bluuebunny/crossref_metadata_2025 huggingface dataset:
5α‐Reductase Type 2 and Androgen Receptor Expression in Gonadotropin Releasing Hormone GT1‐1 Cells
Authors: Poletti A. , Rampoldi A. , Piccioni F. , Volpi S. , Simeoni S. , Zanisi M. , Martini L.
Published: March 2003

Gonadal steroids are potent modulators of gonadotropin releasing hormone (GnRH) secretion, and androgen binding sites and 5α‐reductase activity have been found in the immortalized GnRH secreting cell line GT1‐1, suggesting the existence of a direct androgenic control of GnRH dynamics. Two isoforms of the 5α‐reductase have been cloned with very different biochemical/functional properties: 5α‐reductase type 1 (widely distributed in the body) and 5α‐reductase type 2 (confined in androgen target structures). We have analysed whether, in GT1‐1, androgen binding sites are linked to ‘classical’ androgen receptor, and which 5α‐reductase isoform is active. Reverse transcriptase‐polymerase chain reaction analysis showed that the mRNAs coding for androgen receptor and for the two 5α‐reductase isoforms are all expressed in GT1‐1 cells. However, the 5α‐reductase enzymatic reaction showed a peak of activity at a narrow pH around 5.5, the optimum for the 5α‐reductase type 2. The affinity for testosterone, of the enzyme present in GT1‐1 cells, was very similar to that observed for the recombinant type 2 isozyme expressed in yeasts. The data indicate that GT1‐1 cells (i) express a ‘classical’ androgen receptor and (ii) contain the 5α‐reductase type 2 isoform, a specific marker of androgen‐responsiveness.
Neuropeptide‐Y: A Possible Mediator of Prolactin‐Induced Feeding and Regulator of Energy Balance in the Ring Dove (Streptopelia risoria)
Authors: Strader A. D. , Buntin J. D.
Published: March 2003

Although neuropeptide‐Y (NPY) has been widely reported to be a potent stimulator of feeding activity and regulator of energy homeostasis, most of the supportive evidence for such effects has been gathered in mammalian species. This study characterized the orexigenic potency of NPY in an avian species, the ring dove, and measured changes in hypothalamic NPY‐immunoreactive (NPY‐ir) cell numbers in response to energy state fluctuations or intracranial administration of the potent orexigenic hormone prolactin. Food intake was significantly elevated in male doves at 1 h after intracerebroventricular (i.c.v.) injection of 0.25 and 0.5 µg NPY but not after injection of a higher dose (1.0 µg). In time course studies, food intake was increased at 1 h after i.c.v. injection of 0.5 µg NPY but was not elevated at 2, 3, or 4 h. The number of NPY‐ir cell bodies in the infundibular region of the dove hypothalamus increased two to four‐fold following acute food deprivation, chronic food restriction, or repeated i.c.v. injections of prolactin. No additive effects were observed when food restriction and prolactin treatment were combined. These findings suggest that NPY is involved in energy homeostasis in doves and are consistent with the hypothesis that prolactin‐induced hyperphagia is mediated in part by NPY.
Clock Gene Protein mPER1 is Rhythmically Synthesized and Under cAMP Control in the Mouse Pineal Organ
Authors: Von Gall C. , Schneider‐Hüther I. , Pfeffer M. , Dehghani F. , Korf H.‐W. , Stehle J. H.
Published: March 2003

The mammalian clock gene Per1 is an important element of endogenous oscillators that control daily rhythms in central and peripheral tissues. Although such autonomous clock function is lost in the mammalian pineal gland during evolution, mPer1 mRNA and mPER1 protein were found to be strongly elevated in the mouse pineal organ during the dark period compared to daytime values. In vitro studies showed that mPer1 mRNA and mPER1 protein in mouse pineal gland are induced following the activation of a signalling pathway of fundamental importance for pineal physiology, the norepinephrine/cAMP/phosphoCREB cascade. mPER1 may function in the mouse pineal gland as a time‐measuring molecule to participate in regulating rhythmic cellular responses in vivo.
Skeletal Growth Acceleration with Growth Hormone Secretagogues in Transgenic Growth Retarded Rats: Pattern‐Dependent Effects and Mechanisms of Desensitization
Authors: Wells T. , Houston P. A.
Published: March 2003

The transgenic growth retarded (Tgr) rat is the first genetic model of growth hormone (GH) deficiency whose growth can be accelerated with exogenous GH secretagogues (GHSs). In this study, we have demonstrated that GHS‐receptor (GHS‐R) mRNA expression in the arcuate nucleus of Tgr rats was not significantly different to that in wild‐type littermates. We have confirmed that GHS‐induced elevation in body weight gain was accompanied by acceleration of skeletal growth, and that the effects of the GHS, GHRP‐6, were both dose‐ and pattern‐dependent. The growth response with continuous infusion of GHRP‐6 was transient, accompanied by suppression of GH and corticosterone responses to bolus injection of GHRP‐6. This desensitization occurred without downregulation of arcuate GHS‐R mRNA expression, but was accompanied by elevated periventricular somatostatin mRNA expression. In contrast, pulsatile (3‐hourly) infusion of GHRP‐6 produced sustained growth and GH responses, which were accompanied by suppression of corticosterone responses and elevated arcuate GH‐releasing factor (GRF) mRNA expression. Skeletal growth was further accelerated by coinfusion of GRF, but significant depletion of pituitary GH stores suggested that this growth rate may not be sustainable. These experiments confirm the importance of the Tgr rat for investigating the growth promoting potential of the GHSs in the context of GH‐deficient dwarfism, and suggest that elevated somatostatin expression may mediate the suppression of the GRF‐GH and hypothalamo‐pituitary‐adrenal axes following continuous GHRP‐6 treatment.
Changes in Rat Serum Corticosterone After Treatment with Metabotropic Glutamate Receptor Agonists or Antagonists
Authors: Johnson M. P. , Kelly G. , Chamberlain M.
Published: March 2003

