Publications by authors named "Albert J Feilzer"

134 Publications

Patch test-relevant concentrations of metal salts cause localized cytotoxicity, including apoptosis, in skin ex vivo.

Contact Dermatitis 2021 Nov 15;85(5):531-542. Epub 2021 Aug 15.

Department of Oral Cell Biology, Academic Centre for Dentistry (ACTA), University of Amsterdam and Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.

Background: Metal alloys containing contact sensitizers (nickel, palladium, titanium) are extensively used in medical devices, in particular dentistry and orthopaedic surgery. The skin patch test is used to test for metal allergy.

Objective: To determine whether metal salts, when applied to freshly excised skin at patch test-relevant concentrations and using a method which mimics skin patch testing, cause in changes in the epidermis and dermis.

Methods: Tissue histology, apoptosis, metabolic activity, and inflammatory cytokine release were determined for two nickel salts, two palladium salts, and four titanium salts.

Results: Patch test-relevant concentrations of all metal salts caused localized cytotoxicity. This was observed as epidermis separation at the basement membrane zone, formation of vacuoles, apoptotic nuclei, decreased metabolic activity, and (pro)inflammatory cytokine release. Nickel(II) sulfate hexahydrate, nickel(II) chloride hexahydrate, titanium(IV) bis(ammonium lactato)dihydroxide, and calcium titanate were highly cytotoxic. Palladium(II) chloride, sodium tetrachloropalladate(II), titanium(IV) isopropoxide, and titanium(IV) dioxide showed mild cytotoxicity.

Conclusion: The patch test in itself may be damaging to the skin of the patient being tested. These results need further verification with biopsies obtained during clinical patch testing. The future challenge is to remain above the elicitation threshold at noncytotoxic metal concentrations.
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http://dx.doi.org/10.1111/cod.13940DOI Listing
November 2021

Accuracy of a patient 3-dimensional virtual representation obtained from the superimposition of facial and intraoral scans guided by extraoral and intraoral scan body systems.

J Prosthet Dent 2021 Apr 7. Epub 2021 Apr 7.

Professor and Head, Division of Dental Biomaterials, Clinic for Reconstructive Dentistry, Center for Dental and Oral Medicine, University of Zürich, Zürich, Switzerland.

Statement Of Problem: A patient 3-dimensional virtual representation aims to facilitate the integration of facial references into treatment planning or prosthesis design procedures, but the accuracy of the virtual patient representation remains unclear.

Purpose: The purpose of the present observational clinical study was to determine and compare the accuracy (trueness and precision) of a virtual patient obtained from the superimposition procedures of facial and intraoral digital scans guided by 2 scan body systems.

Material And Methods: Ten participants were recruited. An intraoral digital scan was completed (TRIOS 4). Four fiduciary markers were placed in the glabella (Gb), left (IOL) and right infraorbital canal (IOR), and tip of the nose (TN). Two digitizing procedures were completed: cone beam computed tomography (CBCT) (i-CAT FLX V-Series) and facial scans (Face Camera Pro Bellus) with 2 different scan body systems: AFT (ScanBodyFace) and Sat 3D (Sat 3D). For the AFT system, a reference facial scan was obtained, followed by a facial scan with the participant in the same position as when capturing the CBCT scan. For the Sat 3D system, a reference facial scan was recorded, followed by a facial scan with the patient in the same position as when capturing the CBCT scan. The patient 3-dimensional representation for each scan body system was obtained by using a computer program (Matera 2.4). A total of 14 interlandmark distances were measured in the CBCT scan and both 3-dimensional patient representations. The discrepancies between the CBCT scan (considered the standard) and each 3-dimensional representation of each patient were used to analyze the data. The Kolmogorov-Smirnov test revealed that trueness and precision values were not normally distributed (P<.05). A log transformation was performed with 1-way repeated-measures MANOVA (α=.05).

Results: The accuracy of the virtual 3-dimensional patient representations obtained by using AFT and Sat 3D systems showed a trueness ranging from 0.50 to 1.64 mm and a precision ranging from 0.04 to 0.14 mm. The Wilks lambda detected an overall significant difference in the accuracy values between the AFT and Sat 3D systems (F=3628.041, df=14, P<.001). A significant difference was found in 12 of the 14 interlandmark measurements (P<.05). The AFT system presented significantly higher discrepancy values in Gb-IOL, TN-IOR, IOL-IOR, and TN-6 (P<.05) than in the Sat 3D system. The Sat 3D system had a significantly higher discrepancy in Gb-TN, TN-IOL, IOL-3, IOL-6, TN-8, TN-9, TN-11, IOR-11, and IOR-14 (P<.05) than in the AFT system. The Wilcoxon signed-rank test did not detect any significant difference in the precision values between the AFT and Sat 3D systems (Z=-0.838, P=.402).

Conclusions: The accuracy of the patient 3-dimensional virtual representations obtained using AFT and Sat 3D systems showed trueness values ranging from 0.50 to 1.64 mm and precision values ranging from 0.04 to 0.14 mm. The AFT system obtained higher trueness than the Sat 3D system, but both systems showed similar precision values.
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http://dx.doi.org/10.1016/j.prosdent.2021.02.023DOI Listing
April 2021

Effect of light-curing time on microhardness of a restorative bulk-fill resin composite to lute CAD-CAM resin composite endocrowns.

Am J Dent 2020 Dec;33(6):331-336

Department of Cariology and Endodontology, University of Geneva, Geneva, Switzerland.

Purpose: To evaluate the minimal irradiation time to reach a sufficient polymerization of a photopolymerizable restorative bulk-fill resin composite to lute endocrowns.

Methods: A photopolymerizable restorative bulk-fill resin composite (Filtek One Bulk Fill) was submitted to direct light-curing by a high power LED light-curing unit for 20 seconds as the positive control group (n = 10). Five more test groups (n= 10) were light-cured in a natural tooth mold from three sites (buccal, palatal and occlusal) under a 9.5 mm thick nanohybrid resin composite CAD-CAM endocrown (Lava Ultimate A2 LT), for different irradiation times: 90 seconds per site, 40 seconds per site, 30 seconds per site, 20 seconds per site and 10 seconds per site. Vickers microhardness measurements were made at two different depths and test/control ratios were calculated. Ratios of 0.8 were considered as an adequate level of curing.

Results: Analysis shows that 30 seconds x 3 was the minimal irradiation time that presented a test/control ratio above 0.8. Quantile regressions showed that the required irradiation time to reach a test/control ratio of 0.8 at a confidence level of 95% was 38 seconds and 37 seconds for 200 µm and 500 µm, respectively. There was no statistically significant difference between microhardness of the two depths except for the irradiation time of 10 seconds. A 120-second (40 seconds per buccal, palatal and occlusal site) light-curing of photopolymerizable bulk-fill resin composite to lute a resin composite CAD-CAM endocrown restoration can be considered sufficient to reach adequate polymerization.
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December 2020

Fracture strength of non-invasively reinforced MOD cavities on endodontically treated teeth.

Odontology 2021 Apr 4;109(2):368-375. Epub 2020 Sep 4.

