• Restorative Dentistry and Endodontics
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• v.13 no.1
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• pp.91-101
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• 1988

The purpose of this study was to evaluate Ultrasonic devices in root canal enlargement, about the effects on the canal shape and on the cutting ability beyond the curvature in curved canals. 180 resin blocks with $40^{\circ}$ curvature in apical third and 16mm long canal were made of epoxy resin and smooth broaches. These blocks were devided into six groups. According to the devices (ENAC$^{(R)}$, HARMOSONIC$^{(R)}$, Sonic Air MM 3000$^{(R)}$) and files (Zipperer file, H-file, Flexofile, K-file, Sharper file), five groups were instrumented one minute with # 15 files, then the enlarged size was measured. And # 20 files were used again in the same groups, then the enlarged size was measured. In control group, the time which was taken to enlarge the canal from # 15 to # 20 by hand technique was measured. The data was analyzed statistically. Then the enlarged shapes were evaluated in six groups with the stereomicroscope and recorded in ideal and non-ideal canal shape to compare the effects of ultrasonic devices on the canal shape. Only the ideal shaped canals were used in the study whether the cutting ability beyond the curvature in curved canals was, or not. The files with whole flutes, no flutes, and flutes in apical 5mm only were used. The weight differences of pre-and post-instrumentation by Sonic Air MM 3000$^{(R)}$ for two minutes were compared. The results were as follow: 1. Intracanal instrumentation for 1 minute with ultrasonic devices using # 15 and # 20 file in curved root canal of the epoxy resin block can not reach to the next file size. 2. Sonic Air MM 3000$^{(R)}$ shows higher cutting ability than the other two devices (p=0.001), however the percentage of non-ideal canal shape was the highest. 3. Two ultrasonic devices except Sonic Air MM 3000 considered normal in ideal canal shaping ability. 4. little cutting ability was shown beyond the curvature of curved canals.

• Proceedings of the KACD Conference
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• 2008.05a
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• pp.204-212
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• 2008

The purpose of this study was to compare the apical microleakage in root canal filled with Resilon by methacrylate-based root canal sealer or 2 different self-adhesive resin cements. Seventy single-rooted extracted human teeth were sectioned at the CEJ perpendicular to the long axis of the roots with diamond disk. Canal preparation was performed with crown-down technique using Profile NiTi rotary instruments and GG drill. Each canal was prepared to ISO size 40, .04 taper and 1 mm short from the apex. The prepared roots were randomly divided into 4 experimental groups of 15 roots each and 5 roots each for positive and negative control group. The root canals were filled by lateral condensation as follows. Group 1: Gutta-percha with AH-26, Group 2: Resilon with RealSeal primer & sealer, Group 3: Resilon with Rely-X Unicem, Group 4: Resilon with BisCem. After stored in $37^{\circ}C$, 100% humidity chamber for 7 days, the roots were coated with 2 layers of nail varnish except apical 3 mm. The roots were then immersed in 1% methylene blue dye for 7 days. Apical microleakage was measured by a maximum length of linear dye penetration after roots were separated longitudinally. One way ANOVA and Scheffe's post-hoc test were performed for statistical analysis. Group 1 showed the least apical leakage and there was no statistical significance between Group 2, 3, 4. According to the results, the self adhesive resin cement is possible to use as sealer instead of primer & sealant when root canal filled by Resilon.

• Restorative Dentistry and Endodontics
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• v.33 no.3
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• pp.204-212
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• 2008

