Influence of postprocessing rinsing solutions and duration on flexural strength of aged and nonaged additively manufactured interim dental material

Effects of print orientation and artificial aging on the flexural strength and flexural modulus of 3D printed restorative resin materials

STATEMENT OF PROBLEM

The integration of computer-aided design and computer-aided manufacture (CAD-CAM) technology has revolutionized restorative dentistry, offering both additive and subtractive manufacturing methods. Despite extensive research on 3-dimensionally (3D) printed materials, uncertainties remain regarding the impact of print orientation on their mechanical properties, especially for definitive resin materials, necessitating further investigation to ensure clinical efficacy.

PURPOSE

The purpose of this in vitro study was to investigate the influence of print orientation and artificial aging on the flexural strength (FS) and flexural modulus (FM) of 3D printed resin materials indicated for definitive and interim restorations.

MATERIAL AND METHODS

Specimens (2×2×25 mm) were additively manufactured in 3 orientations (0, 45, and 90 degrees) using five 3D printed resins: VarseoSmile Crownplus (VCP), Crowntec (CT), Nextdent C&B MFH (ND), Dima C&B temp (DT), and GC temp print (GC). A DLP 3D printer (ASIGA MAX UV) was used with postprocessing parameters as per the manufacturer recommendations. FS and FM were tested after storage in distilled water (DW) and artificial saliva (AS) for 24 hours, 1 month, and 3 months at 37 °C. Additional 2×2×16-mm specimens printed at 90 degrees were compared with the milled materials Lava Ultimate (LU) and Telio CAD (TC) after 24 hours of storage in AS at 37 °C (n=10). Measurements were conducted using a universal testing machine (Z020; Zwick/Roell) following the International Organization for Standardization (ISO) 4049 standard. Multiple way ANOVA, 1-way ANOVA, and Tukey HSD post hoc tests (α=.05) were used to analyze the data.

RESULTS

Print orientation significantly influenced the FS and FM of 3D printed resin materials, with the 90-degree orientation exhibiting superior mechanical properties (P<.05). Definitive resins (CT and VCP) exhibited higher FS and FM compared with interim resins (ND, DT, GC) at all time points (P<.001). LU had significantly higher FS and FM compared with other resins (P<.001), while TC had similar FS to definitive 3D printed resins. Aging time and media influenced FS and FM, with varying effects observed across different materials and time points. Strong positive correlations were found between filler weight and both FS (r=.83, P=.019) and FM. All materials met the minimum FS requirement of 80 MPa (ISO 4049) when printed at 90 degrees.

CONCLUSIONS

The 90-degree orientation produced specimens with higher FS than 0- and 45-degree orientations. CT recommended for definitive restorations displayed higher FS compared with VCP and those intended for interim use after 3 months of aging. LU exhibited higher FS and FM than 3D printed resins, while TC had similar FS and FM to the latter. Aging effects on 3D printed resins were minimal and were material specific.

Influence of cleaning solutions and hydrothermal aging on the flexural strength and microhardness of resins for additively manufactured definitive fixed restorations

STATEMENT OF PROBLEM

Studies on the effects of cleaning solutions and hydrothermal aging on the flexural strength and microhardness of additively manufactured (AM) resins are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of cleaning solution on the flexural strength and microhardness of resins marketed for AM definitive restorations. In addition, the effects of hydrothermal aging and material type on these properties were examined.

MATERIAL AND METHODS

Rectangular or disk specimens (n=19) were additively manufactured for flexural strength and microhardness tests from 2 commercially available resins for definitive restorations: a glass-filled composite resin (AM-CR) and a urethane acrylate-based resin (AM-UA). The specimens were divided into 4 groups based on the cleaning solution: 96% ethanol, 98% isopropanol (IPA), water-based solvent, and methyl ether solvent. The specimens were divided into 2 subgroups, nonaged and hydrothermally aged (10 000 thermal cycles), and flexural strength and microhardness tests were performed before and after aging.

