3D printing restorative materials using a stereolithographic technique: a systematic review

Simple post-curing methods to optimize the depth of cure and physicochemical properties of 3D printed resin

OBJECTIVES

This in vitro study evaluated the effect of different post-curing methods on the degree of conversion, mechanical properties, and color change of a 3D printing resin.

METHODS

Specimens of a 3D printing resin were subjected to different post-curing processes: CONo post-curing; PCC-Post-curing in a violet light chamber; VA-Post-curing with VALO; HC-Post-curing in an oven; HP-Post-curing in an autoclave; PCC+HC-Post-curing in a violet light chamber associated with an oven; PCC+HP-Post-curing in a light chamber associated with an autoclave. The 3D printing accuracy, flexural strength, flexural modulus, Knoop microhardness and degree of depth conversion, surface hardness before and after immersion in solvent, gloss and roughness before and after brushing cycles, and color change after aging in UV light were evaluated.

RESULTS

PCC+HC showed a significant reduction in length and no significant difference was detected in width. CO and VA showed higher distortion in thickness and PCC, HC and PCC+HP were statistically similar. PCC+HP had greater flexural strength and flexural modulus. All groups showed significantly decreased hardness after immersion in the solvent. The groups that associated PCC and heat had greater depth curing efficiency. PCC showed the lowest color change followed by PCC+HC and PCC+HP.

CONCLUSIONS

3D printed resins require additional polymerization methods for optimal physicochemical properties. Post-curing combining violet light and a heat source, oven, or autoclave significantly enhances the depth of cure and improves the optical and physicochemical properties of a 3D resin for indirect restoration.

CLINICAL SIGNIFICANCE

Post-curing methods that combine violet light and a heat source can increase the durability and performance of 3D printed resins for indirect restorations, potentially improving clinical outcomes by providing more reliable and durable restorations.

Comparing the Accuracy of Conventional Gypsum and 3D-Printed Dental Casts Using Three-Dimensional Analysis

INTRODUCTION

Dental impressions and casts play a critical role in dental care, facilitating diagnoses and the fabrication of prostheses. Traditional methods of fabrication involve elastomeric materials that are more prone to errors and patient discomfort. Digital advancements offer promising alternatives, yet their accuracy and applicability to military dentistry remain under-explored. This study evaluates the accuracy of digital casts produced with material available in the Military Health System compared to conventional methods.

MATERIALS AND METHODS

Using a digital (n = 10) and analog (n = 10) methodology casts were fabricated from a reference cast (n = 1). The reference and cast samples were scanned with a reference scanner to generate stereolithography files. These files were used to generate full arch, single crown, fixed dental prosthesis, and inlay digital casts which were then compared using a three-dimensional (3D) comparison software to evaluate accuracy. Root mean square values were obtained, giving a quantitative evaluation of the deviation of each sample from the reference cast. Statistical analysis consisted of a Shapiro-Wilk and Levene test to account for homogeneity of variances in each group. An ANOVA and Tukey post-hoc test were used to determine differences in accuracy among the full arch and a two-way ANOVA and Tukey post-hoc test evaluated differences in trueness among the casts of the individual preparations.

RESULTS

Analog full arch casts had an average root mean square of 106 ±19.18 µm when examining trueness and 12 ±2.58 µm for precision. Digital full arch casts had an average root mean square of 51.9 ±5.39 µm when examining trueness and 4.2 ±1.57 µm for precision. Overall digital casts surpassed analog counterparts in accuracy. Fixed dental prostheses were found to be the only group, which showed no statistically significant difference between digital and analog.

CONCLUSION

These findings validate the potential of digital workflows in enhancing the speed and accuracy of dental care in the Military Health System, while underscoring the need for further exploration and refinement in specific clinical contexts.

Effect of aging on optical behavior and color of 3D printing resin-based dental restorative materials

OBJECTIVES

To evaluate the influence of aging on color and optical properties of 3D printing resin-based dental restorative materials.

METHODS

Four 3D printing resin-based dental restorative materials (DFT- Detax Freeprint Temp; FT- Formlabs Temporary CB; FP- Formlabs Permanent Crown; and GCT- GC TempPrint) were evaluated. The structures were printed using digital light processing (DLP) (DFT and GCT groups) and stereolithography (SLA) (FT and FP groups) technologies. Samples (10 × 10 × 1 mm; n = 3) were printed in light (L) and medium (M) shades and at 0° and 90° and then polished to a thickness of 1.00 ± 0.01 mm with silicon carbide (SiC) sandpapers under water cooling. Artificial aging followed the ISO 4892-2 standard. 1) Color differences were evaluated using CIEDE2000 and perceptibility and acceptability thresholds (PT00 and AT00), 2) spectral reflectance (R%) and transmittance (T%) were measured and scattering (S) and absorption (K) coefficients, light reflectivity (RI), infinite optical thickness (X∞) pre- and post-aging were calculated using Kubelka-Munk method and Root Mean Square Error (RMSE) and Goodness of Fit (GFC) were used as performance optical behavior.

RESULTS

1) All 3D-printed dental resins evaluated, irrespectively of the printed angles, showed mean ΔE00 values above AT00 (.ΔE00>1.8), and FT-M and FP-M showed the least color changes among the evaluated materials, 2) GFC<0.999 and RMSE >2 % values were found between pre and post aging for R%, T%, S, K, RI and X∞ properties.

CONCLUSIONS

This study showed poor spectral match and comparative spectral values of R%, T%, S, K, RI and X∞ between after and before aging, resulting in unacceptable color changes. Printing orientation does not influence the change of the optical behavior of the evaluated materials after aging.

CLINICAL SIGNIFICANCE

Aging causes significant changes on the spectral optical behavior for the 3D-printed resin-based restorative materials studied, resulting in clinically unacceptable color changes.

Impact Absorption Power of Polyolefin Fused Filament Fabrication 3D-Printed Sports Mouthguards: In Vitro Study

BACKGROUND/AIM

This study aims to evaluate and compare the impact absorption capacities of thermoformed ethylene vinyl acetate (EVA) mouthguards and 3D-printed polyolefin mouthguards used in sports dentistry applications. The objective is to determine whether 3D-printed polyolefin mouthguards offer superior impact toughness compared to traditional EVA mouthguards commonly used in sports settings.

MATERIALS AND METHODS

Six material samples were assessed: five pressure-formed EVA mouthguards (PolyShok, Buffalo Dental, Erkoflex, Proform, and Drufosoft) and one 3D-printed synthetic polymer (polyolefin). The materials were evaluated using a modified American Society for Testing and Materials (ASTM) D256 Test Method A for Izod pendulum impact resistance of plastics. Polyolefin samples were 3D-printed using fused filament fabrication (FFF) technology. Notably, the FFF process included samples printed with notches placed either parallel or perpendicular to the build direction. This orientation served as a study factor, allowing for comparison of material behavior under different printing conditions. Impact testing was conducted using an Izod impact tester to assess the materials' performance under controlled impact conditions.

RESULTS

The study achieved a high power (1.0) in power analysis, indicating strong sensitivity to detect significant differences. Among molded materials, PolyShok showed significantly lower impact toughness compared to others (p = 0.06). The mean impact absorption of EVA materials was 5.4 ± 0.3 kJ/m2, significantly lower than polyolefin materials, which demonstrated 12.9 ± 0.7 kJ/m2 and superior performance (p = 0.0). Horizontal-notched polyolefin samples exhibited higher impact strength compared to vertical-notched samples (p = 0.009).

CONCLUSIONS

3D-printed polyolefin mouthguards exhibited significantly higher impact toughness than thermoformed EVA mouthguards. While EVA materials demonstrated structural robustness, their lower impact resistance and observed tearing in other test specimens suggest the need for alternative testing standards to better reflect real-world conditions. 3D-printed mouthguards fabricated with build orientations perpendicular to the direction of impact demonstrate significantly enhanced impact absorption. Further research into manufacturing methods and testing protocols is recommended to optimize mouthguard performance under impact scenarios.

[Effect of slurry proportion on the microstructure and properties of dental lithium disilicate ceramics manufactured through 3D printing]

OBJECTIVES

This study aims to use 3D prin-ting technology based on the principle of stereo lithography apparatus (SLA) to shape dental lithium disilicate ceramics and study the effects of different slurry proportions on the microstructure and properties of heat-treated samples.

METHODS

The experimental group comprised lithium disilicate ceramics manufactured through SLA 3D printing, and the control group comprised lithium disilicate ceramics (IPS e.max CAD) fabricated through commercial milling. An array of different particle sizes of lithium disilicate ceramic powder materials (nano and micron) was selected for mixing with photocurable acrylate resin. The proportion of experimental raw materials was adjusted to prepare five groups of ceramic slurries for 3D printing (Groups S1-S5) on the basis of rheological properties, stability, and other factors. Printing, debonding, and sintering were conducted on the experimental group with the optimal ratio, followed by measurements of microstructure, crystallographic information, shrinkage, and mechanical properties.

