Biomedical subjects

M K Wu

Publications and source records attributed to M K Wu.

At least 19 recordsLinked to original sources

PubMed2007

The evaluation of removal of calcium hydroxide paste from an artificial standardized groove in the apical root canal using different irrigation methodologies.

AIM: To evaluate the capacity to remove a calcium hydroxide (Ca(OH)2) paste from the root canal and to evaluate the efficacy of Ca(OH)2 removal during passive ultrasonic irrigation using either sodium hypochlorite (NaOCl) or water as an irrigant. METHODOLOGY: Sixteen mandibular premolars were used. Each root was prepared to the apical foramen using GT instruments of size 30, 0.06 taper. Each root was split longitudinally. In one half of the root, a groove was cut in the canal wall 2-6 mm from the apex which was then filled with a Ca(OH)2 paste. Subsequently the roots were reassembled. In group 1 (n = 16), the teeth were ultrasonically irrigated using 50 mL 2.0% NaOCl as the irrigant. Group 2 (n = 16) was treated in the same manner as group 1, but using 50 mL water in place of the NaOCl. In group 3 (n = 16), the teeth were irrigated by syringe injection of 50 mL 2.0% NaOCl. The quantity of remaining Ca(OH)2 in the groove was scored and the data analysed with Kruskal-Wallis and Mann-Whitney tests. RESULTS: The difference in remaining Ca(OH)2 between all groups was statistically significant (P < 0.001). Group 1 had significantly lower scores than group 2 (P < 0.001) and group 3 (P = 0.002), but there was no significant difference between groups 2 and 3 (P = 0.765). CONCLUSIONS: Passive ultrasonic irrigation with 2% NaOCl was more effective in removing Ca(OH)2 paste from artificial root canal grooves than syringe delivery of 2% NaOCl or water as irrigant.

Calcium Hydroxide↗

PubMed2006

The influence of volume, type of irrigant and flushing method on removing artificially placed dentine debris from the apical root canal during passive ultrasonic irrigation.

AIM: To determine the influence of volume, irrigant and method of flushing on the removal of artificially-placed dentine debris from the apical part of root canals during passive ultrasonic irrigation. METHODOLOGY: Access cavities were prepared in 15 canine teeth and their root canals instrumented to size 20, 0.10 taper. Each root was split longitudinally, forming two halves. A groove was cut in the canal wall 2-6 mm from the apex in each half which was then filled with dentine debris prior to the roots being reassembled. All canals were ultrasonically irrigated, using a size 15, 0.02 taper smooth wire to a length of 21 mm that was placed in the canal to the apical foramen. In group 1 the canal was flushed with a continuous flow of 50 mL 2% sodium hypochlorite (NaOCl). In group 2 the continuous flow was not used but the canal was flushed with 12 mL 2% NaOCl, at a rate of 2 mL 30 s-1 using a syringe. Group 3 was treated in the same way as group 2 but the canal was flushed with 6 mL 2% NaOCl, at a rate of 2 mL min-1. Group 4 was treated in the same way as group 1 but water was used as the irrigant. Before and after irrigation, images of the grooves were captured and stored. The quantity of dentine debris in the groove was evaluated. The differences in debris scores between the experimental groups were analysed with the Kruskal-Wallis test and the Mann-Whitney U-test. The level of significance was set at P=0.05. RESULTS: The difference between all groups was statistically significant (K-W test P<0.001). Groups 1, 2 and 3 differed significantly from group 4 (P<0.001); there was no significant difference between groups 1, 2 and 3 (P=0.550). CONCLUSIONS: Syringe delivery of 2% NaOCl (6 and 12 mL) was as effective as a continuous flow of 2% NaOCl (50 mL). Water was not effective in removing dentine debris from grooves in the apical portion of root canals.

Cuspid↗

PubMed2005

[Local and potential systemic consequences of endodontic root infection].

In root infections, bacteria are present not only in planktonic cells but also in biofilms, which are more resistant to host defence mechanisms and disinfectans. Apical periodontitis, which may be radiographically undetectable, may develop or persist as a host defence mechanism to prevent the systemic spread of bacteria and their by-products to other sites of the body. The risk of spreading microorganisms and septic emboli is present especially in compromised hosts; furthermore, long-standing inflammation may have systemic effects and affect general health. Effective procedures should be developed to minimize the burden of root infection.