From previous work, it appears that glutamate can activate the hypothalamic‐pituitary‐adrenocortical (HPA) axis by an interaction at either ionotopic or metabotropic (G‐protein coupled) receptors. For example, (1S,3R)‐1‐aminocyclopentane‐1,3‐dicarboxylate (ACPD), a metabotropic glutamate (mGlu) receptor agonist, has been shown to increase the levels of serum corticosterone in rats. The present study was undertaken to further characterize which of the mGlu receptors are substantially involved in control of the HPA axis. The group I mGlu receptor agonists, 3,5‐dihydroxyphenylglycine (DHPG), 1S,3R‐ACPD, and 2‐chloro‐5‐hydroxyphenylglycine (CHPG) but not the inactive isomer 1R,3S‐ACPD were found to dose‐dependently increase serum corticosterone 1 h after intracerebroventricular (i.c.v.) injection in male rats. The relative potency, DHPG (EC50 = 520 nmol) > 1S,3R‐ACPD (1.4 µmol) = CHPG (2.7 µmol) ≫ 1R,3S‐ACPD (≫ 3 µmol) is consistent with activation of group I (mGlu1/5) receptors. The effects of DHPG were long lasting with substantial elevations in corticosterone remaining for at least 3 h. In a similar manner, the group III mGlu receptor agonists, L‐AP4 (4‐phosphono‐2‐aminobutyric acid) and L‐SOP (serine‐O‐phosphate), were found to increase serum corticosterone levels at 1 h. In contrast, the mGlu group II selective agonists LY354740 (10 mg/kg, i.p.) and subtype‐selective doses of the group II antagonist LY341495 (1 mg/kg, i.p.) did not significantly elevate serum corticosterone. Given the group I agonists results, it was surprising to find that group I selective and mGlu1 selective antagonists given alone also increased serum corticosterone. As with the agonists, the rise in serum corticosterone with LY393675 (an mGlu1/5 antagonist, EC50 = 20 nmol, i.c.v.) and LY367385 (an mGlu1 antagonist, 325 nmol, i.c.v.) were dose‐dependent and consistent with their relative affinity for the group I mGlu receptors. The selective mGlu5 antagonist MPEP [2‐methyl‐6‐(phenylethylnyl)pyridine] increased serum cortocosterone but only at high doses (> 30 mg/kg, i.p.). A model involving the high glutamatergic tone on GABAergic interneurons in the paraventricular nucleus of the hypothalamus is discussed as a possible explanation for these results.
Alterations in Hypothalamic Insulin‐Like Growth Factor‐I and its Associations with Gonadotropin Releasing Hormone Neurones During Reproductive Development and Ageing
Authors: Miller B. H. , Gore A. C.
Published: March 2003

Insulin‐like growth factor‐I (IGF‐I) is thought to play a role in the onset of reproductive ability at puberty and the control of reproductive function throughout adult life. It is believed that these effects are mediated at least in part by the activation of gonadotropin releasing hormone (GnRH) neurones by IGF‐I, but the interactions of IGF‐I with GnRH neurones in vivo are largely unknown. We first examined the anatomical relationship between GnRH and IGF‐I cells in neuroendocrine regions. Using double‐label immunocytochemistry, we observed that in the preoptic area‐anterior hypothalamus (POA‐AH), the site of GnRH perikarya, the majority (78%) of GnRH cell bodies expressed IGF‐I immunoreactivity. IGF‐I immunoreactivity was also high in the median eminence, the site of GnRH release, and GnRH neuroterminals were seen to interweave among IGF‐I‐immunopositive cells. Due to this substantial overlap of GnRH and IGF‐I immunoreactive elements, we then tested the hypothesis that changes in IGF‐I may regulate the GnRH system. Animals were examined at the two important reproductive life transitions: puberty and reproductive senescence. IGF‐I mRNA levels were measured in POA‐AH and medial basal hypothalamus‐median eminence (MBH‐ME) and effects of IGF‐I treatment on GnRH mRNA levels were quantified by RNase protection assay. Although IGF‐I treatment did not alter GnRH gene expression, there were significant alterations in hypothalamic IGF‐I gene expression at both puberty and reproductive senescence. During puberty, IGF‐I mRNA levels in the MBH‐ME of rats increased from the juvenile stage (P25) to the day of vaginal opening (P35), and from the day of vaginal opening to young adulthood (P45) in the POA‐AH. During reproductive ageing, IGF‐I mRNA levels were significantly lower in middle‐aged than young rats, particularly in the MBH‐ME. At all ages, IGF‐I expression was greater in the MBH‐ME than in the POA‐AH. These experiments demonstrate that: (i) the majority of adult GnRH neurones are immunopositive for the IGF‐I protein; (ii) hypothalamic IGF‐I levels increase at the onset of reproductive function and decrease at reproductive senescence in a regionally specific manner; and (iii) despite the presence of IGF‐I in GnRH perikarya, IGF‐I does not affect GnRH gene expression, suggesting that IGF‐I may act at the level of GnRH release rather than gene expression.
Isoform Specificity for Oestrogen Receptor and Thyroid Hormone Receptor Genes and Their Interactions on the NR2D Gene Promoter
Authors: Vasudevan N. , Kia H. K. , Inoue S. , Muramatsu M. , Pfaff D.
Published: March 2003

