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Kou, Wen
Publications (10 of 14) Show all publications
Wang, T., Li, M., Gu, Z., Qu, C., Segervald, J., Salh, R., . . . Kou, W. (2024). Fluoride releasing in polymerblends of poly(ethylene oxide) and poly(methyl methacrylate). Frontiers in Chemistry, 12, Article ID 1356029.
Open this publication in new window or tab >>Fluoride releasing in polymerblends of poly(ethylene oxide) and poly(methyl methacrylate)
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2024 (English)In: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 12, article id 1356029Article in journal (Refereed) Published
Abstract [en]

Introduction: Polymethyl methacrylate is a polymer commonly used in clinicaldentistry, including denture bases, occlusal splints and orthodontic retainers.

Methods: To augment the polymethyl methacrylate-based dental appliances incounteracting dental caries, we designed a polymer blend film composed ofpolymethyl methacrylate and polyethylene oxide by solution casting and addedsodium fluoride.

Results: Polyethylene oxide facilitated the dispersion of sodium fluoride,decreased the surface average roughness, and positively influenced thehydrophilicity of the films. The blend film made of polymethyl methacrylate,polyethylene oxide and NaF with a mass ratio of 10: 1: 0.3 showed sustainedrelease of fluoride ions and acceptable cytotoxicity. Antibacterial activity of all thefilms to Streptococcus mutans was negligible.

Discussion: This study demonstrated that the polymer blends of polyethyleneoxide and polymethyl methacrylate could realize the relatively steady release offluoride ions with high biocompatibility. This strategy has promising potential toendow dental appliances with anti-cariogenicity.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2024
Keywords
dental materials, polymethyl methacrylate, polyethylene oxide, fluoride ion release, polymer blend
National Category
Medical and Health Sciences Dentistry
Identifiers
urn:nbn:se:umu:diva-220718 (URN)10.3389/fchem.2024.1356029 (DOI)2-s2.0-85185521631 (Scopus ID)
Funder
Region Västerbotten, RV-937838The Kempe Foundations, JCSMK22-0122The Kempe Foundations, SMK-21-0015Swedish Research Council, 2021-04778Swedish Research Council, 2020-04437
Available from: 2024-02-09 Created: 2024-02-09 Last updated: 2024-02-29Bibliographically approved
Feng, X., Kou, W., Liu, H., Gong, B. & Tang, C. (2022). Study on fracture behavior of molars based on three‐dimensional high‐precision computerized tomography scanning and numerical simulation. International Journal for Numerical Methods in Biomedical Engineering, 38(3), Article ID e3561.
Open this publication in new window or tab >>Study on fracture behavior of molars based on three‐dimensional high‐precision computerized tomography scanning and numerical simulation
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2022 (English)In: International Journal for Numerical Methods in Biomedical Engineering, ISSN 2040-7939, E-ISSN 2040-7947, Vol. 38, no 3, article id e3561Article in journal (Refereed) Published
Abstract [en]

A series of three-dimensional (3D) numerical simulations are conducted to investigate the gradual failure process of molars in this study. The real morphology and internal mesoscopic structure of a whole tooth are implemented into the numerical simulations through computerized tomography scanning, digital image processing, and 3D matrix mapping. The failure process of the whole tooth subject to compressions including crack initiation, crack propagation, and final failure pattern is reproduced using 3D realistic failure process analysis (RFPA3D) method. It is concluded that a series of microcracks are gradually initiated, nucleated, and subsequently interconnect to form macroscopic cracks when the teeth are under over-compressions. The propagation of the macroscopic cracks results in the formation of fracture surfaces and penetrating cracks, which are essential signs and manifestations of the tooth failure. Moreover, the simulations reveal that, the material heterogeneity is a critical factor that affects the mechanical properties and fracture modes of the teeth, which vary from crown fractures to crown-root fractures and root fractures depending on different homogeneity indices.

