The effect of the angle of acuteness of additive manufactured models and the direction of printing on the dimensional fidelity: clinical implications

Impact of 3D resin and base designs on the accuracy of additively manufactured casts using a stereolithography technology

STATEMENT OF PROBLEM

Three-dimensional (3D) printed casts can be fabricated using a wide range of 3D polymer resins and designed with varying casts´ base configurations. Nevertheless, the influence of different base designs, in conjunction with various 3D printing resins, on the final dimensional accuracy of casts manufactured through SLA-LCD 3D printing technology remains unclear.

PURPOSE

This study assessed the impact of 3D printing resins and base designs on the dimensional accuracy of diagnostic casts fabricated using a SLA-LCD vat-polymerization 3D printer. Two resins (NextDent Model 2.0 and Aqua Gray 4K) and 5 different base configurations were evaluated for their effect on trueness and precision.

MATERIAL AND METHODS

A digital maxillary cast was modified into three base designs: solid (Group S), honeycomb (Group HC), and hollow (Group H). Honeycomb and hollow designs had subgroups with 1-mm (HC1, H1) and 2-mm (HC2, H2) wall thicknesses, resulting in 50 specimens (n=10 per subgroup). Eleven embedded precision cubes were used for accuracy assessment. A Sonic Mini 4K vat-polymerization printer was used for cast printing, and dimensional deviations were captured using a coordinate measuring device. Trueness was defined by the average dimensional discrepancy, and precision was indicated by the standard deviation. Statistical analysis included Kruskal-Wallis and Mann-Whitney U tests (α=.05).

RESULTS

NextDent resin showed trueness falling between 44.8 5 µm and 64.5 µm and precision values varying between 33.5 5 µm and 48.9 µm, while Aqua Gray 4K resin ranged from 24.1 5 µm to 81.1 µm for trueness and 19.8 5 µm to 65.9 µm for precision. Significant differences (P<.001) were observed in all axes (x-, y-, z-axes) and 3D deviations, influenced by resin and base design.

CONCLUSIONS

Resin type and base design significantly affect the dimensional accuracy of 3D printed casts. Aqua Gray 4K with a 2-mm hollow base provided the highest accuracy, particularly when matched with the printer manufacturer. All casts met clinical standards.

Influence of the print orientation and cast thickness on the accuracy of DLP master casts for fixed dental prostheses

BACKGROUND

This study aimed to evaluate the influence of different print orientations and external shell thickness on the accuracy of master casts printed with direct light processing (DLP) technology for fixed dental prostheses.

METHODS

Seventy-two maxillary hollow master casts were printed with a DLP printer from a standard tessellation language (STL) reference file with dental preparations for a single crown and a 3-unit fixed partial denture. Study groups consisted of six groups (n = 12) according to the print orientation (0, 10, and 20 degrees) and the external shell thickness of the cast (2 mm and 4 mm). Each specimen was digitized with a laboratory scanner. Discrepancies between the reference STL and the experimental STL of the printed cast were measured by using the root mean square (RMS) error. Data were statistically analyzed using one-way ANOVA and Tukey's HDS test to evaluate the trueness, and precision was assessed using the Levene test (α = 0.05).

RESULTS

No significant differences were found in the overall trueness and precision between the groups analyzed for the print orientation and the shell thickness. The 2-mm external shell thickness demonstrated the best trueness on selected points.

CONCLUSIONS

The print orientation in the range of 0 to 20 degrees and the cast thickness did not influence the overall accuracy of DLP-printed master casts for fixed prostheses with clinically acceptable range values. Trueness was affected by the external shell thickness on selected points.

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.

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.

Impact of 3D printing orientation on accuracy, properties, cost, and time efficiency of additively manufactured dental models: a systematic review

BACKGROUND

The evidence on the effect of printing orientation on dimensional accuracy and properties of resinous dental models is unclear. This systematic review aimed to assess the impact of printing orientation on the accuracy and properties of additively manufactured resinous dental models, besides the cost, material consumption, and time efficiency at different orientations.

METHODS

A comprehensive web search (PubMed, Scopus, Cochrane) was performed in July 2024 without language restrictions. The included studies were assessed using the modified consort statement for laboratory studies on dental materials. The outcomes were accuracy and surface quality, besides the cost and time efficiency of additively manufactured dental models printed in different directions.

RESULTS

Following PRISMA guidelines, 14 records were included. Most records favored horizontally printed models with minor controversies regarding accuracy, material consumption, time, and cost efficiency. While orientation can influence surface quality, it is often more significantly affected by factors such as the printing technology used, the material properties, and the layer thickness.

CONCLUSIONS

Horizontal orientation has proven to be the most efficient for producing dental models, particularly for single-model manufacturing, due to its superior time and cost savings. However, large-scale and overnight massive production favors the vertical orientation since the platform accommodates twice to triple the models' numbers as horizontal orientation. The majority of studies favor horizontal orientation for its accuracy. Choosing the optimal orientation in additive manufacturing not only ensures precision of dental models, improving the fit of restorations and prostheses, but also leads to significant reductions in production time, material usage, and energy consumption, ultimately minimizing environmental impact.

TRIAL REGISTRATION

Not applicable.

Mechanical performance of 3-dimensionally printed resins compared with conventional and milled resins for the manufacture of occlusal devices: A systematic review

STATEMENT OF PROBLEM

Digital methods for manufacturing occlusal devices provide advantages over conventional techniques, but information about the mechanical properties of 3-dimensionally (3D) printed resins is scarce.

PURPOSE

The purpose of this systematic review was to evaluate the literature to determine whether 3D-printed resins for occlusal devices present satisfactory mechanical performance when compared with milled and conventional heat polymerized and autopolymerized resins.

MATERIAL AND METHODS

This systematic review followed the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol and was registered in the Open Science Framework. The search strategy was applied without restriction of time and language to Embase, PubMed, Scopus, Science Direct, and Web of Science databases, and to the nonpeer-reviewed literature in ProQuest and Google Scholar. The selection process was conducted independently in 2 stages by 2 reviewers according to the eligibility criteria. The risk of bias was analyzed by using a checklist of important parameters to be considered. The systematic review considered the population, intervention, comparison, outcome, studies (PICOS) format, where population was resins for 3D printing of occlusal devices, intervention was inherent characteristics of the resin, comparison was conventional heat polymerized, autopolymerized, and milled resins, outcome was mechanical performance, and studies were in vitro experimental studies.

RESULTS

A total of 1430 articles were found with the search strategy. After removing 182 duplicates found in Rayyan, the title and abstract of 1248 articles were evaluated, of which 37 articles were screened from the databases, 23 were selected for full reading, and 6 met the eligibility criteria and were included in this review; 1 had a low risk of bias and 5 had a moderate risk. An additional search of the reference list of included articles did not result in the inclusion of any articles. A quantitative meta-analysis could not be performed because of the heterogeneity of the included studies regarding the type of resin used and the method for evaluating mechanical performance.

CONCLUSIONS

Resins for 3D printing had satisfactory mechanical performance for interocclusal devices when compared with conventional heat polymerized and autopolymerized resins, except for hardness. Milled resins were better than 3D-printed resins in hardness, wear resistance, flexural strength, flexural modulus, and fracture resistance when printing angle and thickness were not considered. Further development is needed in terms of printing techniques and chemical composition, as they are important for optimal mechanical properties and clinical performance.

