Comparing accuracy in guided endodontics: dynamic real-time navigation, static guides, and manual approaches for access cavity preparation - an in vitro study using 3D printed teeth.

OBJECTIVES: To assess root canal localization accuracy using a dynamic approach, surgical guides and freehand technique in vitro. MATERIALS AND METHODS: Access cavities were prepared for 4 different 3D printed tooth types by 4 operators (n = 144). Deviations from the planning in angle and bur positioning were compared and operating time as well as tooth substance loss were evaluated (Kruskal-Wallis Test, ANOVA). Operating method, tooth type, and operator effects were analyzed (partial eta-squared statistic). RESULTS: Angle deviation varied significantly between the operating methods (p < .0001): freehand (9.53 ± 6.36°), dynamic (2.82 ± 1.8°) and static navigation (1.12 ± 0.85°). The highest effect size was calculated for operating method (ηP²=0.524), followed by tooth type (0.364), and operator (0.08). Regarding deviation of bur base and tip localization no significant difference was found between the methods. Operating method mainly influenced both parameters (ηP²=0.471, 0.379) with minor effects of tooth type (0.157) and operator. Freehand technique caused most substance loss (p < .001), dynamic navigation least (p < .0001). Operating time was the shortest for freehand followed by static and dynamic navigation. CONCLUSIONS: Guided endodontic access may aid in precise root canal localization and save tooth structure. CLINICAL RELEVANCE: Although guided endodontic access preparation may require more time compared to the freehand technique, the guided navigation is more accurate and saves tooth structure.

Fracture toughness, work of fracture, flexural strength and elastic modulus of 3D-printed denture base resins in two measurement environments after artificial aging.

OBJECTIVES: To investigate the fracture toughness (KIC), work of fracture (WOF), flexural strength (FS) and elastic modulus (E) of four additively manufactured denture base resins in two different measurement environments after artificial aging. METHODS: Rectangular specimens in two different dimensions (n = 480) were 3D-printed with four denture base resins: Denture 3D+ (DEN; NextDent), Fotodent Denture (FOT; Dreve ProDiMed), Freeprint Denture (FRE; Detax), V-Print dentbase (VPR; VOCO)). KIC, WOF, FS and E were measured after (1) water-storage (37 °C; KIC = 7 d; FS = 50 h); (2) water-storage + hydrothermal-aging (20 min, 0.2 MPa, 134 °C); (3) water storage + thermocycling (10,000 cycles, 5/55 °C) in two measurement environments (i) air-23 °C and (ii) water-37 °C. For FS, fracture types were classified, and relative frequencies determined. Univariate ANOVA, Kruskal-Wallis, Mann-Whitney U, and Spearman's correlation were calculated (p < 0.05, SPSS V.27.0). Weibull modulus (m) was calculated using the maximum likelihood estimation method. RESULTS: DEN showed the highest KIC (5/6 groups), WOF and highest corresponding m (1/6 groups), while FRE presented the highest FS (2/6 groups) and E values. Hydrothermal-aging and thermocycling reduced KIC and WOF, FS and E, and the number of FS fracture pieces. For 6/8 groups, hydrothermal aging resulted in lower FS than thermocycling. Measurement in air-23 °C led to higher FS for 7/12 groups and a more brittle fracture behavior. A positive correlation between KIC and FS was observed. SIGNIFICANCE: With measurements in air-23 °C resulting in higher FS than reported in water-37 °C, the measurement environment should be adapted to the clinical situation to allow valid predictions on the mechanical behavior of denture base resins when in situ.

A New Implant System with Directly Screwed Supraconstructions: Impact of Restoration Material and Artificial Aging on the Bending Moment.

PURPOSE: To investigate the bending moment of implants restored with a directly screwed single-unit fixed dental prosthesis (FDP) compared to implants restored with an FDP polymerized to a titanium base before and after thermomechanical aging. MATERIALS AND METHODS: A total of 240 implants (120 with and 120 without a titanium base) were restored with FDPs manufactured from conventionally sintered 3Y-TZP, 5Y-TZP, 4Y-TZP, and CoCrMo, as well as high-speed sintered 4Y-TZP. Half the specimens per subgroup were aged using chewing simulation combined with thermocycling (1,200,000 cycles at 50 N; 6,000 cycles at 5° to 55°). Initial and aged fracture load were measured. The bending moment was calculated and subjected to statistical analysis (Kolmogorov-Smirnov test, one-way ANOVA followed by post hoc Scheffé, t, and chi-square tests; P < .05). Failure types were analyzed. RESULTS: Implants without a titanium base showed higher bending moments for all initially tested zirconia groups compared to implants with a titanium base. The highest initial values were observed for 4Y-TZP FDPs regardless of implant type. High-speed sintered FDPs demonstrated higher initial bending moments compared to conventionally sintered FDPs. Artificial aging led to a decrease of the bending moment in most subgroups. After aging, no differences were found within the restoration materials, sintering protocols, or implant types. Implant deformation occurred mainly with directly screwed FDPs, whereas FDP mobility was predominantly observed among implants with a titanium base. FDP fractures were mainly observed for 5Y-TZP. CONCLUSIONS: Both implant types exhibited similar values after aging. Thus, implants without a titanium base seem to show equally sufficient stability for clinical applications with all tested materials.

