The purpose of this study was to compare the shaping ability of three Ni-Ti file systems used by dental students or the experts and consequently to aid in choosing a proper systems for educational courses of dental students and beginners.

Fifty students and ten dentists who have clinical experience over two years prepared 180 simulated root canals in resin blocks with three Ni-Ti systems; ProFile® (PF), HeroShaper® (HS), K3^TM (K3).

After preparation, the Ni-Ti files were evaluated for distortion and canal preparation time was recorded. The images of pre- and post-instrumented canals were scanned and superimposed. Amounts of increased canal widths, deviation, and centering ratio were calculated at apical 1, 3 and 5 mm levels and statistical analysis was performed.

The results were as follows:

HS showed the shortest preparation time and instrumented canal width in K3 was significantly larger than other groups (P < 0.05).

Based on the results, it is surmised that the ProFile® is the safest and most ideal instrument for students and beginners.

The purpose of this study was to compare and evaluate the shaping abilities of various hybrid instrumentation method using constant tapered file systems with ProTaper® S1 and the difference between experts and inexperienced clinicians in use of NiTi file.

Three hybrid methods used in this study were composed of ProTaper® S1 and K-Flexofile® (group S), ProTaper® S1 and HeroShaper® (group H), and ProTaper® S1 and ProFile® (group P), respectively. The ProTaper®-alone method (group C) was introduced as a control group.

After canal preparation, the lapse of time was recorded. The images of pre- and post-operative canal were scanned and superimposed. Amounts of instrumented canal widths and centering ratio were measured at apical 1, 2 and 3 mm levels and statistical analysis was performed.

In this study, both of the group C and S took more time to prepare canals than other groups. Inexperienced operators required more time for the entire preparation with the groups C and H than the experienced (p < 0.05). And the centering ratio of group P were preferable to ProTaper®-alone method or the hybrid technique using stainless steel files. As such, within experienced operators, group H also showed better results in addition to the group P.

Under these condition, the hybrid methods of each the ProFile® system and HeroShaper® with ProTaper® are recommendable comparative to ProTaper®-alone method. According to the results, the hybrid instrumentation method is a more appropriate method of canal preparation than single file system for narrow or curved canals.

The purpose of this study was to analyze the stress distribution aspect of unrestored and restored combined shape (wedge shape occlusally and saucer shape gingivally) class V cavity, which found frequently in clinical cases.

A maxillary second premolar restored with a combined shape class V composite restorations were modeled using the three dimensional finite element method. Static occlusal load of 170 N was applied on lingual incline of buccal cusp at the angle of 45° with the longitudinal axis of the tooth. And three dimensional finite element analysis was taken by ANSYS (Version 6.0, Swanson Analysis System Co., Houston, U.S.A) program which represent the stress distribution on unrestored and restored cavity wall and margin.

The conclusions were as follows.

Compared to the unrestored cavity, Von Mises stress at the cementoenamel junction and line angle of the cavity base were reduced and in restored cavity.

To evaluate the change of working length with various instrumentation techniques in curved canals, working length and canal curvature were determined before and after canal instrumentation in buccal or mesial canals of extracted human molars. Stainless steel K-files (MANI®, Matsutani Seisakusho Co. Takanezawa, Japan), nickel-titanium K-files (Naviflex NT™, Brassler, Savannah, USA), ProFile®, and ProTaper™ (Dentsply-Maillefer, Ballaigues, Switzerland) were used to prepare the canals with crown-down technique. In two hand instrumentation groups, coronal flaring was made with Gates Glidden burs. Apical canals were instrumented until apical diameter had attained a size of 30. Positional relation between the tooth apex and the #10 K-file tip was examined by using AutoCAD 2000 (Autodesk Corp., San Rafael. CA, USA) under a stereomicroscope before and after coronal flaring, and after apical instrumentation. Degree of canal curvature was also measured with Schneider's method in radiographs. Data of working length and canal curvature changes were statistically analyzed with one-way ANOVA and Tukey's studentized range test.

Working length and canal curvature were decreased significantly in each step in all instrumentation groups. Coronal flaring using Gates Glidden burs in hand instrument groups and whole canal instrumentation using stainless steel hand K-files caused significantly more working length change than in ProFile instrumentation group (p < 0.05).

The result of this study demonstrates that all of the above kinds of instrumentation in curved canals cause reduction of working length and canal curvature at each instrumentation steps, and hand instrumentation causes more working length change than ProFile.