Oestrogens are critical for the display of lordosis behaviour and, in recent years, have also been shown to be involved in synaptic plasticity. In the brain, the regulation of ionotropic glutamate receptors has consequences for excitatory neurotransmission. Oestrogen regulation of the N‐methyl‐d‐aspartate receptor subunit 2D (NR2D) has generated considerable interest as a possible molecular mechanism by which synaptic plasticity can be modulated. Since more than one isoform of the oestrogen receptor (ER) exists in mammals, it is possible that oestrogen regulation via the ERα and ERβ isoforms on the NR2D oestrogen response element (ERE) is not equivalent. In the kidney fibroblast (CV1) cell line, we show that in response to 17β‐oestradiol, only ERα, not ERβ, could upregulate transcription from the ERE which is in the 3′ untranslated region of the NR2D gene. When this ERE is in the 5′ position, neither ERα nor ERβ showed transactivation capacity. Thyroid hormone receptor (TR) modulation of ER mediated induction has been shown for other ER target genes, such as the preproenkephalin and oxytocin receptor genes. Since the various TR isoforms exhibit distinct roles, we hypothesized that TR modulation of ER induction may also be isoform specific. This is indeed the case. The TRα1 isoform stimulated ERα mediated induction from the 3′‐ERE whereas the TRβ1 isoform inhibited this induction. This study shows that isoforms of both the ER and TR have different transactivation properties. Such flexible regulation and crosstalk by nuclear receptor isoforms leads to different transcriptional outcomes and the combinatorial logic may aid neuroendocrine integration.
Temperature Influences the Ontogenetic Expression of Aromatase and Oestrogen Receptor mRNA in the Developing Tilapia (Oreochromis mossambicus) Brain
Authors: Tsai C. ‐L. , Chang S. ‐L. , Wang L. ‐H. , Chao T. ‐Y.
Published: March 2003

Water temperature has a differential influence on the development of central neurotransmitter systems according to the developmental period in tilapia (Oreochromis mossambicus). Aromatase and oestrogen receptors (ERs) represent important components of the mechanism of brain differentiation. Gene expression of aromatase and ERs is modulated by neurotransmitters in the developing brain. In the present study, the quantitative reverse transcription‐polymerase chain reaction method was used to investigate the effects of temperature on the ontogenetic expression of aromatase and ERs in the developing tilapia brain. Before day 10 posthatching, exposure to a higher temperature (32 °C) resulted in a significant increase in the expression of brain aromatase; conversely, a lower temperature (20 °C) resulted in a decrease. ERα expression was depressed in accordance with the decrease of temperature, but ERβ was unaffected by temperature. Between days 10 and 20, neither brain aromatase nor ERα expression was altered by temperature, whereas ERβ expression was significantly enhanced by exposure to 32 °C. Between days 20 and 30, brain aromatase significantly increased at the higher temperature and decreased at 20 °C, but neither ERα nor ERβ was affected by temperature. The expression of both brain aromatase and ERs, differentially regulated according to the temperature and to the developmental period, could be related to brain–sex differentiation.
Effects of a bite‐raising splint on the duration of the chewing cycle and the EMG activities of masticatory muscles during chewing in freely moving rabbits
Authors: Matsuka  , Kitada  , Mitoh  , Adachi  , Yamashita
Published: March 2003

Metal bite‐raising splints of 0.5 mm thickness were attached to the upper molar teeth on both sides of the jaw in rabbits. The effects of these splints on masticatory behaviour during the chewing of soft food (bread) by freely moving rabbits were investigated. We recorded electromyograms (EMGs) of the masseter and digastric muscles. The animals exhibited prolongation of the chewing cycle, decreased EMG activity of the masseter muscle and increased EMG activity of the digastric muscle during chewing after introduction of the bite‐raising splints. The effects of the splints on the activities of masticatory muscles were abolished by bilateral sectioning of the maxillary and inferior alveolar nerves. It seems likely that afferents from oral sensory receptors were responsible for the changes in masticatory behaviour after the introduction of the occlusal splint.
Can chemical softening agents minimize cavity enlargement during removal of failed anterior resin composite restorations?
Authors: Cruickshank  , Chadwick
Published: March 2003

This in‐vitro investigation sought to identify the most effective softening agents for three commercial anterior resin composites (Prisma APH®, Brilliant® and Blend‐a‐Lux®) from four potential agents (75% ethanol, polyacrylic acid, acetone and acetic acid), selected as having close solubility parameter values to BIS‐GMA. The Vickers microhardness test was applied to samples before and following a 180 s application of each agent. In addition, the degree of cavity enlargement following removal of resin composite restorations, aged by thermocycling, was assessed by image analysis. Using the same method the influence of both colour match and the 180 s application of softening agents, in the optimum chemical/material combinations, upon this was determined. Analyses of variance revealed that significant (P < 0·01) reductions in surface microhardness occurred when 75% ethanol was applied to Prisma‐APH® and acetic acid to Blend‐a‐Lux®. Removal of restorations of all materials resulted in highly significant (P < 0·001) increases in cavity size. Application of either 75% ethanol to Prisma‐APH® restorations or acetic acid to Blend‐a‐Lux® did not alter this result. Thermocycling only produced a significant (P < 0·01) (McNemar Test) deterioration in shade match of the Prisma APH® restorations but analyses of variance, for all materials, revealed that the observed changes in colour match had no significant (P < 0·05) effect upon the degree of cavity size enlargement. It is concluded that the application of softening agents to reduce cavity enlargement is not a viable clinical option.
Effect of denture thickness on tooth movement during processing of complete dentures
Authors: Jamani K. D. , Abuzar M. A. Moligoda
Published: March 2003

