Publications by authors named "Jon E Dahl"

29 Publications

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Editorial.

Biomater Investig Dent 2021 10;8(1):180. Epub 2021 Dec 10.

Associate Editor Nordic Institute of Dental Materials, Oslo, Norway.

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http://dx.doi.org/10.1080/26415275.2021.2010366DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8667950PMC
December 2021

Editorial.

Biomater Investig Dent 2020 Oct 14;7(1):158. Epub 2020 Oct 14.

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http://dx.doi.org/10.1080/26415275.2020.1831296DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7594872PMC
October 2020

Dentin to dentin adhesion using combinations of resin cements and adhesives from different manufacturers - a novel approach.

Biomater Investig Dent 2020 Jul 16;7(1):96-104. Epub 2020 Jul 16.

Institute of Clinical Odontology, University of Oslo, Oslo, Norway.

Aims: The aims of this study were to present a novel method to analyse dentin bond strength and to evaluate the bond strength of combining adhesive systems and resin cement from different manufacturers.

Methods: Human wisdom teeth were ground flat to the dentin on parallel surfaces and axially cut into two parts. Dentin cylinders (Ø 3 mm) were drilled from one half of each tooth. The other half from each tooth was embedded in epoxy resin with the dentin surface exposed. The specimens were ground with silicone carbide paper and the dentin cylinders were cemented onto the dentin surface of the other half of the same tooth. Resin cement and adhesive systems from three different manufacturers were used in various combinations ( = 8 per group). Cement and adhesive from the same manufacturer served as control. Shear bond strength (SBS) was measured and fracture modes were registered. The highest median SBS value was found in a bonding combination between cement and a non-corresponding adhesive (33.1 MPa) and one of the lowest values was found in one of the controls (15.3 MPa). Cohesive fractures were most frequent. The results indicated that combining adhesive and cement from different manufacturers did not compromise the dentin bonding. The novel test method is recommended for evaluating dentin bonding.
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http://dx.doi.org/10.1080/26415275.2020.1793677DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7470095PMC
July 2020

Editorial.

Biomater Investig Dent 2020 30;7(1):61. Epub 2020 Mar 30.

Nordic Institute of Dental Materials, Oslo, Norway.

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http://dx.doi.org/10.1080/26415275.2020.1724646DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7170384PMC
March 2020

The dental monomer HEMA causes proteome changes in human THP-1 monocytes.

J Biomed Mater Res A 2019 04 11;107(4):851-859. Epub 2019 Jan 11.

Department of Clinical Dentistry, Faculty of Health Sciences, University of Tromsø, Tromsø, Norway.

Resin-based biomaterials are widely used in medical and dental treatment, and both clinicians and patients are exposed to the materials. The knowledge of toxicity is mainly based on in vitro studies at exposure concentrations that induce cell death. However, severe cell damage and cell death signaling may overshadow essential cellular events caused by a possible toxicant. For dental resins, the knowledge of interaction with living cells at more clinical relevant exposure doses is sparse. 2-Hydroxyethylmethacrylate (HEMA) is a commonly used monomer in dental resins. Measuring cellular adaptation to HEMA at concentrations that did not reduce cell viability was the main focus of this study. Stable isotope labeling with amino acids in cell culture was used to measure proteome changes in cultured THP-1 cells exposed to HEMA. Western blotting verified the results. Cells exposed to HEMA increased their level of several cytoprotective proteins. The observed adaptation is compatible with increased oxidative burden caused by GSH depletion and the electrophilic characteristic of HEMA. The present approach to analyzing the toxic potential of HEMA yielded information on interactions with living cells is not previously reported. This detailed information is of great value to make better predictions of possible side effects in the clinic. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 851-859, 2019.
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http://dx.doi.org/10.1002/jbm.a.36601DOI Listing
April 2019

Digital evaluation of marginal and internal fit of single-crown fixed dental prostheses.

Eur J Oral Sci 2018 12 8;126(6):512-517. Epub 2018 Oct 8.

Department of Prosthetic Dentistry, Institute of Clinical Dentistry, Faculty of Dentistry, University of Oslo, Oslo, Norway.

The present study used a new, digitized version of the impression replica technique, namely the dual-scan technique, to evaluate the adaptation of single-crown fixed dental prostheses (FDPs). Scans of the bare master model and of the master model with a silicone layer representing the cement layer were superimposed and analyzed using designated software. Single crowns produced using the lost-wax metal casting technique were included. The cement space of the band width, 0.5-1.0 mm from the preparation margin (marginal fit), was smallest for crowns made from laser-sintered cobalt-chromium. The internal fit in both mesial-distal and buccal-palatal directions was statistically significantly better for crowns made using the conventional lost-wax metal casting technique than for crowns produced using computer-aided design/computer-aided manufacturing (CAD/CAM). Fixed dental prostheses produced by milled cobalt-chromium had the loosest internal fit. The results agree with those of our previous study of the same test specimens, in which the triple-scan method was used, and imply that the dual-scan method is well suited for adaptation studies.
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http://dx.doi.org/10.1111/eos.12576DOI Listing
December 2018

Optimizing quality and safety of dental materials.

Eur J Oral Sci 2018 10;126 Suppl 1:102-105

Nordic Institute of Dental Materials (NIOM), Oslo, Norway.

