Interim restorations

Effect of electrical grade glass fibres and silver nanoparticles on the mechanical properties of provisional PMMA material

The use of provisional crowns and bridges rendered the necessary care for the prepared teeth. The protection of the prepared tooth is one of the most important factors in the long-term success of fixed dental prosthesis. Temporary crowns and bridges for longer periods of use are most often made of acrylic material. Unfortunately, it does not have the appropriate mechanical properties or resistance to microbial colonization Therefore, the purpose is to modify it by adding glass fibers (2% w/w) and silver nanoparticles (0.5% w/w). A total of 160 samples were prepared which were segregated into 4 groups based on the test performed. Each group had 4 subgroups which consisted of samples containing silver nanoparticles (0.5% w/w) and E-glass fiber (2% w/w) mixed with PMMA in their respective concentrations. The samples were then tested for surface roughness, micro-hardness, flexural strength and SEM Analysis. The results of the study showed that there were no effect on the surface roughness values after incorporating silver nanoparticles and E-glass fibers. However, samples containing silver nanoparticles and E-Glass fibre individually had higher values of microhardness and flexural strength than those who had both together. The SEM images showed clumping of silver nanoparticles non-uniform orientation of E-glass fibers. Thus, it can be concluded that silver nanoparticles and E-glass fibre when added separately to PMMA, enhance its mechanical properties. However, better methods of mixing PMMA with silver particles and glass fibers is needed to attain a uniform distribution. Further, the orientation of E-glass fibers could also have an effect on the flexural properties of PMMA.

Effects of different fabrication techniques on the marginal gap of interim crowns as assessed by optical coherence tomography: An in vitro study

STATEMENT OF PROBLEM

Studies on the assessment of the marginal fit of interim crowns with optical coherence tomography (OCT) are lacking.

PURPOSE

The purpose of this in vitro study was to apply OCT to evaluate and to compare the impact of conventional and computer-aided design and computer-aided manufacturing (CAD-CAM) fabrication methods and different materials, including bis-acryl, conventional polymethyl-methacrylate (PMMA), and CAD-CAM PMMA, on the marginal fit of interim crowns.

MATERIAL AND METHODS

Thirty crown specimens were fabricated, with 20 PMMA crowns divided into 2 groups based on the fabrication method: the conventional method (Group Jet, n=10) and the CAD-CAM method (Group CAD-CAM PMMA, n=10). An additional 10 bis-acryl crowns were fabricated using the conventional method (Group Protemp, n=10). The marginal gap was assessed at 8 specific points using swept-source OCT. Comparisons between the fabrication methods of PMMA crowns and different materials of conventionally made crown were done using an independent t test (α=.05).

RESULTS

Group CAD-CAM PMMA recorded statistically significant lower total mean vertical marginal gap values (22.2 ±4.7 µm) compared with group Jet (62.6 ±2.2 µm) (P<.001). Among the conventional interim material, Group Protemp showed significantly lower values (57.6 ±5.2 µm) compared with group Jet (62.6 ±2.2 µm) (P=.02).

CONCLUSIONS

The CAD-CAM fabrication method presented smaller marginal gaps. Among the conventional interim crown materials, bis-acryl showed smaller marginal gaps than PMMA.

Evaluation of the marginal fit and fracture resistance of interim restorations fabricated using different techniques: an in vitro study

BACKGROUND

Interim restorations are essential for preserving structural integrity and function until the definitive restoration is placed. Their mechanical properties and marginal fit are crucial for clinical performance and are influenced by the fabrication technique and material used.

AIM

The aim of this in vitro study was to investigate the marginal fit and fracture resistance of manually fabricated, computer-aided design and computer-aided manufacturing (CAD/CAM) milled, and CAD/CAM three-dimensionally (3D) printed 3-unit interim fixed dental prostheses (FDPs).

MATERIALS AND METHODS

Sixty-four 3-unit interim FDPs were fabricated on epoxy resin models using different fabrication techniques: manual fabrication with poly methyl methacrylate (PMMA) (n = 16), manual fabrication with Bis-acrylic composite resin (n = 16), CAD/CAM milling (n = 16), and CAD/CAM 3D-printing with a digital light processing (DLP) printer (n = 16). The vertical marginal fit of the interim FDPs was evaluated using a stereomicroscope. Following cementation, the specimens were subjected to cyclic loading and then tested for fracture resistance using a universal testing machine. Data were analyzed using one-way ANOVA, and Tukey's post hoc test was performed to identify statistical differences between the means of independent group pairs.

RESULTS

The smallest marginal gap (31.77 ± 9.0 μm) was observed in the milling group, followed by the 3D-printing group, with no significant difference between the two (p = 0.98). Both groups demonstrated significantly smaller marginal gaps compared to the manual fabrication groups (p < 0.001). In terms of fracture resistance, the 3D-printing group showed the highest values (1244.46 ± 290.04 N), followed by the milling group, with no significant difference between them (p = 0.32). Both groups exhibited significantly higher fracture resistance than the manual fabrication groups (p < 0.001).

CONCLUSION

CAD/CAM 3D-printed and milled interim FDPs demonstrated superior marginal fit and fracture resistance, making them more suitable than conventional techniques, particularly for multi-unit restorations or long-term applications.

Influence of heat-assisted vat photopolymerization on the physical and mechanical characteristics of dental 3D printing resins

The effects of heat-assisted vat photopolymerization (HVPP) on the physical and mechanical properties of 3D-printed dental resins, including the morphometric stability of 3D-printed crowns, were investigated. A resin tank was designed to maintain the resin at 30, 40, and 50 ℃ during the 3D printing process. Test specimens were fabricated using a commercial dental resin, with untreated resin serving as the control group. Key properties such as viscosity, curing kinetics, surface microhardness, flexural properties, and dimensional accuracy were evaluated. The viscosity of the resin decreased significantly (P < 0.05) with increasing temperature, thereby enhancing its flow properties. Photo-DSC analysis revealed a 17.58% increase in peak heat flow at 50 ℃, indicating accelerated polymerization. Surface microhardness improved significantly (P < 0.05) with HVPP, though a slight reduction was observed at 50 ℃ compared to that at 30 and 40 ℃. The flexural strength, modulus, and resilience were significantly enhanced (P < 0.05) at higher temperatures, with 50 ℃ yielding the best mechanical properties. However, 3D morphometric analysis showed increased root mean square deviation from the CAD design at elevated temperatures. Our results suggest that HVPP enhances the durability of dental prostheses, although careful optimization of the printing temperature is essential to balance their strength and accuracy.

Effect of toothbrushing on surface roughness and gloss of CAD-CAM versus conventional interim materials with different surface treatments

STATEMENT OF PROBLEM

Characterizing interim restorations promotes esthetics. However, studies on the effects of characterization materials on the surface roughness and gloss of interim materials after toothbrushing are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the surface roughness and gloss of 5 different interim materials with different surface treatments after 1 year of simulated toothbrushing.

MATERIAL AND METHODS

Cuboid specimens (10×12×2 mm) were fabricated from each interim material: autopolymerized polymethyl methacrylate (UNIFAST Trad), autopolymerized bis-acryl composite resin (Protemp 4), light-activated composite resin (REVOTEK LC), milled polymethyl methacrylate block (DD provi P HI), and 3-dimensionally printed methacrylate oligomer (Nextdent C&B MFH). Each material was divided into 3 groups based on surface treatment (n=10): polishing, application of Lite Art and Resin Glaze, and application of OPTIGLAZE color. The specimens were subjected to 5000 and 10000 cycles of toothbrushing. The surface roughness and gloss were measured and separately analyzed by using 3-way repeated measures ANOVA (α=.05).

RESULTS

Significant interactions of the surface roughness and gloss among interim materials, surface treatments, and toothbrushing durations were found (P<.001). After 5000 and 10000 cycles, each polished material showed no significant difference in surface roughness compared with baseline: Protemp 4 (P>.999), REVOTEK LC (P>.999, P=.922), and Nextdent C&B MFH (P>.999), except for UNIFAST Trad and DD provi P HI (P<.001). Coating with Lite Art and Resin Glaze, as well as OPTIGLAZE color, significantly reduced surface roughness after both 5000 and 10000 cycles for all materials (application of Lite Art and Resin Glaze with UNIFAST TRAD (P<.001), Protemp 4 (P<.001), REVOTEK LC (P<.001), DD provi P HI (P<.001), and Nextdent C&B MFH (P<.001, P=.002), and application of OPTIGLAZE color with UNIFAST TRAD (P<.001), Protemp 4 (P<.001), REVOTEK LC (P<.001, P=.002), DD provi P HI (P<.001), and Nextdent C&B MFH (P<.001, P=.008)). Specimens with these treatments also exhibited significantly better gloss compared with the polished specimens (P<.001).

