bluuebunny/crossref_metadata_2025 huggingface dataset:
Tamoxifen Diminishes Methamphetamine‐Induced Striatal Dopamine Depletion in Intact Female and Male Mice
Authors: Dluzen D. E. , McDermott J. L. , Anderson L. I.
Published: March 2003

It has been demonstrated that the nigrostriatal dopaminergic system of male mice is more sensitive to the neurotoxic effects of methamphetamine (MA). The basis for this difference can be related to oestrogen, which has the capacity to function as a neuroprotectant against neurotoxins that target the nigrostriatal dopaminergic system. We examined the effects of the anti‐oestrogen, tamoxifen (TMX), upon MA‐induced neurotoxicity of the nigrostriatal dopaminergic system in intact female and male CD‐1 mice. Striatal dopamine concentrations of TMX‐treated female and male mice receiving MA were significantly greater than mice receiving MA alone. In female, but not male, mice, oestrogen treatment also resulted in greater striatal dopamine concentrations compared to mice receiving MA alone. Interestingly, male mice treated with oestrogen were particularly sensitive to the acute toxic effects of MA and displayed no evidence of nigrostriatal neuroprotection. The dihydroxyphenylacetic acid/dopamine ratios following MA for female and male mice treated with TMX or females treated with oestrogen were significantly reduced compared to MA‐treated mice and oestrogen + MA‐treated male mice. No differences among the treatment groups were obtained for dopamine in the hypothalamus or olfactory bulb. These data demonstrate that TMX treatment of intact female and male mice diminishes striatal dopamine depletions to the nigrostriatal dopaminergic neurotoxin, MA. Oestrogen also displayed this capacity when administered to female, but accentuated acute toxicity in male mice. These effects are relatively specific for the nigrostriatal dopaminergic system. Such data suggest that TMX can function as a nigrostriatal dopaminergic neuroprotectant against MA‐induced neurotoxicity in intact female and male mice.
Serotonergic Neurones in the Dorsal Raphe Nucleus That Project into the Medial Preoptic Area Contain Oestrogen Receptor β
Authors: Lu H. , Ozawa H. , Nishi M. , Ito T. , Kawata M.
Published: March 2003

Serotonin is involved in female sexual behaviour in which the medial preoptic area (MPA) has a pivotal role. The present study used immunohistochemistry, in situ hybridization and retrograde transport analysis to investigate whether serotonin neurones in the dorsal raphe nucleus (DRN) of females projecting into the MPA contained oestrogen receptor α or β. The projection of serotonin neurones from the DRN to the MPA was confirmed using the microinjection of Fluoro‐Gold (FG), a fluorescent retrograde tracer, into the MPA of ovariectomized (OVX‐group) and OVX‐rats treated with oestradiol benzoate (E2‐group). A number of serotonin neurones in the DRN were labelled with FG, indicating that these serotonin neurones in DRN project their terminals into the MPA. FG‐labelled serotonin neurones expressed ERβ mRNA in the DRN, and the number of the serotonin neurones containing ERβ mRNA between the OVX‐group and the E2‐treated group was not significantly different. Serotonin neurones in the DRN did not express ERα‐immunoreactivity. Since previous findings showed that the density of serotonin‐immunoreactive fibres and the concentration of serotonin within the MPA was significantly lower in the E2‐group than the OVX‐group, our present observations suggested that the regulatory effects of E2 on the serotonergic neurone system in the MPA may be via ERβ within the serotonin‐containing cells in the DRN of female rats.
Oestradiol Increases Phosphorylation of a Dopamine‐ and Cyclic AMP‐Regulated Phosphoprotein (DARPP‐32) in Female Rat Brain
Authors: Auger A. P. , Meredith J. M. , Snyder G. L. , Blaustein J. D.
Published: March 2003

Recent studies suggest that oestrogen and progestin receptors may be activated by the neurotransmitter dopamine, as well as by their respective ligands. Because intracerebroventricular infusion of D1, but not D2, dopaminergic receptor agonists increases oestrous behaviour in oestradiol‐primed rats, we wanted to determine if treatment with oestradiol alters the activity of D1 receptor‐associated processes in steroid receptor‐containing areas in female rat brain. One D1 receptor‐associated phosphoprotein that may be influenced by oestradiol is a dopamine‐ and cyclic AMP‐regulated phosphoprotein, Mr = 32 000 (DARPP‐32). Because DARPP‐32 is phosphorylated in response to dopamine acting via a cAMP‐dependent protein kinase, it provides a useful marker to examine where in the brain a particular stimulus might be altering the activity of D1 receptor‐containing neurones. To determine if oestradiol alters the phosphorylation of DARPP‐32, we stained immunocytochemically brain sections of female rats treated with behaviourally relevant doses of oestradiol or oil vehicle with an antibody that detects only the threonine 34‐phosphorylated form of DARPP‐32. Behaviourally effective doses of oestradiol increase the phosphorylation of DARPP‐32 within the medial preoptic nucleus, bed nucleus of the stria terminalis, paraventricular nucleus of the hypothalamus and the ventromedial nucleus of the hypothalamus, 48 h after treatment. These data suggest that oestradiol increases the activity of D1 dopamine receptor‐associated processes in oestrogen receptor‐containing areas of female rat forebrain.
Photoperiodic Control of the Concentration of Luteinizing Hormone, Prolactin and Testosterone in the Male Emu (Dromaius novaehollandiae), a Bird that Breeds on Short Days
Authors: Blache D. , Talbot R. T. , Blackberry M. A. , Williams K. M. , Martin G. B. , Sharp P. J.
Published: March 2003

