Publications by authors named "Bogna Stawarczyk"

177 Publications

Reduced fracture load of dental implants after implantoplasty with different instrumentation sequences. An in-vitro study.

Clin Oral Implants Res 2021 May 25. Epub 2021 May 25.

Clinic of Conservative and Preventive Dentistry Periodontology and Cariology, Center of Dental Medicine, University of Zurich, Plattenstrasse 11, 8032, Zurich, Switzerland.

Objectives: To assess the mechanical stability of implants after implantoplasty and thermocyclic loading, the residual thickness of the instrumented areas and neighbouring tooth injury due to implantoplasty.

Materials And Methods: Using a phantom head simulator and maxillary model implants were subjected to an implantoplasty procedure. Thirty implants were randomly assigned to receive one of three instrumentation sequences. After instrumentation injury on neighbouring teeth was assessed. Instrumented implants and non-instrumented controls were subjected to 1.2 million cycles of thermo-mechanical loading in a chewing-machine. Afterwards, maximum fracture load for all implants and an additional 5 pristine control implants was tested.

Results: Generally, damage of neighbour teeth was a frequent finding (33±56% of all cases) with considerable inter-group differences. No considerable inter-group difference for the residual implant thickness was found for different areas assessed. No implant fractured during cyclic loading. Fracture load was reduced after cyclic loading of uninstrumented implants from 2724 ± 70 N to 2299 ± 127 N, and after implantoplasty to 1737 ± 165 N, while no effect by the instrumentation sequence could be observed.

Conclusions: Both, implantoplasty and cyclic loading was shown to reduce the implants' maximum bending strength. Cyclic loading in a laboratory masticator, simulating a five-year equivalent of chewing, did not result in fractured implants. Since neighbouring tooth injury was assessed often, care should be taken with the selection of suitable instruments.
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http://dx.doi.org/10.1111/clr.13754DOI Listing
May 2021

Fracture load of veneered and monolithic single-unit fixed dental prostheses made from the high-performance thermoplastic polyphenylene sulfone.

Int J Prosthodont 2021 May 17. Epub 2021 May 17.

Purpose: To investigate the fracture load of different veneers for monolithic single-unit fixed dental prostheses (FDPs) made of a novel potential framework material, polyphenylene sulfone (PPSU).

Materials And Methods: The fracture loads of four PPSU frameworks with different veneers (manual polymer veneer with Ceramage Body A3B; prefabricated polymer veneer with Novo.lign; digital polymer veneer with Telio CAD; digital ceramic veneer with IPS Empress CAD) and a monolithic control group (PPSU, Gehr) were examined initially and after 1,200,000 masticatory (50 N, 1.3 Hz) and 6,000 thermal cycles (5°C/55°C). Fracture analysis was performed using light microscope imaging. Fracture types were classified, and relative frequencies were determined. Univariate analysis of variance, post hoc Scheffé, partial eta squared, Kruskal-Wallis test, and Weibull moduli using the maximum likelihood estimation method were calculated. The defined level of significance was adjusted by Bonferroni correction (P < .005).

Results: Aging did not affect the fracture load values. Single-unit FDPs with a digital ceramic veneer showed lower values than monolithic and manual polymer-veneer specimens. Single-unit FDPs with a prefabricated and digital polymer veneer were in the same value range as specimens with a manual polymer and digital ceramic veneer. No differences were observed between manual polymer veneer and monolithic single-unit FDPs. All veneered specimens showed a fracture of the veneer. For monolithic single-unit FDPs, a plastic deformation was observed.

Conclusion: Veneered and monolithic PPSU showed sufficient fracture load values to indicate successful clinical use in single-unit FDPs. The choice of veneering method and material may play a minor role.
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http://dx.doi.org/10.11607/ijp.7675DOI Listing
May 2021

Impact of resin composite cement on color of computer-aided design/computer-aided manufacturing ceramics.

J Esthet Restor Dent 2021 May 5. Epub 2021 May 5.

Department of Prosthetic Dentistry, LMU Munich, Munich, Germany.

Objective: To analyze the impact of the color of a resin composite cement (RCC) on the optical properties of different computer-aided design and computer-aided manufacturing (CAD/CAM) ceramics.

Materials And Methods: Specimens (N = 220, thickness: 0.9 ± 0.03 mm) were fabricated from: leucite (Initial LRF Block/IPS Empress CAD), lithium disilicate (Amber Mill/IPS e.max CAD), lithium metasilicate (Celtra Duo), and lithium alumina silicate ceramic (n!ce) in translucency levels HT and LT. All specimens were bonded with an RCC (Light+/Warm+). Color was analyzed (spectrophotometer) initially as well as after bonding of RCC with CAD/CAM ceramics using CIELab and CIEDE2000. Kolmogorov-Smirnov test, one-way ANOVA and t test served for analyzing (α = 0.05).

Results: Highest impact on ΔE presented the choice of ceramic (η  = 0.155/p < 0.001), followed by translucency level (HT/LT; η  = 0.050/p = 0.001) as well as interaction between ceramic and translucency level (η  = 0.175/p < 0.001). ΔE00 was mainly influenced by the choice of ceramic (η  = 0.490/p < 0.001), the shade of resin composite (η  = 0.031/p = 0.012) as well as the interaction between ceramic and resin composite (η  = 0.258/p < 0.001).

