detax Freeprint Temp- A1, A2,A3; FP-Formlabs Permanent Crown- A2,A3,B1,C2; FT- Formlabs Temporary CB- A2,A3,B1,C2; GCT-GC Temporary- Light, Medium) were evaluated. Three samples (10×10×1.2 mm) from each material were printed at two different printing orientations (0° and 90°) and polished to 1.00 ± 0,01 mm of thickness. Spectral reflectance was measured against black background using a calibrated spectroradiometer, CIE D65 standard illuminant and the 45°/0°geometry. Color and translucency differences were evaluated using CIEDE2000 metric (ΔE₀₀) and 50:50% perceptibility (PT₀₀ and TPT₀₀) and acceptability (AT₀₀ and TAT₀₀) thresholds.

RESULTS

In general, color changes due to printing orientation at (0° and 90°) were mainly produced by ΔL* or ΔC* . ΔE₀₀ were above PT₀₀ for all DFT shades, FP-B1, FP-C2, FT-A2 and FT-B1. Only for DFT-1, ΔE₀₀ was above AT₀₀. ΔRTP₀₀ values were above TPT₀₀ for DFT-A1, DFT-A3, FP-B1 and FT-B1, but lower than TAT₀₀. The direction of the changes in translucency (ΔRTP₀₀) depends on the material and shade.

SIGNIFICANCE

The selection of building orientation (0° and 90°) for the 3D printed resins influence the visual color and translucency and therefore their esthetic appearance. These aspects should be considered when printing dental restorations using the evaluated materials.

The Influence of Printing Layer Thickness and Orientation on the Mechanical Properties of DLP 3D-Printed Dental Resin

Technological advances are closely related to the development of new materials and their processing and manufacturing technologies. In the dental field, the high complexity of the geometrical designs of crowns, bridges and other applications of digital light processing 3D-printable biocompatible resins is the reason for the need for a deep understanding of the mechanical proprieties and behavior of these materials. The aim of the present study is to assess the influence of printing layer direction and thickness on the tensile and compression proprieties of a DLP 3D-printable dental resin. Using the NextDent C&B Micro-Filled Hybrid (MFH), 36 specimens (24 for tensile strength testing, 12 for compression testing) were printed at different layer angulations (0°, 45° and 90°) and layer thicknesses (0.1 mm and 0.05 mm). Brittle behavior was observed in all specimens regardless of the direction of printing and layer thickness for the tensile specimens. The highest tensile values were obtained for specimens printed with a layer thickness of 0.05 mm. In conclusion, both printing layer direction and thickness influence mechanical proprieties and can be used to alter the materials' characteristics and make the final printed product more suitable for its intended purposes.

Effects of heat-treatment methods on cytocompatibility and mechanical properties of dental products 3D-printed using photopolymerized resin

PURPOSE

The purpose of this study was to test heat-treatment methods for improving the cytocompatibility of dental 3D printable photopolymer resins.

METHODS

Nextdent C&B resin and a digital light processing 3D printer were used to print all specimens, which were divided into seven groups as follows: 1-month storage at controlled room temperature, 20 to 25 °C (RT), 24-hour storage at RT, 24-hour storage in RT water, 1-min immersion in 80 °C water, 1-min immersion in 100 °C water, 5-min immersion in 100 °C water, and autoclaving. Cell viability tests, cytotoxicity tests, and confocal laser scanning microscopy were performed to analyze the cytocompatibility of the 3D-printed resin. Fourier-transform infrared spectroscopy was performed after heat-treatment to determine the degree of conversion (DC).

RESULTS

Immersing printed resin samples in 100 °C water for 1 or 5 min after the curing process was an effective method for increasing cytocompatibility by inducing the preleaching of toxic substances such as unpolymerized monomers, photoinitiators, and additives. Moreover, the DC can be increased by additional polymerization without affecting the mechanical properties of the material.

CONCLUSIONS

Immersing the printed photosensitive dental resins in 100 °C water for 5 min is a suitable method for increasing cytocompatibility and the DC.