Bacterial Infections↗

PubMed2002

The effects of post-extraction time on the hydraulic conductance of human dentine in vitro.

The permeability characteristics of dentine have been used in many in vitro studies to evaluate longitudinally the efficacy of various restorative and preventative procedures. However, the permeability of human dentine increases over time after tooth extraction. The aim here was to determine if there is a steady phase in dentine permeability in vitro over time. The convective permeability of dentine discs cut from extracted human third molars to 0.8% albumin solution was measured initially on day 7 after extraction using a fluid-transport model and the hydraulic conductance was calculated. The permeability of each disc was then re-measured de- and re-mounting the split-chamber 1h after the initial measurement as well as on days 8, 9, and 37 after extraction. No significant difference was found between the initial and 1h hydraulic conductances. A significant increase in hydraulic conductance was seen from day 7 to 9, but there was no significant difference between the hydraulic conductances on days 9 and 37. These results suggest that the measurements were reproducible and that a steady phase of dentine permeability is established 9 days after extraction under these study conditions in vitro.

Albumins↗

PubMed2001

Multifactorial genetics of exencephaly in SELH/Bc mice.

BACKGROUND: The SELH/Bc mouse strain has 10-30% exencephaly and is an animal model for human neural tube closure defects. This study examined the number of causative genes, their dominance relationships, and linkage map positions. METHODS: The SELH/Bc strain (S) was crossed to the normal LM/Bc strain (L) and frequencies of exencephaly were observed in the F(1), BC(1), and F(2) generations. 102 F(2) males were individually testcrossed by SELH/Bc. The extremes, the 10 highest and 10 zero exencephaly-producing F(2) sires, were typed for 109 SSLP marker loci in a genome screen. Next, the resultant five provisional chromosomal regions were tested for linkage in 31 F(2) exencephalic embryos. Finally, 12 males, SS or LL for the Chr 13 region on an LM/Bc background, were testcrossed by SELH/Bc. RESULTS: The exencephaly frequencies in the F(1) (0.3%), BC(1) (4.4%), and F(2) (3.7%), and the distribution of F(2) males' testcross values (0-15.5%), indicated that the high risk of exencephaly in SELH/Bc is due to the cumulative effect of two or three loci. Linkage studies indicated the location of semidominant exencephaly-risk genes on Chr 13 near D13Mit13 (P < 0.001), Chr 5 near D5Mit168 (P < 0.025), and possibly Chr 11 near D11Mit10 (P < 0.07). The gene on Chr 13, Exen1, and the strong role of other loci were confirmed by the congenic males. CONCLUSIONS: The high risk of exencephaly in SELH/Bc mice is caused by the cumulative effect of two to three semidominant genes. Candidate genes include Msx2, Madh5, Ptch, and Irx1 (Chr 13) and Actb and Rac1 (Chr 5).

Animals↗

PubMed2001

The influence of resin composite and bonded amalgam restorations on dentine permeability in Class II cavities in vitro.

OBJECTIVES: This study was conducted to measure and compare dentine permeability reduction in Class II preparations, after restoration with resin composite or bonded amalgam, using either a multi-step or one-bottle dental adhesive system. METHODS: An in vitro fluid transport model was used to measure initial dentine permeability in Class II cavities with an intact smear layer in crown segments from extracted human premolars. One week and 3 months after restoration with resin composite or bonded amalgam, using either multi-step or one-bottle dental adhesive system, the measurements were repeated and the reduction in permeability was calculated as a percentage of the initial values. The data were analyzed statistically using a one-way ANOVA and Least Significant Difference tests. RESULTS: After 1 week the resin composite with one-bottle dental adhesive system provided the highest reduction in dentine permeability, whereas after 3 months the bonded amalgam caused the highest reduction. At both time intervals the resin composite with multi-step adhesive system provided the lowest reduction. (P=0.036 at 1 week, P=0.016 at 3 months). After 3-months storage in water a significant increase in dentine permeability reduction was found in the bonded amalgam group only (P=0.017). The reduction in dentine permeability provided by resin composite with one-bottle dental adhesive system and bonded amalgam in Class II cavities was similar at both time intervals. (P=0.182 at 1 week, P=0.750 at 3 months). SIGNIFICANCE: The results of this study indicated that on the basis of reducing dentine permeability in vitro, resin composite restorations with the investigated one-bottle adhesive system was superior to its multi-step equivalent and bonded amalgam can also be preferred in Class II restorations.