Conclusions: RCC shades presented differential impacts on color change of CAD/CAM ceramics.

Clinical Significance: Knowledge of the impact of available RCC shades on different CAD/CAM ceramics is crucial for an esthetic outcome and proper selection of ceramic restorations.
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http://dx.doi.org/10.1111/jerd.12738DOI Listing
May 2021

3D printing of dental restorations: Mechanical properties of thermoplastic polymer materials.

J Mech Behav Biomed Mater 2021 07 21;119:104544. Epub 2021 Apr 21.

Department of Prosthetic Dentistry, University Hospital, LMU Munich, Goethestrasse 70, 80336, Munich, Germany.

In the seminal field of 3D printing of dental restorations, the time and cost saving manufacturing of removable and fixed dental prostheses from thermoplastic polymer materials employing fused filament fabrication (FFF) is gaining momentum. As of today, the additive manufacturing of the established semi-crystalline polyetheretherketone (PEEK) requires extensive post-processing and lacks precision. In this context, the amorphous polyphenylene sulfone (PPSU) may provide a higher predictability and reliability of the results. The aim of this study was to investigate the mechanical properties of PPSU and PEEK processed by FFF (PPSU1-3D (PPSU Radel) and PPSU2-3D (Ultrason P 3010 NAT)) or extrusion (PPSU1-EX (Radel R-5000 NT) and PEEK-CG (PEEK Juvora)). Three-point flexural strength, two-body wear, and Martens hardness (HM) and indentation modulus (E) were tested after aging. One-way ANOVA, the Kruskal-Wallis and the Pearson's and Spearman's correlation tests were computed (α = 0.05). PPSU1-3D and PPSU2-3D showed lower flexural strength values than PPSU1-EX and PEEK-CG. PPSU1-3D showed the highest, and PEEK-CG and PPSU1-EX the lowest height loss. The highest HM and E results were observed for PEEK-CG and the lowest for PPSU1-3D. Correlations were observed between all parameters except for the application height. In conclusion, the manufacturing process affected the flexural strength of PPSU, with 3D printed specimens presenting lower values than specimens cut from prefabricated molded material. This finding indicates that the 3D printing parameters employed for the additive manufacturing of PPSU specimens in the present investigation require further optimization. For 3D printed specimens, the quality of the filament showed an impact on the mechanical properties, underlining the importance of adhering to high quality standards during filament fabrication. Extruded PPSU led to comparable results with PEEK for flexural strength and two-body wear, indicating this novel dental restorative material to be a suitable alternative to the established PEEK for the manufacturing of both removable and fixed dental prostheses.
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http://dx.doi.org/10.1016/j.jmbbm.2021.104544DOI Listing
July 2021

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

Dent Mater 2021 Jul 10;37(7):1073-1082. Epub 2021 Apr 10.

Department of Prosthetic Dentistry, University Hospital, Ludwig-Maximilians-University, Goethestrasse 70, 80336 Munich, Germany. Electronic address:

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 (O: opaque) 3Y-TZP (T: translucent), 4Y-TZP (ET: extra translucent) and 5Y-TZP (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.
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http://dx.doi.org/10.1016/j.dental.2021.03.013DOI Listing
July 2021

Fatigue resistance of monolithic strength-gradient zirconia materials.

J Mech Behav Biomed Mater 2021 07 7;119:104504. Epub 2021 Apr 7.

Dental Material Unit, Department of Prosthetic Dentistry, University Hospital, LMU Munich, Goethestraße 70, 80336, Munich, Germany. Electronic address:

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.
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http://dx.doi.org/10.1016/j.jmbbm.2021.104504DOI Listing
July 2021

Bonding Behavior Between Polyetheretherketone and Polymethylmethacrylate Acrylic Denture Polymer.

J Adhes Dent 2021 Apr;23(2):145-158

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.
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http://dx.doi.org/10.3290/j.jad.b1079579DOI Listing
April 2021

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

Clin Oral Investig 2021 Apr 3. Epub 2021 Apr 3.

Department of Conservative Dentistry and Periodontology, University Hospital, LMU Munich, Goethestrasse 70, 80336, Munich, Germany.

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.
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http://dx.doi.org/10.1007/s00784-021-03905-9DOI Listing
April 2021

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

Materials (Basel) 2021 Mar 29;14(7). Epub 2021 Mar 29.

Department of Preventive Dentistry, Periodontology and Cariology, University Medical Center Göttingen, 37075 Göttingen, Germany.

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 ( < 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/mm and 4.2 to 3.9 kN/mm 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.
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http://dx.doi.org/10.3390/ma14071680DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8036278PMC
March 2021

Modern CAD/CAM silicate ceramics, their translucency level and impact of hydrothermal aging on translucency, Martens hardness, biaxial flexural strength and their reliability.

J Mech Behav Biomed Mater 2021 06 13;118:104456. Epub 2021 Mar 13.

Department of Prosthetic Dentistry, LMU Munich, Munich, Germany.

