• The Journal of Korean Academy of Prosthodontics
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• v.44 no.4
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• pp.432-442
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• 2006

Statement of problem: One of common problems associated with dental implant is the loosening of abutment screws that retain the implants. Purpose : This study was performed to investigate the influence of abutment screw length and repeated tightening on screw loosening in dental implant. Material and method: Forty nine Hexplants (13mm length, 4.3mm diameter, Ti grade IV, Warantec. Co. Ltd. Seongnam, Korea) and cementation type abutments(straight abutment) and abutment screws (0.4mm/pitch) were divided into 7 groups, depending on abutment screw length. Each implant and abutment was tightened to 30Ncm by torque controller(MGT50, MARK-10 Inc., USA) and the removal torque values were measured during 10 consecutive closure/opening trials. Results and Conclusion: The results of comparing the removal torque value are as follows : 1. There is no significant difference in the removal torque value between groups in 10 consecutive closure/opening trials (p = 0.97). 2. If the fractured abutment screw is engaged in longer than 2.425 thread length, there is no significant difference in the preload between the fractured abutment screw and the new abutment screw when both are equally tightened to 30 Ncm. 3. The removal torque value in the 1st trial(24.510 Ncm) was lower than that in the 2nd, 3rd, 4th, 5th, 6th, 7th trials and the removal torque value in the 2nd trials(25.551 Ncm) was maximum and was decreased in 1311owing trials. The removal torque value in the 1st trial was significantly lower than that in the 2nd, 3rd, 4th trials and was significantly higher than that in the 8th, 9th, l0th trials(p<0.05). 4. In the 2nd, 3rd, 4th, 5th, 6th, 7th trials, the abutment screw was mainly influenced by settling effect and the higher preload was obtained In the 8th, 9th, l0th trials, the abutment screw was mainly influenced by adhesive wear and the progressively lower preload was obtained.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.3
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• pp.295-313
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• 2006

Statement of problem. Higher fracture rates were reported for Branemark implants placed in the maxilla and for 3.75 mm diameter implants installed in the posterior region. Purpose. The purpose of this study was to investigate the fracture of a fixture by finite element analysis and to compare different diameter of fixtures according to the level of alveolar bone resorption. Material and Methods. The single implant and prosthesis was modeled in accordance with the geometric designs for the 3i implant systems. Models were processed by the software programs HyperMesh and ANSA. Three-dimensional finite element models were developed for; (1) a regular titanium implant 3.75 mm in diameter and 13 mm in length (2) a regular titanium implant 4.0 mm in diameter and 13 mm in length (3) a wide titanium implant 5.0 mm in diameter and 13 mm in length each with a cementation type abutment and titanium alloy screw. The abutment screws were subjected to a tightening torque of 30 Ncm. The amount of preload was hypothesized as 650 N, and round and flat type prostheses were 12 mm in diameter, 9 mm in height were loaded to 600 N. Four loading offset points (0, 2, 4, and 6 mm from the center of the implants) were evaluated. To evaluate fixture fracture by alveolar bone resorption, we investigated the stress distribution of the fixtures according to different alveola. bone loss levels (0, 1.5, 3.5, and 5.0 mm of alveolar bone loss). Using these 12 models (four degrees of bone loss and three implant diameters), the effects of load-ing offset, the effect of alveolar bone resorption and the size of fixtures were evaluated. The PAM-CRASH 2G simulation software was used for analysis of stress. The PAM-VIEW and HyperView programs were used for post processing. Results. The results from our experiment are as follows: 1. Preload maintains implant-abutment joint stability within a limited offset point against occlusal force. 2. Von Mises stress of the implant, abutment screw, abutment, and bone was decreased with in-creasing of the implant diameter. 3. With severe advancing of alveolar bone resorption, fracture of the 3.75 and the 4.0 mm diameter implant was possible. 4. With increasing of bending stress by loading offset, fracture of the abutment screw was possible.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.4
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• pp.454-464
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• 1999

