Dimensional Stability and Reproducibility of Varying FFF Models for Aligners in Comparison to Plaster Models.

To test the impact of FFF filaments, printing parameters, thermoforming foils, repeated thermoforming cycles, and type of jaw on the dimensional stability of FFF models for aligners and to compare them with plaster models, FFF models (maxilla, n = 48; mandible, n = 48) from two filaments (SIMPLEX aligner and Renfert PLA HT, both Renfert GmbH) were fabricated using four printing parameters (one, two, or three loops; four loops acted as the default) and conventional plaster models (n = 12) based on a young, female dentition. All models were thermoformed under pressure three times in total using two different thermoforming foils, namely 0.75 mm × 125 mm Ø aligner foil (CA Pro+ Clear Aligner, Scheu Dental) and 1.0 mm × 125 mm Ø Duran foil (Duran+, Scheu Dental). Aligner foil was heated at 220 °C for 25 s and Duran foil at 220 °C for 30 s. All models were scanned after fabrication as well as after each thermoforming cycle. The obtained STL datasets were analyzed using the local best-fit method (GOM Inspect Pro, Carl Zeiss Metrology GmbH). Data were analyzed using a Kolmogorov-Smirnov-test, a one-way ANOVA with post-hoc Scheffé, and a t-test (p < 0.05). The dimensional stability of the models was most strongly affected by the printing parameters (number of loops; ηp2 = 0.768, p < 0.001) followed by the thermoforming foil used (ηp2 = 0.663, p < 0.001) as well as the type of model (ηp2 = 0.588, p < 0.001). In addition, various interactions showed an influence on the dimensional stability (ηp2 = 0.041-0.386, p < 0.035). SIMPLEX maxillary models (default; four loops), thermoformed using aligner foil, showed higher deformation stability than did plaster models. These initial FFF models provide comparable precision to plaster models, but the dimensional stability of the FFF models, in contrast to that of plaster models, decreases with increasing numbers of thermoforming cycles.

Fracture toughness of 3Y-TZP ceramic measured by the Chevron-Notch Beam method: A round-robin study.

OBJECTIVE: This interlaboratory round robin test investigated the robustness of the Chevron-Notch Beam (CNB) test method and the effect of the processing and testing variations on the fracture toughness of a dental 3Y-TZP ceramic. METHODS: The round robin test was performed precisely following the procedures recommended in ISO 24370:2005 and applied on a commercial 3Y-TZP ceramic (product information). A total of 335 test specimens with dimensions 3×4 x 45 mm³ was equally distributed among 10 participating laboratories of varying experience in fracture toughness testing. A standard operating procedure was defined with either narrow processing tolerances or alternative (wider) processing tolerances (as proposed in ISO 24370). Fracture toughness data (series 2) was analyzed using one way ANOVA followed by post hoc Tukey HSD test and 95% Confidence Intervals (CI) were computed (p < 0.05). A further, preceding round-robin (series 1) test was conducted with - more possible variations of test conditions regarding CNB notch processing and storage conditions. Those results are summarized in the supplement and discussed with the actual ISO 24370 test. RESULTS: Fracture toughness of the 3Y-TZP ceramic material, summarized over all laboratories was measured to KIc = 4.48 ± 0.11 MPam0.5 for the standard processing tolerance and KIc = 4.55 ± 0.31 MPam0.5 for the alternative tolerance. The results revealed a significant influence of cutting offset and notch geometry on KIc when using CNB method. The test medium also has a significant influence on KIc in terms of reduced fracture toughness under the influence of water. With defined testing conditions the number of valid tests and reduced standard deviation increased. In case of strictly following such standard operation procedures, KIc can be determined with high reliability. There is no difference between the involved laboratories, but significant influence of cutting offset on KIC was observed. SIGNIFICANCE: The CNB method is suitable method for determination of KIc on fine-grained ceramics such as 3Y-TZP ceramic. By using tighter tolerances for processing and testing, i.e. closely following the ISO 24370 procedure, a highly-precise evaluation of fracture toughness with low data variation is achievable. The information of the storage medium should always be reported along with the data. CNB fracture toughness testing is an alternative method compared to Single-edge V-notch beam (SEVNB), especially for fine-grained ceramics.

Comparison of mechanical properties of different reinforced glass-ceramics.