Place, publisher, year, edition, pages
John Wiley & Sons, 2022
National Category
Biomaterials Science
Identifiers
urn:nbn:se:umu:diva-190525 (URN)10.1002/cnm.3561 (DOI)000730990200001 ()34865323 (PubMedID)2-s2.0-85121364416 (Scopus ID)
Available from: 2021-12-17 Created: 2021-12-17 Last updated: 2022-07-22Bibliographically approved
Ågren, M., Kou, W. & Molin Thorén, M. (2019). Bond strength of surface-treated novel high translucent zirconia to enamel. Biomaterial Investigations in Dentistry, 6(1), 35-42
Open this publication in new window or tab >>Bond strength of surface-treated novel high translucent zirconia to enamel
2019 (English)In: Biomaterial Investigations in Dentistry, ISSN 2641-5275, Vol. 6, no 1, p. 35-42Article in journal (Refereed) Published
Abstract [en]

Aim: The aim of the present study was to evaluate the shear bond strength of zirconia, stabilised with 5% yttria, luted to enamel and to evaluate the fracture pattern at loss of retention.

Methods: A total of 53 test specimen were manufactured from two partially stabilised zirconia materials, Zirkonzahn Prettau Anterior (ZPA) (n = 16) and Whitepeaks CopraSmile Symphony 5 layer (WCS) (n = 18), and a lithium disilicate (Ivoclar e.Max Press) (n = 19) acting as control. All test specimens were cemented to human enamel with Variolink Esthetic DC and then subjected to a shear bond strength test. Fracture and surface analysis were performed using light and scanning electron microscope.

Results: No significant differences in shear bond strength were detected when analysing the three groups. Dividing them according to the fracture pattern significant difference in shear bond strength between the two zirconia groups could be seen analysing test bodies with failure of adhesion to the test body, but not to enamel. The ZPA had higher shear bond strength (23.68 MPa) than WCS (13.00 MPa). No significant differences were seen compared to the control group (19.02 MPa).

Conclusion: Partially stabilised zirconia shows potential as a material to be used where macro mechanical bonding is not possible, although this study does not reveal how or if the bonding deteriorates over time.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
Keywords
Shear strength, zirconium dioxide, dental bonding, dental veneers
National Category
Biomaterials Science
Research subject
Odontology
Identifiers
urn:nbn:se:umu:diva-164925 (URN)10.1080/26415275.2019.1684200 (DOI)2-s2.0-85104490723 (Scopus ID)
Available from: 2019-11-05 Created: 2019-11-05 Last updated: 2021-05-06Bibliographically approved
Sundh, A., Kou, W. & Sjögren, G. (2019). Effects of Pretreatment, Specimen Thickness, and Artificial Aging on Biaxial Flexural Strength of Two Types of Y-TZP Ceramics. Operative dentistry, 44(6), 615-624
Open this publication in new window or tab >>Effects of Pretreatment, Specimen Thickness, and Artificial Aging on Biaxial Flexural Strength of Two Types of Y-TZP Ceramics
2019 (English)In: Operative dentistry, ISSN 0361-7734, E-ISSN 1559-2863, Vol. 44, no 6, p. 615-624Article in journal (Refereed) Published
Abstract [en]

Objectives: To evaluate the effects of surface treatment, specimen thickness, and aging on the biaxial flexural strength (BFS) of two types of yttria-stabilized, tetragonal zirconia polycrystal (Y-TZP) ceramics.

Methods and Materials: Disc-shaped specimens, 0.4 and 1.3 mm thick, made from hot isostatic pressed (Denzir) and non–hot isostatic pressed (ZirPlus) Y-TZP, were sandblasted, heat treated, and autoclaved. The surface topography was assessed in accordance with European Standard 623-624:2004 and the BFS tests in accordance with International Organization for Standardization Standard 6872:2008. For statistical analyses, one-way Shapiro-Wilk test, analysis of variance (post hoc: least significant differences), Mann-Whitney U-test, and Pearson correlation tests (p<0.05) were used.