The metal ceramic crown is currently the most popular complete veneer restoration in dentistry, but in many cases, the metal cervical collar at the facial margin is unesthetic and unacceptable. Facial porcelain margin has been used in place of it. But this dose not solve the problems, such as dark gingival discoloration and cervical opaque reflection of porcelain veneer. Recently, metal copings which were designed to terminate its labio-cervical end on the axial walls coronal to the shoulder have been clinically used to solve the esthetic problem of metal ceramic crown. But in this design, porcelain veneer of labio-cervical area which is not supported by metal may not be able to resist the stress during cementation and mastication. The purpose of this study was to evaluate fracture strength and fractured appearance of crowns according to different coping designs. A resin maxillary left central incisor analogue was prepared for a metal ceramic crown, and metal dies were made with duplication mold. Metal copings were made and assigned to one of four groups based on facial framework designs: group 1, coping with 0.5mm metal collar; group 2, metal extended to the shoulder; group 3, metal extended to 1mm coronal tn the shoulder: group 4, metal extended to 2mm coronal to the shoulder. Copings and crowns were adjusted to be same size and thickness, and cemented to metal dies with zinc phosphate cement by finger pressure. Fracture strength was measured with Instron Universal Testing Machine. Metal dies were anchored in Three-way-vice at 3mm below finish line and at $130^{\circ}$ inclined to the long axis of the crown. Load was directed lingually at 2mm below midincisal edge. Load value at initial crack and at catastrophic fracture was recorded. The results obtained were as follows : 1. Fracture strength values at initial crack were higher in groups 1, 2 than in groups 3, 4 but this difference was not statistically significant(P<0.05). 2. Conventional metal collared crown had greater catastrophic fracture strength than any other collarless crowns. 3. The greater the labial metal coping reduction, the lower the catastrophic fracture strength of crowns but when more than 1mm of labial metal reduction was done, the difference in strengths was not statistically significant(p<0.05). 4. The strongest collarless coping design was group 2.

• The Journal of Korean Academy of Prosthodontics
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• v.39 no.3
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• pp.260-272
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• 2001

All-ceramic restorations have had a more limited life expectancy than metal ceramic restorations because of their low strength. Their relatively lower strength and resistance to fracture have restricted the use of all-ceramic crowns to anterior applications where occlusal loads are lower. But there has been increasing interest in all-ceramic restorations because patients are primarily concerned with improved esthetics. Many efforts have been made to in prove the mechanical properties of dental ceramics. This study was designed to elucidate the influence of the luting agent on the strength of the Empress 2 crown (staining technique) cemented on human teeth. Seventy extracted human permanent molar teeth were chosen. Teeth were prepared for Empress 2 crowns with milling machine on a surveyor. A dental bur was placed in the mandrel that was positioned so that the long axis of the bur was perpendicular to the surveyor base. Dimensions of the Empress 2 crown preparation were $6^{\circ}$ taper on each side, $1.5{\pm}0.1mm$ shoulder margin, and 4mm crown height. The luting cements used in this study were as follow: 1. Uncemented 2. Zinc phosphate cements (Confi-Dental) 3. Conventional glass ionomer cement : Fuji 1 (GC) 4. Resin-modified glass ionomer cements : Fuji plus (GC) 5. Adhesive cements : Panavia F (Kuralay), Variolink II (Vivadent), Choice (Bisco). Fracture test using Instron. The crowns were loaded in compressive force to evaluate the effect of these cements on the breaking strength of these all-ceramic crowns. A steel ball with a diameter of 4mm was placed on the occlusal surface and load was applied to the steel ball by a cylindrical bolt with a crosshead speed of 0.5mm per minute until fracture occurred. The fractured surface was examined using Scanning Electron Microscopic Image (SEM) to discover the correlation between fracture strength and bonding capacity. Within the limitation of this in vitro study design, the results were as follows : 1. fomentations significantly increased the fracture resistance of Empress ceramic crowns compared to control. Uncemented (206.9 N): ZPC (812.9 N): Fuji 1 (879.5 N): Fuji Plus (937.7 N): Choice (1105.4 N): Variolink II (1221.1 N): Panavia F (1445.2 N). 2. Resin luting agent, treated by a silane bond enhancing agents, yielded a significant increase in fracture resistance. In some of the Panavia F group, a fracture extended into dentin. 3. According to SEM images of fractured Empress crowns, the stronger the bond at both interfaces(crown and die), the more fracture strength was acquired.

