Factorial-based response-surface modeling with confidence intervals for optimizing thermal-optical transmission analysis of atmospheric black carbon.

Thermal-optical transmission (TOT) analysis measures black carbon (BC) in atmospheric aerosol on a fibrous filter. The method pyrolyzes organic carbon (OC) and employs laser light absorption to distinguish BC from the pyrolyzed OC; however, the instrument does not necessarily separate the two physically. In addition, a comprehensive temperature protocol for the analysis based on the Beer-Lambert Law remains elusive. Here, empirical response-surface modeling was used to show how the temperature protocol in TOT analysis can be modified to distinguish pyrolyzed OC from BC based on the Beer-Lambert Law. We determined the apparent specific absorption cross sections for pyrolyzed OC (sigma(Char)) and BC (sigma(BC)), which accounted for individual absorption enhancement effects within the filter. Response-surface models of these cross sections were derived from a three-factor central-composite factorial experimental design: temperature and duration of the high-temperature step in the helium phase, and the heating increase in the helium-oxygen phase. The response surface for sigma(BC), which varied with instrument conditions, revealed a ridge indicating the correct conditions for OC pyrolysis in helium. The intersection of the sigma(BC) and sigma(Char) surfaces indicated the conditions where the cross sections were equivalent, satisfying an important assumption upon which the method relies. 95% confidence interval surfaces defined a confidence region for a range of pyrolysis conditions. Analyses of wintertime samples from Seattle, WA revealed a temperature between 830 degrees C and 850 degrees C as most suitable for the helium high-temperature step lasting 150s. However, a temperature as low as 750 degrees C could not be rejected statistically.

Effect of free gingival grafts on naturally-occurring recession in miniature swine.

Miniature swine exhibit naturally-occurring, progressive recession on facial surfaces of the permanent mandibular incisors. The purpose of this study was to determine whether placing a free gingival graft to augment the width of keratinized gingiva of mandibular incisors in miniature swine would prevent or retard recession at the grafted site compared to an untreated contralateral control site. In 8 litter-mate miniature swine, free gingival grafts were placed on the facial surface of the permanent central and lateral incisors on one side of the mandible. The contralateral mandibular incisors did not receive any treatment and served as controls. Clinical measurements, including eruption, recession, pocket depth, attachment level, and keratinized gingival width were obtained preoperatively, 2 to 3 weeks after surgery to assess the success of gingival augmentation, and 3, 6, and 9 months postoperatively. Eight grafted sites were successful and showed significant augmentation of the keratinized gingival width, with a mean increase of 5.8 +/- 0.7 mm, while 6 grafts failed and showed a slight decrease in the mean width of -0.4 +/- 0.5 from the preoperative to postoperative examination. All sites showed significant recession during the experimental period. Successful sites showed no statistically significant or clinically major difference in the rate or amount of recession than contralateral control sites. By 9 months, the average increase in recession from the baseline examination was 2.8 +/- 1.5 mm for successfully grafted sites and 2.6 +/- 1.3 mm for contralateral controls.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of connective tissue in inhibiting epithelial downgrowth on titanium-coated percutaneous implants.

