95 research outputs found
Small animal bone healing models : standards, tips, and pitfalls results of a consensus meeting
No full textSmall animal fracture models have gained increasing interest in fracture healing studies. To achieve standardized and defined study conditions, various variables must be carefully controlled when designing fracture healing experiments in mice or rats. The strain, age and sex of the animals may influence the process of fracture healing. Furthermore, the choice of the fracture fixation technique depends on the questions addressed, whereby intra- and extramedullary implants as well as open and closed surgical approaches may be considered. During the last few years, a variety of different, highly sophisticated implants for fracture fixation in small animals have been developed. Rigid fixation with locking plates or external fixators results in predominantly intramembranous healing in both mice and rats. Locking plates, external fixators, intramedullary screws, the locking nail and the pin-clip device allow different degrees of stability resulting in various amounts of endochondral and intramembranous healing. The use of common pins that do not provide rotational and axial stability during fracture stabilization should be discouraged in the future. Analyses should include at least biomechanical and histological evaluations, even if the focus of the study is directed towards the elucidation of molecular mechanisms of fracture healing using the largely available spectrum of antibodies and gene-targeted animals to study molecular mechanisms of fracture healing. This review discusses distinct requirements for the experimental setups as well as the advantages and pitfalls of the different fixation techniques in rats and mice
Effects of de- and remineralization of dentin on bond strengths yielded by one-, three-, and four-step adhesives
No full textPURPOSE: To assess the effect of different peri- and intertubular dentin mineralization conditions and etching on shear bond strength in vitro. MATERIALS AND METHODS: One hundred fifty crowns of extracted bovine incisors were embedded in resin and ground to expose the buccal coronal dentin. Sixty specimens were subjected to a demineralizing solution (DS) and another 60 teeth to a bacterial-based laboratory caries model (S. mutans, SM). Thirty specimens of each demineralization protocol (DS and SM) were randomly selected and remineralized (-R). Thirty sound dentin specimens served as control (C). Resin composite buildups (Tetric) were bonded after application of one of the following adhesives: a one-step self-etching adhesive (Xeno III), and a self-etching adhesive (Syntac Classic) without (three-step) and with prior additional 35% phosphoric acid etching (etch-and-rinse, four-step). Teeth were subjected to shear bond strength testing in a universal testing device at a crosshead speed of 0.5 mm/min (Ultradent method). RESULTS: Bond strength value for group C ranged from 6.3 to 8.4 MPa (p > 0.05). DS and DS-R samples showed in creased bond strength with the one-step adhesive (11.6 MPa, p 0.05). Remineralization showed no effect on the latter group. CONCLUSION: The degree of mineralization of the dentin is important for adhesion. Additional etching with phosphori acid reduced bond strength of a three-step adhesive
Making things happen : a model of proactive motivation
No full textBeing proactive is about making things happen, anticipating and preventing problems, and seizing opportunities. It involves self-initiated efforts to bring about change in the work environment and/or oneself to achieve a different future. The authors develop existing perspectives on this topic by identifying proactivity as a goal-driven process involving both the setting of a proactive goal (proactive goal generation) and striving to achieve that proactive goal (proactive goal striving). The authors identify a range of proactive goals that individuals can pursue in organizations. These vary on two dimensions: the future they aim to bring about (achieving a better personal fit within one’s work environment, improving the organization’s internal functioning, or enhancing the organization’s strategic fit with its environment) and whether the self or situation is being changed. The authors then identify “can do,” “reason to,” and “energized to” motivational states that prompt proactive goal generation and sustain goal striving. Can do motivation arises from perceptions of self-efficacy, control, and (low) cost. Reason to motivation relates to why someone is proactive, including reasons flowing from intrinsic, integrated, and identified motivation. Energized to motivation refers to activated positive affective states that prompt proactive goal processes. The authors suggest more distal antecedents, including individual differences (e.g., personality, values, knowledge and ability) as well as contextual variations in leadership, work design, and interpersonal climate, that influence the proactive motivational states and thereby boost or inhibit proactive goal processes. Finally, the authors summarize priorities for future researc
Cytostatics. 23. Tumor-inhibiting effect of N,N.',N"-tris(hydroxymethyl)melamine and analogous compounds
No full textThe carcinostatic effects of 7 aminotriazine derivs. [I, R = R1 = NHCH2OH (II), N(CH2OMe)2, NHCH2SO3Na, N(CH2SEt)2, or morpholinomethylamino (III), or R = NHCH2CN, R1 = Cl or NH2] were tested on Yoshida sarcoma and sarcoma 180 in rats. Only N,N',N''-tris(hydroxymethyl)melamine (II) [1017-56-7] had a marked effect. III also inhibited tumor growth, but did not increase the survival time. II and III also had bacteriostatic and fungistatic effects in vitro. II was able to aminomethylate morpholine in vitro under physiol. conditions
What It Takes to Get Proactive: An Integrative Multilevel Model of the Antecedents of Personal Initiative