Three-Dimensional Printed Resin: Impact of Different Cleaning Protocols on Degree of Conversion and Tensile Bond Strength to a Composite Resin Using Various Adhesive Systems.

The present investigation tested the effect of cleaning methods and adhesives on the tensile bond strength (TBS) of a resin-based composite luted to a temporary 3D printed resin. Substrates (n= 360) were printed using a Rapidshape D20II and cleaned with a butyldiglycol-based solution, isopropanol, or by centrifugation. Specimens were air-abraded with Al2O3 (mean particle size 50 µm) at 0.1 MPa followed by pretreatment (n = 30/subgroup) with: (1) Clearfil Ceramic Primer (CCP); (2) Clearfil Universal Bond (CUB); (3) Scotchbond Universal Plus (SUP) or 4. Visio.link (VL) and luted to PanaviaV5. TBS (n = 15/subgroup) was measured initially (24 h at 37 °C water) or after thermal cycling (10,000×, 5/55 °C). The degree of conversion (DC) for each cleaning method was determined prior and after air-abrasion. Univariate ANOVA followed by post-hoc Scheffé test was computed (p < 0.05). Using Ciba-Geigy tables and chi-square, failure types were analyzed. The DC values were >85% after all cleaning methods, with centrifugation showing the lowest. CCP pretreatment exhibited the lowest TBS values, with predominantly adhesive failures. The combination of CCP and centrifugation increased the TBS values (p < 0.001) compared to the chemical cleaning. CUB, SUP, and VL, regardless of cleaning, can increase the bond strength between the 3D printed resin and the conventional luting resin.

Root Maturation of an Immature Dens Invaginatus Despite Unsuccessful Revitalization Procedure: A Case Report and Recommendations for Educational Purposes.

BACKGROUND: The clinical management of teeth with complex dens invaginatus (DI) malformations and apical periodontitis may be challenging due to the lack of routine. The aim of this case report is to describe the endodontic treatment of an immature tooth with DI and to discuss strategies for preclinical training for teeth with such malformations. CASE REPORT: A 9-year-old male presented with an immature maxillary incisor with DI (Oehlers Type II) and apical periodontitis which was diagnosed by cone beam computed tomography (CBCT). Revitalization was initially attempted but then abandoned after failure to generate a stable blood clot. Nevertheless, considerable increase in both root length and thickness could be detected after medication with calcium hydroxide followed by root canal filling with MTA as an apical plug. CONCLUSIONS: The endodontic management of teeth with DI requires thorough treatment planning. In immature teeth, under certain conditions, root maturation may occur even with conventional apexification procedures. From an educational perspective, different strategies including CBCT and 3D-printed transparent tooth models for visualization of the complex internal morphology and redesigned 3D-printed replica with various degrees of difficulty for endodontic training, can be used to overcome the challenges associated with endodontic treatment of such teeth.

Water sorption, water solubility, degree of conversion, elastic indentation modulus, edge chipping resistance and flexural strength of 3D-printed denture base resins.