RESULTS

AM-CR had higher flexural strength with ethanol, IPA, and water-based solvent than AM-UA (P<.004), whereas it had lower flexural strength than AM-UA with methyl ether solvent (P<.001), regardless of aging. AM-CR and AM-UA had higher microhardness with ethanol and IPA compared with the methyl ether solvent (P<.031). AM-CR had higher microhardness with all cleaning solutions than AM-UA, regardless of aging condition (P<.001).

CONCLUSIONS

Resin type, cleaning solution, and aging condition affected the flexural strength and microhardness of AM resins intended for definitive restorations. Regardless of hydrothermal aging, AM-CR had the lowest flexural strength when the methyl ether solvent was used, while cleaning solution type did not affect the strength of AM-UA; AM-CR's strength was lower than AM-UA's with methyl ether. Regardless of hydrothermal aging, AM-CR and AM-UA had higher microhardness with ethanol and IPA than with methyl ether solvent. AM-CR had higher microhardness than AM-UA, regardless of cleaning solution. After hydrothermal aging, the microhardness of AM-CR decreased with the water-based solvent.

Influence of nonhazardous postprocessing solutions and surface treatments on the surface roughness and color stability of resins used for additively manufactured definitive restorations

STATEMENT OF PROBLEM

Knowledge of the surface roughness and color stability of definitively intended additively manufactured (AM) resins when different postprocessing cleaning solutions and surface treatments are applied is limited.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of postprocessing cleaning solution and surface treatment (polishing and coffee thermocycling) on the surface roughness and color stability of resins intended for AM definitive restorations. In addition, the color coordinates were compared with an A1 shade tab.

MATERIAL AND METHODS

Sixty specimens were AM from 2 different resins, a glass-filler reinforced composite resin (AM-CR) and urethane acrylate-based resin (AM-UA), for definitive restorations. The specimens were divided into 3 groups based on the postprocessing cleaning solution (n=10): 96% ethanol, water-based solvent, and methyl ether solvent. The surface roughness (Ra) and color coordinates were measured before polishing, after polishing, and after coffee thermocycling for 5000 cycles. Color difference values (ΔE00) were calculated, and color coordinates were compared with a reference shade tab (α=.05).

RESULTS

AM-CR had a lower Ra with ethanol than methyl ether solvent before polishing (P=.006). AM-UA had the lowest Ra with ethanol and the highest Ra with water-based solvent before polishing (P≤.001). Irrespective of material and postprocessing solution, Ra decreased after polishing (P≤.001). AM-CR had the highest ΔE00 with methyl ether solvent after polishing and after coffee thermocycling (P≤.002). AM-CR had the lowest ΔE00 with ethanol after coffee thermocycling (P≤.003).

CONCLUSIONS

Resin type, postprocessing cleaning solution, and surface treatment affected the surface roughness and color stability of AM resins intended for definitive restorations.

Can nonhazardous postprocessing cleaning solutions enable adequate surface properties for printed dental casts in different resins?

STATEMENT OF PROBLEM

Printed casts and dental devices and prostheses are increasingly being used, and the ecological impact of additive manufacturing should be considered in addition to the fabrication accuracy and surface properties of the printed object. To overcome the ecological drawbacks of alcohol postprocessing, water-washable, 3-dimensionally (3D) printable cast resins and postprocessing cleaning solutions that do not include alcohol have been introduced. However, whether using only water rather than chemical solvents would enable the surface smoothness and hardness required for accurate diagnostic and prosthetic procedures is unknown.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of resin type (water-washable or nonwater washable) and postprocessing cleaning solution on the surface roughness and microhardness of 3D printed dental cast resins.

MATERIAL AND METHODS

One hundred eight disk-shaped specimens (Ø10×2 mm) were additively manufactured (AM) from 3 dental cast resins: 2 water-washable (Epax (WW1) and Phrozen (WW2)) and 1 nonwater-washable resin (KeyModel Ultra resin-beige (NWW)) with a printer (n=36). Specimens in each resin type were divided into 3 groups for the application of postprocessing cleaning solution (water, 98% isopropyl alcohol [IPA] or methyl ether solvent) and polymerized after cleaning. The surface roughness (Ra, µm) and Vickers microhardness (HV) were measured. Laser microscope images were made of 1 specimen from each group.