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.

Influence of base designs on the manufacturing accuracy of vat-polymerized diagnostic casts using two different technologies

STATEMENT OF PROBLEM

Diagnostic casts can incorporate different base designs and be manufactured using different vat-polymerization technologies. However, the influence of the interrelation between the base design and the 3D printing technology on the casts' final accuracy remains unclear.

PURPOSE

The purpose of this in vitro study was to assess the influence of different base designs of 3D printed casts on the accuracy of 2 vat-polymerization technologies.

MATERIAL AND METHODS

A digital maxillary cast was obtained and used to generate 3 different base designs: solid (S group), honeycombed (HC group), and hollow (H group). The HC and H groups were subdivided based on the wall thickness of the cast design, resulting in 2 subgroups with thicknesses of 1 mm (HC1 and H1) and 2 mm (HC2 and H2) (N=100, n=10). Eleven reference cubes were added to each specimen for subsequent measurements. Specimens were manufactured by using 2 vat-polymerization 3D printers: Nextdent 5100 (ND group) and Sonic Mini 4K (SM4K group) and a resin material suitable for both 3D printers (Nextdent Model 2.0). A coordinate measuring machine quantified the linear and 3-dimensional discrepancies between the digital cast and each reference specimen. Trueness was defined as the average absolute dimensional discrepancy between the virtual cast and the specimens produced through additive manufacturing (AM), while precision was delineated as the standard deviation in dimensional discrepancies between the digital cast and the AM specimens. The data were analyzed using the Kruskal-Wallis and Mann-Whitney U pairwise comparison tests (α=.05).

RESULTS

For the NextDent group the trueness ranged from 21.83 µm to 28.35 µm, and the precision ranged from 17.82 µm to 37.70 µm. For the Phrozen group, the trueness ranged from 45.15 µm to 64.51 µm, and the precision ranged from 33.51 µm to 48.92 µm. The Kruskal-Wallis test showed significant differences on the x-, y-, and z-axes and in the 3D discrepancy (all P<.001). On the x-axis, the Mann-Whitney U test showed significant differences for the Phrozen group between the H-2 and H-1 groups (P=.001), H-2 and S groups (P<.001), and HC-2 and S groups (P=.012). On the y-axis, significant differences were found in the Phrozen group between the H-2 and H-1 groups (P=.001), the H-2 and S, H-1 and HC-1, and HC-1 and S groups (P<.001), the H-1 and HC-2 groups (P=.007), and the HC-2 and S groups (P=.009). The NextDent group exhibited significant differences, particularly among the HC-1 and H-2 groups (P=.004), H-1 (P=.020), and HC-2 (P=.001) groups; and on the z-axis significant differences were found in the Phrozen group between the H-2 and H-1 and S groups and the HC-2 group and H-1 and S groups (both P<.001). In the NextDent group, significant differences were found between the H-2 and HC-2 (P=.047) and HC-1 (P=.028) groups. For the 3D discrepancy analysis, significant differences were found in the Phrozen group between the H-2 and H-1 and S groups (P<.001), the H-1 and HC-2 groups (P=.001), the S and HC-1 and HC-2 groups (P<.001), and the H-1 and HC-1 groups (P=.002). In the NextDent group, significant differences were observed between the H-2 and HC-1 groups (P=.012).

CONCLUSIONS

The accuracy of digital casts depends on the manufacturing trinomial and base design of the casts. The honeycomb and hollow based designs provided the highest accuracy in the NextDent and Phrozen groups respectively for the material polymer tested. All specimens fell in the clinically acceptable range.

Trueness of 3D-printed cobalt chromium versus titanium removable partial denture clasps

PURPOSE

The purpose of this in vitro study was to evaluate the trueness of removable partial denture clasps fabricated with titanium (Ti) through the selective laser melting (SLM) technique compared to cobalt-chromium alloys (CoCr).

MATERIALS AND METHODS

A virtual Aker clasp was designed on a scanned tooth, and SLM printers were used to print 20 claps using cobalt chromium (n = 10) and titanium alloy (n = 10). The deviation between the printed clasps and reference design was measured using the surface matching software (Geomagic control x) at rest, retentive tip, reciprocal tip, retentive shoulder, and reciprocal shoulder. An Independent t-test was used to determine the influence of 3D-printed material on the trueness (a = 0.05).

RESULTS

The gap distance in mm between the reference design and printed in titanium showed an average of 0.0001 ±0.0544, 0.0256 ±0.1309, 0.0230 ±0.1028, 0.0701 ±0.1234, and 0.0013 ±0.0735 mm in rest, reciprocal arm tip, retentive arm tip, retentive arm shoulder, and reciprocal arm shoulder, respectively. The gap distance in mm between the reference design and printed clasps in CoCr alloy showed an average of 0.0316 ±0.0692, 0.2783 ±0.1678, 0.1446 ±0.1528, 0.0315 ±0.0906, and 0.0419 ±0.1088 mm in rest, reciprocal arm tip, retentive arm tip, retentive arm shoulder, and reciprocal arm shoulder, respectively. The difference between titanium and CoCr alloys at each observation site was significant.

CONCLUSION

Clasps fabricated from titanium with SLM printing have the least deviation and better trueness compared to those fabricated from cobalt chromium.

Trueness of the apical and middle root portion segments of 3D-printed removable die and alveolar cast designs manufactured using stereolithographic 3D printing

PURPOSE

The present study evaluated the effects of the root portion design, segment (middle vs. apical), and part (die vs. cast) on the trueness of three-dimensional (3D)-printed removable die-cast complex.

MATERIAL AND METHODS

The trueness of apical and middle segments of the root portion of 45 3D-printed removable dies and casts with three different root portion designs (n = 15) was assessed using a metrology-grade computer program. The three removable dies and cast designs (root form [RF], conical [CON], and cylindric [CYL]) were created using professional computer-aided manufacturing computer programs (DentalCAD 3.1 Rijeka, and InLab CAD 22.0), and manufactured using stereolithographic 3D printer (Form3; FormLabs, Somerville, MA). Subsequently, the 3D-printed removable dies and casts were scanned by a single operator with an intraoral scanner (PrimeScan; Dentsply Sirona, Charlotte, NC), and their respective standard tessellation language files were aligned and compared to master reference files in a metrology-grade computer program (Geomagic Control X; 3D systems, Rock Hill, NC). The root mean square (RMS) values of the middle and apical segments for each removable die and cast were calculated and analyzed using a mixed model including a repeated measure 3-way analysis of variance (ANOVA) and post-hoc stepdown Bonferroni-corrected pairwise comparisons (α = 0.05).

RESULTS

A statistically significant 3-way interaction between factors was detected, suggesting that the part (removable die or alveolar cast) and their design affected the RMS values of their apical and middle root portion segment. (p = 0.045). The post-hoc analysis identified significant differences between RMS values of the apical segments of the CON and CYL removable dies (p = 0.005). Significant differences were observed between the middle and apical segments of the CON (p < 0.001) and RF removable die designs (p = 0.004). No statistically significant differences were noticed between the RMS of the different alveolar cast designs (p > 0.05). Significant differences were detected between the apical and middle segments of the same alveolar cast design (p < 0.05).

