Risk aspects of dental restoratives: From amalgam to tooth-colored materials

Dental materials' choice of patients has considerably changed. Whereas cast gold and amalgam have been the predominant biomaterials for decades, today toothcolored materials like resin-based composites and ceramics are more and more successful. However, are we going to replace a good but biologically questionable material(amalgam) with an equal material(resin composite) being more esthetic but also biologically questionable? For amalgam, long-term clinical studies reported some significant hints that in single cases amalgam may be a health hazard for patients, finally Norway banned amalgam completely. The main advantage of a resin-based composite over amalgam is its tooth-like appearance and more or less absence of extensive preparation rules. For many years it was believed that resin-based composites may cause pulpal injury. However, pulpal injury associated with the use of resin-based composites is not correlated with their cytotoxic properties. Nevertheless, resin-based composites and other dental materials require rigorous safety evaluation and continuous monitoring to prevent adverse events similar like with amalgam. Because of nonbiocompatible pulp responses to resin-based composites and amalgam, they should not be placed in direct contact with the dental pulp. The less dentin remaining in the floor of preparations between resin-based composites or other dental materials is more likely to cause pulpitis. Percentage of patients and dental practitioners who display allergic reactions is between 0.7% and 2%. The release of cytotoxic monomers from resin-based materials is highest after polymerization and much lower after 1 wk. Substances released from resin-based composites have been shown to be toxic in cytotoxicity tests. Nevertheless, in vitro cytotoxicity assays have shown that amalgam has greater toxic effects than resin-based composites, sometime 100-700-fold higher. Altogether, the risk of side-effects is low, but not zero, especially for dental personnel.

Synthesis of CaO-SiO₂Compounds Using Materials Extracted from Industrial Wastes

Mineral trioxide aggregate (MTA) cement is an attractive material in endodontic dentistry. The purpose of this study was to produce calcium silicate, which is a major component of MTA, from waste materials. A dental alginate impression gel and used chalks were selected and mixed in a suitable ratio (Code: EXP). As a control, CaCO3 and a commercial diatomite were used (Code: CON). Each powder was heated to 850。C and 1000。C, and then kneaded with water. TG-DTA, compressive tests, SEM observations, elemental mapping analyses, and XRD analyses were performed. TG-DTA indicated that weight reduction of CaCO3 started at 600。C, and it completely decomposed on heating at 850。C. The strength was affected by the temperature. After heating, CaCO3 was transformed into CaO and/or Ca2SiO4, and Ca(OH)2 was formed by mixing with water. There were no differences between EXP and CON. These data suggested that recycled wastes might be promising MTA sources.

高分子聚合材料表面润湿性对成纤维细胞贴附能力的影响

目的:研究高分子聚合体表面润湿性对成纤维细胞初期贴附能力的影响。方法:使用薄膜等离子体聚合法在圆形盖玻片表面生成六甲基二硅氧烷(Hexamethyldisiloxane,HMDSO)薄膜聚合体,然后用低温氧等离子体轰击聚合体表面,根据轰击时间的不同形成一系列的不同润湿性表面,将成纤维细胞系L929接种于不同润湿性表面,观察6h、12h时细胞的贴附率,并观察细胞的形态。结果:随着氧等离子体轰击时间的增加,HMDSO聚合体表面接触角从106°下降为0°,显示表面由高度憎水变为高度亲水。成纤维细胞在亲水表面较憎水表面有更高的早期贴附率,细胞伸展更充分。结论:高分子聚合体的表面润湿性对成纤维细胞的早期贴附和伸展有显著的影响。亲水性表面更有利于细胞的早期贴附和伸展。