Adolescent↗

PubMed2001

A primary observation on the preparation and obturation of oval canals.

AIM: The aim of this study was to observe the existence and assess the quality of obturation of uninstrumented recesses in oval canals. METHODOLOGY: The balanced force technique was used in two groups of oval canals in human mandibular incisors. The canals in group 1 were enlarged to conventional sizes, whereas canals in group 2 were enlarged more widely. All canals were obturated with cold laterally condensed gutta-percha. Two horizontal sections were cut in the apical portion of each filled root. Images of the cross-sections were scanned and analysed using the KS100 Imaging system. RESULTS: Uninstrumented recesses appeared in 13 (65%) oval canals. The recesses in five of these 13 canals were obturated without visible voids. The recesses in the other eight canals were either obturated with visible voids or completely unfilled. The percentage of filled area was significantly higher in group 1 than in group 2 (P < 0.05). CONCLUSIONS: Uninstrumented recesses may be left in many oval canals after preparation using the balanced force technique and these recesses may often not be completely obturated with cold laterally condensed gutta-percha.

Bismuth↗

PubMed2001

The quality of root fillings remaining in mandibular incisors after root-end cavity preparation.

AIM: The aim of this study was to determine the quality of root fillings remaining in mandibular incisors after root-end resection and root-end cavity preparation. METHODOLOGY: Roots of 40 mandibular incisors,12 mm in length, were divided into two groups and instrumented using a balanced force technique and obturated by vertically compacted warm gutta-percha. In one group sealer was used when back-filling the root canal with the Obtura System. The other group was also back-filled with the Obtura System but without sealer. The apical 4 mm of each root filling was removed by root-end resection and root-end cavity preparation. Fluid transport along the 7 mm of remaining root filling was measured. After the leakage test, horizontal sections were cut at a level 3 mm from the apical end of the remaining root filling. The cross sectional area of the canal and gutta-percha was measured using an image analysis program. The quality of the remaining root fillings was also evaluated by calculating the percentage of gutta-percha filled canal area. RESULTS: In total, 27 (67%) out of the 40 roots demonstrated leakage. No significant difference was found between the two groups (P = 0.265). In the cross-sections the bucco-lingual canal diameter was up to 2.6 mm long (mean 1.6 mm). The average percentage of gutta-percha filled canal area was 85.6%. Warm gutta-percha could not obturate areas where debris remained after instrumentation. CONCLUSIONS: The quality of the root fillings in mandibular incisors was poor, probably because the unprepared recesses of oval canals were not clean.

Dental Leakage↗

PubMed2001

Quality of cold and warm gutta-percha fillings in oval canals in mandibular premolars.

AIM: The aim of this study was to determine the quality of cold and warm gutta-percha fillings in oval canals. METHODOLOGY: Two groups of mandibular premolars with oval canals were selected after bucco-lingual and mesio-distal radiographs indicated an internal long: short diameter of > or =1.6 at a level 5 mm from the apex. After instrumentation they were obturated, respectively, by cold lateral compaction of gutta-percha cones (cold GP) and vertical compaction of warm gutta-percha (warm GP). Leakage along apical root fillings was measured using a fluid transport model. After the leakage test, horizontal sections were cut 2 and 4 mm from the apex. The area of the canal and gutta-percha in cross-sections was measured using an image analysis program. The quality of root fillings was evaluated by calculating the percentage of gutta-percha-filled canal area (PGP). RESULTS: No significant difference in leakage was found between the two groups (P = 0.570). The warm GP group produced significantly higher PGPs than the cold GP group 4 mm from the apex only (P = 0.522 at 2 mm: P = 0.000 at 4 mm). CONCLUSIONS: The percentage of gutta-percha-filled canal area using warm GP was greater than that of the cold GP in oval canals.

Bicuspid↗

PubMed2001

An in vitro experiment on the effect of an attempt to create an apical matrix during root canal preparation on coronal leakage and material extrusion.

