[Impressions techniques--Part 2].

A dental impression is a positive replica of the teeth, the surrounding gingiva and the border between them; the purpose of which is to create an accurate master model. Two major techniques for impressions exist today: The conventional and the digital impressions. The current article describes both techniques. In the conventional impressions, it is important to choose a proper tray, stock or custom, and to mix the material properly. The commonly used impression techniques for making a conventional impression are described with a review on the effect of the technique on its accuracy. The effect of the wash bulk on the accuracy of the stone dies and/or the restoration is discussed, as well. The digital impressions with their advantages and disadvantages are described in comparison to the conventional impressions. Although, digital impressions eliminate some of the negative characteristics of conventional impressions, proper soft-tissue management and isolation of tooth preparation margins is still mandatory.

[Tissue displacement and impression techniques--part 1].

In order to create an accurate model of the soft and hard tissues of the mouth, a complete control of the gingiva around the prepared teeth is needed. This gingiva must be displaced and bleeding must be avoided. This article describes the three techniques for tissue displacement: mechanical, chemicomechanical and surgical. Mechanical displacing the gingiva can be done by either the use of copper bands or with plain retraction cord. By combining chemical action with packing of a retraction cord a chemicomechanical displacement of the tissue can take place. The surgical retraction is possible by Laser, Electro surgery or Rotatory curettage. The advantages, disadvantages, and limitations of each of the different techniques are discussed. In addition, the different hemostatic agents are described with their mechanism of action, indications and contra-indications of each one of them.

[Elastomeric impression materials].

Elastomeric impression materials are in common use. The impression taken should be highly precise, thus, requiring specific care when manipulatingthese materials. There are 4 groups of elastomers; polysulfide, condensation silicone, addition silicone and polyether; each differ in their setting mechanism and their physical and chemical properties. This review elaborates the major properties of elastomers and its implications on their use. The impression material is inserted into the patient's mouth in a viscous state and transforms into viscoelastic state, upon withdrawal, influencing the residual deformation. The requirements are minimal residual deformation or maximal elastic recovery. As the mouth is a wet environment a major consideration is hydrophilicity. The wettability which is estimated by measuring either the contact angle of a droplet of water and the substrate post setting or the contact angle of a droplet of impression material and the wet tooth pre setting, determines the interaction of the material with both mouth fluids and gypsum. As the primary end target is to obtain a model depicting accurately the oral details, an attention to the impressions' compatibility with gypsum should also be given. Many studies were conducted to get a thorough understanding of the hydrophilic properties of each material, and the mechanism utilized, such as surfactants in hydrophilic PVS. Polyether is the only material that is truly hydrophilic; it exhibits the lowest contact angle, during and after setting. Recent studies show that during setting the Polyether hydrophilicity is increased compared to the condition after setting. Dimensional stability, a crucial property of the impression, is affected by the physical and chemical attributes of the material, such as its tear strength. Polysulfide has the highest tear strength. Tear Strength is affected by two major parameters, viscosity, a built-in property, and how fast the impression is pulled out of the mouth, the faster the impression is loaded and pulled out, the higher the tear strength is. The clinical use is dictated from the properties of each impression material, and the understanding of those enables the practitioner to minimize failures.

Chronic levodopa or pergolide administration induces down-regulation of dopamine receptors in denervated striatum.

Refractory response to dopamine (DA) agonists is a common problem in the treatment of Parkinson's disease. In rats with unilateral lesions of the substantia nigra, denervation induced significant increases in striatal 3(H)-spiperone binding sites ipsilateral to the lesion. Chronic treatment with levodopa or with pergolide mesylate significantly decreased the number of 3(H)-spiperone striatal binding sites. Agonist-induced decreases were approximately equivalent in intact and denervated striata and did not appear to be affected by lesions. These results suggest that the poor response to DA agonist in certain parkinsonian patients with chronic drug exposure may be mediated by drug-induced DA receptor down-regulation.

Electroconvulsive treatment and haloperidol: effects on pre- and postsynaptic dopamine receptors in rat brain.

