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S A Thompson

Publications and source records attributed to S A Thompson.

At least 55 records · Page 3Linked to original sources
PubMed1999

High level transcription of the complement regulatory protein CD59 requires an enhancer located in intron 1.

CD59 is a complement regulatory protein and may also act as a signal-transducing molecule. CD59 transgenic mice have been generated using a CD59 minigene (CD59 minigene-1). Although this minigene contained a 4.6-kilobase pair 5'-flanking region from the human CD59 gene as a promoter, the expression levels of the CD59 mRNA were substantially lower than those observed in humans, suggesting that CD59 gene expression might also require other transcriptional regulatory elements such as an enhancer. To investigate the transcriptional regulation of the CD59 gene, we used three cell lines that express CD59 at different levels. We have identified DNase I-hypersensitive sites in intron 1 in HeLa cells, which express CD59 at high levels, but not in Jurkat (intermediate level) or Raji cells (low level). Furthermore, cell line-specific enhancer activity was detected in a fragment containing these DNase I-hypersensitive sites. The CD59 enhancer was mapped to between -1155 and -888 upstream of the 5'-end of exon 2. To investigate the enhancer activity in vivo, a new CD59 minigene was constructed by the addition of the enhancer fragment into CD59 minigene-1. High expressor CD59 transgenic mice were generated using the new minigene.

Animals↗
PubMed1999

Vacuolating cytotoxin (vacA) alleles of Helicobacter pylori comprise two geographically widespread types, m1 and m2, and have evolved through limited recombination.

Vacuolating cytotoxin (vacA) alleles of Helicobacter pylori vary, particularly in their mid region (which may be type m1 or m2) and their signal peptide coding region (type s1 or s2). We investigated nucleotide diversity among vacA alleles in strains from several locales in Asia, South America, and the USA. Phylogenetic analysis of vacA mid region sequences from 18 strains validated the division into two main groups (m1 and m2) and showed further significant divisions within these groups. Informative site analysis demonstrated one example of recombination between m1 and m2 alleles, and several examples of recombination among alleles within these groups. Recombination was not sufficiently extensive to destroy phylogenetic structure entirely. Synonymous nucleotide substitution rates were markedly different between regions of vacA, suggesting different evolutionary divergence times and implying horizontal transfer of genetic elements within vacA. Non-synonymous/synonymous rate ratios were greater between m1 and m2 sequences than among m1 sequences, consistent with m1 and m2 alleles encoding functions fitting strains for slightly different ecological niches.

Alleles↗
PubMed1999

Glutathione redox potential in response to differentiation and enzyme inducers.

The reduced glutathione (GSH)/oxidized glutathione (GSSG) redox state is thought to function in signaling of detoxification gene expression, but also appears to be tightly regulated in cells under normal conditions. Thus it is not clear that the magnitude of change in response to physiologic stimuli is sufficient for a role in redox signaling under nontoxicologic conditions. The purpose of this study was to determine the change in 2GSH/GSSG redox during signaling of differentiation and increased detoxification enzyme activity in HT29 cells. We measured GSH, GSSG, cell volume, and cell pH, and we used the Nernst equation to determine the changes in redox potential Eh of the 2GSH/GSSG pool in response to the differentiating agent, sodium butyrate, and the detoxification enzyme inducer, benzyl isothiocyanate. Sodium butyrate caused a 60-mV oxidation (from -260 to -200 mV), an oxidation sufficient for a 100-fold change in protein dithiols:disulfide ratio. Benzyl isothiocyanate caused a 16-mV oxidation in control cells but a 40-mV oxidation (to -160 mV) in differentiated cells. Changes in GSH and mRNA for glutamate:cysteine ligase did not correlate with Eh; however, correlations were seen between Eh and glutathione S-transferase (GST) and nicotinamide adenine dinucleotide phosphate (NADPH):quinone reductase activities (N:QR). These results show that 2GSH/GSSG redox changes in response to physiologic stimuli such as differentiation and enzyme inducers are of a sufficient magnitude to control the activity of redox-sensitive proteins. This suggests that physiologic modulation of the 2GSH/GSSG redox poise could provide a fundamental parameter for the control of cell phenotype.

Adenocarcinoma↗
PubMed1999

Mutation at the putative GABA(A) ion-channel gate reveals changes in allosteric modulation.