The objective of this study was to establish, for a short‐day breeding bird, the male emu, whether the breeding season is principally controlled by changes in photoperiod, and to investigate the endocrine mechanisms involved. Two groups of adult males were subjected to three alternating periods of 150–185 days of 14 h light/day (LD) and 10 h light/day (SD) terminating in a 360‐day period of LD or SD. Transfer from LD to SD led to increases in plasma concentrations of luteinizing hormone (LH) and testosterone, after 82 ± 8 and 73 ± 3 (SEM) days, and an increase in prolactin concentrations after 115 ± 12 days. Concentrations of LH and testosterone began to decrease before transfer back to LD, at a time when prolactin concentrations were approaching peak values. Transfer from LD to 360 days of SD resulted in increases in LH and testosterone concentrations, and these terminated after an increase in prolactin concentrations. After transfer from SD to 360 days of LD, plasma concentrations of LH and testosterone began to increase, after delays of 222 ± 24 and 225 ± 13 days, and were high at the end of the study, while prolactin values remained depressed throughout. These observations clearly show that seasonal breeding in the emu is directly controlled by changes in photoperiod. The dynamics of the hormonal responses to change of photoperiod suggest that, despite being short‐day breeders, the photoregulation of breeding in emus involves mechanisms that are currently accepted for birds, rather than mechanisms that have been proposed for short‐day breeding mammals. The initiation of breeding in emus is due to dissipation of photorefractoriness by short days which leads to an increase in the secretion of gonadotrophins to levels that are sufficient to support full reproductive condition. The termination of breeding, while days are still short, is due to the antigonadotrophic action of prolactin which, unusually for birds, increases while the days are still short. In conclusion, breeding activity in male emus is strongly controlled by photoperiod. Emus are short‐day breeders, but the central mechanisms that regulate the secretion of reproductive hormones seem to be similar to those previously proposed for long‐day breeding birds. The pattern of prolactin secretion in emus suggests an important role for this hormone in the termination of the breeding cycle.
Changes in Basal Hypothalamic Chicken Gonadotropin‐Releasing Hormone‐I and Vasoactive Intestinal Polypeptide Associated with a Photo‐Induced Cycle in Gonadal Maturation and Prolactin Secretion in Intact and Thyroidectomized Starlings (Sturnus vulgaris)
Authors: Dawson A. , Talbot R. T. , Dunn I. C. , Sharp P. J.
Published: March 2003

Chicken gonadotropin‐releasing hormone‐I (GnRH‐I) and the avian prolactin‐releasing hormone, vasoactive intestinal polypeptide (VIP), were measured in the basal hypothalamus in male starlings during photo‐induced gonadal growth and the subsequent development and maintenance of reproductive photorefractoriness. Comparisons were made with thyroidectomized birds, which maintain breeding condition irrespective of changes in photoperiod. In intact birds, basal hypothalamic GnRH‐I increased four‐fold after photostimulation and then decreased 115‐fold over 12 weeks to values characteristic of long‐term photorefractoriness. Pituitary and plasma prolactin increased after photostimulation, reaching peak values when the testes were regressing, and returned to low values in long‐term photorefractory birds. Basal hypothalamic VIP did not change after photostimulation in intact birds. In photostimulated thyroidectomized birds, values for basal hypothalamic GnRH‐I and VIP, and for pituitary and plasma prolactin, remained no different to those of nonphotostimulated intact birds. These observations confirm that reproductive photorefractoriness is related to a decrease in hypothalamic GnRH‐I. However, photorefractoriness in terms of prolactin secretion is not similarly related to a decrease in basal hypothalamic VIP. The mechanisms responsible for the decrease in prolactin in long‐term photorefractory birds and for the total lack of photoperiodic responses in thyroidectomized birds remain unresolved.
Involvement of cAMP‐Response Element Binding Protein in Corticotropin‐Releasing Factor (CRF)‐Induced Down‐Regulation of CRF Receptor 1 Gene Expression in Rat Anterior Pituitary Cells
Authors: Kasagi Y. , Horiba N. , Sakai K. , Fukuda Y. , Suda T.
Published: March 2003

Corticotropin‐releasing factor (CRF) is a major secretagogue of adrenocorticotopic hormone from the anterior pituitary and a key activator of the hypothalamic‐pituitary‐adrenal axis. We previously reported that CRF down‐regulates expression of the CRF type‐1 receptor (CRF‐R1) mRNA in cultured rat anterior pituitary cells. The present study was conducted to clarify the signal transduction systems involved in CRF‐induced down‐regulation of CRF‐R1 gene expression in the anterior pituitary. Northern blot analysis revealed that, under serum‐free conditions, 10 nM CRF decreased CRF‐R1 mRNA levels in cultured rat anterior pituitary cells as we reported previously. Treatment with 5 mM 8‐Br‐cAMP reduced CRF‐R1 mRNA levels within 2 h. The mRNA level fell to 37±3% of the basal level at 2 h and remained low for 16 h after treatment. This CRF‐induced reduction of CRF‐R1 mRNA expression was inhibited completely by pretreatment with protein kinase A (PKA) inhibitor (1 µM H‐89). Further examination revealed that after pretreatment with 10 µM of antisense oligodeoxynucleotide for cyclic AMP‐response element binding protein (CREB), the CRF‐induced inhibition of CRF‐R1 mRNA was partially decreased to 79±4% of the control level 2 h after administration of CRF. These findings indicate that CRF may down‐regulate CRF‐R1 mRNA expression via a cAMP‐PKA‐mediated mechanism in rat anterior pituitary cells, and that CREB may mediate at least a portion of this inhibitory effect.
Autophagy in Hypothalamic Neurones of Rats Expressing a Familial Neurohypophysial Diabetes Insipidus Transgene
Authors: Davies J. , Murphy D.
Published: March 2003

