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Maleki T, Meinen J, Coldea A, Reymus M, Edelhoff D, Stawarczyk B. Mechanical and physical properties of splint materials for oral appliances produced by additive, subtractive and conventional manufacturing. Dent Mater 2024; 40:1171-1183. [PMID: 38851965 DOI: 10.1016/j.dental.2024.05.030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 03/15/2024] [Accepted: 05/29/2024] [Indexed: 06/10/2024]
Abstract
OBJECTIVES To investigate the flexural strength (FS), elastic modulus (E), Martens hardness (HM), water sorption (wsp), water solubility (wsl) and degree of conversion (DC) of 3D-printed, milled and injection molded splint materials. METHODS Specimens (N = 1140) were fabricated from five 3D-printed (GR-22 flex, GR-10 guide, ProArt Print Splint clear, V-Print Splint, V-Print Splint comfort), five milled (BioniCut, EldyPlus, ProArt CAD Splint clear, Temp Premium Flexible, Thermeo) and two injection molded (PalaXPress clear, Pro Base Cold) materials. FS, E, HM, wsp, wsl and DC were tested initially (24 h, 37 °C, H2O), after water storage (90 d, 37 °C, H2O) as well as after thermal cycling (5000 thermal cycles, 5/55 °C). Data were analyzed with Kolmogorov-Smirnov, Kruskal- Wallis, Mann-Whitney U test and Spearman's correlation (p < 0.05). RESULTS Initially, the mean flexural strength values ranged from 1.9 to 90.7 MPa for printed, 3.8 to 107 MPa for milled and 99.7 to 102 MPa for injection molded materials. The initial mean elastic modulus values were 0.0 to 2.4 GPa for printed, 0.1 to 2.7 GPa for milled and 2.8 GPa for injection molded materials. The initial mean Martens hardness values were 14.5 to 126 N/mm2 for printed, 50.2 to 171 N/mm2 for milled and 143 to 151 N/mm2 for injection molded materials. Initially, the mean water sorption values ranged from 23.1 to 41.2 μg/mm3 for printed, 4.5 to 23.5 μg/mm3 for milled and from 22.5 to 23.3 μg/ mm3 for injection molded materials. The initial mean water solubility values ranged from 2.2 to 7.1 μg/mm3 for printed, 0.0 to 0.5 μg/mm3 for milled and 0.1 to 0.3 μg/mm3 for injection molded materials. After water storage and thermal cycling most of the values decreased and some increased. The mean DC values ranged initially from 72.3 to 94.5 %, after water storage from 74.2 to 96.8 % and after thermal cycling from 75.6 to 95.4 % for the printed materials. SIGNIFICANCE The mechanical and physical properties of printed, milled and injection molded materials for occlusal devices vary and are influenced by aging processes. For clinical applications, materials need to be chosen according to the specific indications.
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Affiliation(s)
- Tina Maleki
- Department of Prosthetic Dentistry, University Hospital, LMU Munich, Munich, Germany.
