Publications by authors named "Marlis Eichberger"

62 Publications

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

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

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

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

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

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

Int J Prosthodont 2020 May/Jun;33(3):307-314

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.
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http://dx.doi.org/10.11607/ijp.6669DOI Listing
April 2020

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

Dent Mater J 2020 Aug 21;39(4):539-546. Epub 2020 Feb 21.

Department of Prosthetic Dentistry, University Hospital, Ludwig-Maximilians-University Munich.

Elastic properties of Aryl-Ketone-Polymer (UAKP) and tensile bond strength (TBS) to denture resin (PalaXpress) were tested. Indentation modulus (E) and indentation hardness (H) were measured via Martens hardness (n=10 specimens) with 4.2±0.6 kN/mm and 261±8 N/mm 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 (P=0.715, p<0.001) followed by the opaquer (η=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.
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http://dx.doi.org/10.4012/dmj.2019-125DOI Listing
August 2020

Flexural strength, fracture toughness, three-body wear, and Martens parameters of pressable lithium-X-silicate ceramics.

Dent Mater 2020 03 30;36(3):420-430. Epub 2020 Jan 30.

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

Objectives: To test and compare five pressable lithium-X-silicate-ceramics on their mechanical and wear properties.

Methods: Specimens were pressed and prepared from: i. Amber Press (AP), ii. Celtra Press (CP), iii. Initial LiSi Press (IL), iv. Livento Press (LP), and v. IPS e.max Press (IE). Four-point flexural strength (FS), SEVNB fracture toughness (K), three-body wear (3BW), Martens hardness (HM) and indentation modulus (E) were measured. For CP, FS and HM were measured with and without additional Power Firing. Each subgroup contained 15 specimens. Data were analyzed using Kolmogorov-Smirnov, one-way ANOVA followed by Scheffé test, Kruskal-Wallis-H-, Mann-Whitney-U-, and Spearman-Rho-test (p < 0.05). The Weibull modulus was calculated using the maximum likelihood estimation method.

Results: AP and CP presented higher FS than IL. LP presented the highest Weibull modulus. CP showed lower K values than AP, and AP was not significant compared to LP and IE. The most 3BW material loss was observed for CP. CP revealed higher HM values than the remaining ceramics. IL presented lower E compared to AP and CP. The following correlations were observed between the test parameters: 3BW with FS (r = 0.279, p = 0.015), with HM (r = -0.378, p = 0.001), and with E (r = -0.344, p = 0.004); E with FS (r = 0.203, p = 0.028); and HM with FT (r = -0.223, p = 0.027) and E (r = 0.884, p < 0.001). No correlations were observed between FS and K (r = 0.046; p = 0.346).

Significance: AP followed by LP showed the highest and IL followed by CP the lowest properties tested. Power Firing of CP improved the flexural strength. Ceramics with high flexural strength and Martens parameters showed lower wear. Materials with high Martens hardness presented lower fracture toughness values and ones with high indentation modulus showed high flexural strength.
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http://dx.doi.org/10.1016/j.dental.2020.01.009DOI Listing
March 2020

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

J Prosthet Dent 2020 Dec 21;124(6):790-797. Epub 2020 Jan 21.

Scientific Head of Dental Material Unit, Department of Prosthetic Dentistry, University Hospital, Ludwig Maximilian University of Munich, Munich, Germany. Electronic address:

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 (AlO, 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 (η), followed by the Kruskal-Wallis and Mann-Whitney-U tests. Relative frequency of failure types was analyzed with the Chi-test and a Ciba-Geigy table.

Results: The highest impact on TBS was exerted by the adhesive (η=0.458, P<.001), followed by opaquer (η=0.288, P<.001). The binary combination of the 3 variables was significant for opaquer coupled with adhesive (η=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.
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http://dx.doi.org/10.1016/j.prosdent.2019.10.017DOI Listing
December 2020

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

Dent Mater J 2020 Mar 19;39(2):302-308. Epub 2019 Dec 19.

Department of Prosthetic Dentistry, University Hospital, Ludwig-Maximilians-University Munich.

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.
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http://dx.doi.org/10.4012/dmj.2019-045DOI Listing
March 2020

Influence of different surface treatments on two-body wear and fracture load of monolithic CAD/CAM ceramics.