Objectives: To investigate the impact of hydrothermal aging on Martens parameter (Martens hardness: HM/elastic indentation modulus: E) and biaxial flexural strength (BFS) of recently available CAD/CAM silicate ceramics.

Methods: 220 specimens (diameter: 12 mm, thickness: 0.95 mm) were fabricated from six CAD/CAM ceramics in two translucency levels (LT/HT): (a) two lithium disilicate (Amber Mill, ABM; IPS e.max CAD, IEM), (b) one lithium metasilicate (Cetra Duo, CEL), (c) one lithium alumina silicate (n!ce, NIC), and (d) two leucite ceramics (Initial LRF Block, LRF; IPS Empress CAD, IPR). HM/E and BFS were measured initially and after hydrothermal aging (134 °C/0.2 MPa/100 h) in an autoclave. The Kolmogorov-Smirnov-test, t-test, one-way ANOVA with post-hoc Scheffé test, Kruskal-Wallis-test, Mann-Whitney-U-test with Bonferroni correction and Weibull statistics were performed (α = 0.05).

Results: CEL and IEM showed the highest and the leucite ceramics the lowest Martens parameter. Within HT, ABM and NIC were in same initial HM value range with CEL and IEM. ABM and NIC showed lower initial E values than CEL and IEM, however higher than IPR. The lowest aged values were analyzed for ABM. After aging, Martens parameter decreased for LRF, ABM, and CEL. IEM showed the initial highest BFS, followed by ABM. NIC and LRF showed the lowest BFS. IEM and ABM presented the highest aged BFS. Hydrothermal aging increased BFS values for LRF (HT), IPR, CEL (HT), and NIC (HT) compared to the initial values. CAD/CAM leucite ceramics showed higher Weibull modul values compared to lithium silicate ceramics.

Significance: The well-considered selection of ceramics in relation to the areas of indication has the highest influence on the long-term stability of restorations: CAD/CAM lithium disilicate ceramics presented the highest and leucite ceramics the lowest mechanical properties, whereas the reliability was better for leucite than for lithium silicate ceramics.
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http://dx.doi.org/10.1016/j.jmbbm.2021.104456DOI Listing
June 2021

Food solutions and cigarette smoke-dependent changes in color and surface texture of CAD/CAM resin composites - an in vitro study.

Int J Prosthodont 2021 Feb 23. Epub 2021 Feb 23.

Purpose: To investigate the discoloration and surface properties of four CAD/CAM composite resins provoked by a variety of food solutions and cigarette smoke.

Materials And Methods: A total of 74 specimens (N = 370) were prepared per material (Brilliant Crios [Coltene], CeraSmart [GC], Lava Ultimate [3M Espe], Shofu Block HC [Shofu], and SonicFill 2 [Kerr]). Discoloration (ΔE) was investigated with a spectrophotometer. Measurements were taken before immersion in the storage media for 2 weeks (carrot juice, curry, cigarette smoke, red wine, energy drink, and distilled water), immediately after immersion, and after manual polishing of the specimens following immersion. The mean surface roughness (Ra) was measured using a profilometer. Qualitative surface observation was performed with scanning electron microscopy (SEM). Data were analyzed using Kolmogorov-Smirnov, Mann-Whitney U, and one-way analysis of variance with Tukey post hoc tests.

Results: The highest influence on ΔE after immersion was observed by the storage medium (η. = 0.878, P < .001), followed by the interaction between storage medium and material (η. = 0.770, P < .001) and the material (η. = 0.306, P < .001). For ΔE after polishing, the highest influence was indicated by the interaction of material and medium (η. = 0.554, P < .001), followed by the medium (η. = 0.244, P < .001) and the material (η. = 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 provoked the highest Ra values (0.120 to 0.355 μm). SEM pictures indicated a loss of the organic matrix after manual polishing.

Conclusion: The different materials reacted dissimilarly in the various storage media in terms of discoloration. Surface roughness increased after immersion and polishing. Neither discoloration nor surface roughness could be reset to default by manual polishing.
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http://dx.doi.org/10.11607/ijp.6950DOI Listing
February 2021

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

Int J Prosthodont 2021 Feb 12. Epub 2021 Feb 12.

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.
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http://dx.doi.org/10.11607/ijp.7048DOI Listing
February 2021

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

Int J Prosthodont 2021 Feb 12. Epub 2021 Feb 12.

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.
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http://dx.doi.org/10.11607/ijp.7428DOI Listing
February 2021

Three-dimensionally printed and milled polyphenylene sulfone materials in dentistry: Tensile bond strength to veneering composite resin and surface properties after different pretreatments.

J Prosthet Dent 2021 Feb 15. Epub 2021 Feb 15.

Professor, Head of Dental Material Research, Department of Prosthetic Dentistry, University Hospital, LMU Munich, Munich, Germany.

Statement Of Problem: Polyphenylene sulfone (PPSU) is a thermoplastic that can be processed using 3-dimensional printing. PPSU is new to dentistry, and scientific data on its properties are lacking.

Purpose: The purpose of this in vitro study was to test the surface properties and the tensile bond strength (TBS) between PPSU and a veneering composite resin in comparison with a polyetheretherketone (PEEK).