| | - John Meinen
- Department of Prosthetic Dentistry, University Hospital, LMU Munich, Munich, Germany
| | - Andrea Coldea
- Department of Prosthetic Dentistry, University Hospital, LMU Munich, Munich, Germany
| | - Marcel Reymus
- Department of Conservative Dentistry and Peridontology, University Hospital, LMU Munich, Munich, Germany
| | - Daniel Edelhoff
- Department of Prosthetic Dentistry, University Hospital, LMU Munich, Munich, Germany
| | - Bogna Stawarczyk
- Department of Prosthetic Dentistry, University Hospital, LMU Munich, Munich, Germany
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Orgev A, Donmez MB, Almogbel L, Cakmak G, Marques VR, Kahveci C, Yilmaz B. Cameo and intaglio surface stability and variability of additively, subtractively, and conventionally manufactured occlusal devices after long-term storage. J Prosthet Dent 2024:S0022-3913(24)00427-X. [PMID: 38955603 DOI: 10.1016/j.prosdent.2024.06.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2024] [Revised: 06/10/2024] [Accepted: 06/12/2024] [Indexed: 07/04/2024]
Abstract
STATEMENT OF PROBLEM Additive and subtractive manufacturing have become alternative technologies for fabricating occlusal devices. However, knowledge of the long-term stability of occlusal devices fabricated using these recent technologies is limited. PURPOSE The purpose of this in vitro study was to evaluate the cameo and intaglio surface stability and variability of additively, subtractively, and conventionally manufactured occlusal devices after 18 months of storage. MATERIAL AND METHODS A standard tessellation language (STL) file of a dentate maxillary typodont was used to design a master occlusal device. The STL file of this design was used to fabricate occlusal devices additively either with a digital light processing (AM-1) or a continuous liquid interface production (AM-2) printer, subtractively with 2 different 5-axis milling units (SM-1 and SM-2), and conventionally (TM-HP) (n=10). STL files of each device's cameo and intaglio surfaces were generated using a laboratory scanner after fabrication and after 18 months of storage in a moist environment. These generated files were imported into an analysis software program (Geomagic Control X) to analyze the dimensional stability of tested devices by using the root mean square method. The average deviation values defined the variability of measured changes over time. Cameo and intaglio surface deviations were analyzed using the Kruskal-Wallis and Dunn tests, while the variability of measured deviations was analyzed with 1-way analysis of variance and the Tukey HSD tests (α=.05). RESULTS Significant differences were observed among tested devices when the intaglio surface deviations and the cameo surface variability were considered (P<.001). SM-2 had significantly higher intaglio surface deviations than AM-1, SM-1, and AM-2 (P≤.036). Among the test groups, AM-1 had the greatest cameo surface variability (P≤.004). CONCLUSIONS SM-2 resulted in lower intaglio surface stability than the additive and the other subtractive manufacturing technologies, while AM-1 led to the highest cameo surface variability among the test groups.
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Affiliation(s)
- Ahmet Orgev
- Clinical Associate Professor, Department of Restorative Dentistry, School of Dental Medicine, University at Buffalo, Buffalo, NY.
| | - Mustafa Borga Donmez
- Associate Professor, Department of Prosthodontics, Faculty of Dentistry, Istinye University, Istanbul, Turkey; and ITI Scholar, Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland
| | - Lolowh Almogbel
- Fellow, Advanced Education Program in Implant Dentistry, Loma Linda University School of Dentistry, Loma Linda, Calif.; Restorative and Prosthetic Dental Sciences Department, College of Dentistry, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia; King Abdullah International Medical Research Centre, Ministry of National Guard Health Affairs, Riyadh, Saudi Arabia
| | - Gulce Cakmak
- Senior Research Associate, Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland
| | - Vinicius Rizzo Marques
- Digital Implant Fellow, Department of Restorative Dentistry, School of Dental Medicine, University at Buffalo, Buffalo, NY
| | - Cigdem Kahveci
- Assistant Professor, Department of Prosthodontics, Giresun University Faculty of Dentistry, Giresun, Turkey
