Evaluating the accuracy (trueness and precision) of interim crowns manufactured using digital light processing according to post-curing time: An in vitro study

Edge strength of definitive 3D-printed restorative resin materials

STATEMENT OF THE PROBLEM

With the advent of digital technology in dentistry, manual methods for creating dental restorations are being replaced by digital CAD/CAM processes involving three-dimensional (3D) printing and milling. Marginal degradation and chipping are common issues, yet the literature on the edge strength of 3D-printed restorative materials remains limited. Uncertainties remain regarding the impact of print orientation on edge strength, necessitating further investigation to ensure clinical efficacy.

PURPOSE

The purpose of this study was to evaluate the influence of print orientation on the edge strength of 3D-printed dental restorative resins indicated for definitive and interim use and compare them with milled materials.

MATERIALS AND METHODS

Specimens (14 ×14 ×2 mm) were additively manufactured in three 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 post-processing parameters set according to manufacturer recommendations. Edge strength was measured at 0.5 mm and 1 mm distance from the edge using a CK 10 testing machine. Specimens were tested in dry conditions (0.5 mm) and after 48 hours of storage in artificial saliva at 37°C (0.5 mm and 1 mm). Failure modes were analysed visually and using optical and scanning electron microscopy. Filler content was assessed using the Ash method, and statistical analysis was conducted using ANOVA. Pearson correlation was used to assess the relationship between filler weight and edge strength.

RESULTS

Due to severe deformation before chipping under load at both distances, data for the 3D-printed and milled interim materials were excluded. The 90-degree printing orientation of definitive materials demonstrated significantly higher edge strength after 48 hours in artificial saliva compared to the 0- and 45-degree orientations (P < 0.001). Significant differences were observed between the 3D printed and milled materials at 0.5 (P < 0.001) mm but not at 1 mm (P ≥ 0.804). Failure modes were predominantly surface indentation without visible cracking (58 %), followed by surface indentation with visible cracking (17 %), edge chipping (0.2 %), and specimen fracture (13 %). A non-significant negative correlation was observed between filler weight and edge strength (r = 0.161, P < 0.680).

CONCLUSIONS

Based on the current findings, 3D printing definitive resin materials at a 90-degree orientation provided increased edge strength. 3D-printed materials can better resist crack propagation compared to milled composites.

CLINICAL IMPLICATIONS

Optimizing the print orientation to 90-degree can improve the edge strength of definitive 3D printed materials.

Effects of postcuring times on the trueness of 3D -printed dental inlays made with permanent resins

OBJECTIVE

The aim of this study was to evaluate the trueness of 3D-printed dental inlays fabricated using different permanent dental resins and subjected to distinct postcuring times.

MATERIALS AND METHODS

A total of 180 inlay specimens were fabricated and divided into nine groups of 20 specimens each. The inlays were first designed using 3D design software (Ansys SpaceClaim) and then transferred to a 3D printer. Using LCD technology, 60 inlays were fabricated from Senertek P-CrownV3 Ceramic (Senertek) resin, another 60 inlays from VarseoSmile Crown Plus (Bego) resin and the final 60 inlays from Saremco Print Crowntec (Crowntec) resin. Each of these three groups was divided into three equally sized subgroups (n = 20) cured with 2,000, 4,000 and 6,000 flashes, respectively, using the Otoflash G171 device (NK Optik, Germany). Then, the specimens were scanned and digitised using an intraoral digital scanner, and their trueness was evaluated by superimposing the digital measurements on the reference design and calculating their root mean squares (RMSs) and total overlap ratios (TORs). MANOVA was used to compare the measurements, and Tukey's test was utilised for the post hoc analysis.

RESULTS

Significant differences in trueness were observed among the inlays fabricated with different resin types (p < 0.001). The Crowntec resin had the lowest RMS (0.08 ± 0.018 mm) and the highest TOR (94.59 ± 2.49%), indicating the best trueness, while Senertek had the highest RMS (0.114 ± 0.017 mm) and the lowest TOR (80.15 ± 5.95%), reflecting the lowest trueness. The postcuring time also significantly affected the trueness of the inlays. The 6,000-flashes group had the lowest RMS (0.095 ± 0.02 mm), and the 4000-flashes group had the highest TOR (89.81 ± 0.5%). The interaction between the resin type and the postcuring time was significant for the TOR (p = 0.01), suggesting that trueness improvements are material dependent.

CONCLUSION

Both the resin type and the postcuring time significantly influenced the trueness of the 3D-printed dental inlay restorations. The Crowntec resin consistently exhibited superior trueness, and the Senertek resin demonstrated the lowest trueness. The optimal postcuring time varied by material, but 4,000 flashes generally provided favourable trueness outcomes. These findings highlight the importance of selecting an appropriate resin and optimising the postcuring parameters to enhance the trueness of dental inlays, potentially improving their clinical fit and longevity.