Clin Oral Investig 2020 Sep 13;24(9):3049-3060. Epub 2019 Dec 13.

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

Objectives: To investigate two-body wear (2BW) and fracture load (FL) of monolithic ceramics after different surface pretreatments.

Materials And Methods: Zirconia (MOZ), lithium-disilicate (LIT), and leucite-reinforced (LEU) specimens (n = 60/group) were manufactured with CAD/CAM-technology and underwent (n = 15/subgroup): 1) grinding + polishing (GrPo), 2) grinding + glazing (GrGz), 3) grinding (Gr), or 4) glazing (Gz). Scanning electron microscope (n = 3/subgroup) and 3D measurements of the ceramic crowns and antagonists (N = 180) were performed to determine 2BW before and after 120,000/1,200,000 masticatory cycles. FL was examined for all specimens (N = 180). Data were analyzed using Kolmogorov-Smirnov, one-way ANOVA, Scheffé post hoc, Kruskal-Wallis, Mann-Whitney-U, and Wilcoxon (p < 0.05).

Results: MOZ presented the highest FL independent on pretreatment (6960-9250 N), while LEU (1405-2320 N) showed the lowest (p < 0.001). Ceramic and antagonist wear increased between 120,000 and 1,200,000 masticatory cycles (p < 0.001). For pretreatments GrPo, GrGz, and Gz, MOZ showed the lowest wear of the ceramic, while causing the highest antagonist wear (p < 0.001). GrPo resulted in the lowest wear for MOZ (p < 0.001), with Gr leading to the highest antagonist wear (p = 0.008). LIT specimens presented the highest wear of the ceramic and antagonist after Gz (p < 0.001), while GrPo resulted in the lowest antagonist wear (p < 0.001). GrGz led to the highest antagonist wear for LEU (p < 0.001).

Conclusions: With FL exceeding maximum masticatory forces, the three tested ceramics can be recommended for restorations, even in posterior regions. While glazing resulted in higher wear and impaired FL, polishing improved mechanical properties while largely preserving the antagonist.

Clinical Relevance: While surface pretreatment after grinding is vital to ensure a ceramic's optimal mechanical properties, glazing and polishing varies with regard to material properties, costs, and time.
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http://dx.doi.org/10.1007/s00784-019-03173-8DOI Listing
September 2020

Influence of Different Cleaning Procedures on Tensile Bond Strength Between Zirconia Abutment and Titanium Base.

Int J Oral Maxillofac Implants 2019 Nov/Dec;34(6):1318-1327

Purpose: To investigate the tensile bond strength between zirconia abutments and titanium bases, luted with two different resin composite cements, after different cleaning procedures.

Materials And Methods: Zirconia abutments and titanium bases were luted with either a DMA/HEMA-based cement (n = 80; Multilink Hybrid Abutment, Ivoclar Vivadent) or a Bis-GMA/TEGDMA-based cement (n = 80; Panavia V5, Kuraray Noritake). The adhesive gap of half of the specimens was polished (n = 40 per resin composite cement). Four separate specimens underwent roughness measurements and scanning electron microscopy. The specimens were divided into four groups (n = 10 per subgroup): (1) not cleaned, (2) cleaning in an ultrasonic bath, (3) cleaning in an autoclave, and (4) treatment with low-pressure plasma. The specimens were thermocycled (20,000×, 5°C/55°C), tensile bond strength was tested, and fracture types were analyzed. Data were examined using the Kolmogorov-Smirnov test, univariate ANOVA with additional partial eta-squared (η), and the Mann-Whitney U test. The defined level of significance was adjusted by Bonferroni correction (P < .003).

Results: The tensile bond strength of specimens luted with the DMA/HEMA-based cement was higher than that of specimens luted with the Bis-GMA/TEGDMA-based cement. The polishing step and the cleaning procedures showed no impact on tensile bond strength results. Specimens luted with the DMA/HEMA-based cement presented more cohesive fractures, whereas specimens luted with the Bis-GMA/TEGDMA-based cement presented themselves with more fractures of the interface between the resin composite cement and zirconia abutment. R values showed a decline in roughness after polishing for both resin composite cements.