Material And Methods: Gehr PPSU (PPSU-B1), Radel R-5000 NT (PPSU-B2), and Juvora Dental Disc (PEEK-CG) substrates were cut from bulk material, while FIL-A-GEHR PPSU (PPSU-3D) was 3-dimensionally printed (N=504, n=126/material). TBS to veneering composite resin (CeramageUp) was tested initially and after 5000 and 10 000 thermocycles, and fracture types were analyzed. Surface free energy (SFE) and surface roughness (Ra) were determined after pretreatment with aluminum oxide (AlO) of different grain sizes (50 and 110 μm) applied with different pressures (0.1, 0.2, 0.4 MPa), silicon dioxide (SiO)-coated AlO (0.28 MPa), sulfuric acid, or polished. Qualitative surface characterization was performed by using a scanning electron microscope (SEM). One-way ANOVA, the Kruskal-Wallis, Mann-Whitney U, and the Spearman correlation tests were computed (α=.05).

Results: PPSU-3D and PEEK-CG presented higher TBS results than PPSU-B1 and PPSU-B2. Initial TBS values were higher than after 10 000 thermocycles. Adhesive fractures between substrate and veneering composite resin occurred most frequently. With a few exceptions, PEEK-CG presented higher SFE values than all other materials within a pretreatment group, while PPSU-3D and PEEK-CG showed consistently high Ra values. An increase in pressure and particle size increased SFE and Ra.

Conclusions: FFF-printed PPSU-3D showed similar TBS values with the veneering composite resin to the more established PEEK. Pretreatment methods devised for PEEK represent valid strategies for increasing both the SFE and Ra of the high-performance polymer PPSU.
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http://dx.doi.org/10.1016/j.prosdent.2020.12.042DOI Listing
February 2021

Impact of High-Speed Sintering of Three-Unit 3Y-TZP and 4Y-TZP Fixed Dental Prostheses on Fracture Load With and Without Artificial Aging.

Int J Prosthodont 2021 Jan-Feb;34(1):47-53

Purpose: To investigate the impact of high-speed sintering and artificial aging on the fracture load of three-unit zirconia fixed dental prostheses (FDPs).

Materials And Methods: Three-unit FDPs manufactured from 3Y-TZP (Ceramill Zolid, Amann Girrbach) and 4Y-TZP (Ceramill Zolid HT+, Amann Girrbach; N = 128, n = 64/group) were sintered at 1,580°C (high-speed sintering) or at 1,450°C (control group; n = 32/subgroup). Specimens were bonded to steel abutment models using Multilink Automix (Ivoclar Vivadent), and fracture load was examined without (n = 16/subgroup) and with artificial aging (6,000 thermocycles [5°C/55°C] and 1,200,000 chewing cycles [50 N]; n = 16/subgroup). Univariate analysis of variance, unpaired t test, and Weibull modulus were computed (P < .05).

Results: Sintering protocol (P = .944), artificial aging (P = .630), and zirconia material (P = .445) did not show an influence on the fracture load of three-unit FDPs. High-speed sintering led to superior Weibull modulus results for artificially aged 4Y-TZP specimens, while all other groups showed values in the same range.

Conclusion: The present study shows promising results for the novel high-speed sintering protocol, as it led to comparable fracture load and similar, or even superior, Weibull modulus results compared to the control group. The 4Y-TZP material presented fracture load results similar to the tried-and-tested 3Y-TZP. Artificial aging did not influence zirconia's resistance to fracture for either 3Y-TZP or 4Y-TZP.
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http://dx.doi.org/10.11607/ijp.6775DOI Listing
February 2021

Edge chipping resistance of veneering composite resins.

J Mech Behav Biomed Mater 2021 04 2;116:104349. Epub 2021 Feb 2.

Department of Prosthetic Dentistry, University Hospital, LMU Munich, Goethestrasse 70, 80336, Munich, Germany. Electronic address:

Objectives: To investigate the edge chipping resistance (ECR) of six veneering composite resins after different treatment protocols.

Materials And Methods: Rectangular bar specimens were manufactured from Ceramage Incisal (CER; Shofu), dialog Vario Occlusal (DIA; Schütz Dental), Gradia Plus Heavy Body Enamel (GRA; GC Europe), in:joy incisal (INJ; Dentsply Sirona Deutschland), SR Nexco Paste Incisal (SRN; Ivoclar Vivadent), and Signum composite enamel (SIG; Kulzer). ECR was determined after five treatment protocols: (1) no treatment, (2) after storage in distilled water at 37 °C for 7 days, (3) storage in distilled water with an additional 10 000 thermal cycles (5 °C/55 °C), and hydrothermal treatment at 134 °C at a water vapor pressure of 0.2 MPa for a duration of (4) 3.5 min or (5) 23.5 min. Force was applied with the universal testing machine ZHU 0.2 (Zwick Roell) mounted with a Vickers diamond indenter until the chip fractured off the specimen and ECR values were computed by dividing the applied maximum force by the distance to the center of the applied force. Fracture analysis was performed employing light microscope imaging. Univariate and one-way ANOVA, Scheffé and Tukey-B post hoc, and partial eta squared (ƞ) were computed (p < 0.05).

