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      Surface properties of dental zirconia ceramics affected by ultrasonic scaling and low-temperature degradation

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          Abstract

          Zirconia (3Y-TZP) dental prostheses are widely used in clinical dentistry. However, the effect of ultrasonic scaling performed as a part of professional tooth cleaning on 3Y-TZP dental prostheses, especially in conjunction with low-temperature degradation (LTD), has not been fully investigated. The present study aimed to evaluate the influence of ultrasonic scaling and LTD on the surface properties of 3Y-TZP in relation to bacterial adhesion on the treated surface. 3Y-TZP specimens (4 × 4 × 2 mm) were polished and then subjected to autoclaving at 134°C for 100 h to induce LTD, followed by 10 rounds of ultrasonic scaling using a steel scaler tip for 1 min each. Surface roughness, crystalline structure, wettability, and hardness were analyzed by optical interferometry, X-ray diffraction analysis, contact angle measurement, and nano-indentation technique, respectively. Subsequently, bacterial adhesion onto the treated 3Y-TZP surface was evaluated using Streptococcus mitis and S. oralis. The results demonstrated that the combination of ultrasonic scaling and LTD significantly increased the Sa value (surface roughness parameter) of the polished 3Y-TZP surface from 1.6 nm to 117 nm. LTD affected the crystalline structure, causing phase transformation from the tetragonal to the monoclinic phase, and decreased both the contact angle and surface hardness. However, bacterial adhesion was not influenced by these changes in surface properties. The present study suggests that ultrasonic scaling may be acceptable for debridement of 3Y-TZP dental prostheses because it did not facilitate bacterial adhesion even in the combination with LTD, although it did cause slight roughening of the surface.

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          What future for zirconia as a biomaterial?

          The failure events of Prozyr femoral heads in 2001-2002 have opened a strong, controversial issue on the future of zirconia as a biomaterial. The aim of this paper is to review and analyze the current knowledge on ageing process and on its effect on the long term performance of implants in order to distinguish between scientific facts and speculation. Current state of the art shows the strong variability of zirconia to in vivo degradation, as a consequence of the strong influence of processing on ageing process. As different zirconia from different vendors have different process related microstructure, there is a need to assess their ageing sensitivity with advanced and accurate techniques, and ISO standards should be modified, especially to gain confidence from clinicians. There is a trend today to develop alumina-zirconia composites as an alternative to monolithic alumina and zirconia: the issue of ageing is also discussed for these composites.
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            The influence of abutment surface roughness on plaque accumulation and peri-implant mucositis.

            Bacterial adhesion to intra-oral, hard surfaces is firmly influenced by the surface roughness to these structures. Previous studies showed a remarkable higher subgingival bacterial load on rough surfaces when compared to smooth sites. More recently, the additional effect of a further smoothening of intra-oral hard surfaces on clinical and microbiological parameters was examined in a short-term experiment. The results indicated that a reduction in surface roughness below R(a) = 0.2 microns, the so-called "thresholds R(a)", had no further effect on the quantitative/qualitative microbiological adhesion or colonisation, neither supra- nor subgingivally. This study aims to examine the long-term effects of smoothening intra-oral hard transgingival surfaces. In 6 patients expecting an overdenture in the lower jaw, supported by endosseus titanium implants, 2 different abutments (transmucosal part of the implant): a standard machined titanium (R(a) = 0.2 microns) and one highly polished and made of a ceramic material (R(a) = 0.06 microns) were randomly installed. After 3 months of intra-oral exposure, supra- and subgingival plaque samples from both abutments were compared with each other by means of differential phase-contrast microscopy (DPCM). Clinical periodontal parameters (probing depth, gingival recession, bleeding upon probing and Periotest-value) were recorded around each abutment. After 12 months, the supra- and subgingival samples were additionally cultured in aerobic, CO2-enriched and anaerobic conditions. The same clinical parameters as at the 3-month interval were recorded after 12 months. At 3 months, spirochetes and motile organisms were only detected subgingivally around the titanium abutments. After 12 months, however, both abutment-types harboured equal proportions of spirochetes and motile organisms, both supra- and subgingivally. The microbial culturing (month 12) failed to detect large inter-abutment differences. The differences in number of colony- forming units (aerobic and anaerobic) were within one division of a logarithmic scale. The aerobic culture data showed a higher proportion of Gram-negative organisms in the subgingival flora of the rougher abutments. From the group of potentially "pathogenic" bacteria, only Prevotella intermedia and Fusobacterium nucleatum were detected for anaerobic culturing and again the inter-abutment differences were negligible. Clinically, the smoothest abutment showed a slightly higher increase in probing depth between months 3 and 12, and more bleeding on probing. The present results confirm the findings of our previous short-term study, indicating that a further reduction of the surface roughness, below a certain "threshold R(a)" (0.2 microns), has no major impact on the supra- and subgingival microbial composition.
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              Identification of early microbial colonizers in human dental biofilm.