CONCLUSIONS

After 5000 to 10000 cycles of toothbrushing, Protemp 4, REVOTEK LC, and Nextdent C&B MFH, interim materials containing fillers, exhibited smoother surfaces compared with UNIFAST Trad and DD provi P HI, interim materials without fillers. Coating of all materials reduced surface roughness and increased gloss. After 5000 to 10000 cycles of toothbrushing, the surface roughness of each material remained stable; while the gloss decreased slightly, it remained within clinically acceptable levels.

An In Vitro Study to Assess the Effect of Cigarette Smoke on Color Stability and Surface Roughness of 3D Printed, Milled, and Traditional Provisional Crown and Bridge Materials

Objectives To assess the influence of cigarette smoke (CS) on the color and surface roughness of 3D printed, milled, and traditionally fabricated provisional crown and bridge (PC&B) materials. Materials and methods 112 disc-shaped samples were made employing four techniques and materials (28 per group) to fabricate PC&B prostheses. Specimens were fabricated using standard protocols, such as 3D printing, milling, conventional bis-acrylic resin, and traditional autopolymerizing polymethyl methacrylate (PMMA) resin. After preliminary color and surface roughness recording, each group specimen was divided randomly into two subgroups (14 each). The artificial saliva acted as the storage media for the control group specimens for 30 days, and test group specimens were subjected to CS in a customized smoking chamber (10 minutes twice daily, for 30 minutes). Final color and surface roughness measurements were made. The change in color (∆E00) and surface roughness (∆Sa) were calculated, and the data was tabulated for analysis.  Statistical analysis One-way analysis of variance was used to analyze the change in color and surface roughness. Post-hoc Tukey HSD test was used for comparison between groups. Results The mean ΔE00 and ∆Sa were higher among groups exposed to CS than those exposed to artificial saliva. The maximum change in color was recorded in the autopolymerizing PMMA, whereas the 3D printed resins recorded the minimal change. The traditional bis-acrylic resin recorded the maximum mean surface roughness change, while the milled resin recorded the least change. Conclusions Within the study limitations, it can be inferred that when exposed to CS, 3D printed and milled PC&B materials have superior color stability and displayed less change in surface roughness when equated with traditional bis-acrylic and autopolymerizing PMMA resins.

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

STATEMENT OF PROBLEM

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

PURPOSE

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSIONS

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

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

STATEMENT OF PROBLEM

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

PURPOSE

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSIONS

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

In silico assessment of biocompatibility and toxicity: molecular docking and dynamics simulation of PMMA-based dental materials for interim prosthetic restorations

AIM

This study aimed to comprehensively assess the biocompatibility and toxicity profiles of poly(methyl methacrylate) (PMMA) and its monomeric unit, methyl methacrylate (MMA), crucial components in dental materials for interim prosthetic restorations.

METHODOLOGY

Molecular docking was employed to predict the binding affinities, energetics, and steric features of MMA and PMMA with selected receptors involved in bone metabolism and tissue development, including RANKL, Fibronectin, BMP9, NOTCH2, and other related receptors. The HADDOCK standalone version was utilized for docking calculations, employing a Lamarckian genetic algorithm to explore the conformational space of ligand-receptor interactions. Furthermore, molecular dynamics (MD) simulations over 100 nanoseconds were conducted using the GROMACS package to evaluate dynamic actions and structural stability. The LigandScout was utilized for pharmacophore modeling, which employs a shape-based screening approach to identify potential ligand binding sites on protein targets.

RESULTS

The molecular docking studies elucidated promising interactions between PMMA and MMA with key biomolecular targets relevant to dental applications. MD simulation results provided strong evidence supporting the structural stability of PMMA complexes over time. Pharmacophore modeling highlighted the significance of carbonyl and hydroxyl groups as pharmacophoric features, indicating compounds with favorable biocompatibility profiles.

CONCLUSION

This study underscores the potential of PMMA in dental applications, emphasizing its structural stability, molecular interactions, and safety considerations. These findings lay a foundation for future advancements in dental biomaterials, guiding the design and optimization of materials for enhanced biocompatibility. Future directions include experimental validation of computational findings and the development of PMMA-based dental materials with improved biocompatibility and clinical performance.

A simplified digital workflow for the rapid design and fabrication of interim fixed prostheses using an open-access software program

A digital workflow for the rapid design and fabrication of interim fixed prostheses using an open-access software program and 3-dimensional printing technology is described. After obtaining intraoral scanning data, the prostheses are designed by offset, margin sculpting, and a Boolean operation. Then, the prostheses are finalized and manufactured additively. The use of the open-access software program and simplified design steps enhances the manufacturing efficiency and accessibility of computer-aided design and computer-aided manufacturing of interim restorations.

Comparative Analysis of Periodontal Parameters and Patient Satisfaction Utilising Different Temporary Crown Fabrication Techniques: A Parallel-Group Randomised Controlled Trial

Aim The study aims to evaluate the efficacy of different techniques for temporary crown fabrication in maintaining periodontal health and patient satisfaction, addressing a critical gap in the existing literature and informing evidence-based clinical practices. Materials and methods This study, conducted in accordance with CONSORT guidelines, was a parallel-group randomised trial conducted at a dental institute in India. In total, 36 participants aged 18-65 requiring anterior tooth region crowns were randomly assigned to three groups: direct (control), indirect (Test Group 1) and direct-indirect (Test Group 2) fabrication techniques. Participants were selected from outpatient departments based on eligibility criteria, and interventions were allocated using randomization tables. Outcome assessments included gingival health metrics and patient satisfaction levels, with statistical analyses performed using the Kruskal-Wallis test. Results Significant differences were observed in the pink esthetic score (PES) and patient satisfaction (P=0.029) among the three groups, with the direct-indirect technique group demonstrating the highest median PES (9 out of 10). However, no significant disparities were noted in the plaque index (PI) or probing depth (PD) among the groups. Conclusion The direct-indirect technique demonstrated superior PES and patient satisfaction, indicating potential benefits for periodontal health and patient experiences. Integration of virtual preparation workflows may optimise outcomes, but further research is needed for validation and guideline development.

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

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Effect of intraoral scanning distance on the marginal discrepancy of milled interim crowns

PURPOSE

To compare the marginal discrepancy between milled interim crowns fabricated using intraoral digital scans acquired at different scanning distances.

MATERIALS AND METHODS

Ten acrylic typodont teeth were prepared for interim crowns. Three different resin frames of 2.5-, 5-, and 7.5-mm heights were fabricated and attached to an intraoral scanner (Omnicam). Three groups were created based on the different scanning distances tested: 2.5 mm (Group A), 5 mm (Group B), and 7.5 mm (Group C). Intraoral digital scans were performed on four tooth surfaces: mesial, distal, buccal, and lingual (n = 10). Each experimental scan was used to design and fabricate a milled polymethylmethacrylate anatomically contoured crown. Vinyl polyether silicone was used three times to assess the marginal discrepancy of the specimens by measuring five marginal points on digital photographs. One-way analysis of variance test was used to analyze the data, followed by Tukey's honestly significant difference test (α = 0.05).

RESULTS

The mean marginal discrepancy values in Group C were significantly higher than those in Groups A (p ≤ 0.000) and B (p = 0.001). There was no significant difference between Groups A and B (p = 0.702). There were no significant differences among the four surfaces in any of the scanning distance groups (p1  = 0.583, p2  = 0.390, and p3  = 0.135; p > 0.05).

CONCLUSIONS

The interim crowns fabricated with a scanning distance of 7.5 mm showed the greatest marginal discrepancy when compared with crowns fabricated using 2.5- and 5-mm scanning distances.

28Assessment of thermal variations in the pulpal chamber during fabrication of provisionals using two different techniques and three materials

BACKGROUND

The issue of an increase in pulpal temperature affects direct and indirect techniques, where the fabricating material will come in direct contact with the prepared teeth.

OBJECTIVE

The aim of this study was to assess the pulpal thermal variations during provisional fabrication using direct and indirect-direct techniques, with three commonly commercially available provisional fabricating materials.