This paper discusses aspects of quality and safety improvement of the most commonly used dental restorative materials, the resin-based composites. From a patient's perspective, long-lasting resin-based restorations without complications are important. Recurrent caries and fracture are the most common causes for restoration failures. Proper handling and curing of the composites improve the mechanical properties of the restorations and increase safety by reducing exposure to residual methacrylate monomers. A number of compounds have been introduced in restorative materials to reduce the risk of recurrent caries, even though a real breakthrough has not yet been achieved. It is concluded that simple measures may improve the quality and safety of resin-based composite restorations.
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http://dx.doi.org/10.1111/eos.12422DOI Listing
October 2018

Internal fit of three-unit fixed dental prostheses produced by computer-aided design/computer-aided manufacturing and the lost-wax metal casting technique assessed using the triple-scan protocol.

Eur J Oral Sci 2018 02 24;126(1):66-73. Epub 2017 Nov 24.

Department of Prosthetic Dentistry, Institute of Clinical Dentistry, Faculty of Dentistry, University of Oslo, Oslo, Norway.

Suboptimal adaptation of fixed dental prostheses (FDPs) can lead to technical and biological complications. It is unclear if the computer-aided design/computer-aided manufacturing (CAD/CAM) technique improves adaptation of FDPs compared with FDPs made using the lost-wax and metal casting technique. Three-unit FDPs were manufactured by CAD/CAM based on digital impression of a typodont model. The FDPs were made from one of five materials: pre-sintered zirconium dioxide; hot isostatic pressed zirconium dioxide; lithium disilicate glass-ceramic; milled cobalt-chromium; and laser-sintered cobalt-chromium. The FDPs made using the lost-wax and metal casting technique were used as reference. The fit of the FDPs was analysed using the triple-scan method. The fit was evaluated for both single abutments and three-unit FDPs. The average cement space varied between 50 μm and 300 μm. Insignificant differences in internal fit were observed between the CAD/CAM-manufactured FDPs, and none of the FPDs had cement spaces that were statistically significantly different from those of the reference FDP. For all FDPs, the cement space at a marginal band 0.5-1.0 mm from the preparation margin was less than 100 μm. The milled cobalt-chromium FDP had the closest fit. The cement space of FDPs produced using the CAD/CAM technique was similar to that of FDPs produced using the conventional lost-wax and metal casting technique.
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http://dx.doi.org/10.1111/eos.12394DOI Listing
February 2018

Effect of curing and silanizing on composite repair bond strength using an improved micro-tensile test method.

Acta Biomater Odontol Scand 2017 Jan 19;3(1):21-29. Epub 2017 Mar 19.

Nordic Institute of Dental MaterialsOsloNorway.

To evaluate the micro-tensile repair bond strength between aged and new composite, using silane and adhesives that were cured or left uncured when new composite was placed. Eighty Filtek Supreme XLT composite blocks and four control blocks were stored in water for two weeks and thermo-cycled. Sandpaper ground, etched and rinsed specimens were divided into two experimental groups: A, no further treatment and B, the surface was coated with bis-silane. Each group was divided into subgroups: (1) Adper Scotchbond Multi-Purpose, (2) Adper Scotchbond Multi-Purpose adhesive, (3) Adper Scotchbond Universal, (4) Clearfil SE Bond and (5) One Step Plus. For each adhesive group, the adhesive was (a) cured according to manufacturer's instructions or (b) not cured before repair. The substrate blocks were repaired with Filtek Supreme XLT. After aging, they were serially sectioned, producing 1.1 × 1.1 mm square test rods. The rods were prepared for tensile testing and tensile strength calculated at fracture. Type of fracture was examined under microscope. Leaving the adhesive uncured prior to composite repair placement increased the mean tensile values statistically significant for all adhesives tested, with or without silane pretreatment. Silane surface treatment improved significantly ( < 0.001) tensile strength values for all adhesives, both for the cured and uncured groups. The mean strength of the control composite was higher than the strongest repair strength ( < 0.001). Application of freshly made silane and a thin bonding layer, rendered higher tensile bond strength. Not curing the adhesive before composite placement increased the tensile bond strength.
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http://dx.doi.org/10.1080/23337931.2017.1301211DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5463344PMC
January 2017

Internal fit of single crowns produced by CAD-CAM and lost-wax metal casting technique assessed by the triple-scan protocol.

J Prosthet Dent 2017 Mar 28;117(3):400-404. Epub 2016 Sep 28.

Professor, Institute of Clinical Dentistry, Dental Faculty, University of Oslo, Oslo, Norway; and CEO, Nordic Institute of Dental Materials, Oslo, Norway.

Statement Of Problem: Whether single crowns produced by computer-aided design and computer-aided manufacturing (CAD-CAM) have an internal fit comparable to crowns made by lost-wax metal casting technique is unknown.

Purpose: The purpose of this in vitro study was to compare the internal fit of single crowns produced with the lost-wax and metal casting technique with that of single crowns produced with the CAD-CAM technique.

Material And Methods: The internal fit of 5 groups of single crowns produced with the CAD-CAM technique was compared with that of single crowns produced in cobalt-chromium with the conventional lost-wax and metal casting technique. Comparison was performed using the triple-scan protocol; scans of the master model, the crown on the master model, and the intaglio of the crown were superimposed and analyzed with computer software. The 5 groups were milled presintered zirconia, milled hot isostatic pressed zirconia, milled lithium disilicate, milled cobalt-chromium, and laser-sintered cobalt-chromium.