RESULTS

Five groups of lithium disilicate ceramic slurries were prepared, of which two groups with high solid content (75%) (Groups S2 and S3) were selected for 3D printing. X-ray diffraction and scanning electron microscopy results showed that lithium disilicate was the main crystalline phase in Groups S2 and S3, and its microstructure was slender, uniform, and compact. The average grain sizes of Groups S2 and S3 were (559.79±84.58) nm and (388.26±61.49) nm, respectively (P<0.05). Energy spectroscopy revealed that the samples in the two groups contained a high proportion of Si and O elements. After heat treatment, the shrinkage rate of the two groups of ceramic samples was 18.00%-20.71%. Test results revealed no statistical difference in all mechanical properties between Groups S2 and S3 (P>0.05). The flexural strengths of Groups S2 and S3 were (231.79±21.71) MPa and (214.86±46.64) MPa, respectively, which were lower than that of the IPS e.max CAD group (P<0.05). The elasticity modulus of Groups S2 and S3 were (87.40±12.99) GPa and (92.87±19.76) GPa, respectively, which did not significantly differ from that of the IPS e.max CAD group (P>0.05). The Vickers hardness values of Groups S2 and S3 were (6.53±0.19) GPa and (6.25±0.12) GPa, respectively, which were higher than that of the IPS e.max CAD group (P<0.05). The fracture toughness values of Groups S2 and S3 were (1.57±0.28) MPa·m0.5 and (1.38±0.17) MPa·m0.5, respectively, which did not significantly differ from that of the IPS e.max CAD group (P>0.05).

CONCLUSIONS

The combination of lithium disilicate ceramic powders with different particle sizes can yield a slurry with high solid content (75%) and suitable viscosity and stability. The dental lithium disilicate ceramic material is successfully prepared by using 3D printing technology. The 3D-printed samples show a small shrinkage rate after heat treatment. Their microstructure conforms to the crystal phase of lithium disilicate ceramics, and their mechanical properties are close to those of milled lithium disilicate ceramics.

Effect of surface conditioning on the adhesive bond strength of 3D-printed resins used in permanent fixed dental prostheses

OBJECTIVES

Although pre-treatment parameters for subtractive computer-aided design/computer-aided manufacturing (CAD/CAM) materials have been thoroughly investigated, data regarding additive restorative materials designed for permanent use in the oral cavity are scarce. This study investigated the effects of abrasive materials and blasting pressure on the bond strength of 3D-printed resins used in permanent restorations.

METHODS

A total of n = 44 test specimens additively manufactured from Formlabs' `Permanent Crown Resin' were prepared. Three groups with n = 11 specimens were airborne-particle abraded with 50 µm aluminium oxide at 1 bar, 2 bar or 3 bar. The control group did not receive any further airborne-particle abrasion after post-processing with 50 µm glass beads. Cylindrical superstructures were bonded to the prepared surfaces using RelyX Unicem 2. The bonded specimens were then subjected to artificial ageing via thermocycling. Subsequently, shear bond strength (sbs) tests were conducted. Data were analysed with the Kruskal-Wallis test (α = 0.05).

RESULTS

After post-processing with glass beads, average shear bond strength values of 10.13 ± 7.62 MPa were achieved. When using aluminium oxide and 1 bar blasting pressure, significantly higher average sbs values of 25.57 ± 7.04 MPa were revealed (p = 0.009). The bond strength increased with higher blasting pressures (28.14 ± 6.35 MPa at 2 bar (p = 0.005); 30.15 ± 6.46 MPa at 3 bar (p < 0.001)). However, the shear tests revealed increased failure within the specimen base at higher blasting pressures.

CONCLUSION

Bond strength significantly improved when airborne-particle abrasion with aluminium oxide was applied. However, increased airborne-particle abrasion pressure led to more failures at the base plate level of the specimens.

CLINICAL SIGNIFICANCE

Aluminium oxide increases the adhesive strength of 3D-printed dental restorative materials. Although the adhesive bond increased slightly with increasing airborne-particle abrasion pressure, the 3D restorative materials also exhibited an increased failure rate within the restorative material in the shear bond strength test with increasing blasting pressure.

Comparison of the friction resistance of 3D-printed polyurethane orthodontic brackets with and without zirconium oxide nanoparticles with conventional metal and ceramic brackets: An in vitro study

AIM

To compare the frictional resistance of 3D-printed zirconium oxide nanoparticles reinforced polyurethane orthodontic brackets, 3D-printed Polyurethane orthodontic brackets, conventional metal and ceramic brackets in an in vitro environment.

METHODS

Stereolithography was used to 3D print the polymer orthodontic brackets and zirconium oxide-reinforced polymer orthodontic brackets. Conventional metal brackets and conventional ceramic brackets were used as controls. The frictional force between the bracket and the archwire was measured under dry conditions with an Instron universal testing machine with a sliding velocity of 1mm/minute and a load cell of 50N. The Kruskal-Wallis test with post hoc test (Mann-Whitney U test) was used for statistical analyses (significance level P<0.05).

RESULTS

There is no significant difference observed between 3D-printed zirconium oxide-reinforced polymer orthodontic brackets and 3D-printed polymer orthodontic brackets. The frictional resistance was found to be the least in 3D-printed polyurethane brackets (1.3895+0.72583N), followed by 3D-printed zirconium oxide-reinforced polyurethane brackets (2.15+0.75683N), conventional metal brackets (2.348+0.82682N), and it was highest in conventional ceramic brackets (4.9675+0.88519N).

CONCLUSIONS

The incorporation of zirconium oxide nanoparticles increased the frictional resistance of 3D-printed polymer orthodontic brackets, but it was not statistically significant. Hence, zirconium oxide nanoparticles could be considered as a better reinforcement for polymer brackets for enhanced clinical utility.

Current developments in 3D printing technology for orthopedic trauma: A review

Three-dimensional (3D) printing technology has emerged as a revolutionary tool in orthopedic trauma surgery, offering unprecedented opportunities for personalized patient care. This comprehensive review explores the current developments and applications of 3D printing in orthopedic trauma, highlighting its potential to address complex surgical challenges. We provide an in-depth analysis of various 3D printing technologies applicable to orthopedic surgery, including vat photopolymerization, material extrusion, powder bed fusion, and sheet lamination. The review examines the use of 3D printing in preoperative planning, surgical simulation, and the creation of patient-specific implants and surgical guides. We discuss applications across different anatomical regions, including upper limb, lower limb, and pelvic and spinal trauma. Evidence from recent studies demonstrates that 3D printing-assisted surgeries can lead to reduced operative times, decreased blood loss, improved fracture reduction quality, and potentially better clinical outcomes. This review synthesizes the latest research and clinical experiences, providing insights into the current state of 3D printing in orthopedic trauma and its future perspectives. As the technology continues to evolve, 3D printing holds promise for increasingly personalized and effective treatments in orthopedic trauma care, potentially transforming surgical practices and improving patient outcomes.

Effect of various solvents on the repairability of aged CAD/CAM provisional restorative materials with flowable resin composite: an in vitro study

BACKGROUND

Increased bond strength between aged CAD/CAM (Computer-Aided Design and Computer-Aided Manufacturing) provisional restorative materials is essential for reparability. This study investigated the impact of three different solvents and airborne-particle abrasion on the shear bond strength (SBS) of aged CAD/CAM provisional restorative materials, which are milled PMMA and 3D-printed resin with flowable resin composite.

METHODS

3D-printed resin and milled PMMA (N = 160 per type) were fabricated into cylindrical shapes (5 mm in diameter, 5 mm in height), aged by 5,000 thermocycling cycles, and randomize divided at random into five groups (N = 32) based on surface modification protocols: control; non-surface modification, MEK; application with methyl ethyl ketone, THF; application with tetrahydrofuran, Alc; application with isopropyl alcohol, and APA; airborne-particle abrasion with 50-µm alumina oxide particle. The shear bond strength was tested by a universal testing machine with a notch-edged blade placed parallel to the bonded interphase and a crosshead speed of 1 mm/min until failure occurs. Failure modes analyzed under a ×40 stereomicroscopy. Scanning electron microscopy (SEM) at ×1000 magnification was used to evaluate the qualitative surface morphology (N = 2). The surface roughness was measured using a noncontact surface roughness analyzer at ×50 magnification (N = 10). A high-performance adsorption analyzer was used to determine the specific surface area (N = 10), and the data were analyzed two-way ANOVA with Bonferroni post-hoc test.

RESULTS

SBS results (mean (95% confidence interval) in MPa) revealed that for both the 3D-printed resin and milled PMMA, the samples in the MEK (3D-printed, 23.2 (21.1-25.2); milled, 16.9 (15.3-18.5)), THF (3D-printed, 27.2 (26.0-28.5); milled,18.4 (16.8-20.0)), and APA groups (3D-printed, 27.9 (26.1-29.8); milled, 19.0 (17.2-20.7)) had significantly greater SBSs than did the samples in the Alc (3D-printed, 16.1 (14.4-17.7); milled, 12.2 (10.5-13.9)) and control groups (3D-printed, 11.7 (10.3-12.9); milled, 11.6 (10.8-12.4)). Compared with milled PMMA, 3D-printed resin presented a greater SBS across all surface modifications, except in the control group, where milled PMMA performed better. Failure mode analysis revealed total adhesive failure in the control and Alc groups, whereas APA resulted in 50% cohesive failure, mixed failure was shown more in 3D-printed resin THF and MEK groups (30%) compared to milled PMMA, THF and MEK group groups (10%). SEM analysis indicated that surface modifications produced rougher surfaces, The surface roughness (µm) was highest in the APA groups for both materials (3D-printed, 1834.2 (1803.8-1864); milled, 1052.8 (1027.0-1078.5)). The specific surface area (m2/g) was highest in the THF (5.22 (5.18-5.26)), MEK (5.18 (5.11-5.25)) and APA groups (5.17 (5.07-5.26)) of milled PMMA, but in the 3D-printed resin, the THF (4.95 (4.84-5.07)) and MEK groups (4.83 (4.77-4.89)) exhibited highest specific surface area.

