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The aim of this study was to histopathologically investigate the effects of pulsed Nd: YAG laser irradiation on the periradicular tissues when applied in the root canal of the dog.Six adult mongrel dogs were anesthetized and the tooth pulps of the upper and lower premolars were extirpated. Each root canal was cleaned and shaped to a final apical file size #55. Non-irradiated root canals were served as control.The laser irradiation (100mJl0pps, 100mJ20pps, 100mJ30pps, 200mJ10pps and 200mJ20pps) was performed under an up-and-down motion in the root canal between the apical and cervical portion with an optical fiber (∅=400μm) for 30 sec. After the irradiation, a small cotton pellet soaked with formalin cresol was placed in the pulp chamber and the access cavity was filled with glass ionomer cement. The animals were sacrificed at 7 and 28 days postoperatively.The results were as follows:1. At 7 days postoperatively, no histopathological difference was found between the control and 100mJ10pps group. On the other hand, carbonization and defects of the root canal wall were observed in all laser-treated groups except the 100mJ10pps group.2. At 28 days postoperatively, alveolar bone resorption was often observed again in all laser-treated groups except the 100mJ10pps group. Furthermore, in the 100mJ20pps group, dentoalveolar ankylosis was observed in the periradicular tissues, and severe external root resorption was frequently seen in the 200mJ20pps group. However, in the 100mJ10pps group, the degree of inflammation in the periradicular tissues was similar to the control.3. It was concluded that pulsed Nd: YAG laser with irradiation energy less than 100mJ10pps could be used safely in the root canal of the dog.(J. Jpn. Soc. Laser Dent. 7: 12-21, 1996 Reprint requests to Dr. SEKINE)

The purpose of this study was to investigate the effect of Nd: YAG laser irradiation on Streptococcus mutans.Roots of intact bovine incisors were used in this experiment. After cleaning and shaping of the root canal, they were acid-etched for 1 minute and ultrasonically irrigated. The root surface was coated with nail enamel and the samples were sterilized. Each root canal was filled with 50μl of culture medium where S. mutans was incubated at 37°C for 24 hours. One hundred roots were divided into 10 groups according to irradiation energy and addition of evans blue in the culture medium. Non-irradiated samples were used as control.The culture medium in the root canal was irradiated under up-and-down motion between the apical and cervical portion of the root canal with an optical fiber (∅=600, μm) for 30 seconds using Nd: YAG laser (100mJ or 200mJ and 10 or 30 pps). After the irradiation, bacterial samples of 10μl were taken from each root canal and incubated aerobically on Mitis Salivalius Agar at 37°C for 72 hours. The number of colonies on the medium was counted and colony-forming-units (CFUs) /ml were calculated.Thermal change caused by Nd: YAG laser irradiation in the root canal and culture medium was also monitored with a thermal camera. In addition, the irradiated dentin surface of the canal wall was observed with SEM.The results were as follows:1. In comparison with the control group, the CFUs in 100mJ 10pps, 200mJ 10pps, 100mJ 30pps and 200mJ 30pps irradiated groups without evans blue were reduced to 41%, 37%, 16% and 2%, respectively. Likewise, the CFUs in 100mJ 10pps, 200mJ 10pps, 100mJ 30pps and 200mJ 30pps irradiated groups with evans blue were reduced to 46%, 34%, 3% and 0%, respectively. The bactericidal effect in all experimental groups was statistically significant compared with the control group (t-test, P

The aim of this investigation was to quantitatively compare the amount of debris extruded apically from curved canals when using rotary nickel-titanium files with different pitches and sequences of use under the same preparation technique. Thirty-six extracted human maxillary and mandibular molars with curved root canals were used. They were divided into two groups of 18 teeth each prepared by one of two different sequences with NRT files (MANI Inc., Tochigi, Japan). Each group was further divided into three subgroups according to file pitch length (short, medium and long). The debris extruded apically was collected in glass vials. The liquid inside was dried and the debris in each group was weighed and compared. Two-way analysis of variance and Fisher's PLSD test were used to evaluate differences between the extruded debris weights among the experimental groups. No statistically significant difference was observed between two sequences. There were significant differences in sequence 1 between the short pitch group and the others. Also, there were significant differences between the long pitch and others in sequence 2, except between the short and medium pitches. In conclusion, short pitch design resulted in significantly less amount of debris extrusion compared with the other pitch lengths.