Conclusion: As the DMA/HEMA-based cement showed higher tensile bond strength values, the usage of this resin composite cement for luting implant abutments to titanium bases can be recommended. Neither polishing nor the use of different cleaning procedures had an impact on tensile bond strength.
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http://dx.doi.org/10.11607/jomi.7638DOI Listing
December 2019

Impact of storage media and temperature on color stability of tooth-colored CAD/CAM materials for final restorations.

J Appl Biomater Funct Mater 2019 Oct-Dec;17(4):2280800019836832

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

Background: This in-vitro study examined the impact of storage solution, storage duration, and storage temperature on discoloration of three tooth-colored CAD/CAM materials for final restorations.

Methods: Specimens ( = 288; = 96 per material) with a thickness of 1 ± 0.03 mm of the following CAD/CAM materials were fabricated: resin composite (Lava Ultimate, 3M), polymer-infiltrated ceramic (VITA Enamic, VITA Zahnfabrik), and leucite ceramic (IPS Empress CAD, Ivoclar Vivadent). After baseline measurement, specimens were stored in red wine, curry solution, cress solution, and distilled water at 37°C or 55°C. The discoloration was measured using a spectrophotometer (Lambda 35 Perkin Elmer, Perkin Elmer Inc.) after 1 and 7 days storage. Data were analyzed using four-way ANOVA followed by the Scheffé post-hoc test and partial eta squared (²) test ( < 0.05).

Results: The highest influence on ∆ was exerted by storage duration (² = 0.295, < 0.001), followed by storage solution (² = 0.171, < 0.001), CAD/CAM material (² = 0.049, < 0.001), and storage temperature (² = 0.033, < 0.001). Specimens stored for 7 days in staining solutions showed more discoloration than those stored for just 1 day. Higher ∆ values were achieved for specimens stored in curry solution, followed by red wine, cress solution, and distilled water. Resin composite Lava Ultimate showed larger ∆ values compared with the resin hybrid ceramic VITA Enamic and leucite ceramic IPS Empress CAD. Specimens stored at 37°C showed significantly less discoloration than those stored at 55°C.

Conclusions: The degree of coloration of the materials depends on food and temperature and was most pronounced with Lava Ultimate.
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http://dx.doi.org/10.1177/2280800019836832DOI Listing
May 2020

Different surface modifications combined with universal adhesives: the impact on the bonding properties of zirconia to composite resin cement.

Clin Oral Investig 2019 Nov 12;23(11):3941-3950. Epub 2019 Feb 12.

Scientific Head of Dental Material Unit, Department of Prosthetic Dentistry, University Hospital, Ludwig-Maximilians-University, Munich, Germany.

Objective: The purpose of this study was to analyze the impact of plasma treatment and (universal adhesives) UAs on the bonding properties of zirconia.

Material And Methods: Zirconia specimens (N = 744; n = 186/pretreatment) were prepared, highly polished, and pretreated: (i) plasma (oxygen plasma, 10s, 5 mm), (ii) airborne-particle abrasion (alumina, 50 μm, 0.05 MPa, 5 s, 10 mm), (iii) airborne-particle abrasion + plasma, and (iv) without pretreatment (highly polished surface). Surface roughness (R) and surface free energy (SFE) were measured (n = 6/pretreatment). Tensile bond strength (TBS) specimens (n = 180/pretreatment) were further divided (n = 18/conditioning): Clearfil Ceramic Primer (PCG), All-Bond Universal (ABU), Adhese Universal (AU), Clearfil Universal Bond (CUB), G-Premio Bond (GPB), Futurabond U (FBU), iBond Universal (IBU), One Coat 7 Universal (OCU), Scotchbond Universal (SBU), and no conditioning. PCG was luted with Panavia F2.0 and the remaining groups with DuoCem. After storage in distilled water (24 h; 37 °C) and thermocycling (5000×; 5 °C/55 °C), TBS was measured and fracture types (FTs) were determined. Data were analyzed using univariate ANOVA with a partial eta square (ƞ), the Kruskal-Wallis H, the Mann-Whitney U, and the Chi test (P < .05).

Results: Plasma treatment resulted in an increase of SFE but had no impact on R. Airborne-particle abrasion resulted in the highest R and a higher TBS when compared with plasma and non-treatment. SBU and AU obtained a higher TBS when compared with PCG. OCU, FBU, ABU, IBU, and GPB indicated comparable TBS to PCG. CUB revealed the lowest TBS.

