Horizontal ridge augmentation using autogenous block grafts and the guided bone regeneration technique with collagen membranes: a clinical study with 42 patients

OBJECTIVE: To analyze the clinical outcome of horizontal ridge augmentation using autogenous block grafts covered with an organic bovine bone mineral (ABBM) and a bioabsorbable collagen membrane. MATERIAL AND METHODS: In 42 patients with severe horizontal bone atrophy, a staged approach was chosen for implant placement following horizontal ridge augmentation. A block graft was harvested from the symphysis or retromolar area, and secured to the recipient site with fixation screws. The width of the ridge was measured before and after horizontal ridge augmentation. The block graft was subsequently covered with ABBM and a collagen membrane. Following a tension-free primary wound closure and a mean healing period of 5.8 months, the sites were re-entered, and the crest width was re-assessed prior to implant placement. RESULTS: Fifty-eight sites were augmented, including 41 sites located in the anterior maxilla. The mean initial crest width measured 3.06 mm. At re-entry, the mean width of the ridge was 7.66 mm, with a calculated mean gain of horizontal bone thickness of 4.6 mm (range 2-7 mm). Only minor surface resorption of 0.36 mm was observed from augmentation to re-entry. CONCLUSIONS: The presented technique of ridge augmentation using autogenous block grafts with ABBM filler and collagen membrane coverage demonstrated successful horizontal ridge augmentation with high predictability. The surgical method has been further simplified by using a resorbable membrane. The hydrophilic membrane was easy to apply, and did not cause wound infection in the rare instance of membrane exposure.

The effect of rhBMP-2 around endosseous implants with and without membranes in the canine model

BACKGROUND: Bone morphogenetic protein (BMP) is a potent differentiating agent for cells of the osteoblastic lineage. It has been used in the oral cavity under a variety of indications and with different carriers. However, the optimal carrier for each indication is not known. This study examined a synthetic bioabsorbable carrier for BMP used in osseous defects around dental implants in the canine mandible. METHODS: Twelve canines had their mandibular four premolars and first molar teeth extracted bilaterally. After 5 months, four implants were placed with standardized circumferential defects around the coronal 4 mm of each implant. One-half of the defects received a polylactide/glycolide (PLGA) polymer carrier with or without recombinant human BMP-2 (rhBMP-2), and the other half received a collagen carrier with or without rhBMP-2. Additionally, one-half of the implants were covered with a non-resorbable (expanded polytetrafluoroethylene [ePTFE]) membrane to exclude soft tissues. Animals were sacrificed either 4 or 12 weeks later. Histomorphometric analysis included the percentage of new bone contact with the implant, the area of new bone, and the percentage of defect fill. This article describes results with the PLGA carrier. RESULTS: All implants demonstrated clinical and radiographic success with the amount of new bone formed dependent on the time and presence/absence of rhBMP-2 and presence/absence of a membrane. The percentage of bone-to-implant contact was greater with rhBMP-2, and after 12 weeks of healing, there was approximately one-third of the implant contacting bone in the defect site. After 4 weeks, the presence of a membrane appeared to slow new bone area formation. The percentage of fill in membrane-treated sites with rhBMP-2 rose from 24% fill to 42% after 4 and 12 weeks, respectively. Without rhBMP-2, the percentage of fill was 14% rising to 36% fill, respectively. CONCLUSIONS: After 4 weeks, the rhBMP-2-treated sites had a significantly higher percentage of contact, more new bone area, and higher percentage of defect fill than the sites without rhBMP-2. After 12 weeks, there was no significant difference in sites with or without rhBMP-2 regarding percentage of contact, new bone area, or percentage of defect fill. In regard to these three outcomes, comparing the results with this carrier to the results reported earlier with a collagen carrier in this study, only the area of new bone was significantly different with the collagen carrier resulting in greater bone than the PLGA carrier. Thus, the PLGA carrier for rhBMP-2 significantly stimulated bone formation around dental implants in this model after 1 month but not after 3 months of healing. The use of this growth factor and carrier combination appears to stimulate early bone healing events around the implants but not quite to the same degree as a collagen carrier.

The Young's modulus of fetal preterm and term amniotic membranes

OBJECTIVE: To examine the Young's modulus of the human amniotic membranes, as well as its relationship to gestational age. To determine whether cellular and material-related parameters affect this modulus. STUDY DESIGN: In a prospective study at the Obstetric outpatient clinic of the University Hospital Zurich Young's modulus, thickness and mesenchymal:epithelial cell ratio of amniotic membranes of preterm (N=23) and term (N=40) placentae were examined. Significance (P<0.05) was calculated with the Mann-Whitney two-sample rank sum test and Wilcoxon signed rank test, while correlations were made using the Spearman's correlation. RESULTS: The Young's modulus of preterm amniotic membranes was significantly higher than that of term membranes. It varied within the same amniotic membrane. The thickness of the amnion in both preterm and term membranes did not differ significantly. The thinner the preterm and term amniotic membranes, the higher the Young's modulus was. There was no relation to the mesenchymal:epithelial cell ratio in the amnion. CONCLUSIONS: Preterm amniotic membranes are stiffer than term amniotic membranes. Tentatively, we hypothesise that there may be a correlation between the extracellular matrix components and the elastic properties of the membrane.