Results: The cement space in both the mesiodistal and buccopalatal directions was statistically smaller (P<.05) for crowns made by the conventional lost-wax and metal casting technique compared with that of crowns produced by the CAD-CAM technique.

Conclusions: Single crowns made using the conventional lost-wax and metal casting technique have better internal fit than crowns produced using the CAD-CAM technique.
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http://dx.doi.org/10.1016/j.prosdent.2016.06.017DOI Listing
March 2017

Silanising agents promote resin-composite repair.

Int Dent J 2015 Dec 9;65(6):311-5. Epub 2015 Oct 9.

Faculty of Dentistry, University of Oslo, Oslo, Norway.

Objective: The aim of this study was to investigate the effect of silane in the repair of old and new resin-composite restorations.

Method: Part 1: repair of old composite was performed on 60 resin-composite substrates that were 6 years old and were made of six different brands of composite. Three experiments were performed. In the first experiment, the substrates were ground flat and composite was fixed to the surface with bonding agent without silane (i.e. Clearfil Bond SE only, the control). Shear bond strength (SBS) was tested according to ISO/TS 11405 after thermocycling. In the second experiment, the same 60 substrates were ground again and treated with bis-silane a 2-part silane mixed shortly before application before applying bonding agent (Clearfil Bond SE plus silane) and repair composite before SBS testing. In the third experiment, the same substrates were ground again and a one-step bonding product containing silane (Scotchbond Universal bond containing silane) was used for the repair procedure before SBS testing. Part 2: to evaluate the repair of newly made composite restorations, 66 composite substrates were made and stored in water for 2 months. The specimens were divided into three groups and were tested using the same protocols as used to evaluate repair of old composite.

Results: Mean SBS (± standard deviation), in MPa, for repair of old composite was 6.2 ± 4.0 (Clearfil Bond SE only, control), 14.8 ± 7.8 (Clearfil Bond SE plus silane) and 15.3 ± 5.6 (Scotchbond Universal bond with silane), whereas for new composite mean SBS was 15.4 ± 8.6 (Clearfil Bond SE only, control), 23.4 ± 8.3 (Clearfil Bond SE with silane) and 23.7 ± 5.8 (Scotchbond Universal containing silane). A significant difference was observed between the control and the test groups with silanising agents, both in Part 1 (P < 0.001) and in Part 2 (P < 0.005).

Conclusion: Silanising agents increase the bond strength of the resin composite repair.
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http://dx.doi.org/10.1111/idj.12188DOI Listing
December 2015

element release and biological aspects of base-metal alloys for metal-ceramic applications.

Acta Biomater Odontol Scand 2015 Dec 30;1(2-4):70-75. Epub 2015 Sep 30.

NIOM, Nordic Institute of Dental MaterialsOsloNorway.

The aims of this study were to investigate the release of element from, and the biological response to, cobalt-chromium alloys and other base-metal alloys used for the fabrication of metal-ceramic restorations. Eighteen different alloys were investigated. Nine cobalt-chromium alloys, three nickel-chromium alloys, two cobalt-chromium-iron alloys, one palladium-silver alloy, one high-noble gold alloy, titanium grade II and one type III copper-aluminium alloy. Pure copper served as positive control. The specimens were prepared according to the ISO standards for biological and corrosion testing. Passive leaching of elements was measured by using Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) after incubation in cell culture media, MEM, for 3 days. Corrosion testing was carried out in 0.9% sodium chloride (NaCl) and 1% lactic acid for 7 days, and the element release was measured by Inductively Coupled Plasma - Optical Emission Spectroscopy (ICP-OES). The biological response from the extract solutions was measured though MTT cytotoxicity testing and the Hen's egg test-chorio-allantoic membrane (HET-CAM) technique for irritationt. The corrosion test showed similar element release from base-metal alloys compared to noble alloys such as gold. Apart from the high-copper alloy, all alloys expressed low element release in the immersion test, no cytotoxic effect in the MTT test, and were rated non-irritant in the HET-CAM test. Minimal biological response was observed for all the alloys tested, with the exception of the high-copper alloy.
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http://dx.doi.org/10.3109/23337931.2015.1069714DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5433186PMC
December 2015

TEGDMA and filler particles from dental composites additively attenuate LPS-induced cytokine release from the macrophage cell line RAW 264.7.

Clin Oral Investig 2015 Jan 11;19(1):61-9. Epub 2014 Mar 11.

Nordic Institute of Dental Materials AS, PO Box 3874, Ullevaal Stadion, 0805, Oslo, Norway.

Objectives: Due to incomplete curing and material degradation, cells in the oral cavity may be exposed to monomers and filler particles from dental composite fillings. The objective of the present study was to investigate if combined exposures to particles and a methacrylate monomer from composite fillings resulted in additive effects on the macrophage immune response.

Material And Methods: Two filler particles, Nanosilica (12 nm) and Quartz (1 μm), were studied at concentrations 0.5-4 μg/cm(2), while the methacrylate monomer triethyleneglycol dimethacrylate (TEGDMA) was applied at 5 and 50 μM. RAW 264.7 macrophages were exposed to monomers and/or particles for 24 h, with a subsequent 24 h combined exposure to monomers and/or particles and the bacterial factor lipopolysaccharide (LPS) to stimulate an immune response. Release of the pro-inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) were measured as well as the cellular viability.