CLINICAL RELEVANCE

Appropriate resin selection and adherence to optimised postcuring protocols are essential for achieving clinically true 3D-printed restorations, ultimately improving their adaptations in dental applications.

A Novel 3D-Printing Model Resin with Low Volumetric Shrinkage and High Accuracy

This study aims to assess and compare the shrinkage, accuracy, and accuracy stability of a novel 3D-printing model resin and eight commercially available 3D-printing model resin materials. The experimental model resin was developed by our 3D-printing proprietary resin technology. Eight commercially available 3D-printing model resins were included for comparison. The AcuVol video imaging technique was used to test volumetric shrinkage. Full-arch tooth models were printed for each model resin via digital light processing (DLP) technology. The 3D average distance between the scanned model and the designed CAD digital file was applied to determine the dimensional accuracy of the 3D-printed full-arch tooth models. One-way ANOVA and Tukey's post hoc test (p < 0.05) were utilized to analyze the average values of volumetric shrinkage and 3D average distance (dimensional accuracy). The experimental model resin showed significantly lower volumetric shrinkage (7.28%) and significantly higher or higher accuracy and accuracy stability (11.66-13.77 µm from the initial day to four weeks) than the other commercially available model resins (7.66-11.2%, 14.03-41.14 µm from the initial day to four weeks). A strong correlation was observed between volumetric shrinkage and dimensional accuracy (Pearson correlation coefficient R = 0.7485). For clinically successful modelling applications in restorations, orthodontics, implants, and so on, the new 3D-printing model resin is a promising option.

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.

Factors affecting accuracy in the additive manufacturing of interim dental prostheses: A systematic review

STATEMENT OF PROBLEM

A systematic review of the effect of different factors on the accuracy of additively manufactured (AM) interim dental prostheses is lacking.

PURPOSE

The purpose of this systematic review was to identify potential factors that may affect the accuracy of AM interim dental prostheses.

MATERIAL AND METHODS

The review adhered to the guidelines outlined in the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement. The protocol was registered in the international prospective database of systematic reviews (PROSPERO) (CRD42024521564). The risk of bias in the included studies was assessed by using the Joanna Briggs Institute (JBI) checklist. Two reviewers performed an electronic search on the Web of Science, Scopus, PubMed, and Embase databases for articles published up to the end of 2023.

RESULTS

The electronic search resulted in 406 studies. After removing duplicates, 205 studies remained. Thirty-one studies (30 in vitro and 1 in vivo) were included and categorized into 6 types: AM material (type and composition), prosthetic factor (tooth type, restoration size, finish line, abutment taper), AM system (technique and printer), AM parameters (layer thickness, printing orientation), postprocessing (rinsing, postpolymerization), and aging.

CONCLUSIONS

The accuracy of AM interim dental prostheses is affected by factors that include the AM material, prosthetic factors, the AM system, the AM parameters, postprocessing, and aging.

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.

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

OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

3D Printing of Dental Prostheses: Current and Emerging Applications

Revolutionary fabrication technologies such as three-dimensional (3D) printing to develop dental structures are expected to replace traditional methods due to their ability to establish constructs with the required mechanical properties and detailed structures. Three-dimensional printing, as an additive manufacturing approach, has the potential to rapidly fabricate complex dental prostheses by employing a bottom-up strategy in a layer-by-layer fashion. This new technology allows dentists to extend their degree of freedom in selecting, creating, and performing the required treatments. Three-dimensional printing has been narrowly employed in the fabrication of various kinds of prostheses and implants. There is still an on-demand production procedure that offers a reasonable method with superior efficiency to engineer multifaceted dental constructs. This review article aims to cover the most recent applications of 3D printing techniques in the manufacturing of dental prosthetics. More specifically, after describing various 3D printing techniques and their advantages/disadvantages, the applications of 3D printing in dental prostheses are elaborated in various examples in the literature. Different 3D printing techniques have the capability to use different materials, including thermoplastic polymers, ceramics, and metals with distinctive suitability for dental applications, which are discussed in this article. The relevant limitations and challenges that currently limit the efficacy of 3D printing in this field are also reviewed. This review article has employed five major scientific databases, including Google Scholar, PubMed, ScienceDirect, Web of Science, and Scopus, with appropriate keywords to find the most relevant literature in the subject of dental prostheses 3D printing.

Antifungal activity, mechanical properties, and accuracy of three-dimensionally printed denture base with microencapsulated phytochemicals on varying post-polymerization time

BACKGROUND

Studies on the antifungal activity, flexural strength, Vickers hardness, and intaglio surface trueness of three-dimensionally printed (3DP) denture bases with microencapsulated phytochemicals with respect to changes in post-polymerization time (PPT) are lacking.