CONCLUSION

The application of APA techniques and surface modification using THF and MEK solvents can enhance the shear bond strength of aged milled PMMA and 3D-printed resin provisional restorative materials to flowable resin composites, as compared to the Alc and control groups. Additionally, the effectiveness of the surface modification of APA, THF, and MEK is indicated by dominant cohesive and mixed failure. SEM, surface roughness, and specific surface area indicated that surface morphology change in both CAD/CAM provisional restorative materials.

Effects of post-polymerization on stainability and surface roughness of 3D printed composite resin

STATEMENT OF PROBLEM

Although the post-polymerization is a necessary step to attain the final properties and color of the 3-dimensionally (3D) printed composite resins, research on its effects on color change and surface roughness is lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of post-polymerization time and additional placement in boiling water on the color change and surface roughness of 3D printed composite resins after exposure to coffee for 30 days.

MATERIAL AND METHODS

Sixty disk-shaped specimens (Ø10×2 mm) were 3D printed with composite resin (Crowntec). The specimens were randomly divided into 6 groups (n=10), according to the post-polymerization process at 3 different times (2×5, 2×10, and 2×20 minutes) and depending on subsequent placement in boiling water. The color differences (ΔE00) between the baseline and each aging period (1, 7, 15, and 30 days) were determined by using a spectrophotometer. After 30-day aging period, ΔL*, Δa*, and Δb* values were calculated. The surface roughness (Ra) was measured at various aging periods (initial, 7, 15, and 30 days) by a 3D noncontact optical profilometer. The data were analyzed using 2-way repeated measures ANOVA and 1-way ANOVA tests for each aging period followed by Tukey tests (α=.05).

RESULTS

As the post-polymerization time increased, a significant decrease was found in ΔE00 values (P<.001), while no significant difference was found in Ra values (P=.554). The values of ΔE00 and Ra increased with the aging period (P<.001). Additional placement in boiling water resulted in a statistically significant decrease in both ΔE00 and Ra values (P<.001). As the post-polymerization time increased, the Δa* and Δb* values decreased, while the negative ΔL* values increased (P<.001), except for Δa* between 2×10 and 2×20 (P=.175). Additional placement in boiling water resulted in a significant decrease in Δa* and Δb* values and an increase in the negative ΔL* values (P<.001), except for Δa* in 2×20 (P=.379).

CONCLUSIONS

An increase in post-polymerization time resulted in reduced stainability, while additional placement in boiling water led to reduced stainability and roughness. When subsequently placed in boiling water, the post-polymerization time had no effect on either stainability or roughness.

Mechanical Properties of 3D Printed vs. Subtractively Manufactured Composite Resins for Permanent Restorations: A Systematic Review

OBJECTIVE

To conduct a systematic review on the mechanical properties of 3D printed resin-based composites when compared with those of subtractively manufactured resin-based composites.

MATERIALS AND METHODS

In vitro studies comparing the mechanical properties of additively and subtractively manufactured resin-based composites were sought. A systematic search, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), was performed on four databases (PubMed, Embase, Web of Science, and Scopus) for articles published until 23 December 2024. The quality of the studies was assessed with the QUIN tool (risk-of-bias tool for assessing in vitro studies conducted in dentistry) and those assessed with a high risk of bias were excluded.

RESULTS

Of the 1058 screened articles, 13 were included in this review. A noticeable heterogeneity emerged in the methodologies employed, mainly regarding samples' fabrication techniques, materials involved, and parameters analyzed. The most investigated mechanical property was fracture resistance, followed by microhardness, flexural strength, and wear behavior. Among the tested materials, the most used 3D printable resins were VarseoSmile Crown Plus (Bego) and Crowntec (Saremco Dental), whereas for the subtractive groups, the most investigated was Brilliant Crios (Coltène).

CONCLUSIONS

The mechanical properties of 3D printed resins designed for permanent restorations are still lower than those of their subtractively manufactured counterparts. Moreover, in the long term, the degradation processes that inevitably occur might significantly increase their chances of failure.

Dimensional accuracy of additive and subtractive manufactured ceramic-reinforced hybrid composite inlays: a CBCT-based in vitro study

The dimensional accuracy of digitally processed inlays is often questioned because of inherent manufacturing inconsistencies associated with computer-aided design and manufacturing (CAD/CAM). This study aimed to compare the absolute marginal discrepancy (AMD), marginal gap (MG), internal gap (IG), and overall discrepancy (OD) of three-dimensional (3D) printed, milled and conventional inlays. Forty resin dies were 3D-printed from a class II mesiococclusodistal preparation on a typodont and randomly distributed into four groups of 10 each. Optical impressions were taken for three groups to fabricate CAD/CAM inlays: Group PVC, 3D printed VarseoSmile Crownplus; Group PVT, 3D printed VarseoSmile TriniQ; and Group MVE, milled using Vita Enamic. For Group CGP (control), CGP was conventionally fabricated using Gradia Plus. These inlays were stabilized on dies and subjected to cone‒beam computed tomography to measure discrepancies in mesiodistal and buccolingual sectional images. All the discrepancies differed significantly among the groups (one-way ANOVA, P > 0.05). The mean OD was significantly greater in the MVE than in the PVT and CGP; the mean AMD and MG were significantly greater in the PVC than in the PVT (Tukey test, P > 0.05). Compared with the other groups, the 3D-printed inlays, especially the VarseoSmile TriniQ, presented a closer marginal and internal fit.

Additive-manufactured ceramics for dental restorations: a systematic review on mechanical perspective

Background

Additive manufacturing (AM) is rapidly expanding as a substitute for conventional heat-pressing and milling techniques for ceramic restorations. However, experimental and clinical evidence on the mechanical properties and performance of the final ceramic products is yet insufficient. This systematic review aimed to update the latest advances in additive manufacturing of restorative ceramics with a focus on their mechanical properties.

Methods

This systematic review was structured using the 5-step methodology based on the research question: what are the mechanical properties of additive-manufactured restorative ceramics in comparison with subtractive manufacturing? The electronic literature search was performed independently by 2 authors in the following databases: PubMed/MEDLINE, Web of Science, and Scopus. Published articles from 2019 to 2023 were screened, analysed and the relevant papers were selected for inclusion in this review.

Results

A total of 40 studies were included. The available ceramics include zirconia, alumina and alumina-zirconia composites, lithium disilicate, porcelain and fluorapatite glass ceramic. The mechanical properties were summarized according to material and technique: density (15 studies), flexural strength (31 studies), fracture toughness (7 studies), Young's modulus (7 studies), hardness (11 studies) and performance (7 studies). Overall, the properties exhibited an upward trend toward the values of conventional techniques. Typical processing defects, including porosity, agglomerates, cracks, surface roughness, and other defects, were also analyzed.

Conclusions

With significant technological advancements, the mechanical properties of AM ceramics have come close to ceramics by conventional manufacturing, whereas their reliability, the influence of printing layer orientations, and long-term performance still need further investigation.

Aging and post-polymerization effects on conversion degree and properties of additive splint materials

The study objective was to analyze dimensional change, flexural strength, surface hardness, wear profile, and conversion degree of different additive splint materials under various post-polymerization conditions of time and artificial aging. Two additive manufacturing systems (Cara Print 4.0, Dima Print Ortho, Kulzer; SprintRay Pro, SprintRay Splint, SprintRay), and a thermally activated resin control (Clássico) were evaluated in artificial aging (deionized water or saliva; 28 or 84 days at 37°C), with recommended or doubled post-polymerization cycles. Dimensional change (surface metrology), flexural strength (ISO 20795-1:2013), fractography (SEM), Knoop hardness, two-body wear profilometry (150,000 cycles; 3mmØ; 20N; 2.1Hz), and conversion degree (FTIR spectroscopy) were assessed. Two-way ANOVA and post-hoc Tukey tests were used for parametric data, and Kruskal-Wallis and post-hoc Dunn tests, for non-parametric data (α = 0.05). Results indicated no statistically significant differences in dimensional change or flexural strength among the materials. Recommended post-polymerization cycles resulted in lower hardness for additive resins than the thermally activated control. Doubling post-polymerization time significantly increased flexural strength and hardness of Dima Print Ortho, but decreased flexural strength of SprintRay Splint, and did not affect wear resistance. Dima Print Ortho demonstrated the highest wear resistance. Artificial aging did not affect flexural strength, surface wear, or dimensional change, but negatively impacted the hardness of all materials except Dima Print Ortho. The conversion degree was unaffected by post-polymerization time, and no significant differences were found among the materials. Overall, additive materials exhibited mechanical and dimensional properties comparable to thermally activated resin, with doubling post-polymerization time positively influencing the properties.

Systematic Review of the Quality of Stereolithographic Three-Dimensionally Printed Materials for Provisional Dental Restorations

BACKGROUND AND OBJECTIVES

The use of stereolithographic (SLA) 3D printing technology in dentistry has expanded, particularly for the fabrication of provisional dental restorations. Understanding the mechanical properties and quality of SLA 3D-printed materials is essential to ensure clinical success and patient safety. This systematic review aims to critically evaluate and summarize the available evidence on the mechanical properties and quality of SLA 3D-printed materials.

METHODS

A comprehensive literature search was conducted in PubMed, Scopus, Embase, Cochrane, and Web of Science up to October 2024. Studies comparing the mechanical properties of SLA 3D-printed provisional restoration materials with those of milled, conventional, or other additive manufacturing methods were included. Nine studies met the inclusion criteria. Data on flexural strength, hardness, fracture resistance, surface roughness, marginal adaptation, accuracy, cement film thickness, shear bond strength, and biofilm formation were extracted and analyzed.