Department of Cariology and Endodontology, University of Geneva, 1 rue Michel-Servet, 1211, Geneva, Switzerland.

The purpose of this in-vitro study was to evaluate the fracture resistance and failure mode of non-invasively reinforced endodontically treated mandibular molars. Sixty freshly extracted defect-free mandibular molars were divided into four experimental groups with extensive MOD cavities on endodontically treated teeth with different restoration types and one control group with intact teeth (n  = 12). The groups were as follows: "Normal": direct resin composite; "Ring": glass fiber-reinforced strip (Dentapreg) wrapped around buccal and lingual walls followed by direct resin composite; "Inlay": indirect CAD/CAM resin composite inlay; "Onlay": indirect CAD/CAM resin composite onlay; "Intact": Intact teeth (Control). Tetric EvoCeram and Adhese Universal (Ivoclar Vivadent) were used for direct restorations and Tetric CAD (Ivoclar Vivadent) adhesively luted with Adhese Universal and Variolink Esthetic LC (Ivoclar Vivadent) were used for indirect restorations. All teeth were submitted to thermo-mechanical cyclic loading. All samples were then submitted to a compressive load until fracture. Fracture load was noted and teeth were analyzed to classify the failure mode as either catastrophic (C) or non-catastrophic (NC). No statistically significant difference was found between fracture strength of the five groups when all specimens were considered (p = 0.1461). Intact group showed the lowest percentage of catastrophic failures (41.67%). Ring group presents less catastrophic failures (75%) than Normal group (83.34%), and failures of indirect restorations-Inlay and Onlay-were almost all catastrophic (91.67% and 100%, respectively).
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http://dx.doi.org/10.1007/s10266-020-00552-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7954736PMC
April 2021

Titanium salts tested in reconstructed human skin with integrated MUTZ-3-derived Langerhans cells show an irritant rather than a sensitizing potential.

Contact Dermatitis 2020 Nov 6;83(5):337-346. Epub 2020 Aug 6.

Department of Molecular Cell Biology and Immunology, Amsterdam University Medical Centre, Amsterdam Infection and Immunity Institute, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.

Background: The nature of clinically related adverse reactions to titanium is still unknown.

Objective: To determine whether titanium salts have irritant or sensitizing potential in a reconstructed human skin (RHS) model with integrated Langerhans cells (LCs).

Methods: RHS-LCs (ie, reconstructed epidermis) containing primary differentiated keratinocytes and CFSE CD1a -LCs generated from the MUTZ-3 cell line on a primary fibroblast-populated collagen hydrogel (dermis) were topically exposed to titanium(IV) bis(ammonium lactato)dihydroxide (TiALH). LC migration and plasticity were determined.

Results: TiALH resulted in CFSE CD1a -LC migration out of the epidermis. Neutralizing antibodies to CCL5 and CXCL12 showed that LC migration was CCL5 and not CXCL12 mediated. LCs accumulating within the dermis after TiALH exposure were CFSE Lang CD68 which is characteristic of a phenotypic switch of MUTZ-LC to a macrophage-like cell. Furthermore, TiALH did not result in increased interleukin (IL)-1β or CCR7 messenger RNA (mRNA) in the dermis, but did result in increased IL-10 mRNA. In addition, monocultures of MUTZ-LCs failed to increase LC maturation biomarkers CD83, CD86, and CXCL-8 when exposed to noncytotoxic concentrations of four different titanium salts.

Conclusion: These results classify titanium salts as irritants rather than sensitizers and indicate that titanium implant-related complaints could be due to localized irritant-mediated inflammation arising from leachable agents rather than a titanium metal allergy.
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http://dx.doi.org/10.1111/cod.13666DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7689826PMC
November 2020

Non-heat inactivated autologous serum increases accuracy of in vitro CFSE lymphocyte proliferation test (LPT) for nickel.

Clin Exp Allergy 2020 06 14;50(6):722-732. Epub 2020 Apr 14.

Department of Dental Materials Science, Academic Centre for Dentistry Amsterdam, University of Amsterdam and Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.

Background: Skin patch testing is still seen as the gold standard for the diagnosis of allergic hypersensitivity. For several metals and for patients with a suspected adverse reaction to their medical device implant material, patch testing can be unreliable. The current alternative to metal allergy patch testing is the in vitro lymphocyte proliferation test (LPT) using tritiated thymidine. This method is well-established but requires handling of radioactive material, often uses heat-inactivated allogenic human pooled serum and cannot determine T cell subsets.

Objective: To develop a radioactive free LPT by using carboxyfluorescein succinimidyl ester (CFSE) and to evaluate the influence of serum source (heat-inactivated human pooled serum [HI HPS] vs autologous serum) on the sensitivity and specificity of the nickel-specific LPT.

Methods: Peripheral blood mononuclear cells derived from nickel-allergic patients and healthy controls were collected, labelled with CFSE and cultured in medium containing 10% HI HPS or 10% autologous serum with or without additional T cell skewing cytokine cocktails (Th1: IL-7/IL-12, Th2: IL-7/IL-4 or Th17: IL-7/IL-23/IL-1β) in the absence or presence of NiSO . The stimulation index (SI) was calculated as the ratio of divided cells, that is the percentage of CFSE CD3 CD4 T-lymphocytes upon nickel stimulation compared to the percentage of CFSE CD3 CD4 T-lymphocytes without antigen. These results were compared with the history of Ni allergy, patch test results and the MELISA test.

Results: Autologous serum positively influenced Ni-specific proliferation while HI HPS negatively influenced Ni-specific proliferation. The test protocol analysing CD4 cells and autologous serum without skewing cytokines scored the best diagnostic values (sensitivity 95%; specificity 93%; and overall accuracy 94%) compared to the parallel test using HI HPS (accuracy 60%). Cytokine supplements did not further improve the test protocol which used autologous serum. The protocol using HI HPS could be further improved by addition of the cytokine skewing cocktails.

Conclusions: Here, we describe an optimized and highly accurate flow cytometric LPT which comprises of CFSE-labelled cells cultured in autologous serum (not heat inactivated) and without the presence of T cell skewing cytokines.

Clinical Relevance: The sensitivity and specificity of LPT is enhanced, compared to HI HPS, when autologous serum without skewing cytokines is used.
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http://dx.doi.org/10.1111/cea.13603DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7317482PMC
June 2020

A retrospective study on titanium sensitivity: Patch test materials and manifestations.

Contact Dermatitis 2018 Aug 24;79(2):85-90. Epub 2018 May 24.

Department of Dermatology, VU University Medical Centre, Amsterdam, The Netherlands.

Background: Titanium is being increasingly used. Although it is considered to be a non-allergenic material, allergic reactions to it have been reported. Titanium dioxide has been found to be an unreliable patch test material. Few studies to date have profiled titanium allergy, and it therefore remains difficult to distinguish its manifestations.

Objectives: To evaluate alternatives for titanium dioxide as a patch test preparation, and to profile titanium reactions and manifestations.