CONCLUSIONS

For the manufacturing trinomial and 3D printing strategy used in the present study, the interaction of the part, design, and segment affected the trueness of removable dies and alveolar casts. The trueness was higher on the middle segment on removable dies and alveolar casts in all designs used, except for CYL removable dies, where the trueness difference between segments was small. Higher trueness values may be achieved with designs with simple apical segment geometries.

Two-piece magnet-retained shell manufactured by using milled and vat-polymerized methods for direct interim restorations

The shell technique has been described for fabricating direct interim restorations by using conventional and computer-aided design and computer-aided manufacturing (CAD-CAM) methods. However, the positioning of the shell over the tooth preparations can be challenging. In the present manuscript, the clinical and laboratory steps for manufacturing a 2-piece magnet-retained shell for direct interim restoration fabrication are described. The 2-piece shell was produced by combining milling and additive manufacturing procedures. The described technique aims to simplify the correct positioning of the shell and facilitate direct interim restoration fabrication.

Influence of print orientation and wet-dry storage time on the intaglio accuracy of additively manufactured occlusal devices

STATEMENT OF PROBLEM

Different factors can affect the manufacturing accuracy of additively manufactured dental devices; however, the influence of print orientation and wet-dry storage time on their intaglio accuracy remains uncertain.

PURPOSE

The purpose of this in vitro study was to assess the effect of print orientation (0, 45, 70, and 90 degrees) and wet-dry storage time (0, 30, 60, and 90 days) on the intaglio accuracy of additively manufactured occlusal devices.

MATERIAL AND METHODS

An occlusal device design was obtained in a standard tessellation language (STL) file format (control file) which was used to fabricate all the specimens by using a stereolithography printer (Form 3+) and a biocompatible resin material (Dental LT Clear Resin, V2). Four groups were created based on the print orientation used to manufacture the specimens: 0, 45, 70, and 90 degrees. Each group was divided into 4 subgroups depending on the time elapsed between manufacturing and accuracy evaluation: 0, 30, 60, and 90 days. For the subgroup 0, a desktop scanner (T710) was used to digitize all the specimens. The 30-day subgroup specimens were stored for 30 days with the following daily storage protocol: 16 hours inside a dry lightproof container, followed by 8 hours in artificial saliva (1700-0305 Artificial Saliva) inside the same lightproof container. The specimens were then digitized by following the same procedures used for subgroup 0. For the subgroups 60 and 90, the identical procedures described for subgroup 30 were completed but after 60 and 90 days of storage, respectively. The reference STL file was used to measure the intaglio discrepancy with the experimental scans obtained among the different subgroups by using the root mean square error calculation. Two-way ANOVA and post hoc Tukey pairwise comparison tests were used to analyze the data (α=.05).

RESULTS

Print orientation (P<.001) and usage time (P<.001) were significant predictors of the trueness value obtained. Additionally, the 0-degree print orientation at day 0 group demonstrated the best trueness value among all the groups tested (P<.05). No significant trueness discrepancies were found among the 45-, 70-, and 90-degree print orientation, or among the 30, 60, and 90 days of storage. A significant precision difference was found in the variance between print orientation groups across usage time subgroups.

CONCLUSIONS

The print orientation and wet-dry storage times tested influenced the trueness and precision of the intaglio surfaces of the occlusal devices manufactured with the 3D printer and material selected.

Trueness of five different 3D printing systems including budget- and professional-grade printers: An In vitro study

Problem

Several types of 3D printers with different techniques and prices are available on the market. However, results in the literature are inconsistent, and there is no comprehensive agreement on the accuracy of 3D printers of different price categories for dental applications.

Aim

This study aimed to investigate the accuracy of five different 3D printing systems, including a comparison of budget- and higher-end 3D printing systems, according to a standardized production and evaluation protocol.

Material and methods

A maxillary reference model with prepared teeth was created using 16 half-ball markers with a diameter of 1 mm to facilitate measurements. A reference file was fabricated using five different 3D printers. The printed models were scanned and superimposed onto the original standard tesselation language (.stl) file, and digital measurements were performed to assess the 3-dimensional and linear deviations between the reference and test models.

Results

After examining the entire surface of the models, we found that 3D printers using Fused filament fabrication (FFF) technology -120.2 (20.3) μm create models with high trueness but high distortion. Distortions along the z-axis were found to be the highest with the stereolithography (SLA)-type 3D printer at -153.7 (38.7) μm. For the 4-unit FPD, we found 201.9 (41.8) μm deviation with the digital light processing (DLP) printer. The largest deviation (-265.1 (55.4) μm) between the second molars was observed for the DLP printer. Between the incisor and the second molar, the best results were produced by the FFF printer with -30.5 (76.7) μm.

Conclusion

Budget-friendly 3D printers are comparable to professional-grade printers in terms of precision. In general, the cost of a printing system is not a reliable indicator of its level of accuracy.

Mechanical and chemical characterization of contemporary occlusal splint materials fabricated with different methods: a systematic review

OBJECTIVE

To systematically review studies on various occlusal splint materials and describe their mechanical and chemical properties.

METHODS

MEDLINE (PubMed), Scopus, and Web of Science searches were conducted for in vitro studies focusing on occlusal splint materials. Two reviewers performed an assessment of the identified studies and data abstraction independently, and this was complimented by an additional hand search. The articles were limited to those in the English language that were published between January 1st, 2012, and December 1st, 2022.

RESULTS

The initial search yielded 405 search results of which 274 were selected for full-text review following abstract evaluation. 250 articles that did not meet the inclusion criteria were excluded, and the remaining 25 articles (with 1 article identified from the reference lists of included articles) providing mechanical and chemical values were used in this review. Poly methyl methacrylate (PMMA) -based occlusal splint materials showed the highest values in terms of hardness, wear resistance, flexural strength, flexural modulus, e-modulus, and fracture toughness. The material group with the highest water sorption and water solubility was 3D printed (PR) splint materials. In addition, the lowest degree of double bond conversion was also observed in this group of materials.

CONCLUSIONS

The outcome of this review suggests that mechanically and chemically acceptable properties can be attained with PMMA-based occlusal splint materials using both conventional and digital production methods. PR splint materials should not be considered as the primary choice for long-term treatments due to their low mechanical and chemical properties.

CLINICAL RELEVANCE

This review provides clinical recommendations for selecting the appropriate material and fabrication method for occlusal splints while taking the patients' needs and the materials´ mechanical and chemical properties into account.

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.

Porous metal implants: processing, properties, and challenges

Porous and functionally graded materials have seen extensive applications in modern biomedical devices-allowing for improved site-specific performance; their appreciable mechanical, corrosive, and biocompatible properties are highly sought after for lightweight and high-strength load-bearing orthopedic and dental implants. Examples of such porous materials are metals, ceramics, and polymers. Although, easy to manufacture and lightweight, porous polymers do not inherently exhibit the required mechanical strength for hard tissue repair or replacement. Alternatively, porous ceramics are brittle and do not possess the required fatigue resistance. On the other hand, porous biocompatible metals have shown tailorable strength, fatigue resistance, and toughness. Thereby, a significant interest in investigating the manufacturing challenges of porous metals has taken place in recent years. Past research has shown that once the advantages of porous metallic structures in the orthopedic implant industry have been realized, their biological and biomechanical compatibility-with the host bone-has been followed up with extensive methodical research. Various manufacturing methods for porous or functionally graded metals are discussed and compared in this review, specifically, how the manufacturing process influences microstructure, graded composition, porosity, biocompatibility, and mechanical properties. Most of the studies discussed in this review are related to porous structures for bone implant applications; however, the understanding of these investigations may also be extended to other devices beyond the biomedical field.