Results: Co-exposure to Nanosilica and Quartz resulted in an additive attenuation of the LPS-induced IL-1β release. Moreover, co-exposure to TEGDMA and both types of filler particles also resulted in an additive attenuation, although with a weak synergistic trend. The cellular viability and TNF-α release were not significantly affected by the exposures.

Conclusion: The present findings emphasize the necessity of considering effects of combined exposure to dental degradation products in future risk assessments.

Clinical Relevance: Attenuated cytokine release could have implications for the macrophage immune response and result in impaired bacterial clearance. Further studies are necessary to determine implications for formation of dental biofilms and caries development.
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http://dx.doi.org/10.1007/s00784-014-1212-7DOI Listing
January 2015

Role of bonding agents in the repair of composite resin restorations.

Eur J Oral Sci 2011 Aug 10;119(4):316-22. Epub 2011 Jun 10.

Department of Cariology and Geriodontology, Faculty of Dentistry, University of Oslo, Oslo, Norway.

Six commonly used composite resin materials and recommended bonding systems were tested to assess shear bond strength at the interface between aged and new composites with and without bonding. Test specimens were aged in water for 60 d before new composite was placed. Shear bond strength was assessed after 22 ± 2 h (Test 1) and after additional ageing by thermocycling (5-55°C/5,000 cycles) (Test 2). After an additional 180 d in water, the aged specimens were randomly divided into three groups to blind the test with respect to the aged composite. New composites were placed on aged specimens (two groups with and one without bonding agent) and thermocycled (Test 3). After 24 h (Test 1), the mean shear bond strength of the test specimens was 21-26 MPa when bonding agents were used, as opposed to 10-15 MPa without bonding agents. After thermocycling (Test 2), the mean shear bond strength was 16-23 MPa with a bonding agent and 17 MPa without a bonding agent. After 180 d in water and subsequent thermocycling (Test 3), the mean shear bond strength was 9-13 MPa with bonding agent and 2-3 MPa when no bonding agent was used. The results of this study therefore indicate that the use of bonding agents significantly improves the quality of composite repair.
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http://dx.doi.org/10.1111/j.1600-0722.2011.00833.xDOI Listing
August 2011

In vivo and in vitro irritation testing of low concentrations of hydrofluoric acid.

Acta Odontol Scand 2009 ;67(6):360-5

Department of Prosthetic Dentistry and Oral Function, Faculty of Dentistry, University of Oslo, Oslo, Norway.

Objective: Acidic fluorides are proposed for the treatment of dental erosion. The aim of this study was to examine the irritation properties of dilute hydrofluoric acid (HF) solutions for potential use in the oral cavity.

Material And Methods: Hen's egg test-chorioallantoic membrane (HET-CAM): The CAM was accessed by careful dissection through the egg shell (n=36, 6 eggs/test solution) and exposed to 300 µl of the HF solutions (0.05%, 0.10%, 0.20%, and 1.0%) under macroscope examination over the course of 5 min. Mean time-to-coagulation and average irritation score were recorded based on appearance of hemorrhage, coagulation, and lysis of the blood vessels in the membrane. Mouse skin test: 60 male mice were randomly divided into 10 groups of 6 animals each (control, 0.05%, 0.10%, 0.20%, and 1.0% HF), shaved on the back, exposed to test solution, and euthanized after 2 h or 24 h. Skin samples were evaluated by light microscopy, scoring epithelial leukocyte infiltration, vascular congestion, and edema.

Results: HET-CAM: 0.05% HF was slightly irritant, 0.1% HF moderately irritant, 0.2% and 1% HF strongly irritant. 0.1-1% HF solutions were severely irritating on the eye. Mouse skin test: HF concentration was significantly correlated with tissue response, and 24-h exposure to 1% HF solution showed focal erosion of the epithelium and marked localized subepithelial leukocyte infiltration.

Conclusion: The results of the studies suggest that accidental exposure of soft tissues to solutions containing more than 0.2% HF may be harmful.
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http://dx.doi.org/10.1080/00016350903117118DOI Listing
September 2012

In vitro efficacy and risk for adverse effects of light-assisted tooth bleaching.

Photochem Photobiol Sci 2009 Mar 16;8(3):377-85. Epub 2009 Jan 16.

Nordic Institute of Dental Materials (NIOM), NO-1305, Haslum, Norway.

The use of optical radiation in the so-called light-assisted tooth bleaching procedures has been suggested to enhance the oxidizing effect of the bleaching agent, hydrogen peroxide. Documentation is scarce on the potential adverse effects of bleaching products and on optical exposure risks to eyes and skin. The efficacy of seven bleaching products with or without simultaneous use of seven different bleaching lamps was investigated using extracted human teeth. The bleaching effect was determined immediately after treatment and one week later. Tooth surfaces were examined for adverse alterations after bleaching using a scanning electron microscope. Source characteristics of eight lamps intended for tooth bleaching were determined. International guidelines on optical radiation were used to assess eye and skin exposure hazards due to UV and visible light emission from the lamps. Inspection of teeth one week after bleaching showed no difference in efficacy between teeth bleached with or without irradiation for any of the products. Scratches, probably from the cleaning procedure were frequently seen on bleached enamel irrespective of irradiation. Maximum permissible exposure time (t(max)) and threshold limit values were exceeded for about half the bleaching lamps investigated. One lamp exceeded t(max) even for reflected blue light within the treatment time. This lamp also exceeded t(max) values for UV exposure. The lamps were classified as "low risk" and as borderline to "moderate risk" according to a relevant lamp standard.
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http://dx.doi.org/10.1039/b813132eDOI Listing
March 2009

Filler particles used in dental biomaterials induce production and release of inflammatory mediators in vitro.

