The aim of this study was to investigate average working lengths of Korean posterior teeth and evaluate validity of endodontic file length.

The endodontic working length of the posterior teeth of 670 Korean patients were measured than each mean value and standard deviation were investigated than the frequency deviation and standard deviation per each length were calculated.

Among the canals of premolar, 66.5% of canal length was marked under 20 mm by endodontic working length and 95.4% could be measured under 22 mm and Among the canals of molars, 95.5% of canal length was marked under 20 mm endodontic working length.

With the result of measurement of endodontic working length of premolars of Korean, it suggested that 23 mm endodontic file is more proper than the 21 mm and 25 mm file on the market.

This study aimed to assess prospectively the clinical outcome of nonsurgical endodontic treatment and identify patient- and tooth-related factors, rather than treatment-related factors, that were the best predictors of this outcome.

The inception cohort comprised 441 teeth (320 patients) and 175 teeth (123 patients) were followed up for 1-2 years. Age, gender, presence of medical disease, number of canals, previous endodontic treatment, presence of sensitivity and pain, pulp vitality, swelling or sinus tract of pulpal origin on the gingiva, periapical radiolucency and tendency of unilateral bite on the affected tooth were recorded at treatment start.

The outcome was classified on the basis of periapical radiolucency as healed or non healed. The overall healed rate in these cases, including nonsurgical retreatment, was 81.1%. Four tooth-related factors had a negative impact in the bivariate analysis: previous endodontic treatment, necrotic pulp, preoperative gingival swelling or sinus tract of pulpal origin, and preoperative periapical radiolucency. Stepwise logistic regression analysis including patient-, tooth-related factors and level of the root canal filling as a treatment-related factor showed that preoperative gingival lesion (odds ratio [OR]: 4.4; p = 0.005), preoperative periapical radiolucency (OR: 3.6; p = 0.011), and ≤ 1-2 mm under root filling length (OR: 9.6; p = 0.012) were significant predictors of failure.

A preoperative gingival lesion of pulpal origin can influence the outcome of nonsurgical endodontic treatment in addition to preoperative periapical radiolucency.

The aim of this study was to compare apical sealing ability and physical properties of MTA, MTA - AH-plus mixture (AMTA) and experimental Portland cement - Epoxy resin mixture (EPPC) for a development of a novel retro-filling material.

Forty-nine extracted roots were instrumented and filled with gutta-percha. Apical root was resected at 3 mm and the retro-filling cavity was prepared for 3 mm depth. Roots were randomly divided into 3 groups of 15 roots each. The retro-filling was done using MTA, AMTA, and EPPC as the groups divided. Four roots were used as control groups. After setting in humid condition for 24 hours, the roots were immersed in 1% methylene blue dye solution for 72 hours to test the apical leakage. After immersion, the roots were vertically sectioned and photos were taken to evaluate microleakage. Setting times were measured with Vicat apparatus and digital radiographs were taken to evaluate aluminum equivalent thickness using aluminum step wedge. The results of microleakage and setting time were compared between groups using one-way ANOVA and Scheffe's post-hoc comparison at the significance level of 95%.

AMTA and EPPC showed less microleakage than MTA group (p < 0.05). AMTA showed the highest radio-opacity than other groups and the novel EPPC showed 5 mm aluminum thickness radio-opacity. EPPC showed the shortest initial and final setting times than other groups while the MTA showed the longest (p < 0.05).

Under the condition of this study, the novel composite using Portland cement-Epoxy resin mixture may useful for retro-filling with the properties of favorable leakage resistance, radio-opacity and short setting time.

To evaluate the accuracy and consistency of two different apex locators at both the Apex and 0.5 marks.

Twenty-six root canals was scheduled for extraction for periodontal or prosthodontic reasons. Thirteen canals were measured using Root ZX and the rest by i-ROOT. The root canal length was measured both the at 0.5 mark and the Apex mark. The file was then fixed to the tooth, and the distance from the file tip to the major foramen of each canal was measured after removing the root dentin under the microscope so that the major foramen and the file tip were seen.

When the Apex mark was used, 100% of both the Root ZX and i-ROOT groups were within 0.5 mm of the major foramen.

In this study, the Apex mark was the more consistent mark. Therefore, it is recommended to subtract 0.5 mm, which is the average length between the apex and apical constriction, from the root canal length at the Apex mark to obtain the working length clinically.