Results: DIA presented consistently high ECR values, while CER showed low results. For some groups, seven days' storage in water and hydrothermal treatment for 3.5 min led to higher ECR results than observed in the initial state, while an additional 10 000 thermal cycles and hydrothermal treatment for 23.5 min resulted in lower ECR values.

Conclusions: The examined veneering composite resins differed in regard to their mechanical properties, with DIA possessing the highest resistance to chipping. While post-processing can initially increase a material's edge chipping resistance, intensified treatment protocols reduced the mechanical properties of veneering composite resins.
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http://dx.doi.org/10.1016/j.jmbbm.2021.104349DOI Listing
April 2021

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

Dent Mater 2021 02 22;37(2):284-295. Epub 2020 Dec 22.

Fraunhofer Institute for Ceramics Technologies and Systems IKTS, Michael-Faraday-Str. 1, 07639 Hermsdorf, Germany.

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.
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http://dx.doi.org/10.1016/j.dental.2020.11.016DOI Listing
February 2021

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

Dent Mater J 2021 Mar 18;40(2):487-497. Epub 2020 Dec 18.

Department of Prosthetic Dentistry, University Hospital, LMU Munich.

To investigate the degree of conversion (DC), Martens hardness (HM), elastic indentation modulus (E), 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/E. CI presented the lowest DC and highest HM/E. NP showed the highest DC and lowest HM/E. Within Otoflash G171, Laboligth DUO and PCU LED, highest FS was observed for CI. Storage did not affect DC/HM/E 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.
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http://dx.doi.org/10.4012/dmj.2019-394DOI Listing
March 2021

Influence of Different Postpolymerization Strategies and Artificial Aging on Hardness of 3D-Printed Resin Materials: An In Vitro Study.

Int J Prosthodont 2020 Nov/Dec;33(6):634-640

Purpose: To investigate the influence of different postpolymerization strategies and artificial aging periods on the Martens hardness parameters of 3D-printed resin materials indicated for temporary use.

Materials And Methods: Disks made of four 3D-printed resin materials (n = 30 each) were additively manufactured and postpolymerized with three different postpolymerization devices (n = 10 specimens of each material per device). Disks cut from a prefabricated milling material served as a control. The Martens parameters (ie, Martens hardness [HM] and indentation modulus [E]) were measured initially and after 14- and 28-day storage periods in 37°C distilled water. The data were statistically analyzed using univariate analysis, Kolmogorov Smirnov test, and nonparametric tests, including Kruskal-Wallis, Mann-Whitney U, and Wilcoxon tests (α = .05).

Results: The highest impact on the Martens parameters was exerted by material (HM: η = 0.957, E: η = 0.967, P < .001), followed by postpolymerization device (HM: η = 0.557, E: η = 0.496, P < .001) and duration of water storage (HM: η= 0.068, E: η= 0.038, P < .001). The values for HM ranged between 108 and 282 N/mm, and for E between 2.89 and 7.73 kN/mm. The materials 3Delta Etemp and Temp PRINT showed the highest HM and E values regardless of the postpolymerization device and water storage duration (P < .001). In contrast, NextDent C&B, followed by Freeprint Temp, showed the lowest HM and E values (P < .001). The milled control group Telio CAD ranged between the two lower groups.

Conclusion: Postpolymerization strategy has a high impact on the mechanical properties of 3D-printed resin materials. Materials with a higher filler content showed better results regarding the Martens parameters. Such materials might be an alternative to conventional materials for the milling procedure.
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http://dx.doi.org/10.11607/ijp.6634DOI Listing
December 2020

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

Dent Mater 2021 02 29;37(2):212-222. Epub 2020 Nov 29.

Dental Material Unit, Department of Prosthetic Dentistry, University Hospital, Ludwig-Maximilians-University, Goethestrasse 70, 80336 Munich, Germany. Electronic address:

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 (K) 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.
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http://dx.doi.org/10.1016/j.dental.2020.11.007DOI Listing
February 2021

Mechanical and optical properties of indirect veneering resin composites after different aging regimes.

Dent Mater J 2021 Mar 19;40(2):279-287. Epub 2020 Nov 19.

Department of Prosthetic Dentistry, University Hospital.

This study tested and compared properties of six modern indirect veneering resin composites (VRC), namely Ceramage (Shofu), dialog Vario (Schütz Dental), Gradia Plus (GC Europe), in:joy (Dentsply), Signum composite (Heraeus Kulzer), and SR Nexco (Ivoclar Vivadent). Specimens were fabricated from dentin and enamel pastes and following properties were analyzed: (1) two-body wear (TB), (2) surface roughness (SR), (3) Martens hardness parameters (HM and E), and (4) translucency (T). The highest impact on HM and E was exerted by VRC brand (HM: η=0.960/ E: η=0.968; p<0.001), followed by VRC paste material (HM: η=0.502/ E: η=0.580; p<0.001), and aging duration (HM: η=0.157/ E: η=0.112; p<0.001). Lowest and highest TB were measured for Signum composite and dialog Vario, respectively (p<0.001). Highest T was showed Signum composite and Ceramage (p<0.001). VRCs should be individually selected with respect to the indication area, due to different surface properties.
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http://dx.doi.org/10.4012/dmj.2019-307DOI Listing
March 2021

Comparison of mechanical properties of different reinforced glass-ceramics.