The purpose of this study was to compare the apical microleakage in root canal filled with Resilon by methacrylate-based root canal sealer or 2 different self-adhesive resin cements. Seventy single-rooted extracted human teeth were sectioned at the CEJ perpendicular to the long axis of the roots with diamond disk. Canal preparation was performed with crown-down technique using Profile NiTi rotary instruments and GG drill. Each canal was prepared to ISO size 40, .04 taper and 1 mm short from the apex. The prepared roots were randomly divided into 4 experimental groups of 15 roots each and 5 roots each for positive and negative control group. The root canals were filled by lateral condensation as follows. Group 1: Guttapercha with AH-26, Group 2: Resilon with RealSeal primer & sealer, Group 3: Resilon with Rely-X Unicem, Group 4: Resilon with BisCem. After stored in $37{\circ}C$, 100% humidity chamber for 7 days, the roots were coated with 2 layers of nail varnish except apical 3 mm. The roots were then immersed in 1% methylene blue dye for 7 days. Apical microleakage was measured by a maximum length of linear dye penetration after roots were separated longitudinally. One way ANOVA and Scheffe's post-hoc test were performed for statistical analysis. Group 1 showed the least apical leakage and there was no statistical significance between Group 2, 3, 4. According to the results, the self adhesive resin cement is possible to use as sealer instead of primer & sealant when root canal filled by Resilon.

• Restorative Dentistry and Endodontics
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• v.27 no.4
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• pp.411-420
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• 2002

The aim of this study is to compare the adaptability of thermoplasticized injectable gutta-percha technique to the canal walls in ribbon-shaped canals. Thirty resin models simulated ribbon-shape canals were instrumented to #40 using .06 taper Profile systems. Three groups of each 10 resin models were obturated by the lateral condensation technique(LC) and the two thermoplasticized injectable gutta-percha technique; Ultrafil Endoset+Obtura II(EO) and Ultrafil Firmset(UF), respectively. After resin model were kept at room temperature for 4 days, they were resected horizontally with micro-tome at 1, 2, 3, 4 and 5mm levels from apex. At each levels. image of resected surface were taken using CCD camera under a stereomicroscope at $\times$40 magnification and stored. Ratio of the area of gutta-percha was obtained by calculating area of gutta-percha cone to the total area of canal using digitized image-ana-Iyzing program. The data were collected then analyzed statistically using One-way ANOVA. The results were as follows. 1 At 1mm levels, there was no statistically significant difference in the mean ratio of gutta-percha among the groups. 2. At 2mm level, EO showed the highest mean ratio of gutta-percha (p<0.05) and there was no significant difference between LC and UF. 3. At 3, 4, 5mm levels, EO and UF had significantly greater mean ratio of gutta-percha than LC(p<0.05) and there was no significant difference between EO and UF. In conclusion, the thermoplasticized injectable gutta-percha techniques demonstrated relatively favorable adaptability to canal walls than lateral condensation technique in ribbon-shaped canals except for 1mm level.

• Restorative Dentistry and Endodontics
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• v.13 no.1
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• pp.161-171
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• 1988

The purpose of this study was to examine the morphological changes of different simulated canals according to the preparation procedures. With the use of clear casting resin, simulated straight and curved canals were created so that canal preparation procedures could be directly visualized and compared. Thirty clear polyester casting resin blocks which contained four simulated canals divided into three groups; Group A($0^{\circ}$), Group B($15^{\circ}$), and Group C($30^{\circ}$). In each block, 3 canals were prepared different preparation techniques, which were conventional method, step-back method, and giromatic filing. But, one canal was not prepared as a control group. The results were as follows: 1. There was no difference on canal shape among three canal preparation methods in straight canals (Group A). 2. When conventional method and Giromatic filing were used in curved canals (Group B, C), elbow, zip and hour-glass shape were formed in apical third. 3. When conventional method and Giromatic filing were used in curved canals (Group B, C), tear-drop appearance developed at the site of the canal exit in curved canals. 4. In curved canals (Group B, C), file tend to straighten within the canal. 5. There was no difference on canal shape according to curved angle in step-back method (p > 0.1). But there was significant difference on canal shape according to curved angle in conventional method and Giromatic filing (p < 0.001). 6. Step-back method was significantly more effective than conventional method and Giromatic preparation in morphologic aspects of apical third of original canals.