We have mutated a conserved leucine in the putative membrane-spanning domain to serine in human GABA(A) beta2 and investigated the actions of a number of GABA(A) agonists, antagonists and modulators on human alpha1beta2deltaL259Sgamma2s compared to wild type alpha1beta2gamma2s GABA(A) receptors, expressed in Xenopus oocytes. The mutation resulted in smaller maximum currents to gamma-aminobutyric acid (GABA) compared to alpha1beta2gamma2s receptors, and large leak currents resulting from spontaneous channel opening. As reported, this mutation significantly decreased the GABA EC50 (110 fold), and reduced desensitization. Muscimol and the partial agonists 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) and piperidine-4-sulphonic acid (P4S) also displayed a decrease in EC50. In addition to competitively shifting GABA concentration response curves, the antagonists bicuculline and SR95531 both inhibited the spontaneous channel activity on alpha1beta2deltaL259Sgamma2s receptors, with different degrees of maximum inhibition. The effects of a range of allosteric modulators, including benzodiazepines and anaesthetics were examined on a submaximal GABA concentration (EC20). Compared to wild type, none of these modulators potentiated the EC20 response of alpha1beta2deltaL259Sgamma2s receptors, however they all directly activated the receptor in the absence of GABA. To conclude, the above mutation resulted in receptors which exhibit a degree of spontaneous activity, and are more sensitive to agonists. Benzodiazepines and other agents modulate constitutive activity, but positive modulation of GABA is lost. The competitive antagonists bicuculline and SR95531 can also act as allosteric channel modulators through the same GABA binding site.

Allosteric Regulation↗
PubMed1999

Recombination and clonal groupings within Helicobacter pylori from different geographical regions.

A collection of 20 strains of Helicobacter pylori from several regions of the world was studied to better understand the population genetic structure and diversity of this species. Sequences of fragments from seven housekeeping genes (atpA, efp, mutY, ppa, trpC, ureI, yphC ) and two virulence-associated genes (cagA, vacA) showed high levels of synonymous sequence variation (mean percentage Ks of 10-27%) and lower levels of non-synonymous variation (mean percentage Ka of 0.2-5.6%). Cluster analysis of pairwise differences between alleles revealed the existence of two weakly clonal groupings, which included half of the strains investigated. All six strains isolated from Japanese and coastal Chinese were assigned to the 'Asian' clonal grouping, probably reflecting descent from a distinct common ancestor. The clonal groupings were not totally uniform; recombination, as measured by the homoplasy test and compatibility matrices, was extremely common within all genes tested, except cagA. The fact that clonal descent could still be discerned despite such frequent recombination possibly reflects founder effects and geographical separation and/or selection for particular alleles of these genes.

Aldose-Ketose Isomerases↗
PubMed1999

Residues in transmembrane domains I and II determine gamma-aminobutyric acid type AA receptor subtype-selective antagonism by furosemide.

GABAA receptors in cerebellar granule cells are unique in expressing a subtype containing the alpha6 subunit. This receptor subtype has high affinity for GABA and produces a degree of tonic inhibition on cerebellar granule cells, modulating the firing of these cells via spillover of GABA from GABAergic synapses. This receptor subtype also has selective affinity for the diuretic furosemide over receptors containing other alpha-subunits. Furosemide exhibits approximately 100-fold selectivity for alpha6-containing receptors over alpha1-containing receptors. By making alpha1/alpha6 chimeras we have identified a transmembrane region (209-279) responsible for the high furosemide sensitivity of alpha6beta3gamma2s receptors. Within the alpha1 transmembrane region, a single amino acid was identified that when mutated from threonine to isoleucine, increased furosemide sensitivity by 20-fold. We demonstrate the beta-subunit selectivity of furosemide to be due to asparagine 265 in the beta2 and beta3 transmembrane-domain II similar to that observed with potentiation by the anticonvulsant loreclezole. We also show that Ile in transmembrane-domain I accounts for the increased GABA sensitivity observed at alpha6beta3gamma2s compared with alpha1beta3gamma2s receptors, but did not affect direct activation by pentobarbital or potentiation by the benzodiazepine flunitrazepam. Location of these residues within transmembrane domains leads to speculation that they may be involved in the channel-gating mechanism conferring increased receptor activation by GABA, in addition to conferring furosemide sensitivity.

Amino Acid Sequence↗
PubMed1999

Helicobacter pylori heat shock protein A: serologic responses and genetic diversity.