METHOD

In this vitro analytical study, 120 extracted human teeth were placed in a dentulous mould and dental stone was poured, to create a working model with an embedded natural right maxillary central incisor. Recording of thermal changes in the pulp chamber during provisionalization with direct (technique 1) and indirect-direct (technique 2) using three common types of provisional crown materials. 120 provisional crowns were fabricated using polymethyl methacrylate (DPI) (Group 1), Bis-acryl composite (Protemp 4) (Group 2) and Visible-light polymerizing (VLP) Urethane Dimethacrylate (Revotek LC) (Group 3) by two techniques and recording of peak temperature changes were done. Temperature rise in the pulp chamber was recorded using a thermocouple.

RESULTS

The mean initial and final temperature of the pulp chamber recorded for Groups 1, 2 and 3 was 31.52, 32.56; 31.01, 32.34; 32.29, 34.47 for technique 1 and 29.13, 30.5; 29.29, 31.11; 30.31, 32.65 for technique 2. The mean change in temperature was higher in Group 3 compared to the other groups.

CONCLUSION

The temperature rise detected according to this study was within the safer pulpal health limits with all the investigated materials and techniques. The resin material recommended for clinical use when the direct technique is employed for the fabrication of provisional crowns is bis-acryl composite resin (Protemp-4) as it caused minimal temperature rise in the pulpal chamber.

Influence of aging process and restoration thickness on the fracture resistance of provisional crowns: A comparative study

Background

The advancement of digital dentistry enhanced the fabrication of indirect provisional restorations utilizing durable materials, yet the performance of provisional crowns fabricated with various techniques, and different thickness remains unknown. Thus, this in-vitro study aimed to evaluate the influence of restoration thickness and aging on the fracture behavior of provisional crowns fabricated using different techniques.

Methods

A dentiform maxillary first molar was prepared using a highly filled epoxy resin material to construct identical die replicas. Four groups of provisional crowns were fabricated: Group 1 was milled at 1.5 mm occlusal thickness; Group 2 was milled at 0.9 mm thickness; Group 3 was 3D-printed at 1.5 mm occlusal thickness; and Group 4 was 3D-printed at 0.9 mm occlusal thickness. Eight crowns from each group were subjected to a thermocycling process for 5000 cycles between baths held at 5 °C and 55 °C with a dwell time of 30 s and transfer time of 5 s. All crowns (aged and non-aged (control)) were loaded for fracturing using a universal testing machine at a 0.5 mm/min crosshead speed. Data were analyzed using a two-way analysis of variance and multiple comparisons at (α = 0.05).

Results

The maximum mean force load was found in the non-aged milled group (M1.5) at 1706.36 ± 124.07 N; the minimum mean force load was recorded for the aged 3D-printed group (3D0.9) at 552.49 ± 173.46 N. A significant difference was observed before and after thermocycling (p < 0.01).

Conclusion

Computer-aided design and manufacture of milled provisional crowns is superior to 3D-printed crowns for fracture resistance.

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

STATEMENT OF PROBLEM

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

PURPOSE

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Comparison of the marginal and internal fit of PMMA interim crowns printed with different layer thicknesses in 3D-printing technique

OBJECTIVE

The aim of this in vitro study was to compare the effect of printing layer thickness on the marginal and internal fit of interim crowns.

MATERIAL AND METHODS

A maxillary first molar model was prepared for ceramic restoration. Thirty-six crowns were printed with three different layer thicknesses using a digital light processing-based three-dimensional printer (25, 50, and 100 µm [LT 25, LT 50, and LT 100]). The marginal and internal gaps of the crowns were measured with replica technique. An analysis of variance was conducted to determine if there were significant differences between the groups (ɑ = .05).

RESULTS

The marginal gap of LT 100 group was significantly higher than that LT 25 (p = .002) and LT 50 groups (p ≤ .001). The LT 25 group has significantly larger axial gaps than LT 50 group (p = .013); however, there were no statistically significant differences between other groups. The LT 50 group showed the smallest axio-occlusal gap. The mean occlusal gap differed significantly by printing layer thickness (p ≤ .001), with the largest gap occurring for LT 100.

CONCLUSIONS

Provisional crowns printed with 50 µm layer thickness provided the best marginal and internal fit.

CLINICAL SIGNIFICANCE

It is recommended that provisional crowns be printed with a 50 µm layer thickness to ensure optimal marginal and internal fit.

Evaluation of Load-bearing Capacity of Interim Fixed Partial Dentures Reinforced with Glass Fibers: An In Vitro Study

AIM

To compare the load-bearing capacity of three and four-unit fixed partial denture (FPD) with two different designs of pontics reinforced with industrial glass fibers at two different positions of the FPD.

MATERIALS AND METHODS

A total of 64 samples were made with Bis-acryl composite temporary material and reinforced with industrial glass fibers (E-glass). The specimens were divided into eight groups (groups I-VIII) depending on the number of units, type of pontic design and area of placement of fibers. A universal testing machine was used to evaluate and compare the load-bearing capacity of the specimens. The evaluated data were statistically analyzed using one-way ANOVA and Bonferroni post hoc tests (p ≤ 0.05).

RESULTS

Three-unit interim FPD and modified ridge lap pontic design showed greater load-bearing capacity after reinforcement with glass fibers than a four-unit interim FPD and hygienic pontic design, respectively. Fiber placement at the occlusal plus connector area as well as the cervical plus connector area had comparable results.

CONCLUSION

Industrial glass fibers (E-glass) could be used as a cheaper alternative but clinical performance and their safety are yet to be evaluated.

CLINICAL SIGNIFICANCE

Reinforcement with industrial-grade glass fibers can be a cheaper option for increasing the load-bearing capacity of interim partial dentures, but it needs to be studied in vivo through further studies.

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

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

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

STATEMENT OF PROBLEM

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

PURPOSE

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Flexural strength, surface roughness, micro-CT analysis, and microbiological adhesion of a 3D-printed temporary crown material

OBJECTIVE

To evaluate the thermocycling effect of 3D-printed resins on flexural strength, surface roughness, microbiological adhesion, and porosity.

MATERIALS AND METHODS

150 bars (8 × 2 × 2 mm) and 100 blocks (8 × 8 × 2 mm) were made and divided into 5 groups, according to two factors: "material" (AR: acrylic resin, CR: composite resin, BIS: bis-acryl resin, CAD: CAD/CAM resin, and PRINT: 3D-printed resin) and "aging" (non-aged and aged - TC). Half of them were subjected to thermocycling (10,000 cycles). The bars were subjected to mini-flexural strength (σ) test (1 mm/min). All the blocks were subjected to roughness analysis (Ra/Rq/Rz). The non-aged blocks were subjected to porosity analysis (micro-CT; n = 5) and fungal adherence (n = 10). Data were statistically analyzed (one-way ANOVA, two-way ANOVA; Tukey's test, α = 0.05).

RESULTS

For σ, "material" and "aging" factors were statistically significant (p < 0.0001). The BIS (118.23 ± 16.26A) presented a higher σ and the PRINT group (49.87 ± 7.55E) had the lowest mean σ. All groups showed a decrease in σ after TC, except for PRINT. The CRTC showed the lowest Weibull modulus. The AR showed higher roughness than BIS. Porosity revealed that the AR (1.369%) and BIS (6.339%) presented the highest porosity, and the CAD (0.002%) had the lowest porosity. Cell adhesion was significantly different between the CR (6.81) and CAD (6.37).

CONCLUSION

Thermocycling reduced the flexural strength of most provisional materials, except for 3D-printed resin. However, it did not influence the surface roughness. The CR showed higher microbiological adherence than CAD group. The BIS group reached the highest porosity while the CAD group had the lowest values.

CLINICAL RELEVANCE

3D-printed resins are promising materials for clinical applications because they have good mechanical properties and low fungal adhesion.

Optical properties of esthetic temporary cements and final restoration color

BACKGROUND

Opaque cements can be esthetically unfavorable and alternative translucent materials have been developed. The aim of this study was to evaluate the color interference of a new translucent cement compared with conventional materials, in association with interim restoration with different thickness and shades.

