Resin Interim Research Articles

Investigation of the Effects of Thermal Cycling and Surface Treatments on Interim Resin Materials Produced with Additive Manufacturing

This study aimed to compare the impact of thermal cycling on the flexural strength (σfs) of 3-dimensional (3D) printer resins and polymethyl methacrylate (PMMA). It also aimed to evaluate different surface treatment protocols and surface sealant applications on the surface roughness (Ra) and surface hardness (VHN) of the resins used. Rectangular (25�2�2 mm) and disc (Ø10�2-mm) specimens were fabricated from auto-polymerized PMMA, and 3D-printed resins were tested for mechanical properties (ISO 10477) using thermal cycling (n=10). Disc specimens were separated into three groups (n=10) based on the surface treatments: conventional sanding (C), disk polishing (P), and surface sealant coating (O). Ra and VHN values were statistically analyzed with the Kolmogorov Smirnov, Shapiro Wilk, Independent Samples t-test, Mann-Whitney test, one-way ANOVA test and Kruskal Wallis test (α =.05). A significant main effect was found on the flexural strength analysis for each of the two factors: thermal cycling procedure (p[0.001) and materials (p 0.001). A significant main effect was found on the surface roughness and hardness analysis for each of the two factors: surface treatment protocols (p[0.001) and materials (p[0.001). Based on the results; interim materials produced with 3D-printed resins have better mechanical properties than conventionally polymerized materials. Coated materials had lower surface roughness values than polished ones, and adding a surface sealant agent increased their hardness significantly.

Flexural properties of additive manufactured resin designated for interim fixed dental prosthesis: Effect of nanoparticles, build direction, and artificial aging

ObjectiveThis study investigates the flexural strength and elastic modulus of three-dimension (3D) printed interim resin (ASIGA) incorporating zirconium dioxide (nano-ZrO2) and silicon dioxide (nano-SiO2) nanoparticles (NPs) with different build direction and after artificial aging. MethodsThree hundred 3D-printed specimens were used for testing. Groups were modified with nano-ZrO2 or nano-SiO2 at concentrations of 0.5 wt% or 1 wt% and an unmodified control group remained unmodified (n = 10). The bar-shaped specimens (25 × 2 × 2 mm) were printed at 0, 45, and 90 degree orientations. Flexural properties were assessed using a universal testing machine. The study employed various analyses to assess material properties and bonding. ResultsThe flexural strength was significantly improved (P<0.001) by the inclusion of nano-ZrO2 or nano-SiO2, with a maximum value of 61.8 ± 4.3 MPa with 1 wt% nano-ZrO2 at 45° build direction. The highest elastic modulus value observed was 998.2 ± 91.2 MPa with 0.5 wt% nano-SiO2 at 90° build direction. Build direction, NP type, and NP concentration all had a statistically significant combined effect on flexural strength and elastic modulus (P=0.003*, P=0.045), respectively. ConclusionIncorporation of nano-SiO2 and nano-ZrO2 increased the flexural properties of the interim resin used in 3D printing. Following artificial aging, all the flexural property values in the modified groups showedminimal reduction regardless of the nanoparticle concentration, while the unmodified control group showed a significant reduction. Before and after artificial aging, samples at a 0 degree build direction had a considerably higher flexural strength, although the highest elastic modulus values were found in the 90 degree group. The findings underscore the potential of nanocomposites in strengthening interim dental restorations, offering promising advancements for clinical practice.

Wear Resistance of Additively Manufactured Resin with Different Printing Parameters and Postpolymerization Conditions.

