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At least 1,027 records · Page 57Linked to original sources
PubMed1997

Setting reaction and hardening of an apatitic calcium phosphate cement.

The combination of self-setting and biocompatibility makes calcium phosphate cements potentially useful materials for a variety of dental applications. The objective of this study was to investigate the setting and hardening mechanisms of a cement-type reaction leading to the formation of calcium-deficient hydroxyapatite at low temperature. Reactants used were alpha-tricalcium phosphate containing 17 wt% beta-tricalcium phosphate, and 2 wt% of precipitated hydroxyapatite as solid phase and an aqueous solution 2.5 wt% of disodium hydrogen phosphate as liquid phase. The transformation of the mixture was stopped at selected times by a freeze-drying techniques, so that the cement properties at various stages could be studied by means of x-ray diffraction, infrared spectroscopy, and scanning electron microscopy. Also, the compressive strength of the cement was measured as a function of time. The results showed that: (1) the cement setting was the result of the alpha-tricalcium phosphate hydrolysis, giving as a product calcium-deficient hydroxyapatite, while beta-tricalcium phosphate did not participate in the reaction; (2) the extent of conversion of alpha-TCP was nearly 80% after 24 hr; (3) both the extent of conversion and the compressive strength increased initially linearly with time, subsequently reaching a saturation level, with a strong correlation observed between them, indicating that the microstructural changes taking place as the setting reaction proceeded were responsible for the mechanical behavior of the cement; and (4) the microstructure of the set cement consisted of clusters of big plates with radial or parallel orientations in a matrix of small plate-like crystals.

Bone Cements↗
PubMed1998

Basic studies on hydroxy apatite cement: I. Setting reaction.

Self-setting cements, alpha D-Cement and alpha DT-Cement, were prepared. They consisted of only the calcium phosphates alpha-TCP, TTCP and DCPA. These cements reacted and hardened in a moist environment at 37 degrees C. The powder X-ray diffraction patterns were taken to examine the conversion of their reactions as a function of time. The cements reacted and produced hydroxyapatite. The optimum powder/liquid ratio of alpha D-Cement was 2.0 and that of alpha DT-Cement was 1.8. The initial setting time of alpha D-Cement was 87.5 m and that of alpha DT-Cement was 107.5 m. The component and the product of these cements are calcium phosphates which are the putative minerals in teeth and bones. Therefore, these cements are useful for oral surgery as bone-filling materials.

Bone Substitutes↗
PubMed1993

Effect of adding diamond particles on the fracture toughness of apatite ceramics.

Composite ceramics dispersed through diamond particles with hydroxyapatite as a matrix were prepared by firing at 1250 degrees C under reduced pressure or normal atmosphere. The fracture toughness and physical properties of sintered composite ceramics were examined to determine methods of strengthening hydroxyapatite ceramics. The diamond crystal in composite ceramics was transformed to graphite by firing and the fracture toughness of hydroxyapatite ceramics increased with diamond addition. At 10 wt% diamond, the maximum value for fracture toughness was obtained, and the further addition of diamond particles over 10 wt% caused fracture toughness to decrease. Such increases in fracture toughness were considered the result of microcracking which occurred during the transformation from diamond to graphite.

Dental Porcelain↗
PubMed1998

Development of calcium phosphate cement for rapid crystallization to apatite.

The purpose of this study was to develop an alpha-tricalcium phosphate (alpha-TCP) cement which transforms to hydroxyapatite (HAP) in a relatively short period. We used calcium and phosphate solutions as the liquid phase for the alpha-TCP cement. The alpha-TCP powder was first mixed with CaCl2 solution, and then mixed with NaH2PO4 or Na2HPO3 solution for a total powder/liquid ratio of 1.8. The setting time became shorter with the increase in the concentration of calcium and phosphate solutions, reaching 5 min, whereas the setting time was longer than 30 min when distilled water was used as the liquid phase. X-ray diffraction analysis revealed that the cement was mostly transformed to HAP within 24 h when kept in an incubator. We concluded that alpha-TCP should be mixed with calcium and phosphate solutions since this results in a moderate setting time and fast transformation to HAP even if the method of mixing becomes a little complex.

Calcium Phosphates↗
PubMedDate not supplied

[Milwaukee shoulder syndrome (apatite associated destructive arthritis): therapeutic aspects].

Milwaukee shoulder is a well defined clinical entity that can be observed in particular in older women. It is a destructive arthropathy associated with the deposition of calcium pyrophosphate dihydrate crystals, characterized by the presence of large amount of synovial fluid and a complete tear of the rotator cuff. Clinical features include pain, swelling and progressive functional impairment. The first-line treatment include the use of analgesic drugs and repeated arthrocentesis followed by intra-articular steroid administration; closed-needle tidal irrigation has been reported to be useful. In late phase we can observe narrowing of the acromion-humeral and of the gleno-humeral joint and progressive degenerative changes at the humeral head, leading to almost complete functional impairment. In these cases a surgical approach with total shoulder arthroplasty may be considered.

Editorial↗
PubMed1990

[Experimental study on apatite ceramics used as endodontic endosseous implant].