OBJECTIVE: A common approach to creating an apical matrix (apical stop) in the apical dentin is to enlarge the root canal to 3 sizes greater than that of the first file that binds at the working length. The aim of this study was to test the hypothesis that this procedure will reduce the amount of material extruded and the leakage along the apical root fillings. STUDY DESIGN: The canals of half of 120 maxillary and mandibular canines were prepared to the apical foramen through use of the serial shaping technique; the apical matrix creation procedure was not used. Each of the other 60 canals was prepared to 1 mm short of the apical foramen, and the canal was enlarged to at least 3 sizes greater than that of the first binding file to create an apical matrix. All the canals prepared with and all the canals prepared without the apical matrix creation procedure were obturated with laterally or vertically compacted cold or warm gutta-percha. In the leakage test, after post space preparation, the amount of fluid transport along the apical root fillings was measured. In the material extrusion test, the number of teeth with gutta-percha extrusion was recorded and the weight of the apically extruded materials was measured. RESULTS: In both the leakage and the extrusion tests, no significant difference was found between canals prepared with and canals prepared without the apical matrix creation procedure. CONCLUSION: The hypothesis that a procedure to enlarge root canals to 3 sizes greater than that of the first binding file will reduce the amount of filling materials extruded and the leakage was not proved, as our results show.

Chi-Square Distribution↗

PubMed2000

Apical terminus location of root canal treatment procedures.

The apical termination of root canal treatment is considered an important factor in treatment success. The exact impact of termination is somewhat uncertain; most publications on outcomes are based on retrospective findings. After vital pulpectomy, the best success rate has been reported when the procedures terminated 2 to 3 mm short of the radiographic apex. With pulpal necrosis, bacteria and their byproducts, as well as infected dentinal debris may remain in the most apical portion of the canal; these irritants may jeopardize apical healing. In these cases, better success was achieved when the procedures terminated at or within 2 mm of the radiographic apex (0 to 2 mm). When the therapeutic procedures were shorter than 2 mm from or past the radiographic apex, the success rate for infected canals was approximately 20% lower than that when the procedures terminated at 0 to 2 mm. Clinical determination of apical canal anatomy is difficult. An apical constriction is often absent. Based on biologic and clinical principles, instrumentation and obturation should not extend beyond the apical foramen.

Dental Pulp Cavity↗

PubMed2000

Leakage along warm gutta-percha fillings in the apical canals of curved roots.

The aim of this study was to investigate the leakage along the apical portion of warm gutta-percha obturated curved canals. Human mandibular premolars with single, curved (21 degrees-40 degrees) canals were prepared using the Lightspeed technique. Two groups of prepared canals, matched according to curvature and prevalence of apical transportation, were obturated by two techniques. Coronal gutta-percha was removed immediately after root obturation was completed to simulate the procedure for post space preparation. Leakage along the apical 3 mm of root filling was measured with a fluid transport device. Vertical condensation of warm gutta-percha and Pulp Canal Sealer provided less leakage than Thermafil plastic obturators and AH26 sealer (P = 0.002).

Bicuspid↗

PubMed2000

Diminished leakage along root canals filled with gutta-percha without sealer over time: a laboratory study.

AIM: The aim of this study was to investigate the long-term seal of gutta-percha (GP) without sealer. METHODOLOGY: Extracted human maxillary central incisors were prepared and obturated using heat- or chloroform-softened GP only, or GP in combination with a root canal sealer. Leakage along root fillings was measured at 48 h and after a period of 6 months using a fluid transport model. RESULTS: At 48 h the GP-filled roots without sealer leaked more than the control roots filled with GP and sealer (P < 0.0001). At 6 months a significant reduction in leakage was found in the GP-only groups (P < 0.05 for both heat- and chloroform-softened GP). After 6 months, roots filled by vertical condensation of GP-only had similar leakage as vertically condensed GP with a sealer (P > 0.05). CONCLUSIONS: The long-term seal of root fillings is affected by the volume change of both GP and sealer. Leakage reduction due to expansion of GP may compensate to a certain extent for leakage that may occur from sealer dissolution.

Balsams↗

PubMed2000

Sealer distribution in root canals obturated by three techniques.

AIM: The aim of this study was to observe sealer distribution in root canals filled by different root filling techniques. METHODOLOGY: AH26 (0.05 mL) dyed with carbon black powder was placed into the prepared root canals of maxillary central incisors using a lentulo spiral. Thereafter the canals were obturated using three different gutta-percha root-filling techniques. Horizontal sections were cut in the apical and middle portions of the filled canals. Images of the cross sections were scanned and the percentage of sealer coated canal perimeter (PSCP) was measured using a computer digital imaging system. RESULTS: At 3 mm from the apex, the PSCP after lateral condensation was similar to that after vertical condensation (P > 0.05). At 6 mm from the apex, however, the PSCP was significantly higher after lateral condensation than after vertical condensation (P < 0.05). At both levels the PSCP was significantly higher after single cone (no condensation) than after the other two condensation techniques (P < 0.0001). CONCLUSIONS: Sealer may be removed from the canal wall by the condensation procedures.