OBJECTIVES: To investigate the water sorption (wsp), water solubility (wsl), degree of conversion (DC), elastic indentation modulus (EIT), edge chipping resistance (ECR) and flexural strength (FS) of 3D-printed, milled and conventionally polymerized denture base resin materials. METHODS: Specimens (N = 540) were 3D-printed (NextDent Denture 3D+ (DEN), Fotodent Denture (FOT), Freeprint Denture (FRE), V-Print dentbase (VPR)), cut (Ivotion Base (IVO)) and molded (PalaXpress (PAL)) in three geometries. Wsp,wsl,DC, EIT, ECR and FS were tested initially (24 h, 37 °C, H20) and after additional aging (5000 thermal cycles, 5/55 °C). Data were analyzed with Kolmogorov-Smirnov, univariate ANOVA, Kruskal-Wallis, Mann-Whitney U test and Spearman's correlation (p < 0.05) RESULTS: Most 3D-printed denture base resins showed higher wsp (25.31-37.94 µg/mm3) and wsl (0.08-8.27 µg/mm3), but also higher EIT (3.11-4.09 GPa) and FS (60.81-99.57N/mm2) values than the control groups. DEN and VPR showed high DC (89.36-93.53%), EIT (3.77-4.09 GPa) and FS (79.65-99.57N/mm2), while FOT showed low wsp (25.31-27.35 µg/mm3) and wsl (1.01-3.87 µg/mm3) values. In all materials, the examined parameters were affected by aging. SIGNIFICANCE: Although 3D-printed denture base resins showed promising results with regard to the observed DC and FS, only FOT and FRE surpassed the threshold values defined by the ISO norms.

Bond strength between temporary 3D printable resin and conventional resin composite: influence of cleaning methods and air-abrasion parameters.

OBJECTIVES: The influence of different cleaning methods, air-abrasion parameters, and aging on shear bond strength (SBS) and tensile bond strength (TBS) of 3D resin luted to composite resin. MATERIALS AND METHODS: Nine hundred resin substrates were 3D printed (D20II, Rapid Shape) and cleaned with either isopropanol (ISO), butyldiglycol-based solution (BUT), or centrifugation (CEN). After 24-h storage in 37 °C water, specimens were air-abraded (mean particle size 50 µm; n = 60) with either alumina at 0.1 MPa (AL0.1) or 0.4 MPa (AL0.4) and glass pearls at 0.1 MPa (GP0.1) and 0.4 MPa (GP0.4) or conditioned with visio.link (control) and luted with PanaviaV5. Initially (24 h, 37 °C water storage) or after aging (10,000 thermal cycles), SBS and TBS were measured, and fracture types were examined. Surface free energy (SFE) and roughness (Ra) were determined after air-abrasion. Kolmogorov-Smirnov, Kruskal-Wallis H, Mann-Whitney U, chi-square, and partial eta-squared were computed. RESULTS: SBS measurements presented higher values than TBS (p < 0.001-0.033). Within the pretreatment groups, CEN showed the highest SBS and TBS values compared to cleaning with ISO or BUT (p < 0.001-0.040). Pretreatment with GP0.1 displayed the lowest bond strength values (p < 0.001-0.049), and mostly adhesive fractures occurred. The highest Ra values (p < 0.001) were observed for AL0.4 pretreatment. CONCLUSIONS: Pretreatment with AL0.4 and the control group mainly presented the highest bond strength values. Thermocycling had a positive effect on the bond strength. CLINICAL RELEVANCE: According to this study, 3D-printed restorations should be pretreated with AL0.4 or with visio.link before adhesive luting, regardless of their cleaning.

Food Solutions and Cigarette Smoke-Dependent Changes in Color and Surface Texture of CAD/CAM Composite Resins-An In Vitro Study.

PURPOSE: To investigate the discoloration and surface properties of four CAD/CAM composite resins following storage in various food solutions and exposure to cigarette smoke. MATERIALS AND METHODS: A total of 74 specimens (N = 370) were prepared for five materials: Brilliant Crios (BC), Cerasmart (GC), Lava Ultimate (LU), Shofu Block HC (SH), and Sonic Fill 2 (SO). Discoloration (ΔE) was investigated with a spectrophotometer. Measurements were taken before immersion in storage media (carrot juice, curry, cigarette smoke, red wine, energy drink, and distilled water), after 2 weeks of immersion, and after manual polishing of the specimens following immersion. The average surface roughness (Ra) was measured with a profilometer. Qualitative surface observation was performed with scanning electron microscopy (SEM). Data were analyzed using Kolmogorov-Smirnov test, Mann-Whitney U test, and one-way ANOVA with Tukey post hoc test. RESULTS: The highest influence on ΔE after immersion was observed for storage medium (ηηP2 = 0.878, P < .001), followed by the interaction between storage medium and material (ηP2 = 0.770, P < .001) and material (ηP2 = 0.306, P < .001). For ΔE after polishing, the highest influence was indicated by the interaction between material and medium (ηP2 = 0.554, P < .001), followed by medium (ηP2 = 0.244, P < .001) and material (ηP2 = 0.196, P < .001). Immersion in carrot juice led to the highest color change (ΔE: 8.0 to 10.4), whereas the lowest values were recorded in distilled water (ΔE: 2.0 to 2.4). Carrot juice and the energy drink caused the highest Ra values (0.120 µm to 0.355 µm). SEM pictures indicated a loss of the organic matrix after manual polishing. CONCLUSION: The different materials reacted dissimilarly to the various storage media in terms of discoloration. Surface roughness increased after immersion or polishing. Neither discoloration nor surface roughness could be reset to default by manual polishing. Int J Prosthodont 2023;36:194-202. doi: 10.11607/ijp.6950.

