| 1. |
- Cai, Bing, 1986-, et al.
(författare)
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The effect of curing conditions on compression strength and porosity of metakaolin-based geopolymers
- 2013
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Ingår i: Developments in Strategic Materials and Computational Design IV. - Hoboken, NJ, USA : John Wiley & Sons.
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Konferensbidrag (refereegranskat)abstract
- Geopolymers have been suggested to use as construction, waste treatment and fire proof materials and even drug delivery material due to its excellent mechanical strength, chemical stability and flame resistance. The aim of this study was to investigate the influence of temperature, time and humidity during curing on mechanical strength and porosity of geopolymers.The geopolymer precursor paste was obtained by mixing metakaolin, waterglass and de-ionized water. The paste was molded into cylindrical rubber moulds (6 12 mm) and cured under different conditions: i.e. temperatures (ambient temperature, 37°C and 90°C), humidity and time (24, 48 and 96 hours). The compressive strength was determined using a universal testing machine. Helium pycnometer was used to measure the porosity. Via x-ray diffraction the phase composition of the cured samples was determined.Elongated curing slightly decreased the total porosity of the tested geopolymers. Higher curing temperature increased the compressive strength after 24 hour but did not affect strength for longer curing times. In general, the samples cured in moisture had higher mechanical strength than those cured in air. But low compression strength of samples cured under high temperature and long time showed that some water content in geopolymer was essential to retaining its microstructure.
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| 2. |
- Engqvist, Håkan, et al.
(författare)
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The influence of curing conditions on mechanical strength and porosity of geopolymers
- 2013
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Ingår i: The influence of curing conditions on mechanical strength and porosity of geopolymers.
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Konferensbidrag (refereegranskat)abstract
- Geopolymers have been suggested to be used as construction, waste treatment and even drug delivery material due to its excellent mechanical strength, acid resistance and biocompatibility. The aim of this study is to investigate the influence of temperature, time and humidity during curing on mechanical strength and porosity of geopolymers.The geopolymer was synthesized by mixing metakaolin, waterglass and de-ionized water until a homogenous paste was obtained. The following molar oxide ratio was used: Al2O3/SiO2=0.353, Na2O/SiO2=0.202, H2O/SiO2=2.977. The paste was molded into cylindrical rubber moulds (6 12 mm) and cured under different temperatures (ambient temperature, 37°C and 90°C), humidity and time (24, 48 and 96 hours). The compressive strength was determined using a universal testing machine. Helium pycnometer was used to measure the porosity. Via x-ray diffraction the phase composition of the cured samples was determined.Higher curing temperature increased the compressive strength after 24 hour but did not affect the strength for longer curing times. In general, the samples cured in moisture had higher mechanical strength than those cured in air. More metakaolin remained in samples cured under high temperature, while for samples cured under low temperature for longer time showed a higher conversion to geopolymer. Curing time did not show much influence on the total porosity.
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| 3. |
- Hedenqvist, Patricia, et al.
(författare)
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The effect of housing environment on bone healing in a critical radius defect in New Zealand White rabbits
- 2020
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Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- In animal studies on bone healing, the effect of housing space and physical activity are seldom taken into account. Bone formation was evaluated in New Zealand White rabbits (mean ± SEM BW: 3.9 ± 0.11 kg) with a critical bone defect after 12 weeks of rehabilitation in pair-housing in 3 m2 large floor pens (Floor, n = 10) or standard single housing in 0.43 m2 cages (Cage, n = 10). In the randomised full-factorial study, a bone replica of calcium phosphate cement (CPC, n = 10) or autologous bone (AB, n = 10) was implanted in the unilateral 20 mm radius defect. Post-mortem, the oxidative capacity was measured by citrate synthase (CS) activity in M. quadriceps and the defect filling volume and density evaluated by microcomputer tomography (μ-CT). Histology sections were evaluated by subjective scoring and histomorphometry. Fourteen rabbits remained until the end of the study. Group Floor (n = 7; 3 CPC + 4 AB) had a higher CS activity and a larger bone defect filling volume and lower density by μ-CT measurements than group Cage (n = 7; 3 CPC + 4 AB). Three out of four rabbits in AB-Floor presented fusion of the defect with reorganisation of trabecular bone, whereas three of four in AB-Cage showed areas of incomplete healing. Floor rabbits had a higher score of bony fusion between the radius and ulna than Cage rabbits. There were no differences between groups in histomorphometry. The study found that a larger housing space increased physical activity and promoted bone formation. © 2020 Hedenqvist et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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| 4. |
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| 5. |
- Mellgren, Torbjörn, 1986-, et al.
