The purpose of this study was to evaluate the efficiency of the preparation of oval canals using hand and engine-driven instruments with SEM observation. Thirty single-rooted teeth with oval canal were used in this study. The teeth were divided into 3 groups. In group A, the teeth were instrumented up to a size 35 K-file using RC-prep and irrigated with 5% NaOCl between each file size. In group B, the teeth were instrumented with Profile according to the manufacture's instructions using RC-Prep and irrigated with 5% NaOCl between each file size. In group C, the teeth were instrumented with GT file according to the manufacture's instructions using RC-prep and irrigated with 5% NaOCl between each file size. Then, in all teeth, a final flush of 5ml of distilled water delivered for 30s. Canals were dried with sterile standardized paper points. After preparing the canals, the teeth were sectioned along their mesial and diatal surfaces by using low-speed diamond disc, chisel and mallet. Each root section was then dehydrated in graded concentration of alcohol (70, 80, 90, 100%), mounted on an aluminum stub, sputter-coated with gold-palladium and observed with scanning electron microscope (HITACHI S-4200) in middle and apical area.

The results of this study were as follows:

In the middle area, group B and group C showed less smear layer than group A, and it was statistically significant (p < 0.05).

This study compared the shaping ability of nickel-titanium rotary files with different rake angle and radial land.

The nickel-titanium files used in this study were Profile(Dentsply, Maillefer, Ballaigues, Switzerland), Hero 642(Micromega, Besancon, France), and K3(SybronEndo, Glendora, Ca, USA) file. Resin blocks substituted for root canals. 36 resin blocks were divided into 3 groups with 12 canals each. The time for canal preparation was recorded. The images of pre- and postoperative resin canal were scanned and those were superimposed. Amounts of canal deviation, total canal widths, inner canal widths, and outer canal widths were measured at apical 1, 2, 3, 4, 5, 6, and 7mm levels.

The amount of canal deviation was the smallest in Profile group, and the time for canal preparation was the shortest in Hero 642 group. K3 group resulted in competent characteristics in both measurements. Positive rake angle seemed to result in fast shaping of root canal and radial land guide the instrument in center of the canals and around curvatures. Radial land also tended to reduce the sense of screwing into the root canal.

The proper selection of the nickel-titanium file based on the knowledge about file design is needed for the safer, simpler and faster root canal therapy.

The objectives of this study was to evaluate current visible light curing units regarding microhardness and microleakage. Fourty samples of composite resin(Z-250, 3M) were cured by different light curing units(Flipo, LOKKI; Credi II, 3M; XL 3000, 3M; Optilux 500,Demetron) in acrylic blocks. Microhardness was measured using a calibrated Vickers indenter on both top and bottom surfaces after 24 hours of storage in air at room temperature. Class V cavities were prepared on buccal and lingual surfaces of fourty extracted human molars. Each margin was on enamel and dentin/cementum. Composite resin(Z-250, 3M) was filled in cavities and cured by four different light curing units(Flipo, LOKKI; Credi II, 3M; XL 3000, 3M; Optilux 500, Demetron).

The results of this syudy were as follows:

Microhardness

1. Flipo showed low microhardness compared to Optilux 500, Credi II significantly in upper surface. Flipo didn't show a significant difference compared to XL 3000.

2. The microhardness resulting from curing with Flipo was lower than that of others on lower surfaces.

Microleakage

1. Dentin margin showed significantly high dye penetration rate than enamel margin in all groups(p<0.05).

2. No significant differences were found on both enamel and dentin margin regarding curing units.

The purpose of this study was to evaluate the effects of EDTA and pulsed Nd:YAG laser on apical leakage of canal obturation. Forty-eight single-rooted teeth were used in this study. The teeth were instrumented up to a size 40 K-file and irrigated with 2.5% NaOCl between each file size. And the teeth were divided into 4 groups. In group A, the root canals were irrigated with a final flush of 5ml 2.5% NaOCl as a control group. The teeth in group B were irrigated with a final flush of 5ml 17% EDTA. The teeth in group C and D were irradiated by pulsed Nd:YAG laser(laser parameters were set at 1W, 100mJ, 10Hz, and 2W, 100mJ, 20Hz respectively).

The results were as follows:

1. Apical leakage was observed in 50% of samples in group A, 30% of samples in group B, 20% of samples in group C, and 10% of samples in group D.

2. The teeth in group B had less leakage than group A, but there was no statistically significant differences(p>0.05).

3. The teeth in group C, D had less leakage than group A, and there was statistically significant differences(p<0.05).

4. The teeth in group C, D had less leakage than group B, but there was no statistically significant differences(p>0.05).

5. There was no significant differences in apical leakage between group C and group D(p>0.05).

The purpose of the present study were to evaluate microleakage of a fourth generation dentin-bonding agent following a walking bleaching treatment, to determine the effect of temporary postbleaching dressing with calcium hydroxide on microleakage and to investigate the effect of delayed intracoronal restoration on microleakage.

The results of this study were as follows:

1. Bleached groups showed more microleakage than unbleached group.

2. Immediately restored group following bleaching procedure showed the highest microleakage score.

3. One-week delayed restorations showed less microleakage but there were no statistically significant difference between group II and III.

4. Provisional dressing with calcium hydroxide had no influence on microleakage.

It is necessary to know the time that has elapsed from the bleaching treatment to the restoration procedure to achieve optimal seal, as well as to reduce the risk of microleakage in adhesive restoration.