| | - Burak Yilmaz
- Associate Professor, Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland; Associate Professor, Department of Restorative, Preventive and Pediatric Dentistry, School of Dental Medicine, University of Bern, Bern, Switzerland; and Adjunct Professor, Division of Restorative and Prosthetic Dentistry, The Ohio State University, Columbus, Ohio
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Kollmuss M, Edelhoff D, Schwendicke F, Wuersching SN. In Vitro Cytotoxic and Inflammatory Response of Gingival Fibroblasts and Oral Mucosal Keratinocytes to 3D Printed Oral Devices. Polymers (Basel) 2024; 16:1336. [PMID: 38794529 PMCID: PMC11125196 DOI: 10.3390/polym16101336] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2024] [Revised: 04/29/2024] [Accepted: 05/07/2024] [Indexed: 05/26/2024] Open
Abstract
The purpose of this study was to examine the biocompatibility of 3D printed materials used for additive manufacturing of rigid and flexible oral devices. Oral splints were produced and finished from six printable resins (pairs of rigid/flexible materials: KeySplint Hard [KR], KeySplint Soft [KF], V-Print Splint [VR], V-Print Splint Comfort [VF], NextDent Ortho Rigid [NR], NextDent Ortho Flex [NF]), and two types of PMMA blocks for subtractive manufacturing (Tizian Blank PMMA [TR], Tizian Flex Splint Comfort [TF]) as controls. The specimens were eluted in a cell culture medium for 7d. Human gingival fibroblasts (hGF-1) and human oral mucosal keratinocytes (hOK) were exposed to the eluates for 24 h. Cell viability, glutathione levels, apoptosis, necrosis, the cellular inflammatory response (IL-6 and PGE2 secretion), and cell morphology were assessed. All eluates led to a slight reduction of hGF-1 viability and intracellular glutathione levels. The strongest cytotoxic response of hGF-1 was observed with KF, NF, and NR eluates (p < 0.05 compared to unexposed cells). Viability, caspase-3/7 activity, necrosis levels, and IL-6/PGE2 secretion of hOK were barely affected by the materials. All materials showed an overall acceptable biocompatibility. hOK appeared to be more resilient to noxious agents than hGF-1 in vitro. There is insufficient evidence to generalize that flexible materials are more cytotoxic than rigid materials. From a biological point of view, 3D printing seems to be a viable alternative to milling for producing oral devices.
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Affiliation(s)
- Maximilian Kollmuss
- Department of Conservative Dentistry and Periodontology, University Hospital, LMU Munich, Goethestrasse 70, 80336 Munich, Germany; (F.S.); (S.N.W.)
| | - Daniel Edelhoff
- Department of Prosthetic Dentistry, University Hospital, LMU Munich, Goethestrasse 70, 80336 Munich, Germany;
| | - Falk Schwendicke
- Department of Conservative Dentistry and Periodontology, University Hospital, LMU Munich, Goethestrasse 70, 80336 Munich, Germany; (F.S.); (S.N.W.)
| | - Sabina Noreen Wuersching
- Department of Conservative Dentistry and Periodontology, University Hospital, LMU Munich, Goethestrasse 70, 80336 Munich, Germany; (F.S.); (S.N.W.)
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Simeon P, Unkovskiy A, Saadat Sarmadi B, Nicic R, Koch PJ, Beuer F, Schmidt F. Wear resistance and flexural properties of low force SLA- and DLP-printed splint materials in different printing orientations: An in vitro study. J Mech Behav Biomed Mater 2024; 152:106458. [PMID: 38364445 DOI: 10.1016/j.jmbbm.2024.106458] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 01/29/2024] [Accepted: 02/05/2024] [Indexed: 02/18/2024]
Abstract
OBJECTIVES To investigate the influence of material and printing orientation on wear resistance and flexural properties of one low force SLA- and two DLP-printed splint materials and to compare these 3D-printed splints to a subtractively manufactured splint material. METHODS Two DLP-printed (V-Print splint, LuxaPrint Ortho Plus) and one low force SLA-printed (Dental LT Clear) material, where specimens were printed in three printing orientations (0°, 45°, 90°), were investigated. In addition, one milled splint material (Zirlux Splint Transparent) was examined. A total of 160 specimens were produced for both test series. The two-body wear test was performed in a chewing simulator (80'000 cycles at 50 N with 5-55 °C thermocycling). Steatite balls were used as