Clear guidance to select the most accurate technologies for 3D printing dental models - A network meta-analysis✰

OBJECTIVES

Thus far, the findings of numerous studies conducted on the accuracy of three-dimensional (3D) printed dental models are conflicting. Therefore, the aim of the network meta-analysis (NMA) is to determine the accuracy of 3D printed dental models compared with digital reference models.

DATA

Studies comparing the accuracy of 3D printed full-arch dental models manufactured using different printing techniques to initial STL files were included.

SOURCES

This study was registered in PROSPERO (CRD42021285863). An electronic search was performed across four databases in November 2021, and search was restricted to the English language.

STUDY SELECTION

A systematic search was conducted based on a prespecified search query. 16,303 articles were pooled after the removal of the duplicates. Following study selection and data extraction, 11 eligible studies were included in the NMA in 6 subgroups. The outcomes were specified as trueness and precision and expressed as root mean square (RMS) and absolute mean deviation values. Seven printing technologies were analyzed: stereolithography (SLA), digital light processing (DLP), fused deposition modeling/fused filament fabrication (FDM/FFF), MultiJet, PolyJet, continuous liquid interface production (CLIP), and LCD technology. The QUADAS-2 and GRADE were used to evaluate the risk of bias and certainty of evidence.

CONCLUSIONS

SLA, DLP, and PolyJet technologies were the most accurate in producing full-arch dental models.

CLINICAL SIGNIFICANCE

The findings of the NMA suggest that SLA, DLP, and PolyJet technologies are sufficiently accurate for full-arch dental model production for prosthodontic purposes. In contrast, FDM/FFF, CLIP, and LCD technologies are less suitable for manufacturing dental models.

Marginal and internal discrepancies associated with carbon digital light synthesis additively manufactured interim crowns

STATEMENT OF PROBLEM

The carbon digital light synthesis (DLS) or continuous liquid interface production (CLIP) technology is an innovative additive manufacturing technology using oxygen-inhibited photopolymerization to create a continuous liquid interface of unpolymerized resin between the growing component and the exposure window. This interface eliminates the need for an incremental layer-by-layer approach, allowing for continuous creation and increased printing speed. However, the internal and marginal discrepancies associated with this new technology remain unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the marginal and internal discrepancies by using the silicone replica technique of interim crowns fabricated by 3 different manufacturing technologies: direct light processing (DLP), DLS, and milling.

MATERIAL AND METHODS

A mandibular first molar was prepared, and a crown was designed with a computer-aided design (CAD) software program. The standard tessellation language (STL) file was used to create 30 crowns from the DLP, DLS, milling technologies (n=10). The gap discrepancy was determined using the silicone replica approach, with 50 measurements made with a ×70 microscope for each specimen for the marginal and internal gaps. The data were analyzed using 1-way ANOVA, followed by the Tukey HSD post hoc test (α=.05).

RESULTS

The DLS group had the least marginal discrepancy compared with the DLP and milling groups (P<.001). The DLP group showed the highest internal discrepancy followed by the DLS and milling groups (P=.038). No significant difference was found between DLS and milling in terms of internal discrepancy (P>.05).

CONCLUSIONS

The manufacturing technique had a significant effect on both internal and marginal discrepancies. The DLS technology showed the smallest marginal discrepancies.

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.

Influence of base design on the manufacturing accuracy of vat-polymerized diagnostic casts: An in vitro study

STATEMENT OF PROBLEM

Vat-polymerized casts can be designed with different bases, but the influence of the base design on the accuracy of the casts remains unclear.

PURPOSE

The purpose of the present in vitro study was to evaluate the influence of various base designs (solid, honeycombed, and hollow) with 2 different wall thicknesses (1 mm and 2 mm) on the accuracy of vat-polymerized diagnostic casts.

MATERIAL AND METHODS

A virtual maxillary cast was obtained and used to create 3 different base designs: solid (S group), honeycombed (HC group), and hollow (H group). The HC and H groups were further divided into 2 subgroups based on the wall thickness of the cast designed: 1 mm (HC-1 and H-1) and 2 mm (HC-2 and H-2) (N=50, n=10). All the specimens were manufactured with a vat-polymerized printer (Nexdent 5100) and a resin material (Nexdent Model Ortho). The linear and 3D discrepancies between the virtual cast and each specimen were measured with a coordinate measuring machine. Trueness was defined as the mean of the average absolute dimensional discrepancy between the virtual cast and the AM specimens and precision as the standard deviation of the dimensional discrepancies between the virtual cast and the AM specimens. The Kolmogorov-Smirnov and Shapiro-Wilk tests revealed that the data were not normally distributed. The data were analyzed with Kruskal-Wallis and Mann-Whitney U pairwise comparison tests (α=.05).

RESULTS

The trueness ranged from 63.73 μm to 77.17 μm, and the precision ranged from 44.00 μm to 54.24 μm. The Kruskal-Wallis test revealed significant differences on the x- (P<.001), y- (P=.006), and z-axes (P<.001) and on the 3D discrepancy (P<.001). On the x-axis, the Mann-Whitney test revealed significant differences between the S and H-1 groups (P<.001), S and H-2 groups (P<.001), HC-1 and H-1 groups (P<.001), HC-1 and H-2 groups (P<.001), HC-2 and H-1 groups (P<.001), and HC-2 and H-2 groups (P<.001); on the y-axis, between the S and H-1 groups (P<.001), HC-1 and H-1 groups (P=.001), HC-1 and H-2 groups (P=.02), HC-2 and H-1 groups (P<.001), HC-2 and H-2 groups (P=.003); and on the z-axis, between the S and H-1 groups (P=.003). For the 3D discrepancy analysis, significant differences were found between the S and H-1 groups (P<.001), S and H-2 groups (P=.004), HC-1 and H-1 groups (P=.04), and HC-2 and H-1 groups (P=.002).

CONCLUSIONS

The base designs tested influenced the manufacturing accuracy of the diagnostic casts fabricated with a vat-polymerization printer, with the solid and honeycombed bases providing the greatest accuracy. However, all the specimens were clinically acceptable.

An In Vitro Evaluation of the Effect of 3D Printing Orientation on the Accuracy of Implant Surgical Templates Fabricated By Desktop Printer

PURPOSE

To evaluate the effect of different 3D printing orientations on internal and seating accuracy of implant surgical templates fabricated by a digital light processing (DLP) printer.

MATERIALS AND METHODS

A single maxillary model with a missing central incisor was used to design a surgical template for single implant placement. According to the printing orientation, three surgical template groups were included in the study: horizontal (H), angled (A) and vertical (V) (n = 10). For the H group, the templates were produced parallel to the printing platform, while for the V group, the templates were perpendicular to the platform. The A group templates had a 45° angle orientation to the platform. Each template was scanned at the fitting surface and after seating on the master model. The internal accuracy involved measuring the trueness and precision of the internal surface, while for the seating accuracy, the vertical discrepancy after seating the template was measured. To determine the difference among the groups, ANOVA test was applied followed by Tukey post hoc tests (α = 0.05).

