Rachel Sammons

Direct laser metal sintering as a new approach to fabrication of an isoelastic functionally graded material for manufacture of porous titanium dental implants

OBJECTIVES This work focuses on a titanium alloy implants incorporating a gradient of porosity, from the inner core to the outer surface, obtained by laser sintering of metal powder. Surface appearance, microstructure, composition, mechanical properties and fractography were evaluated. METHODS All the specimens were prepared by a selective laser sintering procedure using a Ti-6Al-4V alloy powder with a particle size of 1-10 microm. The morphological and chemical analyses were performed by SEM and energy dispersive X-ray spectroscopy. The flexure strength was determined by a three-point bend test using a universal testing machine. The surface roughness was investigated using a confocal scanning laser microscope. The surface roughness variation was statistically evaluated by use of a Chi square test. A p value of <0.05 was considered statistically significant. RESULTS The original surface microstructure consisted of roughly spherical particles, diameter range 5-50 microm. After exposure to hydrofluoric acid some of these were removed and the microsphere diameter then ranged from 5.1 microm to 26.8 microm. Following an organic acid treatment, particles were replaced by grooves 14.6-152.5 microm in width and 21.4-102.4 microm depth. The metal core consisted of columnar beta grains with alpha and beta laths within the grains. The alloy was composed of 90.08% Ti, 5.67% Al and 4.25% V. The Youngs modulus of the inner core material was 104+/-7.7 GPa; while that of the outer porous material was 77+/-3.5 GPa. The fracture face showed a dimpled appearance typical of ductile fracture. SIGNIFICANCE In conclusion, laser metal sintering proved to be an efficient means of construction of dental implants with a functionally graded material which is better adapted to the elastic properties of the bone. Such implants should minimize stress shielding effects and improve long-term performance.

Effect of pH on protein adsorption to hydroxyapatite and tricalcium phosphate ceramics

Calcium phosphate ceramics used for clinical applications vary considerably in their phase composition. A range of hydroxyapatite and tricalcium phosphate powders, some of which are used in plasma-sprayed coatings for metal prostheses, were found to leach substances which change the pH of water and cell culture medium. The adsorption of serum proteins from cell culture medium to the same hydroxyapatite and tricalcium phosphate ceramics was compared by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and individual bands identified by enhanced chemiluminescence immunodetection and gas chromatography sequencing. The iron transport protein transferrin showed distinct differences in adsorption to a variety of hydroxyapatite and tricalcium phosphate powders, with higher concentrations of transferrin adsorbed to powders which caused no change or a drop in the pH of cell culture medium or water. Transferrin was also adsorbed to Biotal HA 120 in greater concentrations at a lower pH than it was at a higher pH. These preliminary studies show that pH changes brought about by the leaching of soluble ions may have an effect on protein adsorption.

Towards long-lasting antibacterial stainless steel surfaces by combining double glow plasma silvering with active screen plasma nitriding

Antibacterial surface modification of biomedical materials has evolved as a potentially effective method for preventing bacterial proliferation on the surfaces of devices. However, thin antibacterial coatings or modified layers can be easily worn down when interacting with other surfaces in relative motion, thus leading to a low durability of the antibacterial surface. To this end, novel biomaterial surfaces with antibacterial Ag agents and a wear-resistant S-phase have been generated on stainless steel by duplex plasma silvering-nitriding techniques for application to load-bearing medical devices. The chemical composition, microstructure, surface topography, roughness and wettability of SS surfaces were characterised using glow discharge optical emission spectroscopy, energy-dispersive spectroscopy/wavelength dispersive spectrometry (WDS), X-ray diffraction, atomic force microscopy and a contact angle goniometer. Optimal surface design for high antimicrobial activity and prolonged durability has been achieved, as evidenced by rapid bacterial killing rates (within 6h), an ultra hard matrix (875 ± 25 Hv), high load-bearing capacity (critical load 37 N) and excellent wear resistance (wear rate 4.9 × 10⁻⁶ mm³ m⁻¹). Ag embedded in the hard substrate of fcc compounds M(4)N (M=Fe, Cr, Ag, etc.) and the expanded fcc nitrogen S-phase shows deep infiltration of 6 ± 1 μm, and provides bactericidal activity against both Gram-negative Escherichia coli NCTC 10418 and Gram-positive Staphylococcus epidermidis NCTC 11047 of over 97% and 90%, respectively, within 6h. The presence of silver in the surface before and after scratching under a progressive load applied up to 60 N using a diamond stylus was confirmed by WDS.