METHODS

Bis-acryl composite disks were prepared in 2 thicknesses (1.2 mm, 0.6 mm) and 3 shades (A3.5, A2, bleached) to simulate the restorations. Cementation over dentin disks was performed with 1 translucent cement (Provicol QM Aesthetic; VOCO), 2 conventional cements (Provicol; VOCO, Temp-Bond NE; Kerr Dental), and 1 transparent liquid (polyethylene glycol 400). The difference between the color of the specimens cemented with the transparent liquid and that of the specimens cemented with each cement was calculated (ΔEab). The data were analyzed using 3-way analysis of variance and Tukey tests (5%).

RESULTS

Significant differences were observed for all factors and some interactions (P < .05). For Provicol QM Aesthetic, the shade and thickness did not influence the ΔEab. For Provicol and Temp-Bond NE, the lighter and thinner the specimen, the higher the ΔEab. Only Provicol QM Aesthetic had smaller means than the perceptibility threshold. Temp-Bond NE and Provicol had higher values than the acceptability threshold for some combinations.

CONCLUSIONS

The highly translucent cement had less color interference than the conventional materials. The thickness and resin shade only affected the results for the opaque cements. The thinner specimens and the lighter shades had higher color interference.

PRACTICAL IMPLICATIONS

The use of a more translucent cement can produce a smaller color interference on the esthetic outcome of interim restorations.

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

PURPOSE

To investigate the survival and mechanical properties of 3-unit interim fixed dental prostheses (FDPs) made with additive manufacturing (AM) technology compared to milled and conventional manual fabrication.

MATERIALS AND METHODS

Sixty 3-unit interim FDPs replacing the first left mandibular molar were divided in 6 groups (n = 10): manual (Man) (Protemp 4), milled (Mil) (Telio-CAD Multi), and 4 additive manufacturing (AM) groups were subdivided into 4 AM technology subgroups: direct light positioning (DLP) (Rapidshape P30 [RS]), and stereolitography (SLA) (Formlabs 2 [FL]) and the type of printed interim polymer (P Pro C&B [St] and SHERAprint-cb [Sh]) (RS-St, RS-Sh, FL-St, and FL-Sh). Survival and complications were assessed after thermomechanical aging. The surviving samples were tested for fracture resistance. Kaplan-Meier test followed by log-rank test to show differences between groups was used to calculate the survival and complication rates. For fracture strength, one-way ANOVA and Tukey-b post hoc test were used to compare groups. Descriptive statistics was used for failure modes and Pearson chi-square to compare groups (α = 0.05).

RESULTS

Survival rates among groups varied from 100% (Man, Mil and FL-Sh), 70% (FL-St), 50% (RS-Sh), and 20% (RS-Sh) (p < 0.001), respectively. Additional events were observed in 50% to 80% in FL-St, RS-St, and RS-Sh groups (p < 0.001). Man, FL-St, and RS-S showed lower mean static load resistance (p < 0.001). Fracture through the connector between tooth 35 and the pontic was the most prevalent type of failure.

CONCLUSION

The manufacturing method, type of resin, and the printing mode had a significant influence on the mechanical properties of AM interim 3-unit FDPs.

In vitro comparison of the color degradation of two computer-aided design/computer-aided manufacturing provisional materials: A 12-month simulation

Aim

This study evaluated the color aging of two computer aided design/computer aided manufacturing (CAD/CAM) provisional materials of different compositions (polymethyl methacrylate and composite resin) after exposure to thermal aging and immersion in coffee for 3, 6, and 12 intraoral months.

Setting and Design

The current in vitro study was conducted from September to December 2021 at the Craniofacial laboratory at the Saint Joseph University in Beirut, Lebanon.

Materials and Methods

The shades of 2.0 mm thick, 10.0 mm in diameter disk shaped specimens of VITA CAD Temp® and Ceramill® TEMP were measured using the VITA Linearguide 3D MASTER® and a conversion table to extract the CIE LFNx01aFNx01bFNx01 values on a white background (n = 30).

Statistical Analysis Used

The color differences ΔE at 3, 6, and 12 months were calculated and analyzed by repeated measures ANOVA followed by Bonferroni multiple comparisons, univariate analyses, and one sample t tests.

Results

The mean ΔET1/T0, ΔET2/T0, and ΔET3/T0 values were significantly higher than the cutoff values for acceptability and perceptibility for the VITA CAD Temp® and the Ceramill® TEMP groups. In addition, the increase in ΔE overtime was significantly greater in the Ceramill® TEMP group compared to the VITA CAD Temp® group.

Conclusions

The Ceramill® TEMP changed color more and faster than the VITA CAD Temp®. In addition, whether at 3, 6, or 12 months, the color variations of both materials are not only perceptible but also unacceptable compared to the initial shade.

Marginal Adaptation and Internal Fit of 3D-Printed Provisional Crowns and Fixed Dental Prosthesis Resins Compared to CAD/CAM-Milled and Conventional Provisional Resins: A Systematic Review and Meta-Analysis

The aim of this systematic review was to evaluate the marginal fit and internal adaptation of provisional crowns and fixed dental prostheses (FDPs) fabricated using 3D-printing resins and compared them with those fabricated by CAD/CAM (computer-aided designing/computer-aided manufacturing) milling and conventional resins. The null hypotheses tested were that there would be no differences in the marginal fit and internal adaptation of 3D-printed provisional crowns and FDP resins when compared to CAD/CAM-milled and conventional provisional resins. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used to construct this systematic review. The focused PICO/PECO (Population, Intervention/Exposure, Comparison, Outcome) question was “Do provisional crowns and FDPs (P) fabricated by 3D-printing (I) have similar marginal adaptation and internal fit (O) when compared to those fabricated by CAD/CAM milling and conventional techniques (C)?”. The protocol used for this systematic review was pre-registered in the International Prospective Register of Systematic Reviews (PROSPERO). Electronic databases (e.g., MEDLINE/PubMed and Web of Science (Core Collection)) were systematically searched for indexed English literature published up to June 2022. In the initial electronic search of the selected databases, 519 articles were identified. Duplicates were removed, and screening was performed to select the articles that met the preset inclusion criteria. Sixteen studies were selected for qualitative analysis, but only ten of them provided comparative data and were selected for quantitative analysis. The modified CONSORT scale was used for qualitative analysis, and most of the included studies were rated to be of moderate quality. Based on the findings, it could be concluded that provisional crowns and FDPs fabricated from 3D-printing resins have a superior marginal fit and internal adaptation when compared to CAD/CAM-milled and conventional provisional resins; thus, they can be used as a dependable alternative to other resins.

Polymethyl methacrylate resin for provisional restoration affects rat macrophage function in in vitro conditions

PURPOSE

This study evaluated the cytotoxic effects of polymethyl methacrylate resin extracts on rat macrophage viability in in vitro conditions.

METHODS

Prepared test specimens were immersed in 5 mL of artificial saliva and incubated for 24, 48, and 72 h at 37°C. The cytotoxicity of the obtained solutions of extracted resins, used as a stock solution (100%) and diluted with Roswell Park Memorial Institute (RPMI) medium to obtain the working solutions (50, 40, 30, 20, 10, and 5%), was evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

RESULTS

No dose-dependent toxic activity in macrophage culture was detected for the three types of extracts obtained after 24, 48, and 72 h of material extraction. The shortest extraction of material was found to be completely non-toxic, and the 20% concentration of this extract obtained caused a significant increase in cell ability to metabolize MTT. Extracts obtained after 72 h of extraction showed the highest cytotoxic potential of 50%, 40% and 30%, and extracts obtained after 48 and 72 h of extraction at concentrations of 5% and 10% had a proliferative effect on the macrophage cell line.

CONCLUSION

This study demonstrated that the highest cytotoxic effect was observed in cells exposed to the highest concentrations (50, 40, and 30%) of the extracts that were extracted for 72 h.

The occlusal precision of milled versus printed provisional crowns

OBJECTIVES

The aim of this study was to compare the occlusal precision of computer-aided-design/ computer-assisted-manufacturing (CAD/CAM) milled versus 3D printed polymethylmethacrylate (PMMA) temporary prosthetic crowns , starting from the same digital CAD design.

MATERIALS AND METHODS

The study sample included 34 patients presenting 34 premolars in need of prosthetic rehabilitation: a total of 68 temporary crowns were manufactured, 34 of which milled and 34 printed. Immediately after manufacturing, the milled and printed provisionals were scanned with a desktop scanner (E1, 3Shape) to obtain STL files, that were superimposed to the original CAD design in order to identify the occlusal trueness (Analysis A). A second occlusal comparison was performed by scanning both kind of provisional after being placed intraorally with Trios scanner (3 Shape); intraoral scans were obtained in order to compare STL files of provisionals before and after occlusal adjustments (Analysis B).  The occlusal trueness was identified at three reference points, P1 (vestibular cusp), P2 (palatal / lingual cusp), P3 (central fossa). The statistical analysis was performed using the R 3.4.3 statistical software (The R Foundation for Statistical Computing), with a significance level of p <0.05.