METHODS

Specimens of various shapes and dimensions were fabricated with a 3DP denture base resin mixed with 5 wt% phytoncide-filled microcapsules. Each specimen was subjected to different PPT protocols of 5, 10, 20, and 30 min. Specimens without microcapsules with 5-min PPT were used as the negative control group. Cell colonies were counted to evaluate antifungal activity. Three-point bending and Vickers hardness tests were performed to measure the flexural strengths and hardness of the specimens. Fourier-transform infrared spectrometry was used to inspect the degree of conversion (DC). The intaglio surface trueness was measured using root-mean-square estimates calculated by superimposition analysis. A non-parametric Kruskal-Wallis test or one-way analysis of variance was performed (α = 0.05).

RESULTS

The specimens with microcapsules and 10-min PPT showed the highest antifungal activity among the tested groups. Compared with the positive control group (5-min PPT), the specimens with PPTs of 10 min or longer showed significantly higher mean flexural strength, higher DC, greater hardness, and better trueness (all, P < 0.05). Except for the difference in antifungal activity, no statistically significant differences were detected between the specimens subjected to 10-, 20-, and 30-min PPT.

CONCLUSION

The 3DP denture base filled with microencapsulated phytoncide showed different antifungal activity and physical properties on changing PPT. The 3DP denture base containing phytoncide-filled microcapsules at 5 wt% concentration and subjected to 10-min PPT exhibited sufficient antifungal activity as well as mechanical properties and accuracy within clinical acceptance.

Additively Manufactured Surgical Implant Guides: A Review

Static computer assisted implant surgery (s-CAIS) is an integral part of the digital workflow in implant dentistry and provides the link between the virtual planning environment and surgical field. The accuracy of s-CAIS is influenced by many cumulative factors including the fit of the template which is related to the manufacturing process. This critical review provides an overview of the current research on additively manufactured surgical implant guides.

Extended Post-Curing Light Exposure and Sandblasting Effects on Surface Hydrophobicity of 3D-Printed Denture Base Resin

This in vitro study evaluated the surface hydrophobicity of 3D-printed denture base resin exposed to either an extended post-curing light exposure time or a sandblasting procedure. MATERIALS AND METHODS: Disk-shaped samples (diameter × height: 10 mm × 3 mm) were 3D-printed with stereolithography SLA technology using the denture-base resin. Samples were divided into three groups: control, extended UV-post-curing, and sandblasted. The surface roughness parameters for each group were calculated, and the surface hydrophobicity was evaluated by measuring the drop contact angle. Analysis was done using the T-test; significance was when p < 0.05. RESULTS: The comparison of surface roughness parameters showed significant differences between the control group and the sandblasted group (Sa: p = 0.001, Sz: p < 0.001, Str: p < 0.001, Spc: p = 0.044) as well as between the extended-cure group and the sandblasted group (Sa: p = 0.006, Sz: p < 0.001, Str: p < 0.001, Spc: p = 0.036) except for the Sdr measures. The surface hydrophobicity was also statistically lower in the sandblasted group compared to both the control and extended curing groups (p < 0.001). CONCLUSION: The sandblasting procedure created a less hydrophobic surface of the 3D-printed denture base resin, and the altered surface roughness could be a contributor to this observation.

Influence of 3D analysis software on measured deviations of CAD-CAM resin crowns from virtual design file: an in-vitro study

OBJECTIVES

To evaluate a nonmetrology-grade and a metrology-grade 3D analysis software when measuring the deviations of CAD-CAM fabricated crowns from the virtual design file.

MATERIALS AND METHODS

A right first molar on a mandibular dentate model was prepared and scanned by using an intraoral scanner, i500 (Medit). A complete coverage crown was designed in standard tessellation language format and 20 resin crowns were fabricated by using computer aided design-computer aided manufacturing (CAD-CAM). The crowns were then digitized by using the same intraoral scanner (test-scans). Root mean square (RMS) method was used to evaluate the deviations between the test-scans and the design file of the crowns on 3 surfaces (overall, external, and internal) by using a metrology-grade, Geomagic Control X (3D Systems) and a nonmetrology-grade, Medit Link (Medit) software. The data were analyzed with Welch two-sample t-tests to compare two software for the non-inferiority of the nonmetrology-grade software with a 50 µm threshold and the potential superiority of the metrology-grade software (α = 0.05).

RESULTS

The Welch two-sample t-tests for the non-inferiority analysis showed that the differences between the nonmetrology-grade and the metrology-grade software were below the threshold of 50 µm for each surface tested (p <.001). The differences between the two-tested software were nonsignificant for each surface analyzed when superiority was considered (p ≥.194).

CONCLUSION

The nonmetrology-grade software performed similar to the metrology-grade software when analyzing the deviations of CAD-CAM crowns. Therefore, the nonmetrology-grade 3D analysis software may be considered for the deviation measurements of similar restorations.

CLINICAL SIGNIFICANCE

The trueness of crowns after fabrication may affect their fit, and 3D analysis of trueness prior to the delivery appointment with the tested nonmetrology-grade software after fabrication may facilitate potential clinical adjustments and delivery of the crowns.