Evaluation of three silicone-based materials as potential retrograde fillings in surgical endodontics

Endodontic therapy has played an important role in maintaining the integrity of the natural dentition as a fully functional and esthetic masticatory apparatus. Although the sealing of the root canal system is usually accomplished by the conservative endodontic approach, cases which have failed or which involve perforations, broken instruments, or post-crown restorations are almost always treated surgically by using zinc-free amalgam as a retrograde filling material. However, the literature is controversial concerning the health risks and benefits of this material. For this reason, the study presented here was initiated to evaluate the potential of (a) a medical grade silicone-titanium mesh compound; (b) Endo-Fill (Lee Pharmaceuticals, El Monte, CA); and (c) an experimental expanding Endo-Fill (Lee Pharmaceuticals) as alternatives to amalgam. The three silicone-based materials and amalgam were compared for linear apical dye leakage. The leakage study involved 80 teeth which were instrumented, obturated, and prepared surgically for one of the four test materials. Either the teeth were placed immediately into 1% methylene blue dye or the material was allowed to set for 24 h before placement into the dye. Endo-Fill showed significantly less leakage than did the other materials in both the immediately placed and the 24-h set groups. On the other extreme, the experimental expanding Endo-Fill allowed significantly more dye penetration than did amalgam and the other silicone variations.

The Qa-1 antigenic system. Relation of Qa-1 phenotypes to lymphocyte sets, mitogen responses, and immune functions

The antiserum (B6 X A-Tlab) anti-A (Tlaa) defines several TL antigens expressed exclusively on thymocytes. When reacted with peripheral lymphocytes, the same antiserum defines another antigenic system, provisionally termed Qa-1. The genotypic disparity distinguishing the recipients and donors in this immunization comprises a section of chromosome 17 extending from a crossover point between H-2D and Tla to a presently unmarked point beyond Tla. Therefore although Qa-1 may constitute a single cell surface component, it is equally probable that the Qa-1 system defines two or more cell surface components determined by genes in this region, each of which may be expressed on a different cell set. Cytotoxicity assays indicate that Qa-1 antigen is expressed on Lyt-1 cells and Lyt-123 cells, and may serve to subclassify these two cell sets; it is not known whether Qa-1+ cells may occur within the small Lyt-23 set. There may be also be a cell set with the phenotype Thy-1--:Qa-1+. Another distinctive feature of the Qa-1 system is the characteristic profile of responses to mitogens exhibited by spleen cell populations from which Qa-1+ cells have been eliminated; in conventional assay of [3H]thymidine incorporation the response to lipopolysaccharide was essentially unchanged, the response to phytohemagglutinin M (PHA-M) was virtually abolished, and the response to concanavalin A (Con A) was reduced by 40%. The third distinctive feature of the Qa-1 system is the characteristic profile of changes which elimination of Qa-1+ cells produces in tests of immune function in vitro: (a) proliferation, measured by [3H]thymidine incorporation, in mixed lymphocyte culture (MLC) with major histocompatibility complex (MHC)-incompatible stimulator cells, was not affected. (b) in tests of cell-mediated cytotoxicity (CMC) of MHC-incompatible target cells, neither the generation nor the effector functions of cytotoxic lymphocytes was affected, implying that Lyt-23 prekiller and killer cells are Qa-1--. (c) primary and secondary responses to SRBC were considerably augmented, suggesting that Qa-1+ cells may be responsible for suppression in this test system. (d) accordingly the suppression of the anti-sheep erythrocyte (SRBC) response normally engendered in spleen cells by culture with SRBC was profoundly reduced by elimination of Qa-1+ cells, either before or after culture. (e) the suppression of the anti-SRBC response normally engendered in spleen cells cultured with Con A was reduced by removal of Qa-1+ cells before but not after culture with Con A. Although analysis is as yet far from complete, the Qa-1 system should already be of considerable value because it distinguishes a population of lymphocytes that is not defined by any other antigenic system, according to three criteria: (a) representation of Qa-1 cells among T-cell sets defined by Lyt phenotypes, (b) the profile of responses to mitogens exhibited by lymphocyte populations depleted of Qa-1+ cells, and (c) the profile of immune responses of lymphocyte populations depleted of Qa-1+ cells.

Separation of helper T cells from suppressor T cells expressing different Ly components. I. Polyclonal activation: suppressor and helper activities are inherent properties of distinct T-cell subclasses

Concanavalin A, a nonspecific polyclonal activator of T lymphocytes, activates Lyl and Ly23 subclasses to the same degree. After activation, the Ly23 subclass, but not the Lyl subclass, has the following properties: (a) Suppression of the antibody response to sheep erythrocytes (SRBC) in vitro. (b) Production of a soluble factor that suppresses the anti-SRBC response in vitro. (c) Suppression of the generation of cell-mediated cytotoxicity to H-2 target cells in vitro. Con A-activated cells of the Lyl subclass, but not the Ly23 subclass, express helper function in the anti-SRBC response in vitro. Because the intact Con A-stimulated T-cell population contains both cell types, these cells do not exert detectable helper effects in an anti-SRBC system in vitro, because the helper effect of Lyl cells is masked by the suppressor effect of the Ly23 cells. Each function is revealed by eliminating one or the other population with the relevant Ly antiserum. The resting T-cell population, before activation by Con A, also contains already programmed Lyl and Ly23 cells with similar helper and suppressor potentials, respectively. This is revealed by experiments with Ly subclasses which have been separated from the resting T-cell population and then stimulated by Con A. Thus helper and suppressor functions, as expressed in these systems, are manifestations of separate T-cell-differentiative pathways and do not depend upon stimulation of the cells by antigen.

In vitro effects of isobutyl cyanocrylate on four types of bacteria

Isobutyl cyanoacrylate produced varying degrees of growth inhibition when applied to freshly plated Petri dishes of Staphylococcus aureus, Gaffkya, Neisseria catarrhalis, and a-Streptococcus. A biproduct or diffusible substance produced by the polymer was implicated as the cause. Destruction of growing colonies was observed only with a-Streptococcus after polymer application. The mechanism for this was not determined.