(författare)
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Calcium Phosphate Microspheres as a Delivery Vehicle for Tooth-Bleaching Agents
- 2018
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Ingår i: Journal of Dental Research. - : SAGE PUBLICATIONS INC. - 0022-0345 .- 1544-0591. ; 97:3, s. 283-288
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Tidskriftsartikel (refereegranskat)abstract
- Bleaching of vital teeth has become common practice in cosmetic dentistry today. Tooth sensitivity and demineralization of the enamel are, however, common side effects associated with hydrogen and carbamide peroxide bleaching. This study investigated if calcium phosphate microspheres, which have remineralizing properties, could be used as an additive without hindering the diffusion of the bleaching agent and if the spheres could be used as a carrier for carbamide peroxide. A remineralizing agent could increase the safety of bleaching and decrease the severity of its side effects. Comparisons between current hydrogen peroxide diffusion studies and previously published work are difficult since many studies include challenging-to-replicate conditions or lack reporting of important parameters. Hence, a diffusion model was designed by Wu Lab (School of Dentistry, University of California, Los Angeles) to measure the diffusion flux and determine the diffusivity of hydrogen peroxide. Physical parameters (e.g., diffusivity) could then be used for direct comparison to the results obtained by future studies. Three whitening gels with increasing amounts of spheres were formulated and tested with 2 commercially available whitening gels. The flux of hydrogen peroxide through 1-mm discs of bovine enamel was measured at steady-state conditions, and the diffusivity was calculated. The results showed that the spheres could be used as a carrier for carbamide peroxide and that the amount of spheres did not affect the diffusivity of peroxide through the enamel discs. Hence, the microspheres are considered promising as an additive to minimize side effects in bleaching gel formulation.
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| 6. |
- Mellgren, Torbjörn, 1986-, et al.
(författare)
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Guided bone tissue regeneration using a hollow calcium phosphate based implant in a critical size rabbit radius defect
- 2021
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Ingår i: Biomedical Materials. - : Institute of Physics Publishing (IOPP). - 1748-6041 .- 1748-605X. ; 16:3
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Tidskriftsartikel (refereegranskat)abstract
- Long bone fractures are common and sometimes difficult to treat. Autologous bone (AB), bovine bone and calcium phosphates are used to stimulate bone growth with varying results. In the present study, a calcium phosphate cement (CPC) that previously showed promising grafting capabilities was evaluated for the first time in a long bone defect. A radius defect of 20 mm was created in 20 rabbits. The defect was filled by either a hollow CPC implant that had been manufactured as a replica of a rabbit radius through indirect 3D printing, or by particulate AB as control. Defect filling and bone formation was evaluated after 12 weeks by combining micro computed tomography (mu CT) and scoring of 3D images, together with histomorphometry and histology. The mu CT and histomorphometric evaluations showed a similar amount of filling of the defect (combining graft and bone) between the CPC and AB group, but the scoring of 3D images showed that the filling in the CPC group was significantly larger. Histologically the AB graft could not be distinguished from the new bone. The AB treated defects were found to be composed of more bone than the CPC group, including reorganised cancellous and cortical bone. Both the CPC and AB material was associated with new bone formation, also in the middle of the defect, which could result in closing of the otherwise critically sized gap. This study shows the potential for an indirectly 3D printed implant in guided bone regeneration in critically sized long bone defects.
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| 7. |
- Trbakovic, Amela, et al.
(författare)
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A new synthetic granular calcium phosphate compound induces new bone in a sinus lift rabbit model
- 2018
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Ingår i: Journal of Dentistry. - : Elsevier BV. - 0300-5712 .- 1879-176X. ; 70, s. 31-39
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Tidskriftsartikel (refereegranskat)abstract
- Objectives The aim of this study was to investigate if a synthetic granular calcium phosphate compound (CPC) and a composite bisphosphonate-linked hyaluronic acid–calcium phosphate hydrogel (HABP·CaP) induced similar or more amount of bone as bovine mineral in a modified sinus lift rabbit model. Material and methods Eighteen adult male New Zeeland White rabbits, received randomly one of the two test materials on a random side of the face, and bovine mineral as control on the contralateral side. In a sinus lift, the sinus mucosa was elevated and a titanium mini-implant was placed in the alveolar bone. Augmentation material (CPC, HABP·CaP or bovine bone) was applied in the space around the implant. The rabbits were euthanized three months after surgery and qualitative and histomorphometric evaluation were conducted. Histomorphometric evaluation included three different regions of interest (ROIs) and the bone to implant contact on each installed implant. Results Qualitative assessment (p=<.05), histomorphometric evaluations (p=<.01), and implant incorporation (p=<.05) showed that CPC and bovine mineral induced similar amount of bone and more than the HABP·CaP hydrogel. Conclusion CPC induced similar amount of bone as bovine mineral and both materials induced more bone than HABP·CaP hydrogel. Clinical significance The CPC is suggested as a synthetic alternative for augmentations in the maxillofacial area.
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