• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.76-76
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• 2017

Ni-Ti 파일은 근관치료 시 근관형성에 사용되며 근관계 내 조직 잔사와 세균 을 포함한 모든 내용물을 제거하고 미세누출이 생기지 않도록 성공적으로 근관충전을 할 수 있는 근관의 형태를 만드는데 사용된다. Ni-Ti 파일은 수동형 파일처럼 날이 풀어지거나 예각으로 꺾이는 등 시각적으로 나타나는 파일의 피로도나 손상정도를 인지하기 어려워 파일이 근관 내에서 부러지는 것을 막기가 어렵다. Ni-Ti 파일은 육안으로 관찰 할 수 있는 구부러짐이나 풀림 등의 소성변형 없이 기구의 탄성한계 내에서 갑작스럽게 파절되는 경우가 있는데, 이는 만곡 근관 내에서 기구가 회전하는 동안 만곡의 안쪽에는 압축응력이, 만곡의 바깥쪽에는 인장응력이 반복적으로 가해짐으로써 파절의 표면에 미세 파절과 균열이 발생하고 전파되어 결국 피로파절(fatigue fracture)을 야기하게 된다. 또한 Ni-Ti파일이 반복응력을 받으면 균열이 형성되면서 파절이 야기되며 연성파절(ductile fracture) 양상을 나타낸다고 보고하였다. Ni-Ti 파일을 이용한 피로파절에 대한 이전의 연구에서는 파일의 직경이나 경사도 (taper), 단면 형태 및 회전속도, 표면결함 등이 파절에 영향을 미친다고 보고되고 있다. 사용하지 않은 Ni-Ti파일을 구부려 응력을 가 한 상태에서 주사전자현미경으로 관찰한 결과 기계 가공 과정에서 발생한 균열, 미세 결함, 긁힌 자국 및 불균질성 등이 원인으로 알려져 있다. 따라서 본 연구발표에서는 표면결함을 최소화하고 기구의 회전응력 하에서 피로파절저항성을 향상시키기 위한 방법에 대하여 알아보고자 한다.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.3
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• pp.297-309
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• 2010

The objective of the present study was to perform a fracture analysis on fractured implant fixture after use in vivo and make clear the cause & mechanisms of failure. In case of fatigue fracture, the fractured surface represents fatigue striation. Fatigue striation indicate the progression of the crack front under cyclic loading, are characteristic of stage 2 crack growth. The site of crack initiation and stage 1 crack growth were not easily identified in any of the failure, presumably because of the complex microstructural features of the polycrystalline sample. In case of fractured by overload, dimpled or cleavage surface were observed. Using the interpretation of characteristic markings(ratchet mark, fatigue striation, dimple, cleavage et al) in fracture surfaces, failure events containing the crack origin, crack propagation, material deficiency could be understand.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.3
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• pp.156-161
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• 2012

Purpose: This study was conducted to obtain difference in fracture strength according to the diameter of one-body O-ring-type of mini implant fixture, to determine the resistance of mini implant to masticatory pressure, and to examine whether overdenture using O-ring type mini implant is clinically usable to maxillary and mandibular edentulous patients. Materials and methods: For this study, 13 mm long one body O-ring-type mini implants of different diameters (2.0 mm, 2.5 mm and 3.0 mm) (Dentis, Daegu, Korea) were prepared, 5 for each diameter. The sample was placed at $30^{\circ}$ from the horizontal surface on the universal testing machine, and off-axis loading was applied until permanent deformation occurred and the load was taken as maximum compressive strength. The mean value of the 5 samples was calculated, and the compressive strength of implant fixture was compared according to diameter. In addition, we prepared 3 samples for each diameter, and applied loading equal to 80%, 60% and 40% of the compressive strength until fracture occurred. Then, we measured the cycle number on fracture and analyzed fatigue fracture for each diameter. Additionally, we measured the cycle number on fracture that occurred when a load of 43 N, which is the average masticatory force of complete denture, was applied. The difference on compressive strength between each group was tested statistically using one-way ANOVA test. Results: Compressive strength according to the diameter of mini implant was $101.5{\pm}14.6N$, $149{\pm}6.1N$ and $276.0{\pm}13.4N$, respectively, for diameters 2.0 mm, 2.5 mm and 3.0 mm. In the results of fatigue fracture test at 43 N, fracture did not occur until $2{\times}10^6$ cycles at diameter 2.0 mm, and until $5{\times}10^6$ cycles at 2.5 mm and 3.0 mm. Conclusion: Compressive strength increased significantly with increasing diameter of mini implant. In the results of fatigue fracture test conducted under the average masticatory force of complete denture, fracture did not occur at any of the three diameters. All of the three diameters are usable for supporting overdenture in maxillary and mandibular edentulous patients, but considering that the highest masticatory force of complete denture is 157 N, caution should be used in case diameter 2.0 mm or 2.5 mm is used.