STATEMENT OF PROBLEM: Data concerning the mechanical properties of the newly developed lithium disilicate ceramic HS10PC are lacking. PURPOSE: The purpose of this in vitro study was to investigate the flexural strength (FS), Martens hardness (HM), indentation modulus (EIT), fracture load (FL), and wear resistance (WR) of HS10PC compared with those of the established glass-ceramics IPS e.max Press and IPS Empress Esthetic. MATERIAL AND METHODS: Four pressable glass-ceramics were examined: HS10PC (estetic ceram ag), IPS e.max Press low translucency (LT) and high translucency (HT; Ivoclar Vivadent AG), and IPS Empress Esthetic (ES; Ivoclar Vivadent AG). For each material, a total of 85 specimens were fabricated. Specimens were subdivided into 4 groups for FS (n=30), HM, EIT (n=10), and FL measurement according to the Voss test after artificial aging in an autoclave (n=15), artificial aging in a mastication simulator (n=15), and no artificial aging (n=15). In addition, WR (n=10) was measured after 240 000, 600 000, and 1 200 000 masticatory cycles. Data were statistically analyzed using the global univariate ANOVA, the Scheffé post hoc and paired t tests, and Weibull distribution (α=.05). RESULTS: HT showed the highest FS, while ES presented the lowest FS of all groups (P<.001). ES showed lower values for HM (P<.001), EIT (P<.001), and FL for specimens treated in an autoclave and mastication simulator (P<.001) compared with all other groups. An increase in the wear of the ceramic and enamel antagonist between 240 000 and 1 200 000 masticatory cycles was observed for all groups (P<.001). After 1 200 000 masticatory cycles, HS10PC presented less wear of the ceramic than the other 3 materials (P=.003). CONCLUSIONS: The newly developed lithium disilicate ceramic HS10PC showed comparable results with the established IPS e.max Press for FS, HM, EIT, FL, and WR. Lithium disilicate ceramics presented higher mechanical results than the leucite-reinforced ES, with all the ceramics showing similar results for the WR of the enamel antagonist.

Bonding Behavior Between Polyetheretherketone and Polymethylmethacrylate Acrylic Denture Polymer.

PURPOSE: To investigate the impact of pretreatment and conditioning on shear bond strength (SBS), surface free energy (SFE) and surface roughness (SR) between polyetheretherketone (PEEK) and cold-cured polymethylmethacrylate (PMMA). MATERIALS AND METHODS: PEEK substrates (Dentokeep PEEK Disc, nt-trading) were air abraded with Al2O3 particles of different grain sizes applied with varying pressure at 1) 0.2 MPa - 50 µm Al2O3; 2) 0.4 MPa - 50 µm Al2O3; 3) 0.2 MPa - 110 µm Al2O3; 4) 0.4 MPa - 110 µm Al2O3; or 5) without air abrasion (n = 172/group). Surface properties were quantified using SFE and SR (n = 10/group), and scanning electron microscope imaging (n = 2/group). Substrates were conditioned with a) Visio.link (VL, Bredent); b) Scotchbond Universal (SU, 3M Oral Care); c) Bonding Fluid (BF, Schütz Dental); or d) without conditioning (WC; n = 40/subgroup) and bonded to the polymer (Futura Jet, Schütz Dental). SBS and fracture types were determined before and after 10,000 thermal cycles (n = 20/subgroup). Univariate ANOVA, Kruskal-Wallis test, Mann-Whitney U-test, Kaplan-Meier survival estimates, and Weibull distribution were computed (p < 0.05). Ciba-Geigy tables and the chi-squared test were used to analyze fracture type distributions. RESULTS: An increase in particle size and pressure resulted in similar or increased SBS, Weibull characteristic strength, and Weibull moduli (p < 0.001 - 0.046). The lowest results were observed for the control group (without air abrasion), while pretreatment with 0.4 MPa - 110 µm Al2O3 presented the highest values (p < 0.001). In comparison with the other conditioning procedures, VL showed high (p < 0.001 - 0.03), and SU and WC low SBS (p < 0.001 - 0.006). Although it did not influence SFE, an increase in particle size and pressure led to an increased SR (p < 0.001). CONCLUSION: Pretreatment with 0.4 MPa - 110 µm Al2O3 can be recommended to increase bonding properties between PEEK and PMMA. Application of adhesives such as VL can enhance SBS further.

Characterization of Methacrylate-Based Resins Containing Methacryl-Polyhedral Oligomeric Silsesquioxanes (MA-POSS-8).

The use of functionalized dental adhesives that might prevent degradation of the dentin hybrid layer has been proposed. The aim of the study was to characterize the physicochemical properties and the potential to induce mineral precipitation of methacrylate-based resins containing methacryl-functionalized polyhedral oligomeric silsesquioxane (MA-POSS-8). In total, six different compositions of resins based on bisphenol A glycerolate dimethacrylate (BisGMA, 40 to 60 wt.%), triethylene glycol dimethacrylate (TEGDMA, 5 to 35 wt.%) and 2-hydroxyethyl methacrylate (HEMA, 25 or 35 wt.%) were prepared and infiltrated with 5 wt.% MA-POSS-8. Unfilled resins served as control. Degree of conversion, viscosity, Martens hardness, indentation modulus, water sorption, and sol fraction were investigated. Polymerized specimens were examined by SEM/EDX for the presence of Ca/P precipitates after immersion in artificial saliva for 28 days at 37 °C. Statistical analysis was performed with two-way ANOVA and Tukey's post-hoc test (p < 0.05). The degree of conversion ranged from 55.0 to 59.8% and was not affected by the addition of MA-POSS-8. Viscosity ranged from 60.0 to 422.3 mPa*s and was not affected by MA-POSS-8 except for one methacrylate-based resin with 60 wt.% BisGMA. Martens hardness and indentation modulus ranged from 161.3 to 138.1 N/mm2 and 4.2 to 3.9 kN/mm2 and were affected by MA-POSS-8 in only one resin (50 wt.% BisGMA, 25 wt.% TEGDMA, 25 wt.% HEMA). Water sorption was not affected by MA-POSS-8; sol fraction was below the detection limit. Formation of Ca/P precipitates was observed on all specimens of test and control groups. Material properties were not affected adversely by MA-POSS-8 except for slight differences in Martens hardness, indention modulus, viscosity in some groups. However, bioactive properties could not be improved by MA-POSS-8.