We have tested the hypothesis that familial neurohypophysial diabetes insipidus (FNDI) is initiated by a process of autophagy. FNDI is a dominant, progressive inherited disorder characterized by pronounced drinking and urination caused by loss of secretion of antidiuretic hormone (vasopressin). In rats expressing an FNDI mutant transgene (Cys67stop) in vasopressin magnocellular neurones, the mutant protein fails to enter the regulated secretory pathway, and accumulates in a swollen and distended endoplasmic reticulum (ER) that also contains wild‐type, endogenous vasopressin. Transmission electron microscopy suggested that these are autophagic vesicles. We have now examined the expression of vesicular markers in our transgenic rats, and demonstrate that activation of autolysosomal processes is a consequence of the expression of Cys67stop. Swollen vesicles containing Cys67stop are immunoreactive for cathepsin D (a lysosomal protease), endolyn (a marker of late endosomes) and lysosomal associated membrane protein 1, suggesting that they may be degradative autolysosomes. In addition, there is an up‐regulation of lysosomal markers specifically in cells expressing Cys67stop. The expression of Cys67stop affects neither the trans‐Golgi network nor early endosomes. These data support the proposal that Cys67stop mutant protein aggregates within the ER, which is targeted for lysosomal degradation by autophagy.
Lack of Effect of Testosterone and Dihydrotestosterone Compared to 17β‐Oestradiol in 1‐Methyl‐4‐Phenyl‐1,2,3,6, Tetrahydropyridine‐Mice
Authors: Ekue A. , Boulanger J.‐F. , Morissette M. , Di Paolo T.
Published: March 2003

Previous work from our laboratory has demonstrated prevention of 1‐methyl‐4‐phenyl‐1,2,3,6, tetrahydropyridine (MPTP)‐induced striatal dopamine depletion in C57Bl/6 mice by 17β‐oestradiol, progesterone and raloxifene. The activity of androgenic compounds in MPTP mice has received less attention and was the object of the present investigation. The effects of 17β‐oestradiol (2 µg/day), testosterone (100 µg/day) and dihydrotestosterone (DHT) (2 µg/day or 100 µg/day) were studied during 5 days before and after an acute treatment of four MPTP (10 mg/kg) injections in male C57Bl/6 mice. Striatal concentrations of dopamine and its metabolites dihydroxyphenylacetic acid and homovanillic acid were measured by high‐performance liquid chromatography. MPTP mice treated with saline showed large decreases in dopamine and its metabolites compared to control mice. 17β‐oestradiol partially spared this decrease whereas testosterone and DHT did not. Striatal specific binding to the dopamine transporter (DAT) and to the vesicular monoamine transporter (VMAT2) were measured using [125I] RTI‐121 and [3H] dihydrotetrabenazine autoradiography, respectively. As with striatal dopamine concentrations, MPTP treatment caused a decrease in DAT and VMAT2 specific binding. 17β‐oestradiol partially spared this decrease, whereas androgens did not. In the substantia nigra, DAT mRNA was measured by in situ hybridization. MPTP treatment induced a significant, but smaller decrease in substantia nigra DAT mRNA than striatal DAT protein. In addition, 17β‐oestradiol completely prevented the MPTP‐induced decrease of DAT mRNA, whereas androgens did not. The present results show that androgens are unable to protect against MPTP‐induced dopaminergic toxicity.
Serotonergic Stimulation of Corticotropin‐Releasing Hormone and Pro‐Opiomelanocortin Gene Expression
Authors: Jørgensen H. , Knigge U. , Kjær A. , Møller M. , Warberg J.
Published: March 2003

The neurotransmitter serotonin (5‐HT) stimulates adrenocorticotropic hormone (ACTH) secretion from the anterior pituitary gland via activation of central 5‐HT1 and 5‐HT2 receptors. The effect of 5‐HT is predominantly indirect and may be mediated via release of hypothalamic corticotropin‐releasing hormone (CRH). We therefore investigated the possible involvement of CRH in the serotonergic stimulation of ACTH secretion in male rats. Increased neuronal 5‐HT content induced by systemic administration of the precursor 5‐hydroxytryptophan (5‐HTP) in combination with the 5‐HT reuptake inhibitor fluoxetine raised CRH mRNA expression in the paraventricular nucleus (PVN) by 64%, increased pro‐opiomelanocortin (POMC) mRNA in the anterior pituitary lobe by 17% and stimulated ACTH secretion five‐fold. Central administration of 5‐HT agonists specific to 5‐HT1A, 5‐HT1B, 5‐HT2A or 5‐HT2C receptors increased CRH mRNA in the PVN by 15–50%, POMC mRNA in the anterior pituitary by 15–27% and ACTH secretion three‐ to five‐fold, whereas a specific 5‐HT3 agonist had no effect. Systemic administration of a specific anti‐CRH antiserum inhibited the ACTH response to 5‐HTP and fluoxetine and prevented the 5‐HTP and fluoxetine‐induced POMC mRNA response in the anterior pituitary lobe. Central or systemic infusion of 5‐HT increased ACTH secretion seven‐ and eight‐fold, respectively. Systemic pretreatment with the anti‐CRH antiserum reduced the ACTH responses to 5‐HT by 80% and 64%, respectively. It is concluded that 5‐HT via activation of 5‐HT1A, 5‐HT2A, 5‐HT2C and possibly also 5‐HT1B receptors increases the synthesis of CRH in the PVN and POMC in the anterior pituitary lobe, which results in increased ACTH secretion. Furthermore, the results indicate that CRH is an important mediator of the ACTH response to 5‐HT.
Neurosecretory and Non‐Neurosecretory Parvocellular Neurones of the Hypothalamic Paraventricular Nucleus Express Distinct Electrophysiological Properties
Authors: Luther J. A. , Daftary S. S. , Boudaba C. , Gould G. C. , Halmos K. Cs. , Tasker J. G.
Published: March 2003