A new implant system with directly screwed supra-constructions: Impact of restoration material and artificial aging on the bending moment.

PURPOSE: To investigate the bending moment of implants restored with a directly screwed single-unit fixed dental prosthesis (FDP) compared to implants restored with an FDP polymerized to a titanium base before and after thermomechanical aging. MATERIALS AND METHODS: A total of 240 implants (120 with and 120 without a titanium base) were restored with FDPs manufactured from conventionally sintered 3Y-TZP, 5Y-TZP, 4Y-TZP, and CoCrMo, as well as high-speed sintered 4Y-TZP. Half of the specimens per subgroup were aged using chewing simulation combined with thermocycling (1,200,000 cycles at 50 N; 6,000 cycles at 5°C to 55°C). Initial and aged fracture load were measured. The bending moment was calculated and subjected to statistical analysis (Kolmogorov-Smirnov test, one-way ANOVA followed by post hoc Scheffé, t, and chi-square tests; P < .05). Failure types were analyzed. RESULTS: Implants without a titanium base showed higher bending moments for all initially tested zirconia groups compared to implants with a titanium base. The highest initial values were observed for 4Y-TZP FDPs regardless of implant type. High-speed sintered FDPs demonstrated higher initial bending moments compared to conventionally sintered FDPs. Artificial aging led to a decrease of the bending moment in most of the subgroups. After aging, no differences were found within the restoration materials, sintering protocols, or implant types. Implant deformation occurred mainly with directly screwed FDPs, whereas FDP mobility was predominantly observed among implants with a titanium base. FDP fractures were mainly observed for 5Y-TZP. CONCLUSION: Both implant types exhibited similar values after aging. Thus, implants without a titanium base seem to show equally sufficient stability for clinical applications with all tested materials.

Bending moment of implants restored with CAD/CAM polymer-based restoration materials with or without a titanium base before and after artificial aging.

OBJECTIVES: To test and compare two types of implant systems restored with four monolithic polymer-based materials with regard to their bending moments (BM) before and after aging. METHODS: A total of 192 tissue-level implants (TRI Dental Implants) differing in the presence (TiB, Octa line, n = 96) or absence (NTiB, Matrix line, n = 96) of a titanium base were restored with mandibular right first molar crowns manufactured from composite (CC), polymer-infiltrated ceramic (VE), PMMA (PM) and a 3D printed resin (ND) (n = 24). Half of the specimens (n = 12) were loaded for 1,200,000 cycles (50 N, 1.3 Hz, TC: 5/55 °C, 6000×) and examined for failures. Fracture load was measured according to ISO standard 14801, BM was calculated, and fracture types were examined. Data were analyzed using parametric statistics (p < 0.05). RESULTS: No failures were observed after 600,000 cycles. After 1,200,000 cycles, wear traces were recorded in all groups except PM, VE and CC on TiB implants. In group CC on NTiB implants, three specimens were rated zero in BM testing as they showed fracture of the screw. Regarding BM, TiB implants exhibited higher values than NTiB implants with aged CC (p = 0.023), aged PM (p < 0.001), initial PM (p = 0.011) and initial VE (p < 0.001). No differences occurred among the implant types with initial CC, initial ND, aged ND and aged VE. With regard to initial BM values, NTiB implants showed higher values for ND and CC compared with PM and VE (p < 0.001). No differences in initial BM values were found for the tested materials on TiB implants (p > 0.116). When aged, restoration material had no impact on the BM values of NTiB implants (p ≥ 0.233). Aged TiB implants showed higher values in combination with CC than with ND (p = 0.001). PM and VE showed similar values as ND and CC. Artificial aging led to a decrease of BM within PM, CC and ND on NTiB implants and ND on TiB implants. The majority of failures after testing were characterized by crown fractures in two to four pieces. Fractures in more pieces with smaller fragments occurred primarily for ND. SIGNIFICANCE: The use of NTiB implants with the polymer-based materials tested can only be recommended for clinical use as interim prostheses. CC seems to show a positive effect on the BM. Clinical research investigating the in vivo behavior is necessary to confirm these findings.