Methods: A retrospective chart review was conducted with 458 patients who underwent patch testing with at least 1 of 5 different titanium salts.

Results: At least 1 positive result was noted in 5.7% of the patients. The frequency of positive results for the tested salts ranged from 0.9% to 7.9%. Titanium(IV) oxalate hydrate had the highest yield and titanium dioxide the lowest. Erythema, dermatitis and local swelling were the most common objective complaints. In 16 (61.5%) patients, the test result had partial or full clinical relevance.

Conclusions: No titanium-specific risk factors and clinical picture could be identified. Titanium dioxide is not adequately sensitive for identifying titanium allergy. The titanium salts seem to be possible superior patch test preparations, but appear to be unsuitable if used singly. The patient's medical history and clinical picture remain crucial in the diagnostic work-up.
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http://dx.doi.org/10.1111/cod.13010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6099462PMC
August 2018

Influence of dentin and enamel on the fracture resistance of restorations at several thicknesses.

Am J Dent 2018 Feb;31(1):34-38

Department of Dental Materials Science, Academic Centre for Dentistry Amsterdam (ACTA), Univeristy of Amsterdam and Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.

Purpose: To investigate the effect of substrate and thickness on the fracture resistance of bonded dental restorative materials.

Methods: Cylindrical restorations (d = 4.0 mm) of resin composites Filtek Supreme XTE, Clearfil AP-X, Lava Ultimate and glass-ceramic IPS e.max CAD were fabricated at thicknesses of 0.5 mm, 1.0 mm and 2.0 mm respectively (n = 10 per group) and adhesively bonded to bovine enamel or dentin. The load to failure (LtF in N) of all specimens was determined in a universal testing machine and two one-way ANOVAs with a post hoc LSD tests and separate independent samples t-tests, performed at a significance level of 5%.

Results: At 0.5 and 1.0 mm, direct resin composites bonded to dentin showed a higher LtF than when bonded to enamel, while the indirect materials showed reversed results (P< 0.05). At 2.0 mm there was no difference except for LU. A direct relationship between LtF and increasing thicknesses on enamel was found, while on dentin the LtF of direct resin composite restorations was less dependent on the thickness.

Clinical Significance: For restorations up to 1 mm thickness, a substrate with a matching elastic modulus has a positive effect on the fracture resistance of glass-ceramics and resin composite restorations. When bonded to enamel, restoration thickness plays an important role in the fracture resistance. When bonded to dentin, thickness only affects the fracture resistance of indirect restoratives.
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February 2018

Assessment of metal sensitizer potency with the reconstructed human epidermis IL-18 assay.

Toxicology 2018 01 25;393:62-72. Epub 2017 Oct 25.

Dental Material Sciences, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and Vrije Universiteit Amsterdam, The Netherlands.

According to the new EU Medical Devices (MDR) legislation coming into effect in 2017, manufactures will have to comply with higher standards of quality and safety for medical devices in order to meet common safety concerns regarding such products. Metal alloys are extensively used in dentistry and medicine (e.g. orthopedic surgery and cardiology) even though clinical experience suggests that many metals are sensitizers. The aim of this study was to further test the applicability domain of the in vitro reconstructed human epidermis (RhE) IL-18 assay developed to identify contact allergens and in doing so: i) determine whether different metal salts, representing leachables from metal alloys used in medical devices, could be correctly labelled and classified; and ii) assess the ability of different salts for the same metal to penetrate the skin stratum corneum. Twenty eight chemicals including 15 metal salts were topically exposed to RhE. Nickel, chrome, gold, palladium were each tested in two different salt forms, and titanium in 4 different salt forms. Metal salts were labelled (YES/NO) as sensitizer if a threshold of more than 5 fold IL18 release was reached. The in vitro estimation of expected sensitization induction level (potency) was assessed by interpolating in vitro EC50 and IL-18 SI2 with LLNA EC3 and human NOEL values from standard reference curves generated using DNCB (extreme) and benzocaine (weak). Metal salts, in contrast to other chemical sensitizers and with the exception of potassium dichromate (VI) and cobalt (II) chloride, were not identified as contact allergens since they only induced a small or no increase in IL-18 production. This finding was not related to a lack of stratum corneum skin penetration since EC50 values (decrease in metabolic activity; MTT assay) were obtained after topical RhE exposure to 8 of the 15 metal salts. For nickel, gold and palladium salts, differences in EC50 values between two salts for the same metal could not be attributed to differences in molarity or valency. For chrome salts the difference in EC50 values may be explained by different valencies (VI vs. III), but not by molarity. In general, metal salts were classified as weaker sensitizers than was indicated from in vivo LLNA EC3 and NOEL data. Our in vitro results show that metals are problematic chemicals to test, in line with the limited number of standardized human and animal studies, which are not currently considered adequate to predict systemic hypersensitivity or autoimmunity, and despite clinical experience, which clearly shows that many metals are indeed a risk to human health.
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http://dx.doi.org/10.1016/j.tox.2017.10.014DOI Listing
January 2018

Marginal integrity of low-shrinking versus methacrylate-based composite: effect of different one-step self-etch adhesives.

Odontology 2017 Jul 1;105(3):291-299. Epub 2016 Nov 1.

Division of Cariology and Endodontology and President, School of Dentistry, University of Geneva, Rue Barthélemy-Menn 19, 1205, Geneva, Switzerland.

The aim of the study was to evaluate the influence of composite type and adhesive system on the quality of marginal adaptation in standardized Class V cavities before and after thermo-mechanical loading (TML). The cavities were restored using different combinations of three adhesive systems [(Silorane System Adhesive (SSA), Clearfil S Bond (S3), G-Bond (G-B)] and two resin composite materials (Filtek Silorane, Clearfil AP-X). Six groups (n = 10): Group A (SSA-Primer + SSA-Bond, Filtek Silorane), Group B (SSA-Primer + SSA-Bond, Clearfil AP-X), Group C (S3 + SSA-Bond, Filtek Silorane), Group D (S3 + SSA-Bond, Clearfil AP-X), Group E (G-B + SSA-Bond, Filtek Silorane) and Group F (G-B + SSA-Bond, Clearfil AP-X) were defined. Marginal adaptation was assessed on replicas in the SEM at 200 × magnification before and after TML (3000 × 5-55 °C, 1.2 10 × 49 N; 1.7 Hz) under simulated dentinal fluid. The highest scores of continuous margins (%CM) were observed in the group F (G-B + SSA-Bond, Clearfil AP-X: before loading 96.4 (±3.2)/after loading 90.8 (±7.0)). A significant effect of adhesive system, composite type and loading interval was observed on the results (p < 0.05). Significantly lower scores of %CM were observed for silorane-based composite (Filtek Silorane) after TML in comparison with methacrylate-based composite (Clearfil AP-X) considering total marginal length (p < 0.05). For both Filtek Silorane and Clearfil AP-X, G-Bond performed significantly better than SSA-Primer and Clearfil S Bond (p < 0.05). For all combinations of one-step self-etch adhesives and SSA-Bond resin coating, silorane-based low-shrinking composite exhibited inferior marginal adaptation than did the methacrylate-based composite.
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http://dx.doi.org/10.1007/s10266-016-0274-1DOI Listing
July 2017

Novel non-invasive reinforcement of MOD cavities on endodontically treated teeth.