The gerB region of the Bacillus subtilis 168 chromosome encodes a homologue of the gerA spore germination operon

Spores of gerB spore germination mutants of Bacillus subtilis 168 are defective in response to the germinative mixture of L-asparagine, glucose, fructose and potassium ions (AGFK), but are normal in the L-alanine (ALA) triggered germination response. A lambda clone of 15 kbp carrying the gerB region has been identified. Sequencing of the gerB region of the clone revealed a cluster of three ORFs encoding putative proteins of 53.3, 41.3 and 42.4 kDa (GerBA, GerBB and GerBC, respectively). The first two of these proteins have substantial hydrophobic regions and the third is a possible lipoprotein. At least two, and probably all three products are required for normal germination in AGFK. The three proteins form a set of homologues of the products of the gerA operon, mutations in which cause a defect in the ALA germination pathway, but cause no defect in AGFK. The GerB proteins show 42%, 31% and 35% identity at the amino-acid level to the corresponding GerA proteins, and the homologues occur in the same order in both operons.

Isolation and Properties of Spore Germination Mutants of Bacillus subtilis 168 Deficient in the Initiation of Germination

SUMMARY: Two spore germination mutants of Bacillus subtilis 168 (GerA38 and GerA44) deficient at a very early stage of germination prior to loss of heat resistance and absorbance were isolated. In contrast to the wild-type their spores required higher concentrations of germinant and had a slower germination rate and longer average microlag in L-alanine, L-α-aminobutyrate, DL-β-aminobutyrate and L-valine. Although wild-type spores germinated in 0.1 M-CyCloleucine the mutants did not, but did so normally in L-asparagine plus glucose, fructose and KCl. GerA44 was more defective than GerA38. Their germination abnormalities were partially corrected if glucose, fructose and KCl were added to L-alanine or L-valine. Germination of both mutants in L-alanine was more sensitive than the wild-type to inhibition by D-alanine, the sensitivity of GerA44 being greater than that of GerA38. Two other GerA mutants which did not germinate in L-alanine, even at high concentrations, were able to use it as a source of carbon or nitrogen at rates equal to those of the wild-type. A similar mutant and GerA44 show normal chemotaxis to L-alanine. Thus, the deficiencies of GerA mutants appear to be spore specific. GerA38 and gerA44 mutations were approximately 75% and 43% cotransduced with cysB and thr-5, respectively, with phage PBS1. They mapped within a cluster of gerA mutations that were 70-90% cotransduced with citG4 by phage SPP1. Although other GerA mutants cannot germinate in L-alanine plus KCl no difference in map location between their mutations and gerA38 and gerA44 could be detected.

Prospective Evaluation of 2,549 Morse Taper Connection Implants: 1‐ to 6‐Year Data

BACKGROUND The aim of this study is to evaluate the implant survival, the implant-crown success, and the prosthetic complications of 2,549 Morse taper interference-fit connection implants. METHODS A total of 2,549 Morse taper connection implants were inserted in 893 patients from January 2003 until December 2008. At each annual recall, clinical, radiographic, and prosthetic parameters were assessed. The implant-crown success criteria included the absence of pain, suppuration, and clinical mobility; an average distance between the implant shoulder and the first visible bone contact <2 mm from initial surgery; and the absence of prosthetic complications at the implant-abutment interface. Prosthetic restorations were fixed partial prostheses (462 units); fixed full-arch prostheses (60 units); single crowns (531 units); and overdentures (93 units). RESULTS The cumulative implant survival rate was 98.23% (97.25% maxilla, 99.05% mandible). The implant-crown success was 92.49%. A few prosthetic complications at implant-abutment interface were reported (0.37%). After 6 years, distance between the implant shoulder and the first visible bone contact was 1.10 mm (± 0.30 mm). CONCLUSION The use of Morse taper connection implants represents a successful procedure for the rehabilitation of partially and completely edentulous arches.

Stereo imaging and cytocompatibility of a model dental implant surface formed by direct laser fabrication.

Direct laser fabrication (DLF) allows solids with complex geometry to be produced by sintering metal powder particles in a focused laser beam. In this study, 10 Ti6Al4V alloy model dental root implants were obtained by DLF, and surface characterization was carried out using stereo scanning electron microscopy to produce 3D reconstructions. The surfaces were extremely irregular, with approximately 100 microm deep, narrow intercommunicating crevices, shallow depressions and deep, rounded pits of widely variable shape and size, showing ample scope for interlocking with the host bone. Roughness parameters were as follows: R(t), 360.8 microm; R(z), 358.4 microm; R(a), 67.4 microm; and R(q), 78.0 microm. Disc specimens produced by DLF with an identically prepared surface were used for biocompatibility studies with rat calvarial osteoblasts: After 9 days, cells had attached and spread on the DLF surface, spanning across the crevices, and voids. Cell density was similar to that on a commercial rough microtextured surface but lower than on commercial smooth machined and smooth-textured grit-blasted, acid-etched surfaces. Human fibrin clot extension on the DLF surface was slightly improved by inorganic acid etching to increase the microroughness. With further refinements, DLF could be an economical means of manufacturing implants from titanium alloys.

