The purpose of this study was to evaluate the obturation efficiency of a non-standardized gutta-percha cone in curved root canals prepared with 0.06 taper nickel-titanium instruments.

Sixty simulated curved root canals in clear resin blocks were prepared with crown-down technique using 0.06 taper rotary ProTaper™ and ProFile (Dentsply-Maillefer) until apical canal was size 30. Root canals were randomly divided into 4 groups of 15 blocks and obturated with cold-laterally compacted gutta-percha technique by using either a non-standardized size medium gutta-percha cone or an ISO-standardized size 30 one as a master cone. Gutta-percha area ratio were calculated at apical levels of 1, 3, and 5 mm using AutoCAD 2000 after cross-sectioning, and the data were analyzed with one-way and two-way ANOVAs and Duncan's multiple range test.

Non-standardized size medium cone groups showed significantly higher gutta-percha area ratio than standardized cone groups at all apical levels (p < 0.01).

Non-standardized cone groups used significantly less accessory cones than standardized cone groups (p < 0.01).

The purpose of this study was to measure the flexural strength and hardness of four core materials in 4 different medias and to evaluate the relationship between the physical properties.

For the flexural strength, the specimens were prepared from each of the following materials: Bisfil Core, Core Max, Fuji IX GP, Miracle Mix and randomly divided into four groups and stored at 37 degree C in the following medias: distilled water for 24 hours (DW/1), distilled water for 30 days (DW/30). 2% NaF for 30 days (NF/30), 0.02N lactic acid for 30 days (LA/30). After storage, the specimens were subjected to flexural strength testing and calculated to flexural modulus.

For hardness testing, specimens were prepared from four materials and storaged in the uniform way. After storage, the specimens were subjected to Vicker's hardness testing.

1. The flexural strength of Core Max were the highest, and the flexural strength of Miracle Mix were the lowest.

2. The hardness of Bisfil Core were the highest.

3. The hardness of Core Max were the highest.

4. The hardness of Miracle Mix were the lowest.

5. 2% NaF and 0.02N lactic acid negatively affected the flexural strength and hardness of four core materials.

The aim of this study was to evaluate the microleakage of teeth according to root canal preparation with & without apical enlargement in various size of apical foramen. 60 extracted one canal roots were cross-cutted at 5 mm from root apex and divided into two groups according to their apical foramen size of large (L) and small (S). Each group was subdivided into two groups accordance with their cross-sectional configuration at 5 mm from apex, round (R) and ovoid (O); SR Group, SO Group, LR Group, LO Group. Each group was shaped in .02 taper by Quantec series Nickel-Titanium (NiTi) rotary file, obturated by lateral condensation method. Leakage was measured using a fluid transport model under 40 cmH₂O pressure. After the leakage test, blocks which had showed the leakage retreated with .04 taper and .06 taper and evaluated the degree of fluid filtration in each group. The data was analysed statistically using chi-square test and fisher's exact test.

The results obtained were as follows:

1. Significant difference in leakage was found in groups which had different apical foramen size in .02 taper instrumentation (p < 0.05), but not in .04 taper instrumentation (p > 0.05).

2. The difference in microleakage according to the shape of canal was not evident at 5 mm from apex (p > 0.05).

3. There was correlation between .02 taper instrumentation and .04 taper instrumentation in LR group , LO group (p < 0.05).

The purpose of this study was to assess the incidence of flare-ups among patients who received endodontic treatment and to examine the correlation with pre-operative and operative variables.

Analysis was in two aspects (a) overall incidence of flare-ups as expressed by a percentage of all patients visits and (b) percentage of flare-ups that occurred as related to various factors such as patient demographics, diagnosis, and treatment procedures.

1. From the 840 teeth which were examined in this study, the total number of flare-ups was 13.

2. As to gender of patients, there was no significant difference in flare-ups.

3. As to tooth groups, there was no significant difference in flare-ups.

4. In the teeth with pre-operative symptom, there was a statistically significant higher incidence of flare-ups than the teeth without it.

5. In the teeth with apical periodontitis, there was a statistically significant higher incidence of flare-ups.

6. As to pulp and periapical status, non-vital teeth had a higher incidence as compared with vital teeth, irreversible pulpitis.

7. Multi-visit treatment resulted in the higher incidence of flare-ups than one visit treatment.

8. Re-treatment procedures had a statistically significant higher incidence of flare-ups than root canal treatment.

In this study, overall percentages of flare-ups was 1.55%. It showed a statistically significant higher incidence related to pre-operative symptom, apical periodontitis, and re-treatment. There was no significant difference in flare-ups related to gender, tooth groups, and fistula.

This study was done to evaluate whether there were any differences in microleakage of class V composite restorations according to restoration site and cavity size.

Total sixty-four restorations were made in molar teeth using Esthet-X. Small (2 × 2 × 1.5 mm) and large (4 × 2 × 1.5 mm) restorations were made at the buccal/lingual surface and the proximal surface each. After 1,000 times of thermocycling (5℃ - 55℃), resin replica was made and the percentage of marginal gap to the whole periphery of the restoration was estimated from SEM evaluation.