J Biomed Mater Res B Appl Biomater 2009 Apr;89(1):86-92

Nordic Institute of Dental Materials, Haslum, Norway.

Although dental composites are in extensive use today, little is known about the biological effects of the filler particles. As composite materials are gradually broken down in the aggressive environment of the oral cavity, the filler particles may leak and induce toxic effects on the surrounding tissue and cells. The aim of this study was to elucidate possible adverse biological effects of commonly used dental filler particles; bariumaluminiumsilica (BaAlSi) and bariumaluminiumfluorosilica (BaAlFSi) with mean size of 1 microm. BEAS-2B cells were used as a model system. Particle morphology, mean particle size in solution, and particle surface charge were determined by scanning electron microscopy and Malvern zetasizer technology, respectively. Enzyme-linked immunosorbent assay was used to detect secretion of cytokine and chemokine (IL-8 and IL-6) and quantitative PCR for detection of gene activity. Both types of particle increased the release of IL-6 and IL-8 in a dose-dependent manner. BaAlFSi particles induced a more marked IL-8 response compared to BaAlSi particles, whereas no significant difference was observed for the IL-6 response. Mechanistic studies using specific inhibitors and activators indicated that cyclic AMP-dependent protein kinase A is partly involved in the observed IL-8 response. In conclusion, we consider dental filler particles to have potential to induce adverse biological response in cell cultures.
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http://dx.doi.org/10.1002/jbm.b.31190DOI Listing
April 2009

Corrosion of dental nickel-aluminum bronze with a minor gold content-mechanism and biological impact.

J Biomed Mater Res B Appl Biomater 2009 Feb;88(2):465-73

Department of Odontology/Dental Materials Science, Dental Technician Programme, Umeå University, Umeå, Sweden.

Objectives: To study corrosion and to evaluate biological effects in vitro of corrosion products of a copper-aluminum-nickel alloy with 2% gold.

Methods: The alloy NPGtrade mark+2 with the nominal composition Cu:77.3; Al:7.8; Ni:4.3; Fe:3.0; Zn:2.7; Au:2.0; and Mn:1.7 was characterized. Static immersion in acidic saline, pH 2.2-2.4, was used to determine release of metallic elements in a milieu simulating the condition of plaque build-up in interproximal areas of the tooth. Corrosion and surface reactions in saline and artificial saliva were studied by electrochemical techniques including registration of open-circuit-potentials, polarization curves and impedance spectra. Extracts were made in cell culture media and acidic saline and used for MTT test for cytotoxicity and HET-CAM method for irritation.

Results: The mean amount of elements released in the acidic saline were in microg cm(-2) : Cu:632; Al:210; Ni:144; Fe:122; Zn:48; Mn:52. No protective film was formed on the surface of the alloy, as extensive corrosion was observed in both saline and artificial saliva. The corrosion rate was higher in saline than in artificial saliva. Acidic extracts of the alloy diluted up to 64 times reduced cell viability with 80% or more. The extract induced coagulation of the blood vessels of the CAM and was rated as moderate irritant solution.

Significance: The nickel-aluminum bronze showed high corrosion rate caused by an inability to create a protective surface layer. High levels of toxic elements were found after static immersion testing, and the corrosion products had a distinct adverse effect on the biological activity.
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http://dx.doi.org/10.1002/jbm.b.31143DOI Listing
February 2009

Cytotoxicity of silica-glass fiber reinforced composites.

Dent Mater 2008 Sep 11;24(9):1201-6. Epub 2008 Mar 11.

Department of Prosthetic Dentistry, Institute of Clinical Dentistry, University of Oslo, Oslo, Norway.

Objectives: Silica-glass fiber reinforced polymers can be used for many kinds of dental applications. The fiber reinforcement enhances the mechanical properties of the polymers, and they have good esthetic attributes. There is good initial bonding of glass fibers to polymers via an interface made from silane coupling agents. The aim of this in vitro study was to determine the cytotoxicity of two polymers reinforced with two differently sized silica-glass fibers before and after thermal cycling. Cytotoxicity of the polymers without fibers was also evaluated.

Methods: Two different resin mixtures (A and B) were prepared from poly(vinyl chloridecovinylacetate) powder and poly(methyl methacrylate) (PMMA) dissolved in methyl methacrylate and mixed with different cross-linking agents. The resin A contained the cross-linking agents ethylene glycol dimethacrylate and 1,4-butanediol dimethacrylate, and for resin B diethylene glycol dimethacrylate was used. Woven silica-glass fibers were used for reinforcement. The fibers were sized with either linear poly(butyl methacrylate)-sizing or cross-linking PMMA-sizing. Cytotoxicity was evaluated by filter diffusion test (ISO 7405:1997) of newly made and thermocycled test specimens. Extracts were prepared according to ISO 10993-12 from newly made and from thermocycled specimens and tested by the MTT assay. The results from the experiments were statistically analyzed by one-way ANOVA and Tukey's test (rho<0.05).