J Dent 2016 11 21;54:77-85. Epub 2016 Sep 21.

Department of Cariology and Endodontology, University of Geneva, 19 Rue Barthélemy-Menn, CH-1205 Geneva, Switzerland. Electronic address:

Objectives: To evaluate the biomechanical influence of reconnecting the buccal and lingual walls of endodontically treated lower molar with a large MOD cavity.

Methods: 3D models were created from a micro-CT scan of an extracted intact lower human molar. Finite element analysis was then used to compare the stress distribution and displacement of the structures between different models: Unrestored MOD on ETT (Unrest), MOD on ETT restored with composite resin (Norm), MOD on ETT reinforced with a non-invasive ring (Ring) and intact tooth as the control (Int).

Results: This study showed that the Unrest model presented the highest stress values at the cervical level. The non-invasive Ring model showed the lowest stress values at the cervical level, and the lowest deflection of the cusps.

Conclusions: Mechanically reconnecting the remaining tooth structures has a direct positive effect on stress distribution and deformation of the remaining structures.

Clinical Relevance: Reinforcing ETT in a non-invasive direct approach is efficient in terms of preserving sound tooth structures, reducing the time of treatment and eliminating the laboratory steps required to create the restorations.
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http://dx.doi.org/10.1016/j.jdent.2016.09.008DOI Listing
November 2016

Development of a Full-Thickness Human Gingiva Equivalent Constructed from Immortalized Keratinocytes and Fibroblasts.

Tissue Eng Part C Methods 2016 08;22(8):781-91

1 Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and Vrije Universiteit Amsterdam , MOVE Research Institute Amsterdam, Amsterdam, The Netherlands .

Organotypic models make it possible to investigate the unique properties of oral mucosa in vitro. For gingiva, the use of human primary keratinocytes (KC) and fibroblasts (Fib) is limited due to the availability and size of donor biopsies. The use of physiologically relevant immortalized cell lines would solve these problems. The aim of this study was to develop fully differentiated human gingiva equivalents (GE) constructed entirely from cell lines, to compare them with the primary cell counterpart (Prim), and to test relevance in an in vitro wound healing assay. Reconstructed gingiva epithelium on a gingiva fibroblast-populated collagen hydrogel was constructed from cell lines (keratinocytes: TERT or HPV immortalized; fibroblasts: TERT immortalized) and compared to GE-Prim and native gingiva. GE were characterized by immunohistochemical staining for proliferation (Ki67), epithelial differentiation (K10, K13), and basement membrane (collagen type IV and laminin 5). To test functionality of GE-TERT, full-thickness wounds were introduced. Reepithelialization, fibroblast repopulation of hydrogel, metabolic activity (MTT assay), and (pro-)inflammatory cytokine release (enzyme-linked immunosorbent assay) were assessed during wound closure over 7 days. Significant differences in basal KC cytokine secretion (IL-1α, IL-18, and CXCL8) were only observed between KC-Prim and KC-HPV. When Fib-Prim and Fib-TERT were stimulated with TNF-α, no differences were observed regarding cytokine secretion (IL-6, CXCL8, and CCL2). GE-TERT histology, keratin, and basement membrane protein expression very closely represented native gingiva and GE-Prim. In contrast, the epithelium of GE made with HPV-immortalized KC was disorganized, showing suprabasal proliferating cells, limited keratinocyte differentiation, and the absence of basement membrane proteins. When a wound was introduced into the more physiologically relevant GE-TERT model, an immediate inflammatory response (IL-6, CCL2, and CXCL8) was observed followed by complete reepithelialization. Seven days after wounding, tissue integrity, metabolic activity, and cytokine levels had returned to the prewounded state. In conclusion, immortalized human gingiva KC and fibroblasts can be used to make physiologically relevant GE, which resemble either the healthy gingiva or a neoplastic disease model. These organotypic models will provide valuable tools to investigate oral mucosa biology and can also be used as an animal alternative for drug targeting, vaccination studies, microbial biofilm studies, and testing new therapeutics.
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http://dx.doi.org/10.1089/ten.TEC.2016.0066DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4991602PMC
August 2016

Comparing different enamel pretreatment options for resin-infiltration of natural non-cavitated carious lesions.

Am J Dent 2016 Feb;29(1):3-9

Purpose: To compare two different enamel pretreatments and their effect on the efficiency of penetration of a one-component adhesive into natural carious lesions.

Methods: Eight extracted human molars and premolars with non-cavitated interproximal lesions were selected. ICDAS code 1-2 was assessed by visual, microscopic, X-ray and Diagnocam record analysis. Samples were cut vertically across the demineralization to obtain two symmetrical lesions, (n=16). After isolating the cut surfaces with nail varnish, paired lesion halves' surfaces were pretreated with two different techniques: Group 1: surfaces were firstly abraded with fine diamond-coated metallic strips (Steelcarbo) and then etched with 37% H₃PO₄ acid (Omni-etch, 120 seconds); Group 2: lesion surfaces were etched with 15% HCl acid (Icon-etch, 120 seconds). All teeth were stained with rhodamine isothiocyanate (RITC) solution (12 hours) and subsequently stored in dry chamber (3 hours). All samples were penetrated with a one-component adhesive (Scotchbond Universal) for 180 seconds and coated with a thin layer of flowable composite (Tetric Flow). After light curing, un- encapsulated dye was bleached by immersion in 30% hydogen peroxide for 12 hours at 37°C. Remaining lesion pores were stained with sodium fluorescein solution. Thin cuts of the teeth were observed with confocal microscopy and computer image analysis was performed (ImageJ). The percentage of penetration (area of resin penetration/area of total demineralization x100) was calculated.

Results: Pretreatment with fine aluminum oxide-coated metallic strip followed by 37% H₃PO₄ acid showed a larger infiltration area (51.7% ± 12.2) in almost all samples compared to pretreatment with 15% HCl acid alone (22.1% ± 13.2). Statistical analysis using t-test showed a significant difference between the two groups (P = 0.011).
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February 2016

Fatigue behavior of zirconia under different loading conditions.

Dent Mater 2016 07 7;32(7):915-20. Epub 2016 Apr 7.

Academic Center for Dentistry Amsterdam (ACTA), University of Amsterdam and VU University Amsterdam, Amsterdam, The Netherlands.

Purpose: To investigate the influence of surface damage on the fatigue behavior of zirconia under two different loading conditions.

Materials And Methods: One hundred twenty zirconia bar-shaped received either airborne particle abrasion using 50μm or 120μm alumina particles while polished specimens served as control. The specimens were subjected to two fatigue regimes: dynamic fatigue (1,000,000 cycles, 1hz and 0.5s contact time) or static fatigue (a constant load applied for 5000s) under water using the staircase application of the load. The flexure strength after fatigue (dynamic fatigue strength) was compared to the initial flexure strength of the tested specimens (α=0.05). The critical crack shape and size of fractured specimens was examined using scanning electron microscopy.