In this investigation the effect of denture thickness on tooth movement during processing of complete dentures was studied. A maxillary cast from a patient was duplicated to obtain 10 identical casts. Base plates were constructed on five casts using 1·25 mm thick wax. Base plates were constructed on the other five casts using 2·5 mm thick wax. Teeth were placed on the ridge of each cast and a TMS pin was placed vertically, upright, in each tooth. The dentures were invested, cured, decasted, finished and polished. Each denture was radiographed immediately before processing, after deflasking, on removal from the cast and after finishing and polishing using a standard technique. The radiographs were digitized using an Eikonix image digitizer. The results showed that there were significant variations in tooth movement between thick and thin denture bases. Also an increase in the molar‐to‐molar distance was found in both the thin and thick dentures but the magnitude of tooth movement was more in thick dentures.
The effect of diabetes mellitus on histopathological changes in the tissues under denture base and without mechanical pressure
Authors: Shirai H. , Sato T. , Hara T. , Minagi S.
Published: March 2003

Histopathological changes in the tissues under a denture base were studied with respect to the difference between diabetic and normal rats. Diabetes mellitus was induced in Wistar rats by streptozotocin. The experimental denture base was designed to make contact with the palatal mucosa without any continuous nor masticatory pressure. Histopathological observation periods were 1, 2, 4, 8, 12 and 20 weeks after the insertion of the denture base. Histopathological examination revealed that only the transient slight proliferative reaction observed in mucosal epithelium under a denture base in normal non‐diabetic rats, was lessened by induced diabetes mellitus. Moreover, covering the palatal mucosa with a denture base without any continuous nor masticatory pressure and with the maintenance of mucosal cleanliness under it and of the denture itself, did not cause any inflammatory change or bone resorption in the tissues under the base.
Splinting osseointegrated implants and natural teeth in rehabilitation of partially edentulous patients. Part II: principles and applications
Authors: LauFer B. ‐Z. , Gross
Published: March 2003

Lone standing splinted implant segments are accepted as optimal. However, in the treatment of partial edentulism, clinical reality often predicates the consideration of splinting teeth and implants due to variables of tooth/implant location and available bone support. This article presents a review on biomechanical aspects of splinting teeth and some considerations of splinting teeth and implants. A proposed classification of splinting applicable to both teeth and implants is presented as well as a discussion of the clinical aspects of splinting illustrated with clinical cases.
Facial asymmetry in temporomandibular joint disorders
Authors: Inui M. , Fushima K. , Sato S.
Published: March 2003

In order to investigate skeletal deviation in patients with internal derangement of the TMJ, facial asymmetry was examined by the frontal cephalogram and compared with a control group of asymptomatic subjects. It was demonstrated that mandibular lateral displacement in the patients was significantly greater than that in the controls. The degree of displacement was significantly related to the cant of the frontal occlusal plane and the frontal mandibular plane, indicating the reduced vertical dimension of the posterior occlusal level and the ramus height on the mandibular displaced side. It is concluded that facial asymmetry due to mandibular lateral displacement is a relatively common problem in patients with internal derangement of TMJ. The cant of the frontal occlusal plane seems to be an important occlusal characteristic related to temporomandibular joint dysfunction.
Assessment of tooth preparation designs for posterior resin‐bonded porcelain restorations
Authors: Etemadi S. , Smales R. J. , Drummond P. W. , Goodhart J. R.
Published: March 2003

Tooth preparation designs advocated for posterior resin‐bonded porcelain restorations were evaluated for clinical application. This study examined the design of tooth preparations from stone dies for individual posterior resin‐bonded porcelain onlays and complete porcelain crowns placed in a specialist practice, and compared features that provided retentive and porcelain fracture‐resistance with those in the dental literature. Stone dies of tooth preparations for 57 onlay and 46 crown preparations were provided. Measurements were recorded for the tooth preparations with the aid of interocclusal silicone impressions. Proximal boxes, grooves and occlusal steps resulting from removal of amalgam restorations were common. These retentive features were more evident with onlays, and appeared larger on the distal than the mesial surfaces. Internal tooth preparation tapers or convergence angles were frequently greater than 20 °, leading to relatively‐wide occlusal isthmus widths, especially for onlays. There were wide variations in occlusal surface reductions for the central fossae and supporting cusps. Tapers for tooth preparations were frequently more extensive, and occlusal surface reductions were often less than recommended. The implications of these differences for long‐term clinical success should be resolved.
Dental asymmetry in temporomandibular disorders
Authors: Fushima K. , Inui M. , Sato S.
Published: March 2003