Single-tooth Morse taper connection implants placed in fresh extraction sockets of the anterior maxilla: an aesthetic evaluation

OBJECTIVE The aim of this retrospective study was to evaluate the aesthetic outcome of single-tooth Morse taper connection implants placed in fresh extraction sockets of the anterior maxilla, by means of the pink aesthetic/white aesthetic score (PES/WES) index. MATERIALS AND METHODS Twenty-six adult patients (18 men, 8 women, aged between 20 and 62 years; average: 48.7 years) who were treated with an immediate, single-tooth Morse taper connection implant (Leone Implant System(R) , Florence, Italy) in the aesthetic area of the anterior maxilla, were enrolled in this retrospective study. An independent calibrated examiner applied the PES/WES index to 26 single-tooth implant-supported restorations, respectively, 3 months and 2 years after implant placement. RESULTS No implants were lost. All 26 anterior maxillary single-tooth implants fulfilled the established success criteria for dental implants with regard to osseointegration, including the absence of pain, suppuration, clinically detectable implant mobility, peri-implant radiolucency and prosthetic complications at the implant-abutment interface, with an overall implant-crown success of 100.0%. At the 2-year examination, the mean DIB was 0.44 ± 0.14 mm (95% CI: 0.41-0.47); the mean total PES/WES was 14.30 ± 2.78 (range 8-19); the mean PES was 7.30 ± 1.78 (range 4-10) and the mean WES was 7.00 ± 1.35 (range 4-10). CONCLUSIONS The immediate placement of single-tooth Morse taper connection implants in the anterior maxilla seems to represent a successful procedure, from an aesthetic point of view. Further studies are needed to evaluate the aesthetic outcome of single-tooth Morse taper connection implants placed in fresh extraction sockets of the anterior maxilla.

Alanine germination receptors of Bacillus subtailis

The alanin‐estimulated spore germination responses of Bacillus subtilis 168 have been dissected by combining physiological and genetical approaches. From the analyses the authors infer that there are three classes of alanine response. Two of the responses are mediated via the GerA proteins, with and without germinal adjuncts, the third is mediated via the GerB proteins and obligately requires adjuncts.

Back-scattered electron imaging and elemental analysis of retrieved bone tissue following sinus augmentation with deproteinized bovine bone or biphasic calcium phosphate

OBJECTIVES To compare resorption of a synthetic biphasic calcium phosphate (BCP) bone-graft substitute with deproteinized bovine bone (DBB) used for human maxillary sinus augmentation. MATERIALS AND METHODS Eleven patients underwent bilateral maxillary sinus floor augmentation with DBB in one side and a BCP (40%beta-tricalcium phosphate (beta-TCP) and 60% hydroxyapatite) in the contralateral side. Simultaneously, with the augmentation on each side a microimplant was placed vertically from the top of the alveolar crest penetrating the residual bone and the grafting material. Eight months after initial surgery the microimplants were retrieved with a surrounding bone core. The composition of residual graft material and surrounding bone was analysed by scanning electron microscopy and energy dispersive X-ray spectroscopy. RESULTS Residual graft material of both types was present as 10-500 mum particles in direct contact with, or completely surrounded by, newly formed bone; smaller particles were also present in non-mineralized tissue. In the case of BCP the bone-graft substitute interface showed evidence of superficial disintegration of particles into individual grains. Median Ca/P ratios (at.%), determined from >200 discreet sites within residual graft particles and adjacent bone, were: DBB: 1.61 (confidence interval [CI] 1.59-1.64); BCP: 1.5 (CI 1.45-1.52); DBB-augmented bone: 1.62 (CI 1.59-1.66); BCP-augmented bone: 1.52 (CI 1.47-1.55); P=0.028 for DBB vs. BCP and DBB- vs. BCP-augmented bone. The reduction in Ca/P ratio for BCP over the healing period is consistent with the dissolution of beta-TCP and reprecipitation on the surface of calcium-deficient hydroxyapatite. CONCLUSION The beta-TCP component of BCP may be gradually substituted by calcium-deficient hydroxyapatite over the healing period. This process and superficial degranulation of BCP particles may influence the progress of resorption and healing.