Electroconvulsive treatment (ECT) has a transitory beneficial effect on patients with Parkinson's disease (PD). The possibility that this effect is mediated by dopamine (DA) receptors was investigated in the rat brain. Repeated ECT or chronic haloperidol treatment induced supersensitivity of putative autoreceptors in the nigrostrital and mesolimbic DA pathways as reflected by enhanced apomorphine-induced inhibition of DA synthesis. Effect of simultaneous administration of ECT plus haloperidol on DA receptor sensitivity were not additive. Chronic haloperidol treatment induced significant elevations in the density of 3[H]-spiperone striatal binding sites. Concurrent administration of ECT had no effect on the neuroleptic-induced supersensitivity. ECT alone was also without effect on 3[H]-spiperone binding. Thus, ECT-induced increases in the sensitivity of presynaptic autoinhibition of DA release was not reflected by changes in the striatal 3[H]-spiperone binding sites. This suggests that effects of ECT on the DA system are not mediated by dopamine D2 receptors.

Glutamate agonist activity: implications for antipsychotic drug action and schizophrenia.

Antagonist action at dopamine D2 receptors appears to explain many, but not all of the effects of antipsychotic drugs. Because of the interactions of dopamine with glutamate, and the implication of the latter in the etiology of schizophrenia, possible effects of antipsychotic drugs on glutamate receptors were assessed in the present experiments. These studies showed that, at clinically relevant concentrations, the conventional neuroleptic haloperidol and the atypical antipsychotic clozapine had potent augmenting influences on the NMDA receptor. These data suggest that unique action at glutamate receptors may contribute to antipsychotic efficacy and emphasize the potential importance of glutamatergic dysfunction in the etiology of schizophrenia.

Cocaine adversely affects development of cortical embryonic neurons in vitro: immunocytochemical study of calcium-binding proteins.

Neurons of cerebral cortex from 15-16 day old embryos of white rats (Sprague-Dawley) were cultured in MEM enriched with 5% horse serum. On the 7th day after plating the cultures were divided into three experimental and one control groups (6-8 Petri dishes in each group). In group 1, cultures were grown without additives. In group 2, cocaine chloride was added at concentrations 0.3, 0.6 and 1 mg/ml of culture. In group 3, a monoclonal antibody against calcium-binding proteins, parvalbumin (APV) or calbindin (ACB) was added at a concentration 25 microl/ml. In group 4, a combination of cocaine +APV was added at a concentration 1 mg+25 microl/ml of culture media. On the 10th day cultures were immunostained using APV and ACB antibodies. In developing GABAergic neurons of group 2 cocaine produced cytotoxic effects that were expressed in drastic decrease in number of neurons and in degeneration of their processes. The lower concentrations of cocaine caused milder cytotoxity and their effects were reversible. The highest concentration of cocaine caused irreversible degeneration of neurons. Similar cytotoxity was caused by APV or ACB in group 3. The most severe cytotoxic effects were seen in group 4, where a mixture of cocaine and APV was used. Overall, it can be concluded that cocaine in higher concentrations directly affects development of GABAergic neurons in vitro.

Antipsychotic drug effects on glutamatergic activity.

Previous work from this laboratory indicated that some antipsychotic drugs possess unique action at N-methyl-D-aspartate (NMDA) receptors. A functional neurochemical assay showed that, at concentrations similar to those found in the cerebrospinal fluid (CSF) of schizophrenics, antipsychotic drugs augment NMDA activity while, at higher concentrations, NMDA activity is suppressed. Using similar analysis, the present paper reports that this pattern of response is also shown by the antipsychotic drugs thioridazine and chlorpromazine. In contrast, promazine, which is structurally similar to chlorpromazine but lacking both D2-effects and antipsychotic potency, had no influence on NMDA receptors. In addition, sulpiride and metoclopramide, drugs with high affinity for D2-dopamine receptors but with weak or no antipsychotic efficacy, also lack effects at the NMDA receptor. Thus, the drugs with clinical efficacy that were tested in the present and previous studies all share unique influence on NMDA receptors. Further work with other antipsychotic agents will be necessary to determine if influence on NMDA receptors contributes to antipsychotic effectiveness.

Taurine prevents haloperidol-induced changes in striatal neurochemistry and behavior.