• Restorative Dentistry and Endodontics
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• v.34 no.5
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• pp.424-429
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• 2009

This study aimed to assess the influence of different cross-sectional area on the cyclic fatigue fracture of Ni-Ti rotary files using a fatigue tester incorporating cyclical axial movement. Six brands of Ni-Ti rotary files (ISO 30 size with. 04 taper) of 10 each were tested: Alpha system (KOMET), HeroShaper (MicroMega), K3 (SybronEndo), Mtwo (VDW), NRT (Mani), and ProFile (Dentsply). A fatigue-tester (Denbotix) was designed to allow cyclic tension and compressive stress on the tip of the instrument. Each file was mounted on a torque controlled motor (Aseptico) using a 1:20 reduction contra-angle and was rotated at 300 rpm with a continuous, 6 mm axial oscillating motion inside an artificial steel canal. The canal had a $60^{\circ}$ angle and a 5 mm radius of curvature. Instrument fracture was visually detected and the time until fracture was recorded by a digital stop watch. The data were analyzed statistically. Fractographic analysis of all fractured surfaces was performed to determine the fracture modes using a scanning electron microscope. Cross-sectional area at 3 mm from the tip of 3 unused Ni-Ti instruments for each group was calculated using Image-Pro Plus (Imagej 1.34n, NIH). Results showed that NRT and ProFile had significantly longer time to fracture compared to the other groups (p < .05). The cross-sectional area was not significantly associated with fatigue resistance. Fractographycally, all fractured surfaces demonstrated a combination of ductile and brittle fracture. In conclusion, there was no significant relationship between fatigue resistance and the cross-sectional area of Ni-Ti instruments under experimental conditions.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.2
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• pp.121-143
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• 2010

To investigate the effect of implant types and bone resorption on the fracture characteristics. 4 types of Osstem$^{(R)}$Implant were chosen and classified into external parallel, internal parallel, external taper, internal taper groups. Finite elements analysis was conducted with ANSYS Multi Physics software. Fatigue fracture test was performed by connecting the mold to the dynamic load fatigue testing machine with maximum load of 600N and minimum load of 60N. The entire fatigue test was performed with frequency of 14Hz and fractured specimens were observed with Hitachi S-3000 H scanning electron microscope. The results were as follows: 1. In the fatigue test of 2 mm exposed implants group, Tapered type and external connected type had higher fatigue life. 2. In the fatigue test of 4 mm exposed implants group, Parallel type and external connected types had higher fatigue life. 3. The fracture patterns of all 4 mm exposed implant system appeared transversely near the dead space of the fixture. With a exposing level of 2 mm, all internally connected implant systems were fractured transversely at the platform of fixture facing the abutment. but externally connected ones were fractured at the fillet of abutment body and hexa of fixture or near the dead space of the fixture. 4. Many fatigue striations were observed near the crack initiation and propagation sites. The cleavage with facet or dimple fractures appeared at the final fracture sites. 5. Effective stress of buccal site with compressive stress is higher than that of lingual site with tensile stress, and effective stress acting on the fixture is higher than that of the abutment screw. Also, maximum effective stress acting on the parallel type fixtures is higher. It is careful to use the internal type implant system in posterior area.