高分子聚合体表面润湿性研究模型的建立

目的:利用低温等离子体轰击法建立高分子聚合体表面润湿性研究模型。方法:使用氧低温等离子体轰击六甲基二硅氧烷薄膜聚合体表面,测定表面接触角,建立轰击时间-表面接触角曲线,建立线型回归方程。观察在不同介质中保存时材料表面接触角的变化情况。结果:经过氧等离子体轰击后,六甲基二硅氧烷薄膜聚合体表面接触角明显下降,与处理时间呈现负相关性。在空气中保存时,表面接触角随时间逐渐上升,0度接触角表面24 h后上升为20°左右,而在双蒸水中保存的表面接触角基本保持不变。结论:氧等离子体轰击法能可控性地改变六甲基二硅氧烷薄膜聚合体表面润湿性,处理后的表面在水中接触角保持稳定,该方法可以用来建立表面润湿性研究模型。

QCM-D技术在不同润湿性表面蛋白吸附研究中的应用

目的:利用石英晶体微平衡-分散(QCM-D)技术研究白蛋白在高度亲水和高度疏水表面的吸附情况。方法:利用等离子聚合技术在8片圆形石英传感器上形成六甲基二硅氧烷薄膜聚合体薄膜,将4片上述试样采用低温氧等离子体轰击80 s,这两种表面分别代表高度疏水及高度亲水表面。将处理后的两种传感器装入QCM-D检测仪,将400 mg/L的牛血白蛋白溶液引入传感检测室,观察共振频率和离散因子随时间的变化,计算出蛋白的吸附量。结果:白蛋白在两种表面的吸附主要在早期10 s中完成,此后吸附变慢,在30 min左右达到吸附-离散平衡,30 min时白蛋白在高度疏水表面的平均吸附量为294.6 ng/cm2,而在高度亲水表面平均吸附量为235.1 g/cm2,两者有显著性差异。结论:QCM-D可以用来精确测定蛋白质在石英传感器表面的吸附,高度疏水性表面对白蛋白有较高的吸附能力。

Binary titanium alloys as dental implant materials—a review

Titanium(Ti)has been used for long in dentistry and medicine for implant purpose.During the years,not only the commercially pure Ti but also some alloys such as binary and tertiary Ti alloys were used.The aim of this review is to describe and compare the current literature on binary Ti alloys,including Ti-Zr,Ti-In,Ti-Ag,Ti-Cu,Ti-Au,Ti-Pd,Ti-Nb,Ti-Mn,Ti-Mo,Ti-Cr,Ti-Co,Ti-Sn,Ti-Ge and Ti-Ga,in particular to mechanical,chemical and biological parameters related to implant application.Literature was searched using the PubMed and Web of Science databases,as well as google without limiting the year,but with principle key terms such as‘Ti alloy’,‘binary Ti’,‘Ti-X’(with X is the alloy element),‘dental implant’and‘medical implant’.Only laboratory studies that intentionally for implant or biomedical applications were included.According to available literatures,we might conclude that most of the binary Ti alloys with alloying<20%elements of Zr,In,Ag,Cu,Au,Pd,Nb,Mn,Cr,Mo,Sn and Co have high potential as implant materials,due to good mechanical performance without compromising the biocompatibility and biological behaviour compare to cp-Ti.

Effect of colouring green stage zirconia on the adhesion of veneering ceramics with different thermal expansion coefficients