In our previous study, it was reported that facial asymmetry due to mandibular lateral displacement (MLD) was significant in patients with temporomandibular disorders (TMD). In this study, dental asymmetry in TMD patients was investigated by means of PA cephalogram and study model. Lateral deviation of the midline of the mandibular occlusal table (PA‐mid) and right–left difference of the molar relationship (Molar‐Diff.) were examined, and their relationship with MLD was studied. PA‐mid and Molar‐Diff. were significantly correlated with MLD. In most cases, displaced side of the midline of the lower occlusal table was coincident with that of the mandibular skeletal midline. These results suggest that in TMD patients asymmetries in occlusal relationship of the midline of the mandibular teeth and molars were mainly due to a mandibular skeletal asymmetry and not merely due to a dental malposition on the alveolar basal bone. Many cases had a more distal occlusal relationship of the first molar on mandibular displaced side compared with that on the opposite side. A high incidence of Class II relationship was found (61·8% as a whole) and more remarkable on the mandibular displaced side. Midline discrepancy and right–left difference of the molar relationship seem to be important occlusal characteristics in patients with TMD.
Evaluation of the marginal accuracy of different all‐ceramic crown systems after simulation in the artificial mouth
Authors: Beschnidt S. M. , Strub J. R.
Published: March 2003

The invitro marginal fit of five different all‐ceramic crown systems (In‐Ceram®, Empress® staining technique, Empress® veneering technique, Celay® feldspathic system, Celay In‐Ceram® system) was evaluated before and after cyclic preloading in an artificial mouth. The crowns were adhesively luted to extracted natural maxillary incisors prepared with a 90° shoulder. The results were compared to those for porcelain‐fused‐to‐metal (PFM) crowns with circular porcelain‐butt margins which were cemented with zinc phosphate cement. The analysis of the marginal discrepancies showed significant (P≪0·001) differences among the groups. Crown cementation increased the marginal gaps significantly (P≪0·01). Empress® staining technique crowns showed the smallest marginal gaps (median 47 μm), followed by conventional In‐Ceram® crowns (median 60 μm) and Empress® veneer technique crowns (median 62 μm). Celay In‐Ceram® crowns displayed marginal openings with a median of 78 μm, followed by Celay® feldspathic crowns with a median of 99 μm. The marginal gap of the PFM control crowns showed a median of 64 μm. Ageing in the chewing simulator had no significant influence on the marginal fit of all specimens. The study indicates that all the tested all‐ceramic crowns have clinically acceptable margins. However, in vivo investigations of all all‐ceramic crown systems should be made before clinical routine.
Size effect in resin/glass composite flexure strengths
Authors: Baran George R. , Mccool John I. , Boberick Kenneth G. , Zhang Hanqing
Published: March 2003

The objective of this study was to test the hypothesis that composite restorative materials possess an elastic‐brittle nature and therefore will exhibit a size effect for flexure strength data. The experimental material consisted of 20 wt% 60:40 BISGMA:TEGDMA, 10 wt% colloidal silica, and 70 wt% Sr glass and was cured by light irradiation. Two sizes of flexure specimens were fabricated: 3·2×1·6×35 mm, and 6·25×3·1×35 mm. Half of the specimens made were soaked to equilibrium weight gain in 50:50 ethanol:water. The fracture strengths were measured in four‐point bending tests. The beams under load were modelled by the finite element package ABAQUS. A statistical fracture mechanics methodology embodied in a public domain computer program called CARES/LIFE, developed by NASA, utilized the ABAQUS input and the fracture strengths of the smaller specimens to predict the fracture strengths of the larger specimens. In making the computation it used an approach that combines a Weibull distribution of flaw size with Batdorf's fracture mechanical model for failure at a material flaw. Both the soaked and unsoaked specimens exhibited Weibull behaviour, with shape parameters ranging from 4·04 to 8·15. Soaking had a clearly detrimental effect on the strengths of specimens of both sizes, and produced a comparable percentage reduction in the estimated scale parameter of the fracture strength distribution. Both the soaked and unsoaked specimens also exhibited a clear and comparable size effect, i.e. the larger specimens had a fracture strength that was lower than that of the smaller specimens by roughly the same percentage. Moreover, the magnitude of the size effect was well predicted by the CARES/LIFE methodology for both the soaked and the dry specimens. The elastic–brittle character of both soaked and unsoaked composite specimens was validated by load‐deflection data, the magnitude of the Weibull shape parameters of the observed fracture strength data (<10), and the observed effect of specimen size. The accuracy of CARES/LIFE in predicting the magnitude of the observed size effect in beams of two different sizes strongly suggests that CARES/LIFE will be useful for computation of failure probabilities for clinically relevant structures.
A biomechanical effect of wide implant placement and offset placement of three implants in the posterior partially edentulous region
Authors: Sato Y. , Shindoi N. , Hosokawa R. , Tsuga K. , Akagawa Y.
Published: March 2003

To prevent loosening or fracture of screws retaining the prosthesis to the implants in the posterior partially edentulous region, the use of staggered buccal and lingual offset placement or wide implants is suggested. However, it is not known how this usage compensates for the torque produced by lateral occlusal forces. This study evaluated the effectiveness of offset placement of three implants and a wide implant placement at the most posterior site. Three‐dimensional geometric analysis was used to calculate the tensile force applied to gold screws in clinical situations with buccal or lingual loading perpendicular to cuspal inclination (10 or 20°). Four variations of the placement of three implants (∅ 3·75 mm) are: (1) straight; (2) buccal offset of the second implant; (3) lingual offset of the second implant; (4) a wide implant (∅ 5 mm) placement at most posterior site. The offset placement did not always decrease tensile force at the gold screw, but wide implant placement and decrease in cuspal inclination did.
Kinematic and kinetic observations on ballistic depression and elevation of the human mandible
Authors: Christensen L. V. , McKay D. C.
Published: March 2003