Impact of varying step-stress protocols on the fatigue behavior of 3Y-TZP, 4Y-TZP and 5Y-TZP ceramic.

OBJECTIVE: To test the impact of three varying step-stress protocols on the fatigue behavior of two 3Y-TZP, one 4Y-TZP and one 5Y-TZP zirconia materials. METHODS: Eight specimens per zirconia material (N = 32) were selected for static testing to determine the start load for dynamic tests (30% of the mean value of static fracture load). 45 specimens per material (N = 180) were used for dynamic load tests using three step-stress protocols: 1. 50 N/5000 cycles; 2. 5% of static load/5000 cycles, and 3. 10 N/1000 cycles. Following materials were tested: 3Y-TZP(<0.25 Al2O3) (O: opaque) 3Y-TZP(<0.05 Al2O3) (T: translucent), 4Y-TZP(<0.01 Al2O3) (ET: extra translucent) and 5Y-TZP(<0.01 Al2O3) (HT: high translucent). The specimens (4 ± 0.02 × 3 ± 0.02 × 45 mm) were placed centrally on the support rolls and the load was applied perpendicularly over the 4 mm specimen side (∼4-point flexural strength according to the DIN 6872:2019). Data was analyzed with Kolmogorov-Smirnov-test, t-test, one-way ANOVA with post-hoc Scheffé-test, Chi-square-test, Kaplan-Meier with Log-Rank-test and two-parametric Weibull analysis (p < 0.05). RESULTS: The step-stress protocols showed no impact on the fracture load or Weibull modulus within one zirconia material. However, the zirconia materials T, ET and HT showed differences in cycle number to fracture between the step-stress protocols (T: 3 > 2 > 1; ET: 2 > 3 > 1; HT: 2, 3 > 1) with lowest cycle number to fracture for protocol 1. Within one step-stress protocol, the cycle number to fracture varied according to the zirconia material as follows: 1: T, O ≥ O, ET > HT; 2: ET > O, T, HT; 3: O, T, ET > HT. Cracking started at the tensile side of the specimens at all times. All specimens showed typical compression curls (single or double). Fragmentation patterns were similar for all materials with a lot of crack branching and fragmentation due to secondary cracks indicating high energy fractures. SIGNIFICANCE: Dynamic fatigue tests seem to provide important information on the long-term stability of zirconia materials. Zirconia materials with higher opacity seem to be more robust towards varying step-stress protocols than translucent zirconia materials. Regarding expenditure of time, a step-stress protocol with a load increase of 50 N every 5000 cycles seems favorable to gain information on the long-term stability of zirconia materials.

Fatigue resistance of monolithic strength-gradient zirconia materials.

PURPOSE: Evaluation of the effect of three different dynamic fatigue protocols on the fracture resistance of two monolithic strength-gradient zirconia materials. MATERIALS AND METHODS: A total of 240 specimens (3 × 4 × 45 mm) was milled from two different layers (incisal and middle) of two types of strength-gradient zirconia blanks (IPS e. max ZirCAD MT Multi A2 vs. IPS e. max ZirCAD Prime A2), resulting in 60 specimens per material and layer group (IPS e. max ZirCAD MT Multi A2: incisal (MI), middle (MM); IPS e. max ZirCAD Prime A2: incisal (PI), middle (PM)). Each group was divided into one static (n = 15) and three dynamic fatigue protocols (N = 45, n = 15): i. 50 N increase every 5000 cycles ii. Increase by 5% of static fracture load every 5000 cycles iii. 10 N increase every 1000 cycles until facture. All specimens were loaded until facture in CeraTest 2 k. Kaplan-Meier, Log-Rank and Chi-squared-test as well as Weibull statistics were performed. A fractographic analysis was performed. The specimens were classified according to the number of crack origins and evaluated using the Ciba-Geigy table. RESULTS: With regard to the fracture load, in the static loading MI and PI showed a higher fracture load and in dynamic fatigue protocol 2 PI showed a lower fracture load. The number of cycles until fracture only differed within three groups: MM and MI survived a higher number of cycles in dynamic fatigue protocol 2; PI survived a higher number of cycles in dynamic fatigue protocol 2 than in protocol 1. Within dynamic fatigue protocols, PM resisted the highest number of cycles in protocol 1 and 3 and MI in protocol 2. Comparing groups, Weibull modulus differed only within the static loading, with PI showing lower values than MM and MI. Within the material groups, MI showed higher values in static loading than in dynamic fatigue protocol 1 and 2, and PI showed higher values in the dynamic fatigue protocol 3 than in static loading. With regard to fracture patterns, no differences were found between the groups. CONCLUSIONS: Dynamic fatigue protocols provide clinically relevant information on the long-term stability and reliability of monolithic strength-gradient zirconia materials. However, no definitive instructions for dynamic testing can be provided from this investigation.