Conclusions: Plasma treatment cannot substitute airborne-particle abrasion when bonding zirconia but MDP-containing adhesives are essential for successful clinical outcomes.

Clinical Relevance: Airborne-particle abrasion with a low pressure (0.05 MPa) in combination with UAs promotes the clinical success of adhesively bonded zirconia restorations.
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http://dx.doi.org/10.1007/s00784-019-02825-zDOI Listing
November 2019

Fracture resistance and 2-body wear of 3-dimensional-printed occlusal devices.

J Prosthet Dent 2019 Jan 29;121(1):166-172. Epub 2018 Jun 29.

Scientific Head, Dental Material Unit, Department of Prosthodontics, Ludwig-Maximilians University, Munich, Germany. Electronic address:

Statement Of Problem: Polymeric material for 3-dimensional printing can be used to fabricate occlusal devices. However, information about fracture resistance and wear is scarce.

Purpose: The purpose of this in vitro study was to investigate the fracture resistance and 2-body wear of 3-dimensional-printed (3DP) (FotoDent splint; Dreve Dentamid GmbH), milled polymethylmethacrylate (CAM) (Temp Basic; Transpa 95H16, Zirkonzahn GmbH), and conventionally fabricated polymethylmethacrylate (CAST) (Castdon; Dreve Dentamid GmbH) occlusal devices.

Material And Methods: A total of 96 occlusal devices were prepared according to the 3 different manufacturing techniques 3DP, CAM, and CAST (n=32). For each manufacturing technique, specimens were further divided into initial fracture resistance tests (n=16) and artificial aging in the mastication simulator (50 N, 37°C) with 2-body wear followed by fracture resistance tests (n=16). The fracture resistance was determined using a universal testing machine (1 mm/min). The wear was measured after 20 000 and 120 000 mastication cycles with the replica technique, mapped with a laser scanner, and quantified in R software. Data were analyzed using a 2-way ANOVA followed by a 1-way ANOVA with Scheffé or Games-Howell post hoc tests, repeated measures ANOVA with corrected Greenhouse-Geisser P values, and the Levene, Mann-Whitney, and paired t tests (α=.05).

Results: CAM presented higher initial fracture resistance than 3DP or CAST (P<.001). After mastication simulation, CAM followed by 3DP showed higher fracture resistance than CAST (P<.001). Mastication simulation decreased the fracture resistance for CAM and CAST (P<.001) but not for 3DP (P=.78). Three-dimensional-printed occlusal devices showed the highest material volume loss, followed by CAM and the lowest in CAST (P<.001).

Conclusions: Three-dimensional-printed occlusal devices showed lower wear resistance and lower fracture resistance than those milled or conventionally fabricated. Therefore, only short-term application in the mouth is recommended. Further developments of occlusal device material for 3-dimensional printing are necessary.
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http://dx.doi.org/10.1016/j.prosdent.2018.04.007DOI Listing
January 2019

Flexural strength, fracture toughness, and translucency of cubic/tetragonal zirconia materials.

J Prosthet Dent 2018 Dec 25;120(6):948-954. Epub 2018 May 25.

Head of Dental Materials Unit, Department of Prosthetic Dentistry, Hospital of the University of Munich, Ludwig Maximilian University of Munich, Munich, Germany. Electronic address:

Statement Of Problem: The development of zirconia materials with optimized properties has been rapid, and studies comparing the mechanical and optical properties of recently introduced zirconia with lithium disilicate materials are limited.

Purpose: The purpose of this in vitro study was to compare the mechanical and optical properties of cubic/tetragonal zirconia materials with those of a lithium disilicate ceramic.