To study mandibular motions with respect to time (kinematics) and the forces causing and resulting from these motions (kinetics), four subjects generated rapid depression and elevation of the mandible (displacement of 0·224 m; peak velocity of 0·237 m s−1 during depression and 0·269 m s−1 during elevation). The motion of depression (duration of 0·195 s; kinetic energy of 2·072×10−3 J) could be divided into a phase of acceleration (2·742 m s−2; +0·28 gn) and a phase of deceleration (2·264 m s−2; −0·23 gn), and the terminal excess kinetic energy of depression was absorbed and dissipated by, primarily, the temporomandibular joint. Similarly, the ensuing motion of elevation (duration of 0·182 s; kinetic energy of 2·948×10−3 J) could be divided into a phase of acceleration (3·498 m s−2; +0·36 gn) and a phase of deceleration (2·931 m s−2; −0·30 gn), and the terminal excess kinetic energy of elevation was absorbed and dissipated by, primarily, the dentitions and, secondarily, by the temporomandibular joint. Rapid depression of the mandible appeared to be under the central control of a preprogrammed motor command, and ensuing rapid elevation of the mandible appeared to be under the peripheral control of a segmental and/or transcortical reflex. During rapid depression and elevation of the mandible, the anterior suprahyoid, anterior temporalis, and sternocleidomastoid muscles were myoelectrically active 56%, 73%, and 71% of the time, respectively, and myomechanically active 42%, 59%, and 57% of the time, respectively. Over a follow‐up period of 12 months, the studied mandibular motions did not cause injury to the dentitions and temporomandibular joint.
In vivomeasurement of colour changes in natural teeth
Authors: Russell M. D. , Gulfraz M. , Moss B. W.
Published: March 2003

It has been observed that teeth become lighter when they are dried. The present study was designed to quantify these changes and the time taken for tooth colour to return to normal. The colour of an upper central incisor in each of seven subjects was measured using a reflectance spectrophotometer before and after application of a rubber dam and, in another seven subjects before and after taking a polyvinylsiloxane impression. There were statistically significant changes in theL*,a* andb* values following rubber dam application and in theL* value following impression taking. The results demonstrate that teeth become brighter and less colour saturated after rubber dam application and brighter after impression taking. The original values were regained after 30 min.
Candida albicans growth on thermal cycled materials for maxillofacial prostheses in vitro
Authors: Nikawa H. , Jin C. , Hamada T. , Makihira S. , Polyzois G.
Published: March 2003

In the present study, the growth of a single isolate of Candida albicans on saliva‐, serum‐coated or protein free (uncoated), thermocycled (4–70 °C for 1 min, respectively; 0, 1000 and 10 000 times) 15 commercial maxillofacial materials was investigated, by monitoring pH changes in growth media. The inhibitory effect of the tissue conditioners on fungal growth was analysed using three parameters viz: (i) delay in the onset of the rapid decline in pH (ii) reduction in the rate of pH change and (iii) the pH minima reached. In the case of control materials (non‐thermocycled and uncoated), significant antifungal effect was observed with two products. However, the antifungal effect of the materials was significantly reduced both by thermal cycling (Analysis of covariance [ANOVA]; P < 0·01) and a layer of protein coating (saliva, P < 0·05; serum, P < 0·01). When the interrelation between three parameters of fungal growth and the surface hydrophobicity of the materials were analysed, minimum pH of fungal growth on 10 000‐thermocycled materials correlated well with the contact angles of the materials (Student t‐test, P < 0·01), suggesting that thermocycling process reduced the unpolymerized components of the materials which showed the antifungal effects, resulted in that the cell growth depends on the surface hydrophobicity of the specimens. These results, taken together, suggest that the ageing of the materials and the biological fluids of the host enhanced the fungal growth on maxillofacial materials.
The efficiency of dentine adhesives in treating non‐caries cervical lesions
Authors: Pandurić V. , Knežević A. , Tarle Z. , Šutalo J.
Published: March 2003

The aim of this study was to prove the hypothesis that dentine adhesives can be used as therapeutic material in treating dentine hypersensitivity, regardless of aetiology. The research was conducted on 492 students of Zagreb University School of Dental Medicine (154 male, 338 female), 20–25‐years‐old. The defects of the tooth neck were found in 38 patients, on 133 teeth (38 of male patients, 95 of female) and dentine hypersensitivity was recorded according to the subjective sensations of patients. Therapeutic characteristics of three adhesive materials were examined simultaneously: All Bond 2, fourth generation adhesive, Syntac Single Component and One Step, fifth generation adhesives. Teeth treated with dentine lacquer Cervitec were used as a control group. Tooth necks were treated with selected materials according to instructions of a manufacturer. A completed statistical survey of the results has clearly shown that dentine adhesives can be used in symptomatic therapy of dentine hypersensitivity of the non‐caries cervical lesions (NCCL). The survey has also shown that dentine adhesives of the fifth generation (Syntac Single Component and One Step) have much higher efficiency rate than dentine adhesives of the fourth generation (All Bond 2) and dentine lacquer (Cervitec). According to data complied through this study the conclusion can be brought forward that dentine adhesives are not a final solution to the problem of dentine hypersensitivity, because their efficiency decreases with time.
Effect of length and diameter of tapered posts on the retention
Authors: Nergi̇z İ. , Schmage P. , Özcan M. , Platzer U.
Published: March 2003