Impact of artificial aging by thermocycling on edge chipping resistance and Martens hardness of different dental CAD-CAM restorative materials.

STATEMENT OF PROBLEM: The selection of an appropriate restorative material based on fracture behavior is important for the marginal integrity of a dental restoration. For computer-aided design and computer-aided manufacturing (CAD-CAM) restorative materials, information regarding their edge chipping resistance is scarce. PURPOSE: The purpose of this in vitro study was to determine the edge chipping resistance (ECR) and Martens hardness (HM) of 6 different dental CAD-CAM restorative materials before and after thermocycling. MATERIAL AND METHODS: Four composite resin materials including Brilliant Crios; Cerasmart, an experimental material; Lava Ultimate, a polymer-infiltrated ceramic-network (PICN) material (VITA Enamic), and a glass-ceramic control (IPS Empress CAD) were tested. The specimens were tested before and after thermocycling (30 000 times, 5 °C/55 °C). The ECR was measured for each material (n=25) and related to the point of loading and to the maximum chipping depth. HM was determined for each material (n=25). The Kruskal-Wallis and Mann-Whitney U tests were used to compare materials (α=.05). The impact of thermocycling was analyzed by using the Wilcoxon test (α=.05). The correlations between all parameters were calculated by using the Spearman-Rho test (α=.05). For fractographic analysis of chip patterns, chipped surfaces were analyzed by laser scanning microscopy. RESULTS: For ECR and HM, the materials showed different values. ECRmd and ECRpl showed a positive correlation, but both showed a negative correlation to HM. The materials showed a different chip size (P<.001). Chip patterns revealed brittle material behavior in all cases. CONCLUSIONS: All tested CAD-CAM materials behaved as brittle materials, but HM and ECR differed among the materials. The control glass-ceramic material showed the highest values for HM, followed by the PICN material. ECR values revealed the opposite order of materials, with the highest for composite resins. Artificial aging by thermocycling affected all dental CAD-CAM restorative materials. Especially for composite resin materials, ECR changed after aging.

Impact of hydrothermal aging on the light transmittance and flexural strength of colored yttria-stabilized zirconia materials of different formulations.

STATEMENT OF PROBLEM: Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) materials of different formulations (3Y-TZP, 4Y-TZP, and 5Y-TZP) can be colored by using color liquids. However, practically and clinically relevant factors such as modifications of sintering protocols and hydrothermal aging might affect the extent of light transmittance and flexural strength of zirconia materials of different formulations; studies on these outcomes, however, are lacking. PURPOSE: The purpose of this in vitro study was to test the impact of hydrothermal aging on the light transmittance and flexural strength of colored zirconia materials compared with a lithium-disilicate (LiSi2) ceramic. MATERIAL AND METHODS: A total of 210 specimens were prepared from 3Y-TZP0.25 (n=30), 3Y-TZP0.05 (n=30), 5Y-TZP (n=30), 4Y-TZP (n=60), pre4Y-TZP (preshaded, n=30), and LiSi2 (n=30). All specimens, except for pre4Y-TZP and LiSi2, were manually colored, predried, and either conventionally sintered at 1450 °C (3Y-TZP0.25, 3Y-TZP0.05, 5Y-TZP, and half of 4Y-TZP) or high-speed sintered at 1580 °C (other half of 4Y-TZP and pre4Y-TZP). Light transmittance was measured initially and after 2, 5, 10, 20, 40, and 160 hours of hydrothermal aging (134 °C, 0.2 MPa). Biaxial flexural strength was tested initially and after 160 hours of hydrothermal aging (n=15). The Kolmogorov-Smirnov test, multivariate analysis, and 1-way ANOVA with the Tukey HSD post hoc test, the t test, and linear mixed models were calculated (α=.05). RESULTS: LiSi2 showed the highest translucency, followed by 5Y-TZP, 4Y-TZP, pre4Y-TZPspeed, 3Y-TZP0.05, and 3Y-TZP0.25. 4Y-TZPspeed was most opaque and matte. The decrease in translucency related to aging hours was higher for LiS2 and conventional sintered zirconia materials than for 4Y-TZPspeed and pre4Y-TZPspeed. Initially, 3Y-TZP0.25 had the highest flexural strength, followed by 3Y-TZP0.05, 4Y-TZP, and pre4Y-TZPspeed. pre4Y-TZPspeed was comparable with 4Y-TZPspeed but significantly higher than 5Y-TZP. LiSi2 had the lowest biaxial flexural strength. Hydrothermal aging increased biaxial flexural strength for 3Y-TZP0.25 and 3Y-TZP0.05 (P<.001) but decreased it for 5Y-TZP (P=.005) and pre4Y-TZPspeed (P<.001). After aging, 4Y-TZPspeed showed comparable values of flexural strength with 4Y-TZP (P=.06) and higher values than pre4Y-TZPspeed after aging (P=.019). CONCLUSIONS: Manually colored, conventionally sintered 4Y-TZP was resistant to hydrothermal aging regarding flexural strength. High-speed sintering inhibited color development for manually colored 4Y-TZP but did not affect the resistance to hydrothermal aging. The findings were reversed for industrially preshaded 4Y-TZP.