Results: The filter diffusion test disclosed no change in staining intensity at the cell-test sample contact area indicating non-cytotoxicity in all experimental groups. Cell viability assessed by MTT assay was more than 90% in all experimental groups. All are non-cytotoxic.

Significance: It can be concluded that correctly processed heat polymerized silica-glass fiber reinforced polymers induced no cytotoxicity and that thermocycling did not alter this property.
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http://dx.doi.org/10.1016/j.dental.2008.01.010DOI Listing
September 2008

Adverse patient reactions during orthodontic treatment with fixed appliances.

Am J Orthod Dentofacial Orthop 2007 Dec;132(6):789-95

Nordic Institute of Dental Materials, Senior lecturer, Institute of Dentistry, University of Turku, Turku, Finland.

Introduction: Our aims in this study were to assess adverse patient reactions during orthodontic treatment with nickel-containing appliances and to investigate the need for and the use of nickel-free devices in orthodontic practices in Finland and Norway.

Methods: A questionnaire was mailed to orthodontists and dentists versed in orthodontics in both countries. They were asked to retrospectively assess the number of patients with adverse reactions and to describe the reactions, the appliances used, and any implications on treatment. Previous history of nickel allergy of patients with adverse reactions, and use of and need for nickel-free appliances in clinical practice were also addressed.

Results: Forty-six percent of the respondents (n = 298) reported at least 1 adverse patient reaction during the last 5 years. More than half of the reactions had implications for the treatment. Finnish respondents observed significantly more adverse patient reactions than their Norwegian colleagues, and, in Finland, the adverse reactions were most frequently attributed to headgear treatment. Using nickel-containing fixed appliances in nickel-allergic patients was more common in Finland (77% of the respondents) than in Norway (65%).

Conclusions: Nearly half of the dentists regularly working with fixed appliances had observed at least 1 adverse patient reaction during treatment. Nickel-containing fixed appliances are generally used in most patients-even those with a suspected nickel allergy.
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http://dx.doi.org/10.1016/j.ajodo.2007.01.022DOI Listing
December 2007

Potential of dental adhesives to induce mucosal irritation evaluated by the HET-CAM method.

Authors:
Jon E Dahl

Acta Odontol Scand 2007 Oct;65(5):275-83

NIOM - Nordic Institute of Dental Materials, Haslum and Department of Cariology and Geriodontology, Dental Faculty, University of Oslo, Norway.

Objective: This study was undertaken to determine the potential of dental adhesive products to induce mucosal irritation based on their ability to damage the blood vessels of the chorioallantoic membrane (CAM) in fertilized hen's egg.

Material And Methods: Twenty-seven dental adhesive products (total 36 solutions) covering the four adhesive concepts,etch and rinse with two or three steps procedure and self-etch with one or two steps procedure, were evaluated using the hen's egg test-CAM method (HET-CAM). The blood vessels on the CAM of a fertilized hen's egg were used as the test system, and severity of the irritation was based on an assessment of the reaction of the blood and the blood vessels to the test chemical during 5 min of exposure. Three specific end-points - coagulation of blood, lyses of blood and rupture of blood vessel - were evaluated and their time-points for appearance noted.

Results: Coagulation of the blood was the most frequent injury, and was observed within less than a minute's exposure in 25 of the 36 tested solutions. Seventeen of the solutions were rated as moderate irritants and 16 as strong irritants. The type and severity of reaction could not be linked to the type of solvent (water, ethanol, acetone) nor to the presence of 2-hydroxylethyl methacrylate (2-HEMA) in the products. Conclusions. Most dental adhesives damage the blood vessels of the CAM, indicating irritant effects on mucous membranes.
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http://dx.doi.org/10.1080/00016350701589286DOI Listing
October 2007

In vitro biocompatibility of denture relining materials.

Gerodontology 2006 Mar;23(1):17-22

Nordic Institute of Dental Materials, Haslum, Norway.

Objective: The aim of the present study was to evaluate the in vitro biocompatibility of denture relining materials using cell culture tests and a test for irritation mechanisms.

Background: Denture relining materials contain non-reacted constituents that may leach out during use inducing local toxic or irritative effects.

Materials And Methods: One chemically cured, four visible light cured and five dual-cured products were included. Cured test specimens were used for the filter diffusion test, and extracts of cured specimens were applied in the MTT and the irritation test using the hen's egg test-chorioallantoic membrane (HET-CAM) method.

Results: Five of the tested materials were slightly or moderately cytotoxic in the filter diffusion test, and one product coated with a liner induced severe toxicity. Cell cultures incubated for 24 hour with the test samples were more damaged than those incubated for 2 hour. In the MTT test, extracts of nine of the 11 products induced cytotoxicity. No extracts showed irritation, whereas the coating and two bonding agents tested were strong irritants.

Conclusion: Most of the tested materials contained water soluble, toxic substances that leach out of the products and that some time was needed to obtain cytotoxic amounts of the leachables. Many dental materials elicit cytotoxic response, but this does not necessarily reflect the long-term risk for adverse effects as the oral mucosa is generally more resistant to toxic substances than a cell culture.
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http://dx.doi.org/10.1111/j.1741-2358.2006.00103.xDOI Listing
March 2006

Apoptosis induced by the monomers HEMA and TEGDMA involves formation of ROS and differential activation of the MAP-kinases p38, JNK and ERK.