• Restorative Dentistry and Endodontics
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• v.30 no.1
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• pp.31-37
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• 2005

The aim of this study was to evaluate the effectiveness of sealer placement in simulated root canal extensions. Forty resin blocks were attained from the Endo-training Bloc. In each block. The simulated root canal was made with $\#20$, 80taper GT file. After each block was longitudinally split into two halves, a standardized groove was prepared on one canal wall of two halves to simulate the canal extensions with various irregularities. The two halves of each block were assembled and all simulated root canals were obturated by single cone method with AH26 sealer. Four different methods of sealer placement were used: group A, $\#20$ K-file; group B, ultrasonic file; group C, lentulo spiral; group D, EZ-Fill bi-directional spiral. All obturated blocks were stored in $100\%$ humidity at $37^{\circ}C$ for 1 week, Using a low speed saw, each block was sectioned horizontally. Images of the sections were taken using a stereomicroscope at $\times$ 30 magnification and a digital camera. The amount of the sealer in the groove was evaluated using a scoring system, a higher score indicated better sealing effectiveness. The data was statistically analysed by Fisher's Exact Test. The sealing score was the lowest, specially at the middle area of canal extensions in group A, and that was statistically significant difference from other groups. In conclusion, the ultrasonic file, lentulo spiral and EZ-Fill bi-directional spiral were effective methods of sealer placement in simulated canal extensions. The K file was the least effective method, specially at the middle area of canal extensions.

• Restorative Dentistry and Endodontics
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• v.49 no.2
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• pp.18.1-18.13
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• 2024

Objectives: This study was conducted to evaluate the mechanical properties of relined and non-relined fiberglass posts when cemented to root canal dentin using a conventional dual-cure resin cement or a self-adhesive resin cement. Materials and Methods: Two types of resin cements were utilized: conventional and self-adhesive. Additionally, 2 cementation protocols were employed, involving relined and non-relined fiberglass posts. In total, 72 bovine incisors were cemented and subjected to push-out bond strength testing (n = 10) followed by failure mode analysis. The cross-sectional microhardness (n = 5) was assessed along the root canal, and interface analyses (n = 3) were conducted using scanning electron microscopy (SEM). Data from the push-out bond strength and cross-sectional microhardness tests were analyzed via 3-way analysis of variance and the Bonferroni post-hoc test (α= 0.05). Results: For non-relined fiberglass posts, conventional resin cement exhibited higher pushout bond strength than self-adhesive cement. Relined fiberglass posts yielded comparable results between the resin cements. Type II failure was the most common failure mode for both resin cements, regardless of cementation protocol. The use of relined fiberglass posts improved the cross-sectional microhardness values for both cements. SEM images revealed voids and bubbles in the incisors with non-relined fiberglass posts. Conclusions: Mechanical properties were impacted by the cementation protocol. Relined fiberglass posts presented the highest push-out bond strength and cross-sectional microhardness values, regardless of the resin cement used (conventional dual-cure or self-adhesive). Conversely, for non-relined fiberglass posts, the conventional dual-cure resin cement yielded superior results to the self-adhesive resin cement.

• Macromolecular Research
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• v.13 no.3
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• pp.194-205
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• 2005

The network structure of Ni-coated carbon black (NCB) composites filled with phenolic resin was investigated by means of using scanning electron microscopy, viscosity, interfacial tension, shrinkability, Flory-Huggins interaction parameters, and swelling index. The electrical properties of the composites have been characterized by measurement of the specific conductivity as a function of temperature. Additionally, the variation of conductivity with temperature for the composites has been reported and analyzed in terms of the dilution volume fraction, relative volume expansion, and barrier heights energy. The thermal stability of phenolic-NCB composites has been also studied by means of the voltage cycle processes. The experimental data of EMI wave shielding were analyzed and compared with theoretical calculations. The mechanical properties such as tensile strength, tensile modulus, hardness and elongation at break (EB) of NCB-phenolic resin composites were also investigated.