Helicobacter pylori synthesizes an unusual GroES homolog, heat shock protein A (HspA). The present study was aimed at an assessment of the serological response to HspA in a group of Chinese patients with defined gastroduodenal pathologies and determination of whether diversity is present in the nucleotide sequences encoding HspA in isolates from these patients. Serum samples collected from 154 patients who had an upper gastrointestinal pathology and the presence of H. pylori defined by biopsy were tested for an immunoglobulin G (IgG) serologic response to H. pylori HspA by an enzyme linked immunosorbant assay. HspA-encoding nucleotide sequences in H. pylori isolates from 14 patients (7 seropositive and 7 seronegative for HspA) were analyzed by PCR and direct sequencing of the PCR products. The sequencing results were compared to those of 48 isolates from other parts of the world. Of the 154 known H. pylori-positive patients, 54 (35.1%) were seropositive for HspA. The A domain (GroES homology) of HspA was highly conserved in the 14 isolates tested. Although the B domain (metal-binding site unique to H. pylori) resembled that in the known major variant, particular amino acid substitutions allowed definition of an HspA variant associated with isolates from East Asia. There were no associations between patient characteristics and HspA seropositivity or amino acid sequences. We confirmed in this study that the clinical outcomes of H. pylori infection are not related to HspA antigenicity or to sequence variation. However, B-domain sequence variation may be a marker for the study of the genetic diversity of H. pylori strains of different geographic origins.

Adult↗
PubMed1999

Effects of TGFbeta2 on collagen synthesis in cultured normal and wounded fetal mouse palates.

OBJECTIVE: It has been demonstrated in a number of models that fetal wounds heal with little or no scar. Since collagen is an integral part of the extracellular matrix in adult scar formation, we studied the synthesis and localization of collagen in an in vitro mouse palate model for fetal wound healing. METHODS: Palates, dissected from fetal mice at 15, 16, and 17 days of gestation and from newborn mice, were cultured in medium containing serum (for 8 hours); this was followed by culture in serum-free medium (for 12 hours). One-half of the samples from each age group were wounded in the midline. All samples were placed in serum-free medium containing 20 microCi/mL 3H-proline for 8 hours. In addition, palates from 15-day gestation and from newborn mice were also incubated with transforming growth factor TGF-beta2 (10 ng/mL). Palates were washed with saline, homogenized, and radioactivity was counted. Proline uptake was calculated for each sample as counts per milligram of protein and was subjected to statistical analysis (three-way analysis of variance). Samples of the homogenate were subjected to sodium dodecyl sulfate-gel electrophoresis and Western blotting in order to determine the types of collagen that were synthesized. Immunohistochemical localization of collagen types I, III, and VI was carried out on paraffin-embedded samples from each group. RESULTS: There were no significant differences in proline uptake between wounded mouse palates and nonwounded mouse palates at any age, and there was no histological evidence of regeneration of the palate at the site of the wound. Proline uptake was significantly greater in untreated wounded palates at 15 days' gestation than it was in newborns. After treatment with TGF-beta2, proline uptake was significantly greater in both wounded and nonwounded palates in the newborn group and had no effect on collagen synthesis in palates from 15-day gestation animals. Collagen types I and III were localized in histological specimens using immunohistochemistry and on nitrocellulose using Western blotting. No type VI collagen was demonstrated by Western blotting, but it was localized around blood vessels and on basement membranes using immunohistochemistry. CONCLUSION: Treatment with TGF-beta2 significantly increased collagen synthesis, as assessed by 3H-proline uptake, in cultured palates from newborn mice as compared with palates from untreated newborn mice and from both treated and untreated palates of 15-day gestation mice. These data suggest a differential response to TGF-beta2 by mouse palates as a function of fetal development.

Analysis of Variance↗
PubMed1998

Functional characteristics of recombinant human GABA(A) receptors containing the epsilon-subunit.

(1) This paper further examines the functional characteristics of recombinant human GABA(A) receptors containing the epsilon-subunit expressed in Xenopus oocytes. (2) Alpha1beta1epsilon receptors are not modulated by benzodiazepine ligands or by a number of hypothalamic hormones. (3) The intravenous anaesthetic agents pentobarbital, propofol and etomidate all potentiate sub-maximal GABA currents (EC20) to a similar degree in alpha1beta1epsilon and alpha1beta1gamma2s receptors. (4) Direct activation by pentobarbital produced a similar maximum response on alpha1beta1epsilon and alpha1beta1gamma2s, however, both the EC50 and slope were lower on alpha1beta1epsilon compared to alpha1beta1gamma2s. (5) These results describe a novel pharmacology for recombinant alpha1beta1epsilon receptors.