Biaxial flexural strength of zirconia: A round robin test with 12 laboratories.

OBJECTIVE: The aim of this interlaboratory round robin test was to prove the robustness of the DIN EN ISO 6872:2019 and to identify the influence of processing and testing variations. METHODS: Each of the 12 laboratories participated (A-L) received 60 (n = 720) assigned zirconia specimens. All participants seperated the specimens from the blanks, sintered them, polished half of all specimens and performed the biaxial flexural test (DIN EN ISO 6872:2019). The surface roughness was determined by using tactile measuring device. Fractographic examination was performed under scanning-electron-microscopy (SEM). Data was analysed using Kolmogorov-Smirnov-, Kruskal-Wallis-, Mann-Whitney-U-test and two-parametric Weibull statistic (p < 0.05). RESULTS: The results for both preparation methods (as-fired and polished) showed significant differences for some participants. The values for as-fired groups ranged between 513 (I) and 659 (E) MPa. H showed higher Weibull modulus than C, E and I. Within polished groups flexural strengths values from 465 (L) to 1212 (E) MPa were observed, with a tendency to clustered groups A, I, J, L (465-689 MPa) and remaining groups (877-1212 MPa). E presented the highest and H the lowest Weibull modulus. Within A and J, no impact of the preparation method on flexural strength values was observed. Within L, as-fired specimens showed higher flexural strength than polished ones. The flexural strength increase did only associate to a certain extent with measured surface roughness. Fractography showed defect populations depending on polishing techniques, associated to the strength level, especially for polished groups. Reduced strength is related to machining defects, regardless of the surface state. SIGNIFICANCE: DIN EN ISO 6872:2019 can be seen as guidance to biaxial flexural strength testing but additional effort is necessary to ensure interlaboratory comparability. Calibrated furnaces and reliable sintering conditions are mandatory requirements together with detailed specifications on finishing or polishing procedures. Biaxial flexural testing is really a matter of understanding specimen preparation, alignment and mechanical testing by itself. DIN EN ISO 6872:2019 should further recommend reporting of mean surface roughness along with any biaxial flexural strength data. Fractography is a mandatory tool in interpretation and understanding of strength data.

Evaluation of translucency, Marten's hardness, biaxial flexural strength and fracture toughness of 3Y-TZP, 4Y-TZP and 5Y-TZP materials.

OBJECTIVES: Testing and comparing of different non-shaded zirconia materials (3Y-TZP, 4Y-TZP and 5Y-TZP) on optical and mechanical properties. MATERIALS AND METHODS: Zirconia materials (N = 320, Opaque O, Translucent T, Extra Translucent ET, High Translucent HT) were investigated on translucency, Martens parameter, biaxial flexural strength, Chevron-Notch-Beam (CNB) fracture toughness (KIC) and grain size. The grain size was analyzed using a scanning electron microcopy (SEM). Univariate ANOVA, post-hoc Scheffé, partial eta-squared, Kolmogorov-Smirnov-, Kruskal-Wallis- and Mann-Whitney-U-tests (p < 0.05) were performed. The reliability of flexural strength was calculated with two-parametric Weibull analysis and 95 % confidence level. RESULTS: The translucency of ET and HT increased with the thermo-mechanical aging (p < 0.001). The zirconia material and aging had no impact on the Martens hardness and the indentation modulus. ET showed the highest flexural strength values after initial and thermo-mechanical aging (p < 0.001 - 0.683). All four materials showed the highest flexural strength after thermo-mechanical aging after 1.2 Mio cycles. Thermo-mechanically (1.2 Mio cycles) aged HT presented the highest Weibull modulus (m = 15.0) regardless of aging. Within initial groups, T (p ≤ 0.001) showed the highest fracture toughness, followed by O (p ≤ 0.001), ET (p < 0.003) and HT (p ≤ 0.001). SIGNIFICANCE: Translucency of ET and HT increases with thermo-mechanical aging. Chevron-Notch-Beam (CNB) is a valid alternative to the single-edge-V-notched beam (SEVNB) method for testing fracture toughness.

Effect of Cleaning Protocol on Bond Strength between Resin Composite Cement and Three Different CAD/CAM Materials.