antagonists. The wear pattern was analyzed with a 3D digital microscope in terms of maximum vertical intrusion depth (mm) and total volume loss (mm³). The flexural properties were investigated by three-point bending in accordance with ISO 20795-1: 2013 (denture base polymers). The flexural strength (MPa) and the flexural modulus (MPa) were measured. Two-way ANOVA was performed to investigate the effects of the two independent variables material and printing orientation for the three 3D-printed materials. The comparison of the printing orientations within one material was carried out with one-way ANOVA with post-hoc Tukey tests. RESULTS Two-way ANOVA revealed that wear and flexural properties are highly dependent on the 3D-printed material (p < 0.001). Across groups, a significant effect was observed for wear depth (p = 0.031) and wear volume (p = 0.044) with regard to printing orientation but this was not found for flexural strength (p = 0.080) and flexural modulus (p = 0.136). One-way ANOVA showed that both DLP-printed groups showed no significant differences within the printing orientations in terms of wear and flexural properties. Dental LT Clear showed that 90° oriented specimens had higher flexural strength than 0° oriented ones (p < 0.001) and 45° oriented specimens also showed higher values than 0° ones (p = 0.038). No significant differences were observed within the printing orientations for flexural modulus and wear behaviour within this group. T-tests showed that the milled splints exhibited statistically higher wear resistance and flexural properties compared to all three 3D-printed splint materials (p < 0.001) and that highly significant differences were found between the 3D-printed splint materials for both test series. CONCLUSION Within the limitations of this in vitro study, it can be stated that wear behaviour and flexural properties are highly dependent on the 3D-printed material itself. Currently, milled splints exhibit higher wear resistance and flexural properties compared to 3D-printed splint materials. The printing orientation has a minor influence on the properties investigated. Nevertheless, two-way ANOVA also showed a significant influence of printing orientation in the wear test across groups and one-way ANOVA detected significant effects for SLA material in terms of flexural strength, with printing in 90° showing the highest flexural strength. Therefore, anisotropy was found in SLA material, but it can be limited with the employed printing parameters. Both DLP-printed materials showed no significant difference within the printing orientation.
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Affiliation(s)
- Philipp Simeon
- Charité - Universitätsmedizin Berlin, Center for Oral Health Sciences CC3, Department of Prosthodontics, Geriatric Dentistry and Craniomandibular Disorders, Aßmannshauser Str. 4-6, 14197, Berlin, Germany
| | - Alexey Unkovskiy
- Charité - Universitätsmedizin Berlin, Center for Oral Health Sciences CC3, Department of Prosthodontics, Geriatric Dentistry and Craniomandibular Disorders, Aßmannshauser Str. 4-6, 14197, Berlin, Germany; Department of Dental Surgery, Sechenov First Moscow State Medical University, Bolshaya Pirogovskaya Street, 19с1, Moscow, 119146, Russia
| | - Bardia Saadat Sarmadi
- Charité - Universitätsmedizin Berlin, Center for Oral Health Sciences CC3, Department of Prosthodontics, Geriatric Dentistry and Craniomandibular Disorders, Aßmannshauser Str. 4-6, 14197, Berlin, Germany
| | - Robert Nicic
- Charité - Universitätsmedizin Berlin, Center for Oral Health Sciences CC3, Department of Prosthodontics, Geriatric Dentistry and Craniomandibular Disorders, Aßmannshauser Str. 4-6, 14197, Berlin, Germany
| | - Petra Julia Koch
- Charité - Universitätsmedizin Berlin, Center for Oral Health Sciences CC3, Department of Orthodontics and Orthofacial Orthopedics, Aßmannshauser Str. 4-6, 14197, Berlin, Germany
| | - Florian Beuer
- Charité - Universitätsmedizin Berlin, Center for Oral Health Sciences CC3, Department of Prosthodontics, Geriatric Dentistry and Craniomandibular Disorders, Aßmannshauser Str. 4-6, 14197, Berlin, Germany
| | - Franziska Schmidt
- Charité - Universitätsmedizin Berlin, Center for Oral Health Sciences CC3, Department of Prosthodontics, Geriatric Dentistry and Craniomandibular Disorders, Aßmannshauser Str. 4-6, 14197, Berlin, Germany.