RESULTS

NWW-IPA (control group) had a similar Ra to WW2-water (P=.81) and WW2-methyl ether solvent (P=.511). NWW-IPA had lower HV than WW2-water (P<.001) and WW1-methyl ether solvent (P=.001). Solutions had no significant effect on the Ra of WW1 (P≥.554) and WW2 (P≥.805). WW1 had higher surface irregularities with water, whereas no significant difference was visually observed with IPA or methyl ether solvent. Solutions had a similar effect on the surface of WW2 when evaluated visually with the laser microscope.

CONCLUSIONS

Resin type and postprocessing cleaning solution affected the surface roughness and microhardness of 3D printed dental cast resins, except for the surface roughness of tested water-washable resins. Water or methyl ether solvent cleaned water-washable resin (WW2) had surface roughness and hardness similar to commonly used nonwater-washable cast resin.

Manufacturing accuracy of the intaglio surface of definitive resin-ceramic crowns fabricated at different print orientations by using a stereolithography printer

STATEMENT OF PROBLEM

Stereolithography (SLA) procedures can be chosen for manufacturing definitive crowns; however, how the print orientation impacts the trueness and precision of the intaglio surface of the printed definitive restorations is unclear.

PURPOSE

The purpose of this in vitro investigation was to calculate the manufacturing accuracy of the intaglio surface of SLA definitive resin-ceramic crowns fabricated at varying print orientations (0, 45, 75, or 90 degrees).

MATERIAL AND METHODS

The standard tessellation language (STL) file of an anatomic contour molar crown was obtained and used to fabricate all the crowns by using a definitive resin-ceramic material (Permanent Crown) and an SLA printer (Form 3B+). Four groups were developed depending on the print orientation selected to manufacture the crowns: 0-, 45-, 70-, and 90-degree print orientation (n=30). Each crown specimen was digitized without the use of scanning powder by using a desktop scanner (T710). The crown design file was determined as the reference (control) group and used to calculate the fabricating trueness and precision of the intaglio surface of the specimens using the root mean square (RMS) error computation. Trueness data were examined by using 1-way ANOVA and post hoc pairwise multiple comparison Tukey tests, while precision data were analyzed using the Levene test (α=.05).

RESULTS

The mean ±standard deviation RMS error discrepancies ranged from 37 ±3 μm to 113 ±11 μm. One-way ANOVA exposed significant trueness (P<.001) differences among the groups considered in this study. Furthermore, all the print orientation groups tested were different from each other (P<.001). The 0-degree group presented the best trueness value (37 μm), while the 90-degree group obtained the worst trueness value (113 μm). The Levene test exposed significant precision differences among the groups assessed (P<.001). The 0-degree group had a significantly lower standard deviation (higher precision) (3 μm) than the other groups, with no difference among the other groups tested (P>.05).

CONCLUSIONS

The fabricating trueness and precision of the intaglio surface of the SLA resin-ceramic crowns was impacted by the varying print orientations assessed.

Effect of different post-processing conditions on the accuracy of liquid crystal display-printed orthognathic surgical splints

Objectives

To evaluate the accuracy (trueness and precision) of liquid crystal display (LCD)-printed orthognathic surgical splints under two different post-processing conditions-rinsing solvent and post-polymerization time.

Materials and methods

An LCD 3D printer was used to create 48 surgical splints using the same reference standard tessellation language (STL) files. They were randomly assigned to two experimental studies. In the rinsing solvent study, 24 surgical splints were divided into three groups (n = 8) based on their rinsing solvents: isopropyl alcohol (IPA), ethanol, and water. In the post-polymerization time study, 24 surgical splints were divided into three groups (n = 8) based on the post-polymerization time: (3, 6, and 10 min). The surgical splints were covered with an opaque scanning spray, scanned, and converted into STL files. The images were trimmed and superimposed onto the reference STL file to evaluate trueness and precision, and the deviation was calculated using the root mean square (RMS) formula. Color map data were also obtained. The RMS was statistically analyzed using one-way analysis of variance and Tukey's test (α < 0.05).