Ideally, the surface of epithelium-penetrating implants should impede apical epithelial migration. Previous studies have shown that micromachined grooved surfaces can produce connective-tissue ingrowth, which inhibits epithelial downgrowth on percutaneous implants [Chehroudi et al., J. Biomed. Mater. Res., 24, 9, (1990)]. However, in those studies, connective tissue and epithelium interacted with the same surface so that the effects of the surfaces on each population could not be determined separately. The objectives of this study were (a) to examine cell behavior on implants in which connective tissue contacted surfaces of various topographies and epithelium encountered only a smooth surface, and (b) to compare one-stage and two-stage surgical techniques. Implants had a base component (BC) which was either smooth or had a surface with 19-micron- or 30-micron-deep grooves or 120-micron-deep tapered pits, and a skin-penetrating component (SPC) which was smooth. In the two-stage technique, the BC was implanted subcutaneously for 8 weeks, which permitted the healing of the peri-implant connective tissue. In the second stage the SPC was connected to the BC. For one-stage implants, BC & SPC were connected and implanted percutaneously. Implants (BC & SPC) were removed 1, 2, or 3 weeks after percutaneous implantation and histological sections were measured for recession, connective tissue and epithelial attachment as well as capsule thickness. Light microscopy indicated that both grooved and tapered pitted surfaces encouraged connective tissue ingrowth. On the grooved surfaces, the orientation of fibroblasts changed from an oblique to a more complex pattern which included cells having round nuclei within the grooves, as well as cells oriented oblique or perpendicular to the grooves. In the tapered pits a hammock-like arrangement of fibroblasts was observed. In some cases, foci of mineralization and formation of bonelike tissue were found on the grooved and pitted surfaces. The apical migration of the epithelium was significantly (p less than 0.05) inhibited by those micromachined surfaces which produced connective tissue ingrowth to the BC. This study found that placing the implants in two stages improved the performance of percutaneous devices, and that a further improvement was achieved if the implant had a surface promoting connective tissue ingrowth.

A light and electron microscopic study of the effects of surface topography on the behavior of cells attached to titanium-coated percutaneous implants.

Previous studies using light microscopy have demonstrated that micromachined grooved surfaces inhibit epithelial (E) downgrowth and affect cell orientation at the tissue/implant interface. This study investigates the ultrastructure of the epithelial and connective-tissue attachment to titanium-coated micromachined grooved, as well as smooth control, implant surfaces. V-shaped grooves, 3, 10, or 22 microns deep, were produced in silicon wafers by micromachining, replicated in epoxy resin, and coated with 50-nm titanium. These grooved, as well as smooth, titanium-coated surfaces were implanted percutaneously in the parietal area of rats and after 7 days processed for electron microscopy. The tissue preparation technique used in this study enabled us to obtain ultrathin sections with few artifacts from the area of epithelial and connective-tissue attachment. The histological observations demonstrated that E cells closely attached to, and interdigitated with, the 3-microns and 10-microns grooves. In contrast, E cells were not found inside the 22-microns-deep grooves and made contact only with the flat ridges between the grooves. As a general rule, fibroblasts (F) were oriented parallel to the long axis of the implants and produced a connective tissue capsule with 3-microns and 10-microns-deep grooved surfaces as well as smooth surfaces. On the 22-microns-deep grooved surfaces, however, F inserted obliquely into the implant. The attachment of F to the titanium surface was mediated by two zones; a thin (approximately 20 nm), amorphous, electron dense zone immediately contacting the titanium surface, and a fine fibrillar zone extending from the amorphous zone to the cell membrane. As oblique orientation of F has been associated with the inhibition of epithelial downgrowth, micromachined grooved surfaces of appropriate dimensions have the potential to improve the performance of percutaneous devices.

Effects of reduction of acute hospital services on district nursing services: implications for quality assurance.

Two questions of importance to those concerned with maintaining standards and increasing the efficiency of Community Nursing are: (1) does reducing hospital provision alter the number of patients referred for Community Nursing or the type of care provided; (2) are Community Nursing Services directed towards those who most require them? A base-line study was carried out in the first quarter of 1988, before the closure of one of two general hospitals in an inner London Health Authority and was replicated in the same quarter of 1989, after all acute inpatient services had been transferred to the other hospital. Comparison of patients discharged before and after closure showed no significant differences in patients' age, sex, proportion living alone, length of stay in hospital, readmissions or deaths within one month of discharge. There was some decline in general nursing care. Total discharges declined by 20% while the number of referrals remained the same, indicating that proportionately more patients were discharged with a referral. Comparing referred and unreferred patients showed that Community Nursing Services were already being directed towards those most in need both before and after hospital closure. Results suggest that Community Nursing helps to maintain patients in the community.

