Optical properties of (GaAs)n clusters (n = 2-16).

The electronic and geometrical structures of the lowest triplet states of (GaAs) n clusters ( n = 2-16) are studied using density functional theory with generalized gradient approximation (DFT-GGA). It is found that the triplet-state geometries are different from the corresponding singlet-state geometries; for n = 2-8, 10, and 11, the triplets and singlets have different topologies, while the (GaAs) 9, (GaAs) 12, (GaAs) 15, and (GaAs) 16 triplets possess a reduced symmetry, due to Jahn-Teller distortions. Except for GaAs, the singlet states are the ground states. Excitation energies and oscillator strengths are computed for excitations from the ground state to ten singlet states of all (GaAs) n clusters using time-dependent density functional theory. The adiabatic singlet-triplet gap is compared to the vertical gap, and the difference in the eigenvalues of the highest-occupied and lowest-unoccupied molecular orbitals (the HOMO-LUMO gap). While these three values show large oscillations for small n, they approach each other as the cluster size grows. Thus, the HOMO-LUMO gap computed using the DFT-GGA approach presents a rather reliable estimate of the adiabatic singlet-triplet gap.

Localized antimicrobial peptide expression in human gingiva.

The stratified epithelia of the oral cavity are continually exposed to bacterial challenge that is initially resisted by innate epithelial factors and by the recruitment of neutrophils. Antimicrobial peptides from phagocytes and epithelia contribute to this antimicrobial barrier. Using antibodies and in situ hybridization, we explored antimicrobial peptide expression in the varied epithelia of the periodontium and in cultured gingival epithelial cells. In gingival tissue, mRNA for the beta-defensins, human beta-defensin 1 (hBD-1) and human beta-defensin 2 (hBD-2) was predominately localized in suprabasal stratified epithelium and the peptides were detected in upper epithelial layers consistent with the formation of the stratified epithelial barrier. In cultured epithelial cells, both hBD-1 and -2 peptides were detected only in differentiating, involucrin-positive epithelial cells, although hBD-2 required stimulation by proinflammatory mediators or bacterial products for expression. Beta-defensins were not detected in junctional epithelium (JE) that serves as the attachment to the tooth surface. In contrast, alpha-defensins and cathelicidin family member LL-37 were detected in polymorphonuclear neutrophils (PMNs) that migrate through the JE, a localization that persists during inflammation, when the JE and surrounding tissue are highly infiltrated with PMNs. Thus, the undifferentiated JE contains exogenously expressed alpha-defensins and LL-37, and the stratified epithelium contains endogenously expressed beta-defensins. These findings show that defensins and other antimicrobial peptides are localized in specific sites in the gingiva, are synthesized in different cell types, and are likely to serve different roles in various regions of the periodontium.

Pluronic polyol effects on human gingival fibroblast attachment and growth.

BACKGROUND: Enhanced speed of human gingival fibroblast (HGF) spreading and attachment, as affected by ionic bonding interactions, may facilitate cell orientation and subsequent collagen synthesis to promote early wound healing. The purpose of this study was to determine the in vitro effects of pluronic polyols, a family of widely used surfactants currently used as drug carriers for antibiotic, anti-inflammatory, and anti-neoplastic agents, on the attachment and growth of human gingival fibroblasts (HGF) to dentin and plastic surfaces using established tissue culture techniques. METHODS: Plastic culture wells containing Eagle's minimal essential media (EMEM) with 10% fetal calf serum and Pluronic F-68 or F-127 in concentrations from 1.2 x 10(-2) to 1.2 x 10(-10) M were incubated with HGF and run in replicates of ten. Attached cells were quantified by measuring the optical density of methylene blue-stained cells. Additional experiments were conducted using human dentin sections as a substrate and Pluronic F-68 or F-127 at a concentration of 1.2 x 10(-8) M. In these experiments, HGF were stained with acridine orange and quantified per unit area of dentin by fluorescence microscopy. RESULTS: Attachment and growth of HGF to both plastic and dentin were significantly increased over serum controls by very low concentrations of Pluronic F-68 and F-127 by 30 minutes, with attachment reaching a plateau at 2 hours. CONCLUSIONS: Pluronic polyols, a family of widely used surfactants, in very low dosages may be beneficial in early postsurgical wound healing by facilitating early attachment and enhancing the growth rate of human gingival fibroblasts.