To evaluate the wear resistance of a printed interim resin manufactured with different printing and postpolymerization parameters. Overall, 130 rectangular resin specimens (15 × 10 × 10 mm) were 3D-printed. Among the specimens, 60 were printed with different printing orientations (0, 45, and 90 degrees) and layer thicknesses (50 and 100 μm) to create six groups to investigate the effects of the printing parameters (n = 10 per group). The remaining 70 specimens were used to evaluate the effects of postpolymerization; for this, seven groups were created as follows (n = 10 per group): nonpostpolymerized; postpolymerized for 5, 15, and 30 minutes with an ultraviolet light-emitting diode (LED) device; and postpolymerized for 5, 15, and 30 minutes with an ultraviolet light bulb device. After masticatory simulation, the wear volume loss was calculated with 3D metrology software. One-way and two-way ANOVA were used for intergroup comparisons (α = .05). The group printed with a build angle of 45 degrees showed lower wear volume loss than the 0- and 90-degree groups (P < .01). The wear volume loss in the ultraviolet LED group was significantly greater than that in the ultraviolet light bulb group (P = .04). No significant difference was observed in the wear volume loss of the printed resin with respect to the layer thickness and polymerization time (P > .05). However, the non-postpolymerized group showed significantly greater wear volume loss than the other groups (P < .001). The printed resin showed greater wear resistance when it was printed at a build angle of 45 degrees and postpolymerized with an ultraviolet light bulb device.

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

Statement of problemThree-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. PurposeThe 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 methodsStereolithography, 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). ResultsThere 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). ConclusionsThree-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 surface roughness of additively manufactured implant-supported interim crowns fabricated with different print orientations.

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. 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). 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±0.36μm), followed by the 0-degree orientation (2.23±0.18μm) and the 45-degree group (3.18±0.31μm). Print orientation parameter significantly impacted the surface roughness of the implant-supported interim crowns manufactured by using the additive procedures tested.

Fracture strength test of digitally produced ceramic-filled and unfilled dental resin restorations via 3d printing: An in vitro study.

Purpose of this study was to investigate the mechanical efficiency of 3D-printed permanent and provisional implant cemented fixed bridges produced via CAD/CAM technology using an interim and a permanent ceramic filled hybrid material. Two groups with twenty specimens each were designed and 3D-printed via digital light processing technology (DLP). A fracture strength test was performed. Statistical analysis was performed (p>0.05) for impression distance and force. For the fracture resistance and impression distance no significant difference (p = 0.643) were detected. The specimens of interim resin showed a mean value of 365.90 ± 86.67 N. Whereas specimens of permanent ceramic filled hybrid material showed a mean value of 363.45 ± 87.57 N. In this in vitro study 3D-printed ceramic filled hybrid material and interim resin based on methacrylic acid esters showed an acceptable resistance to bite forces with no differences in fracture mechanism. Key words:CAD-CAM, dental resin, 3D printing.

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

Statement of problemHow postpolymerization conditions affect the color and mechanical properties of 3-dimensional (3D)-printed prostheses is unclear. PurposeThe purpose of this in vitro study was to evaluate the color, microhardness, and flexural strength of 3D printed interim resin materials and to assess the effect of postpolymerization devices, polymerizing locations, and thermocycling on those properties. Material and methodsA total of 270 disk-shaped specimens and 180 bar-shaped specimens were designed and 3D printed with interim resin material (NextDent C&B). The specimens were postpolymerized in 1 of 3 devices (Group ND; NextDent, Group CR; Carima, and Group FL; Formlabs). Each group was divided into 3 circular zones of the polymerizing plate (central, medial, and lateral). Half of the specimens were subjected to 10 000 thermocycles. Color measurement, Vickers microhardness test, and 3-point flexural strength test were performed. Data were statistically analyzed by using the Kruskal-Wallis and Mann-Whitney tests (α=.05). ResultsThe L∗a∗b∗ color coordinates exhibited significant differences among the 3 zones (P<.05). The color and translucency differences according to CIELab and CIEDE among the zones exceeded the clinically perceptible levels in group CR. ΔE and ΔTP between with and without thermocycling were significantly different among the devices (P<.05). Microhardness and flexural strength were significantly different among the zones for those affected by thermocycling (P<.05). ConclusionsDifferent locations in postpolymerization devices influenced the color, translucency, and mechanical properties of 3D printed interim resin materials. Thermocycling induced color and translucency changes and the mechanical weakening of postpolymerized resins, and the impact differed according to the device type.