The force transmission of tapered unthreaded posts along the root has been reported to be homogenous but their retentive strength was found to be lower compared with those of parallel unthreaded or other kinds of threaded posts. The purpose of this in vitro study was to investigate the effect of length and diameter on the retentive strength of sandblasted tapered prefabricated titanium posts (Erlangen post system®). Posts with constant taper angle but with three different lengths (9, 12, 15 mm) and apical diameters (0·5, 0·9, 1·1 mm) were cemented using zinc phosphate cement into the prepared and roughened post spaces of 90 intact anterior teeth. The post retention concerning length and diameter, being independent from each other, was measured by a tensile force test. The retentive strength was found to be proportional to the length as well as to the diameter of the posts. The mean minimum strength (181 ± 14 N) recorded for the thinnest and shortest post was significantly lower than that of mean maximum strength (612 ± 85 N) obtained from those of the thickest and longest post. Proportional bond strengths of the posts comprising their surface areas ranged between 6·8 and 7·9 N mm–2 which were not significantly different between any group. The retention was effected strongly with the increase in the length (approximately 100%) than with the increase in the diameter (approximately 60%). Concerning the posts tested in this study, it is concluded that some caution should be exercised in the choice of post with appropriate length rather than diameter for the tooth concerned.
Mechanical properties of resin cements with different activation modes
Authors: Braga R. R. , Cesar P. F. , Gonzaga C. C.
Published: March 2003

Dual‐cured cements have been studied in terms of the hardness or degree of conversion achieved with different curing modes. However, little emphasis is given to the influence of the curing method on other mechanical properties. This study investigated the flexural strength, flexural modulus and hardness of four proprietary resin cements. Materials tested were: Enforce and Variolink II (light‐, self‐ and dual‐cured), RelyX ARC (self‐ and dual‐cured) and C & B (self‐cured). Specimens were fractured using a three‐point bending test. Pre‐failure loads corresponding to specific displacements of the cross‐head were used for flexural modulus calculation. Knoop hardness (KHN) was measured on fragments obtained after the flexural test. Tests were performed after 24 h storage at 37 °C. RelyX ARC dual‐cured showed higher flexural strength than the other groups. RelyX ARC and Variolink II depended upon photo‐activation to achieve higher hardness values. Enforce showed similar hardness for dual‐ and self‐curing modes. No correlation was found between flexural strength and hardness, indicating that other factors besides the degree of cure (e.g. filler content and monomer type) affect the flexural strength of composites. No statistical difference was detected in the flexural modulus among the different groups.
Forces resisting jaw displacement in relaxed humans: a predominantly viscous phenomenon
Authors: Peck C. C. , Sooch A. S. , Hannam A. G.
Published: March 2003

Forces opening the relaxed human jaw are resisted by intrinsic restraints, including passive tensions in the jaw‐closing muscles. These muscle tensions have been modelled as viscoelastic elements, and static measurements suggest their elastic portions contribute approximately a total of 5 N resistance at wide gape. As the viscous damping properties of muscles which affect the jaw’s dynamic behaviour are unknown, we measured the jaw opening force required to reach maximum gape during fast and slow opening in six relaxed subjects. These data were then incorporated in a dynamic mathematical jaw model to determine the damping properties of the masticatory system. During the 3 and 8 s opening trials, forces increased with gape (6·7 ± 3·3 and 3·9 ± 2·3 N, respectively, at 50% gape) and reached their maxima at wide gape (19·9 ± 4·5 and 13·2 ± 4·4 N, respectively). The muscle damping constant needed by the model to emulate these results was 150 Nsm–1, approximately 25% lower than the calculated critical damping constant. This study suggests low forces are required to open the jaw in relaxed humans, and that jaw viscosity, not elasticity, provides the major resistance to motion.
Changes in occlusal force and occlusal contact area after active orthodontic treatment: a pilot study using pressure‐sensitive sheets
Authors: Sultana M. H. , Yamada K. , Hanada K.
Published: March 2003

The aim of this study was to investigate functional changes in occlusion during retention. Data on occlusal force (OcFr) and occlusal contact area (OcAr) was obtained using the pressure‐sensitive sheet, from a treated group (20 female patients) who had had four premolar extractions and treatment with standard edgewise appliances, and a control sample who matched the treated group of retainer for sex, age and Angle classification at 1 year after removal. A repeated measures analysis of variance showed that the mean values of total OcFr and OcAr in the treatment group gradually increased during retention and were 669·3 N and 15·1 mm2, respectively, at 1 year after removal of retainer. The increases of OcFr and OcAr were larger in the molar region, especially at the second molar. At 1 year after removal of retainer, OcFr and OcAr in the second molar were significantly larger in the treatment group than in the control sample, and a similar distribution pattern of OcFr and OcAr to those in normal occlusion was seen. These results suggested that balanced OcFr and OcAr might be obtained during and after retention, due to the settling of molars that had been discluded by active orthodontic treatment.
Inhibition of artificial secondary caries by fluoride‐releasing adhesives on root dentin
Authors: Itota T. , Nakabo S. , Iwai Y. , Konishi N. , Nagamine M. , Torii Y.
Published: March 2003