RESULTS

The findings from the included studies indicate that SLA 3D-printed materials exhibit varied mechanical properties. Some studies reported that SLA 3D-printed resins had significantly lower flexural strength and hardness compared to milled PMMA and bis-acrylic resins. Other studies found that SLA 3D-printed resins showed clinically acceptable marginal adaptation, surface roughness, and fracture strength comparable to those fabricated by subtractive manufacturing and conventional methods. In terms of accuracy, build orientation influenced the dimensional accuracy of SLA-printed restorations. Studies assessing cement film thickness found that SLA-printed provisional restorations had higher cement film thickness compared to other materials. Regarding repairability and fatigue resistance, limitations were observed in some SLA resins.

CONCLUSIONS

The mechanical properties and quality of SLA 3D-printed materials for provisional dental restorations vary among studies. While SLA technology holds promise for efficient fabrication of provisional restorations, inconsistencies in material properties suggest a need for further research to optimize materials and printing parameters. Standardization of protocols is necessary to ensure reliable clinical performance of SLA 3D-printed provisional restorations.

Comparison of fit and trueness of single-unit and short-span fixed dental restorations fabricated by additive and subtractive manufacturing-A systematic review and meta-analysis

OBJECTIVES

Numerous studies have been conducted on the adaptation of dental restorations fabricated by additive (AM) and subtractive manufacturing (SM); however, the results are conflicting. This systematic review and meta-analysis aimed to evaluate the fit and trueness of fixed restorations made by AM compared to SM.

DATA

Studies investigating internal fit, marginal fit, and trueness of fixed prostheses were involved.

SOURCES

The protocol was registered in PROSPERO (registration number CRD42022323090). An electronic search was performed with a predefined search query across four medical databases on the 6th of September 2023.

STUDY SELECTION

A total of 57 eligible studies were included and sub-grouped by material type (metals, ceramics, acrylic resins, composites). The outcomes were specified as internal fit, marginal fit, and trueness expressed in micrometer (µm). Further subgrouping was based on measurement area: axial, occlusal, and marginal. When we analyzed marginal fit, there were no statistically significant differences between the two techniques in any of the subgroups. The measurement of internal fit metal and ceramic restorations provided no significant differences. However, milled acrylic resin restorations showed a significantly higher occlusal gap compared to 3D printed prostheses with 39.12 µm (95 % CI: 12.44; 65.79). In the case of trueness, a statistically significant difference was observed between ceramic AM and SM restorations with -47.76 µm (95 % CI: -95.51; -0.00). QUIN and GRADE Pro tools were used to evaluate the risk of bias and certainty of evidence.

CONCLUSION

Fixed restorations manufactured with additive manufacturing are valid alternatives to subtractive manufacturing in the digital workflow.

CLINICAL SIGNIFICANCE

Additive manufacturing is an accurate and cost-effective manufacturing method of digital workflow, especially for metal and resin fixed restorations. Once the challenges in ceramics manufacturing are addressed, AM will show more significant promise in the field.

New future dental material: Antimicrobial material "cetylpyridinium chloride-montmorillonite" and implantable material "phosphorylated pullulan"

In dental practice, there are two major diseases: dental caries and periodontal disease. Although dental treatment techniques have advanced along with advances in dental materials, some diseases such as root surface caries and horizontal bone resorption have not yet achieved satisfactory treatment results. Since these diseases are infections caused by oral bacteria, we believe that materials with long-lasting antimicrobial properties would help control these diseases. In addition, materials that can adhere to wet hard tissues would contribute to treatment. In this review, new materials developed based on this idea, the antimicrobial material "cetylpyridinium chloride-montmorillonite" and the hard tissue adhesive implantable material "phosphorylated pullulan" was introduced.

Mechanical analysis of 3D printed dental restorations manufactured using different resins and validation with FEM analysis

PURPOSE

The aim of this study was to compare the wear and fracture resistance of single crowns produced from newly developed 3D printer resins used to produce permanent crowns and currently used composite CAD/CAM discs, after being thermomechanically aged in a chewing simulator.

MATERIALS AND METHODS

A total of 112 stainless steel die models simulating mandibular left first molars were produced, 8 for each group. Single crowns were produced from 3 different discs (Grandio Voco [GR], breCAM HIPC [HC], and Shofu HC [SF]) by CAD/CAM milling method and manufactured from from 4 different permanent composite resins (Nexdent C&B MFH [ND], Permanent Bridge Saremco [PB], VarseoSmile Crownplus [VSC], and Şenertek P-Crown [PC]) using the 3D printing method. Stereomicroscopy, scanning electron microscope (SEM) and Finite Element Method (FEM) analysis was performed. Data were analyzed using ANOVA, paired-t tests and Tukey's HSD test (alpha = 0.05).

RESULTS

As a result of thermomechanical aging, significant difference was found between the groups in wear and fracture resistance (P < .05). The highest wear resistance was found in the VSC group, and the lowest wear resistance in the PC group. As a result of the compression test, the highest fracture resistance was noted in the GR group and the lowest in the PC group. FEM analysis performed to validate fracture experiments showed an 87% similarity to the in-vitro data.

CONCLUSIONS

The crowns in all groups produced by CAD/CAM milling and 3D printing provided acceptable in vitro wear and fracture resistance for clinical application. The wear and fracture resistance of resin-based materials should be supported by clinical studies.

Harnessing machine learning algorithms for the prediction and optimization of various properties of polylactic acid in biomedical use: a comprehensive review

Machine learning (ML) has emerged as a transformative tool in various industries, driving advancements in key tasks like classification, regression, and clustering. In the field of chemical engineering, particularly in the creation of biomedical devices, personalization is essential for ensuring successful patient recovery and rehabilitation. Polylactic acid (PLA) is a material with promising potential for applications like tissue engineering, orthopedic implants, drug delivery systems, and cardiovascular stents due to its biocompatibility and biodegradability. Additive manufacturing (AM) allows for adjusting print parameters to optimize the properties of PLA components for different applications. Although past research has explored the integration of ML and AM, there remains a gap in comprehensive analyses focusing on the impact of ML on PLA-based biomedical devices. This review examines the most recent developments in ML applications within AM, highlighting its ability to revolutionize the utilization of PLA in biomedical engineering by enhancing material properties and optimizing manufacturing processes. Moreover, this review is in line with the journal's emphasis on bio-based polymers, polymer functionalization, and their biomedical uses, enriching the understanding of polymer chemistry and materials science.

Effect of different 3D-printing systems on the flexural strength of provisional fixed dental prostheses: a systematic review and network meta-analysis of in vitro studies

OBJECTIVES

The aim of this systematic review and network meta-analysis was to compare the flexural strength of provisional fixed dental prostheses (PFDPs) fabricated using different 3D printing technologies, including digital light processing (DLP), stereolithography (SLA), liquid crystal display (LCD), selective laser sintering (SLS), Digital Light Synthesis (DLS), and fused deposition modeling (FDM).

MATERIALS AND METHODS

A comprehensive literature search was conducted in databases including PubMed, Web of Science, Scopus, and Open Grey up to September 2024. Studies evaluating the flexural strength of PFDPs fabricated by 3D printing systems were included. A network meta-analysis was performed, using standardized mean differences (SMDs) and 95% confidence intervals (CIs) to assess the effects of each system on flexural strength.

RESULTS

A total of 11 in vitro studies were included, with 9 studies contributing to the network meta-analysis. SLS (77.70%) and SLA (63.82%) systems ranked the highest in terms of flexural strength, while DLP ranked the lowest (23.40%). Significant differences were observed between SLS and multiple other systems, including DLP (-14.58, CI: -22.67 to -6.48), LCD (-14.65, CI: -25.54 to -3.59), FDM (-12.87, CI: -23.30 to -2.52), SLA (-11.41, CI: -18.74 to -4.01), and DLS (-10.89, CI: -21.23 to -0.67). Direct comparisons were limited, with DLP vs. SLA having the most data. Other comparisons were predominantly indirect.

CONCLUSIONS

SLS and SLA systems exhibited superior flexural strength compared to other systems. However, the limited number of direct comparisons and reliance on indirect evidence suggest that further research is necessary to confirm these findings.

Global research interest and publication trends on guided surgery in implant dentistry: A metrics-based analysis

STATEMENT OF PROBLEM

Digital surgical guides improve precision by detailing the direction, position, and angle of implants, which reduces surgery time and complications. A bibliometric analysis of guided surgery in implant dentistry is lacking.

PURPOSE

The aim of this metrics-based analysis was to analyze the trends and key characteristics of articles related to guided surgery in implant dentistry.

MATERIAL AND METHODS

The search was conducted in February 2024 on the Web of Science. The main characteristics of the studies were extracted and analyzed. Collaborative networks were generated using the Vosviewer software program. Dimension was consulted to measure Altmetric data. Correlation among data was determined by using the Spearman test.

RESULTS

A total of 799 articles published between 1993 and 2023 were included. Most were case reports or series (n=26) using static guided surgery (n=672), primarily for dental implant placement (n=754). The studies typically employed a combination of cone beam computed tomography (CBCT) and digital scanning (n=316) for surgical planning. The most frequently used software program was coDiagnostiX (n=89), and the most commonly used guide type was the printed guide (n=161). The country with the most articles was the USA (n=137), though Europe stood out as the leading continent (n=398). The Vosviewer demonstrated strong collaborations among authors. According to Dimensions, significant mentions were identified in Mendeley, news outlets, and X.