Flexural strength of aged and nonaged interim materials fabricated by using milling, additive manufacturing, and a combination of subtractive and additive methods

Statement of problemInterim dental restorations can be fabricated from additively manufactured ingots. However, the flexural strength and surface roughness of restorations fabricated by using this technique are unknown. PurposeThe purpose of this in vitro study was to assess the influence of the manufacturing method (milling, additive manufacturing, or a combination of subtractive and additive methods) and accelerating aging on the flexural strength and surface roughness of interim dental materials. Material and methodsA bar design (25×2×2 mm) was used to fabricate the specimens by using 3 methods: milling (M group), additive manufacturing (AM group), and a combination of subtractive and additive methods (AM+M group). In the M group, an interim material (CopraTemp PMMA) was used to fabricate the milled (350i imes-icore) specimens. In the AM group, specimens were fabricated by using a printer (Form3B+) and an interim resin (Temporary CB) according to the manufacturer’s protocol. In the AM+M group, specimens were milled from AM ingots (Temporary CB) and with the same milling machine as in the M group. Two subgroups were created based on the artificial aging (thermocycling): nonaged and aged (n=10). Flexural strength was calculated by using a universal testing machine, followed by determination of the Weibull distribution. Surface roughness was measured by using a digital microscope. The Shapiro-Wilk test revealed that the flexural strength and surface roughness (Ra) data were normally distributed (P>.05). Two-way ANOVA followed by post hoc multiple comparison Tukey tests were used to examine the data (α=.05). The Shapiro-Wilk test revealed that the surface roughness area data were not normally distributed (P<.05). Therefore, the Kruskal-Wallis followed by pairwise multiple comparisons tests were selected (α=.05). ResultsManufacturing methods (P<.001) and artificial aging (P=.043) were significant factors in the flexural strength measured. The M group had the highest flexural strength mean values (180 MPa), while the AM group showed the lowest flexural strength mean values (77 MPa). Additionally, nonaged specimens (128 MPa) had significantly higher flexural strength values than aged specimens (117 MPa). Manufacturing method (P<.001) was a significant factor in the surface roughness measured. The M group had the highest linear surface roughness mean values (0.86 μm), while the AM group showed the lowest linear surface roughness mean values (0.49 μm). ConclusionsManufacturing method and thermocycling influenced the flexural strength and surface roughness of the groups tested.

Effect of printing orientation on the fracture strength of additively manufactured 3-unit interim fixed dental prostheses after aging

ObjectivesTo evaluate the effect of printing orientation on the fracture strength of 3-unit interim fixed dental prostheses fabricated by using additive manufacturing and to compare with those fabricated by subtractive manufacturing after thermomechanical aging. Materials and methodsA 3-unit fixed dental prosthesis was designed by using a dental design software (exocad DentalCAD 2.2 Valetta) in standard tessellation language (STL) format. This STL file was exported into a nesting software (PreForm) and 3-unit interim fixed dental prostheses with 5 different orientations (0°, 30°, 45°, 90°, and 150°) were printed by using a 3-dimensional (3D) printing interim resin (Temporary CB) (n = 10). The same STL file was also used to mill polymethymethacrylate (DuoCAD) 3-unit interim fixed dental prostheses as the control group (n = 10). All specimens were cemented onto cobalt-chromium test models representing a maxillary first premolar and first molar tooth with a long-term temporary cement (DentoTemp), and subjected to thermomechanical aging (120,000 cycles, 1.6 Hz, 50 N, 5–55 °C). Then, all specimens were loaded until fracture by using a universal tester. The data were analyzed with nonparametric 1-way analysis of variance (Kruskal-Wallis) and Dunn's tests (α = 0.05). ResultsAdditively manufactured specimens printed with 90° showed the lowest fracture strength values (P≤.048). However, the difference between specimens printed with 45° and 90° was nonsignificant (P>.05). Milled 3-unit interim fixed dental prostheses withstood significantly higher loads than 3-unit interim fixed dental prostheses printed with 45° and 150° (P≤.012). In addition, specimens printed with 0° showed higher fracture strength than the specimens printed with 45° (P=.01). Specimens printed with 0° and 30° presented similar fracture strength values with milled (P≥.057) and 150° printed (P>.05) specimens. ConclusionsPrinting orientation had a significant effect on the fracture strength of 3-unit interim fixed dental prostheses. Among the additively manufactured samples, those printed with 0° showed similar fracture strength values with the subtractively manufactured samples. Clinical significanceThree-unit interim fixed dental prostheses fabricated with 0° and 30° using the 3D printing interim resin tested may be alternatives to milled PMMA in terms of fracture strength.

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

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

Biochemical Interaction between Materials Used for Interim Prosthetic Restorations and Saliva.