Results: Compared to the initial flexure strength of the tested specimens, dynamic fatigue strength was 86.3% for the polished specimens, 73.4% for 50μm particle abrasion, and 42.3% for 120μm particle abrasion while the static fatigue strength was 85.9%, 78.5%, and 51.5% respectively. Significant statistical differences (F=223.679, P<0.001) were found between different surface treatments but not between dynamic and static fatigue strengths for the same type of surface treatment.

Conclusions: The dynamic and static fatigue strengths of zirconia are significantly influenced by type of surface damage.

Clinical Implications: Within the limitations of this study, surface damage have great influence on fatigue behavior of zirconia.
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http://dx.doi.org/10.1016/j.dental.2016.03.012DOI Listing
July 2016

Abutment-to-fixture load transfer and peri-implant bone stress.

Am J Dent 2015 Oct;28(5):247-50

Purpose: To uncover design principles for the abutment-fixture complex that reduce the stress concentration on the bone.

Methods: A 3-dimensional finite element model was used to vary shape, elasticity, and connectivity of the abutment-fixture complex. We compared peri-implant bone stress of these designs.

Results: Peri-implant bone stress was increased when the abutment could slide frictionless along the rim of the fixture, allowing the abutment to "lean into" the fixture rim and transfer loads near the bone crest. Conversely, bone stress was reduced when no motion was allowed (or no contact was made at all) between the abutment and the fixture rim. Bone stress was also reduced when the fixture was stiffer and thus more resistant to deformation, or when the fixture was wider.
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October 2015

Silorane, ormocer, methacrylate and compomer long-term staining susceptibility using ΔE and ΔE 00 colour-difference formulas.

Odontology 2016 Sep 16;104(3):305-9. Epub 2015 Jul 16.

Treatment Plan Unit and Division of Cariology and Endodontology, University Clinic of Dental Medicine (CUMD), University of Geneva, Rue Barthélemy-Menn 19, 1205, Geneva, Switzerland.

The aim of this study was to evaluate the staining susceptibility of a silorane (Filtek Silorane), an ormocer (Ceram X Duo), a methacrylate (Tetric EvoCeram) and a compomer (Dyract) exposed on the long term to various staining agents by using ΔE and ΔE 00 colour-difference formulas. Thirty-six disc-shaped specimens were made of each of the four chemically different materials, randomly divided in six groups (n = 6) and immersed in five staining solutions (red wine, juice, coke, tea and coffee) or stored dry (control) in an incubator at 37 °C for 99 days. Spectrophotometric measurements by means of a spectrophotometer (Spectroshade Handy Dental, MHT) were repeated over a white (L* = 92.6, a* = -1.2, b* = 2.9) and black (L* = 1.6, a* = 1.2, b* = -1.0) background made of plasticized paper, in order to determine the colour changes according to ΔE, ΔE 00 and translucency formulas. Statistical analysis was performed by means of factorial Anova, Fisher's LSD test (post hoc) and a Spearman rank correlation between ΔE and ΔE 00. When analysed over a white background, mean ΔE 00 values were highly significantly different and varied from 0.8 (Ceram X Duo/air) to 20.9 (Ceram X Duo/red wine). When analysed over a black background, mean ΔE 00 values were highly significantly different and varied from 1.0 (Ceram X Duo and Tetric/air) to 25.2 (Ceram X Duo/red wine). Differences in translucency varied from 0.3 (Ceram X Duo/air) to 21.1 (Ceram X Duo/juice). The correlation between ΔE and ΔE 00 over a white background was 0.9928, while over a black background, it was 0.9886.
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http://dx.doi.org/10.1007/s10266-015-0212-7DOI Listing
September 2016

Continuing the quest for autoimmunity due to oral metal exposure.

Autoimmunity 2015 27;48(7):494-501. Epub 2015 Apr 27.

a Laboratory of Medical Immunology, Department of Pathology , VU University Medical Centre , Amsterdam , The Netherlands .

Aim: The role of metal exposure in the development of autoimmune disease (AID) is still controversial. Here, we studied the relationship between oral metal exposure, metal allergy and autoimmunity.

Methods: A mixed population (n = 78) of non-allergic volunteers, metal-allergic patients and patients with oral problems putatively due to metal alloys was evaluated for oral Ni, Pd, Au and Hg exposure and skin hypersensitivity. Clinical autoimmune parameters were based on medical histories; additionally, serum levels of the four most common autoantibodies were measured.

Results: Skin hypersensitivity, as seen mainly for Ni and/or Pd, was not positively associated with autoimmune parameters. In contrast, metal hypersensitive individuals showed an extremely low frequency of thyroid autoantibodies (3% vs 20% in non-hypersensitive controls). Next, the relation between metal exposure and autoimmunity was evaluated in individuals >35 years (n = 58), since from that age on metal exposure had plateaued and was not correlated with age. In this subgroup, oral Ni exposure was associated (p < 0.01) with self-reported AID, irrespective of autoantibody levels. These unexpected findings warrant further confirmation in a larger test group. Of note, oral Pd, Au or Hg contacts were not associated with any of the clinical or serological autoimmune phenomena tested.

Conclusion: The results of this study support the view that development of metal contact allergies may prevent autoimmune activation, and, second, that oral exposure to Pd, Au or Hg does not facilitate the development of AID.
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http://dx.doi.org/10.3109/08916934.2015.1033688DOI Listing
August 2016

Three-dimensional finite element analysis of anterior two-unit cantilever resin-bonded fixed dental prostheses.

ScientificWorldJournal 2015 24;2015:864389. Epub 2015 Mar 24.

Department of Restorative Dentistry and Endodontology, Dental School, Ghent University Hospital, Ghent University, De Pintelaan 185/P8, 9000 Gent, Belgium.

The aim of this study was to evaluate the influence of different framework materials on biomechanical behaviour of anterior two-unit cantilever resin-bonded fixed dental prostheses (RBFDPs). A three-dimensional finite element model of a two-unit cantilever RBFDP replacing a maxillary lateral incisor was created. Five framework materials were evaluated: direct fibre-reinforced composite (FRC-Z250), indirect fibre-reinforced composite (FRC-ES), gold alloy (M), glass ceramic (GC), and zirconia (ZI). Finite element analysis was performed and stress distribution was evaluated. A similar stress pattern, with stress concentrations in the connector area, was observed in RBFDPs for all materials. Maximal principal stress showed a decreasing order: ZI>M>GC>FRC-ES>FRC-Z250. The maximum displacement of RBFDPs was higher for FRC-Z250 and FRC-ES than for M, GC, and ZI. FE analysis depicted differences in location of the maximum stress at the luting cement interface between materials. For FRC-Z250 and FRC-ES, the maximum stress was located in the upper part of the proximal area of the retainer, whereas, for M, GC, and ZI, the maximum stress was located at the cervical outline of the retainer. The present study revealed differences in biomechanical behaviour between all RBFDPs. The general observation was that a RBFDP made of FRC provided a more favourable stress distribution.
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http://dx.doi.org/10.1155/2015/864389DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4387912PMC
July 2016

The influence of FRCs reinforcement on marginal adaptation of CAD/CAM composite resin endocrowns after simulated fatigue loading.