Anesthetics, Intravenous↗
PubMed1998

Homologue scanning mutagenesis of heregulin reveals receptor specific binding epitopes.

The EGF domain of heregulin has all the receptor binding characteristics of full-length heregulin and has strong homology to the ligands for erbB-1. Despite this, it does not bind erbB-1 but instead binds erbB-3 and erbB-4. The sequence similarity between HRG and the erbB-1 ligands suggest that a few residues are responsible for receptor binding specificity. To determine the sequences involved in receptor binding, we performed homologue scanning mutagenesis on the EGF domain of HRGalpha using sequences of TGFalpha or EGF. We found three sets of mutations in the N-terminal subdomain that were responsible for receptor binding specificity. Mutations in the C-terminal subdomain affected the binding affinity, but did appear to confer any specificity.

Adenocarcinoma↗
PubMed1998

A common requirement for the catalytic activity and both SH2 domains of SHP-2 in mitogen-activated protein (MAP) kinase activation by the ErbB family of receptors. A specific role for SHP-2 in map, but not c-Jun amino-terminal kinase activation.

The ErbB family of receptors, which include the epidermal growth factor receptor (EGFR), ErbB2, ErbB3, and ErbB4 mediate the actions of a family of bioactive polypeptides. EGF signals through EGFR, whereas heregulin (HRG) signaling is initiated through binding to either ErbB3 or ErbB4. In this report we studied the role of protein-tyrosine phosphatase SHP-2 in ErbB-mediated activation of mitogen-activated protein kinase (MAPK) by overexpressing SHP-2 mutants in COS-7 cells. We demonstrate that enzymatic activity and both NH2- and COOH-terminal SH2 domains of SHP-2 are required for EGF-induced MAPK activation, but not for c-Jun amino-terminal kinase stimulation or MAPK activation which occurred in response to myristoylated son of sevenless, activated Ras, or phorbol ester. Dominant-negative forms of SHP-2 had no effect on EGF-stimulated interaction of GRB2 with EGFR or SHC, nor did they influence phosphorylation of SHC and SHC/EGFR association. The same mutant SHP-2 structures that inhibited EGF-mediated stimulation of MAPK also blocked HRG alpha/beta-induced MAPK activation. EGF or HRG beta caused SHP-2 SH2 domains to engage multiple phosphotyrosine proteins, and mutation of either domain disrupted these associations. These results demonstrate that SHP-2 performs a common and essential function(s) in ligand-stimulated MAPK activation by the ErbB family of receptors.

Animals↗
PubMed1998

Molecular characterization of the Helicobacter pylori uvr B gene.

Helicobacter pylori persists in the human stomach where it may encounter a variety of DNA-damaging conditions, including gastric acidity. To determine whether the nucleotide excision repair (NER) pathway contributes to the repair of acid-induced DNA damage, we have cloned the putative H. pylori NER gene, uvrB. Degenerate oligonucleotide primers based on conserved amino acid residues of bacterial UvrB proteins were used in PCR with genomic DNA from H. pylori strain 84-183, and the 1.3-kb PCR product from this reaction was used as a probe to clone uvrB from an H. pylori genomic library. This plasmid clone had a 5.5-kb insert containing a 2.0-kb ORF whose predicted product (658 amino acids; 75.9 kDa) exhibited 69.5% similarity to E. coli UvrB. We constructed an isogenic H. pylori uvrB mutant by inserting a kanamycin-resistance cassette into uvrB and verified its proper placement by Southern hybridization. As with uvrB mutants of other bacteria, the H. pylori uvrB mutant showed a greatly increased sensitivity to the DNA-damaging agents methylmethane sulfonate and ultraviolet radiation. The uvrB mutant also was significantly more sensitive than the wild-type strain to killing by low pH, suggesting that the H. pylori nucleotide excision repair (NER) pathway is involved in the repair of acid-induced DNA damage.

Amino Acid Sequence↗
PubMed1998

Shaping ability of Mity Roto 360 degrees and Naviflex rotary nickel-titanium instruments in simulated root canals. Part 1.