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

Alcohol and light-polymerizing glaze effect on the physical and mechanical properties of a bisacrylate composite resin before and after immersion in chlorhexidine gluconate

Statement of problemThe use of 0.12% chlorhexidine gluconate (CHX) may damage bisacrylate composite resin interim restorations, but whether they can be protected with an application of alcohol and/or the use of a glaze is unclear. PurposeThe purpose of this in vitro study was to evaluate the effect of applying a 70% alcohol solution on the physical and mechanical properties of a bisacrylate composite resin, with and without the application of a light-polymerizing glaze subjected to 0.12% CHX twice a day for 7 days. Material and methodsForty specimens of an autopolymerized bisacrylate composite resin were divided into 4 groups (n=10): Group C (without alcohol, without glaze), Group G (without alcohol, with glaze), Group A (with alcohol, without glaze), and Group AG (with alcohol, with glaze). All specimens were submitted to in vitro treatment with 0.12% CHX for 7 days, and tests of color alteration (ΔE00), microhardness, roughness, and surface were performed initially and after treatment. Data were submitted to analysis of variance (ANOVA) and the Tukey HSD test (α=.05). ResultsGroup A had the lowest mean value of ΔE00 with a significant statistical difference from Group C. The groups with alcohol presented higher microhardness mean values compared with groups without alcohol in both periods of analysis, except for the groups with glaze in the final period. Group C showed higher mean roughness values in comparison with Group A in both periods. Group AG presented higher mean roughness values than Group G. Surface energy values did not vary significantly among groups, except between Groups C and A in the final period. ConclusionsThe application of alcohol optimized the properties of the autopolymerized bisacrylate composite resin analyzed, with and without the application of glaze. Overall, the use of CHX changed the microhardness and roughness when the glaze was applied.

Influence of postpolymerization methods and artificial aging procedures on the fracture resistance and flexural strength of a vat-polymerized interim dental material

Statement of problemThe influence of postpolymerization methods and artificial aging procedures on the fracture resistance and flexural strength of additively manufactured interim polymers remains unclear. PurposeThe purpose of this in vitro study was to evaluate the effect of the conditions (dry and water- and glycerin-submerged) and time (25, 30, 35, 40, and 45 minutes) of postpolymerization methods with and without artificial aging procedures on the fracture resistance and flexural strength of an additively manufactured interim material. Material and methodsBar specimens (25×2×2 mm) were manufactured from an interim resin (NexDent C&B MFH N1) with a 3-dimensional printer (NexDent 5100) as per the manufacturer’s recommendations. Three groups were created based on the postpolymerization condition: dry (D group) and submerged in a container with water (W group) or glycerin (G group) inside the ultraviolet polymerization machine (LC-3DPrint Box). Each group was divided into 5 subgroups (D1 to D5, W1 to W5, and G1 to G5) depending on the polymerizing time (25, 30, 35, 40, and 45 minutes) (n=20). Each subgroup was divided into nonaged and aged subgroups. The aged groups were treated in a mastication simulator. Fracture strength was measured on a universal testing machine. The flexural strength was calculated as per International Organization for Standardization (ISO) 10477-2018. The Kolmogorov-Smirnov test demonstrated that data were normally distributed. The 3-way ANOVA test was used to analyze the data (α=.05). ResultsA significant main effect was found on the fracture strength analysis for each of the 3 factors: postpolymerization condition (F[2, 449]=81.00, P<.001), treatment duration (F[4, 449]=2.84, P=.024), and aging procedure (F [1, 449] =7.62, P=.006). The only significant 2-way interaction was between postpolymerization condition and treatment duration (F[8, 449]=3.12, P=.002). Furthermore, a significant main effect was found on the flexural strength for each of the 3 factors including postpolymerization condition (F[2, 449]=82.55, P<.001), treatment duration (F[4, 449]=2.85, P=.024), and artificial aging procedure (F[1, 449]=6.72, P=.010). The only significant 2-way interaction was between postpolymerization condition and treatment duration (F[8, 449]=3.33, P=.001). Dry postconditions at 25 minutes and nonaged procedures obtained the significantly highest fracture resistance and flexural strength values. ConclusionsPostpolymerization conditions and duration time affected the fracture resistance and flexural strength of the additively manufactured interim material assessed. Artificial aging procedures significantly decreased the fracture resistance and flexural strength of the additively manufactured interim dental material.