Parvocellular neurones of the hypothalamic paraventricular nucleus (PVN) comprise neurosecretory and non‐neurosecretory subpopulations. We labelled neurosecretory neurones with intravenous injection of the retrograde tracer, fluoro‐gold, and recorded from fluoro‐gold‐positive and negative PVN parvocellular neurones in hypothalamic slices. Non‐neurosecretory parvocellular neurones generated a low‐threshold spike (LTS) and robust T‐type Ca2+ current, whereas neurosecretory neurones showed no LTS and a small T‐current. LTS neurones were located in non‐neurosecretory regions of the PVN, and non‐LTS neurones were located in neurosecretory regions of the PVN. These findings indicate that neurosecretory and non‐neurosecretory subtypes of parvocellular PVN neurones express distinct membrane electrical properties.
Further Delineation of the Sequences Required for the Expression and Physiological Regulation of the Vasopressin Gene in Transgenic Rat Hypothalamic Magnocellular Neurones
Authors: Davies J. , Waller S. , Zeng Q. , Wells S. , Murphy D.
Published: March 2003

We have introduced transgenes into rats with a view to defining genomic regions that mediate the cell‐specific and physiological regulation of the vasopressin gene. These transgenes consist of the rat vasopressin structural gene with a reporter inserted into exon III, flanked by different lengths of upstream and downstream sequences. 11‐VCAT‐3 is flanked by 11 kbp of upstream sequences and 3 kbp of downstream sequences. The previously described 5‐VCAT‐3 is flanked by 5 kbp of upstream and 3 kbp of downstream sequences. 3‐VCAT‐3 has 3 kbp of upstream and 3 kbp of downstream sequences, and 3‐VCAT‐0.2 is flanked by 3 kbp of upstream and 0.2 kbp of downstream sequences. All four transgenes elicit the same expression patterns; low basal expression is seen in the magnocellular supraoptic and paraventricular nuclei, and is negligible in the suprachiasmatic nucleus. Expression increases markedly in vasopressin magnocellular cells following dehydration. The sequences responsible for the cell‐specific expression and physiological regulation of our transgenes thus reside within the confines of the smallest construct studied, 3‐VCAT‐0.2.
Bisphenol A Increases Progesterone Receptor Immunoreactivity in the Hypothalamus in a Dose‐Dependent Manner and Affects Sexual Behaviour in Adult Ovariectomized Rats
Authors: Funabashi T. , Sano A. , Mitsushima D. , Kimura F.
Published: March 2003

Recently, we reported that bisphenol A (BPA), an endocrine disrupter, increased progesterone receptor (PR) mRNA in the preoptic area (POA) in adult ovariectomized rats. In the present study, we examined whether BPA also induced expression of PR proteins in both the POA and the ventromedial hypothalamic nucleus (VMH), and whether those proteins were involved in the induction of sexual behaviour. Two weeks after ovariectomy, rats received a subcutaneous (s.c.) injection of BPA, 17β‐oestradiol or vehicle. Twenty‐four hours after the injection, the rats were killed and their tissues were examined by immunocytochemistry. Some rats that received a s.c. injection of BPA, E2 or vehicle alone on the day before were injected with progesterone at 15.00 h and examined for sexual behaviour 5–7 h later. As expected, injection of 10 µg E2 significantly increased the number of PR immunoreactive cells in both the POA and the VMH compared to the number after injection of vehicle alone. In both the POA and the VMH, injection of BPA at a dose of 10 mg also significantly increased the number of PR immunoreactive cells compared to the number after injection of sesame oil alone. Furthermore, BPA induced a dose‐dependent increase in the number of PR immunoreactive cells in both the POA and the VMH, demonstrating that the number of PR cells was significantly increased by as little as 100 µg of BPA. Ovariectomized (OVX) rats that were primed with 10 mg of BPA, followed by 1 mg of progesterone, displayed mainly rejection behaviour, but not lordosis as typically observed in OVX rats primed with E2 followed by progesterone. The present study suggests that BPA influences reproductive functions, including sexual behaviour even in adulthood, by altering the PR system in the hypothalamus.
Cocaine‐ and Amphetamine‐Regulated Transcript is Present in Hypothalamic Neuroendocrine Neurones and is Released to the Hypothalamic‐Pituitary Portal Circuit
Authors: Larsen P. J. , Seier V. , Fink‐Jensen A. , Holst J. J. , Warberg J. , Vrang N.
Published: March 2003