Repeated daily administration of haloperidol produces changes in striatal neurochemistry (decreased dopamine synthesis, upregulation of D2 receptors) and behavior (increasing catalepsy). Coadministration of taurine greatly attenuated these neuroleptic-induced changes. Possible mechanisms of taurine's mitigating effects are its attenuating influences on glutamatergic transmission and its actions as a GABAA agonist. The possibility was discussed of adding taurine to chronic antipsychotic regimens to block the side-effects typically accompanying such therapy.

Anti-glutamatergic effects of clozapine.

Clozapine (Cz) is unique in its efficacy with treatment refractory patients and its freedom from motor side effects. The present work shows that Cz, even after dopamine depletion, suppresses responses evoked via the monosynaptic glutamatergic corticostriatal pathway. In addition, Cz is effective in displacing [3H]MK-801 from striatal homogenates. These data indicate that Cz is a glutamate antagonist. It is unclear, however, if this pharmacological action could explain Cz's lack of motor effects and it's antipsychotic potency.

The influence of long term water immersion on shear bond strength of amalgam repaired by resin composite and mediated by adhesives or resin modified glass ionomers.

OBJECTIVE: To assess the shear bond strength between amalgam and resin composite mediated by either multipurpose adhesive systems or RMGI when subjected to long term immersion in saline. METHODS: Part I: Cylindrical specimens (6 mm × 6 mm) composed of equal parts of sandblasted set amalgam (Oralloy) and composite (Z-100), with a thin layer of either Scotchbond Multipurpose, All Bond 2, Amalgam Bond Plus, High Q Bond Plus or Vitrebond in between were fabricated (n = 100 × 5). Each group was divided into 3 subgroups, immersed in saline at 37 °C for either 48 h, 3 or 6 months, followed by thermocycling (5000; 5/55 °C) and shear bond strength testing (SBS). Part II: Identical specimens were fabricated with intermediary of either Ketac Cem, Fuji Lining LC, Rely X Luting, Fuji Plus or Meron Plus (n = 100 × 5). Immersion periods, followed by thermocycling and SBS testing as in Part I. Two representative specimens from each subgroup were sectioned and inspected under SEM. RESULTS: The two classes of intermediary agents yielded SBS which differed mainly in the 6 months incubation period. While multipurpose adhesives provided SBS values of ~9-10 MPa RMGI provided higher SBS of ~16 MPa. All Bond 2 and Amalgam Bond Plus exhibited deterioration of SBS during the 6 month period as well as Rely X Luting. Gap sizes between 0.5 and 3 µm exist between all intermediaries and the amalgam; on the other hand all intermediaries exhibit gap-free interfaces between the adhesives/RMGI and the composite. CONCLUSIONS: Vitrebond in particular and RMGIs in general can serve as an excellent coupler of resin composite to amalgam, providing a durable bond.

Sexually dimorphic development and binding characteristics of NMDA receptors in the brain of the platyfish.

This study investigated age- and gender-specific variations in properties of the glutamate N-methyl-d-aspartate receptor (NMDAR) in a freshwater teleost, the platyfish (Xiphophorus maculatus). Prior localization of the immunoreactive (ir)-R1 subunit of the NMDAR protein (R1) in cells of the nucleus olfactoretinalis (NOR), a primary gonadotropin-releasing hormone (GnRH)-containing brain nucleus in the platyfish, suggests that NMDAR, as in mammals, is involved in modulation of the platyfish brain-pituitary-gonad (BPG) axis. The current study shows that the number of cells in the NOR displaying ir-R1 is significantly increased in pubescent and mature female platyfish when compared to immature and senescent animals. In males, there is no significant change in ir-R1 expression in the NOR at any time in their lifespan. The affinity of the noncompetitive antagonist ((3)H)MK-801 for the NMDAR is significantly increased in pubescent females while maximum binding of ((3)H)MK-801 to the receptor reaches a significant maximum in mature females. In males, both MK-801 affinity and maximum binding remain unchanged throughout development. This is the first report of gender differences in the association of NMDA receptors with neuroendocrine brain areas during development. It is also the first report to suggest NMDA receptor involvement in the development of the BPG axis in a nonmammalian vertebrate.