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Influence of Bioactive Glass-Coating of Zirconia Implant Surfaces on Human

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Influence of Bioactive Glass-Coating of Zirconia Implant Surfaces on Human d e n t a l m a t e r i a l s 3 5 ( 2 0 1 9 ) 862–870 Available online at www.sciencedirect.com ScienceDirect jo urnal homepage: www.intl.elsevierhealth.com/journals/dema Influence of bioactive glass-coating of zirconia implant surfaces on human osteoblast behavior in vitro a,b,∗ b a b Nadja Rohr , J. Barbara Nebe , Fredy Schmidli , Petra Müller , c c a Michael Weber , Horst Fischer , Jens Fischer a Division of Dental Materials and Engineering, Department of Reconstructive Dentistry, University Center for Dental Medicine, University of Basel, Basel, Switzerland b Department of Cell Biology, University Medical Center Rostock, Rostock, Germany c Department of Dental Materials and Biomaterials Research, RWTH Aachen University Hospital, Aachen, Germany a r t a b i c s t l e i n f o r a c t Article history: Objective. The recently developed bioactive glass PC-XG3, which is suitable to coat zirco- Received 25 October 2018 nia implant surfaces with high adhesion strength may reduce the time of osseointegration Received in revised form and the marginal bone loss following implantation. The glass composition has been previ- 14 February 2019 ously evaluated for cytotoxicity on fibroblast cells, and will now be used to evaluate the cell Accepted 27 February 2019 behavior of osteoblast cells. Methods. Three different surface morphologies were created with PC-XG3 on zirconia discs. A clinically tested zirconia implant surface as well as polished and machined zirconia served Keywords: as a reference. Cell viability after 24 h, cell spreading after 30 min and 24 h and the respec- Zirconia implant tive morphology of human osteoblasts using scanning electron microscopy were evaluated. Bioglass coating Additionally, the corrosive process of PC-XG3 in cell culture medium up to 7 d was measured. Human osteoblasts Results. Initial cell behavior of human osteoblasts was not accelerated by the PC-XG3 surface Microstructure when compared to zirconia. Additionally, it was found that a decreased surface roughness promoted initial cell spreading. Storage in cell culture medium resulted in the accumulation of C and N on the bioglass surface while Mg, Si, K and Ca were decreased and crack formation was observed. Significance. Since initial spreading quality to a biomaterial is a crucial factor that will deter- mine the subsequent cell function, proliferation, differentiation, and viability it can be assumed that a coating of zirconia implants with this bioactive glass will unlikely reduce osseointegration time. © 2019 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved. ∗ Corresponding author at: Division of Dental Materials and Engineering, Department of Reconstructive Dentistry, University Center for Dental Medicine, University of Basel, Hebelstrasse 3, CH-4056, Basel, Switzerland. E-mail address: [email protected] (N. Rohr). https://doi.org/10.1016/j.dental.2019.02.029 0109-5641/© 2019 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved. d e n t a l m a t e r i a l s 3 5 ( 2 0 1 9 ) 862–870 863 Table 1 – Zirconia specimens were prepared or coated 1. Introduction with bioglass PCX-G3 as given in the table to create differing micro-structured surfaces. Dental implants made of zirconia can be considered an Code Surface esthetic and biocompatible alternative to the well-established titanium implants [1–5]. Zirconia is however susceptible to Zp Zirconia, sintered, hot isostatically pressed, polished tensile stress and displays a high elastic modulus of 210 GPa Zm Zirconia, sintered, hot isostatically pressed Z14 Zirconia, cer.face 14 [6]. To accelerate osseointegration, surface modifications of ◦ G1 PCX-G3, sintered 830 C 100 min the endosseous part of the implant are created using dif- ◦ ◦ G2 PCX-G3, sintered 830 C 100 min + sintered 760 C 10 min ferent techniques. For titanium it has been shown that the ◦ ◦ G3 PCX-G3, sintered 830 C 100 min + sintered 750 C 25 min implant surface should be moderately roughened with an Ra of 1 to 2 ␮m to increase bone implant contact and resistance to torque [7]. For zirconia implants a micro-structuring of the SiO2 content in bioglasses are reported to feature fast bonding endosseous implant part has therefore also been postulated. rates to tissue within 5–10 days [13,15]. Zirconia implants pre-treated with sandblasting, hydrofluo- Bioglass 45S5 invented in the late 1960s by Hench LL, is still ric acid etching [8] or laser, are currently available. However, considered as the gold standard of bioactive materials [12,16]. three-year data on the clinical performance of commercially However, due to its high crystallization tendency and the high −6 −1 × available zirconia implants only exists for the sandblasted, coefficient of thermal expansion (CTE) of 15.1 10 K [11], hydrofluoric acid etched ZLA surface (pure, Straumann, Basel, Bioglass 45S5 is not suitable for a thermal coating process on −6 −1 × Switzerland) [5] and additionally heat treated cer.face 14 sur- zirconia with a CTE of 10.8 to 12.5 10 K [17,18]. There- face (ceramic implant, vitaclinical, VITA, D-Bad Säckingen) fore, the glass composition of Bioglass 45S5 has recently been [4]. modified by a partial substitution of Na2O and CaO by K2O and The production of a cer.face 14 zirconia implant surface MgO to display a similar thermal expansion as zirconia [19]. 