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Ikemoto S, Komagata Y, Yoshii S, Masaki C, Hosokawa R, Ikeda H. Impact of CAD/CAM Material Thickness and Translucency on the Polymerization of Dual-Cure Resin Cement in Endocrowns. Polymers (Basel) 2024; 16:661. [PMID: 38475344 DOI: 10.3390/polym16050661] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2024] [Revised: 02/18/2024] [Accepted: 02/27/2024] [Indexed: 03/14/2024] Open
Abstract
The objective of this study is to evaluate the impact of the thickness and translucency of various computer-aided design/computer-aided manufacturing (CAD/CAM) materials on the polymerization of dual-cure resin cement in endocrown restorations. Three commercially available CAD/CAM materials-lithium disilicate glass (e.max CAD), resin composite (CERASMART), and a polymer-infiltrated ceramic network (ENAMIC)-were cut into plates with five different thicknesses (1.5, 3.5, 5.5, 7.5, and 9.5 mm) in both high-translucency (HT) and low-translucency (LT) grades. Panavia V5, a commercial dual-cure resin cement, was polymerized through each plate by light irradiation. Post-polymerization treatment was performed by aging at 37 °C for 24 h under light-shielding conditions. The degree of conversion and Vickers hardness measurements were used to characterize the polymerization of the cement. The findings revealed a significant decrease in both the degree of conversion and Vickers hardness with increasing thickness across all CAD/CAM materials. Notably, while the differences in the degree of conversion and Vickers hardness between the HT and LT grades of each material were significant immediately after photoirradiation, these differences became smaller after post-polymerization treatment. Significant differences were observed between samples with a 1.5 mm thickness (conventional crowns) and those with a 5.5 mm or greater thickness (endocrowns), even after post-polymerization treatment. These results suggest that dual-cure resin cement in endocrown restorations undergoes insufficient polymerization.
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Affiliation(s)
- Soshi Ikemoto
- Division of Biomaterials, Kyushu Dental University, Kitakyushu 803-8580, Japan
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu 803-8580, Japan
| | - Yuya Komagata
- Division of Biomaterials, Kyushu Dental University, Kitakyushu 803-8580, Japan
| | - Shinji Yoshii
- Division of Promoting Learning Design Education, Kyushu Dental University, Kitakyushu 803-8580, Japan
| | - Chihiro Masaki
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu 803-8580, Japan
| | - Ryuji Hosokawa
- Division of Oral Reconstruction and Rehabilitation, Kyushu Dental University, Kitakyushu 803-8580, Japan
| | - Hiroshi Ikeda
- Division of Biomaterials, Kyushu Dental University, Kitakyushu 803-8580, Japan
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Wulff J, Rauch A, Schmidt MB, Rosentritt M. Biaxial Flexural Strength of Printed Splint Materials. MATERIALS (BASEL, SWITZERLAND) 2024; 17:1112. [PMID: 38473585 PMCID: PMC10934272 DOI: 10.3390/ma17051112] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Revised: 01/14/2024] [Accepted: 02/27/2024] [Indexed: 03/14/2024]
Abstract
One therapeutical alternative in the treatment of functional disorders is the use of printed oral splints. The mechanical properties of these materials are highly essential to their clinical effectiveness, and their performance may vary depending on factors such as cleaning, post-polymerization, or their orientation during construction. The objective of this in vitro investigation is to evaluate the effectiveness of the selected materials in terms of their biaxial flexural strength in relation to the criteria listed above. Splint materials were used in the printing of 720 discs. The printing process was carried out in different orientations in relation to the building platform. Either an automatic or manual cleaning process was performed on the samples. For post-polymerization, either an LED or Xenon light was utilized. A piston-on-three-ball test was used to measure the biaxial flexural strength (BFS) of the materials after they were stored in water for either 24 h or 60 days. The homogeneity of the data was controlled by employing the Levene method, and the differences between the groups were analyzed using the ANOVA and Bonferroni methods. After being stored for twenty-four hours, the mean BFS ranged anywhere from 79 MPa to 157 MPa. Following a period of sixty hours, the BFS exhibited a substantial drop and revealed values that ranged from 72 to 127 MPa. There was no significant difference that could be identified between the materials or between the various cleaning processes. The results of post-polymerization showed that the LED light produced higher means than the Xenon light did. In terms of position, the mean values varied greatly, with 0°'s mean value being 101 MPa, 45°'s mean value being 102 MPa, and 90°'s mean value being 115 MPa. The use of a build orientation of 90° and post-polymerization with LED light resulted in significantly increased biaxial flexural strength. According to this study, this design should be implemented in order to ensure that splint materials have the highest possible strength.