Rate of pull-out strength gain of dual-etched titanium implants: a comparative study in rabbits.

The purpose of this study was to investigate the rate of pull-out strength gain of an etched titanium implant surface. Rabbit tibiae were used to compare machined titanium and proprietary dual-etched titanium implants. Two custom cylindric implants (3 mm in diameter and 4 mm in length) were placed in each right anteromedial tibia in 31 rabbits. At weeks 1, 2, 3, 4, 5, and 8, the implants in 5 rabbits were subjected to failure shear loading in a pull-out test. For shear failure testing, each tibial segment was mounted in a precision alignment jig, and an Instron pull-out test was performed on each implant. Beginning at week 3, there was a statistically significant difference (P < .01) between the dual-etched and the machined implants. There was a significant increase in strength for dual-etched implants between week 5 and week 8, while the machined implants did not show an increase during this time interval. The etched implants maintained a significantly greater pull-out strength for the remainder of the study, with a 3.2-fold greater mean strength at 8 weeks, equivalent to 6 months in humans. At 3 weeks, the etched implant's strength exceeded the strength that the machined implant had achieved at 8 weeks. In short-term healing in the rabbit tibia, the dual-etched surface demonstrated a more rapid rate of pull-out strength gain than the machined surface and remained significantly stronger throughout the 8 weeks of the study.

Evaluation of titanium implants placed into simulated extraction sockets: a study in dogs.

The purpose of this study was to evaluate the effect of gap width on bone healing around implants placed into simulated extraction socket defects of varying widths in 10 mongrel dogs. All premolars were removed and the alveolar ridges were reduced to a width of 7 mm. Nine weeks later, a total of 80 implants, 10 mm long by 3.3 mm wide, were placed into osteotomy sites prepared to 3 different diameters in the coronal half, simulating extraction sockets. Three experimental sites, with gap sizes of 0.5 mm, 1.0 mm, and 1.4 mm, were created; the control sites had no gap. The depth of each defect was measured at the time of implant placement. All implants were stable at the time of placement. The dogs were euthanized 12 weeks after implant placement, and blocks containing the implants and adjacent bone were submitted for histologic evaluation. Clinically, all control and test sites healed, with complete bone fill in the defect. Percentages of bone-to-implant contact were measured histologically. As the gap widened, the amount of bone-to-implant contact decreased, and the point of the highest bone-to-implant contact shifted apically. These changes were statistically significant (P < .001). No statistically significant differences in bone-to-implant contact were found between the sites when the apical 4 mm of implants were compared. Within the limits of this study, the simulated extraction socket defects healed clinically, with complete bone fill, regardless of the initial gap size. However, the width of the gap at the time of implant placement had a significant impact on the histologic percentage and the height of bone-to-implant contact.

Role of pilot instrument proficiency in the safety of helicopter emergency medical services.

OBJECTIVES: To determine whether instrument-proficient pilots would more safely manage a flight into unplanned instrument meteorologic conditions (IMC) than would nonproficient pilots. METHODS: A controlled experimental study was performed using a full-motion helicopter simulator. Participants were emergency medical services (EMS) pilots with commercial licenses and previous simulator experience who were blinded to the study design and hypothesis. During a simulated EMS mission, cloud ceiling and visibility were decreased until IMC prevailed, and pilot actions were recorded. Data included the altitude at which the aircraft entered IMC, and whether the pilots maintained control of the aircraft, flew within aviation standards (i.e., bank angle, airspeed), and safely landed. RESULTS: Twenty-eight pilots (13 instrument-proficient, 15 nonproficient) participated; they had a median of 6,300 hours of helicopter experience. Two pilots crashed, both from the nonproficient group. The instrument-proficient pilots lost control less often (15% vs 67%, p < 0.05), maintained instrument standards more often (77% vs 40%, p < 0.05), and entered IMC at a higher altitude (689 feet vs 517 feet, p < 0.05) compared with the nonproficient pilots. Instructor comments indicated that the nonproficient pilots made more errors than did the instrument-proficient pilots. CONCLUSIONS: Instrument-proficient pilots more safely manage an unexpected encounter with IMC. Helicopter EMS programs should strongly consider maintaining instrument proficiency to enhance safety.

