Jiin Huey Chern Lin

Brittle and ductile adjustable cement derived from calcium phosphate cement/polyacrylic acid composites

OBJECTIVESnBone filler has been used over the years in dental and biomedical applications. The present work is to characterize a non-dispersive, fast setting, modulus adjustable, high bioresorbable composite bone cement derived from calcium phosphate-based cement combined with polymer and binding agents. This cement, we hope, will not swell in simulated body fluid and keep the osteogenetic properties of the dry bone and avoid its disadvantages of being brittle.nnnMETHODSnWe developed a calcium phosphate cement (CPC) of tetracalcium phosphate/dicalcium phosphate anhydrous (TTCP/DCPA)-polyacrylic acid with tartaric acid, calcium fluoride additives and phosphate hardening solution.nnnRESULTSnThe results show that while composite, the hard-brittle properties of 25wt% polyacrylic acid are proportional to CPC and mixing with additives is the same as those of the CPC without polyacrylic acid added. With an increase of polyacrylic acid/CPC ratio, the 67wt% samples revealed ductile-tough properties and 100wt% samples kept ductile or elastic properties after 24h of immersion. The modulus range of this development was from 200 to 2600MPa after getting immersed in simulated body fluid for 24h.nnnSIGNIFICANCEnThe TTCP/DCPA-polyacrylic acid based CPC demonstrates adjustable brittle/ductile strength during setting and after immersion, and the final reaction products consist of high bioresorbable monetite/brushite/calcium fluoride composite with polyacrylic acid.

In vivo testing of nanoparticle-treated TTCP/DCPA-based ceramic surfaces

This study reports the development of a non-dispersive calcium phosphate cement (nd-CPC) paste containing tetracalcium phosphate and anhydrous dicalcium phosphate that can be used as a filling material in dental and orthopedic applications. The nd-CPC bone cement is compared with two commercial materials, OsteoSet and Collagraft bone grafts. Gross examination of retrieved implants/bone composite samples indicated that none of the implants in this study evoked an inflammatory response. The OsteoSet (calcium sulfate) implant was resorbed too quickly to allow for osteo-remodeling, and it led to the formation of fibrous connective tissue in the fracture site, which remained even 24 weeks after implantation. Histological examination revealed that nd-CPC and Collagraft (hydroxyapatite/tricalcium phosphate/collagen) had greater remodeling and osteoconductive activity than OsteoSet at both 12 and 24 weeks after implantation. Greater remodeling activities were found with nd-CPC cement than with the other materials at 12 weeks after implantation, and the Fourier transform infrared absorption band of carbonate or cellulose derivatives grew from 6 weeks to 24 weeks after implantation in nd-CPC cement. These findings show that nd-CPC compares favorably to commercial bone remodeling materials, and the fact that it is in a paste formulation makes it an ideal material to fill regeneration defects.

Structure, properties and animal study of a calcium phosphate/calcium sulfate composite cement.

In-vitro and in-vivo studies have been conducted on an in-house-developed tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)/calcium sulfate hemihydrate (CSH)-derived composite cement. Unlike most commercial calcium-based cement pastes, the investigated cement paste can be directly injected into water and harden without dispersion. The viability value of cells incubated with a conditioned medium of cement extraction is >90% that of Al2O3 control and >80% that of blank medium. Histological examination reveals excellent bonding between host bone and cement without interposition of fibrous tissues. At 12 weeks-post implantation, significant remodeling activities are found and a new bone network is developed within the femoral defect. The 26-week samples show that the newly formed bone becomes more mature, while the interface between residual cement and the new bone appears less identifiable. Image analysis indicates that the resorption rate of the present cement is much higher than that of TTCP or TTCP/DCPA-derived cement under similar implantation conditions.

In-Vitro and In-Vivo Evaluation of a New Ti-15Mo-1Bi Alloy

The newly developed Ti-15Mo-1Bi alloy not only possesses all the desirable mechanical properties inherent to beta-Ti Mo alloys, but may even enjoy better clinical applicability with the addition of bismuth element, which has long been administered as antibacterial and antitumor medicines. A significantly higher viability of 3T3 cells was demonstrated when they were grown on Ti-15Mo-1Bi alloy than on Ti-15Mo and Ti-6Al-4V. Cells incubated in the medium conditioned by Bi powder at 37 degrees C for 96 h exhibited viability similar to that in the blank group and higher than that in the Ni conditioned group. In vivo experiments using 6 mm x 2 mm metal pin implanted into the epicondyle of rabbit femur revealed superior potential of new bone growth and better persistence of the deposited bony tissue with the Ti-15Mo-1Bi alloy in contrast to that with Ti-6Al-4V. The difference is evident at 12th week and become even more prominent after 26 weeks, with the new bone area measuring 249% of that around Ti-6Al-4V alloy. In summary, Ti-15Mo-1Bi alloys show no cytotoxicity in the in-vitro test and demonstrates superior ability to retain bone in the in-vivo implantation experiment as compared with Ti-6Al-4V alloys.

