Neonicotinoids: insecticides acting on insect nicotinic acetylcholine receptors.

Imidacloprid is increasingly used worldwide as an insecticide. It is an agonist at nicotinic acetylcholine receptors (nAChRs) and shows selective toxicity for insects over vertebrates. Recent studies using binding assays, molecular biology and electrophysiology suggest that both alpha- and non-alpha-subunits of nAChRs contribute to interactions of these receptors with imidacloprid. Electrostatic interactions of the nitroimine group and bridgehead nitrogen in imidacloprid with particular nAChR amino acid residues are likely to have key roles in determining the selective toxicity of imidacloprid. Chemical calculation of atomic charges of the insecticide molecule and a site-directed mutagenesis study support this hypothesis.

The continuous locking suture technique.

The continuous locking suture technique is described for use in endodontic surgery. The technique is an effective way to close Ochsenbein-Luebke flaps. The importance of the assistant's role is described. The technique's advantages and disadvantages are discussed.

Endodontics in the 21st century: the rotary revolution.

Endodontic therapy is becoming an increasingly routine facet of general dental practice. Advances in technology and techniques have made endodontics in the contemporary clinical environment more pleasant and predictable for both the patient and the provider. The development of rotary instrumentation with nickel-titanium files has revolutionized the cleaning and shaping aspects of treatment. A sequenced model is discussed that has been shown to have encouraging outcomes in both predoctoral and continuing education experiences. The protocol may use more instruments than some other approaches, but has evolved as a technique that provides reliable and predictable outcomes.

Use of nickel-titanium rotary files for root canal preparation in primary teeth.

This article reviews the use of nickel-titanium rotary files for root canal instrumentation in primary teeth. The pulpectomy technique is described and the advantages and disadvantages of using rotary files are discussed. Specific recommendations for the selection of materials and devices are made.

Radiographic appearance of titanium posts in endodontically treated teeth.

Titanium and titanium alloy posts are currently being used in complex dental restorations. Titanium posts have been shown to be less radiopaque than stainless steel and to have a radiographic density similar to gutta-percha. This radiographic similarity can make detection of a titanium post difficult. Failure to identify the presence of a titanium post before the initiation of retreatment could cause significant complications for the treating endodontist. Five cases are presented to describe the radiographic subtleties that can be used to detect the presence of a titanium post.

Use of nickel-titanium rotary files for root canal preparation in primary teeth.

This article reviews the use of nickel-titanium rotary files for root canal instrumentation in primary teeth. The pulpectomy technique is described and the advantages and disadvantages of using rotary files are discussed. Specific recommendations for the selection of materials and devices are made.

Management of the latex hypersensitive patient in the endodontic office.

This case report documents the treatment of an endodontic patient who experienced a type 1 hypersensitivity reaction to latex. The dental, medical, and environmental aspects of treating latex allergic patients are reviewed. Because gutta-percha and latex rubber are similar compounds, the possible cross-reactivity of these materials is discussed.

Polycyclic dinitriles: a novel class of potent GABAergic insecticides provides a new radioligand, [3H]BIDN.

The polycyclic dinitriles are a potent class of insecticides which are non-competitive GABA (gamma-aminobutyric acid) antagonists acting at the convulsant site. Comparison with other classes of GABA convulsant site ligands using molecular modelling has shown significant structural similarities. We have developed a pharmacophore model which unifies this class and some previous classes of GABA convulsants. Key pharmacophore elements are a polarizable functionality separated by a fixed distance from two H-bond accepting elements. This model is based on information from X-ray crystal structures and Sybyl using the Tripos force field. Using this pharmacophore model, numerous structural modifications were explored to enhance understanding of structure-activity relationships at the GABA receptor convulsant site of insects and mammals. A radiolabelled bicyclic dinitrile, [3H]BIDN [3H]3,3-bis-trifluoromethyl-bicyclo[2,2,1]heptane-2,2-dicarbonitrile+ ++), was prepared from this area of chemistry and was used as a probe for the interaction of polycyclic dinitriles at the target site.

The use of tungsten carbide needle holders to remove intracanal objects.

The removal of metallic filling materials and posts is necessary before endodontic retreatment. Retreatment in such cases can require considerable time and effort. This article presents a technique to facilitate the removal of metallic obstructions from root canals using tungsten carbide needle holders. Clinical cases demonstrate the effectiveness of this technique.

Phloem mobility of xenobiotics VIII. A short review.

Great strides have been made in the last 15 years in our understanding of phloem mobility of xenobiotics. The subject has been transformed from a poorly understood phenomenon to a process that can be accurately described by the physicochemical properties of the xenobiotic and the nature of the vascular system through which it moves. The basic tenet of the unified mathematical model is that the combination of the permeability and the acid dissociation constant (pK(a)) determines phloem mobility, and this has been largely validated for many compounds in many plant systems. More precise testing of the model is, however, difficult due to the lack of requisite knowledge on the membrane composition of the sieve tube, permeation characteristics and sieve-cell biochemistry. Furthermore, attempts to relate quantitatively a compound's intrinsic mobility to its whole-plant mobility are often confounded by competing loss mechanisms. On the practical side, there is the challenge of coming up with efficacious phloem-mobile pesticides. Considerations are forwarded to explain why so far there are numerous phloem-mobile herbicides and yet precious few such insecticides and fungicides, and why the situation might be difficult to change. The knowledge of phloem mobility is robust enough to allow specific structural prescriptions to impart such mobility to existing pesticides. However, such structural changes often lead to a reduction of pesticidal activity. Recently, it has been demonstrated that this problem can be circumvented by combining oxamyl glucuronide (a phloem-mobile pro-nematicide) with a transgenic tobacco plant harboring a root-specific ß-glucuronidase gene to release oxamyl for root-knot nematode control. This propesticide and in situ activation strategy is one way to use the existing body of knowledge for practical purposes. The same principle should be generally applicable to other plant-xenobiotic technologies.