Effect of Cartridge Storage Time and Ambient Laboratory Conditions on the Stability of Mechanical Properties of Bis-Acryl Interim Resin Materials.

To investigate the stability of mechanical properties during the entire shelf life of chemically-activated bis-acryl interim resin materials stored at ambient laboratory conditions. Four bis-acryl interim resin materials with no explicit recommendation for refrigerator storage were selected (Luxatemp Plus, Visalys Temp, Structur3, Structur Premium). Following cartridge storage at ambient laboratory conditions in 6-month intervals, 30 specimens (2.0 × 2.0 × 25.0mm3 ) were prepared in each case and stored in distilled water (37.0 ± 1.0 °C) with 3 different water storage times (2hours, 24hours, 7days). Flexural strength, modulus of elasticity, modulus of toughness, and elastic recovery were determined (3-point bend test). Data were subjected to a three-way multivariate analysis of variance (MANOVA) to determine overall significance, followed by a series of separate one-way ANOVAs after data were split, using Tukey and Games-Howell posthoc tests to identify significant differences between groups (α = 0.05). While Luxatemp Plus showed no significant decrease for all mechanical properties during the investigated shelf life of 21 months (p > 0.05), Visalys Temp exhibited a continuous decline of the corresponding values (p < 0.05), irrespective of the water storage time. Structur3 and Structur Premium properties remained almost unchanged during the first 6 months of the examination period. Subsequently, a progressive decrease was observed for flexural strength and modulus of elasticity, while most modulus of toughness and elastic recovery results revealed little alteration. Depending on the bis-acryl interim resin material, mechanical properties appeared to be susceptible to continuous degradation processes during cartridge storage at ambient conditions, especially towards the end of the material shelf life. For some materials, the chemical stabilization and recommended storage conditions should be revised by the manufacturers to prevent premature aging during shelf life.

Wear of 3D printed and CAD/CAM milled interim resin materials after chewing simulation.

PURPOSEThe purpose of this in vitro study was to investigate the wear resistance and surface roughness of three interim resin materials, which were subjected to chewing simulation.MATERIALS AND METHODSThree interim resin materials were evaluated: (1) three-dimensional (3D) printed (digital light processing type), (2) computer-aided design and computer-aided manufacturing (CAD/CAM) milled, and (3) conventional polymethyl methacrylate interim resin materials. A total of 48 substrate specimens were prepared. The specimens were divided into two subgroups and subjected to 30,000 or 60,000 cycles of chewing simulation (n = 8). The wear volume loss and surface roughness of the materials were compared. Statistical analysis was performed using one-way analysis of variance and Tukey's post-hoc test (α=.05).RESULTSThe mean ± standard deviation values of wear volume loss (in mm3) against the metal abrader after 60,000 cycles were 0.10 ± 0.01 for the 3D printed resin, 0.21 ± 0.02 for the milled resin, and 0.44 ± 0.01 for the conventional resin. Statistically significant differences among volume losses were found in the order of 3D printed, milled, and conventional interim materials (P<.001). After 60,000 cycles of simulated chewing, the mean surface roughness (Ra; μm) values for 3D printed, milled, and conventional materials were 0.59 ± 0.06, 1.27 ± 0.49, and 1.64 ± 0.44, respectively. A significant difference was found in the Ra value between 3D printed and conventional materials (P=.01).CONCLUSIONThe interim restorative materials for additive and subtractive manufacturing digital technologies exhibited less wear volume loss than the conventional interim resin. The 3D printed interim restorative material showed a smoother surface than the conventional interim material after simulated chewing.