RESULTS

Overall, the printed crowns showed lower occlusal differences than the milled crowns, when compared to the CAD design file, with a statistically significant difference in P1 (difference of 0.025 ± 0.046 mm), P2 (difference of 0.027 ± 0 0.044 mm) and P3 ( difference of 0.018 ± 0.050) for Analysis A (p <0.05). In the Analysis B the direct comparison between the degree of average difference between the pre-adjustment and the post-occlusal adjustment of the milled and printed crowns shows that the printed crowns have lower occlusal mean difference values in all three points compared to the milled ones (difference of 0.146 ± 0.273 mm in P1, 0.285 ± 0.360 mm in P2 and 0.257 ± 0.277 mm in P3).

CONCLUSIONS

Within the limitation of this study, the data obtained showed a better occlusal surface dimensional accuracy of the 3D printed provisional crowns, when compared to the milled ones. Comparing the results obtained, it is possible to assume that the intraoral scans also had a contribution to occlusion, beside the manufacturing method. 3D printing can be successfully applied for manufacturing temporary PMMA crowns.

Surface roughness and shear bond strength to composite resin of additively manufactured interim restorative material with different printing orientations

STATEMENT OF PROBLEM

Additive manufacturing (AM) is a technology that has been recently introduced into dentistry for fabricating dental devices, including interim restorations. Printing orientation is one of the important and influential factors in AM that affects the accuracy, surface roughness, and mechanical characteristics of printed objects. However, the optimal print orientation for best bond strength to 3D-printed interim restorations remains unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of printing orientation on the surface roughness, topography, and shear bond strength of AM interim restorations to composite resin.

MATERIAL AND METHODS

Disk-shaped specimens (Ø20×10 mm) were designed by a computer-aided design software program (Geomagic freeform), and a standard tessellation language (STL) file was obtained. The STL file was used for the AM of 60 disks in 3 different printing orientations (0, 45, and 90 degrees) by using E-Dent 400 C&B material. An autopolymerizing interim material (Protemp 4) was used as a control group (CNT), and specimens were fabricated by using the injecting mold technique (n=20). Surface roughness (Sa, Sz parameters) was measured by using a 3D-laser scanning confocal microscope (CLSM) at ×20 magnification. For shear bond testing, the specimens were embedded in polymethylmethacrylate autopolymerized resin (n=20). A flowable composite resin was bonded by using an adhesive system. The specimens were stored in distilled water at 37 °C for 1 day and thermocycled 5000 times. The shear bond strength (SBS) was measured at a crosshead speed of 1 mm/min. The data were analyzed by 1-way ANOVA, followed by the Tukey HSD test (α=.05).

RESULTS

The 45-degree angulation printing group reported the highest Sa, followed by the CNT and the 90-degree and 0-degree angulations with significant difference between them (P<.001). The CNT showed the highest Sz, followed by the 45-degree, 90-degree, and 0-degree angulations. The mean ±standard deviation SBS was 28.73 ±5.82 MPa for the 90-degree, 28.21 ±10.69 MPa for the 45-degree, 26.21 ±11.19 MPa for the 0-degree angulations and 25.39 ±4.67 MPa for the CNT. However, no statistically significant difference was found in the SBS among the groups (P=.475).

CONCLUSIONS

Printing orientation significantly impacted the surface roughness of 3D-printed resin for interim restorations. However, printing orientation did not significantly affect the bond strength with composite resin.

Marginal adaptation of three-unit interim restorations fabricated by the CAD-CA systems and the direct method before and after thermocycling

Background

Limited information is available regarding the marginal adaptation of three-unit interim restorations fabricated by different techniques from different materials. Also, the efficacy of computer-aided design/computer-aided manufacturing (CAD-CAM) systems for their fabrication is still questionable. This study aimed to assess the marginal adaptation of three-unit interim restorations fabricated by the CAD-CAM systems and the direct method from different materials before and after thermocycling.

Material and Methods

A sound mandibular second premolar and a second molar were prepared for a three-unit all-ceramic restoration. Metal dies were fabricated to simulate a case of mandibular first molar missing, and were mounted in an acrylic block. Seventy-two three-unit interim restorations were fabricated by different techniques from different materials in six groups (n=12). In the first four groups, restorations were fabricated from Tempron, Visalys Temp, Unifast III, and Acropars by the direct technique, while the Amann Girrbach and Arum CAD-CAM systems and Ceramill Temp blocks were used in the last two groups. Marginal gap in each group was measured under a stereomicroscope at ×100 magnification. The specimens then underwent 5000 thermal cycles (5-55°C), and the marginal gap was measured again afterwards. ANCOVA and Bonferroni test (for pairwise comparisons) were applied for statistical analyses (α=0.05).

Results

Amann Girrbach and Arum CAD-CAM systems were not significantly different regarding the marginal gap of restorations (P=0.999). Among the traditional interim materials, Acropars showed significantly higher marginal gap than others (P<0.001). No significant difference was noted between other traditional materials. CAD-CAM interim materials showed significantly smaller marginal gap than traditional materials (P<0.001).

Conclusions

The CAD-CAM interim materials yielded superior marginal adaptation in three-unit interim restorations compared with traditional interim materials. The type of CAD-CAM system had no significant effect on the final marginal adaptation of restorations.

Key words:Dental marginal adaptation, interim dental prosthesis, CAD-CAM.

In vitro comparison of the surface roughness of polymethyl methacrylate and bis-acrylic resins for interim restorations before and after polishing

STATEMENT OF PROBLEM

Polymethyl methacrylate and bis-acrylic based resins are widely used for interim restorations. Their initial surface roughness is important because it determines their aesthetic properties and the potential for biofilm adhesion.

PURPOSE

The purpose of this in vitro study was to assess the surface roughness and morphology of 6 bis-acrylic and 2 polymethyl methacrylate resins widely used for interim dental restorations, both before and after polishing.

MATERIAL AND METHODS

Specimens made of different bis-acrylic resins (Protemp 4, Luxatemp Star, Systemp, Telio, Structur Premium, Structur 3) or of polymethyl methacrylate (Unifast Trad, Unifast 3) were polished using a 2-step polishing system (Diatech). The average surface roughness before and after polishing (10 seconds at low speed in dry conditions) was measured by optical profilometry. Atomic force microscopy and scanning electron microscopy were used to analyze surface morphology. The Mann-Whitney and Kruskal-Wallis tests were used to evaluate the differences in roughness among specimens (α=.05), and the Pearson r correlation was computed to assess the relationship between fillers and average surface roughness.

RESULTS

In the 8 groups evaluated, the roughness significantly increased (P<.001) for Protemp 4 (from 0.12 to 0.50 μm), Luxatemp Star (0.17 to 1.19 μm), Unifast 3 (0.40 to 1.00 μm), Systemp (0.46 to 1.51 μm), Structur 3 (0.85 to 1.06 μm), Structur Premium (1.00 to 1.74 μm), and Telio (1.13 to 1.21 μm), except for Unifast Trad (9.20 to 2.59 μm). Pairwise multiple comparisons identified Protemp 4 as having the smoothest surface before and after polishing, while Unifast Trad was the roughest in both. Atomic force microscopy and scanning electron microscopy observations showed that the surface roughness of bis-acrylic resins was related to their surface morphology and average filler sizes. A positive relation between fillers and roughness was assessed (r=0.345, P<.001).

CONCLUSIONS

For the bis-acrylic interim resins, the surface roughness after polishing was correlated to the material used and its filler sizes. Nanofiller-based resins showed the smoothest surfaces. For the polymethyl methacrylate-based resins, the recently marketed Unifast 3 had the lowest overall roughness values.