CONCLUSIONS

An emerging trend in guided implant dentistry research was identified over the past 30 years through the use of software programs and 3D-printers for the fabrication of surgical guides. Europe showed the greatest interest in this topic, predominantly conducting research on static guided surgery for implant placement. Additional clinical studies and systematic reviews are needed.

A completely digital workflow to fabricate a double-layered template for anterior esthetic veneers

In the esthetic restoration of anterior teeth, trial restorations are an efficient way of communicating among patients, doctors, and dental laboratory technicians. Although the development of digital technologies has made it popular to design digital diagnostic waxing in a software program, problems such as the polymerization inhibition of silicone materials and time-consuming trimming remain. The silicone mold based on a 3-dimensionally printed resin cast still has to be transferred to the digital diagnostic waxing and to the patient's mouth to generate a trial restoration. A digital workflow is proposed to fabricate a double-layer guide to reproduce the digital diagnostic waxing in the patient's mouth. This technique is suitable for esthetic restorations of anterior teeth.

Shear bond strength of porcelain to milled and stereolithography additively manufactured zirconia with and without surface treatment: An in vitro study

STATEMENT OF PROBLEM

Delamination of veneering ceramic is one of the most common challenges relating to veneered zirconia restorations. Additive manufacturing (AM) is a fast-expanding technology that has gained widespread acceptance in dentistry and is increasingly being used to produce dental restorations. However, information about bonding of porcelain to AM zirconia is lacking.

PURPOSE

The purpose of this in vitro study was to investigate the shear bond strength (SBS) of porcelain to milled and additively manufactured zirconia, and the effect of surface treatment on bond strength.

MATERIAL AND METHODS

A Ø12×5-mm disk was designed virtually to fabricate all specimens, which were divided into 2 groups according to the manufacturing technique: additively manufactured or milled zirconia. The effect of airborne-particle abrasion and a zirconia liner before porcelain application was investigated in both groups. Veneering porcelain was fired into an alumina ring mold on the zirconia surface. SBS was measured by using a universal testing machine at a crosshead speed of 1 mm/min before and after aging (n=10). SBS data were analyzed with 3-way ANOVA (α=.05) RESULTS: A significant difference was found between milled and AM zirconia. The SBS of porcelain to milled zirconia was significantly higher (1.38 MPa) than to AM zirconia (0.68 MPa) (P<.001). The surface treatment of zirconia had no significant effect on porcelain SBS in either group (P=.254), whereas thermocycling significantly reduced the SBS of porcelain to zirconia in both milled and AM groups (P=.001).

CONCLUSIONS

Porcelain bonding to milled zirconia was better than to AM zirconia. Pretreating the zirconia substrate before porcelain application did not improve the porcelain bond.

Accuracy, Reproducibility, and Gaps in Different Angulations of 3D-Printed versus Milled Hybrid Ceramic Crown

OBJECTIVES

 This article compared the accuracy, reproducibility, and gap of crowns resulting from variations in print angulation of three-dimensional (3D)-printed VarseoSmile Crownplus (VS) and milled resin-ceramic hybrid materials (Cerasmart 270, CS, and Enamic, E).

MATERIALS AND METHODS

 A total of 60 specimens, consisting of VS printed at four different angulations (30, 45, 60, and 90 degrees), along with CS and E were investigated. External and internal accuracy and reproducibility were measured with the 3D deviation analysis. External and internal gaps were measured with the silicone replica technique. The results were analyzed using Welch's one-way analysis of variance with Dunnett T3 post hoc comparison at p ≤ 0.05.

RESULTS

 Across all groups, external and internal accuracy were 0.55 to 20.02 μm and external and internal reproducibility were 0.05 to 0.69 μm. Overall external accuracy was not significant (p = 0.063), whereas significance was noted in overall internal accuracy and reproducibility among groups (p < 0.001). External and internal gaps were 33.76 to 93.11 μm. Statistically significant differences were found in internal and external gaps among groups (p < 0.001), with milled crowns demonstrating larger internal and smaller external gaps than 3D-printed crowns. Within the 3D-printed group, statistically, 90-degree angles exhibited the smallest external and internal gaps.

CONCLUSION

 Both milled and 3D-printed methods achieved clinically acceptable accuracy, reproducibility, and gap dimensions, offering viable options for hybrid ceramic crown restoration. Among 3D-printed crowns, the 90-degree printing angle group exhibited satisfactory accuracy and reproducibility, alongside the best internal and external fit.

The Accuracy of 3D-Printed Fixed Dental Restorations

OBJECTIVE

The aim of this in vitro study was to evaluate the accuracy of resin-based fixed dental restorations, namely veneers, single crowns, and four-unit fixed partial dental prosthesis (FPDs), using two different 3D printing technologies and polymer-based materials.

MATERIALS AND METHODS

A standard maxillary polyurethane jaw model containing prepared teeth was scanned using an intraoral scanner. The generated STL data were used to design the restorations virtually using CAD software. Two 3D printers were utilized for the provisional digital light processing and stereolithography for the castable resin patterns. Each printer produced 10 specimens of each type of restoration, for a total of 80 restorations. The 3D-printed restorations were then 3D scanned using the same intraoral scanner and evaluated for external and internal dimensional accuracy in terms of trueness and precision. A one-way ANOVA and two-sample T-test were implemented to compute the precision (variability between groups) and trueness (with the designed CAD model). A level of statistical significance of p-value < 0.05 was set.

RESULTS

Statistical differences in the external dimensional analysis of the incisors, molars, and four-unit FPD with p-values < 0.001, 0.002, and 0.004, respectively. For the internal dimensional analysis, the overall mean values of trueness ranged between 17 and 52 μm, and the variability was significant.

CONCLUSION

The external and internal dimensional accuracy values of the 3D-printed fixed dental restorations in this in vitro study in terms of trueness can be clinically accepted after chairside modifications. However, significant variability between the 3D-printed restorations was observed. Further investigations are needed to improve the accuracy of the 3D-printed fixed dental restorations.

CLINICAL SIGNIFICANCE

In terms of clinical applications, 3D-printed fixed dental restorations produced by both 3D-printing technologies and polymer-based materials achieved acceptable levels of trueness, although some variability was observed. Significant deviations from the CAD model may require further chairside adjustments. Future integration of AI with 3D-printing may further improve the accuracy and efficiency of fixed dental restoration production.

Progress in 3D Printing Applications for the Management of Orbital Disorders: A Systematic Review

Introduction: 3D printing technology has gained considerable interest in the domain of orbital illnesses owing to its capacity to transform diagnosis, surgery planning, and treatment. This systematic review seeks to deliver a thorough examination of the contemporary applications of 3D printing in the treatment of ocular problems, encompassing tumors, injuries, and congenital defects. This systematic review of recent studies has examined the application of patient-specific 3D-printed models for preoperative planning, personalized implants, and prosthetics. Methods: This systematic review was conducted according to the PRISMA guidelines. The PICOS is "What are the current advances and applications of 3D printing for the management of orbital pathology?" The databases analyzed for the research phase are MEDLINE, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), ClinicalTrials.gov, ScienceDirect, Scopus, CINAHL, and Web of Science. Results: Out of 314 studies found in the literature, only 12 met the inclusion and exclusion criteria. From the included studies, it is evident that 3D printing can be a useful technology for the management of trauma and oncological pathologies of the orbital region. Discussion: 3D printing proves to be very useful mainly for the purpose of improving the preoperative planning of a surgical procedure, allowing for better preparation by the surgical team and a reduction in operative time and complications. Conclusions: 3D printing has proven to be an outstanding tool in the management of orbit pathology. Comparing the advantages and disadvantages of such technology, the former far outweigh the latter.

Effects of a hollow pontic design with various wall thicknesses on the axial internal fit and failure load of 3D printed three-unit resin prostheses

STATEMENT OF PROBLEM

A 3-dimensionally (3D) printed 3-unit interim fixed dental prosthesis (FDP) undergoes inward polymerization shrinkage to the pontic region, leading to nonuniform internal fit and improper accuracy. Whether axial wall thickness influences accuracy is unclear.

PURPOSE

The purpose of this in vitro study was to analyze the axial internal fit and failure load associated with a hollow pontic design of varying wall thicknesses in stereolithography (SLA) 3D printed 3-unit interim FDPs.

MATERIAL AND METHODS

A master model for a 3-unit interim FDP with 2 implant abutments was designed. Two master models were produced by using milling and direct metal laser sintering (DMLS). Sixty SLA 3D printed specimens were produced with a hollow pontic design of 4 wall thicknesses (solid and 2.5, 2.0, and 1.5 mm). Fifteen milled specimens were produced with a solid pontic design. The axial internal fit in the coronal section was measured in terms of intaglio and cameo mid-axial wall areas relative to the abutments by using microcomputed tomography (μCT). The failure load was measured by using a universal testing machine at a loading rate of 1 mm/minute. For statistical analysis, parametric tests were performed (α=.05). Horizontal μCT sections were compared qualitatively, and failure patterns were categorized among groups.

RESULTS

The hollow pontic designs with 2.0- and 1.5-mm wall thicknesses presented significantly lower mean intaglio mid-axial gaps than the solid pontic design (P<.001) and similar intaglio and cameo mid-axial gaps in the horizontal μCT sections. The hollow pontic design with the 2.0-mm wall thickness had a significantly higher mean failure load than that with the 1.5-mm wall thickness (P<.001) and a statistically similar mean failure load to that of the solid pontic design (P=.549). As the wall thickness of the hollow pontic decreased from 2.5 to 1.5 mm, the ratio of pontic fracture to complete fracture of the prosthesis increased.