Results: As delivered, the BFS of the 0.4-mm ZirPlus was >1.3-mm ZirPlus (p<0.01), and the BFS of the 0.4-mm Denzir was >1.3-mm Denzir (p<0.001). Sandblasting with 0.2 MPa reduced the BFS of the ZirPlus and Denzir discs (p<0.01), whereas sandblasting with 0.6 MPa increased the BFS of the 0.4-mm Denzir (p<0.001) and reduced the BFS of the 0.4-mm ZirPlus (p<0.05). Heat treatment significantly reduced the BFS of all the groups except for the 0.6 MPa sandblasted 0.4-mm ZirPlus. Autoclaving reduced the BFS of the as-delivered ZirPlus and Denzir specimens (p<0.001), whereas autoclaving the 0.6 MPa sandblasted and heat-treated specimens had no effect (p>0.05) on the BFS. The 0.6 MPa sandblasted, heat-treated, and autoclaved 0.4-mm Denzir exhibited higher BFS than the 0.6 MPa sandblasted, heat-treated, and autoclaved 0.4-mm ZirPlus (p<0.05).

Conclusions: Thickness and surface treatment of Y-TZP–based ceramics should be considered since those factors could influence the BFS of the material.

Place, publisher, year, edition, pages
Operative Dentistry, 2019
National Category
Dentistry
Identifiers
urn:nbn:se:umu:diva-158901 (URN)10.2341/18-071-L (DOI)000496715600008 ()30978157 (PubMedID)2-s2.0-85074963737 (Scopus ID)
Available from: 2019-05-14 Created: 2019-05-14 Last updated: 2020-01-07Bibliographically approved
Kou, W., Gabrielsson, K., Borhani, A., Carlborg, M. & Molin Thorén, M. (2019). The effect of artificial aging on high translucent zirconia. Biomaterial Investigations in Dentistry, 6(1), 54-60
Open this publication in new window or tab >>The effect of artificial aging on high translucent zirconia
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2019 (English)In: Biomaterial Investigations in Dentistry, ISSN 2641-5275, Vol. 6, no 1, p. 54-60Article in journal (Refereed) Published
Abstract [en]

Zirconia is known for its high strength but lacking translucency. Recently, a new type of high translucent zirconia, 5 mol% yttria partially stabilized zirconia (5Y-PSZ), with a larger fraction of cubic zirconia phase has become commercially available. However, the resistance to aging of these commercially available zirconia materials is not yet fully established.

Purpose: The aim of the present study was to analyze the effects of artificial aging on surface roughness, transparency, phase transformation and biaxial flexural strength of two 5Y-PSZ products, DD cubeX2 and Prettau Anterior.

Materials and methods: The artificial aging was performed in an autoclave under 2 bars of pressure at 134 °C for 10 hours, which is estimated to correspond to 30–40 years in vivo. Artificial aging for 10 hours had no significant effect on surface roughness, transparency, or phase transformation for either of the tested materials.

Results: DD cubeX2 had higher mean flexural strength than Prettau Anterior both before and after artificial aging for 10 hours (p < .05). DD cubeX2 showed, however, a significant reduction in flexural strength after artificial aging (p < .05), whereas Prettau Anterior showed a slight increase in flexural strength after artificial aging but not at a significant level.

Conclusion: Within the limitation of the present study, both DD cubeX2 and Prettau Anterior seems to be relatively resistant to aging. However, a wider range of measured flexural strength indicated that Prettau Anterior probably is a less stable material than DD cubeX2, which also means that the flexural strength of DD cubeX2 could be more predictable.