J Prosthet Dent 2020 Nov 6. Epub 2020 Nov 6.

Head of Dental Material Research, Department of Prosthetic Dentistry, University Hospital, LMU Munich, Munich, Germany.

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 (E), 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, E (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), E (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, E, 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.
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http://dx.doi.org/10.1016/j.prosdent.2020.06.027DOI Listing
November 2020

Retention force of polyetheretherketone and cobalt-chrome-molybdenum removable dental prosthesis clasps after artificial aging.

Clin Oral Investig 2021 May 16;25(5):3141-3149. Epub 2020 Oct 16.

Department of Prosthetic Dentistry, University Hospital, LMU Munich, Goethestraße 70, 80336, Munich, Germany.

Objectives: To examine the retention force of removable dental prosthesis (RDP) clasps made from polyetheretherketone (PEEK) and cobalt-chrome-molybdenum (CoCrMo, control group) after storage in water and artificial aging.

Materials And Methods: For each material, 15 Bonwill clasps with retentive buccal and reciprocal lingual arms situated between the second pre- and first molar were manufactured by milling (Dentokeep [PEEKmilled1], NT digital implant technology; breCAM BioHPP Blank [PEEKmilled2], bredent), pressing (BioHPP Granulat for 2 press [PEEKpressed], bredent), or casting (remanium GM 800+ [CoCrMo], Dentaurum); N = 60, n = 15/subgroup. A total of 50 retention force measurements were performed for each specimen per aging level (initial; after storage [30 days, 37 °C] and 10,000 thermal cycles; after storage [60 days, 37 °C] and 20,000 thermal cycles) in a pull-off test. Data were statistically analyzed using one-way ANOVA, post hoc Scheffé and mixed models (p < 0.05).

Results: Initial, PEEKpressed (80.2 ± 35.2) and PEEKmilled1 (98.9 ± 40.3) presented the lowest results, while PEEKmilled2 (170.2 ± 51.8) showed the highest values. After artificial aging, the highest retention force was observed for the control group (131.4 ± 56.8). The influence of artificial aging was significantly higher for PEEK-based materials. While PEEKmilled2 and PEEKpressed showed an initial decline in retention force, all other groups presented no impact or an increase in retention force over a repetitive insertion and removal of the clasps.

Conclusions: Within the tested PEEK materials, PEEKmilled2 presented superior results than PEEKpressed. Although CoCrMo showed higher values after artificial aging, all materials exhibited sufficient retention to recommend usage under clinical conditions.

Clinical Relevance: As RDPs are still employed for a wide range of indications, esthetic alternatives to conventional CoCrMo clasps are sought.
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http://dx.doi.org/10.1007/s00784-020-03642-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8060199PMC
May 2021

Is the high-performance thermoplastic polyetheretherketone indicated as a clasp material for removable dental prostheses?

Clin Oral Investig 2021 May 7;25(5):2859-2866. Epub 2020 Oct 7.

Department of Prosthetic Dentistry, University Hospital, LMU Munich, Goethestraße 70, 80336, Munich, Germany.

Objectives: To investigate the retention force of polyetheretherketone (PEEK) removable dental prosthesis clasps in comparison with a cobalt-chrome-molybdenum control group after storage in artificial saliva.

Materials And Methods: Clasps were milled (Dentokeep (PEEKmilled1), NT digital implant technology; breCAM BioHPP Blank (PEEKmilled2), bredent), pressed (BioHPP Granulat for 2 press (PEEKpressed), bredent), or cast (remanium GM 800+ (cobalt-chrome-molybdenum), Dentaurum); N = 60, n = 15/subgroup. Retention force was examined 50 times/specimen in a pull-off test using the universal testing machine (Zwick 1445), where pull-off force was applied with a crosshead speed of 5 mm/minute until the maximum force dropped by 10%, at different aging levels: (1) initial, after storage in artificial saliva for (2) 90 and (3) 180 days. Statistical analysis was performed using one-way ANOVA followed by post hoc Scheffé-test and mixed models (p < 0.05).

Results: Cobalt-chrome-molybdenum presented the highest retention force. No differences were observed between polyetheretherketone materials. Cobalt-chrome-molybdenum showed a significant decrease of its values after artificial aging, while polyetheretherketone materials presented similar results over the course of aging. Regarding a repetitive insertion and removal, even though PEEKmilled2 and cobalt-chrome-molybdenum showed an initial increase, ultimately, a decrease in retention force was observed for all tested groups.

Conclusions: Although the control group showed significantly higher results, the retention force of polyetheretherketone materials indicate a potential clinical application. Neither the manufacturing process nor artificial aging showed an impact on the retention force of polyetheretherketone clasps.

Clinical Relevance: Mechanical properties of novel removable dental prosthesis clasp materials devised to meet the growing esthetic demands of patients need to be investigated to ensure a successful long-term clinical application.
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http://dx.doi.org/10.1007/s00784-020-03603-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8060225PMC
May 2021

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

Materials (Basel) 2020 Sep 18;13(18). Epub 2020 Sep 18.