No full textBuilding upon and extending Parker, Bindl, and Strauss's (2010) theory of proactive motivation, we develop an integrated, multilevel model to examine how contextual factors shape employees' proactive motivational states and, through these proactive motivational states, influence their personal initiative behavior. Using data from a sample of hotels collected from 3 sources and over 2 time periods, we show that establishment-level initiative-enhancing human resource management (HRM) systems were positively related to departmental initiative climate, which was positively related to employee personal initiative through employee role-breadth self-efficacy. Further, department-level empowering leadership was positively related to initiative climate only when initiative-enhancing HRM systems were low. These findings offer interesting implications for research on personal initiative and for the management of employee proactivity in [email protected]
Cytostatics. 21. Synthesis and carcinostatic action of N-[bis(2-chloroethyl)aminomethyl]amides
No full textTen title compds. RCONHCH2N(CH2CH2Cl)2 (I, R = Ph, 4-ClC6H4, 3-ClC6H4, 2-ClC6H4, 4-BrC6H4, 4-FC6H4, 4-O2NC6H4, 3-O2NC6H4, 4-MeC6H4, and CCl3 were prepd. by reaction of RCONHCH2Cl and NH(CH2CH2Cl)2 in Et2O at 0 Deg. All I had a higher carcinostatic activity on Yoshida sarcoma of rats and sarcoma 180 of mice than bis(2-chloroethyl)amine and were at least as effective as bis(2-chloroethyl)methylamine
Synthesis and local anesthetic action of N-(piperidinomethyl)-4-alkoxybenzamides
No full textHeating 4-BuOC6H4CONH2, HCHO, and piperidine gave 67% I (R = BuO) (II). Similarly prepd. were 4 other I (R = C1-5 alkoxy) and I (R = H). I inhibits impulse conduction in frog ventricle strips. II had a 50% inhibitory concn. of 3.4 micro M at pH 7.6
Modulation of fixation stiffness from flexible to stiff in a rat model of bone healing
No full textConstant fixator stiffness for the duration of healing may not provide suitable mechanical conditions for all stages of bone repair. Therefore, we investigated the influence of stiffening fixation on callus stiffness and morphology in a rat diaphyseal osteotomy model to see if healing time was shortened and callus stiffness increased through modulation of fixation from flexible to stiff. \ud
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An external unilateral fixator was applied to the osteotimised femur and stiffened by decreasing the offset of the inner fixator bar at 3, 7, 14, and 21 days post-operation. After 5 weeks the rats were killed and healing was evaluated with mechanical, histological and micro-computed tomography methods. Constant fixation stiffness control groups with either stiff or flexible fixation were included for comparison.\ud
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The callus stiffness of the stiff group and all 4 experimental groups was greater than in the flexible group. The callus of the flexible group was larger but contained a higher proportion of unmineralized tissue and cartilage. The stiff and modulated groups (3, 7, 14, and 21 days) all showed bony bridging at 5 weeks, as well as signs of callus remodeling. Stiffening fixation at 7 and 14 days post-osteotomy produced the highest degree of callus bridging. Bone mineral density in the fracture gap was highest in animals where the fixation was stiffened after 14 days. \ud
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The predicted benefit of a large robust callus formed through early flexible fixation could not be shown, however the benefits of stabilizing a flexible construct to achieve timely healing was demonstrated at all time points
Identity of Leu-19 (CD56) leukocyte differentiation antigen and neural cell adhesion molecule.
No full textNeural cell adhesion molecule (N-CAM) is a membrane glycoprotein expressed on neural and muscle tissues that is involved in homotypic adhesive interactions. We have demonstrated that N-CAM also is expressed on hematopoietic cells, and is recognized by the anti-Leu-19 mAb. Leu-19 is preferentially expressed on NK cells and T lymphocytes that mediate MHC-unrestricted cytotoxicity, but is also present on some myeloid leukemia cell lines. On NK cells, T cells, the KG1a.5 hematopoietic cell line, and a neuroblastoma cell line, Leu-19 is a approximately 140-kD polypeptide with N-linked carbohydrates and abundant sialic acid residues. Sequential immunoprecipitation and peptide mapping demonstrated that the Leu-19 and N-CAM molecules expressed on leukocyte and neuroblastoma cell lines are similar structures. These findings suggest that the Leu-19 antigen on leukocytes may be involved in cell adhesion, analogous to the function on N-CAM on neural cells
Sinus floor elevation using an osteotome technique without grafting materials or membranes
No full textThis retrospective study aimed to radiographically assess sinus floor remodeling after using a modified osteotome technique without graft materials or membranes. After pilot drilling, residual bone was fractured and raised with the schneiderian membrane to the final implant length using osteotomes. Self-tapping implants were placed, and restorations were placed 6 months later. Twenty-four patients were available for follow-up after a mean observation period of 17.6 +/- 8.4 months. The implant survival rate at that time was 100%. Bone filling around the implants was measured and compared with baseline digital radiographs. New bone formation was 86.3% +/- 22.1% mesially and 89.7% +/- 13.3% distally. In nine cases, digital volume tomography was used to verify regeneration. Within the limitations of this study, use of the schneiderian membrane led to considerable bone regeneration, and good clinical success was achieved despite the omission of graft materials
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