RESULTS

The H group had the lowest internal surface inaccuracy (trueness = 100.7 μm; precision = 69.1 μm) followed by A (trueness = 114.0 μm; precision = 77.3 μm) and V (trueness = 120.3 μm; precision = 82.4 μm) groups, respectively (p < 0.001). Similarly, the H group had the most superior seating accuracy (543.8 μm) followed by A group (1006.0 μm) and V group (1278.0 μm), respectively (p < 0.001).

CONCLUSIONS

The orientation of 3D printing of implant surgical templates fabricated by the DLP desktop printer influenced the accuracy of the templates. The horizontally printed templates consistently exhibited superior accuracy. To reduce deviation of implant placement, it is recommended to print the surgical templates with their largest dimension parallel to the printing platform.

Compressive and Flexural Strength of 3D-Printed and Conventional Resins Designated for Interim Fixed Dental Prostheses: An In Vitro Comparison

A provisionalization sequence is essential for obtaining a predictable final prosthetic outcome. An assessment of the mechanical behavior of interim prosthetic materials could orient clinicians towards selecting an appropriate material for each clinical case. The aim of this study was to comparatively evaluate the mechanical behavior—with compressive and three-point flexural tests—of certain 3D-printed and conventional resins used to obtain interim fixed dental prostheses. Four interim resin materials were investigated: two 3D-printed resins and two conventional resins (an auto-polymerized resin and a pressure/heat-cured acrylic resin). Cylindrically shaped samples (25 × 25 mm/diameter × height) were obtained for the compression tests and bar-shaped samples (80 × 20 × 5 mm/length × width × thickness) were produced for the flexural tests, observing the producers’ recommendations. The resulting 40 resin samples were subjected to mechanical tests using a universal testing machine. Additionally, a fractographic analysis of failed samples in bending was performed. The results showed that the additive manufactured samples exhibited higher elastic moduli (2.4 ± 0.02 GPa and 2.6 ± 0.18 GPa) than the conventional samples (1.3 ± 0.19 GPa and 1.3 ± 0.38 GPa), as well as a higher average bending strength (141 ± 17 MPa and 143 ± 15 MPa) when compared to the conventional samples (88 ± 10 MPa and 76 ± 7 MPa); the results also suggested that the materials were more homogenous when produced via additive manufacturing.

Additively Manufactured Scan Bodies for Virtual Patient Integration: Different Designs, Manufacturing Procedures, and Clinical Protocols

Additively manufactured intraoral scan bodies can be used to guide the alignment of a patient's digital file information, including facial and intraoral digital scans both with and without a cone beam computed tomography scan, and to obtain a 3D virtual patient's representation. The present manuscript reviews the different intraoral scan body designs, procedures involved in additive manufacturing, clinical protocols for fabricating an additively manufactured scan body, performing a patient's digital data collection, and completing the alignment techniques.

Additive Manufacturing Technologies: Current Status and Future Perspectives

A review of the main additive manufacturing technologies including vat-polymerization, material extrusion, material jetting, binder jetting, powder-based fusion, sheet lamination, and direct energy deposition is provided. Additionally, the dental applications of polymer, metal, and ceramic printing technologies are discussed.

Accuracy of Fixed Implant-Supported Dental Prostheses Additively Manufactured by Metal, Ceramic, or Polymer: A Systematic Review

PURPOSE

Additive manufacturing (AM) in prosthodontics is used as an alternative to casting or milling. Various techniques and materials are available for the additive manufacturing of the fixed and removable tooth-supported restorations, but there is a lack of evidence on the accuracy of AM fixed implant-supported prostheses. Recent studies investigated the accuracy of ceramic AM prostheses. Therefore, the aim of this systematic review was to evaluate the accuracy of additively manufactured metal, ceramic or polymers, and screw- or cement-retained fixed implant-supported prostheses.

MATERIALS AND METHODS

Two calibrated investigators performed an electronic search of relevant publications in the English language following selected PICOS criteria and using a well-defined search strategy (latest search date-1st of June, 2021). Based on the exclusion criteria (no control group, less than five samples per group, 3D printing of the implant abutment part, only subjective evaluation of accuracy, etc.) studies were not included in the review. Quantitative data of accuracy evaluation such as marginal gap, strain analysis, and linear measurements was extracted and interpreted. QUADAS-2 tool was used to assess the risk of methodological bias of all included studies.

RESULTS

Sixteen in vitro studies were selected for the final analysis. Six of the selected studies evaluated screw-retained restorations and 10 cement-retained implant-supported restorations. Only 4 publications concluded that AM restorations were more accurate than conventionally made (cast or milled) ones. The most common finding was that AM restorations were more accurate than cast and demonstrated less or similar accuracy compared to milled ones (n = 10 studies). Detected marginal discrepancies mean values of the AM prosthesis varied from 23 to more than 200 µm, but most of them were categorized as clinically acceptable.

CONCLUSIONS

AM implant-supported fixed prostheses demonstrate similar accuracy compared to conventional and computer-aided design and computer-aided manufacturing techniques in vitro. Detected inaccuracies of AM restorations do not exceed clinically acceptable limits. Clinical studies with longer follow-up periods are needed to show the reliability of AM prostheses.

Biochemical Interaction between Materials Used for Interim Prosthetic Restorations and Saliva

The purpose of this study was to analyze the oxidative stress level and inflammatory status of saliva in the presence of certain materials used for obtaining interim prosthetic restorations. Four types of interim resin materials were investigated: a pressure/heat-cured acrylic resin (Superpont C+B, SpofaDental a.s Czech Republic, /KaVo Kerr Group), a milled resin (Telio CAD polymethyl methacrylate, Ivoclar Vivadent AG, Liechtenstein), a 3D printed resin (NextDent C&B MFH, NextDent by 3D Systems, the Netherlands), and a pressure/heat-cured micro-filled indirect composite resin (SR Chromasit, Ivoclar Vivadent AG, Liechtenstein). The disk-shaped resin samples (30 mm diameter, 2 mm high) were obtained in line with the producers' recommendations. The resulting resin specimens were incubated with saliva samples collected from twenty healthy volunteers. In order to analyze the antioxidant activity of the tested materials, certain salivary parameters were evaluated before and after incubation: uric acid, gamma glutamyl transferase (GGT), oxidative stress responsive kinase-1 (OXSR-1), and total antioxidant capacity (TAC); the salivary levels of tumor necrosis factor (TNFα) and interleukin-6 (IL-6) (inflammatory markers) were measured as well. The obtained results are overall favorable, showing that the tested materials did not cause significant changes in the salivary oxidative stress level and did not influence the inflammatory salivary status.

Accuracy of Additively Manufactured and Milled Interim 3-Unit Fixed Dental Prostheses

PURPOSE

To investigate the accuracy of additive manufacturing (AM) by means of internal fit of fixed dental prostheses (FDPs) fabricated with two AM technologies using different resins and printing modes (validated vs non-validated) compared to milling and direct manual methods.