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Affiliation(s)
| | | | | | - Martin Rosentritt
- Department of Prosthetic Dentistry, UKR University Hospital Regensburg, 93042 Regensburg, Germany; (J.W.); (A.R.); (M.B.S.)
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Ikemoto S, Nagamatsu Y, Masaki C, Hosokawa R, Ikeda H. Development of zirconia-based polymer-infiltrated ceramic network for dental restorative material. J Mech Behav Biomed Mater 2024; 150:106320. [PMID: 38134584 DOI: 10.1016/j.jmbbm.2023.106320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2023] [Revised: 12/09/2023] [Accepted: 12/11/2023] [Indexed: 12/24/2023]
Abstract
Polymer-infiltrated ceramic network (PICN) materials have gained considerable attention as tooth restorative materials owing to their mechanical compatibility with human teeth. However, the mechanical strength of contemporary PICN materials is lower than those of conventional resin composites and ceramics. This study aims to develop novel high-strength PICN for use as a dental restorative material. Zirconia-based PICN (EXP) was fabricated using 3 mol% yttria tetragonal polycrystalline zirconia powder and resin monomers via slip casting, followed by sintering and polymer infiltration. Comprehensive analyses of the microstructure, mechanical properties, and physicochemical properties of EXP were performed using scanning electron microscopy with energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, inorganic content measurements, three-point bending test, Vickers hardness test, two-body wear test, shear bond strength (SBS) test, surface free energy analysis, and water sorption/solubility test. Commercially available computer-aided design/computer-aided manufacturing (CAD/CAM) materials, including resin composite (CERASMART), silicate-based PICN (ENAMIC), and zirconia ceramic (e.max ZirCAD), were used for comparison. The analyses highlight the dual network structure of EXP, which comprised a zirconia skeleton and an infiltrated resin phase. EXP exhibits a flexural strength of 346.0 ± 46.0 MPa, flexural modulus of 44.0 ± 3.7 GPa, and Vickers hardness of 440.1 ± 51.2 VHN. The mechanical properties of EXP are significantly higher than those of CERASMART and ENAMIC but lower than those of ZirCAD. Notably, the EXP hardness closely mimics that of the human enamel. The wear volume, SBS, and water sorption/solubility of EXP are comparable to those of CERASMART and ENAMIC. Therefore, EXP has potential applications as a tooth restorative material.
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Affiliation(s)
- Soshi Ikemoto
- Division of Biomaterials, Department of Oral Functions, Kyushu Dental University, Kitakyushu, 803-8580, Japan; Division of Oral Reconstruction and Rehabilitation, Department of Oral Functions, Kyushu Dental University, Kitakyushu, 803-8580, Japan
| | - Yuki Nagamatsu
- Division of Biomaterials, Department of Oral Functions, Kyushu Dental University, Kitakyushu, 803-8580, Japan
| | - Chihiro Masaki
- Division of Oral Reconstruction and Rehabilitation, Department of Oral Functions, Kyushu Dental University, Kitakyushu, 803-8580, Japan
| | - Ryuji Hosokawa
- Division of Oral Reconstruction and Rehabilitation, Department of Oral Functions, Kyushu Dental University, Kitakyushu, 803-8580, Japan
| | - Hiroshi Ikeda
- Division of Biomaterials, Department of Oral Functions, Kyushu Dental University, Kitakyushu, 803-8580, Japan.
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