Keywords
High translucent zirconia, 5Y-PSZ, aging, biaxial flexural strength, transparency, surface roughness
National Category
Other Medical Sciences
Research subject
Odontology
Identifiers
urn:nbn:se:umu:diva-165606 (URN)10.1080/26415275.2019.1684201 (DOI)
Available from: 2019-11-28 Created: 2019-11-28 Last updated: 2023-03-07Bibliographically approved
André, M., Kou, W., Sjögren, G. & Sundh, A. (2016). Effects of pretreatments and hydrothermal aging on biaxial flexural strength of lithium di-silicate and Mg-PSZ ceramics. Journal of Dentistry, 55, 25-32
Open this publication in new window or tab >>Effects of pretreatments and hydrothermal aging on biaxial flexural strength of lithium di-silicate and Mg-PSZ ceramics
2016 (English)In: Journal of Dentistry, ISSN 0300-5712, E-ISSN 1879-176X, Vol. 55, p. 25-32Article in journal (Refereed) Published
Abstract [en]

Objectives: To evaluate the effect of specimen thickness, pretreatment and hydrothermal aging on the biaxial flexural strength (BFS) of lithium di-silicate glass (e.max Cad) and magnesia-stabilized zirconia (ZirMagnum) ceramic discs. Methods: The e.max Cad discs was studied: i) crystallized, ii) crystallized and glazed and iii) crystallized, glazed and unglazed side etched with hydrofluoric acid. The ZirMagnum discs were studied: i) as delivered, ii) after sandblasting and iii) after heat treatment similar to veneering. Hydrothermal aging was simulated by autoclave treatment. Results: The BFS of all the ZirMagnum specimens was superior (p < 0.001) to all the e.max Cad specimens. Glazing the 0.4 mm e.max Cad discs reduced (p < 0.05) their BFS compared with the unglazed 0.8 mm specimens, whereas glazing of 0.8 mm discs had no influence (p > 0.05) on the strength. Etching and autoclaving of e.max Cad did not affect (p > 0.05) the BFS. For ZirMagnum sandblasting with 0.2 MPa or 0.6 MPa did not influence the biaxial flexural strength (p > 0.05), whereas heat treatment reduced (p < 0.01) the BFS of 0.6 MPa sandblasted ZirMagnum. Autoclaving reduced the strength (p < 0.05) compared with ZirMagnum as delivered, whereas autoclaving of the 0.6 MPa sandblasted and heat treated specimens did not influence (p > 0.05) the BFS. Glazing, etching and sandblasting increased (p < 0.05) surface roughness. Conclusions: The effects of glazing, heat treatment, aging and mechanical treatment of the materials evaluated should be considered since their strength could be affected. Clinical significance: Mechanical properties of restorations made from prefabricated ceramic blocks could be affected of various treatments and could change over time.

Keywords
Accelerated aging, Ceramic, CAD/CAM, Magnesia-stabilized zirconia
National Category
Dentistry
Identifiers
urn:nbn:se:umu:diva-126919 (URN)10.1016/j.jdent.2016.09.002 (DOI)000390738500004 ()27638179 (PubMedID)2-s2.0-84991216968 (Scopus ID)
Available from: 2016-10-20 Created: 2016-10-20 Last updated: 2023-03-24Bibliographically approved
Kou, W., Qiao, J., Chen, L., Ding, Y. & Sjögren, G. (2015). Numerical simulation of the fracture process in ceramic FPD frameworks caused by oblique loading. Journal of The Mechanical Behavior of Biomedical Materials, 50, 206-214
Open this publication in new window or tab >>Numerical simulation of the fracture process in ceramic FPD frameworks caused by oblique loading
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2015 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 50, p. 206-214Article in journal (Refereed) Published
Abstract [en]