MATERIAL AND METHODS

Sixty 3-unit interim FDPs replacing the first mandibular molar were divided into 6 groups (n = 10): manual (Protemp 4), milled (Telio-CAD), and AM groups were subdivided based on AM technology (direct light processing (Rapidshape P30 [RS]) and stereolithography (FormLabs 2 [FL])) and the polymer type (P-Pro-C&B [St] and SHERAprint-cb [Sh]) (RS-St, RS-Sh, FL-St, FL-Sh). Validated (RS-Sh and RS-St) or non-validated (FL-St and FL-Sh) modes were adopted for AM. The specimens were scanned to 3D align (GOM inspect) according to the triple scan method. The internal space between the FDPs and preparation surfaces in four sites (marginal, axial, occlusal, and total) was measured using equidistant surface points (GOM Inspect). Statistical analysis was done using Kruskal Wallis and Dunn post-hoc tests. (α = .05).

RESULTS

One AM group (FL-Sh) and milling exhibited better adaptation compared to manual and RS-St at molar site (P<.05). FDPs with St resin (FL-St and RS-St) displayed bigger marginal space than milled, FL-Sh, and RS-Sh. The non-validated printing mode showed better mean space results (P<.05) with higher predictability and repeatability (P<.001).

CONCLUSIONS

The AM interim FDPs tested provided valid alternatives to the milled ones in regard to their accuracy results. The printing mode, resin, and the AM technology used significantly influenced the manufacturing accuracy of interim FDPs, particularly at the marginal area. The non-validated printing mode with lower-cost 3D printers is a promising solution for clinical applications. This article is protected by copyright. All rights reserved.

Influence of the base design on the accuracy of additive manufac tured casts measured using a coordinate measuring machine

PURPOSE

To measure the accuracy of the additively manufactured casts with 3 base designs: solid, honeycomb-structure, and hollowed bases.

METHODS

A virtual cast was used to create different base designs: solid (S Group), honeycomb-structure (HC group), and hollowed (H group). Three standard tessellation language files were used to fabricate the specimens using a material jetting printer (J720 Dental; Stratasys) and a resin (VeroDent MED670; Stratasys) (n=15). A coordinate measuring machine was selected to measure the linear and 3D discrepancies between the virtual cast and each specimen. Shapiro-Wilk test revealed that all the data was not normally distributed (P<.05). Kruskal Wallis and Mann Whitney U tests were used (α=.05).

RESULTS

The S group obtained a median ±interquartile range 3D discrepancy of 53.00 ±73.25 µm, the HC group of 58.00 ±67.25 µm, and the H group of 34.00 ±45.00 µm. Significant differences were found in the x- (P<.001), y- (P<.001), and z-axes (P<.001), and 3D discrepancies among the groups (P<.001). Significant differences were found between the S and H groups (P=.002) and HC and H groups (P<.001) on the x-axis; S and H groups (P<.001) and HC and H groups (P<.001) on the y-axis; S and H groups (P<.001) and HC and H groups (P<.001) on the z-axis; and S and H groups (P<.001) and HC and H groups (P<.001) on the 3D discrepancy.

CONCLUSIONS

The base designs influenced on the accuracy of the casts but all the specimens obtained a clinically acceptable manufacturing range. The H group obtained the highest accuracy.

3D printing parameters, supporting structures, slicing, and post-processing procedures of vat-polymerization additive manufacturing technologies: A narrative review

OBJECTIVE

To review the elements of the vat-polymerization workflow, including the 3D printing parameters, support structures, slicing, and post-processing procedures, as well as how these elements affect the characteristics of the manufactured dental devices.

DATA

Collection of published articles related to vat-polymerization technologies including manufacturing workflow description, and printing parameters definition and evaluation of its influence on the mechanical properties of vat-polymerized dental devices was performed.

SOURCES

Three search engines were selected namely Medline/PubMed, EBSCO, and Cochrane. A manual search was also conducted.

STUDY SELECTION

The selection of the optimal printing and supporting parameters, slicing, and post-processing procedures based on dental application is in continuous improvement. As well as their influence on the characteristics of the additively manufactured (AM) devices such as surface roughness, printing accuracy, and mechanical properties of the dental device.

RESULTS

The accuracy and properties of the AM dental devices are influenced by the technology, printer, and material selected. The printing parameters, printing structures, slicing methods, and the post-processing techniques significantly influence on the surface roughness, printing accuracy, and mechanical properties of the manufactured dental device; yet, the optimization of each one may vary depending on the clinical application of the additively manufactured device.

CONCLUSIONS

The printing parameters, supporting structures, slicing, and post-processing procedures have been identified, but additional studies are needed to establish the optimal manufacturing protocol and enhance the properties of the AM polymer dental devices.

CLINICAL SIGNIFICANCE

The understanding of the factors involved in the additive manufacturing workflow leads to a printing success and better outcome of the additively manufactured dental device.

Additively Manufactured Ingot for Interim Dental Restorations Fabrication Using a Chairside Milling Machine

This manuscript describes a technique to fabricate additively manufactured ingots for producing tooth- and implant-supported interim dental restorations using a chairside milling machine. The technique aimed to ease the additively manufactured interim restoration's manufacturing by using a chairside milling machine, optimize the manufacturing workflow time, and eliminate the surface roughness of additively manufactured restorations.

The Effect of Build Orientation on the Dimensional Accuracy of 3D-Printed Mandibular Complete Dentures Manufactured with a Multijet 3D Printer

PURPOSE

To compare the dimensional accuracy of 3D-printed mandibular complete dentures with different build orientations.

MATERIAL AND METHODS

A mandibular complete denture was digitized as a virtual reference file. The reference file was 3D-printed at the 0°, 45°, and 90° build orientations with a MultiJet 3D printer (Projet MJP 3600 Dental, 3D systems, Rock Hill, SC). A total of 27 complete dentures were 3D-printed with 9 samples for each orientation. All printed dentures were digitized and separated into teeth, denture extension and intaglio test surfaces. The dimensional accuracy (in root mean square, RMS) was evaluated by comparing whole denture and 3 test surfaces with the reference file. One-way analysis of variance (ANOVA) and a Post-Hoc all pairs Bonferroni test were used to determine statistical differences (α = 0.05).

RESULTS

For the dimensional accuracy on whole denture, the 45° build orientation group showed the smallest RMS (0.170 ± 0.043 mm) than those of the 0° build orientation group (0.185 ± 0.060 mm, p < 0.001) and 90° build orientation group (0.183 ± 0.044 mm, p < 0.001). For the dimensional accuracy on the teeth, denture extension and intaglio test surfaces, the 45° build orientation group also show the smallest RMS values (0.140 ± 0.044 mm at teeth surface, 0.176 ± 0.058 mm at denture extension and 0.207 ± 0.006 mm at intaglio surface). The 0°and 90° build orientation groups had similar accuracy at the teeth (0.149 ± 0.056 mm versus 0.154 ± 0.056 mm, p = 0.164) and denture extension surfaces (0.200 ±0.025 mm vs 0.196 ± 0.013 mm, p = 1.000). However, 0° build orientation group (0.228 ± 0.010 mm) has significantly higher RMS values then those of 90° build orientation group (0.218 ± 0.057 mm) in the intaglio surface (p = 0.032). The teeth surfaces were most accurate in each build orientation groups, while the intaglio surfaces were least accurate.