Odontology 2016 May 9;104(2):220-32. Epub 2015 Apr 9.

Division of Cariology and Endodontology, School of Dentistry, University of Geneva, 19 Rue, Barthélémy Menn, 1205, Geneva, Switzerland.

To evaluate the marginal adaptation of endodontically treated molars restored with CAD/CAM composite resin endocrowns either with or without reinforcement by fibre reinforced composites (FRCs), used in different configurations. 32 human endodontically treated molars were cut 2 mm over the CEJ. Two interproximal boxes were created with the margins located 1 mm below the CEJ (distal box) and 1 mm over the CEJ (mesial box). All specimens were divided in four groups (n = 8). The pulp chamber was filled with: group 1 (control), hybrid resin composite (G-aenial Posterior, GC); group 2, as group 1 but covered by 3 meshes of E-glass fibres (EverStick NET, Stick Tech); group 3, FRC resin (EverX Posterior, GC); group 4, as group 3 but covered by 3 meshes of E-glass fibres. The crowns of all teeth were restored with CAD/CAM composite resin endocrowns (LAVA Ultimate, 3M). All specimens were thermo-mechanically loaded in a computer-controlled chewing machine (600,000 cycles, 1.6 Hz, 49 N and simultaneously 1500 thermo-cycles, 60 s, 5-55 °C). Marginal analysis before and after the loading was carried out on epoxy replicas by SEM at 200× magnification. For all the groups, the percentage values of perfect marginal adaptation after loading were always significantly lower than before loading (p < 0.05). The marginal adaptation before and after loading was not significantly different between the experimental groups (p > 0.05). Within the limitations of this in vitro study, the use of FRCs to reinforce the pulp chamber of devitalized molars restored with CAD/CAM composite resin restorations did not significantly influenced their marginal quality.
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http://dx.doi.org/10.1007/s10266-015-0202-9DOI Listing
May 2016

Mechanical performance of implant-supported posterior crowns.

J Prosthet Dent 2015 Jul 24;114(1):59-66. Epub 2015 Mar 24.

Faculty Dean and Full Professor, Department of Dental Material Sciences, Academic Centre for Dentistry Amsterdam (ACTA) University of Amsterdam and VU University Amsterdam, Amsterdam, The Netherlands.

Statement Of Problem: The fracture of implant-supported restorations, especially of the veneering layer, is a common problem in dentistry. Monolithic ceramic or resin restorations might help solve this problem.

Purpose: The purpose of this in vitro study was to obtain additional insight into the risk of fracture of implant-supported restorations.

Material And Methods: Identical crowns (n=10) of 10 different ceramic and composite resin materials were cemented on conventional abutments on implant replicas embedded in polymethyl methacrylate blocks. The specimens were subjected to compressive load in a universal testing machine to record initial load to failure (ILF). Additionally, the flexural strength (FS), compressive strength (CS), and elastic modulus (E) of the investigated materials were determined. These results were used in a finite element analysis model of a composite resin and a lithium disilicate crown.

Results: Anatomic contour zirconia (Lava Plus) crowns had the highest ILF (6065 N), followed by lithium disilicate (IPS e.max) (2788 N) and the composite resin materials (Protemp 4, Majesty Flow, Telio CAD, Estenia C&B, Lava Ultimate, VITA Enamic) (2386 to 1935 N). Veneered zirconia (Lava) crowns showed the lowest ILF (1477 N). The highest FS, CS, and E were found for Lava Plus and IPS e.max. No direct relationship was found between ILF and the FS, CS, or E. The finite element analysis showed stresses that did not exceed the FS or CS of IPS e.max. The surface roughness of these crowns might have caused initial failure at relatively low stresses.

Conclusions: In this laboratory study, monolithic implant-supported crowns showed a higher ILF than conventional veneered ceramic crowns. Monolithic ceramic restorations might perform better than composite resin crowns.
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http://dx.doi.org/10.1016/j.prosdent.2014.10.015DOI Listing
July 2015

Influence of shape and finishing on the corrosion of palladium-based dental alloys.

J Adv Prosthodont 2015 Feb 17;7(1):56-61. Epub 2015 Feb 17.

Department of Dental Materials Science, ACTA, University of Amsterdam and VU University Amsterdam, Nederland.

Purpose: The purpose of this study was to evaluate the effects of the surface treatment and shape of the dental alloy on the composition of the prosthetic work and its metallic ion release in a corrosive medium after casting.

Materials And Methods: Orion Argos (Pd-Ag) and Orion Vesta (Pd-Cu) were used to cast two crowns and two disks. One of each was polished while the other was not. Two as-received alloys were also studied making a total of 5 specimens per alloy type. The specimens were submersed for 7 days in a lactic acid/sodium chloride solution (ISO standard 10271) and evaluated for surface structure characterization using SEM/EDAX. The solutions were quantitatively analysed for the presence of metal ions using ICP-MS and the results were statistically analysed with one-way ANOVA and a Tukey post-hoc test.

Results: Palladium is released from all specimens studied (range 0.06-7.08 µg·cm(-2)·week(-1)), with the Pd-Cu alloy releasing the highest amounts. For both types of alloys, ion release of both disk and crown pairs were statistically different from the as-received alloy except for the Pd-Ag polished crown (P>.05). For both alloy type, disk-shaped pairs and unpolished specimens released the highest amounts of Pd ions (range 0.34-7.08 µg·cm(-2)·week(-1)). Interestingly, in solutions submerged with cast alloys trace amounts of unexpected elements were measured.

Conclusion: Shape and surface treatment influence ion release from dental alloys; polishing is a determinant factor. The release rate of cast and polished Pd alloys is between 0.06-0.69 µg·cm(-2)·week(-1), which is close to or exceeding the EU Nickel Directive 94/27/EC compensated for the molecular mass of Pd (0.4 µg·cm(-2)·week(-1)). The composition of the alloy does not represent the element release, therefore we recommend manufacturers to report element release after ISO standard corrosion tests beside the original composition.
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http://dx.doi.org/10.4047/jap.2015.7.1.56DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4341188PMC
February 2015

Sensitization to palladium and nickel in Europe and the relationship with oral disease and dental alloys.

Contact Dermatitis 2015 May 12;72(5):286-96. Epub 2015 Jan 12.

Department of Dental Materials Science, Academic Centre for Dentistry Amsterdam, University of Amsterdam and VU University Amsterdam, Gustav Mahlerlaan 3004, 1081 LA, Amsterdam, The Netherlands.

Background: The role of palladium and nickel sensitization in oral disease and dermatitis is not fully understood.

Objectives: To investigate whether sensitization to these metals was associated with exposure to dental alloys and oral and skin complaints/symptoms in a European multicentre study.