The present investigation tested the effect of the cleaning method on the tensile bond strength (TBS) between one resin composite cement (RCC) and three different computer aided design/computer aided manufacturing (CAD/CAM) materials, namely zirconia, lithium disilicate ceramic and resin composite. Ninety specimens were prepared from each CAD/CAM material (N = 270). The specimens were pre-treated respectively, divided into five subgroups and subjected to five different cleaning protocols, namely i. 37% phosphoric acid, ii. ethanol, iii. phosphoric acid + ethanol, iv. cleaning paste, v. distilled water. After cleaning, the specimens were either conditioned using a universal primer or a universal adhesive and bonded using a dual-curing RCC. After thermo-cycling (20,000x at 5 °C/55 °C), TBS and fracture patterns were evaluated. The data was analyzed using 1- and 2-way Analysis of Variance (ANOVA) with post-hoc Scheffé and partial eta-squared (ƞP²), Kruskal-Wallis, Mann-Whitney U and Chi2 tests (p < 0.05). The CAD/CAM material showed an impact on the BS while the cleaning protocol did not affect the results. Zirconia obtained the highest BS, followed by lithium-disilicate-ceramic. Resin composite resulted in the overall lowest BS. For most fracture patterns, the cohesive type occurred. All tested cleaning protocols resulted in same BS values within one CAD/CAM material indicating that the impact of the cleaning method for the restorative material seems to play a subordinate role in obtaining durable bond strength to resin composite cement. Further, it indicates that the recommended bonding protocols are well adjusted to the respective materials and might be able to compensate the impact of not accurately performed cleaning protocols.

Translucency, flexural strength, fracture toughness, fracture load of 3-unit FDPs, Martens hardness parameter and grain size of 3Y-TZP materials.

OBJECTIVE: This investigation tested pre-shaded 3Y-TZP materials on optical, mechanical and structural properties and calculated correlations between these properties. METHODS: Seven A2-shaded 3Y-TZP zirconia materials were investigated on translucency (T) via UV-vis-spectrophotometer, fracture load of 3-unit FDPs (FL), biaxial flexural strength (FS), Chevron-Notch Beam (CNB), fracture toughness (KIC) and Martens parameter (hardness: HM and indentation modulus: EIT). FL, FS and KIC were measured in a universal testing machine. The grain size was evaluated by scanning electron microscopy (SEM). Data was analyzed using one-way ANOVA followed by post hoc Scheffé, Kruskal-Wallis-, Mann-Whitney-U- and Pearson-test (p<0.05). RESULTS: For translucency, negative correlations were found with results of facture load (R=-0.444, p<0.001) and KIC (R=-0.503, p<0.001). While a positive correlation was found between translucency and flexural strength (R=0.238, p=0.019), between fracture load and EIT (R=0.227, p<0.029), between fracture load and KIC (R=0.362, p<0.001) as well as between fracture load and the grain size (R=0.598, p=0.007). While the grain size positively correlated with EIT (R=0.534, p=0.017) as well as EIT with HM (R=0.720, p<0.001). SIGNIFICANCE: Despite of being based on the same raw material, tested zirconia materials significantly differed regarding optical, mechanical (except biaxial flexural strength and Martens hardness) and structural properties. Materials with highest optical properties were those with lowest mechanical properties (CER, COP).

Fracture Load of Veneered Telescopic Secondary Crowns Made of High-Performance Polymer on Zirconia Primary Crowns: Impact of Veneering Technique.

PURPOSE: To analyze the impact of different veneering techniques on the fracture load of telescopic secondary crowns made of a high-performance polymer (Ultaire aryl ketone polymer [UAKP]). MATERIALS AND METHODS: Zirconia primary crown models (taper of 0 degrees) were prepared (N = 48), polished, scanned, and divided into four veneering groups (n = 12 each): premanufactured, digital, full anatomical, and vestibular. For all groups except vestibular, a standardized telescopic secondary crown (thickness: 0.6 mm, circular margin: 1 mm) was constructed, adapted to the corresponding primary crown, milled from UAKP, and veneered. The veneered master crown was developed based on the premanufactured group. After surface polishing, all specimens were artificially aged in a chewing simulator (1.2 million cycles, 50 N, 1.1 Hz, between 5°C and 55°C). Fracture load was tested in a universal testing machine with a piston (Ø = 6 mm, 1 mm/minute). Fracture patterns were analyzed. For statistical analysis, Kolmogorov-Smirnov test and descriptive statistics followed by one-way ANOVA with post hoc Scheffé test were conducted (P < .05). RESULTS: Significant differences in fracture load were found between different veneering techniques (P < .001), with the highest values for the vestibular and digital groups, followed by the premanufactured group. Full anatomical veneering showed the significantly lowest fracture load (1,885 ± 397 N). For all specimens, cohesive brittle fractures with similar fracture patterns occurred, irrespective of the veneering technique. CONCLUSION: The veneering technique of telescopic secondary crowns made of high-performance polymer affects overall stability. All veneering techniques provided sufficient fracture load values for telescopic secondary crowns made of UAKP. Digital veneers seem the most recommendable.