Results

The lowest RMS values of trueness and precision were observed in the IPA group and the 6-min post-polymerization time groups (p < 0.05). The IPA-rinse and 6-min polymerization groups (p < 0.05) demonstrated the highest accuracy for LCD-printed orthognathic surgical splint fabrication.

Conclusion

The dimensional accuracy of LCD-printed surgical splints is affected by the post-processing conditions, including the rinsing solvent and polymerization time. The RMS and color map data associated with the IPA-rinse and 6-min polymerization corresponded to the highest accuracy.

Influence of print orientation on the intaglio surface accuracy (trueness and precision) of tilting stereolithography definitive resin-ceramic crowns

STATEMENT OF PROBLEM

Vat-polymerization tilting stereolithography (TSLA) technology can be selected for fabricating definitive crowns; however, how the printing variables, including print orientation, influence its manufacturing accuracy remains unclear.

PURPOSE

The purpose of this in vitro study was to assess the influence of different print orientations (0, 45, 75, or 90 degrees) on the intaglio surface accuracy (trueness and precision) of TSLA definitive resin-ceramic crowns.

MATERIAL AND METHODS

The virtual design of an anatomic contour molar crown was obtained in standard tessellation language (STL) file format and used to manufacture all the specimens by using a TSLA printer (DFAB Chairside) and a resin-ceramic material (Irix Max Photoshade single-use cartridges). Four groups were created depending on the print orientation used to manufacture the specimens: 0- (Group 0), 45- (Group 45), 70- (Group 75), and 90-degree (Group 90) print orientation (n=30). Each specimen was digitized by using a laboratory scanner (T710) according to the manufacturer's scanning protocol. The reference STL file was used as a control to measure the volumetric discrepancies of the intaglio surface with the digitized specimens by using the root mean square (RMS) error calculation. The trueness data were analyzed by using 1-way ANOVA followed by post hoc pairwise multiple comparison Tukey tests, and precision data were analyzed using the Levene test (α=.05).

RESULTS

Significant mean trueness (P<.001) and precision (P<.001) value discrepancies were found among the groups tested. Additionally, all the groups were significantly different from each other (P<.001), except for the 45- and 90-degree groups (P=.868). Group 0 showed the best mean trueness and precision values, while the Group 90 demonstrated the lowest mean trueness and precision values.

CONCLUSIONS

The print orientations tested influenced the intaglio surface trueness and precision values of the TSLA definitive resin-ceramic crowns.

Influence of print orientation on the accuracy (trueness and precision) of diagnostic casts manufactured with a daylight polymer printer

STATEMENT OF PROBLEM

Print orientation may affect the manufacturing accuracy of vat-polymerized diagnostic casts. However, its influence should be analyzed based on the manufacturing trinomial (technology, printer, and material) and printing protocol used to manufacture the casts.

PURPOSE

The purpose of this in vitro study was to measure the influence of different print orientations on the manufacturing accuracy of vat-polymerized polymer diagnostic casts.

MATERIAL AND METHODS

A standard tessellation language (STL) reference file containing a maxillary virtual cast was used to manufacture all specimens using a vat-polymerization daylight polymer printer (Photon mono SE. LCD 2K) and a model resin (Phrozen Aqua Gray 4K). All specimens were manufactured using the same printing parameters, except for print orientation. Five groups were created depending on the print orientation: 0, 22.5, 45, 67.5, and 90 degrees (n=10). Each specimen was digitized using a desktop scanner. The discrepancy between the reference file and each of the digitized printed casts was measured using the Euclidean measurements and root mean square (RMS) error (Geomagic Wrap v.2017). Independent (unpaired) sample t tests and multiple pairwise comparisons using the Bonferroni test were used to analyze the trueness of the Euclidean distances and RMS data. Precision was assessed using the Levene test (α=.05).