Development and clinical evaluation of a root coverage procedure using a collagen barrier membrane.

The use of guided tissue regeneration (GTR) procedures in the treatment of gingival recession has shown promising results and is gaining clinical acceptance. The purpose of this study was to assess the use of a bioabsorbable collagen membrane as a barrier device in root coverage treatment of gingival recession defects. The study consisted of 10 patients with 10 defects of either Miller Class I or II description and gingival recession > or =2.5 mm. Clinical measurements taken at baseline included plaque index (PI) and gingival index (GI), clinical attachment level (CAL) measured with an automated probe and reference stent, recession depth (RD; mean = 3.19 +/- 0.26 mm), recession width (RW; 3.95 +/- 0.41 mm), probing depth (PD; 2.3 +/- 0.2 mm), and width of keratinized tissue (KT; 2.4 +/- 0.3 mm); measurements were repeated at 1, 2, and 4 weeks and 3 and 6 months post-treatment. During the surgical procedure, a mucoperiosteal flap was elevated and the respective root thoroughly planed. The collagen membrane was cut to cover the defect and surrounding bone, positioned over the root, and secured with 5-0 gut interdental sutures. The flap was coronally positioned to cover the membrane and sutured with 5-0 silk. Data were analyzed using the Student paired t-test to compare pre- and postsurgery measurements. The nonparametric Wilcoxon matched pairs test was used to analyze the significance of PI and GI at different time intervals. A statistically significant (P < 0.01) reduction in RD (-1.66 +/- 0.25 mm) was observed at 6 months, representing 51.6% total attainable root coverage. Clinically, a statistically significant mean gain of 1.34 +/- 0.47 mm CAL and 0.90 +/- 0.32 mm KT was observed at 6 months. No statistical differences were found in PD and RW between baseline and 6 months postoperatively. PI and GI remained low and showed no statistically significant change (P < 0.05) throughout the study period. Results from this study suggest that a collagen membrane can be used successfully as a barrier device in GTR-based root coverage procedures.

Bacterial adherence to guided tissue regeneration barrier membranes exposed to the oral environment.

Microbial colonization of barrier materials used in guided tissue regeneration (GTR) is known to adversely affect treatment outcomes. The purpose of this study was to compare the rate at which 11 commonly-occurring oral bacteria species colonize three different barrier materials (collagen, expanded polytetrafluoroethylene, and polylactic acid). The study group consisted of 10 systemically healthy individuals with no history of periodontal disease and absence of antimicrobial therapy within the previous 3 months. In each patient, 4 teeth per quadrant (P1, P2, M1, M2) were selected and 3 teeth were randomly assigned as test teeth while the remaining tooth acted as a control site (i.e., natural colonization of the tooth surface). These teeth were then randomly assigned to receive one of the three barrier types (i.e., each patient received 4 barriers of each type, 1 per quadrant). A 2 x 5 mm piece of barrier material was positioned over the oral surface of the buccal marginal gingiva and secured with an external sling suture. With oral hygiene procedures suspended, one barrier of each type was collected at 1, 3, 7, and 14 days. Slot immunoblot assay demonstrated that all species types (A. actinomycetemcomitans, A. viscosus, B. melaninogenicus, F. nucleatum, P. gingivalis, P. intermedia, S. mutans, S. sanguis, Selenomonas sputigena, T. denticola, and T. vincentii) were present. Semi-quantitative scoring (scale 0 to 3) of slot blot results and analysis by chi-square ratio and Pearson correlation test indicated that while total bacteria adherence increased over time (P < 0.05), the 3 barrier types and the control sites did not differ in numbers or species of colonizing bacteria detected per time point. These results suggest that under these experimental conditions the barrier materials tested do not differ in bacteria adherence or antimicrobial properties.