Cocaine‐ and amphetamine‐regulated transcript (CART) is present in a number of hypothalamic nuclei. Besides actions in circuits regulating feeding behaviour and stress responses, the hypothalamic functions of CART are largely unknown. We report that CART immunoreactivity is present in hypothalamic neuroendocrine neurones. Adult male rats received a systemic injection of the neuronal tracer Fluorogold (FG) 2 days before fixation, and subsequent double‐ and triple‐labelling immunoflourescence analysis demonstrated that neuroendocrine CART‐containing neurones were present in the anteroventral periventricular, supraoptic, paraventricular (PVN) and periventricular nuclei of the hypothalamus. In the PVN, CART‐positive neuroendocrine neurones were found in all of cytoarchitectonically identified nuclei. In the periventricular nucleus, approximately one‐third of somatostatin cells were also CART‐immunoreactive. In the medial parvicellular subnucleus of the PVN, CART and FG coexisted with thyrotrophin‐releasing hormone, whereas very few of the corticotrophin‐releasing hormone containing cells were CART‐immunoreactive. In the arcuate nucleus, CART was extensively colocalized with pro‐opiomelanocortin in the ventrolateral part, but completely absent from neuroendocrine neurones of the dorsomedial part. To assess the possible role of CART as a hypothalamic‐releasing factor, immunoreactive CART was measured in blood samples from the long portal vessels connecting the median eminence with the anterior pituitary gland. Adult male rats were anaesthetized and the infundibular stalk exposed via a transpharyngeal approach. The long portal vessels were transected and blood collected in 30‐min periods (one prestimulatory and three poststimulatory periods). Compared to systemic venous plasma samples, baseline concentrations of immunoreactive CART were elevated in portal plasma. Exposure to sodium nitroprusside hypotension triggered a two‐fold elevation of portal CART42‐89 immunoreactivity throughout the 90‐min stimulation period. In contrast, the concentration of portal plasma CART immunoreactivity dropped in the vehicle infused rats. The current study provides further evidence that CART is a neuroendocrine‐releasing factor with a possible impact on anterior pituitary function during states of haemodynamic stress.
The influence of dentine permeability on cytotoxicity of four dentine bonding systems, in vitro
Authors: Bouillaguet  , Virgillito  , Wataha  , Ciucchi  , Holz
Published: March 2003

Dentine adhesives are often placed directly on dentine from which the smear layer has been removed, the thickness of the dentine is minimal and the potential for diffusion of adhesive components into the pulp is greatest. The permeability of the dentine is one factor that should be critical to whether sufficient diffusion of adhesive components occurs to cause damage to pulpal cells. Dentine discs were prepared and divided into those with low‐, medium‐, and high‐permeability. They were then treated with four different dentine adhesives, after which the pulpal side of the dentine was placed in contact with 1 mL of cell‐culture medium. The medium was collected at 24 h intervals for 168 h, and was then placed on monolayers of human pulpal fibroblasts for 24 h. The response of the cells was assessed by succinic dehydrogenase activity (MTT method). The results showed that four dentine adhesive systems released sufficient components to cause suppression of cellular metabolism through dentine. High‐permeability dentine generally allowed more diffusion of these components, but the effect of dentine permeability depended on the material. On the other hand, the time interval between the application of the bonding agent and collection of the eluant was consistently important for all materials. Materials were most cytotoxic at early intervals, and were generally less cytotoxic at later intervals, although there were exceptions and there was persistent (> 15%) suppression of cellular metabolism even at late (168 h) intervals. The results suggest that application of these materials to dentine, and particularly dentine with high permeability, poses a potential risk to the health of pulpal tissues.
Corrosion behaviour of dental metals and alloys in different media
Authors: Kedici S. P. , Aksüt A. Abbas , Kílíçarslan M. Ali , Bayramog Lu G. , Gökdemir K.
Published: March 2003

The corrosion tendencies of metals are related with their position in the electromotive series. These electrode potential degrees may change due to the compositions of the alloys, the surrounding media, or due to alterations in the composition because of recurrent casting. Therefore in this research, the electrode potentials and their changes over a period of time were measured in different pH media simulating the oral electrochemical conditions in vitro. The surface structure of the first and second castings of 29 different dental metals and alloys were examined under a scanning electron microscope and their composition in percentage weight was calculated by the Energy‐dispersive X‐ray Analysor system. Further the current–potential curves of the dental alloys were found by the potentiodynamic method in three different solutions and, in addition, the changes of corrosion potentials over time were also determined. The corrosion rates, corrosion potentials, their changes over time and their cathodic Tafel slopes were determined. All alloys tested showed ion leakage in corrosive media. Titanium exhibited the least, but alloys with tin and cobalt content displayed the greatest corrosion tendencies. Alloys with iron and copper corroded in the acid media, conversely alloys containing chromium, nichel and molybdenum proved to be resistant to corrosion. The recurrent castings were also corrosion resistant.
Artificial caries formation around fluoride‐releasing restorations in roots
Authors: Dionysopoulos P. , Kotsanos N. , Papadogiannis Y. , Konstantinidis A.
Published: March 2003

Secondary caries is one of the most important factors leading to replacement of dental restorations. This investigation assessed the capacity of fluoride‐releasing restorative materials to resist caries

in vitro

when used in roots. Class 5 cavities were prepared in the buccal and lingual surfaces of 30 extracted premolars. The six materials used were: glass–ionomer cement (Fuji®), glass–ionomer cement with silver particles added (Ketac‐silver®), fluoride‐containing composite resin (Tetric®), composite resin (Silux plus®), fluoride‐containing amalgam (Fluor‐Alloy®) and high‐copper amalgam (Dispersalloy®). After 5 weeks in an acid gel for caries‐like lesion formation, the teeth were sectioned longitudinally and examined with polarized light. The results showed that repair with glass–ionomer materials of a carious lesion may be of great importance in the prevention of secondary caries around the restorations in roots.
Temperature rise during polymerization of light‐activated resin composites
Authors: Shortall A. C. , Harrington E.
Published: March 2003