Suitability of the new Aryl-Ketone-Polymer indicated for removable partial dentures: Analysis of elastic properties and bond strength to denture resin.

Elastic properties of Aryl-Ketone-Polymer (UAKP) and tensile bond strength (TBS) to denture resin (PalaXpress) were tested. Indentation modulus (EIT) and indentation hardness (HIT) were measured via Martens hardness (n=10 specimens) with 4.2±0.6 kN/mm2 and 261±8 N/mm2 respectively. TBS was tested in dependence of different adhesives (visio.link (VL), Adhese Universal (AU), All-Bond Universal (ABU), CLEARFIL UNIVERSAL BOND (CUB), G-Premio BOND (GPB), iBOND Universal (IBU), ONE COAT 7 UNIVERSAL (OCU), Scotchbond Universal (SBU) and without adhesive (CG), n=18/group) and the application of opaquer (n=9/group) after thermocycling (5°C/55°C, 10,000×). TBS was affected by the adhesive (η (P2=0.715, p<0.001) followed by the opaquer (ηP2=0.335, p<0.001). VL and CG showed highest TBS followed by AU and ABU. IBU and GPB resulted in lowest TBS. Opaquer increased TBS for all adhesives (p<0.05), except VL and CG (p<0.258). Elastic properties are well-suited for the indication of removable partial dentures. Bonding to denture resin is no limiting factor.

Bond strength between a high-performance thermoplastic and a veneering resin.

STATEMENT OF PROBLEM: High-performance thermoplastics have been adopted as framework materials. However, their bond strength to an esthetic veneering material is unclear. PURPOSE: The purpose of this in vitro study was to test the tensile bond strength (TBS) between an aryl-ketone polymer (Ultaire AKP) and veneering resins. MATERIAL AND METHODS: AKP substrates (N=324) were prepared, airborne-particle abraded (Al2O3, 50 µm, 0.2 MPa), and divided into 9 groups (n=36) with different bonding systems (visio.link, Adhese Universal, All-Bond Universal, CLEARFIL UNIVERSAL BOND, G-Premio BOND, iBOND Universal, ONE COAT 7 UNIVERSAL, Scotchbond Universal) and without a bonding system as a control. Each group was further divided for opaquer (n=18). Further subdivision followed according to flowable or paste veneering resin (n=9). Specimens were stored in distilled water for 24 hours at 37 °C and thermocycled (×5000, 5/55 °C). TBS was measured and analyzed with the Kolmogorov-Smirnov test and 3-way ANOVA with partial eta squared (ηP2), followed by the Kruskal-Wallis and Mann-Whitney-U tests. Relative frequency of failure types was analyzed with the Chi2-test and a Ciba-Geigy table. RESULTS: The highest impact on TBS was exerted by the adhesive (ηP2=0.458, P<.001), followed by opaquer (ηP2=0.288, P<.001). The binary combination of the 3 variables was significant for opaquer coupled with adhesive (ηP2=0.173, P<.001). Visio.link showed the highest TBS followed by All-Bond Universal and Scotchbond Universal. Opaquer increased the TBS for all adhesives except for visio.link. Without adhesive, opaquer obtained comparable TBS to visio.link. Flowable veneering resin showed higher TBS than paste resin. CONCLUSIONS: The application of opaquer increased TBS for all universal adhesives. Using opaquer and flowable veneering resin is beneficial for bonding to Ultaire AKP.

Different polishing methods for zirconia: impact on surface, optical, and mechanical properties.

OBJECTIVES: To test the impact of polishing strategies on zirconia properties. MATERIALS AND METHODS: One hundred eight zirconia specimens were divided into nine groups (n = 12/group). Seven groups were polished in the white-stage with either (1) a felt wheel (FW), (2) a felt wheel combined with a polishing paste (FWP), (3) a goat hair brush (GB), (4) a goat hair brush combined with a polishing paste (GBP), (5) a green-state finishing kit (FK), (6) a universal polisher (UP), or (7) with SiC polishing paper (PP), and sintered. Thereafter, the seven groups were divided into two subgroups each and polished using (1) a fine polisher (one-step, n = 6) or (2) a rough and fine polisher (two-steps, n = 6). The positive control group (polish-lab-kit, PLK) was sintered and polished in two-steps. The no polished group (NP) acted as negative control group. Translucency (T%) was measured after white-stage polishing and sintering, and after sintered-stage polishing. Surface free energy (SFE), surface roughness (SR), and flexural strength (FS) were determined. Data were analyzed using one-way ANOVA with Tukey-B post-hoc, t test, and Wilcoxon-test (p < 0.05). RESULTS: FWP, GB, FK, UP, and PP presented decreased T% after one-step, while FWP, GB, GBP, FK, and UP presented decreased T% following two-steps polishing. FW showed the highest T% after white-stage, one-, and two-steps polishing. PP presented the lowest SFE. Two-steps polishing resulted in a lower SR for FW, FWP, GB, FK, UP, and PP and increased FS in all groups. CONCLUSIONS: White-stage polishing improved zirconia properties. Two-steps polishing in the sintered stage, especially when combined with a polishing paste, can decrease SR and increase T% and FS. CLINICAL RELEVANCE: With polishing in the sintered-stage impairing the polishing material and being time consuming, alternatives such as white-stage polishing should be investigated.