RESULTS

In terms of Euclidean measurements, significant differences in trueness and precision values were found among the groups tested (P<.001). The 22.5- and 45-degree groups resulted in the best trueness values, and the 67.5-degree group had the lowest trueness value. The 0- and 90-degree groups led to the best precision values, while the 22.5-, 45-, and 67.5-degree groups showed the lowest precision values. Analyzing the RMS error calculations, significant differences in trueness and precision values were found among the groups tested (P<.001). The 22.5-degree group had the best trueness value, and the 90-degree group resulted in the lowest trueness value among the groups. The 67.5-degree group led to the best precision value, and the 90-degree group to the lowest precision value among the groups.

CONCLUSIONS

Print orientation influenced the accuracy of diagnostic casts fabricated by using the selected printer and material. However, all specimens had clinically acceptable manufacturing accuracy ranging between 92 μm and 131 μm.

Effects of Post-Processing Parameters on 3D-Printed Dental Appliances: A Review

In recent years, additive manufacturing (AM) has been recognized as a transformative force in the dental industry, with the ability to address escalating demand, expedite production timelines, and reduce labor-intensive processes. Despite the proliferation of three-dimensional printing technologies in dentistry, the absence of well-established post-processing protocols has posed formidable challenges. This comprehensive review paper underscores the critical importance of precision in post-processing techniques for ensuring the acquisition of vital properties, encompassing mechanical strength, biocompatibility, dimensional accuracy, durability, stability, and aesthetic refinement in 3D-printed dental devices. Given that digital light processing (DLP) is the predominant 3D printing technology in dentistry, the main post-processing techniques and effects discussed in this review primarily apply to DLP printing. The four sequential stages of post-processing support removal, washing, secondary polymerization, and surface treatments are systematically navigated, with each phase requiring meticulous evaluation and parameter determination to attain optimal outcomes. From the careful selection of support removal tools to the consideration of solvent choice, washing methodology, and post-curing parameters, this review provides a comprehensive guide for practitioners and researchers. Additionally, the customization of post-processing approaches to suit the distinct characteristics of different resin materials is highlighted. A comprehensive understanding of post-processing techniques is offered, setting the stage for informed decision-making and guiding future research endeavors in the realm of dental additive manufacturing.

Effect of postprocessing parameters on the flexural strength of vat-polymerized additively manufactured interim fixed dental prostheses: A systematic review with postprocessing guidelines

STATEMENT OF PROBLEM

Limited data exist regarding the effects of postprocessing on the flexural strength of vat-polymerized additively manufactured (AM) interim fixed dental prostheses.

PURPOSE

The purpose of this systematic review was to determine how the postprocessing workflow affects the mechanical properties of vat-polymerized additively manufactured interim fixed dental prostheses and to establish clinical guidelines.

MATERIAL AND METHODS

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed. The population, intervention, comparison, and outcome (PICO) question was "For vat-polymerized additively manufactured interim fixed dental prostheses (P), does varying the postprocessing workflow/ protocol (I and C) affect mechanical properties/physical properties/flexural strength (O)?" Searches were conducted in 3 databases: PubMed/Medline, EMBASE, and Web of Science, with 2 investigators performing the title and abstract screening and setting the inclusion and exclusion criteria to identify publications. The risk of bias was evaluated by applying the Joanna Briggs Institute Critical Appraisal Checklist for Quasi-Experimental Studies (nonrandomized experimental studies). The reported independent variables of rinse solution, rinse time, and polymerization time on the flexural strength results were extracted for qualitative review.