Dent Mater 2007 Jan 23;23(1):34-9. Epub 2006 Jan 23.

NIOM-Nordic Institute of Dental Materials, PO Box 70, N-1305 Haslum, Norway.

Objectives: Cytotoxic methacrylate monomers have been identified in aqueous extracts of freshly cured compomers. Some of these compounds, including HEMA and TEGDMA, induce apoptosis and necrosis in vitro. The aim of the present study was to elucidate possible signaling pathways involved in apoptosis following exposure to HEMA or TEGDMA in a salivary gland cell line.

Methods: The cells were exposed to various concentrations of HEMA or TEGDMA. ROS formation was determined by dichlorofluorescein assay. Phosphorylated MAP-kinases ERK1/2, p38 and JNK, as well as specific caspases were identified by Western blotting. Apoptosis was assayed by fluorescence microscopy.

Results: HEMA or TEGDMA exposure resulted in ROS formation and concentration-dependent apoptosis as well as phosphorylation of ERK. Phosphorylation of JNK and p38 was induced by HEMA. Selective inhibitors of ERK and JNK modified the apoptotic response after HEMA and TEGDMA exposure, whereas p38 inhibition modified the apoptotic response only after HEMA exposure. Vitamin C reduced HEMA-induced apoptosis.

Significance: ROS formation and differential MAP kinase activation appear to be involved in the apoptotic response following exposure to HEMA and TEGDMA.
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http://dx.doi.org/10.1016/j.dental.2005.11.037DOI Listing
January 2007

Pattern of cell death after in vitro exposure to GDMA, TEGDMA, HEMA and two compomer extracts.

Dent Mater 2006 Jul 10;22(7):630-40. Epub 2005 Oct 10.

Noraic Institute of Dental Materials, Haslum, Norway.

Objectives: In vitro exposure to chemical compounds in dental materials may cause cell death by apoptosis, necrosis or a combination of both. The aim of this paper was to evaluate aqueous extracts of freshly cured compomers Freedom (SDI) and F2000 (3M ESPE), and constituents identified in the extracts, GDMA (glycerol dimethacrylate), TEGDMA (triethylene glycol dimethacrylate) and HEMA (2-hydroxyethyl methacrylate) for their ability to induce necrosis and apoptosis in primary rat alveolar macrophages and the J744A1 macrophage cell line.

Methods: The cells were exposed to either extracts of freshly cured samples of the products or to one of the constituents identified in the extracts. Cytotoxicity and necrosis were assayed by MTT test and fluorescence microscopy, respectively. Apoptosis was assayed by fluorescence microscopy and flow cytometry.

Results: Concentration-related apoptosis and necrosis were found in both cell types after exposure to extracts from Freedom and F2000. GDMA appeared to be the most cytotoxic of the tested constituents in the J744A1 cell line as evaluated by the MTT test. TEGDMA was more cytotoxic than HEMA using the MTT test and fluorescence microscopy, whereas HEMA caused a greater accumulation of apoptotic cells seen by fluorescence microscopy and flow cytometry. For various concentrations of HEMA and TEGDMA, the extent of apoptosis appeared inversely related to the cytotoxicity evaluated by the MTT test.

Significance: As an apoptotic response elicits less inflammatory response in the surrounding tissues than a necrotic process, the role of cell death pattern could be important for the evaluation of the biocompatibility of dental materials.
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http://dx.doi.org/10.1016/j.dental.2005.05.013DOI Listing
July 2006

Irritation and cytotoxic potential of denture adhesives.

Gerodontology 2005 Sep;22(3):177-83

NIOM - Scandinavian Institute of Dental Materials, Haslum, Norway.

Objective: The present study aimed to examine the in vitro biocompatibility of denture adhesives.

Background: Denture adhesives absorb water to become viscous and sticky, and by this process, other constituents like colouring, flavouring, wetting and preserving agents may be released. Some of these constituents may induce adverse reactions among users of denture adhesives.

Materials And Methods: Five commercially available denture adhesives; three different creams, a powder, and a cushion were included in the study. The irritation and cytotoxic potential was evaluated using the Hen's Egg Test Chorioallantoic Membrane (HET-CAM) method and three cell culture methods; filter diffusion, dimethylthiazol diphenyltetrazolium bromide (MTT) assay and agar diffusion.

Results: None of the tested denture adhesives showed a noteworthy acute irritation as evaluated by the HET-CAM method. None of the tested denture adhesives induced cytotoxicity in the filter diffusion test. One of the denture adhesives induced a severe cytotoxic reaction in both the MTT and agar diffusion assays. These tests employ longer exposure times than in both the filter diffusion and the HET-CAM test.

Conclusion: Denture adhesives are commonly used throughout the day, and our results raise the concern that denture adhesives may contribute to mucosal inflammation in denture wearers.
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http://dx.doi.org/10.1111/j.1741-2358.2005.00073.xDOI Listing
September 2005

Physicochemical evaluation of silica-glass fiber reinforced polymers for prosthodontic applications.

Eur J Oral Sci 2005 Jun;113(3):258-64

NIOM, Scandinavian Institute of Dental Materials, PO Box 70, N-1305 Haslum, Norway.