Suture materials and techniques.

Surgical improvements in periodontics have been achieved because of advances in basic science, animal and clinical research, and the insight of outstanding clinicians. Industry continues to develop new surgical materials, improving the quality of sutures and needles and in turn, supporting advances in all surgical specialties. The purpose of this article is to review sutures and suturing by focusing on both materials and methods as they relate to the present practices of surgical periodontics and dental implants.

Utilization of a resorbable collagen membrane in repairing gingival recession defects.

Predictable coverage of exposed root surfaces and the corresponding treatment of gingival recession defects remain important objectives of periodontal therapy. A variety of techniques have been developed during the past several decades to address this common clinical challenge. Traditional surgical approaches have been relatively successful in achieving root coverage. Attempts have been made recently to achieve root coverage with surgical techniques based on the principles of guided tissue regeneration, using resorbable and nonresorbable materials. The learning objective of this article is to present case documentations of root coverage, using a resorbable collagen barrier. The results achieved illustrate the potential of this material in the treatment of gingival recession. The biologic properties of collagen as a barrier material, the surgical approach, and the principles of case selection are reviewed.

Evaluation of a collagen membrane with and without bone grafts in treating periodontal intrabony defects.

The aim of this study was to compare the clinical regenerative capacity of collagen membrane with and without demineralized freeze-dried bone allografts (DFDBA) in treating periodontal intrabony defects. Ten systemically healthy patients with similar bilateral periodontal defects were scheduled for surgery. Each patient had at least > or = 6 mm clinical probing depth and loss of attachment at selected sites. Baseline measurements included gingival index (GI), plaque index (PI), gingival recession (GR), clinical attachment level (CAL), probing depth (PD), and mobility. At the time of surgery, the defects were randomly assigned to either test (collagen membrane plus DFDBA) or control group (collagen membrane only). Stent to base of the defects, stent to crest bone, crest of bone to base of the defect, and width of the defects were recorded at the time of surgery and reentry. Eight patients returned after 6 months for reentry surgery. Statistical analysis with a paired t test was used to evaluate the treatment effect and comparison between test and control groups. In addition, a McNemar test was used to analyze the significance of GI, PI, and mobility at different times. The result of this study indicated that both the collagen plus DFDBA and the collagen alone treatment groups had a significant decrease of PD (3.4 +/- 0.4 and 3.2 +/- 0.4 mm), gain of CAL (2.3 +/- 0.5 and 2.0 +/- 0.4 mm), and defect fill (1.7 +/- 0.3 and 1.9 +/- 0.9 mm) (P < 0.05) when compared to the presurgery status. However, there was no significant difference in PD, AL, GR, defect fill, crestal bone resorption, GI, PI, or mobility between the test group and control group. No adverse tissue reaction, infection, or delayed wound healing was noted throughout the treatment in either group. This study suggests that the collagen membrane is well tolerated by the human tissues. Both treatments, either collagen membrane plus DFDBA or collagen membrane alone, promoted significant resolution of periodontal intrabony defects. The addition of a bone graft (DFDBA) with a collagen membrane appears to add no extra benefit to the collagen membrane treatment.

Regenerative treatment of periodontal defects utilizing a bioresorbable collagen membrane.

Barrier membranes composed of resorbable collagen have demonstrated potential for use in guided tissue regeneration (GTR) procedures for repair and regeneration of periodontal defects. This article reviews the rationale for use of a collagen membrane in GTR therapy and related clinical procedures. Characteristics of the material are outlined, and indications and contraindications for utilization are discussed. Two cases are presented to demonstrate details of these principles and techniques. The learning objective of this article is to familiarize the reader with a new absorbable collagen membrane and its application in the periodontal area.

Evaluation of an absorbable collagen membrane in treating Class II furcation defects.