Material And Methods: Specimens were fabricated from 6 different noncolored zirconia materials: Ceramill Zolid FX (CZ), CopraSmile (CS), DD cubeX (DD), NOVAZIR MaxT (NZ), priti multidisc ZrO₂ (PD), and StarCeram Z-Smile (SC), and 1 lithium disilicate ceramic as a control, IPS e.max Press LT A2 (CG). Four-point flexural strength (N=105/n=15) and fracture toughness using the single-edge V-notched beam (N=105/n=15) were examined according to International Organization for Standardization standard 6872:2015. Translucency (N=70/n=10) was evaluated with an ultraviolet spectrophotometer. Grain size (N=6/n=1) of zirconia was investigated by using scanning electron microscopy. Data were analyzed using the Kolmogorov-Smirnov test, multivariate analysis, 1-way analysis of variance, followed by the post hoc Scheffé test and Kruskal-Wallis and Mann-Whitney U tests, and Weibull analysis, using the maximum likelihood estimation method at 95% confidence level (α=.05).

Results: Zirconia materials showed higher mechanical and lower optical properties than CG (P<.001). No differences were observed among the zirconia materials with respect to flexural strength (P=.259) or fracture toughness (P=.408). CG and CS showed significantly higher Weibull modulus than SC and PD. The lowest translucency values were measured for NZ and SC, followed by CS, DD, and PD (P<.001). CZ showed the highest translucency values (P<.001). The lowest grain sizes were found for NZ, DD, and SC; the largest were shown for CS (P<.001).

Conclusions: Cubic/tetragonal zirconia showed better mechanical properties than lithium disilicate ceramic. However, the optical properties and the reliability of zirconia are lower than those of lithium disilicate ceramic.
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http://dx.doi.org/10.1016/j.prosdent.2017.12.021DOI Listing
December 2018

Bonding to new CAD/CAM resin composites: influence of air abrasion and conditioning agents as pretreatment strategy.

Clin Oral Investig 2019 Feb 27;23(2):529-538. Epub 2018 Apr 27.

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

Objectives: Because of their industrially standardized process of manufacturing, CAD/CAM resin composites show a high degree of conversion, making a reliable bond difficult to achieve.

Purpose: The purpose of this experiment was to investigate the tensile bond strength (TBS) of luting composite to CAD/CAM resin composite materials as influenced by air abrasion and pretreatment strategies.

Material And Methods: The treatment factors of the present study were (1) brand of the CAD/CAM resin composite (Brilliant Crios [Coltene/Whaledent], Cerasmart [GC Europe], Shofu Block HC [Shofu], and Lava Ultimate [3M]); (2) air abrasion vs. no air abrasion; and (3) pretreatment using a silane primer (Clearfil Ceramic Primer, Kuraray) vs. a resin primer (One Coat 7 Universal, Coltene/Whaledent). Subsequently, luting composite (DuoCem, Coltene/Whaledent) was polymerized onto the substrate surface using a mold. For each combination of the levels of the three treatment factors (4 (materials) × 2 (air abrasion vs. no air abrasion; resin) × 2 (primer vs. silane primer)), n = 15, specimens were prepared. After 24 h of water storage at 37 °C and 5000 thermo-cycles (5/55 °C), TBS was measured and failure types were examined. The resulting data was analyzed using Kaplan-Meier estimates of the cumulative failure distribution function with Breslow-Gehan tests and non-parametric ANOVA (Kruskal-Wallis test) followed by the multiple pairwise Mann-Whitney U test with α-error adjustment using the Benjamini-Hochberg procedure and chi-square test (p < 0.05).

Results: The additional air abrasion step increased TBS values and lowered failure rates. Specimens pretreated using a resin primer showed significantly higher TBS and lower failure rates than those pretreated using a silane primer. The highest failure rates were observed for groups pretreated with a silane primer. Within the Shofu Block HC group, all specimens without air abrasion and pretreatment with a silane primer debonded during the aging procedure.

Conclusions: Before fixation of CAD/CAM resin composites, the restorations should be air abraded and pretreated using a resin primer containing methyl-methacrylate to successfully bond to the luting composite. The pretreatment of the CAD/CAM resin composite using merely a silane primer results in deficient adhesion.

Clinical Relevance: For a reliable bond of CAD/CAM resin composites to the luting composite, air abrasion and a special pretreatment strategy are necessary in order to achieve promising long-term results.
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http://dx.doi.org/10.1007/s00784-018-2461-7DOI Listing
February 2019

Color change of CAD-CAM materials and composite resin cements after thermocycling.

J Prosthet Dent 2018 Oct 25;120(4):546-552. Epub 2018 Apr 25.