Department of Prosthetic Dentistry, Dental School, University Hospital, LMU Munich, 80336 Munich, Germany.

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 (²), Kruskal-Wallis, Mann-Whitney U and Chi tests ( < 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.
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http://dx.doi.org/10.3390/ma13184150DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7560426PMC
September 2020

Comparison between novel strength-gradient and color-gradient multilayered zirconia using conventional and high-speed sintering.

J Mech Behav Biomed Mater 2020 11 6;111:103977. Epub 2020 Aug 6.

Department of Prosthetic Dentistry, University Hospital, LMU Munich, Goethestrasse 70, 80336, Munich, Germany. Electronic address:

Objectives: To investigate and compare the mechanical and optical properties of novel strength- and color-gradient multilayered zirconia and the impact of conventional and high-speed sintering.

Materials And Methods: Following zirconia materials were analyzed and compared: the high-speed sintered Katana Zirconia Block STML (4Y-TZP, KZC), the conventionally sintered Katana Zirconia Disc STML (4Y-TZP, KZL) and IPS e. max ZirCAD Prime (5Y-TZP/3Y-TZP, EZL). As control group acted the crystallized lithium disilicate ceramic IPS e. max CAD (ELC). Monolithic single molar crowns were fabricated and half of them were aged in a chewing simulator with human enamel antagonists (1.2 × 10 cycles, 50 N, lateral movement of 0.7 mm, 5/55 °C). The fracture load was tested in a universal testing machine (N = 96/n = 12). The two-body wear was determined using 3D matching of pre- and post-scans (N = 48/n = 12). Translucency (N = 36/n = 10) was evaluated with UV/Vis spectrophotometer. Data was analyzed using Kolmogorov-Smirnov test, one-way ANOVA followed by post-hoc Scheffé test, unpaired t-test and Weibull analysis (p < 0.05).

Results: Zirconia groups showed higher fracture load than ELC (p ≤ 0.001). Initially, all zirconia materials ranged in the same values (p > 0.05). After chewing simulation, EZL showed higher fracture load than KZC (p < 0.001) and KZL (p = 0.043). Zirconia materials showed no material loss, whereas the ELC showed the volumetric wear of 0.334 ± 0.34 mm and vertical wear of 0.155 ± 0.07 mm. Enamel antagonist wear ranged in the same values (p = 0.083-0.906). The translucency values within each zirconia material showed significant differences between the enamel and the dentin layers (p < 0.001).

Conclusions: The novel strength and color-gradient multilayered zirconia showed higher mechanical properties than lithium disilicate ceramic. The high-speed sintering of zirconia showed neither a negative impact on the fracture load nor on the two-body wear. However, the optical properties and the reliability of zirconia is lower than those of highly translucent lithium disilicate ceramic.
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http://dx.doi.org/10.1016/j.jmbbm.2020.103977DOI Listing
November 2020

Impact of thermocycling on mechanical properties and discoloration of veneering composite resins after storage in various staining media.

J Prosthet Dent 2021 Jun 2;125(6):940-945. Epub 2020 Jul 2.

Scientific Head of Dental Materials Unit, Department of Prosthetic Dentistry, University Hospital, LMU Munich, Munich, Germany.

Statement Of Problem: Veneering composite resins (VCRs) are often used to veneer frameworks, but knowledge of mechanical, surface, and discoloring properties is scarce.

Purpose: The purpose of this in vitro study was to evaluate the impact of thermocycling on flexural strength (FS) and the influence of different staining media on the discoloration (ΔE) and surface free energy (SFE) of VCRs.

Material And Methods: The following VCRs were tested: Ceramage, dialog Vario, Gradia Plus, in:joy, Signum composite, and SR Nexco. FS was tested with enamel and dentin pastes (except SR Nexco: only enamel paste), whereas ΔE and SFE were analyzed for enamel pastes. ΔE was determined by using a spectrophotometer, and SFE was evaluated with contact angle measurements. For FS, rod-shaped specimens (N=660, n=10/subgroup; 25×2×2 mm) were fabricated, thermocycled for 220, 1500, 10 000, 20 000, and 40 000 cycles (5 °C/55 °C). and tested immediately after fabrication (initial) and after aging. For ΔE and SFE, disc-shaped specimens (N=300, n=10/subgroup; 15x15x1.4 mm) were fabricated and stored for 14 days in coffee, red wine, carrot juice, beetroot juice, or curry solution. ΔE and SFE were measured initially after polishing, after discoloration, and after repolishing. Data were analyzed using univariate analysis, 1-way ANOVA followed by the Scheffé post hoc test, Kolmogorov-Smirnov test, Kruskal-Wallis test, Mann-Whitney U test, and Wilcoxon test (α=.05).

Results: Ceramage had the highest FS, followed by dialog Vario and SR Nexco. Gradia Plus, and in:joy had the lowest FS, followed by Signum composite. FS was reduced by increasing of thermocycles. The highest ΔE was measured for curry and the lowest for carrot juice and red wine, followed by beetroot juice and coffee. The highest ΔE between the initial polished specimens and repolished specimens were observed for Ceramage. The remaining VCRs showed differences in ΔE between 0.95 (Signum composite) and 1.30 (SR Nexco). The SFE of the VCRs was similar. After storage in discoloring media, all VCRs had higher SFE than directly after polishing (initial). Repolishing decreased the SFE values compared with those of specimens measured after storage.