Effect of two different bioabsorbable collagen membranes on guided bone regeneration: a comparative histomorphometric study in the dog mandible

BACKGROUND: This study compared bone regeneration following guided bone regeneration with two bioabsorbable collagen membranes in saddle-type bone defects in dog mandibles. METHODS: Three standardized defects were created, filled with bone chips and deproteinized bovine bone mineral (DBBM), and covered by three different methods: control = no membrane; test 1 = collagen membrane; and test 2 = cross-linked collagen membrane (CCM). Each side of the mandible was allocated to one of two healing periods (8 or 16 weeks). The histomorphometric analysis assessed the percentage of bone, soft tissue, and DBBM in the regenerate; the absolute area in square millimeters of the bone regenerate; and the distance in millimeters from the bottom of the defect to the highest point of the regenerate. RESULTS: In the 8-week healing group, two dehiscences occurred with CCM. After 8 weeks, all treatment modalities showed no significant differences in the percentage of bone regenerate. After 16 weeks, the percentage of bone had increased for all treatment modalities without significant differences. For all groups, the defect fill height increased between weeks 8 and 16. The CCM group showed a statistically significant (P = 0.0202) increase over time and the highest value of all treatment modalities after 16 weeks of healing, CONCLUSIONS: The CCM showed a limited beneficial effect on bone regeneration in membrane-protected defects in dog mandibles when healing was uneventful. The observed premature membrane exposures resulted in severely compromised amounts of bone regenerate. This increased complication rate with CCM requires a more detailed preclinical and clinical examination before any clinical recommendations can be made.

Ridge augmentation by applying bioresorbable membranes and deproteinized bovine bone mineral: a report of twelve consecutive cases

OBJECTIVE: Lateral ridge augmentations are traditionally performed using autogenous bone grafts to support membranes for guided bone regeneration (GBR). The bone-harvesting procedure, however, is accompanied by considerable patient morbidity. AIM: The aim of the present study was to test whether or not resorbable membranes and bone substitutes will lead to successful horizontal ridge augmentation allowing implant installation under standard conditions. MATERIAL AND METHODS: Twelve patients in need of implant therapy participated in this study. They revealed bone deficits in the areas intended for implant placement. Soft tissue flaps were carefully raised and blocks or particles of deproteinized bovine bone mineral (DBBM) (Bio-Oss) were placed in the defect area. A collagenous membrane (Bio-Gide) was applied to cover the DBBM and was fixed to the surrounding bone using poly-lactic acid pins. The flaps were sutured to allow for healing by primary intention. RESULTS: All sites in the 12 patients healed uneventfully. No flap dehiscences and no exposures of membranes were observed. Nine to 10 months following augmentation surgery, flaps were raised in order to visualize the outcomes of the augmentation. An integration of the DBBM particles into the newly formed bone was consistently observed. Merely on the surface of the new bone, some pieces of the grafting material were only partly integrated into bone. However, these were not encapsulated by connective tissue but rather anchored into the newly regenerated bone. In all of the cases, but one, the bone volume following regeneration was adequate to place implants in a prosthetically ideal position and according to the standard protocol with complete bone coverage of the surface intended for osseointegration. Before the regenerative procedure, the average crestal bone width was 3.2 mm and to 6.9 mm at the time of implant placement. This difference was statistically significant (P<0.05, Wilcoxon's matched pairs signed-rank test). CONCLUSION: After a healing period of 9-10 months, the combination of DBBM and a collagen membrane is an effective treatment option for horizontal bone augmentation before implant placement.

Local degradation of structural, mechanical, electrical and chemical properties of membrane electrode assembly in polymer electrolyte fuel cell

Polymer electrolyte fuel cell (PEMFC) is promising source of clean power in many applications ranging from portable electronics to automotive and land-based power generation. However, widespread commercialization of PEMFC is primarily challenged by degradation. The mechanisms of fuel cell degradation are not well understood. Even though the numbers of installed units around the world continue to increase and dominate the pre-markets, the present lifetime requirements for fuel cells cannot be guarantee, creating the need for a more comprehensive knowledge of material’s ageing mechanism. The objective of this project is to conduct experiments on membrane electrode assembly (MEA) components of PEMFC to study structural, mechanical, electrical and chemical changes during ageing and understanding failure/degradation mechanism. The first part of this project was devoted to surface roughness analysis on catalyst layer (CL) and gas diffusion layer (GDL) using surface mapping microscopy. This study was motivated by the need to have a quantitative understanding of the GDL and CL surface morphology at the submicron level to predict interfacial contact resistance. Nanoindentation studies using atomic force microscope (AFM) were introduced to investigate the effect of degradation on mechanical properties of CL. The elastic modulus was decreased by 45 % in end of life (EOL) CL as compare to beginning of life (BOL) CL. In another set of experiment, conductive AFM (cAFM) was used to probe the local electric current in CL. The conductivity drops by 62 % in EOL CL. The future task will include characterization of MEA degradation using Raman and Fourier transform infrared (FTIR) spectroscopy. Raman spectroscopy will help to detect degree of structural disorder in CL during degradation. FTIR will help to study the effect of CO in CL. XRD will be used to determine Pt particle size and its crystallinity. In-situ conductive AFM studies using electrochemical cell on CL to correlate its structure with oxygen reduction reaction (ORR) reactivity