CONCLUSIONS

For SLA 3D printed 3-unit interim FDPs, axial internal fit was enhanced by the application of an appropriate hollow pontic design. Considering both the structural strength and fit, a hollow pontic design with a 2.0-mm wall thickness should be selected.

Synthesis and evaluation of novel urethane macromonomers for the formulation of fracture tough 3D printable dental materials

3D printing of materials which combine fracture toughness, high modulus and high strength is quite challenging. Most commercially available 3D printing resins contain a mixture of multifunctional (meth)acrylates. The resulting 3D printed materials are therefore brittle and not adapted for the preparation of denture bases. For this reason, this article focuses on toughening by incorporation of triblock copolymers in methacrylate-based materials. In a first step, three urethane dimethacrylates with various alkyl spacer length were synthesized in a one-pot two-step synthesis. Each monomer was combined with 2-phenoxyethyl methacrylate as a monofunctional monomer and a polycaprolactone-polydimethylsiloxane-polycaprolactone triblock copolymer was added as toughener. The formation of nanostructures via self-assembly was proven by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The addition of the triblock copolymer resulted in a strong increase in fracture toughness for all mixtures. The nature of the urethane dimethacrylate had a significant impact on fracture toughness and flexural strength and modulus of the cured materials. Most promising systems were also investigated via dynamic fatigue propagation da/dN measurements, confirming that the toughening also works under dynamic load. By carefully selecting the length of the urethane dimethacrylate spacer and the amount of block copolymer, materials with the desired physical properties could be efficiently formulated. Especially the formulation containing the medium alkyl spacer length (DMA2/PEMA) and 5 wt% BCP1 (block copolymer), exhibits excellent mechanical properties and high fracture toughness.

Assessing the Current Landscape and Future Directions of Digital Denture Technology

Digital dentures are removable dental prostheses fabricated using computer-aided design/computer-aided manufacturing (CAD/CAM) technology. This study aimed to explore the trends in digital dentures. A comprehensive four-phase search and selection strategy was framed.

Dimensions and Lens.org databases were used. Boolean operators were used to combine keywords.

The most significant growth occurred by 2021, with 71 publications and 984 citations. Egypt had the highest publication rankings, with 46 total publications (TP) and 45 total citations (TC). The University of Geneva played a significant role in contributing to 16 TP and 491 TC. Egyptian Dental Journal ranked at the top. The group with four authors had an even higher number of authorships, with a total of 60. The top four keywords were CAD/CAM, 3D printing, CAD-CAM, complete denture, and digital dentistry. The Glossary of Prosthodontic Terms, Ninth Edition, was referenced 614 times and had the highest average number of citations (75.2). The top three writers had strong relationships with the three sources and preferred to publish using four keywords. The 11-author group, cluster 6, had the highest level of network cooperation.

In conclusion, research on digital dentures has grown in terms of number of articles and citations.

Analysis of Mechanical Properties and Printing Orientation Influence of Composite Resin for 3D Printing Compared to Conventional Resin

This study aimed to compare the flexural strength, surface roughness, and microhardness of a resin for three-dimensional (3D) printing and a conventional composite resin and to evaluate whether the printing orientation influences these properties. To evaluate the flexural resistance, test specimens were produced and divided into four groups: three groups of resins for 3D printing with inclinations of 0°, 45°, and 90° and one group of conventional composite resin. Forty discs were produced and subjected to a sandpaper-polishing sequence, and the surface roughness was measured using a roughness meter. The Vickers microhardness (HV) test was performed at three different points, and the average was obtained. The results were subjected to ANOVA statistical analysis and Tukey's test. There were statistical differences in the flexural strength and microhardness between the conventional resin and the resin used for 3D printing. No statistical difference in surface roughness was observed. The resin for 3D printing exhibited lower flexural strength and microhardness than conventional composite resins. We concluded that the resin for 3D printing had lower flexural strength and HV than the conventional composite resin but similar surface roughness. The printing orientation did not affect the flexural strength, whereas the hardness increased as the printing angle increased.

Three-Dimensionally-Printed Polymer and Composite Materials for Dental Applications with Focus on Orthodontics

Three-dimensional printing has transformed dentistry by enabling the production of customized dental restorations, aligners, surgical guides, and implants. A variety of polymers and composites are used, each with distinct properties. This review explores materials used in 3D printing for dental applications, focusing on trends identified through a literature search in PubMed, Scopus, and the Web of Science. The most studied areas include 3D-printed crowns, bridges, removable prostheses, surgical guides, and aligners. The development of new materials is still ongoing and also holds great promise in terms of environmentally friendly technologies. Modern manufacturing technologies have a promising future in all areas of dentistry: prosthetics, periodontology, dental and oral surgery, implantology, orthodontics, and regenerative dentistry. However, further studies are needed to safely introduce the latest materials, such as nanodiamond-reinforced PMMA, PLA reinforced with nanohydroxyapatite or magnesium, PLGA composites with tricalcium phosphate and magnesium, and PEEK reinforced with hydroxyapatite or titanium into clinical practice.

3D Bioprinting in Cancer Modeling and Biomedicine: From Print Categories to Biological Applications

The continuous interaction between tumor cells and the local microenvironment plays a decisive role in tumor development. Selecting effective models to simulate the tumor microenvironment to study the physiological processes of tumorigenesis and progression is extremely important and challenging. Currently, three-dimensional (3D) bioprinting technology makes it possible to replicate a physiologically relevant tumor microenvironment and induce genomic and proteomic expression to better mimic tumors in vivo. Meanwhile, it plays a crucial role in the prevention and treatment of human diseases, contributing to drug delivery and drug screening, tissue development and regenerative medicine. This paper provides an overview of the categories of 3D bioprinting technology, and the recent advances in the bioinks required for printing. In addition, we summarize the current tumor models based on 3D bioprinting and provide an assessment of possible future biological applications.

The colour stability of 3D-printed, non-invasive restorations after 24 months in vivo - esthetically pleasing or not?

OBJECTIVES

The aim of the present prospective study was to evaluate the colour stability of 3D-printed non-invasive restorations after 24 months in vivo.

METHODS

The study included 29 patients, who received 3D-printed restorations made of a computer-aided design (CAD) / computer aided-manufacturing (CAM) hybrid material (n = 354). Restoration colour of 190 restorations was measured using a spectrophotometer. By applying the CIELAB system, *L (lightness), a* (red-green) and b* (blue-yellow) values were recorded. An evaluation of the colour differences (ΔE) after 6, 12 and 24 months was conducted.

RESULTS

Analysis of colour differences of 3D-printed restorations showed continuous discolouration of the restorations. After one year 34 % and after two years 18 % of the restorations were rated alpha or bravo, indicating no or hardly visible colour change. After two years, 54 % of the evaluated restorations yielded a colour difference with ΔE > 6.8 (delta). More than 82 % of the evaluated restorations showed values between ΔE 3.8 - 6.8 (charlie) and ΔE ˃ 6.8 (delta) after two years.

CONCLUSIONS

3D-printed non-invasive restorations showed an overall reduced colour stability after 24 months in vivo.

CLINICAL SIGNIFICANCE

The present study provides first clinical data regarding 3D-printed restorations. These restorations are recommended for a wearing time of about 6 months.

Application effect of perioperative nursing mediated by 3D printing and mind mapping in gynecological tumor laparoscopy

Probing influence by perioperative nursing mediated by 3D printing and mind mapping in gynecological tumor laparoscopy. 90 subjects divided into three groups: A (n=30), B (n=30) and C (n=30). Each group was given a different type of nursing intervention postoperative recovery (postoperative anal gas exhausting time, eating time, hospital stay, leaving bed-time, and drainage tube extraction time) were compared among the three groups. Hamilton Anxiety Scale (HAMA)/Hamilton Depression Scale (HAMD), strategies Used by People to Promote Health (SUPPH), Generic quality-of-life Inventory (GQOLI-74) scores and complication rates were compared among the three groups. The postoperative recovery of group A and B was better than group C, and group A was better than group B (P<0.05). Post-intervening, HAMA/HAMD scorings within groups A/B reduced compared with group C, with group A＞group B (P<0.05). The complication rate of group A and B was lower than that of group C (P<0.05). Perioperative nursing mediated by 3D printing and mind mapping works well.

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

STATEMENT OF PROBLEM

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

PURPOSE

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Mechanical properties and crown accuracy of additively manufactured zirconia restorations

OBJECTIVES

We evaluated the mechanical properties of zirconia restorations produced via additive manufacturing (AM) and the crown accuracy of zirconia crowns.

METHODS

Zirconia disks, bars, and crowns were manufactured via subtractive (CNC group) and additive manufacturing (AM group) techniques. Disk-shaped specimens in each group were autoclaved at 134 °C and 216 kPa for 5, 10, and 24 h. The phases of the specimens were analyzed using an X-ray diffractometer. The flexural strengths were measured via biaxial flexural tests. The morphologies were examined using a scanning electron microscope. The correlation between the m-phase fraction and biaxial flexural strength by autoclave time in each group was analyzed via linear mixed model and Pearson's correlation analysis. For each group, crown specimens were used to assess the marginal and internal gaps using the replica technique. Buccolingual and mesiodistal cross-sections were measured, and a repeated measures one-way ANOVA was performed.