RESULTS

The initial search identified 149 records, with 12 in vitro studies meeting the inclusion criteria. Significant heterogeneity was observed in the manufacturing process and materials. Eleven of 12 included studies reported flexural strength above 100 MPa when following the manufacturer's recommendation. Postprocessing rinsing ranged from 5 seconds to 90 minutes, with potentially reduced flexural strength with extended rinsing. A rinse of 5 to 10 minutes was recommended for optimal mechanical properties, degree of conversion, and biocompatibility. Isopropyl alcohol (IPA) and tripropylene glycol monomethyl ether (TPM) were the most investigated rising solutions, while experimental solutions including 99.5% acetone and 100% bio-ethyl alcohol reportedly decreased flexural strength. Polymerization time and intensity correlated positively with the flexural strength, whereas an artificial aging process reduced the flexural strength.

CONCLUSIONS

Heterogeneity existed in the reported postprocessing protocols for AM interim fixed prostheses, including manufacturer materials, methods, and study outcomes. While polymerization time and intensity correlated with greater strength, consistent patterns regarding rinsing solution or time were lacking. Rinsing solution, extended rinsing time, and artificial aging may reduce flexural strength. Further investigation is indicated.

Effects of solvent type and UV post-cure time on 3D-printed restorative polymers

OBJECTIVES

This study evaluated the impact of different solvents and UV post-curing times on properties of 3D printing resins for provisional restorations.

METHODS

The post-processing methods were tested using two solvents (isopropyl alcohol or absolute ethanol) and three UV times (5, 10, or 30 min). The resins tested were Resilab 3D Temp, Printax Temp, and Prizma Bioprov. Microhardness (kgf/mm2), fracture toughness (KIC, MPa√m), surface roughness (Ra, µm), gloss (gloss units), and degree of CC conversion (%DC) were measured (n = 8). All response variables were collected from the same specimen. The specimens were 3D printed using an SLA/LCD printer (150° angulation, 50 µm layer thickness). Light exposure times were adjusted for each material, and the post-processing methods were applied using an all-in-one machine immediately after printing. Data were analyzed using Three-Way ANOVA (α = 0.05).

RESULTS

Microhardness was affected by UV post-cure time and 3D resin. Resilab showed higher microhardness with isopropyl alcohol and 30-min UV time, while Printax had higher microhardness with absolute ethanol. KIC was influenced by solvent type, UV time, and 3D resin, with varying effects on different resins. Roughness was affected by 3D resin and UV time, but no significant differences were seen for Resilab or Prizma. Gloss was influenced by 3D resin, and for Prizma, it was lower with specific solvent/UV time combinations. DC was influenced by 3D resin, with each resin behaving differently.

SIGNIFICANCE

Tailoring the combination of 3D resin, solvent washing type, and UV post-curing time is important to achieve optimal mechanical and aesthetic outcomes for restorations.

Comparison of surface roughness of additively manufactured implant-supported interim crowns fabricated with different print orientations

PURPOSE

To assess the influence of print orientation on the surface roughness of implant-supported interim crowns manufactured by using digital light processing (DLP) 3D printing procedures.

MATERIALS AND METHODS

An implant-supported maxillary right premolar full-contour crown was obtained. The interim restoration design was used to fabricate 30 specimens with 3 print orientations (0, 45, and 90 degrees) using an interim resin material (GC Temp PRINT) and a DLP printer (Asiga MAX UV) (n = 10). The specimens were manufactured, and each was cemented to an implant abutment with autopolymerizing composite resin cement (Multilink Hybrid Abutment). Surface roughness was assessed on the buccal surface of the premolar specimen by using an optical measurement system (InfiniteFocusG5 plus). The data were analyzed with a Shapiro-Wilk test, resulting in a normal distribution. One-way ANOVA and the Tukey HSD tests were selected (α = 0.05).

RESULTS

Statistically significant discrepancies were found in the surface roughness mean values among the groups tested (p < 0.001). The lowest mean ± standard deviation surface roughness was found with the 90-degree group (1.2 ± 0.36 μm), followed by the 0-degree orientation (2.23 ± 0.18 μm) and the 45-degree group (3.18 ± 0.31 μm).

CONCLUSIONS

Print orientation parameter significantly impacted the surface roughness of the implant-supported interim crowns manufactured by using the additive procedures tested.