• The Journal of Advanced Prosthodontics
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• v.1 no.2
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• pp.85-90
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• 2009

STATEMENT OF PROBLEM. Over the years, resin-bonded fixed partial dentures (RBFPDs) have gone through substantial development and refinement. Several studies examined the biomechanics of tooth preparation and framework design in relation to the success rate of RBFPDs and considered retention and resistance form essential for increase of clinical retention. However, these criteria required preparations to be more invasive, which violates not only the original intentions of the RBFPD, but may also have an adverse effect on retention due to loss of enamel, an important factor in bonding. PURPOSE. The object of this in vitro study was to compare the dislodgement resistance of the new types of RBFPDs, the conventional three-unit fixed partial denture, and conventional design of RBFPD (Maryland bridge). MATERIAL AND METHODS. Fifty resin mandibular left second premolars and second molars were prepared on dentiforms, according to the RBFPD design. After model fabrication (five group, n = 10), prostheses were fabricated and cemented with zinc phosphate cement. After cementation, the specimens were subjected to tensile loading at a cross head speed of 4 mm/min in a universal testing machine. The separation load was recorded and analyzed statistically using one-way analysis of variance followed by Duncan's multiple range test. RESULTS. Group V, the pin-retained RBFPDs, had the highest mean dislodgement resistance, whereas specimens of group II, the conventional RBFPDs, exhibited a significantly lower mean dislodgement resistance compared to the other 4 groups (P <.05). There were no significant differences between group I, III, and IV in terms of dislodgement resistance (P>.05). Group V had the highest mean MPa (N/$mm^2$) (P <.05). There was no significant difference between groups I, II, III and IV (P > .05). CONCLUSION. Within the limits of the design of this in vitro study, it was concluded that: 1. The modified RBFPDs which utilizes the original tooth undercuts and requires no tooth preparation, compared with the conventional design of RBFPDs, has significantly high dislodgement resistance (P < .05). 2. The modified RBFPDs which utilizes the original tooth undercuts and requires minimal tooth preparation, compared with the conventional FPDs, has significantly no difference in retention and dislodgement resistance)(P>.05). 3. The pin-retained FPDs showed a high dislodgement resistance compared to the conventional three-unit FPDs (P<.05).

• Journal of Dental Rehabilitation and Applied Science
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• v.16 no.2
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• pp.105-112
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• 2000

In-Ceram system is one of contemporary esthetic all ceramic restorations and has relatively high flexural strength. The purpose of this study was to evaluate the marginal fit of In-Ceram crown according to shoulder width and measuring position. In this study, twenty seven In-Ceram crowns devided into three groups, each prepared with shoulder width of 0.6mm, 0.9mm and 1.2mm. All specimens were cemented with glass ionomer cement. After cementation, specimens were measured marginal gap between the margin of the In-Ceram crown and the finishing line of resin master die by using a refrective microscope. Marginal gaps were recorded at the labial, lingual, mesial and distal measuring points on the resin master die. The results of this study were as follows: 1. Mean marginal fits of each group were $81.28{\mu}m$ in 0.6mm shoulder width, $70.78{\mu}m$ in 0.9mm shoulder width and $67.75{\mu}m$ in 1.2mm shoulder width. 2. There was significant difference between group 0.6mm and 0.9mm, 1.2mm.(p<0.05). 3. In comparison of marginal fit according to the measuring points, there was no significant difference.

• The Journal of the Korean bone and joint tumor society
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• v.15 no.1
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• pp.44-51
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• 2009

Purpose: We evaluated the results of surgical treatment for metastatic pathologic or impending pathologic fractures. Materials and Methods: From January 2004 to December 2007, 18 patients 19 cases were included. Male were 6 and female were 12. The mean age was 65.1. Mean follow up period was 15.2 months. Pathologic fractures were 14 and impending pathologic fractures were 5. MSTS score, periodic radiologic follow up and postoperative complications were evaluated. Results: The primary malignancies were 6 cases of multiple myeloma, 4 cases of renal cell carcinoma, 2 cases of cholangiocarcinoma, 2 cases of colon cancer, 2 cases of breast cancer and 2 cases of leiomyosarcoma. Metastatic lesions were 10 cases of femur, 4 cases of clavicle, 2 cases of humerus, 2 cases of tibia and 1 case of radius. Surgical options were curettage, cementation, internal fixation and arthroplasty. Mean MSTS score was 15.9. Postoperative complications were 1 case of infection, 1 case of local recurrence and 1 case of implant loosening. Ten patients were alive with disease, 8 patients died of disease. Conclusion: Surgical treatment of metastatic skeletal lesions allowed early ambulation and improving dexterity. It improved pain and emotional acceptance. Surgery is necessary for improving qualities of remaining lives.