RESULTS

Linear mixed model analysis indicated that for both groups, with an increase in the autoclave time, the flexural strength decreased, whereas the m-phase fraction increased. Pearson's correlation analysis revealed no correlation between the m-phase fraction and flexural strength for either group. A repeated measures one-way ANOVA was conducted on instrumented sections (buccal, lingual, mesial, and distal), revealing that the marginal and internal gaps of AM-produced zirconia crowns were less accurate than those of CNC-produced zirconia crowns.

SIGNIFICANCE

These findings suggest that additively produced zirconia restorations have mechanical properties comparable to those of conventionally produced ceramics and may be suitable for clinical applications.

New scenarios for training in oral radiology: clinical performance and predoctoral students' perception of 3D-printed mannequins

OBJECTIVES

This study aimed to evaluate the impact of 3D-printed mannequins on the training of predoctoral students.

METHODS

Two 3D-printed training models were developed: a traditional model that simulates a sound adult patient and a customized model with pathological and physiological changes (impacted third molar and edentulous region). Students accomplished their pre-clinical training divided into a control group (CG, n = 23), which had access to the traditional model, and a test group (TG, n = 20), which had access to both models. Afterward, they performed a full mouth series on patients and filled out a perception questionnaire. Radiographs were evaluated for technical parameters. Descriptive statistics and the Mann-Whitney test were used to compare the groups.

RESULTS

Students provided positive feedback regarding the use of 3D printing. The TG reported a more realistic training experience than the CG (P = .037). Both groups demonstrated good clinical performance (CG = 7.41; TG = 7.52), and no significant differences were observed between them.

CONCLUSIONS

3D printing is an option for producing simulators for pre-clinical training in Oral Radiology, reducing student stress and increasing confidence during clinical care.

Dimensional Accuracy in 3D Printed Medical Models: A Follow-Up Study on SLA and SLS Technology

Background: With the rise of new 3D printers, assessing accuracy is crucial for obtaining the best results in patient care. Previous studies have shown that the highest accuracy is achieved with SLS printing technology; however, SLA printing technology has made significant improvements in recent years. Methods: In this study, a realistic anatomical model of a mandible and skull, a cutting guide for mandibular osteotomy, and a splint for orthognathic surgery were replicated five times each using two different 3D printing technologies: SLA and SLS. Results: The SLA group had a median trueness RMS value of 0.148 mm and a precision RMS value of 0.117 mm. The SLS group had a median trueness RMS value of 0.144 mm and a precision RMS value of 0.096 mm. There was no statistically significant difference in RMS values between SLS and SLA technologies regarding trueness. Regarding precision, however, the RMS values for SLS technology were significantly lower in the splint and cutting guide applications than those printed with SLA technology. Conclusions: Both 3D printing technologies produce modern models and applications with equally high dimensional accuracy. Considering current cost pressures experienced by hospitals, the lower-cost SLA 3D printer is a reliable choice for point-of-care 3D printing.

Effect of Build Orientation on Mechanical and Physical Properties of Additively Manufactured Resins Using Digital Light Processing Technology in Dentistry: A Systematic Review

AIM

The aim of this systematic review was to evaluate the effect of build orientation on the mechanical and physical properties of additively manufactured resin using digital light processing (DLP).

BACKGROUND

The properties of 3D-printed materials are influenced by various factors, including the type of additive manufacturing (AM) system and build orientation. There is a scarcity of literature on the effect of build orientation on the mechanical and physical properties of additively manufactured resins using DLP technology in dentistry.

METHODS

This study followed the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines and was registered in PROSPERO. The formulated population, intervention, comparison, outcome (PICO) question was "What is the effect of build orientation on the mechanical and physical properties of additively manufactured resins produced using DLP in dentistry."  The search strategy used three main electronic databases and an additional manual search was done until February 2024. All the studies that evaluated the correlation of build orientation and the properties of printed resin using DLP were included. Two different analysis was used for in vivo and in vitro studies to assess the risk of bias.

REVIEW RESULTS

On search 237 studies were yielded for systematic review, out of which 13 studies were included for the systematic review evaluation. On evaluation and reviewing the included studies, though the build orientation angle influenced the properties of printed resins the results obtained were varied as 90° angle had increased compressive strength, low surface roughness, and best accuracy. The 0° angle had better wear resistance, tensile strength, and high flexural strength. There was no influence of build orientation on microhardness, shear bond strength, gloss and color difference. The studies on denture base showed that 45° build angle showed the truest with best accuracy.

CONCLUSION

The build orientation angle effects on both the mechanical and physical properties of the additively manufactured resin but varies with each property. The build orientation can be chosen based on the type of properties to be achieved based on the treatment modality.

CLINICAL SIGNIFICANCE

Based on the systematic review results the specific build orientation angle should be used during fabrication of any denture designs, crowns, and bridges as it is correlated with the properties to be achieved by particular designs. How to cite this article: Paranna S, Thosar N, Kanitkar A. Effect of Build Orientation on Mechanical and Physical Properties of Additively Manufactured Resins Using Digital Light Processing Technology in Dentistry: A Systematic Review. J Contemp Dent Pract 2024;25(9):891-903.

Impact of postpolymerization devices and locations on the color, translucency, and mechanical properties of 3D printed interim resin materials

STATEMENT OF PROBLEM

How postpolymerization conditions affect the color and mechanical properties of 3-dimensional (3D)-printed prostheses is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the color, microhardness, and flexural strength of 3D printed interim resin materials and to assess the effect of postpolymerization devices, polymerizing locations, and thermocycling on those properties.

MATERIAL AND METHODS

A total of 270 disk-shaped specimens and 180 bar-shaped specimens were designed and 3D printed with interim resin material (NextDent C&B). The specimens were postpolymerized in 1 of 3 devices (Group ND; NextDent, Group CR; Carima, and Group FL; Formlabs). Each group was divided into 3 circular zones of the polymerizing plate (central, medial, and lateral). Half of the specimens were subjected to 10 000 thermocycles. Color measurement, Vickers microhardness test, and 3-point flexural strength test were performed. Data were statistically analyzed by using the Kruskal-Wallis and Mann-Whitney tests (α=.05).

RESULTS

The L∗a∗b∗ color coordinates exhibited significant differences among the 3 zones (P<.05). The color and translucency differences according to CIELab and CIEDE among the zones exceeded the clinically perceptible levels in group CR. ΔE and ΔTP between with and without thermocycling were significantly different among the devices (P<.05). Microhardness and flexural strength were significantly different among the zones for those affected by thermocycling (P<.05).

CONCLUSIONS

Different locations in postpolymerization devices influenced the color, translucency, and mechanical properties of 3D printed interim resin materials. Thermocycling induced color and translucency changes and the mechanical weakening of postpolymerized resins, and the impact differed according to the device type.

Additive manufacturing of ceria and yttria incorporated toughened monolithic zirconia dental ceramic crowns: In vitro simulated aging behavior

STATEMENT OF PROBLEM

The comprehensive characterization of additively manufactured zirconia-based dental prostheses can promote widespread clinical application. However, simulated in vitro analysis of the aging behavior is lacking.

PURPOSE

The purpose of this in vitro study was to assess the simulated in vitro durability of monolithic transformation toughened additively manufactured zirconia-based restorations with different compositions to predict the clinical reliability depending on their ceramic composition.

MATERIAL AND METHODS

Crowns were 3-dimensionally (3D) printed by using a combination of custom-made stereolithography and a laser polymerized digital light processing process with high solid content slurries with suitable photo-interactive polymers. The main characteristics tested for mechanical behavior (structural reliability and flexural strength) were overall toughness and fatigue limits. Combinations of chemical compositions including yttria and ceria additives and processing conditions including pressing and sintering temperatures were applied to transform custom stereolithography and digitally light activated polymerized green parts to high strength and toughened ceramic crowns. The fluctuations in strength and toughness of as-sintered parts before and after physical thermocycling, physiochemical hydrothermal aging, and mechanical mastication simulation were studied via statistical methods (ANOVA) to indicate variable dependencies (α=.05).

RESULTS

Near theoretical density as high as 99.1%, minimum surface porosity as low as 0.25%, medium translucency, and high contrasts were achieved. The high original hardness near 19 GPa, a toughness of 6 to 7 MPa.m1/2, and 1300 MPa flexural strength with 95% confidence interval in as-sintered specimens satisfied the requirements for crowns. The simultaneously yttria and ceria stabilized systems should be able to resist low-temperature degradation aging with decreases as small as 2% in flexural strength and near 25% in fatigue fracture limits. The structure and process dependency of the mechanical properties of flexural strength (P<.020), hardness (P<.030), and modulus of elasticity (P<.020) were statistically significant while the toughness showed significant dependency (P≤.001).

CONCLUSIONS

The 3D printed posterior crowns with enhanced mechanical properties and augmented simulated in vitro durability can be manufactured by adding tetragonal phase stabilizer oxides (ceria and yttria) to zirconia-based ingredients. The combination of both oxide stabilizers in the additive manufacturing of crowns is a significant approach to improving clinical performance, enhanced toughness, and fatigue limit before and after physicomechanical, mechanochemical, and thermocyclic aging analysis.

Comparison of the flexural strength of printed and milled denture base materials

BACKGROUND

To evaluate the flexural strength of digitally milled and printed denture base materials.

METHODS

The materials tested were Lucitone 199 denture base disc (Dentsply Sirona), AvaDent denture base puck (AvaDent), KeyMill denture base disc (Keystone), Lucitone digital print denture base resin (Dentsply Sirona), Formlab denture base resin (Formlabs), and Dentca base resin II (Dentca). Sixty bar-shaped specimens of each material were prepared for flexural strength testing and were divided into five groups: control, thermocycled, fatigue cycled, and repair using two different materials. The flexural strength and modulus were tested using a 3-point bend test performed on an Instron Universal Testing Machine with a 1kN load cell. The specimens were centered under a loading apparatus with a perpendicular alignment. The loading rate was a crosshead speed of 0.5 mm/min. Each specimen was loaded with a force until failure occurred. A one-way ANOVA test was used to analyze the data, followed by Tukey's HSD test (α = 0.05).