Methods: In six dermatology clinics, patch tests with palladium (3% Na2 PdCl4 ; Pd = 102.0 µmol/g) and nickel (5% NiSO4 .6H2 O; Ni = 190.2 µmol/g) were performed in consecutive patients, and patients' characteristics were collected with a questionnaire and a clinical investigation.

Results: In total, 906 patients were included, of whom 24.3% reacted to palladium and 25.2% to nickel. The rate of monosensitization was 6-7% for both metals. Palladium sensitization (as opposed to no sensitization to both metals) was associated with exposure to dental crowns [odds ratio (OR) 2.0], skin reactivity to metals (OR 2.8), oral lichenoid lesions (OR 4.7), xerostomia (OR 7.3), and metal taste (OR 20.7), but not with eczema, stomatitis, or oral burning sensation. Additionally, xerostomia (OR 8.7) and metal taste (OR 4.6) were associated with sensitization to both metals.

Conclusions: Clinically, it is important for palladium-sensitized patients to undergo an oral examination, with particular attention to the presence of/exposure to dental crowns. In the case of metal contact allergy, exposure to dental crowns could play a role.
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http://dx.doi.org/10.1111/cod.12327DOI Listing
May 2015

In vitro cytotoxicity of metallic ions released from dental alloys.

Odontology 2016 May 31;104(2):136-42. Epub 2014 Dec 31.

Department of Dental Materials Science, ACTA, University of Amsterdam and VU University, Gustav Mahlerlaan 3004, 1081 LA, Amsterdam, The Netherlands.

The cytotoxicity of a dental alloy depends on, but is not limited to, the extent of its corrosion behavior. Individual ions may have effects on cell viability that are different from metals interacting within the alloy structure. We aimed to investigate the cytotoxicity of individual metal ions in concentrations similar to those reported to be released from Pd-based dental alloys on mouse fibroblast cells. Metal salts were used to prepare seven solutions (concentration range 100 ppm-1 ppb) of the transition metals, such as Ni(II), Pd(II), Cu(II), and Ag(I), and the metals, such as Ga(III), In(III), and Sn(II). Cytotoxicity on mouse fibroblasts L929 was evaluated using the MTT assay. Ni, Cu, and Ag are cytotoxic at 10 ppm, Pd and Ga at 100 ppm. Sn and In were not able to induce cytotoxicity at the tested concentrations. Transition metals were able to induce cytotoxic effects in concentrations similar to those reported to be released from Pd-based dental alloys. Ni, Cu, and Ag were the most cytotoxic followed by Pd and Ga; Sn and In were not cytotoxic. Cytotoxic reactions might be considered in the etiopathogenesis of clinically observed local adverse reactions.
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http://dx.doi.org/10.1007/s10266-014-0192-zDOI Listing
May 2016

In vitro debonding of orthodontic retainers analyzed with finite element analysis.

Eur J Orthod 2015 Oct 1;37(5):491-6. Epub 2014 Dec 1.

Department of Dental Materials Sciences, ACTA, University of Amsterdam and VU University, The Netherlands.

Objective: The aim of this in vitro study was to determine the load and deflection at failure of different lingual retainers bonded with composite to enamel in a standardized three-point bending test. The results were rationalized with finite element analysis (FEA) models.

Materials And Methods: Four types of multistranded wires, Dead Soft Respond, Twisted ligature, Penta-One, Gold-plated Penta-One, and two glass fibre-reinforced composite retainers, Fibre 07 and Fibre 09, were bonded to enamel with composite and submitted to a three-point bending test. The load and deflection at failure and the mode of debonding were recorded. The stiffness of the wires was determined and all experimental data were used in FEA models to rationalize the observed values and mode of debonding.

Results: Significant higher load and deflection were found for the most flexible retainers Twisted ligature and Dead Soft Respond. All retainers failed between the wire and composite, which was confirmed by FEA showing the highest stress in the composite around the retainer. The FEA models showed that the amount of composite used for bonding the retainers should be 2-4mm.

Conclusions: Based on the in vitro results, optimal bonding of lingual retainers can be achieved by flexible retainers, bonded with intrinsically strong composites. According to the FEA models the retainer should be bonded with 2-4mm composite, leaving the critical 'free-wire' length for the success of the retainer system.
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http://dx.doi.org/10.1093/ejo/cju074DOI Listing
October 2015

Sensitization to palladium in Europe.

Contact Dermatitis 2015 Jan 28;72(1):11-9. Epub 2014 Oct 28.

Department of Dental Materials Science, Academic Centre for Dentistry Amsterdam, University of Amsterdam and VU University Amsterdam, Gustav Mahlerlaan 3004, 1081 LA, Amsterdam, The Netherlands.

Background: Recently, sodium tetrachloropalladate (Na2 PdCl4 ) was found to be a more sensitive palladium patch test allergen than palladium dichloride (PdCl2 ).

Objectives: To determine the optimal test concentration of Na2 PdCl4 , to evaluate the prevalence of palladium sensitization with Na2 PdCl4 and PdCl2 , and to compare the results with nickel sensitization in a European multicentre study.

Materials And Methods: In addition to the European or national baseline series including NiSO4 ·6H2 0 5% pet., consecutive patients were tested with PdCl2 and Na2 PdCl4 2%, 3% and 4% pet. in eight European dermatology clinics. The age and sex distributions were also evaluated in patients sensitized to nickel and palladium.

Results: In total, 1651 patients were tested. Relative to 3% Na2 PdCl4 , 4% Na2 PdCl4 did not add any information. Two per cent Na2 PdCl4 resulted in more doubtful reactions and showed suboptimal reactivity. The prevalence of palladium sensitization doubled with Na2 PdCl4 and was similar to that of nickel. Interestingly, in contrast to nickel sensitization, palladium sensitization was not related to female sex.

Conclusions: Three per cent Na2 PdCl4 pet. is the most suitable patch test concentration. Sensitization to palladium is almost as prevalent as sensitization to nickel. The sex distribution is different between nickel-sensitized and palladium-sensitized patients, suggesting different sources of exposure.
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http://dx.doi.org/10.1111/cod.12295DOI Listing
January 2015

Effect of modulated photo-activation on polymerization shrinkage behavior of dental restorative resin composites.

Eur J Oral Sci 2014 Aug;122(4):293-302

Department of Preventive Dentistry, Periodontology and Cariology, Center for Dental Medicine, University of Zurich, Zurich, Switzerland.

This study investigated the influence of modulated photo-activation on axial polymerization shrinkage, shrinkage force, and hardening of light- and dual-curing resin-based composites. Three light-curing resin composites (SDR bulk-fill, Esthet X flow, and Esthet X HD) and one dual-curing material (Rebilda DC) were subjected to different irradiation protocols with identical energy density (27 J cm(-2) ): high-intensity continuous light (HIC), low-intensity continuous light (LIC), soft-start (SS), and pulse-delay curing (PD). Axial shrinkage and shrinkage force of 1.5-mm-thick specimens were recorded in real time for 15 min using custom-made devices. Knoop hardness was determined at the end of the observation period. Statistical analysis revealed no significant differences among the curing protocols for both Knoop hardness and axial shrinkage, irrespective of the composite material. Pulse-delay curing generated the significantly lowest shrinkage forces within the three light-curing materials SDR bulk-fill, Esthet X flow, and Esthet X HD. High-intensity continuous light created the significantly highest shrinkage forces within Esthet X HD and Rebilda DC, and caused significantly higher forces than LIC within Esthet X flow. In conclusion, both the composite material and the applied curing protocol control shrinkage force formation. Pulse-delay curing decreases shrinkage forces compared with high-intensity continuous irradiation without affecting hardening and axial polymerization shrinkage.
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http://dx.doi.org/10.1111/eos.12139DOI Listing
August 2014

The fracture resistance of a CAD/CAM Resin Nano Ceramic (RNC) and a CAD ceramic at different thicknesses.