Digital immediate tooth restoration: Fabricating acrylic resin interim crowns from CBCT scans for immediate implant-supported prostheses: A case series

Statement of problemAdjusting an interim screw-retained crown made of acrylic resin for maintenance of peri-implant soft tissues after immediate implant insertion requires accuracy and time. Assessments of these factors by using digital techniques are sparse. PurposeThe purpose of this clinical study was to describe a technique to fabricate an acrylic resin interim crown by using the data acquired from a cone beam computed tomography (CBCT) scan. The 3D tomography files were converted to a standard tessellation language (STL) file format used to print or to mill the interim crown with a technique called digital immediate tooth restoration (DITR). Additionally, the chair time spent during the prosthetic phase was evaluated in comparison with a protocol in which a standard interim crown (SIC) was fabricated with an indirect-direct technique. Material and methodsPatients who needed to replace a single nonrestorable tooth were treated from February to June 2018 with an immediately placed implant and an acrylic resin screw-retained interim prosthesis that was connected to the implant immediately after placement of the implant. The participants were divided into 2 groups according to the acrylic resin interim crown fabrication technique: group DITR and group SIC. The average time to finalize the prostheses was compared between the groups. The total chair time (TCT) taken for the adaptation of the interim crown was noted and distinguished in 3 different times corresponding to each phase of adaptation of the interim restoration of the interproximal contact areas (CT1), adaption of the postextractive alveolar bone walls (CT2), and adaption of the occlusal contacts (CT3). For each time, the number of changes (N-CT1, N-CT2, N-CT3, and TN) needed to complete each prosthetic phase was also marked and observed. Generalized linear mixed models and generalized linear models were used for data analysis. All the sites were definitively restored with a screw-retained crown after 6 months of healing, and the participants were provided with standard hygiene recall appointments for the next year. ResultsA total of 82 crowns at sites distributed across the mandible and the maxilla were included in the study. Thirty-five were restored with an SIC and 47 with a DITR interim crown. None of the implants were lost during the 18-month follow-up period. The analysis of the chair times registered for the adaptation of the interim crown to the implant healing abutment and to the neighboring teeth between the 2 groups showed a reduction if a DITR interim crown was used (average CT1 of 15 ±14 seconds, CT2 of 2 ±5 seconds, CT3 of 59 ±19 seconds, and TCT of 76 ±28 seconds for group DITR and average CT1 of 135 ±27 seconds, CT2 of 185 ±30 seconds, CT3 of 73 ±16 seconds, and TCT of 394 ±61 seconds for group SIC). The number of corrections to finalize the interim crown adaptations was lower for the group DITR (0.81 ±0.74 for N-CT1, 0.19 ±0.39 for N-CT2, and 2.81 ±0.74 for N-CT3) when compared with the number of corrections needed for the group SIC (4.37 ±0.81 for N-CT1, 5.57 ±0.77 for N-CT2, and 3.86 ±0.64 for N-CT3). ConclusionsThe data from CBCT scans led to interim acrylic resin crowns that needed fewer adjustments with the immediate implant placement and interim restoration approach, reducing chair time.

Comparison of material properties and biofilm formation in interim single crowns obtained by 3D printing and conventional methods

Statement of problemThree-dimensionally printed interim restorations are among the recent technological advancements in dentistry. However, evidence of their performance is lacking. PurposeThe purpose of this in vitro study was to compare the properties of interim restorations made by 3D printing with different technologies, laser stereolithography (SLA), technology and selective laser sintering (SLS) with those obtained by conventional techniques from acrylic resin and bis-acryl resin. Material and methodsFour different groups (acrylic resin, bis-acryl resin, SLS, SLA) were tested for flexural strength, Vickers microhardness, fatigue test, compressive strength, surface roughness before and after polishing, and biofilm formation. Specimens were made in the form of rectangular blocks, disks, and single crowns by following the manufacturing technique of each material. One-way ANOVA was used to test biofilm formation, Vickers microhardness, and the results of the 3-point bend flexural test, while the paired t test was used to assess differences in surface roughness between the materials (α=.05 for all tests). ResultsThe highest Vickers microhardness value was for acrylic resin interim crowns, while the elastic moduli were lower for both the 3D printed materials. Only the SLA resin fractured during the fatigue test. For surface roughness, a statistically significant difference was found among the studied materials (P<.001), with SLA resin and bis-acryl resin having the lowest values. No statistically significant differences were found for biofilm formation (P>.05). ConclusionsSLS resin had favorable results for the Vickers microhardness, higher maximum flexural strength, and peak stress in load-to-fracture tests, the fatigue test, and biofilm formation compared with acrylic resin and bis-acryl resin, while SLA resin showed favorable results only for biofilm formation and surface roughness.

