Hideaki Suda

New electronic canal measuring device based on the ratio method

The most striking disadvantage of most apex locators is that if there are electrolytes in the canal the meter shows a reading which is too short or sometimes the measurement itself becomes impossible. To overcome this drawback, a new concept for electrically measuring the root canal length has been developed. The device simultaneously measures two impedances of the canal using current sources with two different frequencies. Then the ratio between the two electric potentials proportional to each impedance is calculated. The quotient is shown on the devices meter and represents the position of a file tip in the canal. The present study found that the quotient was only negligibly influenced by the electrolyte present in the canal and decreased considerably as the file tip approached the apical foramen.

Radiographic evaluation of root canal multiplicity in mandibular first premolars

The purpose of this study was to examine the accuracy of radiographic evaluation of root canal multiplicity in mandibular first premolars in vitro. One hundred thirty-nine extracted human mandibular premolars were used. Buccolingual radiographs were taken, and the number of canals in each tooth was determined on radiographs by four dentists using a view box. A sudden narrowing of the main canal was interpreted as a sign of multiple canals. After the radiographic evaluation, the tooth crown was removed. India ink was injected into the root canal system, and the root was cleared to observe the canal morphology. There was no statistically significant difference among the four dentists with respect to the coincidence rate (93%-96%) of the canal number evaluated on radiographs with that identified by cleared teeth observation (p > 0.05, one-way analysis of variance). A sudden narrowing of the main canal on the radiograph was a good criterion to judge root canal multiplicity.

Osteogenic differentiation of the mesenchymal progenitor cells, Kusa is suppressed by Notch signaling.

Notch receptor plays a crucial role in proliferation and differentiation of many cell types. To elucidate the function of Notch signaling in osteogenesis, we transfected the constitutively active Notch1 (Notch intracellular domain, NICD) into two different osteoblastic mesenchymal cell lines, KusaA and KusaO, and examined the changes of their osteogenic potentials. In NICD stable transformants (KusaA(NICD) and KusaO(NICD)), osteogenic properties including alkaline phosphatase activity, expression of osteocalcin and type I collagen, and in vitro calcification were suppressed. Transient transfection of NICD attenuated the promoter activities of Cbfa1 and Ose2 element. KusaA was capable of forming trabecular bone-like tissues when injected into mouse abdomen, but this in vivo bone forming activity was significantly suppressed in KusaA(NICD). Osteoclasts were induced in the KusaA-derived bone-like tissues, but lacked in the KusaA(NICD)-derived tissues. These results suggest that Notch signaling suppresses the osteoblastic differentiation of mesenchymal progenitor cells.

Effect of NOS Inhibitor on Cytokine and COX2 Expression in Rat Pulpitis

Various kinds of chemical mediators are synthesized in the course of pulpitis; thus, control of their production would assist in inducing a reduction in pulpal inflammation. We hypothesized that nitric oxide (NO) would be an important mediator of pulpal inflammation. Pulpal inflammation was induced by the application of LPS in rat incisor pulp, and inducible nitric oxide synthase (iNOS) expression was evaluated by reverse-transcription/polymerase chain-reaction and immunohistochemical staining. After LPS application, iNOS mRNA was first detected after 3 hrs, peaked at 6 hrs, and decreased thereafter. iNOS-positive cells were macrophages and neutrophils. An NOS inhibitor caused drastic decreases in the expression of pro-inflammatory cytokines and COX2 mRNA, which was highly induced in the LPS-induced pulpitis. These results indicate that NO synthesis is related to the initiation of mediator production, and that its down-regulation should contribute to the prevention of pro-inflammatory mediator synthesis. Abbreviations: ANOVA, analysis of variance; COX2, cyclo-oxygenase 2; EDTA, ethylenediaminetetraacetic acid; iNOS, inducible nitric oxide synthase; IL, interleukin; L-NAME, NG-nitro L-arginine methyl ester; LPS, lipopolysaccharide; NO, nitric oxide; NOS, nitric oxide synthases; PG, prostaglandin; RT-PCR, reverse-transcription/polymerase chain-reaction; TNFα, tumor necrosis factor alpha.

Effect of calcium hydroxide on the dissolution of soft tissue on the root canal wall

Calcium hydroxide [Ca(OH)2] paste can aid in the cleaning of a root canal because of its soft tissue-dissolving potential. In this study, we examined with a scanning electron microscope the dissolution by Ca(OH)2 paste of pulpal tissue attached to uninstrumented bovine root canal walls. Extracted bovine anterior teeth were divided into small specimens at the middle portion of the roots. The experimental groups were treated with sodium hypochlorite (NaOCl), Ca(OH)2, or a combination of Ca(OH)2 + NaOCl. The control group was given no treatment. The root canal walls were observed with a scanning electron microscope, and the amount of remaining pulp tissue was compared. The amount of debris was reduced remarkably in the groups treated with NaOCl for > 30 s, or Ca(OH)2 for 7 days. The combination of Ca(OH)2 + NaOCl was more effective than the separate treatments. The results suggest that Ca(OH)2 as a root canal medicine serves as an effective agent in removing tissue debris remaining on the root canal walls.