Color and Translucency Stability of Three-Dimensional Printable Dental Materials for Crown and Bridge Restorations

The purpose of this study was to examine and compare color and translucency stability of three-dimensional (3D) printable dental materials for crown and bridge restorations. Five different materials were investigated, and twelve disc-shaped specimens of two different thicknesses (1 and 2 mm) were prepared using a digital light processing 3D printer. Color measurements were made according to the CIELAB color scale (L*, a*, and b*) using a spectrophotometer 1 h, 1 day, 1 week, one month, and six months after post-curing of the materials, and the translucency parameter (TP) was calculated. The L*, a*, b*, and TP values were compared among the different materials and storage periods using repeated measures analysis of variance. Color and translucency changes of the specimens after the different storage periods were compared with 1 h measurements to determine whether they exceeded clinically perceivable thresholds. The L*, a*, b*, and TP values showed significant differences according to the storage periods, as well as among the materials. Until one month, some materials demonstrated distinct color differences, while others showed small color differences below a clinically perceivable threshold. The translucency differences were not clinically perceivable for any specimen. After six months, all specimens demonstrated large color changes, whereas the changes in translucency were relatively small. In conclusion, the color of 3D printable dental materials changed with time, and the differences varied with the materials used. On the contrary, the changes in translucency were small. Overall, the materials became darker, more yellowish, and more opaque after six months of water storage.

Evaluation of Internal Fit and Marginal Adaptation of Provisional Crowns Fabricated with Three Different Techniques

Different techniques have been used to construct provisional crowns to protect prepared teeth. The purpose of this in vitro study was to assess the internal fit and marginal discrepancy of provisional crowns made by different methods. A total of 48 provisional crowns were constructed and divided into three groups (n = 16) according to the fabrication methods: fabricated manually-group MAN; computer-aided design/computer aided manufacturing technology-group CAM; and 3-dimensional (3D)-printed technology-group 3DP. The same standard tessellation language (STL) file was used for both CAD/CAM and 3D-printed group. The silicone-checked method was used to measure the internal gap distance. The marginal discrepancy was measured by using the polyvinyl siloxane (PVS) replica method and swept-source optical coherence tomography (OCT) scanning technique. Data were analyzed with one-way analysis of variance (ANOVA) nonparametric Kruskal-Wallis and Tukey tests at α = 0.05. At the central pit and axial walls, the gap distance mean values of group CAM were higher than those from group MAN and 3DP. The group 3DP was statistically significantly higher in gap distance at the location of occlusion than group MAN and group CAM (p < 0.05). The total gap distances assessed by silicone-checked method revealed there were no statistically significant differences between the tested groups (p > 0.05). The total mean values of absolute and horizontal marginal discrepancy of the group 3DP obtained by using the PVS-replica method and OCT scanning technique were significantly higher than the group MAN and CAM (p < 0.05). Regression correlation results of marginal discrepancy indicated a positive correlation (r = 0.902) between PVS-replica method and OCT scanning technique. The manually fabricated provisional crowns presented better internal fit and a smaller marginal discrepancy. Between different assessment techniques for marginal adaptation, PVS-replica method and OCT scanning technique have a positive correlation.

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

STATEMENT OF PROBLEM

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

PURPOSE

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Influence of the Postcuring Process on Dimensional Accuracy and Seating of 3D-Printed Polymeric Fixed Prostheses

The postcuring process is essential for 3-dimensional (3D) printing of photopolymer-based dental prostheses. However, the deformation of prostheses resulting from the postcuring process has not been fully investigated. The purpose of this study was to evaluate the effects of different postcuring methods on the fit and dimensional accuracy of 3D-printed full-arch polymeric fixed prostheses. A study stone model with four prosthetic implant abutments was prepared. A full-arch fixed dental prosthesis was designed, and the design was transferred to dental computer-aided manufacturing (CAM) software in which supports were designed to the surface of the prosthesis design for 3D printing. Using a biocompatible photopolymer and a stereolithography apparatus 3D printer, polymeric prostheses were produced (N = 21). In postcuring, the printed prostheses were polymerized in three different ways: the prosthesis alone, the prosthesis with supports, or the prosthesis on a stone model. Geometric accuracy of 3D-printed prostheses, marginal gap, internal gap, and intermolar distance was evaluated using microscopy and digital techniques. Kruskal-Wallis and Mann-Whitney U tests with Bonferroni correction were used for the comparison of results among groups (α = 0.05). In general, the mean marginal and internal gaps of cured prostheses were the smallest when the printed prostheses were cured with seating on the stone model (P < 0.05). With regard to the adaptation accuracy, the presence of supports during the postcuring process did not make a significant difference. Error in the intermolar distance was significantly smaller in the model seating condition than in the other conditions (P < 0.001). Seating 3D-printed prosthesis on the stone model reduces adverse deformation in the postcuring process, thereby enabling the fabrication of prostheses with favorable adaptation.

Evaluation of the Color Stability of 3D-Printed Crown and Bridge Materials against Various Sources of Discoloration: An In Vitro Study

Recent advances in three-dimensional (3D) printing have introduced new materials that can be utilized for dental restorations. Nonetheless, there are limited studies on the color stability of restorations using 3D-printed crowns and bridge resins. Herein, the color stability of conventional computer-aided design/computer-aided manufacturing (CAD/CAM) blocks and 3D-printing resins was evaluated and assessed for their degrees of discoloration based on material type, colorant types (grape juice, coffee, curry, and distilled water (control group)), and storage duration (2, 7, and 30 days) in the colorants. Water sorption, solubility, and scanning electron microscope (SEM) analyses were conducted. A three-way ANOVA analysis showed that all three factors significantly affected the color change of the materials. Notably, the discoloration (ΔE₀₀) was significantly higher in all 3D printing resins (4.74–22.85 over the 30 days) than in CAD/CAM blocks (0.64–4.12 over the 30 days) following immersion in all colorants. 3D-printing resins showed color differences above the clinical limit (2.25) following storage for 7 days or longer in all experimental groups. Curry was the most prominent colorant, and discoloration increased in almost all groups as the storage duration increased. This study suggests that discoloration must be considered when using 3D printing resins for restorations.

Strength and stiffness of interim materials and interim fixed dental prostheses when tested at different loading rates

STATEMENT OF PROBLEM

How the loading rate might affect the mechanical properties of interim materials and interim fixed dental prostheses is unclear.

PURPOSE

The purpose of this in vitro study was to compare the material stiffness, material strength, and structural strength of interim 3-unit fixed dental prostheses fabricated from 3 interim materials when stressed at different loading rates.

MATERIAL AND METHODS

Bar-shaped specimens and anatomically correct interim 3-unit fixed dental prostheses with a modified-ridge lap pontic were fabricated from polyethyl methacrylate resin (Trim) and 2 bis-acrylic composite resins (TempSmart; Integrity) (n=10). Flexural modulus and strength of the bar specimens, representing material stiffness and strength, were determined with a 4-point bend test in a universal testing machine. The structural strength of the prosthesis was assessed from the failure load from a vertical force applied on the occlusal surface of the pontic. Three loading rates, 0.5, 5, or 10 mm/min, were evaluated. Results were statistically analyzed with 2-way analysis of variance and multiple comparisons (α=.05).

RESULTS

Loading rate and material significantly affected flexural modulus, flexural strength, and structural strength (P<.05). Increasing loading rate significantly increased the flexural modulus of all materials (P<.05), but the effect of loading rate on the flexural strength of bis-acrylic composite resins was mostly insignificant. Polyethyl methacrylate specimens did not fracture when loaded at 0.5 or 5 mm/min, and the interim fixed dental prostheses made from polyethyl methacrylate did not fracture at the 0.5 mm/min loading rate. Dual-polymerizing bis-acrylic composite resin had significantly higher flexural modulus and strengths than autopolymerizing bis-acrylic composite resin.

CONCLUSIONS

Polyethyl methacrylate resin had the lowest stiffness among the interim materials tested and did not fracture but excessively deformed at the low loading rate. Dual-polymerizing bis-acrylic composite resin consistently had higher stiffness and material strength and provided higher structural strength than the autopolymerizing bis-acrylic composite resin. Loading rate significantly affected the mechanical properties of polyethyl methacrylate resin (P<.05), but the effect was indistinct for the bis-acrylic materials.