2+ is very time consuming, expensive and etching with 40 % This absorbable glass called PC-XG3 also contains Ca and 3− hydrofluoric acid a potential health risk to the technical oper- PO4 that potentially contribute to the mineralization pro- ator. The etching procedure is, however, required to create a cess. Smooth and micro-structured glass coatings of PC-XG3 micro-structured surface to increase the implants torque and were applied on polished zirconia surfaces with promising achieve its osseointegration. results [19]. The glass coating revealed a strong adhesion to the Balmer et al. revealed that a certain immediate loading of zirconia substrates as well as a significant bioactive behavior zirconia implants is possible without crestal bone loss [4]. It in simulated body fluid (SBF) in in vitro experiments. The cell would be attractive to both, dentist and patient if the final proliferation of L929 mouse fibroblasts on the PC-XG3 glass restoration were placed directly after implant insertion using was similar to the one on bioglass 45S5 and both displayed the technique to establish an appropriate emergence profile a very low cytotoxicity of around 10% [19]. A complete dis- ␮ recommended by Lambert and Mainjot [9]. This would elimi- solution of a layer of 50 m of PC-XG3 when in contact to nate additional appointments with the patient and therefore artificial saliva can be expected within 30 days. In a next step significantly reduce time and costs. If the osseointegration the osteoblast behavior on the bioactive glass PC-XG3 has to be process could be accelerated even faster to guarantee the analyzed to evaluate its potential for improving the osseoin- successful placement of the final restoration with immediate tegration behavior. loading directly after inserting the implant, the efficiency of The objective of the present study was therefore to evaluate zirconia implant placement could be significantly increased. osteoblast behavior on bioactive glass PC-XG3 and to further Therefore, in order to improve the clinical concept, further characterize its corrosion. Three differently micro-structured research on how to improve the quality of osseointegration glass coatings were created and compared to polished and and reduce healing time by optimizing the surface morphol- machined zirconia as well as the clinically tested cer.face ogy of zirconia implants is of high priority. 14 implant surface. Hypothesis were that (1) cell viability of To address the mentioned requirements and potentially human osteoblasts will be increased on PC-XG3 coated sur- slow down the marginal bone loss following implantation faces compared to zirconia surfaces and (2) cell spreading will coatings made of bioactive glasses can be applied onto the be accelerated on PC-XG3 surfaces compared to zirconia sur- implant surfaces [10–12]. faces. Bioactive glasses are able to create a direct chemical bond to bone over the formation of hydroxyl carbonated apatite on 2. Materials and methods its surface [13,14]. The mechanism is initiated by the rapid dissolution of alkalis from the glass surface when in con- 2.1. Specimen production tact with aqueous solutions. A Ca-rich and P-rich layer at the inner alkali-depleted silica layer and consequently, a layer of Six different surface morphology options for a zirconia hydroxyapatite or hydroxyl carbonated apatite is created on implant surface were compared in the present study (Table 1). the glass surface [12]. The bioglass itself undergoes degra- Sintered and hot isostatically pressed yttria-stabilized zirco- dation over time when in contact with body fluids, being nia specimens with a diameter of 13 mm and a height of gradually replaced by new bone [13]. The corrosion kinetic 2 mm were provided by the manufacturer (VITA Zahnfabrik, depends on the glass network structure, type of ions present Bad Säckingen, Germany). These specimens were used with in the glass and dissolution medium [13]. Thus, 45–52 % of an as machined, sintered and hot isostatically (Zm) as well 864 d e n t a l m a t e r i a l s 3 5 ( 2 0 1 9 ) 862–870 as with an additionally polished surface (Zp). The surface of a and maximum height (Sz) was calculated (filter tc ␭c 20.0 ␮m; zirconia implant (“cer.face 14”), with documented clinical suc- area 7000 ␮m). cess [4] was provided by the manufacturer of the implant (Z14). To verify 3D data also 2D roughness parameters arithmeti- To create the Z14 structure, the zirconia substrates were sand- cal mean height (Ra) and maximum height of profile (Rz) were blasted, etched with 40% hydrofluoric acid and heat treated as measured with a profilometer (T1000/TKK50, Hommelwerke, previously described [8].
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