This study evaluated the adhesion of zirconia core ceramics with their corresponding veneering ceramics, having different thermal expansion coefficients （TECs）, when zirconia ceramics were coloured at green stage. Zirconia blocks （N=240; 6 mm x 7 mm x 7 mm） were manufactured from two materials namely, ICE Zirconia （Group 1） and Prettau Zirconia （Group 2）. In their green stage, they were randomly divided into two groups. Half of the specimens were coloured with colouring liquid （shade A2）, Three different veneering ceramics with different TEC （ICE Ceramic, GC Initial Zr and IPS e.max Ceram） were fired on both coloured and non-coloured zirconia cores. Specimens of high noble alloys （Esteticor Plus） veneered with ceramic （VM 13） （n= 16） acted as the control group. Core-veneer interface of the specimens were subjected to shear force in the Universal Testing Machine （0.5 mm-min-1）. Neither the zirconia core material （P=0.318） nor colouring （P=0.188） significantly affected the results （three-way analysis of variance, Tukey＇s test）. But the results were significantly affected by the veneering ceramic （P=0.000）. Control group exhibited significantly higher mean bond strength values （45.7__.8） MPa than all other tested groups （（27.1__.4.1）-（39.7__.4.7） and （27.4__.5.6）-（35.9___4.7） MPa with and without colouring, respectively） （P^0.001）. While in zirconia-veneer test groups, predominantly mixed type of failures were observed with the veneering ceramic covering ~ 1/3 of the substrate surface, in the metal-ceramic group, veneering ceramic was left adhered 1/3 of the metal surface. Colouring zirconia did not impair adhesion of veneering ceramic, but veneering ceramic had a significant influence on the core-veneer adhesion. Metal-ceramic adhesion was more reliable than all zirconia-veneer ceramics tested.

Biomimetic Mineralization and Degradation of Bioelectret Film in vitro

To explore the behaviour of bioelectret film in mineralization and degradation in vitro, chitosan film was prepared and polarized in an electric field at room temperature. Polarized and unpolarized chitosan films were soaked in 1.5 × SBF （ simalated body fluid） .sohaions for 7, 14 and 28 d at 37℃. The negativelycharged surface of the bioelectret film promoted greater mineralization than did unpolarized chitosan. Apatite formarion on the surface of the films was identified by X- ray diffraction and scanning electron microscopy. Bioelectret films had a higher rate of degradation than unpolarized material in vitro （ pH 7.4, 37℃ ） in the presence of 1.5 mg/mL lysozyme aver 7 d. The electret effect facilitated the degradation of the film. After 14 d, the degradation rates of the two kinds of film were the same.

Cell Proliferation Ability of Mouse Fibroblast-Like Cells and Osteoblast-Like Cells on a Ti-6Al-4V Alloy Film Produced by Selective Laser Melting

Successful regeneration of tissues and organs relies on the application of suitable substrates or scaffolds in scaffold-based regenerative medicine. In this study, Ti-6Al-4V alloy films (Ti alloy film) were produced using a three-dimensional printing technique called Selective Laser Melting (SLM), which is one of the metal additive manufacturing techniques. The thickness of produced Ti alloy film was approximately 250 μm. The laser-irradiated surface of Ti alloy film had a relatively smooth yet porous surface. The non-irradiated surface was also porous but also retained a lot of partially melted Ti-6Al-4V powder. Cell proliferation ability of mouse fibroblast-like cells (L929 cells) and mouse osteoblast-like cells (MC3T3-E1 cells) on both the surfaces of Ti alloy film was examined using WST assay. Both L929 and MC3T3-E1 cells underwent cell proliferation during the culture period. These results indicate that selective laser melting is suitable for producing a cell-compatible Ti-6Al-4V alloy film for biomaterials applications.

Osteocyte morphology and orientation in relation to strain in the jaw bone

Bone mass is important for dental implant success and is regulated by mechanoresponsive osteocytes. We aimed to investigate the relationship between the levels and orientation of tensile strain and morphology and orientation of osteocytes at different dental implant positions in the maxillary bone. Bone biopsies were retrieved from eight patients who underwent maxillary sinus-floor elevation with β-tricalcium phosphate prior to implant placement. Gap versus free-ending locations were compared using 1) a three-dimensional finite-element model of the maxilla to predict the tensile strain magnitude and direction and 2) histology and histomorphometric analyses. The finite-element model predicted larger, differently directed tensile strains in the gap versus freeending locations. The mean percentage of mineralised residual native-tissue volume, osteocyte number(mean ± standard deviations:97 ± 40/region-of-interest), and osteocyte shape(90% elongated,10% round) were similar for both locations. However, the osteocyte surface area was 1.5-times larger in the gap than in the free-ending locations, and the elongated osteocytes in these locations were more cranially caudally oriented. In conclusion, significant differences in the osteocyte surface area and orientation seem to exist locally in the maxillary bone, which may be related to the tensile strain magnitude and orientation. This might reflect local differences in the osteocyte mechanosensitivity and bone quality, suggesting differences in dental implant success based on the location in the maxilla.