The aim of this study was to determine the shaping ability of Mity Roto 360 degrees and Naviflex nickel-titanium rotary instruments in simulated root canals. In all, 80 canals consisting of four different shapes in terms of angle and position of curvature were prepared by Mity Roto 360 degrees and Naviflex instruments using the techniques recommended by the manufacturers. This study describes the efficacy of the instruments in terms of preparation time, instrument failure, canal blockages, change in canal length, and three-dimensional canal form. Overall, the mean preparation time for canals prepared using Mity instruments was 5.99 min and 5.81 min when using Naviflex instruments. Canal shape had no significant effect on the speed of preparation with either instrument. No instruments separated during the study; however, 14 Naviflex and 2 Mity instruments were deformed. Canal type did not influence significantly the tendency of either instrument to deform. None of the canals became blocked with debris during preparation. The majority of canals prepared by both instruments retained their original working length, and there was no significant difference between the canal shapes in terms of the mean loss of distance or category of distance change for either instrument. Apical stops as judged from intracanal impressions were present in 29 (72%) of the canals prepared with Mity instruments and in 33 (82%) of those prepared with Naviflex instruments. However, the majority were judged to be of poor quality. Significant differences (p < 0.05) were noted in the quality of apical stops between the canal types using Mity instruments. Canals prepared with Mity and Naviflex instruments were found to be smooth in the apical half of the canal in approximately one-half of the specimens and coronally in nearly all canals. Neither instrument produced horizontal or longitudinal grooves. Favorable flow characteristics were apparent in over one-half of the canals prepared with Mity Roto instruments; however, nearly all specimens had poor taper. Flow and taper were generally poor in the specimens prepared with Naviflex instruments. Under the conditions of this study, Mity Roto 360 degrees and Naviflex instruments prepared canals rapidly, with no separations, canal blockages, and with minimal change in working length. Although, flow was adequate using Mity Roto 360 degrees instruments, the taper characteristics were less than ideal compromising the three-dimensional form of the canals. Naviflex instruments, while creating better taper, produced poorer flow characteristics. The results suggest that when using Mity Roto 360 degrees or Naviflex instruments, the stepdown sequence should be modified to improve canal flow and taper. Alternatively, an instrument with increased taper should be used to complete preparation before obturation.

Dental Instruments↗
PubMed1998

Shaping ability of Mity Roto 360 degrees and Naviflex rotary nickel-titanium instruments in simulated root canals. Part 2.

The aim of this study was to determine the shaping ability of Mity Roto 360 degrees and Naviflex rotary nickel-titanium instruments in simulated canals. Forty simulated root canals made up of four different shapes in terms of angle and position of curvature were prepared by both sets of instruments using a stepdown approach. This study describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation, and thus the overall postoperative shape. Pre- and postoperative images of the canals were taken using a videocamera attached to a computer with image analysis software. The pre- and postoperative views were superimposed to highlight the amount and position of material removed during preparation. Neither Mity Roto 360 degrees nor Naviflex instruments created any zips or elbows. Ledges were produced in 20 (50%) canals prepared with Mity instruments and in 29 (72%) canals prepared with Naviflex instruments. Statistically significant differences (p < 0.001) between canal shapes occurred in relation to the incidence of ledges with 40 degrees canals (35) associated with more aberrations than 20 degrees canals (14); the position of the beginning of the curve had no effect. The distance of ledges from the end point of preparation was also affected significantly (p < 0.01) by canal shape. Neither instrument created any perforations or danger zones. At specific positions along the canal length, canal shape had a significant influence on total width and the amount of material removed from the inner and outer aspects of the canal curve. The direction of canal transportation at the end point of preparation was most frequently toward the outer aspect of the curve in canals prepared with Naviflex instruments, whereas the Mity instruments produced a more balanced preparation. At the apex and beginning of the curve, transportation with both instruments was generally toward the outer aspect of the curve. Overall, mean absolute transportation was small and was below 0.1 mm at every position except the orifice. Under the conditions of this study, Mity Roto 360 degrees and Naviflex rotary instruments prepared canals with a high incidence of ledges. However, in the absence of other aberrations, both instruments would seem to be a valuable addition to the endodontic armamentarium.

Dental Instruments↗
PubMed1998

Shaping ability of ProFile rotary nickel-titanium instruments with ISO sized tips in simulated root canals: Part 2.