UNLABELLED: The purpose of this study was to investigate the possibility of applying hydroxyapatite ceramics as endodontic-endosseous implants. The upper medial incisors of 3 monkeys (Macaca fuscatae) were used. To prepare the implant cavity, the teeth were extracted and drilled from the apex by steel burns under water-cooling. Then, dense hydroxyapatite implants, 10mm in length, 2mm in maximum diameter and 1/20 tapered, were inserted into the cavity to have the implant project 3-4mm above the apex. When the teeth with the implants were replanted, the bone around the apex was removed. The teeth were splinted to the neighbouring teeth for 1 month. Five months after the operation, the specimens were taken out and fixed by 10% formalin alcohol. They were embedded in polyester resin and undecalcified sections were prepared. The sections were stained with toluidine blue and observed under light microscope. RESULTS: 1) At 5 months, no ankylosis between the tooth and the surrounding alveolar bone was observed. 2) There was newly formed hard tissue which extended from the cementum, on the surface of the implant. 3) Fiber bundles were observed around the implants which connected the newly formed hard tissue to the surrounding bone tissue. The results suggest that the application of hydroxyapatite ceramics as an endodontic-endosseous implant is effective.

Animals↗
PubMed1991

[Studies on biocompatibility of apatite-silicone composite material and investigation of its clinical application].

As reconstructive and prosthetic material of the bone or soft tissue, the author developed a hydroxyapatite composite with silicone (HA-Si composite and studied its biocompatibility to the bone and investigated its clinical application. Si and HA-Si composite containing 30wt%, 50wt%, 70wt% of HA particles were implanted into the rabbit femurs and 2, 4, 12 weeks after, the histological observation was performed. On the surface of the Si fibrous tissue was formed directly, but with the composite, of with the higher HA content, new trabecula were formed from the cortical bone 2 weeks after and the bone developed and contacted the surface directly 4 weeks after and then progressed along the surface. Twelve weeks after the remodeling of the bone progressed and the lamellar structure was recognized. In the bone marrow region new bone formation was observed along the composite and the lamellar structure was recognized. The 70wt% composite showed a good affinity like hydroxyapatite. This composite had elasticity and good handling and biocompatibility to the bone, and it was suggested to be potentially useful for implantation. The 70wt% composite was applied in the clinical cases: mandibular reconstruction (8 cases), additional implantation for deformity of the face (3 cases), alveolar ridge augmentation (3 cases) and supporting of the retention of facial prosthesis (2 cases). The results in the cases of mandibular reconstruction were not satisfactory, however those in the other cases were good so far now. Therefore it was considered that the 70wt% HA-Si composite could be useful in the statical condition.

Adolescent↗
PubMed1998

[The characteristics of plasma--sprayed coatings of hydroxy apatite in vitro].

In order to investigate the stability of Hydroxyapatite (HA) coated material, the plasma-sprayed coatings of HA were divided into four groups: 1. Keeping in water vapour at 125 degrees C, with a pressure of 0.15 MPa for 6 hr; 2. Heating at 650 degrees C in air for half an hr; 3. Keeping in water vapour at 490 degrees C, with a pressure of 0.01 MPa for 2 hr; and 4. The control. The XRD, FTIR analysis and the dissolution test were carried out. The results showed: 1. The degree of crystalization in XRD analysis was 3. > 1. > 2. > 4.; 2. The ampitude of OH- peak in FTIR analysis was 3. > 1. > 2. > 4. and 3. The dissolution rate in tris-HCl buffer was 3. < 1. < 2. < 4. The conclusions were 1. The treating with water vapour could decrease the transformation temperature which was needed to convert the amorphous phase into cystalline phase; 2. Water vapour treatment could accelerate the transformation of Z-TCP, TCPM into crystalline HA; 3. Water vapour treatment could promote the structural integrity of plasma--sprayed coated of and HA and 4. Water vapour treatment could lower the dissolution rate of HA coated in Tris-HCl buffer.

Coated Materials, Biocompatible↗
PubMed2001

[The collagen-apatite implant and repair of jaw bone tissue defects].

The calcified material (the collagen and calcium hydroxyphosphate--base material) has been used for the first time with a high degree of the structural integrability of components. This material has been obtained according to an unique technology. The material was implanted in 17 patients: after cystectomy--12, after root apex resection--5. The teeth which were in the defective region were preimmobilized by means of archbar structures. The material biotransformation was checked by scintigraphy, roentgenography. According to the obtained data forming of bone tissue was registered on day 20-21 after the operation, after 2-2.5 months this process ended.

Adult↗
PubMed1999

Use of an intermediary in total joint replacement: hydroxy-apatite ceramic.

More than 30 years ago John Charnley and others created total hip replacement. The problems they faced were formidable. Two major problems dominated the scene: namely fixation and wear. Fifty years ago Austin Moore devised a new replacement for aged patients with fractured neck of the femora, but he did not achieve total fixation, nor was this necessary in the ambience of the patient's functional demands.

Journal Article↗
PubMed2003

[Experimental study of using xenologous sclera as wrapping materials for hydroxy apatite(HA)].

OBJECTIVE: Use xenologous sclera (pig sclera) as wrapping materials for hydroxyapatite (HA) ocular implants in enucleated New Zealand white rabbits. METHODS: Ten rabbits were unilaterally enucleated and the sockets implanted with 10 mm HA spherical implants. All implants were wrapped with pig sclera. The rabbits were killed 4 weeks later and the sockets were examined clinically for inflammation and implant exposure. Exenterated specimens were assessed histopathologically for inflammation and vascularization. RESULTS: No clinical evidence of implant exposure or extrusion was detected in rabbits receiving pig sclera wrapped implants. Histopathologically the xenologous (pig) sclera displayed moderate inflammation, as well as maintain its lamellar arrangement without disruption. Fibrovascular ingrowth was complete in all implants. CONCLUSION: Xenologous (pig) sclera behaves similar clinically to homologous sclera as a wrapping material for spherical HA ocular implants in a rabbit model, and may represent a reasonable alternative to sclera in such procedures in humans.

Animals↗