Mechanical and biological properties of Ti–(0–25 wt%)Nb alloys for biomedical implants application

Binary titanium–niobium(Ti–Nb)alloys have recently been attracted due to low Young’s moduli and non-toxic properties.This study explores the influence of low Nb content(0–25 wt%)on the comprehensive parameters of tensile stress–strain relationships(ultimate strength(rUTS),yield strength(r0.2)and elastic modulus(E)),surfaces properties(Vickers microhardness,surface roughness(Ra),water contact angle(WCA),X-ray diffraction(XRD)and scanning electron microscopy(SEM)),corrosion resistance(in artificial saliva and lactic acid)and biological properties(cytotoxicity and alkaline phosphatase activity of MC3T3-E1 pre-osteoblasts)of Ti–xNb alloys(x紏5,10,15,20 and 25 wt%),with using commercially pure grade 2 titanium(cp-Ti)as control.XRD results shown that all the Ti–xNb alloys comprised atb Ti alloy phases,such that the b phase increased correspondingly with the increased amount of Nb in the alloy,as well as the reduction of E(69–87 GPa).Except Ti–5Nb,all other Ti–xNb alloys showed a significantly higher hardness,increased rUTS and r0.2,and decreased WCA compared with cp-Ti.No corrosion was detected on Ti–xNb alloys and cp-Ti in artificial saliva and lactic acid solutions.The cytotoxicity of Ti–xNb alloys was comparable to that of cp-Ti in MC3T3-E1 pre-osteoblasts without interference from differentiation behaviour,but the proliferation rate of the Ti–5Nb alloy was lower than other groups.In overall,binary Ti–(10–25 wt%)Nb alloys are promising candidate for orthopaedic and dental implants due to their improved mechanical properties and comparable biological performance,while Ti–5Nb should be used with caution.

Candida albicans aspects of binary titanium alloys for biomedical applications

Titanium and its alloys are widely used in biomedical devices,e.g.implants,due to its biocompati-bility and osseointegration ability.In fact,fungal(Candida spp.)infection has been identified as one of the key reasons causing the failure of the device that is inevitable and impactful to the society.Thus,this study evaluated the surface morphology,surface chemical composition and Candida albicans adhesion on specimens of 16 binary Tialloys(-5 wt%of any one of the alloy elements:Ag,AI,Au,Co,Cr,Cu,Fe,In,Mn,Mo,Nb,Pd,Pt,Sn,V and Zr)compared with cp-Ti,targeting to seek for the binary Ti-alloys which has the lowest C.albicans infection.Candida albicans cultures were grown on the specimens for 48 h,and colony forming units(CFUs)and real-time polymerase chain reaction(RT-PCR)were used to evaluate the biofilm formation ability.Scanning electron mi-croscopy and confocal laser scanning microscopy confirmed the formation of C.albicans biofilm on all specimens'surfaces,such that CFU results showed Ti-Mo,Ti-Zr,Ti-AI and Ti-V have less C.albicans formed on the surfaces than cp-Ti.RT-PCR showed Ti-Zr and Ti-Cu have significantly higher C.albicans DNA concentrations than Ti-AI and Ti-V(P<0.05),whereas Ti-Cu has even showed a statistically higher concentration than Ti-Au,Ti-Co,Ti-In and Ti-Pt(P<0.05).This study confirmed that Ti-Mo,Ti-Zr,Ti-AI and Ti-V have lower the occurrence of C.albicans which might be clinically advantageous for medical devices,but Ti-Cu should be used in caution.