Mechanical testing and osteointegration of titanium implant with calcium phosphate bone cement and autograft alternatives

The purpose of this study was to evaluate the osteointegration of a titanium (Ti) implant with the calcium phosphate cement (CPC) and autograft prostheses by pull-out test and histological examination. Stems of sixty Ti cylinders were bilaterally inserted into femoral medullary canals in 30 rabbits at the 1st, 4th, 12th, 26th and 70th postoperative weeks. The bone autograft and CPC were filled into the pre-trimmed bone marrow cavity with a polymethyl methacrylate retarder in the distal end, and then a Ti cylinder was inserted into femurs. The CPC group was significantly (p<0.05) associated with a larger pull-out force at 4th (37%) and 12th (62%) weeks compared to the autograft group. The bone area and the bone-to-implant contact ratios of the CPC groups were significantly higher than that of the autograft groups at early healing stage. The histological exams suggest that the CPC enhanced the earlier bone formation around the implant at a period not longer than 12 weeks postoperation. We conclude that CPC graft has the higher ability to facilitate the osteointegration and stabilize the Ti implant at a relatively early stage than the autograft in vivo.

Setting solution concentration effect on properties of a TTCP/DCPA-derived calcium phosphate cement.

The present work was to investigate the effects of concentration of (NH4)2HPO4 (diammonium hydrogen phosphate) setting solution on properties of a tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)—derived calcium phosphate cement. Experimental results indicated that working/setting time of the cement paste decreased with increasing (NH4)2HPO4 concentration of the setting solution. After being immersed in Hanks’ solution for 1xa0day or longer, the XRD intensities of initial TTCP and DCPA phases largely decreased, while apatite phase became dominant. More residual TTCP phase was observed in the 1xa0day-immersed cement prepared from higher concentration setting solutions. Compressive strength of the cement immersed for 1xa0day was consistently higher than that immersed for 30xa0min or 7xa0days. After being immersed for 1xa0day, the average CS value reached a maximal value (59xa0MPa) as (NH4)2HPO4 concentration was increased to 0.6xa0M, beyond that the cement strength decreased and maintained in a relatively high range of 47–54xa0MPa. Cells incubated with conditioned medium of Al2O3 powder and with blank medium exhibited similar average viability values (0.80 and 0.78, respectively). The OD value with extractions of cement decreased with increasing (NH4)2HPO4 concentration of the setting solution. The average 0.25, 0.5 and 0.6xa0M—OD values were 0.78, 0.67 and 0.66, respectively. When setting solution concentration was greater than 0.6xa0M, the OD value sharply declined to 0.47.

Microstructural investigation of stress-assisted α″-α' phase transformation in cold-rolled Ti-7.5Mo alloy.

The present study investigated the microstructure and stress-assisted α″-α phase transformation of a solution-treated Ti-7.5Mo alloy being cold-rolled with a series of different thickness reductions using transmission electron microscopic (TEM) and electron backscatter diffraction (EBSD) techniques. The EBSD/IPF results indicated a substantially random texture in ST sample. When the alloy was mildly cold-rolled, a texture toward 〈101¯0〉 preferred orientation was established, which gradually shifted toward 〈21¯1¯0〉 with increased reduction in thickness. The TEM results indicated that substantially all fine platelets in the solution-treated (ST) sample had an orthorhombic α″ phase, and that a stress-assisted α″-to-α phase transformation took place when the alloy was cold-rolled, confirming the XRD results. In the mildly rolled (CR20) sample, the existence of α phase could be easily identified, indicating that the stresses involved in the mild rolling process were sufficient to initiate the α″-α phase transition. On the other hand, in the heavily rolled (CR80) sample, the presence of residual α″ phase was still observed throughout the sample, indicating that the α″-to-α phase transition was never complete even after a severe cold rolling process. The SAD analysis indicated an orientation relationship, α()(12¯10)//α(″)(202¯) and α [0001]//α″ [020], existing between the two phases.

Effect of ball milling on structures and properties of dispersed-type dental amalgam

OBJECTIVESnThe purpose of the present study was to investigate the effect of ball milling on the initial mercury vapor release rate and mechanical properties such as compressive strength, diametral tensile strength and creep value, of the dispersed-type dental amalgam, and comparison was made with respect to two commercial amalgam alloys.nnnMETHODSnBall milling was employed to modify the configuration of the originally spherical-shaped Ag-Cu-Pd dispersant alloy particles. Improvement in mechanical properties while maintaining a low early-stage mercury vapor release rate of the amalgam is attempted.nnnRESULTSnThe experimental results show that the amalgam (AmB10) which was made from Ag-Cu-Pd dispersant alloy particles that were ball-milled for 10 min and heat-treated at 300 °C for 2 days exhibited a low initial mercury vapor release rate of 69 pg/mm(2)/s, which was comparable with that of commercial amalgam alloy Tytin (68 pg/mm(2)/s), and was lower than that of Dispersalloy (73 pg/mm(2)/s). As for mechanical properties, amalgam AmB10 exhibited the highest 1h compressive strength (228 MPa), which was higher than that of commercial amalgam alloy Dispersalloy by 72%; while its 24h diametral tensile strength was also the highest (177 MPa), and was higher than that of Dispersalloy by 55%. Furthermore, the creep value of the amalgams made from Ag-Cu-Pd alloy particles with 10 min ball-milling and heat treatment at 300 °C for 2 days was measured to be 0.12%, which was about 20% that of Dispersalloy.nnnSIGNIFICANCEnIt is found that ball milling of the dispersant Ag-Cu-Pd alloy particles for 10 min was able to modify the configuration of the alloy particles into irregular-shapes. Subsequently, heat treatment at 300 °C significantly lowered the initial mercury vapor release rate, increased its 1h compressive strength and 1h diametral tensile strength, and lowered its creep value.