Recent research has focused upon the utilization of an absorbable collagen membrane in guided tissue regeneration (GTR). Concern exists as to whether this type of membrane is beneficial in the treatment of periodontal defects. The purpose of this study was to evaluate the effect of a type I bovine collagen membrane on treatment of Class II furcation defects. Twelve systemically healthy patients (six male and six female, ages 32 to 68) were treated. Each had bilateral mandibular furcation defects with attachment loss > or = 6 mm. Prior to surgery all patients completed initial therapy including scaling and root planing. At the time of the surgery, teeth were randomly assigned to either a control (flap debridement alone) or test (flap debridement plus collagen membrane) group. Data were collected on the day of surgery, and 2, 4, and 6 months post-surgery and at the 12 month re-entry surgery. Clinical measurements included probing depth (PD), clinical attachment level (CAL), gingival recession (GR), stent to base of defect (SB), crestal bone to base of defect (CB), width of defect, and mobility. Statistical analysis was performed utilizing the paired t test. Both control and test groups demonstrated significant (P < 0.05) improvement at 12 months re-entry in PD, CAL, SB, and CB when compared to the presurgery status. While there is no significant difference in PD, CAL, GR, width of defect, and mobility between control and test groups, sites treated with the collagen membrane had significantly higher bone fill (SB and CB) at re-entry.(ABSTRACT TRUNCATED AT 250 WORDS)

Overview of the space environmental effects observed on the retrieved Long Duration Exposure Facility (LDEF).

The Long Duration Exposure Facility (LDEF), which encompassed 57 experiments with more than 10,000 test specimens, spent 69 months in low Earth orbit (LEO) before it was retrieved by the Space Shuttle in January 1990. Hundreds of LDEF investigators, after studying for over two years these retrieved test specimens and the onboard recorded data and systems hardware, have generated a unique first-hand view of the long term synergistic effects that the LEO environment can have on spacecraft. These studies have also contributed significantly toward more accurate models of the LEO radiation, meteoroid, manmade debris and atomic oxygen environments. This paper provides an overview of some of the many LDEF observations and the implications these can have on future spacecraft such as Space Station Freedom.

Cells and materials involved in guided tissue regeneration.

Just over 10 years ago a group of imaginative periodontal researchers reported that tissues lost to the destructive mechanisms of inflammatory periodontal disease could be regenerated either in part or whole by the use of a surgical technique that would become universally known as guided tissue regeneration. Since then, tremendous progress has been made in adapting these early research principles into a clinical treatment modality that is now recognized as a viable component of contemporary periodontal therapy. However, many questions remain as to the mechanisms involved in regenerative tissue formation and how to design surgical procedures and materials to best harness the regenerative capacities of the periodontium. This article reviews current concepts and controversies regarding the biologic basis of periodontal regeneration and biomaterials used in guided tissue regeneration therapy. Pros and cons related to regenerative techniques currently in use are discussed along with future directions in the field of periodontal regeneration.

Evaluation of ferric oxalate as an agent for use during surgery to prevent post-operative root hypersensitivity.

The aim of this study was to evaluate the effectiveness of a 6% ferric oxalate solution applied during periodontal surgery to prevent post-operative tooth hypersensitivity. Twenty-five adult patients with similar bilateral periodontal defects participated in this study. Data were collected at baseline (1 week prior to surgery) and 1, 2, 4, and 6 weeks following surgery. Sensitivity level was determined using the visual analog scale (VAS) with the following stimuli: 1) mechanical stimulation with a No. 23 dental explorer; 2) water at 50 degrees C; 3) ice; and 4) electric pulp tester (EPT). Teeth were randomly assigned to either test (6% ferric oxalate in 0.9% saline) or control (0.9% saline) groups. Solutions were applied to the exposed root surfaces for 1 minute during surgery. Data were analyzed by repeated measures ANOVA, paired t-test, and Pearson's correlation test. Results from this study demonstrated statistically significant reduction in the responses to thermal stimuli, especially cold, between groups treated with ferric oxalate as compared to those treated with saline. For the cold test the difference increased with time from baseline to 6 weeks. Statistically significant (P < 0.05) differences in sensitivity to heat between groups were also observed, but only at 2 and 4 weeks following surgery. There were no differences at any time period between the test and control groups when tactile or EPT techniques were used. In addition, there was no correlation between sensitivity and other clinical parameters. It was concluded from this study that 6% ferric oxalate was effective in reducing post-surgical cold sensitivity when applied during periodontal surgical procedures.