Dent Mater 2014 Sep 15;30(9):954-62. Epub 2014 Jul 15.

Department of Dental Materials Science, ACTA, University of Amsterdam and VU University Amsterdam, The Netherlands.

Objectives: This study aimed to investigate the influence of restoration thickness to the fracture resistance of adhesively bonded Lava™ Ultimate CAD/CAM, a Resin Nano Ceramic (RNC), and IPS e.max CAD ceramic.

Methods: Polished Lava™ Ultimate CAD/CAM (Group L), sandblasted Lava™ Ultimate CAD/CAM (Group LS), and sandblasted IPS e.max CAD (Group ES) discs (n=8, Ø=10 mm) with a thickness of respectively 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, and 3.0 mm were cemented to corresponding epoxy supporting discs, achieving a final thickness of 3.5 mm. All the 120 specimens were loaded with a universal testing machine at a crosshead speed of 1 mm/min. The load (N) at failure was recorded as fracture resistance. The stress distribution for 0.5 mm restorative discs of each group was analyzed by Finite Element Analysis (FEA). The results of facture resistances were analyzed by one-way ANOVA and regression.

Results: For the same thickness of testing discs, the fracture resistance of Group L was always significantly lower than the other two groups. The 0.5 mm discs in Group L resulted in the lowest value of 1028 (112) N. There was no significant difference between Group LS and Group ES when the restoration thickness ranged between 1.0 mm and 2.0 mm. There was a linear relation between fracture resistance and restoration thickness in Group L (R=0.621, P<0.001) and in Group ES (R=0.854, P<0.001). FEA showed a compressive permanent damage in all groups.

Significance: The materials tested in this in vitro study with the thickness above 0.5 mm could afford the normal bite force. When Lava Ultimate CAD/CAM is used, sandblasting is suggested to get a better bonding.
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http://dx.doi.org/10.1016/j.dental.2014.05.018DOI Listing
September 2014

Palladium-based dental alloys are associated with oral disease and palladium-induced immune responses.

Contact Dermatitis 2014 Aug 22;71(2):82-91. Epub 2014 May 22.

Department of Dental Materials Science, Academic Centre for Dentistry Amsterdam, University of Amsterdam & VU University Amsterdam, Gustav Mahlerlaan 3004, 1081 LA, Amsterdam, The Netherlands.

Background: Palladium (Pd) and gold (Au) based dental alloys have been associated with oral disease.

Objectives: This study was designed to explore possible associations between the presence of Au-based and Pd-based dental alloys, and oral lesions, systemic complaints, and specific in vivo and in vitro immune responses.

Methods: The investigated population consisted of three groups: 26 non-metal-allergic volunteers, 25 metal-allergic patients, and 20 oral disease patients. Medical histories were taken, oral examinations were carried out, and compositions of all dental alloys were determined. Then, Au and Pd patch tests and in vitro assays were performed, revealing cytokine production by peripheral blood mononuclear cells [T helper (Th)1, interferon-γ; Th2, interleukin (IL)-5 and IL-13] and lymphocyte proliferation (LTT-MELISA(®) ).

Results: Non-plaque-related gingivitis was associated with the presence of Pd-based dental alloys, and Pd-positive patch tests and in vitro assays. Collectively, participants with Pd-based dental alloys showed increased Pd patch test reactivity (p < 0.05) and lymphoproliferation (p < 0.05). In contrast, oral lichenoid lesions were associated with Au-based alloys (p < 0.05), but this was not reflected by Au-specific immunoreactivity.

Conclusions: Oral lesions and Pd-induced immune responses are associated with the presence of dental alloys. However, most oral disease patients did not show positive patch test results or in vitro signs of specific immunoreactivity, suggesting local toxic reactions or the involvement of innate immune responses.
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http://dx.doi.org/10.1111/cod.12238DOI Listing
August 2014

Staining of dentin from amalgam corrosion is induced by demineralization.

Am J Dent 2013 Aug;26(4):185-90

Purpose: To evaluate the effect of artificial demineralization upon color change of dentin in contact with dental amalgam.

Methods: Sound human molars (n = 34) were embedded in resin and coronal enamel was removed. Dentin was exposed to artificial caries gel (pH 5.5) at 37 degrees C for 12 weeks (n = 24). Non-demineralized teeth served as controls (n = the 10). A dispersive high-Cu amalgam or conventional low-Cu amalgam was condensed onto dentin surfaces of all groups. After 10 weeks storage in saline, amalgam was removed and teeth were cut into three slices. Surfaces were inspected under optical microscopy and photographed.

Results: Penetration of black pigments was observed in dentin underneath both high-Cu and low-Cu amalgams in demineralized specimens. Black deposits were unevenly distributed and observed predominantly in dentin near to pulp horns. Discoloration was not limited to outer demineralized dentin but extended beyond this zone. Evenly distributed bluish-green discoloration was observed underneath all high-Cu amalgam specimens independent of demineralization.
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August 2013

Perceptibility and acceptability thresholds for colour differences in dentistry.

J Dent 2014 Jun 12;42(6):637-44. Epub 2013 Dec 12.

Department of Dental Materials Science, Academic Center for Dentistry Amsterdam, Amsterdam, The Netherlands.

Introduction: Data on acceptability (AT) and perceptibility thresholds (PT) for colour differences vary in dental literature. There is consensus that the determination of ΔE* is appropriate to define AT and PT, however there is no consensus regarding the values that should be used. The aim of this clinical review was to provide a systematic approach to the topic of colour science of high clinical relevance to dental research.

Materials And Methods: MEDLINE/PubMed, WoS and EBSCO databases were searched up to January 7, 2013; the outcome was restricted to English, and to clinical studies were spectrophotometers were used for measurement.

Results: Forty-eight studies were eligible and met the inclusion criteria. Of the 48 studies there appeared to be a trend in their source references: 44% referred to the same study for the PT (ΔE*=1); and 35% referred to the same article for the AT (ΔE*=3.7).

Conclusions: More than half the studies defined PT as ΔE*=1, and one third of the studies referred to ΔE*=3.7 as the threshold at which 50% of observers accepted the colour difference. Most clinical studies refer to the same few in vitro literature that have attempted to determine PT and AT from decades ago.
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http://dx.doi.org/10.1016/j.jdent.2013.11.017DOI Listing
June 2014
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