• Restorative Dentistry and Endodontics
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• v.33 no.5
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• pp.443-451
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• 2008

The purpose of this study was to evaluate the effect of additional etching procedure prior to Maxcem resin cement application in indirect restoration cementation using push-out bonding strength. One hundred and two extracted human molars were used to make indirect resin restorations of gold inlay and Synfony. These restorations were cemented using Maxcem and Variolink II. Additional etching procedures were done for one group with Maxcem. Three groups have 17 specimens in both restoration types. Push-out bond strength was measured using multi-purpose tester and calculated for bonding strength per sqaure-millimeter area. The mean bonding strength values were compared using SPSS 12.0K program for one-way ANOVA and Scheffe's Test with 95% significance. Under the condition of this study, the additional etching procedure prior to usage of Maxcem resulted in reduced bond strength for both of restoration types.

• Journal of the Korean Institute of Gas
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• v.21 no.1
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• pp.27-33
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• 2017

In this study, the stability of trench slope was analysed in summer and winter seasons for the construction of pipelines in permafrost regions. The construction standards of Korea, Russia and UK were compared for obtaining an optimum trench shape for a pipeline of 30 in. diameter. Using the geotechnical properties of soil in Yakutsk (Russia), the stability of trench slope was analysed using Strength Reduction Method (SRM) according to the horizontal slope angle values of $0^{\circ}$, $10^{\circ}$, $20^{\circ}$ and $30^{\circ}$ and vertical slope angle values of $20^{\circ}$, $30^{\circ}$ and $40^{\circ}$. In both seasons, an increase in the slope angle results in a decrease in the factor of safety. The results show that horizontal slope angle of $30^{\circ}$ was not safe in summer season. At the vertical slope angle of $20^{\circ}$, trench side failure was observed, whereas, ground slope failure was observed at the vertical slope angles of $30^{\circ}$ and $40^{\circ}$. Due to the solidification of pore water at temperatures below $0^{\circ}C$, cementation of soil particles take place. Therefore, the trench slope was found to be stable in the winter season at all vertical and horizontal slop angles, except for special load cases and abrupt temperature changes.

• Restorative Dentistry and Endodontics
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• v.21 no.2
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• pp.619-627
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• 1996

There are increasing use of composite resin in the posterior teeth and the new indirect inlay technique was introduced for compensating much troubles faced in direct technique. Many researchers insisted that overall properties of restorative materials were enhanced by an additional curing but this technique still has a problems about using cement material. Resin inlay obtains retention force from friction and another adhesion to tooth structure. A shape of cavity preparation was noted but studies about cement thickness and bond strength with cavity divergency are rare. The purpose of this study is to assess the effect of cavity divergency on cement thickness and bond strength of resin inlay. Cavities, which divergency was $6^{\circ}$, $16^{\circ}$, and $26^{\circ}$ in each group, were prepared and their divergency was verified by Adobe Photoshop program through the image capture with stereo microscope and FlexCam. Inlays were fixed into the cavities with a resin cement, Superbond and were handled under chemical (in 75% ethanol for 24 hrs.) and thermal stress (500 cycles from $5^{\circ}$ to $55^{\circ}C$). MXT 70 (x400) was used for measuring the cement thickness and bond strength was evaluated with a universal testing machine. Following results were obtained : 1. The cement thickness in Mean (S.D.) were; 35.58 (10.31)${\mu}m$ in $6^{\circ}$ group, 35.97 (10.49)${\mu}m$ in $16^{\circ}$ group, and 41.43 (9.33)${\mu}m$ in $26^{\circ}$ group. But there was no significant difference between groups. 2. The bond strength in Mean (S.D.) were ; 33.18 (5.53)kg in $6^{\circ}$ group, 23.47 (13.40)kg in $16^{\circ}$ group, and 19.75 (10.48)kg in $26^{\circ}$ group. $6^{\circ}$ group showed significantly higher value compared to $16^{\circ}$ and $26^{\circ}$ groups (p<0.05). Although the results of this study indicate $6^{\circ}$ divergency will be good for resin inlay, cavity preparation with this type will have lots of difficulties in manufacturing, try-in, and cementation procedures, such as deformation. So it is concluded that $16^{\circ}$ divergent cavity preparation is recommended in resin inlay technique.