Titanium-coated micromachined grooves of different dimensions affect epithelial and connective-tissue cells differently in vivo.

A desirable feature of an implant surface which penetrates epithelium would be that the surface impedes epithelial downgrowth. Previous experiments have shown that the micromachined, horizontally oriented grooves on the percutaneous implant surface can impede epithelial downgrowth (Chehroudi et al., J. Biomed. Mater. Res., 22, 459 (1988) and 23, 1067 (1989)). However, little is known of the effect of varying groove parameters such as depth, spacing, and orientation on epithelial downgrowth and attachment of epithelial (E)-cells and fibroblasts (F) to percutaneous implants in vivo. Grooves were produced with a 30-micron pitch and depths of 22 microns, 10 microns, or 3 microns. In addition, 10-microns- and 3-microns-deep grooves were made with pitches of 39 microns and 7 microns, respectively. Implants with grooves oriented either horizontally or vertically to the long axis of the implant as well as smooth control surfaces were coated with 50 nm of titanium and placed in the parietal area of rats for a period of 7 days. Close attachment of E-cells was found on the smooth, 10-microns- and 3-microns-deep, horizontally or vertically aligned grooved surfaces; in contrast, E-cells bridged over the 22-microns-deep, horizontally oriented grooves. F formed a capsule on the smooth surface as well as the 10-microns- and 3-microns-deep horizontally oriented grooves, but F inserted obliquely into the 22-microns-deep, horizontally aligned grooved surface. Histomorphometric measurements indicated that the epithelial downgrowth was greatest on the vertically oriented grooved and smooth surfaces and was shortest on the 22-microns-deep and 10-microns-deep horizontally aligned grooved surfaces. These differences indicate that epithelial downgrowth was accelerated on the vertically oriented grooved surfaces and inhibited on the horizontally oriented grooved surfaces. Moreover, the mechanism of inhibition of the epithelial downgrowth may differ among these surfaces. E-cells bridged over the 22-microns-deep grooves and their migration appeared to be inhibited by the F that inserted into the implant surface. In the shallower horizontal grooves, however, epithelial downgrowth was probably inhibited by contact guidance because there was no evidence of F inserting obliquely into the implant surface.

Effects of a grooved titanium-coated implant surface on epithelial cell behavior in vitro and in vivo.

The effects of a grooved titanium-coated substratum on epithelial (E) cell behavior were studied in vitro and in vivo. V-shaped grooves, 10 microns deep, were produced in silicon wafers by micromachining, a process which was developed for the fabrication of microelectronic components. The grooved substrata were replicated in epoxy resin and coated with 50 nm of titanium. More E cells were found attached to the grooved titanium surfaces than to adjacent smooth surfaces. In comparison to the smooth surfaces where clusters of E cells were randomly oriented, on the grooved surfaces, clusters of E cells were markedly oriented along the long axis of grooves. Grooved and smooth titanium-coated epoxy implants were placed percutaneously in the parietal area of rats. Electron and light microscopic observations indicated that E cells were tightly attached to the implant surfaces and this attachment is through basal lamina-like and hemidesmosome-like structures. In the grooved portion of the implant, E cells interdigitated into the grooves and had rounded nuclei. Histomorphometric measurements indicated that there was a shorter length of epithelial attachment, longer length of connective tissue attachment, and less recession in the grooved, compared to the smooth portion of implants after 7 and 10 days. These results indicate that horizontal grooves produced by micromachining can significantly impede epithelial downgrowth on titanium-coated epoxy implants.

Effects of a grooved epoxy substratum on epithelial cell behavior in vitro and in vivo.