Flexural strength and fracture toughness of two different lithium disilicate ceramics.

To test the impact of the pressing furnace on flexural strength and facture toughness of the lithium-disilicate-ceramics HS10PC (HS) and IPS e.max Press (IP). Three hundred and sixty specimens (3×4×30 mm) were pressed (n=180/ceramic) using different pressing furnaces, namely Austromat 654 Press-i-dent (AUS), Programat EP5000 (PRO), and Vario Press 300 (VAR). Three-point flexural strength (n=30) and fracture toughness (n=30) were measured. Flexural strength (336-360 MPa) was not affected by pressing furnace or ceramic and showed comparable values between all groups. Fracture toughness (2.65-2.81 MPa√m) provided higher values for HS pressed using AUS compared to specimens pressed in PRO and VAR. For IP, no impact of the pressing furnace on fracture toughness was found. IP presented higher fracture toughness than HS when pressed using PRO. No correlations were found. Both lithium disilicate ceramics showed comparable flexural strength regardless of the pressing furnace. Fracture toughness depended on the ceramic and on the pressing furnace.

3D-printed material for temporary restorations: impact of print layer thickness and post-curing method on degree of conversion.

AIM: The purpose of this investigation was to evaluate the impact of print layer thickness and post-curing method on the degree of conversion (DC) of a three-dimensional (3D) print material for temporary restorations. MATERIALS AND METHODS: 120 specimens of the resin material NextDent C&B were additively manufactured in three different print layer thicknesses (25 µm, 50 µm, and 100 µm) using a DLP printer, and post-cured by either Labolight DUO (LL), Otoflash G171 (OF), LC-3DPrint Box (PB) or PCU LED (PCU). Each subgroup contained 10 specimens. Raman spectra were measured for the liquid state of the resin (n = 10), directly after printing (Rprint) and after post-curing (Rcured). DC and ΔDC were calculated. The data were statistically analyzed using the Kolmogorov-Smirnov test, the general linear model analysis together with partial eta-squared (ηP²), Kruskal-Wallis, and Mann-Whitney U tests (P < 0.05). RESULT: Specimens post-cured by OF showed the highest ΔDC, followed by specimens post-cured by PB, PCU, and LL (P < 0.001). Post-curing by PB, PCU, and LL resulted in the same ΔDC value range (P = 0.076 to 0.209). The print layer thicknesses of 100 µm and 50 µm (P = 0.931) showed higher ΔDC than the print layer thickness of 25 µm (P < 0.001). CONCLUSION: The choice of the post-curing method has a high impact on the DC of the tested 3D print material followed by the specific print layer thickness. Overall, specimens post-cured by OF showed the highest DC and ΔDC values. Brands Technology Duration Wavelength Manufacturer LC-3DPrint Box (PB) Ultraviolet light (UV) 30 min Range 315 to 550 nm, peaks at approximately 360 and 435 nm NextDent (Soesterberg, Netherlands) Otoflash G171 (OF) Flashlight, nitrogen atmosphere Two processes of 2000 flashes Range 300 to 700 nm, peaks at approximately 480 and 530 nm NK Optik (Baierbrunn, Germany) Labolight DUO (LL) Light-emitting diode (LED) Two processes of 3 min Range 380 to 510 nm, peaks at approximately 395 and 475 nm GC Europe (Leuven, Belgium) PCU LED (PCU) Light-emitting diode (LED), vacuum 5 min Peaks at approximately 410 nm Dreve (Unna, Germany).

Comparison of fracture toughness measurements for zirconia materials using two test methods.

To determine the influence of the fracture toughness (KIC) methods [single-edge-V-notch-beam (SEVNB) and chevron-notch-beam (CNB)] as well as an optional heat treatment on the KIC of three different zirconia generations (1st: ZI, 3rd: FX, 4th: HT). One hundred and twenty specimens each (3×4×45 mm) were fabricated, sintered, notched (n=360) and half of them heat treated before KIC measurements with 4-point-flexural-strength test. SEM images of the notches were recorded. Highest KIC was found for ZI followed by HT and FX. SEVNB resulted in significantly higher KIC than CNB. Heat treatment resulted in decrease for SEVNB and increase for CNB of KIC (except for FX). Groups tested using CNB showed higher reliability of values (Weibull modulus) than tested using SEVNB. SEM images present crack path and fracture surface. Different zirconia materials lead to different KIC values. The test method and a prior heat treatment showed an influence on the KIC values and their reliability.