The aim of this study was to determine the shaping ability of ProFile 0.04 taper rotary nickel-titanium instruments with ISO sized tips in simulated canals. A total of 40 simulated root canals made up of four different shapes in terms of angle and position of curvature were prepared by ProFile instruments using the 'crown down' approach recommended by the manufacturer. Part 2 of this two-part report describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation and the overall post-operative shape. Out of 37 completed specimens 9 zips (24%) and one ledge (3%) were created, but no perforations or danger zones were found. There were significant differences (P < 0.01) between canal shapes for the incidence of zips and elbows but not for their distance from the end-point of preparation. At specific positions along the canal length there were significant differences between the canal types in terms of their mean total width; overall, at the end-point of preparation and along the curved portion of the canals those specimens with 40 degrees curves were widest. This trend continued for the width of material removed from the outer aspect of the canal curves, whereas along the inner aspect of curves more material was removed in the 20 degrees canals. Overall, transportation was towards the outer aspect of the curve at the end-point of preparation and along the curved portion of canals but more balanced along the straight coronal section. Absolute transportation was small and below 0.1 mm at every position including the zips. Under the conditions of this study, ProFile nickel-titanium rotary instruments with ISO sized tips produced a larger number of zips than expected; however, the degree of zipping was limited and relatively minor.

Dental Instruments↗
PubMed1998

Shaping ability of Quantec Series 2000 rotary nickel-titanium instruments in simulated root canals: Part 1.

The aim of this study was to determine the shaping ability of Quantec Series 2000 nickel-titanium instruments in simulated canals. A total of 40 simulated root canals made up of four different shapes in terms of angle and position of curvature were prepared by Quantec instruments using the technique recommended by the manufacturer. Part 1 of this two-part report describes the efficacy of the instruments in terms of preparation time, instrument failure, canal blockages, change in canal length and three-dimensional canal form. The time necessary for canal preparation was on average 5.7 min and was significantly influenced (P < 0.01) by canal shape. One instrument fractured and three size nine instruments deformed; however, canal shape did not influence significantly instrument failure. All of the canals remained patent, none became blocked with debris. The majority of the canals maintained working distance (26 out of 40), however the mean change in length differed significantly (P < 0.05) between canal types. Overall, canals with 40 degrees curves lost length whilst those with 20 degrees curves gained in length. Examination of intracanal impressions revealed that preparation with Quantec Series 2000 instruments produced canals with definite apical stops, smooth canal walls and good flow and taper. However, the quality of apical smoothness and flow was influenced significantly (P < 0.0001) by canal shape with specimens having 40 degrees canals displaying less desirable qualities. Under the conditions of this study, Quantec Series 2000 rotary nickel-titanium instruments prepared simulated canals rapidly, safely and with good three-dimensional form.

Dental Instruments↗
PubMed1998

Shaping ability of Quantec Series 2000 rotary nickel-titanium instruments in simulated root canals: Part 2.

The aim of this laboratory based study was to determine the shaping ability of Quantec Series 2000 nickel-titanium rotary instruments in simulated root canals. A total of 40 canals with four different shapes in terms of angle and position of curve were prepared with Quantec Series 2000 instruments using the technique recommended by the manufacturer. Part 2 of this report describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation and overall post-operative shape. Pre- and post-operative images of the canals were taken using a video camera attached to a computer with image analysis software. The pre- and post-operative views were superimposed to highlight the amount and position of material removed during preparation. Twenty-one zips and elbows were created during preparation with a significant difference (P < 0.005) between canal shapes in terms of the incidence of aberrations. Four perforations were created, with significant differences (P < 0.005) between the canal shapes; three ledges were also created but no danger zones. Highly significant differences (P < 0.001) were apparent between the canal shapes in total canal width at specific points along the canal length and in the amount of resin removed from the inner and outer aspects of the curve. Canal transportation at the end-point of preparation was most frequently directed towards the outer aspect of the curve, and without exception in canals with 40 degrees curves. At the beginning of the curve, transportation became more evenly balanced between the inner and outer aspect of the curve, although predominated towards the outer. Transportation was generally directed towards the outer at the orifice, especially in canals with 40 degrees curves. Mean absolute transportation at the various measurement points was less than 0.11 mm; significant differences occurred between canal shapes at the end-point of preparation (P < 0.0001), at the zips (P < 0.005), at the apex (P < 0.0001) and beginning of the curve (P < 0.05) and at the orifice (P < 0.0001). Under the conditions of this study, Quantec Series 2000 rotary nickel-titanium instruments created a relatively large number of aberrations including four perforations. The aberrations were created by the larger instruments implying that these should be used with caution at the full working distance. Scanning electron micrographs of these instruments revealed sharp instrument tips which appeared likely to predispose to transportation and the creation of defects along the outer aspect of severely curved canals.

Dental Instruments↗