This investigation was designed to formulate silica-glass fiber reinforced polymeric materials. Fused silica-glass fibers were chosen for the study. They were heat-treated at various temperatures (500 degrees C, 800 degrees C and 1100 degrees C), silanized, sized and incorporated in two modified resin mixtures (A and B). The flexural properties in dry and wet conditions were tested and statistically analyzed, and the content of residual methyl methacrylate (MMA) monomer, dimensional changes with temperature, water sorption and solubility were determined. Woven fibers [36.9% (wt/wt)], heat-treated at 500 degrees C, gave the highest strength values for the polymeric composites (an ultimate transverse strength of 200 Mpa and a flexural modulus of 10 GPa) compared with the fibers heat-treated at other temperatures. There was no statistically significant difference in the measured flexural properties between resins A and B regarding fiber treatment and water storage time. These fiber composites had a small quantity of residual MMA content [0.37 +/- 0.007% (wt/wt)] and very low water solubility, indicating good biocompatibility. It was suggested that silica-glass fibers could be used for reinforcement as a result of their anticipated good qualities in aqueous environments, such as the oral environment.
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http://dx.doi.org/10.1111/j.1600-0722.2005.00209.xDOI Listing
June 2005

Static immersion and irritation tests of dental metal-ceramic alloys.

Eur J Oral Sci 2005 Feb;113(1):83-9

Scandinavian Institute of Dental Materials, Haslum, Norway.

The expansion of the European Union is bringing new types of metal-ceramic alloys to the market, i.e. alloys probably unknown in Western-European dentistry. The aim of this study was to investigate recent developments and "classic" alloy compositions (one iron and two cobalt alloys, unalloyed titanium and an experimental titanium-zirconium alloy, and one gold alloy containing copper and zinc). The alloys and titanium were subject to static immersion in a 0.1 mol l(-1) solution of saline lactic acid before and after oxidation, hence simulating the temperature cycles for the application of ceramic to metal. The greatest amounts of released metal ions were found in the electrolytes of the oxidized gold alloy and of a cobalt alloy not exposed to high-temperature oxidation. Corrosion of the titanium and alloy surfaces was related to the condition of the specimen. The irritation potentials of some metal ions found in the electrolyte were investigated by performing the hen's egg test-chorio-allantoic membrane (HET-CAM) procedure with 1 mmol l(-1) solutions of Ce(3+), Co(2+), Cu(2+), Zn(2+), Fe(2+), and Ti(4+) ions. The irritation potential of the electrolyte of the oxidized gold alloy with a high concentration of metal elements was also investigated. Of these solutions, only the 1 mmol l(-1) Cu(2+) solution was graded as slightly irritating.
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http://dx.doi.org/10.1111/j.1600-0722.2005.00187.xDOI Listing
February 2005

In vitro cell death induced by irradiation and chemicals relevant for dental applications; dose-response and potentiation effects.

Eur J Oral Sci 2004 Jun;112(3):273-9

NIOM-Scandinavian Institute of Dental Materials, Haslum, Norway.

Resin-based dental materials polymerized using blue light are frequently used in dental practice and may come in contact with the oral mucosa. Remnants from oral hygiene product ingredients, such as sodium lauryl sulfate (SLS), add to the chemical exposure of the mucosa. The aim of the present in vitro study was to elucidate the cytotoxic effects in terms of apoptosis and necrosis after exposures to combinations of an adhesive (0.5% and 0.6%), SLS (concentration range 0.0025%-0.0075%), and irradiation from a dental curing lamp (radiant exposure of 8 J cm(-2)). The test system chosen was rat submandibular salivary gland acinar cells, and the cytotoxic effects were measured by fluorescence microscopy and flow cytometry methods. Cytotoxicity was observed as a result of irradiation. The most pronounced cytotoxic effects were seen in cells exposed to a combination of adhesive and SLS compared with those exposed to either agent alone. Necrosis was the dominating form of cell death for all exposures, except for the highest concentration of SLS. Apoptosis was dose-dependent on SLS in the rat submandibular acinar cells. Cytotoxic considerations of dental materials should include contributions from irradiation and other chemicals that might be present in the oral cavity.
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http://dx.doi.org/10.1111/j.1600-0722.2004.00128.xDOI Listing
June 2004

Placement and replacement of restorations in primary teeth.

Acta Odontol Scand 2002 Jan;60(1):25-8

Department of Operative Dentistry, University of Florida, Gainesville 32610, USA.

This practice-based study aimed to record the use of restorative materials, the type of restoration by class, and the reason for and the age of failed restorations in primary teeth by means of a survey of placement and replacement of restorations in 1996 and 2000/2001. Written alternative criteria for placement and replacement of restorations were provided for the participating clinicians. Details on 2281 restorations showed that primary caries was the main reason for inserting restorations in primary teeth. Replacements of failed restorations represented 14% of the fillings (n = 2040) in 1996 and 9% in 2000/2001 (n = 241). More than 80% or the fillings in primary teeth were of tooth-colored material, predominantly of the light-cured type. About 50% of failed amalgam and glass ionomer-type restorations were replaced due to secondary caries. The median age of amalgam restorations (3 years) was significantly higher than that of tooth-colored restorations (2 years). Any possible advantage of a cariostatic effect of glass ionomer-type materials is apparently annulled by their short longevity compared with amalgam.
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http://dx.doi.org/10.1080/000163502753471961DOI Listing
January 2002
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