Influence of interdental spaces and the palate on the accuracy of maxillary scans acquired using different intraoral scanners

PURPOSE

To assess the influence of interdental spaces and scanning the palate on the accuracy of maxillary scans acquired using three intraoral scanners (IOSs).

MATERIALS AND METHODS

A virtual completely dentate maxillary cast without interdental spaces was obtained and modified to create 1, 2, and 3 mm of interdental spacing between the anterior teeth. These three files (reference standard tessellation language files) were used to print three reference casts. The reference casts were scanned using three IOSs: TRIOS4, iTero Element 5D, and Aoralscan2. Three groups were created based on the interdental spaces: 0, 1, 2, and 3 mm (n = 10). The groups were subdivided into two subgroups: no palate (NP subgroup) and palate (P subgroup). The reference STL files were used to measure the discrepancy with the experimental scans by calculating the root mean square (RMS) error. Three-way analysis of variance (ANOVA) and post hoc Tukey pairwise comparison tests were used to analyze trueness. The Levene test was used to analyze precision (α = 0.05).

RESULTS

Trueness ranged from 91 to 139 μm and precision ranged from 5 to 23 μm among the subgroups tested. A significant correlation was found between IOS*group (p<0.001) and IOS*subgroup ( p<0.001). Tukey test showed significant trueness differences among the interdental spaces tested (p<0.001). The 1- and 2-mm groups obtained better trueness than the 0- and 3-mm groups (p<0.001). An 11 μm mean trueness discrepancy was measured among the different interdental space groups tested. The P subgroups demonstrated significantly higher trueness when compared to the NP subgroups (p<0.001). The discrepancy between the maxillary scans with and without the palate was 4 μm. Significant precision discrepancies were found (p = 0.008), with the iTero group showing the lowest precision.

CONCLUSION

Interdental spaces and incorporation of the palate on maxillary intraoral scans influenced trueness and precision of the three IOSs tested. However, the scanning discrepancy measured may be of no clinical relevance.

Effect of print orientation, storage conditions, and storage time on intaglio surface accuracy of implant surgical guides fabricated by using a stereolithography technology

STATEMENT OF PROBLEM

The accuracy of printed implant surgical guides can be affected by different factors that negatively impact the planned implant position. How print orientation, storage time, and conditions influence manufacturing accuracy remains uncertain.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of print orientation, storage conditions, and storage time on the intaglio surface accuracy of implant surgical guides manufactured by using a stereolithography (SLA) printer.

MATERIAL AND METHODS

A tooth-supported maxillary implant surgical guide design (control file) was used to fabricate the specimens (N=40, n=10). Four groups were created based on the print orientation used: 0 (Group 0), 45 (Group 45), 70 (Group 70), and 90 degrees (Group 90). The specimens were fabricated using an SLA printer (Form 3B+) and a biocompatible dental resin (Surgical Guide Resin V1) following the manufacturer's recommended protocol. Each group was divided into 2 subgroups based on the storage conditions: light (L subgroup) and dark (D subgroup) settings. Each specimen was digitized by using a desktop scanner (Medit T710) at days 0, 1, 7, and 14. The control file and each digitized specimen were superimposed by using the best-fit technique with a metrology program (Geomagic Control X). The root mean square (RMS) error was used to calculate the discrepancies between the control files and specimen files. Three-way ANOVA and pairwise comparison Tukey tests were used to analyze trueness. The Levene test was used to assess precision (α=.05).

RESULTS

Significant trueness discrepancies were found among the groups tested (P<.001), but no significant differences were found among the subgroups (P=.100) and the storage times analyzed (P=.609). Additionally, the Tukey test showed significant RMS error mean value discrepancies between Group 0 and Group 45 (P<.001), Group 0 and Group 90 (P<.001), Group 45 and Group 70 (P<.001), and Group 70 and Group 90 (P<.001). The Levene test revealed significant SD discrepancies among the groups tested (P<.05).