RESULTS

The milled materials exhibited higher flexural strength than the printed materials. Thermocycling and fatigue reduce the flexural strengths of printed and milled materials. The repaired groups exhibited flexural strengths of 32.80% and 30.67% of the original flexural strengths of printed and milled materials, respectively. Nevertheless, the type of repair material affected the flexural strength of the printed materials; the composite resin exhibited higher flexural strength values than the acrylic resin.

CONCLUSIONS

The milled denture base materials showed higher flexural strength than the printed ones.

Mechanical properties of 3D printed prosthetic materials compared with milled and conventional processing: A systematic review and meta-analysis of in vitro studies

STATEMENT OF PROBLEM

Three-dimensional (3D) additive manufacturing (AM) is an evolving technology in dentistry, proposed as an alternative to subtractive milling manufacture (MM) or conventional processing. However, a systematic review of the use of AM technology instead of milling or conventional processing is lacking.

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the mechanical properties of 3D printed prosthetic materials compared with MM and conventional techniques.

MATERIAL AND METHODS

An electronic search of the literature was conducted on the MEDLINE (via PubMed), Scopus, and Web of Science databases. The inclusion criteria were in vitro studies published in the last 5 years, in English or Italian, and with 3D AM printed dental prosthetic materials. Data extraction was focused on dental prosthetic materials (ceramics, polymers, and metals) and their mechanical properties: flexural strength, fracture load, hardness, roughness, removable partial denture (RPD) fit accuracy, trueness, marginal discrepancy, and internal fit. Data considered homogenous were subjected to meta-analysis using the Stata17 statistical software program (95% confidence interval [CI]; α=.05). Since all variables were continuous, the Hedge g measure was calculated. A fixed-effects model was used for I2=0%, while the statistical analysis was conducted using a random-effects model with I2>0%.

RESULTS

From a total of 3624 articles, 2855 studies were selected, and 76 studies included after full-text reading. The roughness of AM-printed ceramics generally increased compared with that of conventional processing while the marginal discrepancy was comparable both for ceramics and polymers. The flexural strength, hardness, and fracture load of AM-printed polymers were statistically lower than those of the conventional group (P<.05). No significant difference was detected in terms of hardness, roughness, marginal discrepancy, fracture load, trueness, or internal fit between the AM and MM techniques (P>.05). Milling techniques showed significantly higher values of flexural strength (Hedge g=-3.88; 95% CI, -7.20 to -0.58; P=.02), also after aging (Hedge g=-3.29; 95% CI, -6.41 to -0.17; P=.04), compared with AM printing.

CONCLUSIONS

AM is comparable with MM in terms of mechanical properties, in particular with polymeric materials. The flexural strength of AM-printed prostheses is lower than with conventional and MM techniques, as are the parameters of hardness and fracture load, while the marginal discrepancy is similar to that of MM and conventional techniques. AM prostheses are commonly used for interim crowns and fixed partial dentures, as their rigidity and fracture resistance cannot support mastication forces for extended periods. More comparative studies are needed.

Post-processing of a 3D-printed denture base polymer: Impact of a centrifugation method on the surface characteristics, flexural properties, and cytotoxicity

OBJECTIVES

To investigate the impact of a centrifugation method on the surface characteristics, flexural properties, and cytotoxicity of an additively manufactured denture base polymer.

METHODS

The tested specimens were prepared by digital light processing (DLP). A centrifugation method (CENT) was used to remove the residual uncured resin. In addition, the specimens were post-processed with different post-rinsing solutions: isopropanol (IPA), ethanol (EtOH), and tripropylene glycol monomethyl ether (TPM), respectively. A commercial heat-polymerized polymethyl methacrylate was used as a reference (REF). First, the values of surface topography, arithmetical mean height (Sa), and root mean square height (Sq) were measured. Next, flexural strength (FS) and modulus were evaluated. Finally, cytotoxicity was assessed using an extract test. The data were statistically analyzed using a one-way analysis of variance, followed by Tukey's multiple comparison test for post-hoc analysis.

RESULTS

The Sa value in the CENT group was lower than in the IPA, EtOH, TPM, and REF groups (p < 0.001). Moreover, the CENT group had lower Sq values than other groups (p < 0.001). The centrifugation method showed a higher FS value (80.92 ± 8.65 MPa) than the EtOH (61.71 ± 12.25 MPa, p < 0.001) and TPM (67.01 ± 9.751 MPa, p = 0.027), while affecting IPA (72.26 ± 8.80 MPa, p = 0.268) and REF (71.39 ± 10.44 MPa, p = 0.231). Also, the centrifugation method showed no evident cytotoxic effects.

CONCLUSIONS

The surfaces treated with a centrifugation method were relatively smooth. Simultaneously, the flexural strength of denture base polymers was enhanced through centrifugation. Finally, no evident cytotoxic effects could be observed from different post-processing procedures.

CLINICAL SIGNIFICANCE

The centrifugation method could optimize surface quality and flexural strength of DLP-printed denture base polymers without compromising cytocompatibility, offering an alternative to conventional rinsing post-processing.

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

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

Additive manufacturing of dental ceramics in prosthodontics: The status quo and the future

PURPOSE

This review aims to summarize the available technologies, material categories, and prosthodontic applications of additive manufacturing (AM) dental ceramics, evaluate the achievable accuracy and mechanical properties in comparison with current mainstream computer-aided design/computer-aided manufacturing (CAD/CAM) subtractive manufacturing (SM) methods, and discuss future prospects and directions.

STUDY SELECTION

This paper is based on the latest reviews, state-of-the-art research, and existing ISO standards on AM technologies and prosthodontic applications of dental ceramics. PubMed, Web of Science, and ScienceDirect were amongst the sources searched for narrative reviews.

RESULTS

Relatively few AM technologies are available and their applications are limited to crowns and fixed partial dentures. Although the accuracy and strength of AM dental ceramics are comparable to those of SM, they have the limitations of relatively inferior curved surface accuracy and low strength reliability. Furthermore, functionally graded additive manufacturing (FGAM), a potential direction for AM, enables the realization of biomimetic structures, such as natural teeth; however, specific studies are currently lacking.

CONCLUSIONS

AM dental ceramics are not sufficiently developed for large-scale clinical applications. However, with additional research, it may be possible for AM to replace SM as the mainstream manufacturing technology for ceramic restorations.

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

BACKGROUND

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

PURPOSE

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

METHODS

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

RESULTS

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

SIGNIFICANCE

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

The influence of filler load in 3D printing resin-based composites

OBJECTIVE

To evaluate the influence of the barium glass (BG) filler in 3D printing resin-based composites for restorative structures.

METHODS

Experimental 3D printing resin-based composites were formulated with UDMA 70%wt, Bis-EMA 20%wt, and TEGDMA 10%wt. Photoinitiators TPO and DFI (2%wt) were used. BG was incorporated at 40%wt and 50%wt. 0%wt BG was used as negative control and the VarseoSmile Crownplus (Bego) was used as a commercial control. Specimens were printed using a 3D printer. Subsequently, specimens were washed and submitted to post-curing with 405 nm at 60ºC for 2 × 20 min at FormCure (FormLabs). 3D printing resin-based composites were evaluated by flexural strength, degree of conversion, softening in solvent, radiopacity, and cytotoxicity against gingival fibroblasts. Data were statistically analyzed using one-way ANOVA (α = 0.05).

RESULTS

No significant differences in flexural strength were showed between BG40% (90.5 ± 5,4 MPa), BG50% (102.0 ± 11.7 MPa) and VA (105.2 ± 11.7 MPa). Addition of 40% and 50% of BG showed no influence in the degree of conversion compared to VA (p > 0.05). All groups showed softening in solvent after immersion in ethanol (p < 0.05). All groups showed more than 1mmAl of radiopacity. BG50% showed significantly higher radiopacity (2.8 ± 0.3 mmAl) than other groups (p < 0,05). Cytotoxicity evaluation showed gingival cell viability higher than 80% for all groups.

SIGNIFICANCE

Addition of up to 50%wt of barium glass in experimental 3D printing resin-based composites showed promising results for long-term restorative structures.

Customized Orthosis for Nonsurgical Correction of Congenital Auricle Deformities in Newborns

SUMMARY

A misshaped pinna, caused by extrinsic pressures such as birth canal extrusion or incorrect position, is a common congenital auricular deformity in newborns. Surgery is a routine option to address this deformity, but it is traumatic and may lead to unacceptable aesthetic outcomes. Commercial ear mold orthoses with uniform size have been used for nonsurgical orthotic treatment, but are not applicable in all cases, depending on the auricle morphology. The authors used computer-aided design and three-dimensional (3D) printing technology to develop a novel customized orthosis for congenital auricular deformities. 3D ear models were constructed using computer-aided design software and a novel customized orthosis model was established after a process of correction, adjustment, and construction, with precise matching to allow tight attachment to the outer ear free from uneven skin pressing. After 3D-printing a customized orthosis injection mold, medical silicone injection molding was used to produce customized orthoses. Clinical application was conducted in 3 newborns and achieved satisfactory results. This novel customized auricle orthosis is an effective option for nonsurgical correction of a misshaped pinna.