Effect of Fabrication Method on Fracture Strength of Provisional Implant-Supported Fixed Dental Prostheses

There has been an increase in utilizing 3D printers in dental restorations. The purpose of the study is to compare mechanical properties of 3D-printed prostheses to those of self-cured and/or computer-aided design-computer-aided manufacturing (CAD-CAM) restorations. A metal master typodont was prepared for the mandibular left sextant with implant analogs embedded at the first premolar and first molar positions with a missing second premolar. Three-unit provisional fixed dental prosthesis (FDP) was designed utilizing the 3Shape tooth library and forty-five uniform specimens were fabricated with different materials: self-cured poly(methyl methacrylate) (PMMA) (N = 15), milled PMMA CAD-CAM blocks (N = 15) and 3D-printed resin (N = 15). All specimens were tested using an Instron machine at a crosshead speed of 0.5 mm/min by an axial load on the occlusal surface of the second premolar pontic site. Statistical analysis was completed with Shapiro-Wilk, ANOVA and Tukey post-hoc tests. Mean fracture force was 300.61 N, 294.64 N and 408.49 N for self-cured PMMA, milled PMMA and 3D-printed resin, respectively. Mean force at FDP fracture of 3D-printed resin was significantly greater than the mean fracture force of either self-cured (p = 0.016, 95% CI [17.86, 197.91]) or milled (p = 0.010, 95% CI [23.83, 203.88]) PMMA.

Accuracy evaluation of 3D printed interim prosthesis fabrication using a CBCT scanning based digital model

OBJECTIVES

This study aimed to evaluate the marginal and internal gaps in 3D-printed interim crowns made from digital models of cone-beam computed tomography (CBCT) conversion data.

MATERIALS AND METHODS

Sixteen polyvinylsiloxane impressions were taken from patients for single crown restorations and were scanned using CBCT. The scanning data were converted to positive Standard Triangulation Language (STL) files using custom-developed software. The fabricated stone models were scanned with an intraoral optical scanner (IOS) to compare the surface accuracy with the STL data obtained by CBCT. The converted STL files were utilized to fabricate interim crowns with a photopolymer using a digital light-processing 3D printer. The replica method was used to analyze the accuracy. The marginal and internal gaps in the replica specimen of each interim crown were measured with a digital microscope. The Friedman test and Mann-Whitney U test (Wilcoxon-signed rank test) were conducted to compare the measurements of the marginal and internal gaps with a 95% level of confidence.

RESULTS

The root-mean-square values of the CBCT and IOS ranged from 41.00 to 126.60 μm, and the mean was 60.12 μm. The mean values of the marginal, internal, and total gaps were 132.96 (±139.23) μm, 137.86 (±103.09) μm, and 135.68 (±120.30) μm, respectively. There were no statistically significant differences in the marginal or internal gaps between the mesiodistal and buccolingual surfaces, but the marginal area (132.96 μm) and occlusal area (255.88 μm) had significant mean differences.

CONCLUSION

The marginal gap of the fabricated interim crowns based on CBCT STL data was within the acceptable range of clinical success. Through ongoing developments of high-resolution CBCT and the digital model conversion technique, CBCT might be an alternative method to acquire digital models for interim crown fabrication.

Methacrylate perspective in current dental practice

OBJECTIVE

To provide a current perspective concerning dental personnel sensitivity to methacrylate materials.

OVERVIEW

Methacrylate related sensitivity and allergies are currently beyond traditional thoughts concerning denture base resins and methyl methacrylate provisional materials. Methacrylates are now ubiquitous in current dental practice and dental personnel should be aware that dental adhesives contain potent sensitizers that may also cross-sensitize individuals to other methacrylates not experienced. The growing sensitivity to 2-hydroxyethyl methacrylate (HEMA) has been described to be epidemic in nature due to the artificial nail industry with dental patients and dental personnel may be more susceptible to dental methacrylate sensitization. While contact dermatitis remains the most prevalent methacrylate-related clinical presentation, respiratory complications and asthma are increasing associated with methacrylate exposure. While additional personal protective equipment (PPE) is thought to be first protective choice, the National Institute for Occupational Safety and Health (NIOSH) considers PPE overall largely ineffective and should be considered only as a last resort.

CONCLUSION

Dental personnel need to be more aware of methacrylate sources and use workplace control measures to limit methacrylate exposures to both dental personnel and patients.

CLINICAL SIGNIFICANCE

Sensitivity to methacrylate materials is a growing dental workplace major concern and dental personnel should be aware of both the methacrylate content of current materials and the products that contain ingredients with the most sensitization potential.

Evaluation of the effects of finish line type and width on the fracture strength of provisional crowns

This study aimed to investigate the impacts of finish line type and width on the fracture resistance of provisional crowns, and to determine the suitable type of crown material to use for that purpose. Chamfer and rounded shoulder preparations were done with stainless steel master models with a width of 0.6 mm and 1.0 mm and a total convergence angle of 6°. The provisional crowns were obtained using computer-aided design/computer-aided manufacturing (CAD/CAM) polymethyl methacrylate (PMMA) material in the mandibular left first molar. From the obtained molar tooth, a silicon mold was used to obtain the provisional crowns from the CAD/CAM PMMA, bis-acrylic resin, and self-curing composite materials. The lowest fracture strength was found in the bis-acrylic resin group made using the rounded shoulder preparation with a width of 0.6 mm (699 N). The highest fracture strength was found in the CAD/CAM PMMA group made using the rounded shoulder preparation with a width of 1 mm (1339 N). The fracture strength is higher for CAD/CAM PMMA than the other provisional crown materials; thus, it is recommended that this material be used in provisional crown restorations due to its other advantages.

Shear bond strength of provisional repair materials bonded to 3D printed resin

Background/purpose

There is limited literature on the materials of choice and their properties when repairing 3-D printed resin-based restorations. The objective of this in-vitro study is to determine the shear bond strength of various repair materials to 3D printed SLA (stereolithography) resin.

Materials and methods

For Group A (control), fifteen cylinders of 3-D printing SLA resin were printed as one unit of a Ø6.8 × 8 mm (diameter and height) cylindrical block with a Ø3 × 5 mm cylindrical block at the center. For the test groups, forty-five specimen cylinders of 3-D printing SLA resin (Ø6.8 × 8 mm) were fabricated and the surfaces were treated with 3 different test materials: Group B: Poly-Methyl Methacrylate (PMMA); Group C: Bis-acrylic composite resin, and Group D: Bis-GMA composite All specimens were tested using an Instron machine at a crosshead speed of 0.5 mm/min. A Shapiro-Wilk test was used to assess normality within the data, then the data was statistically analyzed by a Mann-Whitney test.

Results

There were no statistically significant differences between testing groups, except Group A. Group B displayed mixed (87%) and adhesive (13%) failure at the fractured surface. Group C showed both mixed (60%) and adhesive failure at the fractured surface (40%). All Group D showed mixed fracture patterns, partly cohesive fractured surface within the base cylinder area and partly adhesive fractured surface at the bonded interface.

Conclusion

No statistically significant differences in the shear bond strength of the different repair materials to 3D printed cylinders were observed. The 3D printed cylinder repaired with Bis-GMA composite demonstrated the most predictability from the fractography analysis.

Cytotoxicity of acrylic resin-based materials used to fabricate interim crowns

STATEMENT OF PROBLEM

If the components in the acrylic resins used to fabricate interim crows are cytotoxic, they can interfere with the integrity of the adjacent periodontal tissue and the dentin-pulp complex.

PURPOSE

The purpose of this in vitro study was to assess the cytotoxicity of resin-based materials used to prepare interim crowns.

MATERIAL AND METHODS

The following materials were used in this study: CAR, conventional acrylic resin powder and liquid; BR, bis-acrylic resin; and PAR, pressed acrylic resin of the CAD-CAM type. Glass disks were used as the control (Co). Oral epithelial cells (NOK) were seeded on glass disks and standardized disks prepared with the resins under study. After incubation for 24 hours, the cells were analyzed for viability (Alamar Blue and Live or Dead), adhesion, and morphology (SEM and fluorescence), as well as epidermal growth factor synthesis (EGF-ELISA). The surface roughness (Ra) of test specimens was evaluated under a confocal microscope. The data were submitted to ANOVA and the Tukey HSD statistical tests (α=.05).

RESULTS

The highest Ra value was observed in BR in comparison with CAR, PAR, and Co (P<.05). The highest viability, adhesion, and EGF synthesis values were determined for the cells in contact with PAR (P<.001).

CONCLUSIONS

The computer-aided design and computer-aided manufacturing (CAD-CAM)-type resin favored adhesion, metabolism, and epithelial cell proliferation, and it was therefore considered cytocompatible.

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

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

Assessment of the Adaptation of Interim Crowns using Different Measurement Techniques

PURPOSE

To compare the internal fit and marginal discrepancy of acrylic resin interim crowns fabricated by different manufacturing methods, and to test the consistency of measuring marginal discrepancy and internal fit between different measuring techniques.