Fluoride‐releasing materials can be expected to inhibit the secondary caries. The aim ;of this study was to evaluate the effect of fluoride‐releasing adhesives on inhibition of secondary caries in outer and wall lesions. Two commercial fluoride‐releasing adhesives, Reactmer bond (RB) and One‐up bond F (OB), and a commercial adhesive without fluoride release, Mac‐bond II (MB), were used prior to placement of restorative materials without fluoride release, Lite‐fil II A (LF) and Estelite (EL), and a fluoride‐releasing restorative material, Reactmer paste (RP). Class V cavities prepared on extracted human premolars were restored with various combinations of the materials: MB/EL, OB/EL, RB/LF and RB/RP. The restored teeth were incubated in bacterial medium containing sucrose with Streptoccus mutans for 14 days. Microradiographs of specimens showed no wall lesions in all groups and an acid‐resistant layer adjacent to the restoration in the caries‐like lesion. OB/EL, RB/LF and RB/RP groups showed thicker layers than the MB/EL group. The RB/RP group formed the shallowest outer lesion among all groups. These results indicate that fluoride‐releasing adhesives are effective in the prevention of wall lesions but exhibit little outer lesion inhibition. Therefore, combined restoration using a fluoride‐releasing adhesive and fluoride‐releasing restorative material should be selected to inhibit secondary caries.
Variation in masticatory muscle activity during subsequent, submaximal clenching efforts
Authors: Lobbezoo F. , Huddleston Slater J. J. R.
Published: March 2003

In previous studies to the relative contribution of the jaw closing muscles to the maintenance of submaximal clenching levels, a considerable variation in the electromyography (EMG) activities of these muscles during subsequent efforts was found. In this study, it was examined to what extent this variation could be explained by coincidental variations in mandibular positioning. From seven healthy individuals, a total of 90 EMG sweeps was recorded: three conditions (intercuspal position and two types of stabilization appliances) × three clenching levels (10, 30 and 50% of maximum voluntary contraction level) × 10 repetitions. Mandibular position was monitored with a six degrees of freedom opto‐electronic jaw movement recording system. Variations in mandibular positioning during subsequent, submaximal clenching efforts explained up to 25% of the variance in the indices that quantify the relative contribution of the jaw closing muscles to the total clenching effort (P=0·000; ANOVA). Only a weak dependency of positioning upon clenching condition was found whereas during higher clenching levels, the positioning effect tended to be smaller than during lower levels. In conclusion small, coincidental variations in mandibular positioning during subsequent clenching efforts partly explain the variance in EMG activity of jaw closing muscles, especially at lower clenching levels.
Heterogeneity of temporomandibular disorders: cluster and case–control analyses
Authors: Velly A. M. , Philippe P. , Gornitsky M.
Published: March 2003

summary Cluster analysis has been applied to the classification of temporomandibular disorders (TMD). The factors most often used in these classification systems are psychological and psychosocial. The aim of this study is to classify individuals diagnosed with TMD, by using cluster analysis based on their clinical condition and the global severity of the disease. In this study, one investigator selected the patients at the dental clinics located at the Jewish General and Montreal General hospitals, Montreal, Canada, from September 1994 to December 1997. The study population included 162 outpatients. The results of this study indicated the existence of four TMD subgroups: three TMD pain groups with localized or generalized disorder related to different levels of interferences in their life and a non‐pain, but disabled group. External validation of the cluster solution support the replication of the four groups and allow for further interpretation of the patients' profiles. Clenching‐grinding and depression were related to the groups presenting generalized TMD. Orthodontic treatment and female sex, however, were the factors associated with a more localized condition. This classification system may provide a better understanding of the TMD subgroups and clues for the treatment and prognosis of TMD patients.
Three‐year clinical evaluation of a resin modified glass–ionomer cement and a composite resin in non‐carious class V lesions
Authors: Özgünaltay G. , Önen A.
Published: March 2003

SUMMARY  The purpose of this study was a 3‐year clinical evaluation of a resin modified glass–ionomer and a composite resin restorative material in non‐carious class V lesions. In 24 patients 98 non‐carious class V lesions were restored with either a resin modified glass–ionomer (Vitremer), or a composite resin restoration (Z100). The restorations were clinically evaluated after 6, 12, 24 and 36 months with the US Public Health Service criteria. At 3 years, 88 teeth of 21 patients were evaluated. All restorations were rated clinically acceptable for colour match, marginal discoloration, marginal adaptation and anatomical form. Restoration retention of both groups was high without any statistically significant difference. However, Vitremer restorations showed a lower incidence of Alfa scores for colour match and marginal discoloration than Z100 restorations (P < 0·05).
Postnatal development of protein gene product 9·5 and calcitonin gene‐related peptide immunoreactive nerve fibres in rat temporomandibular joint disc
Authors: Ueki N. , Tanaka E. , Watanabe M. , Wakida K. , Takahashi O. , Uchida T. , Tanne K.
Published: March 2003

summary  Protein gene product 9·5 (PGP 9·5), an immunohistochemical marker of whole nerve fibres, and calcitonin gene‐related peptide (CGRP), a marker of thin nerve fibres, were used to elucidate the postnatal development of nerve fibres in rat temporomandibular joint (TMJ) disc. At birth, PGP 9·5‐immunoreactive nerve fibres exhibited running towards the central area of the disc, invading by approximately 95 m from the disc attachment. The nerve fibres existing inside the disc became longer during postnatal development. The number of nerve fibres in the disc increased in a progressive manner up to 40 days after birth. CGRP‐immunoreactive nerve fibres also presented changes essentially similar to those of PGP 9·5‐immunoreactive nerve fibres. However, the proportion of CGRP‐immunoreactive nerve fibres to PGP 9·5‐immunoreactive ones was approximately 80%, and remained constant up to 40 days after birth. In conclusion, the distribution and the number of nerve fibres are variable during postnatal development, although the ratio of thin nerve fibres remains invariable. It is emphasized that these changes of innervation in the TMJ are associated with the development of masticatory function.