Key Engineering Materials Vols. 361-363

Abstract: Dental ceramic-bioactive glass composites support the attachment and proliferation of human periodontal ligament cells, while their immersion in a simulated body fluid (SBF) results in the precipitation of biological hydroxyapatite further supporting cell proliferation [1]. The aim of the present study was the comparative evaluation of three dental ceramic-bioactive glass composites’ crystal structure relative to bioactive glass amount and the evaluation of their bioactivity. All composites consisted of leucite and Na2CaSi3O9 crystals dispersed in amorphous glassy matrix. Leucite and Na2CaSi3O9 crystals decreased significantly in all composites with the highest amount of dental ceramic, which did not precipitated apatite during the examined immersion time in SBF. An increase of Na2CaSi3O9 crystals in the composites with the highest amount of bioactive glass resulted in faster apatite formation. Increased bioactivity was linearly correlated to increased amount of bioactive glass.

Abstract: The present study evaluated the influence of different radiopacifiers on an established mineral trioxide aggregate (MTA)-like Portland cement system. Commercial MTA contains bismuth oxide (Bi2O3) as the radiopacifier and inert alternatives tested were barium sulphate (BaSO4), lanthanum oxide (La2O3) and tantalum pentoxide (Ta2O5). The radiopacity of the different formulations was measured with densitometry, whilst relative porosity was determined using helium pycnometry and compressive strength was measured as an indicator for the potential longevity of the alternative cement formulations. At 20wt% radiopacifier content the order of radiopacity was, Bi2O3 (3.71mm Aluminium equivalent), Ta2O5 (2.76mm Al), La2O3 (1.85mm Al) and BaSO4 (1.48mm Al). The commercial MTA control had a radiopacity of 3.65mm Al. The addition of all radiopacifiers caused a deterioration in strength and increased porosity; the incorporation of 20wt% Bi2O3 reduced strength from 68MPa by 36%. Ta2O5-containing cement had a strength comparable with that containing Bi2O3 (43MPa), whilst La2O3 and BaSO4 addition generated even weaker cements. Commercial MTA had a similar strut density to the Bi2O3- containing model system although had a lower strength (34MPa) due to its higher porosity. Bi2O3 appeared to be the best of the investigated radiopacifiers for this endodontic filling material as it provided the highest mechanical stability, lowest porosity and was the most radiopaque.

Abstract: This study was performed to investigate the bond strength between 4 dentin adhesives and resin luting cements by means of μTBS test. The materials used in this study were four resin cements (Choice, Panavia F, RelyX ARC, Bistite II DC), one 3-step adhesive (All-Bond2), one 2- step self-etching adhesive (Clearfil SE-Bond) and two 1-step self-etching adhesives(Prompt L-Pop and One-Up Bond F). Combination of 4 different dentin adhesives with 4 resin cements made up 16 experimental groups. Extracted human mandibular third molars without caries and restoratives were stored in saline and used within 1 month of extraction. All adhesive systems and resin cements were manipulated and applied to the dentin surfaces according to the manufactures’ instructions. The resin composite “overlays” prepared with 6 mm thickness (Tescera, Bisco Inc., Schaumburg, IL, USA) were luted with each resin cement. Each sample was measured μTBS. 1-step self-etching adhesives coupled with all resin luting cements used in this study resulted in lower bond strength except of OU-PA group. When Choice, RelyX ARC and Bistite II were used, Clearfil SE-Bond showed significantly higher μTBS values than 1-step self-etching adhesives (p<0.05). Clearfil SE-Bond did not show significant μTBS values than All-Bond 2 that is conventional 3-step dentin adhesive (p>0.05).

Abstract: Human teeth has “structure” and yet is mostly treated as material. Differentiation between material and structure is crucial to understand complex biological material such as human dentine. The aim of the present work is to determine the bioceramic gradient phases of the crystal structure of the teeth across the crown and root region with age. Around 50 samples of teeth of different age groups were collected, decontaminated and sintered at 400, 600 and 800°C. After removal of the enamel the root and crown regions were machined and characterized for their vibrational states by FTIR investigations. The studies indicate the presence of hydroxyapatite as the major phase after sintering along with the typical hydroxyl peaks. A weight loss ranging from 7 - 42 % after sintering at 400 and 800°C respectively was observed across the different age groups. A through analysis would provide us an understanding in studying the desired nature of the teeth and kinetics of tooth mineralization.

