RESUMEN
In this study, sintering effects on microstructural behavior of bovine derived hydroxyapatite doped with powder mullite are considered in the temperature range between 1000°C and 1300°C. Results show that maximum values of both compressive strength and microhardness are achieved in the samples sintered at 1200°C for all mullite additions of 5, 7.5, 10 and 12.5wt%. Moreover, above 1000°C, decomposition of HA and new phase formations such as whitlockite and gehlenite play a major role in both compressive strength and microhardness properties which increase up to 10wt% mullite reinforcement.
Asunto(s)
Durapatita/química , Silicatos de Aluminio , Animales , Bovinos , Fuerza Compresiva , Ensayo de Materiales , PolvosRESUMEN
The fabrication and characterization of bovine hydroxyapatite (BHA) and cerium oxide (CeO2) composites are presented. CeO2 (at varying concentrations 1, 5 and 10wt%) were added to calcinated BHA powder. The resulting mixtures were shaped into green cylindrical samples by powder pressing (350MPa) followed by sintering in air (1000-1300°C for 4h). Density, Vickers microhardness (HV), compression strength, scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies were performed on the products. The sintering behavior, microstructural characteristics and mechanical properties were evaluated. Differences in the sintering temperature (for 1wt% CeO2 composites) between 1200 and 1300°C, show a 3.3% increase in the microhardness (564 and 582.75HV, respectively). Composites prepared at 1300°C demonstrate the greatest compression strength with comparable results for 5 and 10wt% CeO2 content (106 and 107MPa) which are significantly better than those for 1wt% and those that do not include any CeO2 (90 and below 60MPa, respectively). The results obtained suggest optimal parameters to be used in preparation of BHA and CeO2 composites, while also highlighting the potential of such materials in several biomedical engineering applications.
Asunto(s)
Materiales Biocompatibles/química , Sustitutos de Huesos/química , Cerio/química , Durapatita/química , Animales , Ingeniería Biomédica , Bovinos , Cerámica , Fuerza Compresiva , Dureza , Ensayo de Materiales , Microscopía Electrónica de Rastreo , Polvos , Presión , Estrés Mecánico , TemperaturaRESUMEN
The influence of bond-coating on the mechanical properties of plasma-spray coatings of hydroxyatite on Ti was investigated. Plasma-spray powder was produced from human teeth enamel and dentine. Before processing the main apatite coating, a very thin layer of Al2O3/TiO2 was applied on super clean and roughened, by Al2O3 blasting, Ti surface as bond-coating. The experimental results showed that bond-coating caused significant increase of the mechanical properties of the coating layer: In the case of the enamel powder from 6.66 MPa of the simple coating to 9.71 MPa for the bond-coating and in the case of the dentine powder from 6.27 MPa to 7.84 MPa, respectively. Both tooth derived powders feature high thermal stability likely due to their relatively high content of fluorine. Therefore, F-rich apatites, such those investigated in this study, emerge themselves as superior candidate materials for calcium phosphate coatings of producing medical devices. The methods of apatite powder production and shaping optimization of powder particles are both key factors of a successful coating. The methods used in this study can be adopted as handy, inexpensive and reliable ways to produce high quality of powders for plasma spray purposes.
Asunto(s)
Apatitas , Fosfatos de Calcio/química , Materiales Biocompatibles Revestidos , Apatitas/química , Cerámica/química , Esmalte Dental/química , Dentina/química , Humanos , Polvos , Reología , TitanioRESUMEN
STATEMENT OF PROBLEM: Determination of the fracture resistance of various restorative materials in Class II approximal slot restorations has not been studied. PURPOSE: This study evaluated the effects of retention grooves and different restorative materials in Class II approximal slot restorations. To explore the possibilities for further research, the probable effects of preparation size and loading angle were investigated in a limited manner. MATERIAL AND METHODS: Ninety sound, caries-free human maxillary premolars were divided into 9 groups. The cavities were prepared either by hand or in a computer-controlled CNC machine with or without retention grooves. Four were restored with adhesive amalgam, another 4 with composite, and a single group with Compomer resin. The gingival floor depth was 1.5 mm. The specimens were loaded at an angle of 13. 5 degrees to their longitudinal axes by using a computer-controlled material testing machine until failure occurred. For one specific preparation of adhesive amalgam, loading was applied at 0 and 30 degrees to determine the probable effects of the loading angle. For a specific composite, resin application, the effects of the change in gingival floor depth were analyzed by assigning the depth to 2.0 mm. RESULTS: Composite and Compomer resin and composite exhibited better performance than amalgam. The existence of the retention grooves proved to be effective for adhesive amalgam restorations but did not have any advantageous effect in composite and Compomer restoration. CONCLUSION: For improved fracture resistance in small approximal restorations, the use of composite was the appropriate choice. Compomer also gave satisfactory results. Use of amalgam restoration should be accompanied with retention grooves and an adhesive system to improve its performance.
Asunto(s)
Preparación de la Cavidad Dental/métodos , Restauración Dental Permanente/métodos , Diente Premolar , Compómeros , Resinas Compuestas , Amalgama Dental , Fracaso de la Restauración Dental , Análisis del Estrés Dental , Humanos , Ensayo de Materiales , Estadísticas no ParamétricasRESUMEN
Hyaluronic acid (HA) is a glycosaminoglycan polymer that has been found to have some beneficial effects on the prevention of adhesions in primary tendon repairs. The need for slow elimination preparations of HA has been identified. We have combined HA and carboxymethylcellulose (CMC) in order to get a slow elimination preparation of HA and studied its possible effect on primary tendon healing. A gel form of NaHe (19 mg/ml; mw: 6.5 x 10(6)) was mixed with Na CMC (degree of substitution: 0.8) under sterile conditions. A jelly like mixture was thinned and HA membrane was achieved after drying in the refrigerator. The right legs of Leghorn chickens (n = 30) were prepared under IM ketamine anaesthesia by making partial cuts (75%) of flexor profundus tendons at zone II in the second, third and fourth toes, and repaired using a modified Kessler type suture (5/0 nylon). HA-membranes were applied around the repair sites in the third toes while 0.5 ml of hyaluronic acid and saline were poured on to the repair sites in the second and fourth toes, respectively. Skin incisions were closed and the legs were splinted for 15 days. Biomechanical and histological controls were made at the first, second and third postoperative months. No wound dehiscence or exposure of repaired tendons was observed on the operated toes. After collection of samples by amputation at MP levels, two-phalanx free biomechanical assessment was done. The calculated peaks of differential joint motion were very similar to the corresponding non-operated contralateral toes in the HA-membrane treated group. The toe tip displacement curves also resembled the non-operated ones in this group. HA membrane was detected as blue particles on specimens taken at the 30th day following surgery. There were few adhesions in this group microscopically at the third month. Adhesions were similar in the HA treated group while dense adhesions were seen in the saline treated group. These findings suggest that HA membrane acting as a physicochemical barrier can prevent restrictive adhesions in primary tendon repairs.