CONCLUSIONS

The build orientation affected the dimensional accuracy of 3D-printed mandibular complete dentures, and the 45° build orientation resulted in the most accurate 3D-printed denture from a MultiJet 3D printer.

Fracture resistance of additive manufactured and milled implant-supported interim crowns

STATEMENT OF PROBLEM

Interim dental prostheses can be fabricated by using subtractive or additive manufacturing technologies. However, the fracture resistance of implant-supported interim crowns fabricated by using vat-polymerization additive manufacturing methods remains unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the fracture resistance of anterior and posterior screw-retained implant-supported interim crowns fabricated by using subtractive and vat-polymerization direct light processing (DLP) additive manufacturing procedures.

MATERIAL AND METHODS

An implant (Zinic Implant RP ∅4.0×10 mm) was placed in a 15×15-mm polymethylmethacrylate block. An implant abutment (ZiaCam, nonrotatory RP) was positioned on each implant. The virtual implant abutment standard tessellation language (STL) file provided by the manufacturer was imported into a software program (Exocad v2.2 Valletta) to design 2 anatomic contour crowns, a maxillary right central incisor (anterior group) and a maxillary right premolar (posterior group). Each group was subdivided into 2 subgroups depending on the manufacturing method: milled (milled subgroup) and additive manufacturing (additive manufacturing subgroup). For the milled subgroup, an interim material (Vivodent CAD Multi) and a milling machine were used to fabricate all the specimens (N=40, n=10). For the additive manufacturing subgroup, a polymer interim material (SHERAprint-cb) and a DLP printer (SHERAprint 30) were used to manufacture all the specimens at a 50-μm layer thickness and 45-degree build orientation as per the manufacturer's instructions. Then, each specimen was cemented to an implant abutment by using composite resin cement (Multilink Hybrid Abutment HO) as per the manufacturer's instructions. A universal testing machine was used for fracture resistance analysis, and the failure mode was recorded. The Shapiro-Wilk test revealed that data were normally distributed. One-way ANOVA and Tukey multiple comparison were selected (α=.05).

RESULTS

One-way ANOVA revealed significant differences among the groups (P<.05). The anterior milled subgroup obtained a significantly higher fracture resistance mean ±standard deviation value of 988.4 ±54.8 N compared with the anterior additive manufacturing subgroup of 636.5 ±277.1 N (P<.001), and the posterior milled subgroup obtained significantly higher mean ±standard deviation of 423.8 ±68 N than the additive manufacturing subgroup of 321.3 ±128.6 N (P=.048). All groups presented crown fracture without abutment fracture.

CONCLUSIONS

Manufacturing procedures and tooth type influenced the fracture resistance of screw-retained implant-supported interim crowns. Milled specimens obtained higher fracture resistance compared with the DLP additive manufacturing groups. The anterior group was higher than the posterior group.

A Review of 3D Printing in Dentistry: Technologies, Affecting Factors, and Applications

Three-dimensional (3D) printing technologies are advanced manufacturing technologies based on computer-aided design digital models to create personalized 3D objects automatically. They have been widely used in the industry, design, engineering, and manufacturing fields for nearly 30 years. Three-dimensional printing has many advantages in process engineering, with applications in dentistry ranging from the field of prosthodontics, oral and maxillofacial surgery, and oral implantology to orthodontics, endodontics, and periodontology. This review provides a practical and scientific overview of 3D printing technologies. First, it introduces current 3D printing technologies, including powder bed fusion, photopolymerization molding, and fused deposition modeling. Additionally, it introduces various factors affecting 3D printing metrics, such as mechanical properties and accuracy. The final section presents a summary of the clinical applications of 3D printing in dentistry, including manufacturing working models and main applications in the fields of prosthodontics, oral and maxillofacial surgery, and oral implantology. The 3D printing technologies have the advantages of high material utilization and the ability to manufacture a single complex geometry; nevertheless, they have the disadvantages of high cost and time-consuming postprocessing. The development of new materials and technologies will be the future trend of 3D printing in dentistry, and there is no denying that 3D printing will have a bright future.

Comparison of hardness and polishability of various occlusal splint materials

OBJECTIVES

To measure polishability of occlusal splint materials manufactured by various methods.

METHODS

Seven occlusal splint materials manufactured by four different methods - Heat cured (Vertex Rapid simplified Clear), CAD-milled (Ceramill a-splint), Vacuum-formed (Proform splint) and 3D-printed (Freeprint Ortho, KeySplint Soft, DentaClear and FreePrint Splint 2.0) were tested for gloss, roughness, and surface hardness and elastic modulus. For all groups, the tests were repeated with the materials polished with three different polishing burs, pumice and high shine. All polishing procedures were standardised by applying the force of 1 N for 1 min at the set speed. 3D printed materials were further tested with additional specimens manufactured at different printing angles of 0°, 45° and 90°. Data was statistically analysed using ANOVA (SPSS Version 26) and MatLab (R2020a). Polished surfaces of each specimen were analysed under scanning electron microscope.

RESULTS

Vacuum-formed materials showed the highest polishability (80.61 ± 0.98 GU) with no statistical significance to heat-cured or CAD-milled (p = 1.00). Pumice and high shine polish significantly improved the gloss for all groups. The mean gloss and surface roughness for all 3D-printed materials ranged from 75.24 ± 25.05 GU to 0.18 ± 0.21 GU and 2.73 ± 3.18 μm to 0.06 ± 0.01 μm, which was significantly lower (p < 0.001) than heat-cured, CAD-milled and vacuum-formed materials. The highest hardness (0.40 ± 0.009 GPa), elastic modulus (6.06 ± 1.49 GPa) and gloss were found when materials were 3D-printed at 45°, with the lowest surface roughness.

CONCLUSION

Statistically significant differences in polishability were found among the different occlusal splint materials. The polishability and surface hardness of 3D-printed occlusal splint materials was influenced by the print angle. The 0° 3D-printed occlusal splint materials produced the highest gloss and the lowest surface roughness pre-polished, indicating that no polishing is required. While the 3D-printed occlusal splint materials at 45^oand 90° required polishing with burs, pumice and high shine to reduce the surface roughness, there were layering structures created during printing.

Influence of the Rinsing Postprocessing Procedures on the Manufacturing Accuracy of Vat-Polymerized Dental Model Material

PURPOSE

To evaluate the influence of rinsing solvents, namely isopropyl alcohol (IPA) and tripropylene glycol monomethyl ether (TPM), and rinsing times (5-, 7-, 9-, and 11-minutes) for the postprocessing procedures on the manufacturing accuracy of an additively manufactured dental model resin material.

MATERIAL AND METHODS

The standard tessellation language (STL file) of the digital design of a bar (15 mm × 4 mm × 3 mm) was obtained. A resin dental material (E-Model Light; Envisiontec, Dearborn, MI) and a 3D printer (VIDA HD; Envisiontec) was selected to manufacture all the specimens using the STL file following the recommended printing parameters at a room temperature of 23 °C. Two groups were generated based on the rinsing solvent used on the postprocessing procedures, namely isopropyl alcohol (IPA-group) and tripropylene glycol monomethyl ether (TPM-group). Each group was further divided into 4 subgroups (IPA-1 to IPA-4 and TPM-1 to TPM-4) depending on the rinsing time performed (5-, 7-, 9-, and 11-minutes). Twenty specimens per subgroup were fabricated. The dimensions (length, width, and height) of all the specimens were measured using a low force digital caliper (Absolute Low Force Caliper Series 573; Mitutoyo, Takatsu-ku, Kawasaki, Kanagawa). Each measurement was performed 3 times and the mean value determined. The volume of each specimen was calculated using the formula V = l × w × h. Shapiro-Wilk test revealed that the data were not normally distributed. Data were analyzed using Kruskal-Wallis (α = 0.05), followed by pairwise Mann-Whitney U tests (α = 0.0018).