Recovery of visual field and acuity after removal of epiretinal and inner limiting membranes

BACKGROUND: Visual acuity serves as only a rough gauge of macular function. The aim therefore was to ascertain whether central an assessment of the central visual field afforded a closer insight into visual function after removal of epiretinal membranes and Infracyanine-Green- or Trypan-Blue-assisted peeling of the inner limiting membrane. Patients and methods: Fourty-three patients undergoing pars-plana vitrectomy for the removal of epimacular membranes and dye-assisted peeling of the inner limiting membrane using either Infracyanine Green (n = 29; group 1) or Trypan Blue (n = 14; group 2) were monitored prospectively for 12 months. Preoperatively, and 1, 6 and 12 months postoperatively, distance and reading visual acuities were evaluated; the central visual field was assessed by automated static perimetry. RESULTS: Twelve months after surgery, distance and reading visual acuities had improved in both groups, but to a significant degree only in Trypan-Blue-treated eyes. The difference between the two groups was not significant. Likewise at this juncture, the mean size of the visual-field defect remained unchanged in Trypan-Blue-treated eyes (preoperative: 4.3 (SD 2.1) dB; 12 months: 4.0 (2.1) dB (p = 0.15)), but had increased in Infracyanine-Green-treated ones (from 5.3 (3.7) dB to 8.0 (5.2) dB (p = 0.027)). CONCLUSION: Unlike visual acuity, the central visual field had deteriorated in Infracyanine-Green-treated eyes but not in Trypan-Blue-treated eyes 12 months after surgery. Hence, as a predictor of functional outcome, testing of the central visual field may be a more sensitive gauge than visual acuity. Furthermore, Infracyanine Green may have a chronic and potentially clinically relevant effect on the macula which is not reflected in the visual acuity.

An Investigation of the Anodic Oxidation of Aluminum in a Sulfuric Acid Electrolyte

When aluminum is allowed to stand in air or is heated in air, a thin oxide film is produced on the metal. If aluminum is made the anode in a suitable electrolyte and a current applied, a coating is obtained which is similar to that produced in air, but may be effected much quicker. This film is thicker, harder, more resistant to corrosion and abrasion, and more adhesive than the natural oxide. The film is porous and makes an excellent adsorptive for dyes and pigments.

The Characteristics of the Electrolyte in the Series System of Electrolytic Copper Refining

Almost everyone is familiar with the tremendous importance of copper in our everyday life. One of the pro­perties of copper which determines its great usefulness to mankind is its electrical conductivity. This property alone has more to do with the prominence of copper among useful metals then does any other.

Effect of two bioabsorbable barrier membranes on bone regeneration of standardized defects in calvarial bone: a comparative histomorphometric study in pigs

BACKGROUND: The effect of two different bioabsorbable collagen membranes on bone regeneration was assessed in standardized, membrane-protected calvarial defects in pigs. METHODS: Two standardized defect types (6 x 6 x 6 mm and 9 x 9 x 9 mm) were produced in the calvaria of pigs: empty defects without a membrane (group 1; eight defects per size); defects filled with deproteinized bovine bone mineral (DBBM) without a membrane (group 2; eight defects per size); defects filled with DBBM and covered by a collagen membrane (group 3; eight defects per size); and defects filled with DBBM and covered by a cross-linked collagen membrane (CCM) (group 4; eight defects per size). Sacrifice took place 16 weeks after surgery, and the following parameters were analyzed: descriptive histology; semiquantitative histology (SQH), assessing bone regeneration in the whole defect area; and histomorphometric analysis of the percentage of bone and DBBM in the regenerated area at three different depth levels of the defect. RESULTS: Using SQH, both membrane types resulted in significantly better bone regeneration compared to groups 1 and 2, irrespective of the defect size (P <0.005), with no difference between the two membranes. In the histomorphometric analysis, the layer immediately below the surface exhibited a significantly higher percentage of bone in groups 3 (27%) and 4 (36%) versus the two other groups for the 9 x 9 x 9-mm defects. No such differences were apparent for the 6 x 6 x 6-mm defects or the other two depth levels (bottom and middle layer) for either defect size. CONCLUSIONS: The two collagen membranes tested significantly enhanced bone regeneration, especially in the superficial level of the calvarial bone defects. The prototype CCM did not provide any further advantage in the present animal model.