There has been a steady rise in the use of resin‐based composites in the restoration of large posterior cavities. Visible light‐activated materials have come to dominate the market for direct posterior composites because of the convenience offered to the operator by their command set nature. Manufacturers have produced more powerful light‐activation units in response to concerns over inadequate depth of cure. However, some authors have warned of the danger to the dental pulp induced by excessive heat generated during polymerization. Variables governing heat generation include output intensity of the light‐activation unit, quality of light filter, irradiation time, material composition and material surface‐light guide exit window distance, residual dentine thickness and cavity dimensions. This

in vitro

study assessed the relative influence of some of these factors under controlled conditions. The findings suggest that minimum irradiation times should be used when curing bonding agents in unlined cavities where residual dentine thickness is limited and high output intensity light‐activation units are employed. Material composition is identified as an important variable in determining the magnitude of the temperature rise.
The effect of diabetes mellitus on histopathological changes in the tissues under denture base bearing masticatory pressure
Authors: Maruo Y. , Sato T. , Hara T. , Shirai H.
Published: March 2003

The effect of streptozotocin‐induced diabetes mellitus on histopathological changes in tissues bearing masticatory pressure exerted through an experimental denture base has been studied in animal specimens. Experimental dentures, which prescribed the masticatory pressure by the amount of subsidence of the denture base (100, 50 or 13 μm), were constructed for the hard palate of the molar regions of rats. It was revealed that streptozotocin‐induced diabetes mellitus (1) weakened the intercellular junctions in the epithelium and gradually enhanced this state with time, (2) lessened the atrophic and proliferative reactions in the epithelial ridge and prolonged their appearance period, (3) enhanced the compression of lamina propria mucosae and prolonged the appearance period of this reaction, (4) enhanced the inflammatory change and extended its appearance period, (5) lowered the threshold for the inflammatory reaction induced by the masticatory pressure, (6) increased the number of osteoclasts and prolonged the period of their presence, (7) lowered the threshold for osteoclastic bone resorption induced by the masticatory pressure, (8) inhibited the appearance of osteoblasts following the disappearance of osteoclasts and (9) accelerated the decline rate of masticatory pressure exerted to the denture supporting tissues. Therefore, it can be concluded that the streptozotocin‐induced diabetes mellitus in the animals tested deteriorated the tolerance of the denture supporting tissues to masticatory pressure.
Relationship between anterior guidance and mesiodistal inclination of lower incisor in human subject with or without TMJ noise
Authors: Minagi Shogo , Hara Tetsuya , Sato Takashi , Natsuaki Nobukuni , Akamatsu Yutaka
Published: March 2003

The relationship between anterior guidance and the mesiodistal inclination of the lower incisors relative to the existence of temporomandibular joint (TMJ) noise was investigated. One hundred and thirty‐four individuals, 21 to 40 years of age (mean age 23·8; 104 men and 30 women), were examined. A highly significant correlation was observed between the mean lower‐incisor inclination and the difference in steepness between the right and left anterior guidances in the subject group showing TMJ noise (P<0·001), whereas no significant correlation was observed in the group without TMJ noise.
The effects of oscillating forces upon the flow of dental cements
Authors: Judge R. B. , Wilson P. R.
Published: March 2003

The aim of this study was to evaluate the effect of oscillating forces upon the flow of five dental cements. A laboratory investigation was carried out using a crown and die. It showed that the application of oscillating forces improved the flow of the tested dental cements when combined with low static loads and wide crown–die separations. The oscillating forces enhanced the late, particle‐dominated phase of cement flow. Further investigations characterised the nature of the oscillating forces applied in this experiment and revealed yield stress behaviour shown by one cement.
Advances in biomaterials from 1957 to 1997
Authors: Craig Robert G.
Published: March 2003

The developments in biomaterials over the past 40 years were listed in a questionnaire. Groups of dentists with and without a Master's degree ranked each development on the basis of the impact they believed it has had on the practice of dentistry. The results of the questionnaires were analysed and the rankings were discussed and used as a guide to the projection of the probable future needs and developments in biomaterials, based on the needs of current and future dental patients.
The effect of propolis exposure on microhardness of human enamel in vitro
Authors: Giamalia I. , Steinberg D. , Grobler S. , Gedalia I.
Published: March 2003

Propolis is a resinous wax‐like material that is used by bees as a glue‐like matrix in their hives. The in vitro effect of propolis solutions was investigated on the microhardness of human dental enamel. The calcium concentration of the solution was 7·8 ppm, the pH values varied between 5 and 6. The fluoride concentration was negligible. The Vickers hardness number of exposed enamel showed a steady increase with the percentage of propolis in the solution. The microhardness increase may be attributed to particular components of mineralization activity in propolis.
Masseter muscle activity during the whole day in children and young adults
Authors: Miyamoto K. , Ishizuka Y. , Ueda H. M. , Saifuddin M. , Shikata N. , Tanne K.
Published: March 2003