• Restorative Dentistry and Endodontics
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• v.34 no.2
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• pp.103-112
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• 2009

The purpose of this study was to compare the effect of curing methods of adhesive resins and resin cements in the root canal. Crown portions of 32 single-rooted mandibular premolars were removed. Routine endodontic treatment was done, and 9 mm deep post spaces were prepared within root canals. No.3 FRC Postec posts (Ivoclar-Vivadent AG, Liechtensteih) were cemented in the post spaces by self-(SC) or light-curing (LC) using two dual-cured adhesives (Adper Scotchbond multi-purpose plus and Exite DSC )and resin cements (RelyX ARC and Variolink II). They were assigned to 4 groups (n=8): R-SC, R-LC, V-SC, V-LC group. After stored in distilled water for 24 hours, each root was transversally sectioned with 1.5 mm thick and made three slices. The specimens were subjected to push-out test in a universal testing machine (EZ Test, Shimadzu Co., Japan) with a crosshead speed of 1 mm/min. The data were analyzed with repeated ANOVA and one-way ANOVA. Also the interface of post-resin cement and resin cement-canal wall of each group was observed under FE-SEM. When fiber posts were cemented into the root canal using total-etch adhesives, the bond strength and adaptation between post and root canal dentin was affected by curing method. Self-cure of adhesives and resin cements showed higher bond strength and closer adaptation than light-cure of them.

• Restorative Dentistry and Endodontics
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• v.26 no.5
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• pp.418-435
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• 2001

Root canal preparation process is of utmost importance in successful treatment of root canal. Also, one of the most important purpose of the root canal preparation is to enlarge the root canal three dimensionally without changing the curvature of the root canal However as the curvature of the root canal increases, there are many difficulties involved in formation of optimum root canal. Therefore in order to solve the above mentioned problems, new developments in methods of root canal preparation and equipments for such purposes were made. Recently, vigorous studies about newly introduced engine-driven nickel-ti-tanium rotary file are conducted. As shown in research results to dates, it is well established that the use of nickel-titanium file is better suited for curved root canal than stainless steel file in maintaining the curvature or root canal and reducing the deformation of root canal. However it is also acknowledged that there are a few discrepancies in research results according to protocol, due to failure to remove variables in experiments. In addition, although it is recommended by the manufacturer that the GT rotary file should maintain a low rotational speed of 150~350rpm and 'light pressure' as light as not to break the lead of a pencil, academic studies about the vertical force which is not yet standardized are not sufficiently explored. Therefore, this research devised and utilized a special research equipment to standardize the appropriate range of vertical force for GT rotary file through experiments by breaking of the lead of a pencil as expressed by the manufacturer and to accurately measure factors involved through repeating and recreating the environment of root canal preparation. Forming nine experimental groups by varying the vertical forces (150g. 220g, 300g) and rpm (150rpm, 250rpm, 350rpm), the effects of changing vertical forces and rpm on working efficiency were measured in terms of time expended in root canal preparation by crown-down method using a transparent resin block with 35 degree curvature and GT rotary file (z-test). The following research using this special research equipment that involved nine experimental groups and varying the vertical force for root canal preparation from 300g which is within the normal vertical force range to 700g and 1000g which fall outside the normal rpm range. The results were as follows : 1. Analysis of the experiment results revealed that the time spent in root canal preparation decreased as the vertical forces and rpm increased (p<0.05). Also, the effects of rpm were greater than those of the vertical forces within the normal vertical force range ($\beta$-weight test). 2. Observation of the deformation of GT rotary file revealed that deformation increases in a direct correlation with the vertical force increase and in a reverse correlation with the rpm decrease. In the case of the vertical forces close to the normal range, the probability of GT rotary file deformation were quite different depending on the rpm changes. In the case of greater vertical forces, the occurrences of deformation of the file were more frequent regardless of the rpm changes. 3. Deformation and breakage of file were also commonly observed in the expended time measurement experiments and GT rotary file deformation experiments in which low speed rpm (150rpm) was used and at the curved portion of the resin block.