RESULTS

The IPA groups obtained significantly lower trueness and precision values compared with TPM groups (p < 0.0018). Among the IPA groups, IPA-1 subgroup obtained the highest trueness and precision values compared to the rest of the IPA subgroups. The TPM-1 and TPM-2 subgroups obtained the highest trueness and prevision values among the TPM group and among all the groups tested. No significant difference was found between the TMP-1 and TPM-2 subgroups (p > 0.0018).

CONCLUSIONS

None of the manufacturing workflows tested were able to manufacture a perfect match of the bar virtual design dimensions. TPM solvent group obtained higher trueness and precision values compared to the IPA solvent group. The IPA-1 subgroup that replicated the manufacturer´s recommendations obtained the highest manufacturing accuracy among the IPA subgroup. TPM solvent used in a rinsing ultrasonic bath between 3 and 4 minutes followed by a second ultrasonic clean bath between 2 and 3 minutes of the just printed vat polymerized dental model specimens obtained the highest manufacturing accuracy values.

Accuracy of 3D printed polymers intended for models and surgical guides printed with two different 3D printers

The purpose of the study was to evaluate the accuracy: trueness and precision of photopolymers used for dental models and surgical guides printed with two different digital light processing (DLP) printers. Forty specimens of four materials; E-dentstone^®, E-shell^®, NextDent™ Model, NextDent™ SG, and two designs; models A and B (n=5), were manufactured (DDDP, EvoDent). Trueness was evaluated by comparing values for 26 parameters with the CAD models' reference values and precision through standard deviation. The trueness and precision were higher for linear than for angle parameters. X- and Y-axes showed higher trueness than Z-axis and model B higher trueness than model A. The conclusions are; the accuracy is dependent on the design of the object. The linear precision appears to be high. The highest trueness was observed for a surgical guide polymer (NextDent™ SG). The definition of clinically relevant accuracy and acceptable production tolerance should be evaluated in future studies.

Effect of Printing Direction on the Accuracy of 3D-Printed Dentures Using Stereolithography Technology

This study evaluated the effects of the differences in the printing directions of stereolithography (SLA) three-dimensional (3D)-printed dentures on accuracy (trueness and precision). The maxillary denture was designed using computer-aided design (CAD) software with an STL file (master data) as the output. Three different printing directions (0°, 45°, and 90°) were used. Photopolymer resin was 3D-printed (n = 6/group). After scanning all dentures, the scanning data were saved/output as STL files (experimental data). For trueness, the experimental data were superimposed on the master data sets. For precision, the experimental data were selected from six dentures with three different printing directions and superimposed. The root mean square error (RMSE) and color map data were obtained using a deviation analysis. The averages of the RMSE values of trueness and precision at 0°, 45°, and 90° were statistically compared. The RMSE of trueness and precision were lowest at 45°, followed by 90°; the highest occurred at 0°. The RMSE of trueness and precision were significantly different among all printing directions (p < 0.05). The highest trueness and precision and the most favorable surface adaptation occurred when the printing direction was 45°; therefore, this may be the most effective direction for manufacturing SLA 3D-printed dentures.

A Review on the Biocompatibility of PMMA-Based Dental Materials for Interim Prosthetic Restorations with a Glimpse into their Modern Manufacturing Techniques

This paper's primary aim is to outline relevant aspects regarding the biocompatibility of PMMA (poly(methyl methacrylate))-based materials used for obtaining interim prosthetic restorations, such as the interaction with oral epithelial cells, fibroblasts or dental pulp cells, the salivary oxidative stress response, and monomer release. Additionally, the oral environment's biochemical response to modern interim dental materials containing PMMA (obtained via subtractive or additive methods) is highlighted in this review. The studies included in this paper confirmed that PMMA-based materials interact in a complex way with the oral environment, and therefore, different concerns about the possible adverse oral effects caused by these materials were analyzed. Adjacent to these aspects, the present work describes several advantages of PMMA-based dental materials. Moreover, the paper underlines that recent scientific studies ascertain that the modern techniques used for obtaining interim prosthetic materials, milled PMMA, and 3D (three-dimensional) printed resins, have distinctive advantages compared to the conventional ones. However, considering the limited number of studies focusing on the chemical composition and biocompatibility of these modern interim prosthetic materials, especially for the 3D printed ones, more aspects regarding their interaction with the oral environment need to be further investigated.

Additive manufacturing of dental polymers: An overview on processes, materials and applications

Additive manufacturing (AM) processes are increasingly used in dentistry. The underlying process is the joining of material layer by layer based on 3D data models. Four additive processes (laser stereolithography, polymer jetting, digital light processing, fused deposition modeling) are mainly used for processing dental polymers. The number of polymer materials that can be used for AM in dentistry is small compared to other areas. Applications in dentistry using AM are limited (e.g. study models, maxillo-facial prostheses, orthodontic appliances etc.). New and further developments of materials are currently taking place due to the increasing demand for safer and other applications. Biocompatibility and the possibility of using materials not only as temporarily but as definitive reconstructions under oral conditions, mechanically more stable materials where less or no post-processing is needed are current targets in AM technologies. Printing parameters are also open for further development where optical aspects are also important.

An update on applications of 3D printing technologies used for processing polymers used in implant dentistry

Polymer additive manufacturing (AM) technologies have been incorporated in digital workflows within implant dentistry. This article reviews the main polymer AM technologies in implant dentistry, as well as their applications in the field such as manufacturing surgical guides, custom trays, working implant casts, and provisional restorations.

A review on chemical composition, mechanical properties, and manufacturing work flow of additively manufactured current polymers for interim dental restorations

OBJECTIVES

Additive manufacturing (AM) technologies can be used to fabricate 3D-printed interim dental restorations. The aim of this review is to report the manufacturing workflow, its chemical composition, and the mechanical properties that may support their clinical application.

OVERVIEW

These new 3D-printing provisional materials are typically composed of monomers based on acrylic esters or filled hybrid material. The most commonly used AM methods to manufacture dental provisional restorations are stereolithography (SLA) and material jetting (MJ) technologies. To the knowledge of the authors, there is no published article that analyzes the chemical composition of these new 3D-printing materials. Because of protocol disparities, technology selected, and parameters of the printers and material used, it is notably difficult to compare mechanical properties results obtained in different studies.

CONCLUSIONS

Although there is a growing demand for these high-tech restorations, additional information regarding the chemical composition and mechanical properties of these new provisional printed materials is required.

CLINICAL SIGNIFICANCE

Additive manufacturing technologies are a current option to fabricate provisional dental restorations; however, there is very limited information regarding its chemical composition and mechanical properties that may support their clinical application.