Influence of 3D-printing method, resin material, and sterilization on the accuracy of virtually designed surgical implant guides.

STATEMENT OF PROBLEM: Three-dimensional printing has introduced new manufacturing methods. However, information on the influence of the specific printing technology, material, sterilization, and the comparison between printing and milling on the accuracy of surgical guides is lacking. PURPOSE: The purpose of this in vitro study was to evaluate the influence of the manufacturing method (printing and milling), printing technology stereolithography (SLA) and digital light processing (DLP), material, and sterilization on the accuracy of digitally designed surgical implant guides. MATERIAL AND METHODS: Resin patient replicas with a single edentulous space were used to place 132 implants with digitally designed surgical guides. The accuracy of postoperative implant position was analyzed for the manufacturing method (printing and milling), resin materials, and preoperative autoclaving. To determine 3D accuracy, angular displacement, mean horizontal crestal, apical displacement, and the linear vertical displacement at the apex were calculated separately for each group (n=12). In addition, the surgical guides were qualitatively analyzed by using field emission scanning electron micrograph. RESULTS: The postoperative angular deviation ranged from 0.76 ±0.52 degrees (Rapidshape D20II with NextDent SG) to 2.43 ±0.64 degrees (Form2 with NextDent SG) (P<.001). Linear horizontal displacement at the crest was smallest for Rapidshape D20II with 3Delta Guide (0.27 ±0.08 mm) and highest for Form2 with NextDent SG (0.54 ±0.10 mm) (P<.001). Linear horizontal displacement at the apex ranged from 0.36 ±0.10 mm (SolFlex 350 with V-Print SG) to 0.89 ±0.32 mm (Form2 with NextDent SG) (P<.001). Considering the vertical position displacement was no more than 0.43 ±0.07 mm (Form2 with NextDent SG) short of the apex, none of the implant tips were displaced apically. Preoperative autoclaving differentially impaired the accuracy of surgical guides. CONCLUSIONS: The specific manufacturing technique, the 3D printing device, the resin material, and the application of preoperative sterilization all affected the accuracy of the postoperative implant position. Irrespective of the manufacturing method, all implants were placed within the commonly accepted safety distance.

Methodology investigation: Impact of crown geometry, crown, abutment and antagonist material and thermal loading on the two-body wear of dental materials.

OBJECTIVES: To investigate the impact of crown geometry, crown/abutment/antagonist material and thermal loading on the two-body wear of dental materials caused by chewing simulation. MATERIALS AND METHODS: For the crown geometry, crowns (polymethylmethacrylate (PMMA), polyetheretherketone (PEEK) and silicate ceramic (SiO2)) were milled with a flat, steep, or medium cusp inclination (CINC). For the crown/abutment material, crowns (PMMA, PEEK and SiO2) were combined with PMMA, polymer-infiltrated-ceramic-network (PICN), cobalt-chrome alloy (CoCr) and natural teeth (ENAM) abutments. For the antagonist material, antagonists were fabricated from PICN, CAD/CAM resin composite (RECO), steatite (STEA), steel (STL) and ENAM and tested against flat specimens (substrates) made of veneering ceramic (VC). For thermal loading, the duration (30 s, 60 s, 120 s) and presence of temperature changes (37 °C versus 5 °C/55 °C) was varied. Material losses were determined by matching scanned specimens before and after aging (400,000 chewing cycles, 50 N, 1.3 Hz). Martens parameters were determined for the antagonists/substrates. Data were analyzed using Kolmogorov-Smirnov-test, Kruskal-Wallis H, Scheffé-Post-Hoc-tests, pairwise comparisons, Bonferroni correction, one-way ANOVA, Mann-Whitney-U and Spearman rho. RESULTS: PMMA crowns presented the highest and PEEK the lowest material losses. Flat CINC showed the lowest material losses for PEEK and SiO2 crowns. CoCr and ENAM abutments presented material losses in the same range. Antagonist and cumulative material losses for RECO and ENAM were similar. Thermal loading did not influence material losses. SIGNIFICANCE: Crown geometry influences the crown and antagonists wear, with an increased cusp inclination entailing increased wear. For in vitro set-ups, CoCr abutments and RECO antagonists present valid alternatives to natural teeth. For polymers, in vitro chewing simulations may be performed at a constant temperature (37 °C).