Flexural strength of CAD-CAM and conventional interim resin materials with a surface sealant

Statement of problemThe flexural strength of computer-aided design and computer-aided manufacturing (CAD-CAM) and conventional interim resin materials when they are used with a surface sealant is unclear. PurposeThe purpose of this in vitro study was to evaluate the flexural strength of different CAD-CAM polymethyl methacrylate (PMMA)-based polymers and conventional interim resin materials, autopolymerized bisacrylate composite resin and polyethyl methacrylate (PEMA) with and without a surface sealant after thermocycling. Material and methodsFourteen rectangular-shaped specimens (25×2×2 mm) were fabricated from 5 different interim resin materials, 3 different CAD-CAM PMMA-based polymers: Polident-PMMA, Telio CAD, M-PM-Disc; 2 different conventional interim resin materials, and 1 autopolymerized bisacrylate composite resin: Acyrtemp and 1 PEMA resin: Bosworth Trim according to ISO 10477:2018. Two different types of surface treatments (n=7), conventional polishing and surface sealant application, were applied to 1 surface of the specimens. Ten thousand thermocycles were applied in distilled water for all specimens (5 °C and 55 °C). A 3-point bend test was used to measure the flexural strength of specimens in a universal testing device at a 1 mm/min crosshead speed. The flexural strength data (σ) were calculated in megapascals (MPa) and analyzed by using a 2-way ANOVA. Post hoc pairwise comparisons and independent t test analysis were done (α=.05). ResultsAccording to the 2-way ANOVA, material type (P<.001) significantly affected the flexural strength. Surface treatment type (P=.818) had no significant effect on flexural strength, and no significant interaction was found between material type and surface treatment type (P=.111). CAD-CAM PMMA-based polymers had significantly higher flexural strength than the conventional interim resin materials. However, no significant difference was found within groups of the same type. Also, no significant difference was found in flexural strength values between the conventional polishing and surface sealant groups within each interim resin material (P≥.162). ConclusionsThe flexural strength of CAD-CAM PMMA-based polymers was higher than the flexural strength of conventional bisacrylate composite resin and PEMA interim resin materials after thermocycling. The surface treatment type (conventional polishing and surface sealant application) was not found to affect the flexural strength of CAD-CAM PMMA-based polymers, conventional bisacrylate composite resin, or PEMA interim resin materials.

Nanofilled bis-acryl composite resin materials: Is it necessary to polish?

Statement of problemManufacturers of the recently introduced nanofilled bis-acryl composite resins no longer recommend polishing to produce interim restorations; however, whether this advice is appropriate is unclear. PurposeThe purpose of this in vitro study was to evaluate the effect of the type of interim resin material, polishing procedure, and artificial staining on surface roughness, gloss, and color. Material and methodsDisk-shaped specimens were prepared from 1 unfilled acrylic resin (Duralay) and 3 bis-acryl composite resins (Structur 3—nanofilled, Systemp C&B—microhybrid, Proviplast—microhybrid). The specimens of each material were assigned to 2 subgroups (n=15): polished and unpolished. Surface roughness (Ra—μm), gloss (UB), and color (ΔE) were analyzed at baseline and after 14 days of artificial staining. Roughness and gloss data were separately analyzed by 3-way ANOVA and color by 2-way ANOVA, followed by the post hoc Tukey test (α=.05). ResultsThe baseline roughness of all materials was significantly reduced by the polishing procedure, whereas the baseline gloss was increased (P<.001). Only the unpolished Proviplast had a significant increase in Ra values after aging. Structur 3 had higher gloss than Systemp C&B and Proviplast. The acrylic resin had the lowest color change after staining. ConclusionsThe polishing procedure produced smother and glossier surfaces for all the materials tested. The nanofilled bis-acryl composite resin material had higher gloss than the microhybrid bis-acryls tested, but it was not different from the acrylic resin. The 14 days of artificial staining did not promote significant changes in Ra or gloss values, except for Ra in the unpolished Proviplast subgroup, indicating excellent performance of the materials. The acrylic resin had the highest color stability.

Assessment of the Adaptation of Interim Crowns using Different Measurement Techniques.

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. 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. 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 coefficientof 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 coefficientof determination between the VPS impression and OCT techniques for marginal discrepancy measurement was low (R2 = 0.23). 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.