Changes in size and shape of the craniofacial skeleton during growth may be related to the masticatory muscle function in daily life. The purpose of this study was to measure the masseter muscle activity during the whole day in children and to investigate the differences between children and young adults. Fifteen children (7·8–13·0 years of age) and 30 young adults (20·3–34·7 years of age), who had acceptable occlusions without any remarkable skeletal discrepancy or temporomandibular disorder, were used as the subjects. In both children and young adults, most high‐amplitude bursts of masseter muscle appeared mainly during mealtime, whereas a substantially larger number of low‐amplitude ones were widely distributed throughout the whole day. The number and total duration of bursts of masseter muscle activity during the whole day was greater in children than in young adults, although significant differences were not found between the sexes. During daytime and sleep, both the number and total duration of bursts were greater in children. During mealtime, no significant differences in the number of bursts were found between children and young adults, however, the duration of bursts tended to be longer in children. It is concluded that the masseter muscle activity during the whole day is greater in children than in young adults.
Incidence of occlusal contacts with complete dentures during mastication using a 6‐channel telemetry system: preliminary measurements
Authors: Kumagai H. , Watanabe T. , Kobayashi K. , Suzuki T. , Nagao M. , Nikawa H. , Hamada T.
Published: March 2003

The purpose of this study was to observe the incidence of occlusal contact with complete dentures during mastication using a 6‐channel telemetry system whose accuracy had been improved. The telemetry system consisted of the transmitter unit and the receiver unit. The transmitter unit was embedded in the lower complete denture. This system detects occlusal contacts by the shift of frequency in 100 kHz. The transmitter allowed 6 channels for the occlusal contacts. The data was telemetered by a time division multiplex communication method. A special switch was designed to measure excursive movement on the occlusal surface. After careful occlusal adjustment, the special switches were inserted in the lower first molars. On the basis of preliminary measurements on a 64‐year‐old edentulous male, it appears that the width of the gliding on the occlusal surface at the lower first molar was mostly 0·2–1·2 mm and the majority of the excursive movements ended at the centric occlusal position.
pH changes of glass–ionomer lining materials at various time intervals
Authors: Ben‐Amar A. , Liberman R. , Apatowsky U. , Pilo R.
Published: March 2003

The purpose of this in vitro study was to evaluate pH changes of resin modified glass–ionomer (RMGI) and conventional glass–ionomer liners at short‐term intervals after mixing to relate the timing of light activation on the acidity of RMGI lining materials. The RMGI liners tested were Vitrebond™ (3M), Variglass VLC™ (Dentsply), Fuji Lining LC™ (GC Dental Industrial Corp.) compared to a traditional glass–ionomer liner: Lining Cement™ (GC, control). Light activation of liners was carried out at different time intervals after mixing. The pH changes of each liner were evaluated immediately after mixing and thereafter every minute for 8 min using a surface pH meter. All liners tested exhibited a gradual increase in surface pH over time. The delay of light activation of RMGI lining materials after mixing did not significantly decrease the acidity of the liner during the first 9 min post‐mixing.
Assessment of occlusal stability by measuring contact time and centric slide
Authors: Kirveskari P.
Published: March 2003

The aim of the present study was to evaluate two different methods for the assessment of the positional stability of occlusion. The time taken from first contact on closure to full intercuspation was measured by the T‐scan®, and the length of the slide between centric relation (CR) and maximum intercuspation was clinically assessed in a sample of healthy adolescents and young adults undergoing a clinical trial which involved repeated occlusal adjustment. The T‐scan® readings and the clinical assessments of the centric slide were obtained at baseline and at the third and fourth annual examination. There was an overall, but statistically not significant, decline in the contact time. The length of the centric slide did decrease significantly. However, there was no systematic correlation between the two variables. They appear to describe different qualities of occlusion, and their validity as a measure of ‘goodness’ of occlusion remains an unanswered question.
The effects of different additives on the dielectric relaxation and the dynamic mechanical properties of urethane dimethacrylate
Authors: Mohsen N. M. , Craig R. G. , Filisko F. E.
Published: March 2003

The polymer–filler interaction of a dental composite was examined by dielectric measurements to determine how a non‐compatible inorganic phase modifies the molecular behaviour of the polymer chains and how modification of this phase by silanation can affect these molecular behaviours. Urethane dimethacrylate (UDMA) monomer and zirconia–silica (ZS) powder were used as organic and inorganic phases, respectively. 3‐Acryloxypropyltrimethoxysilane (MAPM) and 4‐aminobutyltriethoxysilane (ABTE) were used as silanating coupling agents. The components of the composite were mixed in different ratios after treating the filler with from 0 to 30 times the minimum uniform coverage with the silane, then the composite was made into thin films. The dielectric spectra of five replicas for each filler–monomer ratio were measured, and three replicas were measured for each silane and for each amount of silane used to treat the filler. Increasing the filler concentration in the composites decreased the intensity of Tan(Δ) for the α‐ and β‐relaxations, where the β‐relaxations also became broader and the α‐relaxations were totally obstructed. The α‐relaxations were shifted to higher temperatures, while the β‐relaxations were shifted to lower temperatures. Filler treatment with small amounts of MAPM shifted the α‐relaxations to higher temperatures; they were shifted back to lower temperatures when the filler was treated with large amounts of silane. Filler treatment with large amounts of ABTE (30‐fold) caused an extra peak to emerge in the high‐temperature region. It can be concluded that increasing filler concentration restricts the mobility of the main chains and decreases the thickness of the surface layer, while allowing more movement of the local chains. Filler treatment with MAPM was shown to be a compatible coupling agent with the ZS and the UDMA systems. Such compatibility was observed through the effectiveness of the chemical linkage of the silane to the filler and the polymer without forming a separate inter‐phase. Filler treatment with ABTE was shown to be an incompatible coupling agent for the ZS‐filled UDMA system. The incompatibility was observed by the occurrence of a new peak that characterizes an inter‐phase.
Effect of intrinsic and extrinsic moisture on bond strength to dentine
Authors: Moll K. , Haller B.
Published: March 2003