• Journal of Dental Rehabilitation and Applied Science
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• v.28 no.1
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• pp.57-66
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• 2012

The purpose of this study was to evaluate the relation between intentionally induced internal stress and cyclic fatigue failure of ProTaper Universal. ProTaper Universal (Dentsply Maillefer) S1, S2, F1, F2, F3, F4 and F5 (25 mm length) were used in this study. To give the internal stress, the ProTaper Universal were put into the .02 taper Endo-Training-Bloc (Dentsply Maillefer) until auto-stop by torque controlled motor. The rotation speed was 300 rpm and torque value was 1.0 Ncm. ProTaper Universal were grouped by the induced number of internal stress and randomly distributed among one control group and three experimental groups (n=10). The four groups were Stress 0 (control), Stress 1, Stress 2 and Stress 3. These instruments were rotated until separation. For cyclic fatigue measurement, inclined plane was used and time for separation was recorded. It was statistically analyzed using two-way ANOVA and Duncan post-hoc test at 95% confidential level. In all ProTaper Universal, there was statistically significant decrease on time for separation in Stress 3. In F2 and F3, there were statistically significant difference between control group and all experimental groups. And in F4 and F5, Stress 2 and 3 groups showed significantly lower cyclic fatigue resistance from Stress 0 group. In the limitation of this study, cyclic fatigue failure of ProTaper Universal is influenced by accumulated internal stress.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.4
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• pp.424-434
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• 2009

Statement of problem: Problems such as loosening and fractures of retained screws and fracture of implant fixture have been frequently reported in implant prosthesis. Purpose: Implant has weak mechanical properties against lateral loading compared to vertical occlusal loading, and therefore, stress analysis of implant fixture depending on its material and geometric features is needed. Material and methods: Total 28 of external hexed implants were divided into 7 of 4 groups; Group A (3i, FULL $OSSEOTITE^{(R)}$Implant), Group B (Nobelbiocare, $Br{\aa}nemark$ $System^{(R)}$Mk III Groovy RP), Group C (Neobiotec, $SinusQuick^{TM}$ EB), Group D (Osstem, US-II). The type III gold alloy prostheses were fabricated using adequate UCLA gold abutments. Fixture, abutment screw, and abutment were connected and cross-sectioned vertically. Hardness test was conducted using MXT-$\alpha$. For fatigue fracture test, with MTS 810, the specimens were loaded to the extent of 60-600 N until fracture occurred. The fracture pattern of abutment screw and fixture was observed under scanning electron microscope. A comparative study of stress distribution and fracture area of abutment screw and fixture was carried out through finite element analysis Results: 1. In Vicker's hardness test of abutment screw, the highest value was measured in group A and lowest value was measured in group D. 2. In all implant groups, implant fixture fractures occurred mainly at the 3-4th fixture thread valley where tensile stress was concentrated. When the fatigue life was compared, significant difference was found between the group A, B, C and D (P<.05). 3. The fracture patterns of group B and group D showed complex failure type, a fracture behavior including transverse and longitudinal failure patterns in both fixture and abutment screw. In Group A and C, however, the transverse failure of fixture was only observed. 4. The finite element analysis infers that a fatigue crack started at the fixture surface. Conclusion: The maximum tensile stress was found in the implant fixture at the level of cortical bone. The fatigue fracture occurred when the dead space of implant fixture coincides with jig surface where the maximum tensile stress was generated. To increase implant durability, prevention of surrounding bone resorption is important. However, if the bone resorption progresses to the level of dead space, the frequency of implant fracture would increase. Thus, proper management is needed.