An in vitro study of dentinal tubule occlusion by ferric oxalate.

This study examined ferric oxalate's ability to occlude dentinal tubules both in the presence of a smear layer and after its removal. Radicular dentinal chips were prepared with a smear layer created from a high speed carbide bur. The dentinal chips were then grouped as follows: 1) those with the smear layer remaining intact; 2) those sonicated for 7 minutes; 3) those treated with 10% tetracycline HCl; 4) those treated with 0.5M EDTA; 5) those treated with 20% citric acid; or 6) those treated with saturated citric acid. Six percent ferric oxalate was applied for 1 minute to the dentinal chips under blinded conditions. The chips were examined under SEM and the number of small and large crystals formed were counted. The results indicate that a decrease in the number of small crystals occurs following pretreatment of the smear layer by chemical means. An increased variability in size and shape of the crystals is also observed when no chemical pretreatment is used. Thus, relative to the number of crystals that form, no chemical pretreatment of radicular dentin is indicated prior to application of ferric oxalate in the treatment of root sensitivity.

Surgical treatment of induced peri-implantitis in the micro pig: clinical and histological analysis.

The purpose of this pilot study was to determine if lost osseous support adjacent to root form implants could be regenerated using a guided tissue regeneration technique. Three fixtures were placed in each edentulous mandibular bicuspid region of two micro pigs. A total of 6 fixtures were placed in each pig. Due to the presence of a pathologic condition, which was in no way related to the research, the results of one pig were not evaluated. Following osseointegration, peri-implantitis were induced by the use of ligatures and a soft diet. Three modalities of treatment were performed. Utilizing a surgical flap approach, one third of the fixtures (one per quadrant) were covered with expanded polytetrafluoroethylene (ePTFE) membrane and submerged under the soft tissue complex. The second group of fixtures were submerged under the soft tissue complex with no ePTFE membrane. The control fixtures along with their abutments were debrided and remained non-submerged. All fixtures were debrided using an air-abrasive polishing system. The osseous defects around the fixtures were measured from a fixed reference point at the time of surgery and after obtaining block sections.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of nicotine on reproduction and attachment of human gingival fibroblasts in vitro.

The ability of fibroblasts to reproduce and attach to teeth is of paramount importance in re-establishing the lost connective tissue attachment after periodontal therapy. This study examined the effect of nicotine, a major component of the particulate phase of tobacco smoke, on human gingival fibroblast (HGF) reproduction and attachment to tissue culture surfaces. Pooled HGF cultures made from explants of gingival biopsies were utilized between passages 5 and 10 and plated in 96-well plates at 1.0 x 10(4) cells per well. Cell numbers were determined using 3-(4,5-dimethylthiazol-2-y)-2,5-diphenyl tetrazolium bromide (MTT), which is a reflection of mitochondrial dehydrogenase activity. The concentrations of nicotine used were 0.025, 0.05, 0.1, 0.2, and 0.4 microM, the average serum concentration for a smoker being approximately 0.1 microM. The effect of continuous nicotine exposure on HGF reproduction was determined by incubating cell cultures and media containing nicotine for up to 48 hours. Residual toxicity was determined by preincubating cells with nicotine for 1 or 6 hours. HGF suspensions and increasing concentrations of nicotine were added together to determine the effect on attachment. Results showed an enhanced effect of nicotine on HGF attachment, with increasing numbers of cells attaching with increasing nicotine concentrations, compared to the control. Low concentrations of nicotine had a stimulatory effect on cell replication, while higher concentrations of nicotine appear to have no significant effect on HGF reproduction. The responses of cells to some concentrations of nicotine may persist after its removal.