This study evaluated microtensile bond strength (µTBS) and short-rod fracture toughness to explain fractural behavior of repaired composite restorations according to different surface treatments.

Thirty composite blocks for µTBS test and sixty short-rod specimens for fracture toughness test were fabricated and were allocated to 3 groups according to the combination of surface treatment (none-treated, sand blasting, bur roughening). Each group was repaired immediately and 2 weeks later. Twenty-four hours later from repair, µTBS and fracture toughness test were conducted. Mean values analyzed with two-way ANOVA / Tukey's B test (α = 0.05) and correlation analysis was done between µTBS and fracture toughness. FE-SEM was employed on fractured surface to examine the crack propagation.

The fresh composite resin showed higher µTBS than the aged composite resin (p < 0.001). Mechanically treated groups showed higher bond strength than non-mechanically treated groups except none-treated fresh group in µTBS (p < 0.05). The fracture toughness value of mechanically treated surface was higher than that of non-mechanically treated surface (p < 0.05). There was no correlation between fracture toughness and microtensile bond strength values. Specimens having high K_IC showed toughening mechanism including crack deviation, microcracks and crack bridging in FE-SEM.

Surface treatment by mechanical interlock is more important for effective composite repair, and the fracture toughness test could be used as an appropriate tool to examine the fractural behavior of the repaired composite with microtensile bond strength.

This study was performed to investigate the biocompatibility of newly introduced Bioaggregate on human pulp and PDL cells.

Cells were collected from human pulp and PDL tissue of extracted premolars. Cell culture plate was coated either with Bioaggregate or white MTA, then the same number of cells were poured to cell culture dishes. Cell attachment and growth was examined under a phase microscope after 1,3 and 7 days of seeding. Cell viability was measured and the data was analyzed using Student t-test and one way ANOVA.

Both types of cells used in this study were well attached and grew healthy on Bioaggregate and MTA coated culture dishes. No cell inhibition zone was observed in Bioaggregate group. There was no statistical difference of viable cells between bioaggreagte and MTA groups.

Bioaggregate appeared to be biocompatible compared with white MTA on human pulp and PDL cells.

The aim of this study was to compare the push-out bond strengths of resin cement/fiber post systems to post space dentin using different application methods of resin cement.

Thirty extracted human premolars were selected and randomly divided into 3 groups according to the technique used to place the cement into root canal: using lentulo-spiral instrument (group Lentulo), applying the cement onto the post surface (group Direct), and injecting the material using a specific elongation tip (group Elongation tip). After shaping and filling of the root canal, post space was drilled using Rely-X post drill. Rely-X fiber post was seated using Rely-X Unicem and resin cement was light polymerized. The root specimens were embedded in an acrylic resin and the specimens were sectioned perpendicularly to the long axis using a low-speed saw. Three slices per each root containing cross-sections of coronal, middle and apical part of the bonded fiber posts were obtained by sectioning. The push-out bond strength was measured using Universal Testing Machine. Specimens after bond failure were examined using operating microscope to evaluate the failure modes.

Push-out bond strengths were statistically influenced by the root regions. Group using the elongation tip showed significantly higher bond strength than other ways. Most failures occurred at the cement/dentin interface or in a mixed mode.

The use of an elongation tip seems to reduce the number of imperfections within the self-adhesive cement interface compared to the techniques such as direct applying with the post and lentulo-spiral technique.

This study examined the effect of 2% chlorhexidine on the µTBS of a direct composite restoration using one-step self-etch adhesives on human dentin.

Twenty-four extracted permanent molars were used. The teeth were assigned randomly to six groups (n = 10), according to the adhesive system and application of chlorhexidine. With or without the application of chlorhexidine, each adhesive system was applied to the dentin surface. After the bonding procedure, light-cure composite resin buildups were produced. The restored teeth were stored in distilled water at room temperature for 24 hours, and then cut and glued to the jig of the microtensile testing machine. A tensile load was applied until the specimen failed. The failure mode was examined using an operating microscope. The data was analyzed statistically using one-way ANOVA, Student's t-test (p < 0.05) and Scheffé's test.

Regardless of the application of chlorhexidine, the Clearfil S³ Bond showed the highest µTBS, followed by G-Bond and Xeno V. Adhesive failure was the main failure mode of the dentin bonding agents tested with some samples showing cohesive failure.

The application of 2% chlorhexidine did not affect the µTBS of the resin composite to the dentin using a one-step self-etch adhesive.