Postpolymerization of a 3D-printed denture base polymer: Impact of post-curing methods on surface characteristics, flexural strength, and cytotoxicity.

OBJECTIVE: This study investigated the influence of postpolymerization of a three-dimensional (3D) printed denture base polymer. The effect of post-curing methods on surface characteristics, flexural strength, and cytotoxicity was evaluated. METHODS: A total of 172 specimens were additively manufactured using one denture base material (V-Print dentbase, VOCO) and further post-cured by different light-curing devices, including Otoflash G171 (OF), Labolight DUO (LL), PCU LED (PCU), and LC-3DPrintbox (PB), respectively. Polymethyl methacrylate resin (PalaExpress Ultra) was used as a reference (REF). Afterward, surface topography was observed using scanning electron microscopy, and surface roughness was measured (n = 6). Furthermore, flexural strength was tested (n = 20). Cytotoxicity was evaluated by the extract and direct contact tests. The data were analyzed using the Kolmogorov-Smirnov test and one-way ANOVA followed by Tukey's multiple comparisons and Kruskal-Wallis tests (p < 0.05). RESULTS: The different post-curing methods applied did not significantly influence surface topography and roughness (Ra). Meanwhile, specimens post-cured by PCU (162.3 ± 44.16 MPa) and PB (171.2 ± 34.41 MPa) showed significantly higher flexural strength than those post-cured by OF (131.3 ± 32.87 MPa) and REF (131.2 ± 19.19 MPa), respectively. Additionally, various post-curing methods effectively decreased the cytotoxic effects of 3D-printed denture base polymer. CONCLUSIONS: Different post-curing methods did not significantly alter the Ra values of the 3D-printed denture base material. However, flexural strength was significantly affected by the postpolymerization methods, which might be attributed to the different wavelengths of post-curing devices. In addition, various postpolymerization methods reduced the cytotoxic effects of the 3D-printed denture base polymer. CLINICAL SIGNIFICANCE: Flexural strength of additively manufactured denture bases depends on the postpolymerization strategy. Therefore, an appropriate post-curing method is required to optimize the flexural strength of 3D-printed denture materials.

Influence of cleaning methods after 3D printing on two-body wear and fracture load of resin-based temporary crown and bridge material.

OBJECTIVES: To investigate the impact of different cleaning methods on the fracture load and two-body wear of additively manufactured three-unit fixed dental prostheses (FDP) for long-term temporary use, compared to the respective outcomes of milled provisional PMMA FDPs. MATERIALS AND METHODS: Shape congruent three-unit FDPs were 3D printed using three different resin-based materials [FPT, GCT, NMF] or milled [TEL] (N = 48, n = 16 per group). After printing, the FDPs were cleaned using: Isopropanol (ISO), Yellow Magic 7 (YEL), or centrifugal force (CEN). Chewing simulation was carried out with a vertical load of 50 N (480,000 × 5 °C/55 °C). Two-body wear and fracture load were measured. Data were analyzed using global univariate ANOVA with partial eta squared, Kruskal-Wallis H, Mann-Whitney U, and Spearman's rho test (p < 0.05). RESULTS: TEL showed less wear resistance than FPT (p = 0.001) for all cleaning methods tested. Concerning vertical material loss, NMF and GCT were in the same range of value (p = 0.419-0.997), except within FDPs cleaned in ISO (p = 0.021). FPT showed no impact of cleaning method on wear resistance (p = 0.219-0.692). TEL (p < 0.001) showed the highest and FPT (p < 0.001) the lowest fracture load. Regarding the cleaning methods, specimens treated with ISO showed lower fracture load than specimens cleaned with CEN (p = 0.044) or YEL (p = 0.036). CONCLUSIONS: The material selection and the cleaning method can have an impact on two-body wear and fracture load results. CLINICAL RELEVANCE: Printed restorations showed superior two-body wear resistance compared to milled FDPs but lower fracture load values. Regarding cleaning methods, ISO showed a negative effect on fracture load compared to the other methods tested.

Impact of high-speed sintering on accuracy and fit of 4 mol% yttria-stabilized tetragonal zirconia polycrystals (4Y-TZPs).