• Restorative Dentistry and Endodontics
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• v.31 no.2
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• pp.96-102
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• 2006

There are various factors affecting the fracture of NiTi rotary files. This study was performed to evaluate the effect of cross sectional area, pecking motion and pecking distance on the cyclic fatigue fracture of different NiTi files. Five different NiTi $files-Profile^{(R)}$ (Maillefer, Ballaigue, Switzerland), $ProTaper^{TM}$(Maillefer, Ballaigue, Switzerland), $K3^{(R)}$ (SybronEndo. Orange, CA) , Hero $642^{(R)}$ (Micro-mega, Besancon, France), Hero $Shaper^{(R)}$ (Micro-mega, Besancon, France)-were used. Each file was embedded in temporary resin, sectioned horizontally and observed with scanning electron microscope. The ratio of cross-sectional area to the circumscribed circle was calculated. Special device was fabricated to simulate the cyclic fatigue fracture of NiTi file in the curved canal,. On this device, NiTi files were rotated (300rpm) with different pecking distances (3 mm or 6 mm) and with different motions (static motion or dynamic pecking motion) . Time until fracture occurs was measured. The results demonstrated that cross-sectional area didn't have any effect on the time of file fracture. Among the files, $Profile^{(R)}$ took the longest time to be fractured. Between the pecking motions, dynamic motion took the longer time to be fractured than static motion. There was no significant difference between the pecking distances with dynamic motion, however with static motion, the longer time was taken at 3mm distance. In this study, we could suggest that dynamic pecking motion would lengthen the time for NiTi file to be fractured from cyclic fatigue.

• Restorative Dentistry and Endodontics
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• v.33 no.1
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• pp.54-65
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• 2008

The purpose of this study was to determine the effect of sodium hypochlorite and steam autoclaving on the cyclic fatigue of nickel-titanium endodontic files. Two types of files with a .06 taper and #30 were used, $K3^{(R)}$ (SybronEndo, Glendora, California, USA) and Hero $642^{(R)}$(Micro-Mega, BesanCon, France). The files were divided into 6 experimental groups containing 10 files each group depending the soaking time in 6% sodium hypochlorite solution and number of cycles of steam autoclave. After sterilization, a cyclic fatigue test was performed on each file, and the fracture time was recorded in seconds. The control group underwent the cyclic fatigue test only. After the test, the surface characteristics of the files were observed using scanning electron microscopy (SEM). All groups containing the Hero 64~ files showed a similar cyclic fatigue fracture time. However, the cyclic fatigue fracture time with the $K3^{(R)}$ files was significantly shorter in groups which were treated with sodium hypochlorite than in the control group (P < 0.05), SEM revealed both Hero $642^{(R)}$ and $K3^{(R)}$ files to have significant corrosion on the file surface in groups treated with sodium hypochlorite, compared with the sharp and regular blades of the control group. $K3^{(R)}$ files showed more corrosion than the Hero $642^{(R)}$ files. Bluntness of the blades of the $K3^{(R)}$ file was observed in groups treated with steam autoclave. Although there was no obvious destruction on the surface of steam autoclaved Hero $642^{(R)}$ files, slight bluntness was observed. Sterilizing with a steam autoclave is much less destructive to $K3^{(R)}$ files than sodium hypochlorite. The longer time exposed to sodium hypochlorite, the more destructive pattern was shown on the blades of the files. Therefore, when using sodium hypochlorite solution, the exposure time should be as short as possible in order to prevent corrosion and increase the cyclic fatigue fracture time.

• Journal of Dental Rehabilitation and Applied Science
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• v.38 no.3
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• pp.138-149
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• 2022

The clinical applicability of ceramics can be increased by analyzing the causes of fractures after fracture testing of dental ceramics. Fractography to analyze the cause of fracture of dental ceramics is being widely applied with the development of imaging technologies such as scanning electron microscopy. Setting the experimental conditions is important for accurate interpretation. The fractured specimens should be stored and cleaned to avoid contamination, and metal pretreatment is required for better observation. Depending on the type of fracture, there are dimple rupture, cleavage, and decohesive rupture mainly observed in metals, and fatigue fractures and conchoidal fractures observed in ceramics. In order to reproduce fatigue fracture in the laboratory, which is the main cause of fracture of ceramics, a dynamic loading for observing slow crack growth is essential, and the load conditions and number of loads must be appropriately set. A typical characteristic of a fracture surface of ceramic is a hackle, and the causes of fracture vary depending on the shape of hackle. Fractography is a useful method for in-depth understanding of fractures of dental ceramics, so it is necessary to follow the exact experimental procedure and interpret the results with caution.