Localization of anatomic structures before endodontic surgery with tomograms. Report of a case.

Tomograms taken before endodontic surgery can demonstrate the location of root apices relative to adjacent anatomic structures. This buccolingual perspective is not depicted on conventional periapical or panoramic radiographs. Accurate length determination from the root apex to the inferior alveolar canal is simplified, and the relationship of root surfaces to the buccal and lingual plates is well visualized on the tomographic images.

Salicylic acid is a systemic signal and an inducer of pathogenesis-related proteins in virus-infected tobacco.

Systemic induction of pathogenesis-related (PR) proteins in tobacco, which occurs during the hypersensitive response to tobacco mosaic virus (TMV), may be caused by a minimum 10-fold systemic increase in endogenous levels of salicylic acid (SA). This rise in SA parallels PR-1 protein induction and occurs in TMV-resistant Xanthi-nc tobacco carrying the N gene, but not in TMV-susceptible (nn) tobacco. By feeding SA to excised leaves of Xanthi-nc (NN) tobacco, we have shown that the observed increase in endogenous SA levels is sufficient for the systemic induction of PR-1 proteins. TMV infection became systemic and Xanthi-nc plants failed to accumulate PR-1 proteins at 32 degrees C. This loss of hypersensitive response at high temperature was associated with an inability to accumulate SA. However, spraying leaves with SA induced PR-1 proteins at both 24 and 32 degrees C. SA is most likely exported from the primary site of infection to the uninfected tissues. A computer model predicts that SA should move rapidly in phloem. When leaves of Xanthi-nc tobacco were excised 24 hr after TMV inoculation and exudates from the cut petioles were collected, the increase in endogenous SA in TMV-inoculated leaves paralleled SA levels in exudates. Exudation and leaf accumulation of SA were proportional to TMV concentration and were higher in light than in darkness. Different components of TMV were compared for their ability to induce SA accumulation and exudation: three different aggregation states of coat protein failed to induce SA, but unencapsidated viral RNA elicited SA accumulation in leaves and phloem. These results further support the hypothesis that SA acts as an endogenous signal that triggers local and systemic induction of PR-1 proteins and, possibly, some components of systemic acquired resistance in NN tobacco.

A study of endodontically apexified teeth.

This study was undertaken to determine the clinical and radiographic success of calcium hydroxide apexification in a group of 48 patients requiring endodontic therapy because of pulpal necrosis prior to root-end closure. The study examined tooth number, etiology of pulpal necrosis, age, sex, size of root-end opening, size of radiolucency, crown discoloration, interappointment symptoms, and total treatment time from initial instrumentation to completion of apexification. Apexification required an average of 1 year +/- 7 months. A statistically significant relationship was found between: the presence of a radiolucency and development of interappointment symptoms (p less than 0.04); and the size of apex opening and development of interappointment symptoms (p less than 0.02). If symptoms did develop, apexification was delayed an additional 5 months when compared to patients who did not have symptoms. Calcium hydroxide apexification was found to be statistically highly successful regardless of the clinical variables encountered.

Phloem Mobility of Xenobiotics: II. Bioassay Testing of the Unified Mathematical Model.

TWO BIOASSAYS WERE USED TO TEST PHLOEM MOBILITY OF SELECTED XENOBIOTIC COMPOUNDS: (a) excised bean leaf assay; (b) rooted bean leaf assay. Compounds assayed were N-alkylpyridiniums with systematic variation in octanol-water partition coefficients (log K(ow)), substituted benzoic acids with about the same log K(ow) value but variable acidities. Results of the assays strongly conform, quantitatively, to the predictions of the unified mathematical model. Results also indicate that the membrane permeability value of a compound, which depends directly on log K(ow) value, is the overriding factor in determining phloem mobility. When the weak acid functionality of a compound confers increased phloem mobility, it does so principally by making the log K(ow) value, and consequently the membrane permeability of the compound more optimal.

Phloem mobility of xenobiotics: I. Mathematical model unifying the weak Acid and intermediate permeability theories.

A passive diffusion model has been developed which simultaneously accounts for the dependence of phloem mobility on permeability and acid dissociation. The model is consistent with the observation that the addition of an acid moiety to an otherwise phloem immobile compound may enhance that compound's ability to move in the phloem. However, acid trapping in the basic phloem is not the only enhancement factor. Acid functionalization also lowers the effective permeability usually towards its optimum value. The unified theory predicts that for a given acid dissociation constant there is an optimum permeability and conversely for a given permeability there is an optimum dissociation constant.