An Observation of the Healing Process of Periapical Lesions by Digital Subtraction Radiography

The purpose of this study was to evaluate the efficacy of digital subtraction radiography using a direct digital imaging system in the follow-up study of endodontically treated teeth. The RVG-S was used as a direct digital imaging system. The intraimage variation of the original RVG-S image caused by dark current and sensitivity variations among pixels was corrected by pixel-to-pixel. The interimage variation was further corrected using a copper step-wedge attached to the sensor. Standardized images were obtained from the same geometrical setup during the follow-up. Pixel values at the regions of interest positioned on the periapical lesion increased after the endodontic treatment, and this change continued during the observation period up to 545 days. The subtraction method with direct digital radiography will be a useful tool to evaluate the healing process in endodontic treatments.

Electronic detection of root canal constrictions.

The aim of this study was to investigate the possibility of detecting root canal constrictions by using an apex locator. Seventy impenetrable canals in extracted human teeth were used. Based on contact microradiographic findings, they were divided into three groups: group A (constricted within 3 mm of the radiographic apex, 23 canals), group B (nonconstricted within 3 mm of the radiographic apex, 28 canals), and group C (constricted more than 3-mm short of the radiographic apex, 19 canals). Electrical impedances at two different frequencies (8 kHz and 0.4 kHz), as well as the meter values of the Root ZX were recorded at the position where a file tip could reach. The impedance ratios (Z8kHZ:Z0.4kHz) and the meter values of the Root ZX showed a statistically significant difference between groups A and B. It was suggested that the Root ZX might be useful for detecting root canal constrictions.

Molecular and cell biological properties of mouse osteogenic mesenchymal progenitor cells, Kusa

A cell line of murine osteogenic progenitor cells, Kusa, was established from femoral bone marrow stromal cells with other types of mesenchymal progenitor cells. We characterized two sublines of Kusa (Kusa-A1 and Kusa-O) from several aspects, including the use of an expression profiling system, a cDNA microarray. The original Kusa subline (Kusa-A1) had high alkaline phosphatase activity and high accumulation of calcium deposits in a condition inducing mineralization, with ascorbic acid and β-glycerophosphate. Kusa-O, a low osteogenic subline of Kusa, had high alkaline phosphatase activity but slow accumulation of calcium deposits even in the inducing condition. These two Kusa sublines differed in the expression of the osteogenic marker genes, osteocalcin and osteopontin, during mineralization. A type of cDNA microarray revealed marked downregulation of gene expression in the inducing condition in both Kusa-A1 and Kusa-O. Another type of high-throughput microarray was performed to examine the difference in gene expression patterns between Kusa-A1 and Kusa-O. By this analysis, periostin, which would be involved in a stage of osteogenesis, was low in Kusa-A1. On the contrary, Myocyte enhancer factor 2C (MEF2C), a myogenic transcriptional factor, was high in Kusa-A1, although no expression of any other myogenic genes was shown.

Reduced cytotoxicity of a root canal sealer through eugenol substitution

The cytotoxicity of two zinc oxide root canal sealers was investigated in vitro. The sealers were freshly mixed and set for 24 and 168 h. The sealers had identical powders but different liquid components. One (Canals) used eugenol, while the other (Canals-N) used fatty acids. L929 cells were incubated for 4 and 24 h in direct contact with the materials or with an eluate of the materials. The toxicity was evaluated using the radiochromium release assay. In the direct exposure assay, both sealers were cytotoxic when freshly prepared or after 24 h of setting. After 1 wk of setting, Canals was still toxic, while Canals-N was not significantly different from the control in the 4-h assay. In the elution assay the materials showed very low cytotoxicity. Only the eluate from freshly prepared Canals was clearly cytotoxic after 24 h. The liquid of Canals-N was clearly less cytotoxic than liquid from Canals. The results showed that the cytotoxicity of a root canal sealer can be reduced by replacing eugenol with fatty acids.

Subjective sensation and objective neural discharges recorded from clinically nonvital and intact teeth

The aim of this study was to compare subjective sensation with objective neural discharges recorded by microneurography. We examined human teeth that did not respond to pulp vitality testing, but that responded to cavity preparation for endodontic treatment (pathophysiological). Intact teeth and endodontically obturated teeth were used as controls. Pulpal blood flow in the clinical crown and histological examination were also used. Most teeth, both in normal and pathophysiological conditions, did not respond to all pulp vitality tests. Even when teeth in the pathophysiological group showed spike discharges evoked by pulp vitality tests or from spontaneous activity no sensation was elicited. These results confirmed the usefulness of microneurography for research on pulpal sensation and the significance of summation in the perception of sensation in chronically inflamed tooth pulp.