Thermocycled tooth was dye penetrated with 50% silver nitrate solution. After imbedding in an auto-curing resin, it was serially ground with a thickness of 0.25 mm. Volumetric microleakage was estimated after reconstructing three dimensionally.

Two-way ANOVA and independent T-test for dye volume, Mann-Whitney U test for the percentage of marginal gap, Spearman's rho test for the relationship between two techniques were used.

The results were as follows:

1. The site and size of the restoration affected on the microleakage of restoration. Namely, much more leakage was seen in the proximal and the large restorations rather than the buccal/lingual and the small restorations.

2. Close relationship was found between two techniques (Correlation coefficient = 0.614 / P = 0.000).

Within the limits of this study, it was noted that proximal and the large restorations leaked more than buccal/lingual and the small restorations. Therefore, it should be strictly recommended large exposure of margins should be avoided by reducing unnecessary tooth reduction.

A variety files made of stainless steel (S-S) or nickel-titanium (Ni-Ti) are used during endodontic treatment. The purpose of this study was to evaluate the corrosion susceptibility of S-S and Ni-Ti endodontic files. Three brands of files were used for this study: K-flex® S-S files (Maillefer, USA), Profile® Ni-Ti files (Maillefer, USA), K-3® Ni-Ti files (SybronEndo, USA). 120 files of each brands (21mm, ISO size #20) were divided into 12 groups according to 1) sterilization methods using Autoclave or Ethylene Oxide (E-O) gas, 2) Irrigation solutions using 5.25 % NaOCl or Saline, 3) the number of sterilization (1, 5, 10 times). After above procedures, each of the files was inspected by three examiners with a light microscope and camera at X25. Each file was judged and ranked according to the following criteria: 0; no corrosion, 1; mild corrosion, 2; moderate corrosion, and 3; severe corrosion. The files of high score were examined under the Scanning Electron Microscope.

Data were statistically analyzed with the Kruskal-Wallis test (p < 0.05). Most of the ten time-autoclaved files had showed mild to moderate corrosion. But, one or five time-autoclaved files did not show corrosive surface. NaOCl treatment and E-O gas sterilization did not influence on corrosion. There was a significant difference in corrosion susceptibility between sterilization methods and the number of autoclaving. However, there was no significant difference between brands and file materials.

In this study we measured the amount of light energy that was projected through the tooth material and analyzed the degree of polymerization by measuring the surface hardness of composites. For polymerization, Optilux 501 (Demetron, USA) with two types of light guide was used: a 12 mm diameter light guide with 840 mW/cm² light intensity and a 7 mm diameter turbo light guide with 1100 mW/cm².

Specimens were divided into three groups according to thickness of penetrating tooth (1 mm, 2 mm, 0 mm). Each group was further divided into four subgroups according to type of light guide and curing time (20 seconds, 40 seconds). Vickers'hardness was measured by using a microhardness tester. In 0 mm and 1 mm penetrating tooth group, which were polymerized by a turbo light guide for 40 seconds, showed the highest hardness values. The specimens from 2 mm penetrating tooth group, which were polymerized for 20 seconds, demonstrated the lowest hardness regardless of the types of light guides (p < 0.05).

The results of this study suggest that, when projecting tooth material over a specified thickness, the increase of polymerization will be limited even if light intensity or curing time is increased.

This in vitro study monitored MMP-8 production on PMN by stimulated with the following three groups; Sonicated extracts of E. faecalis (SEF), SEF treated with Ca(OH)₂ (12.5mg/ml) for 7 days, and lipopolysaccharides (LPS) of E. coli. The level of MMP-8 in each group was immediately measured by ELISA. The data were analyzed with Kruskal-Wallis test and Mann-Whitney U test.

In the SEF group, the level of production of MMP-8 was higher than the negative control group in low concentration (0.05µg/ml) of SEF (p < 0.05), but it decreased with an increase in the concentration of SEF (p < 0.05). In the case of SEF treated with Ca(OH)₂, all of the MMP levels were higher than negative control group (p < 0.05), but no statistical difference was found among the different SEF concentrations (p > 0.05). All of the levels in E. coli LPS were increased with increasing concentrations (p < 0.05).

According to this study we could summarize as follows:

1. MMP-8 was expressed at low level in untreated PMN group and the levels of MMP-8 were upregulated in PMN stimulated by E. coli LPS groups.

2. In the SEF groups, the level of production of MMP-8 decreased with an increase in the concentration of SEF (p < 0.05). So E. faecalis may have suppressive effect on the production of MMP-8 by PMN.

3. In the case of SEF treated with Ca(OH)₂, all of the MMP levels at different SEF concentrations were higher than untreated PMN group (p < 0.05), but no statistical difference was found among the different SEF concentrations (p > 0.05).