Bismuth↗

PubMed2000

Prevalence and extent of long oval canals in the apical third.

OBJECTIVE: The aim of this study was to investigate the canal diameters in the apical roots of human teeth to determine prevalence and extent of long oval canals. STUDY DESIGN: This investigation was carried out on 180 extracted human teeth, 20 for each tooth group. Each root was horizontally sectioned at 1, 2, 3, 4, and 5 mm from the apex. Canal diameters were measured with a measuring microscope. RESULTS: In 293 (25%) of the 1181 cross sections investigated, a long oval canal (the long canal diameter was at least 2 times the short canal diameter) was identified. In some tooth groups, the percentage of long oval canals exceeded 50%. In most cases, the long diameter decreased apically; that is, the canal tended toward a rounder cross section. A wide range of diameters existed in all canals. CONCLUSION: Long oval canal is common in the apical 5 mm in human teeth. Many long and narrow oval canals would be impossible to instrument completely without perforating or significantly weakening the roots. Care should be taken in cleaning, shaping, and obturating these oval canals.

Adult↗

PubMed2000

Leakage along apical root fillings in curved root canals. Part I: effects of apical transportation on seal of root fillings.

Occurrence of apical transportation (AT) may complicate the root filling procedure and result in a compromised seal. In part I of this study, human mandibular premolars with single, curved (21 to 39 degrees), or straight canals were prepared by Lightspeed or a step-back hand filing technique. An AT index was determined using a double exposure radiographic technique. The prepared canals were obturated using lateral condensation of gutta-percha. Leakage along the apical 3 mm of root filling was measured with a fluid transport model. After hand filing, AT and perforation occurred in 87% of the curved canals. The AT indices were > or = 0.4 mm. After Lightspeed preparation, AT occurred in only 19% of the curved canals. The hand filing/curved group leaked statistically significantly more than the hand filing/straight and Lightspeed/curved groups (p = 0.002). We conclude that occurrence of AT is a factor that negatively influences the apical seal when curved canals are obturated by lateral condensation of gutta-percha.

Bicuspid↗

PubMed1999

Cloning, tissue-specific expression, gene structure and chromosomal localization of human phosphatidylcholine transfer protein.

Phosphatidylcholine transfer protein (PC-TP) is a cytosolic protein that catalyzes intermembrane transfer of phosphatidylcholines in vitro. We have cloned a cDNA encoding the human ortholog of PC-TP and have determined its tissue-specific expression as well as genomic organization. Radiation hybrid mapping localized the human gene, PCTP, to chromosome 17q21-22 and PCR-based single strand conformation polymorphism analysis of an interspecific backcross assigned mouse Pctp to the region of syntenic conservation on chromosome 11.

Amino Acid Sequence↗

PubMed1999

Cloning and gene structure of rat phosphatidylcholine transfer protein, Pctp.

Phosphatidylcholine transfer protein (PC-TP) is a cytosolic lipid transfer protein that promotes intermembrane transfer of phosphatidylcholines but no other phospholipids. Although its physiological function remains unknown, phosphatidylcholine transfer protein is enriched in liver and evidence from model systems suggests a role in hepatocellular selection and transport of biliary phospholipids. To facilitate in vivo studies, a cDNA encoding rat PC-TP was cloned by library screening and 5'-rapid amplification of cDNA ends. Genomic cloning demonstrated the rat Pctp gene spans 10. 8kb and is comprised of six exons. The putative transcription initiation site was identified 50bp upstream of the translation initiation site. Nucleotide sequence analysis of the 5'-flanking region revealed a CAAT- but no TATA-box. Transient transfection of a series of 5'-deleted Pctp-promoter-firefly luciferase constructs into Reuber H35 rat hepatoma cells, which express Pctp mRNA, and Gunn rat fibroblasts, which do not, suggest that cis-acting elements in a 637bp promoter region contribute to enhanced expression of PC-TP in liver.

Amino Acid Sequence↗