MATERIALS AND METHODS

A dentoform mandibular left first molar was prepared for an all-ceramic crown. Thirty-six interim crowns were fabricated and divided into three groups (n = 12): group BAC (Bis-acrylic composite, fabricated manually), group CAM (CAD/CAM polymethylmethacrylate resin, milled), and group 3DP (3D printed methacrylic oligomers, printed). The internal fit of the interim crowns was evaluated by the silicone replica technique and by X-ray microcomputed tomography (µCT) technique. The marginal discrepancy of the interim crowns was evaluated by the vinyl polysiloxane (VPS) (Aquasil Ultra XLV) impression technique and by optical coherence tomography (OCT) technique. Data were statistically analyzed using ANOVA and Turkey tests at α = 0.05. Pearson correlation test was used to evaluate the correlation between the different measurement techniques and marginal discrepancy/internal fit.

RESULTS

The manually fabricated interim crowns (group BAC) had significantly greater discrepancy of internal fit than did the digitally fabricated crowns (group CAM and group 3DP) measured by both silicone replica technique and µCT 2-dimensional (2D) image measurement. There were no statistically significant differences in the cement space volume values obtained by the µCT image technique between group BAC and group 3DP (p = 0.285). The coefficient of determination between the two volumetric measurement techniques was low (R² = 0.30). For marginal discrepancy, the manually fabricated interim crowns had a wider absolute marginal discrepancy than both digitally fabricated groups (p < 0.05). In both the VPS impression and OCT assessment, there was no statistically significant difference between group CAM and group 3DP (p = 0.798 and 0.994, respectively). The coefficient of determination between the VPS impression and OCT techniques for marginal discrepancy measurement was low (R² = 0.23).

CONCLUSIONS

Digitally fabricated interim crowns (group CAM and group 3DP) had better internal fit and smaller marginal discrepancy than manually fabricated interim crowns (group BAC). For comparison of the different evaluation techniques, the silicone replica technique and µCT measurements had low correlation for internal fit assessment, as did the PVS impression and OCT techniques for marginal discrepancy test.

Color alterations of a PMMA resin for fixed interim prostheses reinforced with silica nanoparticles

PURPOSE

The aim of the present study was to evaluate the color changes of an autopolymerizing PMMA resin used for interim fixed restorations, reinforced with SiO₂ nanoparticles.

MATERIALS AND METHODS

Silica nanoparticles were blended with the PMMA resin powder through high-energy ball milling. Four shades of PMMA resin were used (A3, B3, C3, D3) and total color differences were calculated through the equations ΔE_ab= [(ΔL^*)² + (Δa^*)² + (Δb^*)²]^½ and ΔE00=[ΔL′KLSL2+ΔC′KCSC2+ΔH′KHSH2+RTΔC′KCSCΔH′KHSH]1/2. Statistically significant differences between ΔE_ab and the clinically acceptable values of 3.3 and 2.7 and those between ΔE₀₀ and the clinically acceptable value of 1.8 were evaluated with one sample t-test (P<.05). Differences among the different shades were assessed through One-Way ANOVA and Bonferroni multiple comparison tests.

RESULTS

Significantly lower values were detected for all groups concerning ΔE_ab compared to the intraorally clinical acceptable values of 3.3 and 2.7. Significantly lower mean values were detected for groups B3, C3, and D3, concerning ΔE₀₀ compared to the intraorally clinical acceptant value of 1.8. Color pigments in red-brown (A3) and red-grey (D3) shades affect the total color change to a greater extent after the reinforcement with SiO₂ nanoparticles compared to the red-yellow (B3) shade.

CONCLUSION

Within the limitations of this in vitro study, it can be suggested that reinforcing PMMA with SiO₂ nanoparticles at 0.25 wt% slightly affects the optical properties of the PMMA resin without being clinically perceivable.

Wear resistance and microhardness of various interim fixed prosthesis materials

The aim of the present study is to evaluate the wear resistance and microhardness of various interim fixed prosthesis materials with different chemical compositions and curing methods. One heat-cured and four self-cured acrylic resins, and three self-cured, one light-cured, and one dual-cured composite-based materials were tested. For microhardness, samples from each group were tested after storing either at 37°C in artificial saliva for 7 days, followed by thermocycling, or in distilled water solution at 37°C for 24 h. For the evaluation of wear, the remaining samples were evaluated using a 3D scanner and a surface analysis program before loading in the chewing simulator and after every 10,000 cycles. There was a significant difference in wear behavior among the materials tested at both 10,000 and 20,000 cycles (P < 0.001). Microhardness and wear resistance were significantly different between acrylic and composite materials.

Effects of Printing Parameters on the Fit of Implant-Supported 3D Printing Resin Prosthetics

The purpose of the study was to investigate the influence of 3D printing parameters on fit and internal gap of 3D printed resin dental prosthesis. The dental model was simulated and fabricated for three-unit prostheses with two implants. One hundred prostheses were 3D printed with two-layer thicknesses for five build orientations using a resin (NextDent C&B; 3D systems, Soesterberg, The Netherlands) and ten prostheses were manufactured with a milling resin as control. The prostheses were seated and scanned with micro-CT (computerized tomography). Internal gap volume (IGV) was calculated from 3D reconstructed micro-CT data. IGV, marginal fit, and lengths of internal gaps were measured, and the values were analyzed statistically. For the 3D printed prostheses, IGV was smaller at 45°, 60°, and 90° compared to other build orientations. The marginal fit evaluated by absolute marginal discrepancy was smaller than other build orientations at 45° and 60°. IGV was smaller at 50 µm layer thickness than at 100 µm layer thickness, but the marginal fit was smaller at 100 µm layer thickness than at 50 µm layer thickness. The 3D printed prosthesis had smaller internal gap than the milled prosthesis. The marginal fit of the 3D printed resin prosthesis was clinically acceptable, and build orientation of 45° and 60° would be recommended when considering fit and internal gap.

Assessment of the internal fit and marginal integrity of interim crowns made by different manufacturing methods

STATEMENT OF PROBLEM

The adaptation of interim crowns made by subtractive and additive manufacturing has not been well investigated.

PURPOSE

The purpose of this in vitro study was to evaluate the internal fit and marginal discrepancy of interim crowns made by different manufacturing methods.

MATERIAL AND METHODS

A dentoform mandibular left first molar was prepared for a ceramic crown and scanned for the fabrication of 48 stereolithical resin dies and interim crowns. Group CAM included 16 ZCAD interim crowns made by computer-aided design and computer-aided manufacturing (CAD-CAM) technology; group 3DP, 16 NextDent MFH interim crowns made by digital light processing technology; and group APP, 16 Jet interim crowns manually made by using autopolymerizing acrylic resin and used as controls. The silicone replica technique was used to determine the internal discrepancy volume before definitive cementation. All crowns were cemented with Temp-Bond NE under a 50-N load and bench set for 10 minutes before microcomputed tomographic (μCT) scan assessment. The volume of cement space was measured by using the μCT scan 3-dimensional (3D) images, and gap distance at assigned locations was recorded by using the μCT scan 2-dimensional (2D) images. The marginal discrepancy was measured by the polyvinyl siloxane (PVS) impression technique and using a stereomicroscope. Data were analyzed by ANOVA and the Tukey honestly significant difference tests (α=.05). The association between different measuring techniques was analyzed by the Pearson correlation test.

RESULTS

The gap distance between interim crowns and dies from all 3 groups measured by using the μCT scan 2D images ranged from 0.13 mm to 0.55 mm, with the highest value found at the central occlusal location in group APP. The total average gap distance values recorded for group APP were significantly higher than those for group CAM and group 3DP (P<.05). No significant differences were found in internal discrepancy and cement space volume between group CAM and group 3DP (P>.05). The Pearson correlation test showed a moderate correlation (r=0.69) between the silicone replica technique and the μCT scan technique in determining cement space volume. When the PVS impression technique was used to measure the marginal discrepancy, the mean values obtained from group APP were statistically significantly higher than those from group CAM and group 3DP (P<.05). No statistically significant difference in marginal discrepancy was found between group CAM and group 3DP (P=.70).

CONCLUSIONS

Digitally fabricated interim crowns had better internal fit and smaller marginal discrepancy than manually constructed interim crowns. The silicone replica technique and μCT scan technique measurements had a moderate correlation in assessing the adaptation of cemented interim crowns.