Objectives: The aim of this in vitro study was to investigate the effects of simulated pulpal pressure (PP) and moist bonding (MB) on the shear bond strength of three different dentine bonding systems (DBSs). Methods: Dentine surfaces were exposed on 120 extracted human molars and bonded with one out of three restorative systems (A.R.T. Bond/Brilliant, OptiBond FL/Herculite XRV, Scotchbond 1/Z100). In one‐half of the specimens, the DBSs were applied under hydrostatic pulpal pressure of 30 cm H2O (PP). Forty specimens were prepared for each DBS according to the following experimental groups (each n=10): no PP/no MB; with PP/no MB; no PP/with MB; with PP/with MB. Shear bond stengths after 24 h were measured in a universal testing machine (Zwicki 1120) and statistically analysed by 2‐way
anova. Fractured surfaces were investigated for the type of failure under an optical stereomicroscope and by SEM. Results: In all DBSs, pulpal pressure resulted in a decrease of dentinal bond strength. This effect was significant in A.R.T. Bond and OptiBond FL (P<0·001), but not in Scotchbond 1 (P=0·060). Moist bonding significantly increased the bond strength of Scotchbond 1 (P<0·001), significantly decreased the bond strength of A.R.T. Bond (P=0·032), but had no effect in the case of OptiBond FL (P=0·691). In A.R.T. Bond, the combination of hydrostatic pulpal pressure and moist bonding resulted in complete failure of most of the specimens prior to the debonding tests. The fracture patterns as detected by SEM fracture analyses were typical for each DBS and specific bonding condition and consistent with the results of the bond strength measurements. Significance: The results indicate that continuous intrinsic moisture in the form of hydrostatic pulpal pressure adversely affects the efficacy of DBSs, while limited extrinsic moisture by moist bonding is acceptable or even essential. The effect of moist bonding on the efficacy of DBSs seems to depend not only on the monomers used and the solvents per se, but also on the water content of the dentine primer and the self‐priming adhesive, respectively.
Corrosion resistance of a magnetic stainless steel ion‐plated with titanium nitride
Authors: Hai K. , Sawase T. , Matsumura H. , Atsuta M. , Baba K. , Hatada R.
Published: March 2003

This in vitro study evaluated the corrosion resistance of a titanium nitride (TiN) ion‐plated magnetic stainless steel (447J1) for the purpose of applying a magnetic attachment system to implant‐supported prostheses made of titanium. The surface hardness of the TiN ion‐plated 447J1 alloy with varying TiN thickness was determined prior to the corrosion testing, and 2 μm thickness was confirmed to be appropriate. Ions released from the 447J1 alloy, TiN ion‐plated 447J1 alloy, and titanium into a 2% lactic acid aqueous solution and 0·1 mol/L phosphate buffered saline (PBS) were determined by means of an inductively coupled plasma atomic emission spectroscopy (ICP‐AES). Long‐term corrosion behaviour was evaluated using a multisweep cyclic voltammetry. The ICP‐AES results revealed that the 447J1 alloy released ferric ions into both media, and that the amount of released ions increased when the alloy was coupled with titanium. Although both titanium and the TiN‐plated 447J1 alloy released titanium ions into lactic acid solution, ferric and chromium ions were not released from the alloy specimen for all conditions. Cyclic voltamograms indicated that the long‐term corrosion resistance of the 447J1 alloy was considerably improved by ion‐plating with TiN.
Impression pressures against teeth in a partially edentulous model with a mobile tooth: influence of impression tray design
Authors: Nishi Y. , Tsuru K. , Kishita C. , Hamano T. , Kawahata N. , Nagaoka E.
Published: March 2003

The purpose of the present study was to examine the effect of custom tray designs on local pressures against teeth during the impression procedure. In a previous study, a partially edentulous simulation model with a mobile tooth was used, and the effect of custom tray designs on the displacement of the mobile tooth was examined during the impression procedure. Based on that study's results, we have assumed that the differences in impression pressures between the labial and the lingual sides of a mobile tooth could either cause or affect displacement. The present study was undertaken to determine the local impression pressures against each side of three anterior teeth, including one mobile tooth, using the same simulation model and the same custom trays as in the previous study. It was found that the local pressures exerted against teeth during the impression procedure were affected by the custom tray designs and varied according to the coronal shape, axis inclination and location of the teeth.
The effect of pH on the corrosion of dental metal alloys
Authors: Bayramoğlu G. , Alemdaroğlu T. , Kedici S. , Aksüt A. A.
Published: March 2003

The aim of this study was to determine the effects of the oral environment's pH on the corrosion of dental metals and alloys that have different compositions, using electrochemical methods. The corrosion rates and the cathodic Tafel slopes were obtained from the current–potential curves. The effect of pH on the corrosion of dental metals and alloys was dependent on their composition. Dissolution of the ions occurred in all of the tested pH states. The dissolution was moderately low for samples containing titanium because its surface was covered with a protective layer, whereas the dissolution was maximal for the samples containing tin and copper. Addition of cobalt and molybdenum to the alloys improved their corrosion resistance; these cobalt and molybdenum alloys were not effected by changes in the pH. Dissolution of the precious metal alloys increased as the percentage of noble metals increased. The corrosion characteristics of dental metals and alloys are important because the corrosion tendencies of dental alloys in the mouth may cause health hazards, weakening and the aesthetic loss of dental restorations.