PURPOSE: To investigate the impact of high-speed sintering on the accuracy (trueness and reproducibility) and fit of 4Y-TZP full-coverage single-unit fixed dental prostheses (FDPs) and three-unit FDPs. MATERIALS AND METHODS: Single-unit FDPs, conventional three-unit FDPs, and cantilever three-unit FDPs (N = 108; n = 12 per subgroup) were fabricated from: (1) high-speed sintered (1,580°C, about 20 minutes) multi-layer 4Y-TZP (Zolid RS, Amann Girrbach; ZMLH group), as well as two conventionally sintered (1,450°C, about 10 hours) materials: (2) multi-layer 4Y-TZP (Zolid Gen-X, Amann Girrbach; ZMLC group) and (3) monochrome 4Y-TZP (Ceramill Zolid HT+ PS, Amann Girrbach; ZMOC group). All specimens were scanned. Trueness, reproducibility, and fit were measured with 3D analysis software. For data analysis, Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests were performed (α = .05). RESULTS: Three-unit FDPs made from ZMLH presented a deterioration of accuracy in comparison to ZMLC (P ≤ .001 to .008). The influence of highspeed sintering on marginal and general fit was not clinically relevant (P = .154 to .877). CONCLUSION: High-speed sintering influenced the accuracy of 4Y-TZP full-coverage single-unit and three-unit FDPs. However, no clinically relevant impact on fit was observed.

Temporary 3D printed fixed dental prosthesis materials: Impact of post printing cleaning methods on degree of conversion as well as surface and mechanical properties.

PURPOSE: To investigate the influence of different cleaning methods for additively manufactured fixed dental prostheses (FDPs) for long-term temporary use on the degree of conversion (DC), surface roughness, Martens parameters, and biaxial flexural strength. MATERIALS AND METHODS: A total of 180 specimens per material (3Delta Etemp, DeltaMed; Freeprint Temp, Detax; Temp PRINT, GC Europe; Temp C&B and C&B MFH, NextDent; N = 180) were additively manufactured (D20 II, Rapid Shape) and subsequently cleaned by different methods: by rinsing for 5 minutes in acetone (Höfer Chemie; 99.5%); butyl glycol (Algin Chemie; 100%); ethanol (Otto Fischar; 96%); isopropanol (SAV LP; 100%); Yellow Magic 7 (Bradley Systems; 100%); or by applying centrifugal force for 4 minutes (n = 30 per subgroup). After postpolymerization (Otoflash G171, NK-Optik), the DC was measured using Raman spectroscopy, and the surface roughness, as well as the Martens parameters, were recorded. Biaxial flexural strength was investigated after artificial aging (thermocycling for 10,000 cycles). Data were statistically analyzed (Kolmogorov-Smirnov, Kruskal-Wallis, and Mann-Whitney U tests, and Pearson correlation coefficient). RESULTS: The highest DC was recorded after the use of butyl glycol or isopropyl (P < .001 to P = .047). The highest surface roughness was measured after the use of butyl glycol (P < .001 to P = .024). The use of centrifugal force or Yellow Magic resulted in the highest Martens parameter values (P < .001 to P = .036) and the highest biaxial flexural strength (P < .001 to P = .013), while acetone and butyl glycol led to the lowest values. CONCLUSION: The use of centrifugal force and Yellow Magic resulted in the highest Martens parameter values and the highest biaxial flexural strength. Concerning Yellow Magic, no negative effect on the mechanical properties was observed. The 3Delta Etemp material especially was prone to degradation after chemical cleaning.

Treatment outcomes after uncomplicated and complicated crown fractures in permanent teeth.

OBJECTIVES: The objectives of this retrospective clinical study were to describe characteristics of crown fractures in permanent teeth and to investigate the survival of pulp vitality and restorations in uncomplicated and complicated crown fractures. MATERIALS AND METHODS: This retrospective study collected information from patients suffering from dental trauma who were treated between January 2004 and June 2017. The study population consisted of 434 patients (253 males/181 females; mean age 20.7 years) with 489 uncomplicated and 127 complicated crown fractures. The Kaplan-Meier survival curves and Cox proportional hazard regression analyses were performed to explore the data statistically. RESULTS: The mean observation time was 522 days. Uncomplicated crown fractures without luxation showed a higher success rate of 82.3% (345/419) than complicated crown fractures without luxation (72.3%, 73/101). An additional luxation in uncomplicated crown fractures resulted in significantly reduced success rates in terms of survival of the pulp and restoration. Direct restorations survived significantly better independent of the fracture mode than did adhesively reattached crown fragments. No superiority of mineral trioxide aggregate or calcium hydroxide as pulp capping agent in complicated crown fractures was documented. Approximately 85.5% of all complications occurred within 2 years after the accident. CONCLUSION: The treatment of crown fractures resulted mostly in successful outcomes and only a moderate number of complications were observed. CLINICAL RELEVANCE: Primary dental management of crown fractures should follow recently published clinical guidelines, and close monitoring over at least 2 years seems to be justified.