              To elucidate the first colonizers within in vivo dental biofilm and to establish potential population shifts that occur during the early phases of biofilm formation. A 'checkerboard' DNA-DNA hybridization assay was employed to identify 40 different bacterial strains. Dental biofilm samples were collected from 15 healthy subjects, 0, 2, 4 and 6 h after tooth cleaning and the composition of these samples was compared with that of whole saliva collected from the same individuals. The bacterial distribution in biofilm samples was distinct from that in saliva, confirming the selectivity of the adhesion process. In the very early stages, the predominant tooth colonizers were found to be Actinomyces species. The relative proportion of streptococci, in particular Streptococcus mitis and S. oralis, increased at the expense of Actinomyces species between 2 and 6 h while the absolute level of Actinomyces remained unaltered. Periodontal pathogens such as Tannerella forsythensis(Bacteroides forsythus), Porphyromonas gingivalis and Treponema denticola as well as Actinobacillus actinomycetemcomitans were present in extremely low levels at all the examined time intervals in this healthy group of subjects. The data provide a detailed insight into the bacterial population shifts occurring within the first few hours of biofilm formation and show that the early colonizers of the tooth surface predominantly consist of beneficial micro-organisms. The early colonizers of dental plaque are of great importance in the succession stages of biofilm formation and its overall effect on the oral health of the host.
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                Author and article information

                Contributors
                Role: Data curationRole: Formal analysisRole: InvestigationRole: Writing – review & editing
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: SupervisionRole: Writing – original draftRole: Writing – review & editing
                Role: Funding acquisitionRole: InvestigationRole: Writing – review & editing
                Role: InvestigationRole: Methodology
                Role: Funding acquisitionRole: Investigation
                Role: ConceptualizationRole: SupervisionRole: Writing – review & editing
                Role: ConceptualizationRole: SupervisionRole: Writing – review & editing
                Role: ConceptualizationRole: SupervisionRole: Writing – review & editing
                Role: ConceptualizationRole: Formal analysisRole: SupervisionRole: Writing – review & editing
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                13 September 2018
                2018
                : 13
                : 9
                : e0203849
                Affiliations
                [1 ] Division of Molecular and Regenerative Prosthodontics, Tohoku University Graduate School of Dentistry, Sendai, Japan
                [2 ] Department of Advanced Free Radical Science, Tohoku University Graduate School of Dentistry, Sendai, Japan
                [3 ] Tohoku University School for Dental Laboratory Technicians, Sendai, Japan
                [4 ] Department of Cariology, Institute of Odontology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
                [5 ] Department of Clinical Dentistry/Faculty of Health Sciences, The Arctic University of Norway, Tromsø, Norway
                [6 ] Faculty of Nursing, Shumei University, Chiba, Japan
                Institute of Materials Science, GERMANY
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Author information
                http://orcid.org/0000-0002-6368-2569
                Article
                PONE-D-18-18557
                10.1371/journal.pone.0203849
                6136777
                30212528
                02fd67fc-1ac2-4146-b8eb-5d16c1014ebc
                © 2018 Nakazawa et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 21 June 2018
                : 28 August 2018
                Page count
                Figures: 7, Tables: 2, Pages: 18
                Funding
                Funded by: funder-id http://dx.doi.org/10.13039/501100001691, Japan Society for the Promotion of Science;
                Award ID: KAKENHI Grant-in-Aid for Scientific Research (C), 16K11583
                Award Recipient :
                Funded by: funder-id http://dx.doi.org/10.13039/501100001691, Japan Society for the Promotion of Science;
                Award ID: AKENHI Grant-in-Aid for Young Scientists (B), 16K20481
                Award Recipient :
                This research was supported by Japan Society for the Promotion of Science ( https://www.jsps.go.jp/); KAKENHI Grant-in-Aid for Scientific Research (C), 16K11583 to RI, and KAKENHI Grant-in-Aid for Young Scientists (B), 16K20481 to AH. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Research and Analysis Methods
                Equipment Preparation
                Equipment Sterilization
                Autoclaving
                Biology and Life Sciences
                Biotechnology
                Medical Devices and Equipment
                Assistive Technologies
                Prosthetics
                Medicine and Health Sciences
                Medical Devices and Equipment
                Assistive Technologies
                Prosthetics
                Engineering and Technology
                Manufacturing Processes
                Surface Treatments
                Biology and Life Sciences
                Microbiology
                Bacteriology
                Bacterial Biofilms
                Biology and Life Sciences
                Microbiology
                Biofilms
                Bacterial Biofilms
                Research and Analysis Methods
                Microscopy
                Light Microscopy
                Confocal Microscopy
                Confocal Laser Microscopy
                Biology and Life Sciences
                Organisms
                Bacteria
                Physical Sciences
                Materials Science
                Material Properties
                Surface Properties
                Research and Analysis Methods
                Specimen Preparation and Treatment
                Custom metadata
                All relevant data are within the paper and its Supporting Information files.

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