The purpose of this study was to compare the cytotoxicity by MTT test and genotoxicity by Ames test of new calcium phosphate-based root canal sealers (CAPSEAL I, CAPSEAL II) with commercially available resin-based sealers (AH 26, AH Plus), zinc oxide eugenol-based sealers (Tubliseal EWT, Pulp Canal Sealer EWT), calcium hydroxide-based sealer (Sealapex), and tricalcium phosphate based sealers (Sankin Apatite Root Canal Sealer I, II, III).

According to this study, the results were as follows:

The extracts of freshly mixed group showed higher toxicity than those of 24 h set group in MTT assay (p < 0.001).

The purpose of this study was to investigate influence of each file step of ProTaper® system on canal transportation.

Twenty simulated canals were prepared with either engine-driven ProTaper® or manual ProTaper®. Group R-resin blocks were instrumented with rotary ProTaper® and group M-resin blocks were instrumented with manual ProTaper®. Pre-operative resin blocks and post-operative resin blocks after each file step preparation were scanned. Original canal image and the image after using each file step were superimposed for calculation of centering ratio. The image after using each file step and image after using previous file step were superimposed for calculation of the amount of deviation. Measurements were taken horizontally at five different levels (1, 2, 3, 4 and 5 mm) from the level of apical foramen.

In rotary ProTaper® instrumentation group, centering ratio and the amount of deviation of each step at all levels were not significantly different (p > 0.05). In manual ProTaper® instrumentation group, centering ratio and the amount of deviation of each step at all levels except of 1 mm were not significantly different (p > 0.05). At the level of 1 mm, F2 file step had significantly large centering ratio and the amount of deviation (p < 0.05).

Under the condition of this study, F2 file step of manual ProTaper® tended to transport the apical part of the canals than that of rotary ProTaper®.

The possibility of applying a bi-axial flexure strength test on composite resin was examined using three point and bi-axial flexure strength tests to measure the strength of the light-cured resin and to compare the relative reliability using the Weibull modulus.

The materials used in this study were light-curing restorative materials, MICRONEW™, RENEW® (Bisco, Schaumburg, USA). The bi-axial flexure strength measurements used the piston-on-3-ball test according to the regulations of the International Organization for Standardization (ISO) 6872 and were divided into 6 groups, where the radius of the specimens were 12 mm (radius connecting the 3-balls: 3.75 mm), 16 mm (radius connecting the 3-balls: 5 mm), and the thickness were 0.5 mm, 1 mm, 2 mm for each radius.

The bi-axial flexure strength of the MICRONEW™ and RENEW® were higher than the three point flexure strength and the Weibull modulus value were also higher in all of the bi-axial flexure strength groups, indicating that the bi-axial strength test is relatively less affected by experimental error.

In addition, the 2 mm thick specimens had the highest Weibull modulus values in the bi-axial flexure strength test, and the MICRONEW™ group showed no significant statistical difference (p > 0.05). Besides the 2 mm MICRONEW™ group, each group showed significant statistical differences (p < 0.05) according to the thickness of the specimen and the radius connecting the 3-balls.

The results indicate that for the 2 mm group, the bi-axial flexure strength test is a more reliable testing method than the three point flexure strength test.

To evaluate the ratio of gutta-percha area in the canal after canal obturation with Continuous Wave of Condensation Technique (CWCT) with varying depths of plugger penetration, forty root canals of extracted human teeth were prepared up to size 40 of 0.06 taper with ProFile®. Canals of three groups were filled with CWCT with System B™ (Analytic Tech., USA) and different plugger penetration depths of 3, 5, or 7 mm from the apex. Canals of one group were filled with lateral condensation technique as a control. The filled teeth were cross-sectioned at 1, 2, and 3 mm levels from the apical foramen. The ratio of gutta-percha area in the canal was analyzed using Auto®Cad 2000. Data were analyzed with one-way ANOVA and Duncan's multiple range test.

At all levels, higher gutta-percha area ratio was found with deeper plugger penetration depth in CWCT, and cold lateral condensation group showed higher ratio than group of plugger penetration to apical 7 mm in CWCT.

At apical 1 mm and 2 mm levels, group of plugger penetration to apical 3 mm showed significantly higher gutta-percha area ratio than those of apical 7 mm and lateral condensation (p < 0.05).

It is concluded therefore that, under the conditions of the present study, deeper plugger penetration depth results in more favorable and efficient obturation in CWCT.