Using a newly developed three-dimensional (3D) numerical modeling code, an analysis was performed of the fracture behavior in a three-unit ceramic-based fixed partial denture (FPD) framework subjected to oblique loading. All the materials in the study were treated heterogeneously; Weibull׳s distribution law was applied to the description of the heterogeneity. The Mohr-Coulomb failure criterion with tensile strength cut-off was utilized in judging whether the material was in an elastic or failed state. The simulated loading area was placed either on the buccal or the lingual cusp of a premolar-shaped pontic with the loading direction at 30°, 45°, 60°, 75° or 90° angles to the occlusal surface. The stress distribution, fracture initiation and propagation in the framework during the loading and fracture process were analyzed. This numerical simulation allowed the cause of the framework fracture to be identified as tensile stress failure. The decisive fracture was initiated in the gingival embrasure of the pontic, regardless of whether the buccal or lingual cusp of the pontic was loaded. The stress distribution and fracture propagation process of the framework could be followed step by step from beginning to end. The bearing capacity and the rigidity of the framework vary with the loading position and direction. The framework loaded with 90° towards the occlusal surface has the highest bearing capacity and the greatest rigidity. The framework loaded with 30° towards the occlusal surface has the least rigidity indicating that oblique loading has a major impact on the fracture of ceramic frameworks.

Keywords
Finite element analysis, Fixed partial denture, Fracture process, Numerical simulation, Oblique loading
National Category
Biomaterials Science
Research subject
Numerical Analysis
Identifiers
urn:nbn:se:umu:diva-105213 (URN)10.1016/j.jmbbm.2015.06.017 (DOI)000361775000019 ()26143353 (PubMedID)2-s2.0-84969718668 (Scopus ID)
Available from: 2015-06-19 Created: 2015-06-19 Last updated: 2023-03-24Bibliographically approved
Kou, W., Tsukasa, A., Watari, F. & Sjögren, G. (2013). An in vitro evaluation of the biological effects of carbon nanotube-coated dental zirconia. ISRN Dentistry, 2013(Article ID 296727)
Open this publication in new window or tab >>An in vitro evaluation of the biological effects of carbon nanotube-coated dental zirconia
2013 (English)In: ISRN Dentistry, ISSN 2090-4371, E-ISSN 2090-438X, Vol. 2013, no Article ID 296727Article in journal (Refereed) Published
Abstract [en]

The purpose of this study is to evaluate functionalized multiwalled carbon nanotubes (fMWCNTs) as a potential coating material for dental zirconia from a biological perspective: its effect on cell proliferation, viability, morphology, and the attachment of an osteoblast-like cell. Osteoblast-like (Saos-2) cells were seeded on uncoated and fMWCNT-coated zirconia discs and in culture dishes that served as controls. The seeding density was 104 cells/cm2, and the cells were cultured for 6 days. Cell viability, proliferation and attachment of the Saos-2 cells were studied. The results showed that Saos-2 cells were well attached to both the uncoated and the fMWCNT-coated zirconia discs. Cell viability and proliferation on the fMWCNT-coated zirconia discs were almost the same as for the control discs. Better cell attachment was seen on the fMWCNT-coated than on the uncoated zirconia discs. In conclusion, fMWCNTs seem to be a promising coating material for zirconia-based ceramic surfaces to increase the roughness and thereby enhance the osseointegration of zirconia implants.

Place, publisher, year, edition, pages
United States: Hindawi Publishing Corporation, 2013
Keywords
carbon-nanotube, MWCNTs
National Category
Dentistry
Identifiers
urn:nbn:se:umu:diva-78252 (URN)10.1155/2013/296727 (DOI)
Available from: 2013-07-17 Created: 2013-07-17 Last updated: 2018-06-08Bibliographically approved
Kou, W., Li, D., Qiao, J., Chen, L., Ding, Y. & Sjögren, G. (2011). A 3D numerical simulation of stress distribution and fracture process in a zirconia-based FPD framework. Journal of Biomedical Materials Research. Part B - Applied biomaterials, 96B(2), 376-385
Open this publication in new window or tab >>A 3D numerical simulation of stress distribution and fracture process in a zirconia-based FPD framework
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2011 (English)In: Journal of Biomedical Materials Research. Part B - Applied biomaterials, ISSN 1552-4973, E-ISSN 1552-4981, Vol. 96B, no 2, p. 376-385Article in journal (Refereed) Published
Abstract [en]