Head, Dental Materials Unit, Department of Prosthodontics, Dental School, Ludwig Maximilian University, Munich, Germany.

Statement Of Problem: The color of resin cements and computer-aided-design and computer-aided-manufacturing (CAD-CAM) restorations may change with aging.

Purpose: The purpose of this in vitro study was to analyze the influence of thermocycling on the color of CAD-CAM materials with underlying resin cement.

Material And Methods: Seven different CAD-CAM materials, composite resins and glass-ceramics were cut into 0.7-mm and 1.2-mm thicknesses (n=10) and cemented with a dual-polymerizing resin cement, a light-polymerizing resin cement, and a preheated composite resin (N=420). Color values were measured by using spectrophotometry. Specimens were subjected to thermocycling (5°C and 55°C; 5000 cycles). The measured color difference (ΔE) data were analyzed by using descriptive statistics. Normality of data distribution was tested by using the Kolmogorov-Smirnov test. Three-way and 1-way ANOVA followed by the Scheffé post hoc test and unpaired 2-sample Student t test were computed to determine the significant differences among the tested parameters (α=.05).

Results: ΔE values were significantly influenced by the CAD-CAM material (η=0.85, P<.001) and the resin composite cement (η=0.03, P=.003) but were not influenced by thickness (P=.179). Significant interactions were present among thickness, cement, and CAD-CAM materials (P<.001). Vita Suprinity and GC Cerasmart showed significantly the lowest ΔE values (P<.001). The highest ΔE values were observed for IPS Empress CAD. The dual-polymerizing resin cement showed significantly lower ΔE values than the preheated composite resin (P=.003).

Conclusions: Restoration materials and composite resin cement types used for cementation influence the amount of color change due to aging.
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http://dx.doi.org/10.1016/j.prosdent.2017.12.003DOI Listing
October 2018

Accuracy of Digitally Fabricated Wax Denture Bases and Conventional Completed Complete Dentures.

Dent J (Basel) 2017 Dec 19;5(4). Epub 2017 Dec 19.

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

The purpose of this investigation was to analyze the accuracy of digitally fabricated wax trial dentures and conventionally finalized complete dentures in comparison to a surface tessellation language (STL)-dataset. A generated data set for the denture bases and the tooth sockets was used, converted into STL-format, and saved as reference. Five mandibular and 5 maxillary denture bases were milled from wax blanks and denture teeth were waxed into their tooth sockets. Each complete denture was checked on fit, waxed onto the dental cast, and digitized using an optical laboratory scanning device. The complete dentures were completed conventionally using the injection method, finished, and scanned. The resulting STL-datasets were exported into the three-dimensional (3D) software GOM Inspect. Each of the 5 mandibular and 5 maxillary complete dentures was aligned with the STL- and the wax trial denture dataset. Alignment was performed based on a best-fit algorithm. A three-dimensional analysis of the spatial divergences in -, - and -axes was performed by the 3D software and visualized in a color-coded illustration. The mean positive and negative deviations between the datasets were calculated automatically. In a direct comparison between maxillary wax trial dentures and complete dentures, complete dentures showed higher deviations from the STL-dataset than the wax trial dentures. The deviations occurred in the area of the teeth as well as in the distal area of the denture bases. In contrast, the highest deviations in both the mandibular wax trial dentures and the mandibular complete dentures were observed in the distal area. The complete dentures showed higher deviations on the occlusal surfaces of the teeth compared to the wax dentures. Computer-aided design/computer-aided manufacturing (CAD/CAM)-fabricated wax dentures exhibited fewer deviations from the STL-reference than the complete dentures. The deviations were significantly greater in the vicinity of the denture teeth area and the bases. The conventional transfer of CAD/CAM-fabricated wax dentures into acrylic resin leads to the highest deviations from the STL-reference.
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http://dx.doi.org/10.3390/dj5040036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5806961PMC
December 2017

Impact of the heating/quenching process on the mechanical, optical and thermodynamic properties of polyetheretherketone (PEEK) films.

Dent Mater 2017 12 10;33(12):1436-1444. Epub 2017 Oct 10.

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

Objective: The aim of this study was to investigate the impact of a heating/quenching process on the optical, mechanical and thermodynamic properties of filled (20%_4000) and unfilled PEEK films (0%_2000 and 0%_4000). Heating/quenching was performed to simulate thermoforming as possible method to process thermoplastic polymers for dental application.