The effects of grooved epoxy substrata on epithelial (E) cell behavior were studied in vitro and in vivo. V-shaped grooves, 10 microns deep, were produced in silicon wafers by micromachining, a process which was developed for the fabrication of microelectronic components. The grooved substrata were replicated in epoxy resin. More E cells attached to grooved surfaces than to adjacent smooth surfaces. Clusters of E cells were markedly oriented by the grooved surfaces in comparison to the adjacent smooth surfaces where the orientation was random. Grooved and smooth epoxy implants were placed percutaneously in the parietal area of rats. One week after implantation E cells were found to adhere tightly to the implant surfaces. In the grooved portion of the implant E cells interdigitated into the grooves and had rounded nuclei. Histomorphometric measurements indicated that there was a shorter length of epithelial attachment and a longer length of connective tissue attachment in the grooved, compared to the smooth, portion of implants. After 10 days the epithelial attachment had migrated down the length of the protruding smooth portion of the implant and was located on the base of the implant. However, epithelium remained attached to the grooved portion of the implant. These observations indicate that grooved surfaces have the potential to impede epithelial downgrowth on percutaneous devices.

Acquired C1 esterase inhibitor deficiency.

A case of acquired C1 esterase inhibitor deficiency and its anaesthetic implications is presented. Prophylaxis against angioneurotic oedema using danazol and tranexamic acid is described and the resultant complication of mesenteric venous thrombosis reported.

Ultrastructural study of the attachment of human gingiva to titanium in vivo.

A study was conducted to determine if the behavior of epithelium in vitro is similar to its attachment behavior in vivo by the use of small sections of titanium-coated implants that could be inserted in human gingiva. The size of the implants allowed their insertion in a limited region and enabled the fixation and embedding procedures that are necessary for electron microscopy to be effective. Examination of the thin sections obtained from this material demonstrated that the epithelial cells attached to titanium in a manner similar to that observed in vitro and similar to the way that epithelium attaches to the tooth in vivo (Fig. 2). That is, there was a formation of hemidesmosomes and basal lamina. Because the ability of the oral epithelium to form such an attachment with an implant may be a crucial factor in the determination of clinical success or failure, this study provides further evidence that one reason for the apparent clinical success of titanium dental implants may lie in the firm attachment of epithelial cells to this material.

Grooved titanium surfaces orient growth and migration of cells from human gingival explants.

A silicon mask-etching technique was used to prepare grooved surfaces that control the direction of outgrowths of human gingival explants. The method used to produce the grooves is excellent in terms of both the uniformity of the grooves and the control with which surfaces of the desired specifications can be obtained.

Ultrastructural characteristics of progenitor cell populations in the periodontal ligament.

Electron microscope radio-autography was used in an attempt to identify any relationship between the location and degree of differentiation of progenitor cells in the periodontal ligament (PDL). Ligament fibroblasts were classified on the basis of their nuclear/cytoplasmic ratio and their distance to the closest blood vessel measured. It was determined that an undifferentiated paravascular progenitor cell population exists, and that the PDL also contains progenitor cells showing a range of cytodifferentiation.

Dentin matrix gelatin (DMG) as a possible "universal" grafting material in periodontics.

The ideal of periodontal surgery is the total regeneration of the lost periodontal complex. A promising new osseous grafting material is Dental Matrix Gelation (DMG). DMG was prepared by a method similar to that of Conover and Urist (1979). This consisted of sequential extraction in 1:1 chloroform-methanol, 25 degrees C for 1 hour; 0.6 N HCl, 2 degrees C for 24 hours with constant agitation; 2 M CaCl2, 2 degrees C for 1 hour; 0.5 M EDTA pH 7.4, 2 degrees C for 1 hour; washed in distilled water 1 hour. Twelve rats were anesthetized, had heads shaved, midline flaps reflected, and 2 mm holes drilled through the right and left parietal bones. This type of osseous defect normally heals only by fibrous scarring and has been used to define osteoinductive materials. The DMG was cut into pieces about 1 mm square and placed into the right side defect while the left side remained open as a control. The animals were sacrificed on a schedule of two rats every 2 weeks until the 10th week when four rats were killed. The results showed complete osseous closure of the DMG site while the control healed by fibrous scarring. DMG seems to have strong osteoinductive power, and used allogenically has great potential as a commercially viable implant material.