CONCLUSIONS

The trueness and precision of the intaglio surface of the implant surgical guides manufactured by using the printer and material tested were affected by the print orientation. However, storage conditions over a 14-day period did not impact the intaglio accuracy of the specimens.

Effect of build orientation and layer thickness on manufacturing accuracy, printing time, and material consumption of 3D printed complete denture bases

OBJECTIVES

To evaluate the influence of build orientation and layer thickness on manufacturing accuracy, material consumption, and printing time of complete denture (CD) bases fabricated using digital light processing (DLP).

METHODS

The CD base was designed on the basis of a standard maxillary edentulous model. Seventy CD bases were fabricated using a DLP 3D printer (Pro95, SprintRay, USA) and printable CD base material (DENTCA Denture Base II, Dentca, USA) at seven build orientations (0°, labial 45°, labial 90°, posterior 45°, posterior 90°, buccal 45°, and buccal 90°) and two types of layer thicknesses (50- and 100 μm) (n = 5). All test CD bases were digitalized and superimposed on the reference cast by section-based best-fit alignment. For evaluating manufacturing accuracy, deviation analysis was performed to compare the test data with the reference cast using the "3D Compare" in the 3D metrology software. The printing time and material consumption were calculated using slicing software and recorded, respectively. The two-way ANOVA test was used for accuracy evaluation, and the non-parametric test was used to evaluate printing time and material consumption (α = 0.05).

RESULTS

Statistically significant differences were found in the manufacturing accuracy (p < 0.001), printing time (p < 0.001), and material consumption (p < 0.001) among the build orientation groups. The labial 45° and labial 90° groups showed the best accuracy. The 90° build orientations required the least material consumption and longest printing time; the labial 45° group consumed the most printing materials; the 0° group required the shortest printing time to fabricate a CD base. Moreover, the layer thickness influenced the printing time (p < 0.001) rather than the accuracy (p = 0.560) and material consumption (p = 1.000).

CONCLUSIONS

When DLP was used to fabricate the CD bases, the build orientation influenced the manufacturing accuracy, material consumption, and printing time. However, the layer thickness only affected the printing time.

CLINICAL SIGNIFICANCE

This study suggests that optimizing the build orientation can improve the manufacturing accuracy and reduce the material consumption and printing time of a DLP-printed CD base. The fast-printing setting (100 μm layer thickness) can reduce the printing time without compromising the manufacturing accuracy of the CD base.

Influence of the layer thickness on the flexural strength of aged and non-aged additively manufactured interim dental material

PURPOSE

To measure the flexural strength and Weibull characteristics of aged and non-aged printed interim dental material fabricated with different layer thickness.

MATERIAL AND METHODS

Bars (25×2×2 mm) were additively fabricated by using a polymer printer (Asiga Max) and an interim resin (Nexdent C&B MFH). Specimens were fabricated with the same printing parameters and postprocessing procedures, but with 7 different layer thickness: 50 (control or 50-G group), 10 (10-G group), 25 (25-G group), 75 (75-G group), 100 (100-G group), 125 (125-G group), and 150 μm (150-G group). Two subgroups were created: non-aged and aged subgroups (n = 10). A universal testing machine was selected to measure flexural strength. Two-parameter Weibull distribution values were computed. Two-way ANOVA and Tukey tests were elected to examine the data (α = .05).

RESULTS

Artificial aging methods (P<.001) were a significant predictor of the flexural strength computed. Aged specimens acquired less flexural strength than non-aged specimens. The Weibull distribution obtained the highest shape for non-aged 50-G and 75-G group specimens compared with those of other non-aged groups, while the Weibull distribution showed the highest shape for aged 125-G specimens.

CONCLUSIONS

The flexural strength of the additively fabricated interim material examined was not influenced by the layer thickness at which the specimens were fabricated; however, artificial aging techniques reduced its flexural strength. Aged specimens presented lower Weibull distribution values compared with non-aged specimens, except for the 125-G specimens. This article is protected by copyright. All rights reserved.