In vitro study on the influence of postpolymerization and aging on the Martens parameters of 3D-printed occlusal devices.

STATEMENT OF PROBLEM: Additive manufacturing has been proposed for the fabrication of occlusal devices. However, information about the mechanical properties of additively manufactured devices is lacking. PURPOSE: The purpose of this in vitro study was to evaluate the influence of the postpolymerization unit and artificial aging on the Martens hardness (HM) and indentation modulus (EIT) of different 3D-printed materials in comparison with a conventionally milled material. MATERIAL AND METHODS: Thirty disks (20 mm in diameter and 5 mm in thickness) were additively manufactured (D20 II, Rapidshape & Form 2) for each 3D-printed material (NextDent Splint, Formlabs Dental LT Clear, and Freeprint Splint). As a control, 10 disks of the same thickness were cut from a conventionally milled material (Temp Premium). Each specimen was measured for HM and EIT (ZHU 0,2) after fabrication. The specimens were stored in water at 37 °C and measured again after 2 and 4 weeks. The data were analyzed statistically by using the Kruskal-Wallis, Mann-Whitney U, and Wilcoxon tests (adjusted by Bonferroni correction α=.05/27=.002). RESULTS: The highest influence on HM parameters was shown by artificial aging (partial eta squared: HM: ηP2=0.840, EIT: ηP2=0.855, P<.001), followed by the material (HM: ηP2=0.690 EIT: ηP2=0.845, P<.001) and the postpolymerization unit (HM: ηP2=0.649, EIT: ηP2=0.778, P<.001). Initial HM values ranged from 147 ±8.11 N/mm2 for Formlabs postpolymerized in Otoflash to 89.5 ±8.55 N/mm2 for Detax postpolymerized in the Labolight unit. EIT values ranged from 3.92 ±0.061 kN/mm2 for Formlabs postpolymerized in Otoflash to 2.48 ±0.212 kN/mm2 for Detax postpolymerized in the Labolight unit. In general, HM and EIT values decreased after water storage, whereas the values remained unchanged for the control group. CONCLUSIONS: HM parameters of additively manufactured occlusal devices depend on postpolymerization strategy. Otoflash and Printbox result in higher HM and EIT values. The 3D-printed materials are more prone to artificial aging than the control group, which brings into question their long-term service.

Impact of polymerization and storage on the degree of conversion and mechanical properties of veneering resin composites.

To investigate the degree of conversion (DC), Martens hardness (HM), elastic indentation modulus (EIT), and flexural strength (FS) of veneering resin composites (SR Nexco Paste (NP), Ceramage Incisal (CI), Gradia Plus (GP); n=60/group) cured with different polymerization devices (bre.Lux Power Unit, Labolight DUO, Otoflash G171, LC-3DPrint Box, PCU LED; n=12/subgroup) after storage. Otoflash G171 and Labolight DUO showed increased DC/HM/EIT. CI presented the lowest DC and highest HM/EIT. NP showed the highest DC and lowest HM/EIT. Within Otoflash G171, Laboligth DUO and PCU LED, highest FS was observed for CI. Storage did not affect DC/HM/EIT for specimens cured with Otoflash G171 or Labolight DUO. With storage not showing an influence on the tested parameters for polymerization devices that otherwise presented superior results, increased storage time cannot be recommended. For the tested resin composites, this study observed a high/low degree of conversion to coincide with respectively low/high amounts of fillers/mechanical properties.

Development and evaluation of an interdisciplinary teaching model via 3D printing.

The investigation aimed to assess the feasibility of creating an interdisciplinary training model simulating endodontic, restorative as well as implantologic treatment procedures by using 3D printing technology. A CBCT scan of the mandible of a real patient was initially taken. The generated DICOM-data were converted to a STL-file, which was further processed to design spaces for exchangeable replica teeth, a bone segment and an adapter to fix the model in a mannequin's head. After the manufacturing process, the model was evaluated by dental students performing a root canal treatment, the insertion of a glass fibre post and the insertion of an implant. The workflow allowed a simple and cost-effective way of manufacturing a single model, which is suitable for several training scenarios in the fields of endodontics, prosthodontics and implantology. The model was rated as being comparable to the real patient situation and offers repetitive treatment simulations. The present workflow is a feasible way of using DICOM-data and 3D printing for an interdisciplinary training model. The dental schools can design models according to their own curriculum and put the focus on a patient centered education.