The ultimate goals of endodontic treatment are complete removal of bacteria, their byproducts and pulpal remnants from infected root canals and the complete seal of disinfected root canals. Intracanal medicaments have been thought an essential step in killing the bacteria in root canals; however, in modern endodontics, shaping and cleaning may be assuming greater importance than intracanal medicaments as a means of disinfecting root canals. Until recently, formocresol and its relatives were frequently used as intracanal medicaments, but it was pointed out that such bactericidal chemicals dressed in the canal distributed to the whole body from the root apex and so might induce various harmful effects including allergies. Furthermore, as these medicaments are potent carcinogenic agents, there is no indication for these chemicals in modern endodontic treatment. Today, biocompatibility and stability are essential properties for intracanal medicaments. The more modern meaning of intracanal dressing is for a blockade against coronal leakage from the gap between filling materials and cavity wall. Calcium hydroxide has been determined as suitable for use as an intracanal medicament as it is stable for long periods, harmless to the body, and bactericidal in a limited area. It also induces hard tissue formation and is effective for stopping inflammatory exudates. Single-visit endodontics, where intracanal medicaments are not used, is generally not now contraindicated and various reports have shown that the clinical outcomes between single- and multiple- visit endodontics are similar. There is no reason to counsel against single-visit endodontics: however, if multiple-visit endodontics is chosen, calcium hydroxide is recommended to be used as an intracanal medicament.

Background: The aim of this study was to examine the effects of root canal irrigants on the accuracy of Dentaport ZX™® electronic apex locator (EAL) in enlarged root canals. Our previous study revealed that as the diameter of the root canal increased, the electronically measured length with small size files became shorter in the presence of blood. It is not known whether different canal irrigants would interfere with the reading accuracy of an EAL in enlarged root canals. Methods: A total of 45 extracted single-rooted human teeth were used. In Stage 1, canals were instrumented using #10–40 K-files with a #40 K-file as the master apical file (MAF). The teeth were randomly divided into five groups and mounted in an experimental apparatus. The following irrigants were used during electronic canal measurements: Group A = 0.5% NaOCl; Group B = 2.5% NaOCl; Group C = 15% EDTA; Group D = 0.8% chlorhexidine (CHX); and Group E = RC Prep. In Stage 2, the canals were enlarged using a #60 K-file as the MAF. In Stages 1 and 2, the apical portion of the canals was instrumented using the step-back sequence (up to a #80 K-file). In Stage 3, the canals were enlarged again using a #80 K-file as the MAF. In each stage, the canal length was measured with a Dentaport ZX™® using #10 and #40, #10 and #60, and #10 and #80 K-files for Stages 1, 2 and 3, respectively. Data were analysed by two-way ANOVA and Fisher's PLSD test. Results: Statistical analysis showed significant differences among all groups (p < 0.01). There was no significant difference between Group A and B at each stage and between Group D and E at Stage 2. A statistical significant difference was observed between #10 K-file and other files (#40, #60 and #80) at each stage (p < 0.01). In Groups A and B, there was no significant difference between #10 and 40 K-files (Stage 1) and between #10 and #60 K- files (Stage 2). Conclusion: The Dentaport ZX™® was accurate and not adversely affected by the presence of 0.5% or 2.5% NaOCl and EDTA in the enlarged canals, and the measured lengths obtained with small and large size files were comparable. However, it was accurate in the presence of CHX and RC Prep only when large size files were used, and the length measured with small size files was greater than the actual length.

The aim of this in vitro study was to compare three nickel-titanium (Ni-Ti) rotary instruments: EndoWave, K3 and ProFile, with respect to their debris retention and wear. Thirty simulated root canal models made from resin blocks with 40 degrees canal curvature were used. They were divided into three groups of 10 samples each; EndoWave, K3 and ProFile were used in Groups A, B and C respectively. They were prepared with four serial size files. The weight of each file was measured to evaluate debris retention and wear at four representative time points: prior to root canal preparation (W1), immediately after root canal preparation (W2), after ultrasonic cleaning (W3), after further additional cleaning (W4). The weight of debris on each file after root canal instrumentation and ultrasonic cleaning was calculated as D1: (W2 - W4) and D2: (W3 - W4) respectively. Also, wear of the file was calculated as WF: (W1 - W4). There was a significant difference in the amount of debris remaining on the file among the three files; EndoWave retained more debris (D1) than K3 and ProFile (P < 0.001, one-way anova). ProFile had the largest amount of debris (D2) remaining after ultrasonic cleaning (P < 0.001). Wear was not detectable in this study. Under the conditions of this study, immediately after root canal preparation, EndoWave retained the largest amount of debris, while ProFile retained the most debris even after ultrasonic cleaning.