Methods: For the investigation, films of different PEEK qualities (0%_2000, 0%_4000, 20%_4000) were produced using isostatic pressing (n=10/quality). From each PEEK film, round specimens (n=20/PEEK film) with a diameter of 34mm were cut and following parameters were determined: translucency (T%), Martens-Hardness (HM), indentation modulus (E), glass transition temperature (T), melting temperature (T) and enthalpy of fusion (ΔH). Same specimens were exposed to heating/quenching using defined parameters. Afterwards, T%, HM, E, TG, TM and ΔH were determined again. Data were analysed using Kolmogorov-Smirnov test, univariate ANOVA followed by post-hoc Scheffé test with partial eta squared (η), Kruskal-Wallis and Mann Whitney U test. Level of significance was defined to 95%.

Results: Materials showed significant differences for all investigated parameters in the initial state, except of T (p=0.249). The heating/quenching process showed a significant increase on T% for the unfilled materials 0%_2000 and 0%_4000. HM and E decreased significantly through heating/quenching for all materials. Moreover, heating/quenching showed a reduction of T for 0%_2000 and 20%_4000, while T decreased for 0%_2000 and 0%_4000. ΔH confirms different crystallinities of tested materials.

Significance: The heating/quenching process showed a significant impact on all investigated parameters. The highest impact was found for mechanical properties resulting in decreased values of HM and E.
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http://dx.doi.org/10.1016/j.dental.2017.09.016DOI Listing
December 2017

Accuracy of digitally fabricated trial dentures.

J Prosthet Dent 2018 Jun 29;119(6):942-947. Epub 2017 Sep 29.

Head, Dental Materials Unit, Department of Prosthodontics, Ludwig-Maximilians-University, Munich, Germany. Electronic address:

Statement Of Problem: Information about the accuracy of digital computer-aided design and computer-aided manufacturing (CAD-CAM) complete dentures is scarce.

Purpose: The purpose of this in vitro study was to assess the reproducibility of the occlusion of wax dentures fabricated with digital steps and the contraction behavior of wax trial dentures processed with combined conventional-digital steps. These were compared with those fabricated completely conventionally in terms of storage duration.

Material And Methods: Five sets of maxillary and mandibular wax trial dentures were milled from a gingiva-colored wax blank (Ceramill D-Wax, Amann Girrbach AG) using the Ceramill Motion 2 System (Amann Girrbach), scanned, and matched by best-fit triangulation for each of the 5 denture pairs. Processing deformation was measured and the maximum deviations calculated. A 3-dimensional color-coded mapping of the differences between each pair of dentures was generated. Five sets of maxillary and mandibular wax trial dentures were processed with digital steps, and 5 sets of maxillary and mandibular wax trial dentures were fabricated in the conventional way with the help of a silicone index from a CAM-fabricated wax trial denture to standardize the wax amount. All dentures were scanned immediately after waxing and after 1 week of storage. After surface matching, the deformation was measured, and the milled wax bases were compared with those conventionally fabricated. Data were interpreted using descriptive statistics.

Results: The occlusion of wax trial dentures fabricated with digital steps was not reproducible. The deviations in the maxillary dentures were mostly marginal, with exceptions for single teeth/tooth groups in denture No. 2 (occlusal areas of teeth in second quadrant, second molars) and No. 4 (central incisor and canine in second quadrant inclined to palatal side, and first premolar in first quadrant and first molar in second quadrant displayed greater deviations). Among the mandibular dentures, denture Nos. 4 and 5 the central incisor (fourth quadrant) inclined to the labial side. Additionally, in denture No. 5 the lateral incisor (fourth quadrant) inclined to the lingual side.

Conclusions: In digitally fabricated dentures, the manual placing of the teeth into the denture base sockets can lead to deviations from the planned arrangement. The deviations were greater in the area of the denture bases in the conventionally fabricated dentures compared with those processed with combined conventional-digital steps. The milled wax bases showed better contraction behavior than the conventionally fabricated wax bases.
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http://dx.doi.org/10.1016/j.prosdent.2017.06.020DOI Listing
June 2018