Abstract: Leucite (KAlSi2O6) is the main crystalline phase in feldspathic dental materials used for ceramic-fused-to-metal restorations. It occurs in two modifications, low temperature – tetragonal and at temperatures above 600 °C high temperature – cubic modification. The aim of this work was to develop a low-temperature preparation technology of submicron leucite powders with varying ratio of tetragonal and cubic modification. The results show that analcime synthesized in hydrothermal conditions is the suitable precursor for the preparation of leucite with controlled fraction of the c-modification. Homogenous t-leucite having particle size from 2 - 4 μm was prepared by 4h ion-exchange in 4M KCl. Partially stabilized c-leucite was obtained by dual ionexchange; 4h in 4M CsCl led to 48 % of c-modification in the final product.

Abstract: The demand in the medical industry for load bearing materials is ever increasing. The techniques currently used for the manufacture of such materials are not optimized in terms of porosity and mechanical strength. This study adopts a microstructural shape design approach to the production of open porous materials, which utilizes spatial periodicity as a simple way to generate the models. A set of triply periodic surfaces expressed via trigonometric functions in the implicit form are presented. A geometric description of the topology of the microstructure is necessary when macroscopic properties such as mechanical strength, stiffness and isotropy are required to be optimised for a given value of volume fraction. A distinction between the families of structures produced is made on the basis of topology. The models generated have been used successfully to manufacture both a range of structures with different volume fractions of pores and samples of functional gradient material using rapid prototyping.

Abstract: Porous Titanium Scaffolds were produced by using a rapid prototyping technique. These scaffolds were either coated or not with a calcium phosphate coating via an eletrodeposition method. Rat bone marrow mesenchymal stem cells were cultured on the scaffolds at a density of 106 cells/scaffold for a period of 3 days. Cell proliferation was measured by using the Alamar Blue assay. The scaffolds were observed by SEM and polarized light microscopy. Constructs were then implanted subcutaneously for 4 weeks in syngenic rats. Cells proliferated well after seeding. After subcutaneous implantation, histology and SEM revealed the presence of uniform coatings as well as Ca and P deposits in the non-coated scaffolds suggesting mineralization.

Abstract: A new porous unsintered CaP-compound material for bone graft substitutes is described. A modified sol-gel freeze casting process enables preparation of sophisticated shaped bodies. By adapted chill molds and the variation of the freeze process the porosity of the material can be engineered, i.e. the pore size distribution as well as the preferred direction of the oblong pores. Thereby controlled osteoconduction can be achieved. The mechanical properties of the CaP compounds are improved by embedding supporting structures. Due to its huge inner surface the material can serve as a scaffold supplied with agents.

Abstract: In the last few years new fabrication methods, called rapid prototyping (RP) techniques, have been developed for the fabrication of hydroxyapatite scaffolds for bone substitutes or tissue engineering applications. With this generative fabrication technology an individual tailoring of the scaffold characteristics can be realised. In this work two RP techniques, a direct (dispense-plotting) and an indirect one (negative mould technique), are described by means of fabricating hydroxyapatite (HA) scaffolds for bone substitutes or bone tissue engineering. The produced scaffolds were characterised, mainly regarding their pore and strut characteristics. By these data the performance of the two fabrication techniques was compared. Dispense-plotting turned out to be the faster technique while the negative mould method was better suited for the fabrication of exact pore and strut geometries.

Abstract: Colloidal processing was used to cast zirconia and hydroxyapatite materials. The cast materials reached densities around 99% when sintered at 1500°C and 1200°C respectively. By controlling the colloidal process the sintered density of hydroxyapatite was also reduced to around 80% when the same sintering condition was used. The casting process was combined with free form fabrication to prepare designed scaffolds with identical macroporosity. These scaffolds were used to evaluate the early bone tissue response in rabbit femur. After six weeks of implantation the bone area in scaffolds of zirconia and hydroxyapatite were compared. In scaffolds of hydroxyapatite the bone area was roughly three times larger compared to corresponding scaffolds of zirconia. When the scaffolds of hydroxyapatite also contained an open microporosity of around 20% the amount of bone was even more pronounced. The results showed the importance of the material composition and the microstructure on the bone regenerating performance of scaffolds.