Background: The aim of this ex vivo study was to evaluate the accuracy of four electronic apex locators (EALs) to determine the working length in teeth with various foramen diameters. Our previous study revealed that electronically measured canal length was influenced by the root canal diameter. It is not known whether foramen size would interfere with the reading accuracy of an EAL. Methods: A total of 36 extracted human lower single rooted premolar teeth were divided into four groups of nine teeth each. In groups A, B and C, the root canals were instrumented using #10–80, #10–100 and #10–120 K-files, and the tip of size #80, #100 and #120 K-files were permitted to pass through the apical foramen to a length of 1mm, respectively. In group D, the teeth were instrumented using #10–140 K-files and the tip of #140 K-file was permitted to pass through the apical foramen to a length of 5mm. Thus, the average apical foramen diameters in groups A, B, C and D were approximately 0.82mm, 1.02mm, 1.22mm and 1.5mm, respectively. The teeth were then mounted in 1% agar and four EALs were used: Root ZX, Foramatron D10, Apex NRG and Apit 7. For electronic measurement, sizes #10 and #80, #10 and #100, #10 and #120, and #10 and #140 K-files were used for groups A, B, C and D, respectively. During electronic measurement the canals were flushed with 6% sodium hypochlorite solution. Results: Three-way ANOVA and Bonferroni test showed that EAL, file size and foramen size all had a significant influence on the measurement error (P

In 2002, the Dental Hospital of Tokyo Medical and Dental University set up a working group for risk management. This working group analyzed 225 incident and accident reports submitted to the hospital in 2001 and 2002. Each report was analyzed with regard to "type," "place," "reporter," "severity," and "cause" in order to diagnose hospital safety and prevent future incidents and accidents. The cause of incidents and accidents was analyzed using the SHEL model, where S stands for Software, H for Hardware, E for Environment, and L for Liveware. The severity of the consequence was classified into 6 levels, where level 0 = "error not applied," level 1 = "not affected," level 2 = "watch and see or additional test," level 3 = "treatment," level 4 = "aftereffect," and level 5 = "death." The incidents and accidents judged to have potentially high risk were given a score of "+H," irrespective of the level. The results of the analyses revealed that most of the incidents and accidents happened in "wards," "operation rooms," and "oral surgery clinics." This is probably because the incident and accident reporting system is well established by nurses working in these clinics. Additional analysis revealed that most of the reports were written and submitted by nurses. The frequencies of "treatment procedure," "misuse of dental instruments," "mis-prescription," "falling down" and "needlestick" related incidents and accidents were the highest and were caused mainly by L and S. There were only 3 accidents above level 4, however, less severe cases were given a score of +H due to the high potential risk involved.

Calcium hyroxide has been used for eliminating persistent intracanal exudation. In order to address the mechanism behind this action, we investigated whether calcium hydroxide solutions cause the constriction of microvessels in the mesenteric microcirculation bed of rats. The exteriorised mesentery from anaesthetised rats was spread in a chamber, and arterioles, venules and capillaries were viewed under a digital microscope. Various concentrations of calcium hydroxide solutions were applied for 10 sec, and the diameter of the microvessels was recorded. In arterioles, calcium hydroxide solutions caused rapid and transient constriction. A statistically significant difference versus original diameter was detected I min after the application of 4.0 times 10−3 mol/l and 1.0 times 10−2 mol/l solutions (p < 0.05, one-way analysis of variance and Tukey-Kramer test). No statistically significant constriction occurred in capillaries and venules. It was concluded that the arteriolar constriction might be an explanation for the exudation-controlling effect of intracanal calcium hyroxide dressings.

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 (NaOCI), Ca(OH) 2 , or a combination of Ca(OH) 2 + NaOCI. 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 NaOCI for > 30 s, or Ca(OH) 2 for 7 days. The combination of Ca(OH) 2 + NaOCI 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.