In this study, a numerical approach to the fracture behavior in a three-unit zirconia-based fixed partial denture (FPD) framework was made under mechanical loading using a newly developed three-dimensional (3D) numerical modeling code. All the materials studied were treated heterogeneously and Weibull distribution law was applied to describe the heterogeneity. The Mohr-Coulomb failure criterion with tensile strength cut-off was utilized to judge whether the material was in an elastic or failed state. For validation, the fracture pattern obtained from the numerical modeling was compared with a laboratory test; they largely correlated with each other. Similar fracture initiation sites were detected both in the numerical simulation and in an earlier fractographic analysis. The numerical simulation applied in this study clearly described the stress distribution and fracture process of zirconia-based FPD frameworks, information that could not be gained from the laboratory tests alone. Thus, the newly developed 3D numerical modeling code seems to be an efficient tool for prediction of the fracture process in ceramic FPD frameworks.

Place, publisher, year, edition, pages
John Wiley & Sons, 2011
Keywords
ceramics, finite element analysis, fixed partial denture, fracture process, numerical simulation
National Category
Dentistry
Identifiers
urn:nbn:se:umu:diva-38966 (URN)10.1002/jbm.b.31782 (DOI)000286169600023 ()2-s2.0-78651091304 (Scopus ID)
Available from: 2011-01-12 Created: 2011-01-12 Last updated: 2023-03-23Bibliographically approved
Kou, W. & Sjögren, G. (2010). Fracture behaviour of zirconia FPDs substructures: fractographic analysis of zirconia. Journal of Oral Rehabilitation, 37(4), 292-299
Open this publication in new window or tab >>Fracture behaviour of zirconia FPDs substructures: fractographic analysis of zirconia
2010 (English)In: Journal of Oral Rehabilitation, E-ISSN 1365-2842, Vol. 37, no 4, p. 292-299Article in journal (Refereed) Published
Abstract [en]

 The purpose of this study was to evaluate the occurrence of superficial flaws after machining and to identify fracture initiation and propagation in three-unit heat-treated machined fixed partial dentures (FPDs) substructures made of hot isostatic pressed (HIPed) yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) after loaded to fracture. Four three-unit HIPed Y-TZP-based FPDs substructures were examined. To evaluate the occurrence of superficial flaws after machining, the surfaces were studied utilizing a fluorescent penetrant method. After static loading to fracture, characteristic fracture features on both mating halves of the fractured specimens were studied using a stereomicroscope and a scanning electron microscope. Grinding grooves were clearly visible on the surfaces of the machined FPDs substructures, but no other flaws could be seen with the fluorescent penetrant method. After loading to fracture, the characteristic fracture features of arrest lines, compression curl, fracture mirror, fracture origin, hackle and twist hackle were detected. These findings indicated that the decisive fracture was initiated at the gingival embrasure of the pontic in association with a grinding groove. Thus, in three-unit heat-treated machined HIPed Y-TZP FPDs substructures, with the shape studied in this study, the gingival embrasure of the pontic seems to be a weak area providing a location for tensile stresses when they are occlusally loaded. In this area, fracture initiation may be located to a grinding groove.

Place, publisher, year, edition, pages
Blackwell Publishing Ltd, 2010
Keywords
ceramics, fixed partial denture, fractographic analysis, machined surface, Y-TZP, zirconia
National Category
Dentistry
Research subject
Odontology
Identifiers
urn:nbn:se:umu:diva-31637 (URN)10.1111/j.1365-2842.2009.02057.x (DOI)000275206600009 ()20085616 (PubMedID)2-s2.0-77954353775 (Scopus ID)
Available from: 2010-02-12 Created: 2010-02-12 Last updated: 2024-01-17Bibliographically approved
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