Conclusions: FS, ΔE, and SFE differed between the VCRs tested. Discoloration of the VCRs depended on the food and beverage and could be corrected to a clinically acceptable range by repolishing.
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http://dx.doi.org/10.1016/j.prosdent.2020.03.030DOI Listing
June 2021

Effect of high-speed sintering on the flexural strength of hydrothermal and thermo-mechanically aged zirconia materials.

Dent Mater 2020 09 30;36(9):1144-1150. Epub 2020 Jun 30.

Department of Prosthetic Dentistry, University Hospital, Ludwig-Maximilians University, Goethestrasse 70, 80336 Munich, Germany.

Objective: To investigate the influence of high-speed and conventional sintering on the flexural strength (FS) of three zirconia materials initial and after artificial aging.

Methods: Milled zirconia specimens (3Y-TZP: ZI and Zolid; 4Y-TZP: Zolid HT+; Amann Girrbach AG; N = 288, n = 96/group) were sintered in a high-speed sintering protocol (final temperature 1580 °C, n = 48/subgroup) or a conventional sintering protocol (control group, final temperature 1450 °C, n = 48/subgroup). FS was tested initially and after artificial aging (10 h in an autoclave or 1,200,000 chewing cycles; n = 16/subgroup). Univariate ANOVAs, post-hoc Scheffé, partial eta-squared, Kolmogorov-Smirnov-, Kruskal-Wallis- and Mann-Whitney-U-test were performed (p < 0.05).

Results: ZI showed the highest and HT+ the lowest FS, regardless of the sintering protocols and aging regimens (p < 0.001). High-speed sintered HT+ showed higher initial FS than the control group (p < 0.001). ZI (p < 0.001-0.004) and Zolid (p < 0.001-0.007) showed higher FS after thermo-mechanical aging. High-speed sintered HT+ showed higher FS in the initial stage (p < 0.001). The Weibull modulus of the three thermo-mechanically aged materials was negatively influenced by high-speed sintering.

Significance: As shorter sintering times represent a cost and time efficient alternative, high-speed sintering is a valid alternative to conventional sintering protocols.
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http://dx.doi.org/10.1016/j.dental.2020.05.013DOI Listing
September 2020

Measuring the polymerization stress of self-adhesive resin composite cements by crack propagation.

Clin Oral Investig 2021 Mar 15;25(3):1011-1018. Epub 2020 Jun 15.

Department of Prosthetic Dentistry, University Hospital of Munich (LMU), Goethestraße 70, 80336, Munich, Germany.

Objectives: To test the polymerization stress of nine self-adhesive resin composite cements (G-CEM, iCEM, Bifix SE, Maxcem Elite, PANAVIA SA, SoloCem, SmartCem 2, SpeedCEM, RelyX Unicem 2) and one glass ionomer cement (control group; Ketac Cem).

Materials And Methods: The crack propagation of a feldspar ceramic (n = 130) was determined by measuring crack lengths that originated from Vickers indentations, prior to and after the application and polymerization of the self-adhesive resin cements. Results for crack propagation were converted to polymerization stress values, and statistical analysis was performed using one-way ANOVA followed by Scheffé post hoc test.

Results: SmartCem 2 presented higher stress values than iCEM, SoloCem, and Ketac Cem, while Ketac Cem showed lower values than Bifix SE, Maxcem Elite, SmartCem 2, SpeedCEM, and RelyX Unicem 2.

Conclusions: Self-adhesive resin composite cements differ in their polymerization stress, which may affect the durability of the restoration. For restorations made from ceramics with lower flexural strength, such as feldspar ceramics, resin composite cement materials with less polymerization stress should be preferred.

Clinical Relevance: As a high polymerization shrinkage may increase crack propagation, the determination of the polymerization stress of self-adhesive resin composite cements employed for fixing all-ceramic restorations is an important factor.
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http://dx.doi.org/10.1007/s00784-020-03391-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7878217PMC
March 2021

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

J Prosthet Dent 2021 May 19;125(5):817-823. Epub 2020 May 19.

Professor, Department of Prosthetic Dentistry, University Hospital, LMU Munich, Munich, Germany.

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 (E) 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 E (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: η=0.840, E: η=0.855, P<.001), followed by the material (HM: η=0.690 E: η=0.845, P<.001) and the postpolymerization unit (HM: η=0.649, E: η=0.778, P<.001). Initial HM values ranged from 147 ±8.11 N/mm for Formlabs postpolymerized in Otoflash to 89.5 ±8.55 N/mm for Detax postpolymerized in the Labolight unit. E values ranged from 3.92 ±0.061 kN/mm for Formlabs postpolymerized in Otoflash to 2.48 ±0.212 kN/mm for Detax postpolymerized in the Labolight unit. In general, HM and E 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 E values. The 3D-printed materials are more prone to artificial aging than the control group, which brings into question their long-term service.
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http://dx.doi.org/10.1016/j.prosdent.2019.12.026DOI Listing
May 2021