• Composites Research
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• v.15 no.4
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• pp.23-31
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• 2002

The two dimensional size effect of specimen gauge section ($length{\;}{\times}{\;}width$) was investigated on the compressive behavior of a T300/924 $\textrm{[}45/-45/0/90\textrm{]}_{3s}$, carbon fiber-epoxy laminate. A modified ICSTM compression test fixture was used together with an anti-buckling device to test 3mm thick specimens with a $30mm{\;}{\times}{\;}30mm,{\;}50mm{\;}{\times}{\;}50mm,{\;}70mm{\;}{\times}{\;}70mm{\;}and{\;}90mm{\;}{\times}{\;}90mm$ gauge length by width section. In all cases failure was sudden and occurred mainly within the gauge length. Post failure examination suggests that $0^{\circ}$ fiber microbuckling is the critical damage mechanism that causes final failure. This is the matrix dominated failure mode and its triggering depends very much on initial fiber waviness. It is suggested that manufacturing process and quality may play a significant role in determining the compressive strength. When the anti-buckling device was used on specimens, it was showed that the compressive strength with the device was slightly greater than that without the device due to surface friction between the specimen and the device by pretoque in bolts of the device. In the analysis result on influence of the anti-buckling device using the finite element method, it was found that the compressive strength with the anti-buckling device by loaded bolts was about 7% higher than actual compressive strength. Additionally, compressive tests on specimen with an open hole were performed. The local stress concentration arising from the hole dominates the strength of the laminate rather than the stresses in the bulk of the material. It is observed that the remote failure stress decreases with increasing hole size and specimen width but is generally well above the value one might predict from the elastic stress concentration factor. This suggests that the material is not ideally brittle and some stress relief occurs around the hole. X-ray radiography reveals that damage in the form of fiber microbuckling and delamination initiates at the edge of the hole at approximately 80% of the failure load and extends stably under increasing load before becoming unstable at a critical length of 2-3mm (depends on specimen geometry). This damage growth and failure are analysed by a linear cohesive zone model. Using the independently measured laminate parameters of unnotched compressive strength and in-plane fracture toughness the model predicts successfully the notched strength as a function of hole size and width.

• Journal of Dental Rehabilitation and Applied Science
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• v.16 no.1
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• pp.51-60
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• 2000

The purpose of this study was to compare the microleakage at the interface of cast post and tooth according to the type of cement. Forty anterior teeth with single root were used. The teeth were cut 2 mm coronal from the cementoeamel junction and chamfer finish line was made on 1 mm coronal from the cementoeamel junction. After the routine endodontic treatment, post space was prepared using #5.5 Parapost drill to a depth of 7 mm. After the pick up impression, core building was made to 3 mm of clinical crown with burnout wax, then post and core was cast with nonprecious metal. The teeth were divided into four groups of ten each. In Group I, post and core were cemented with Fleck's(Zinc phosphate cement) In Group II, post and core were cemented with Fuji I(Glass ionomer cement) In Group III, post and core were cemented with Superbond C & B(Composite resin cement) In Group IV, post and core were cemented with Panavia 21(Composite resin cement) All cemented teeth were stored in normal saline at $37^{\circ}C$ for 7 days and thermocycled from $5^{\circ}C$ to $55^{\circ}C$ for 500 cycles with a dwell time of 30 seconds. After thermocycling, teeth were immersed in 1% Basic fuchsin dye for 48 hours. All 40 teeth were then embedded in the epoxy resin and cut buccolingually with a cutting instrument. The degree of penetration of dye at interface was graded on a scale of 0 to 4 using a stereomicroscope at 25 to 40 times magnification. Through the findings of this study, the following conclusion were obtained. 1. All the groups showed the microleakage at the interface of cast post core and tooth. 2. Group I showed the highest microleakage score among the groups with a significant difference(p<0.05). 3. Group II showed higher microleakage score than Group III and Group IV with a significant difference(p<0.05). 4. Group IV showed the lowest microleakage score but there were no significant difference with Group III(p>0.05).

• Composites Research
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• v.12 no.4
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• pp.71-78
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• 1999

To determine the effect of chemical structure of linear amine curing agents on thermal and mechanical properties, standard epoxy resin DGEBA was cured with diaminodiphenyl methane (DDM), diaminodiphenyl sulphone (DDS) in a stoichiometrically equivalent ratio. From this work, the effect of aromatic amine curing agents. In contrast, the results show that the DGEBA/DDS cure system having the sulfone structure between the benzene rings had higher values in the conversion of epoxide, density, shrinkage (%), glass transition temperature, tensile modulus and strength, flexural modulus and strength than the DGEBA/DDM cure system having methylene structure between the benzene rings, whereas the DGEBA/DDM cure system presented higher values in the maximum exothermic temperature, thermal expansion coefficient, and thermal stability. These results are caused by the relative effects of sulfone group having strong electronegativity and methylene group having (+) repulsive property and stem from the effect of the conversion ratio of epoxide group. The result of fractography shows that the each grain size of the DDM/DGEBA system with feather-like structure is larger than that of the DDS/DGEBA system.

• The Journal of Korean Academy of Prosthodontics
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• v.32 no.1
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• pp.120-147
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• 1994

This study was performed for the purpose of evaluating the stress distribution around threaded type implants, cylindrical type implants and teeth connected with rigid or non-rigid connector. The stress distribution around the surrounding bone was analyzed by three-dimensional photoelastic method. Twelve mandibular photoelastic epoxy resin models and a circular polariscope were used to record the isochromatic fringes. After the stress distribution around the implant and tooth was observed, the results were as follows ; 1. In threaded type implants, stress concentrated patterns were observed at the neck either vertical or 25 degree lateral force. 2. The stress concentrated patterns were observed at the tooth apical portion and neck portions of the implant and tooth when a threaded implant was connected with the tooth by either a rigid or non-rigid connector. More force was generated at the tooth neck portion by a rigid connector and more force at the implant neck portion by a non-rigid connector. 3. The stress concentrated patterns were observed at the apical portion of the implant and tooth when a cylindrical type ,implant was connected with the tooth either by a rigid or non-rigid connector. More force was generated at the tooth apical portion by a rigid connector and more force at the neck portion of the tooth and implant by a non-rigid connector. 4. The stress around the tooth was more equally distributed in a threaded type implant than in a cylindrical implant when the tooth was connected with either a rigid or non-rigid connector. 5. The stress around a threaded type implant was progressively more equally distributed in the following order : 1) when used a single implant, 2) a non-rigid connection with the implant and tooth, 3) a rigid connection with the implant and tooth, 4) a rigid connection with two implant fixtures.

• Restorative Dentistry and Endodontics
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• v.31 no.4
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• pp.300-311
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• 2006

The purpose of this study is to evaluate prospectively the effect of different bonding systems and retention grooves on the clinical performance of resin restorations in non-carious cervical lesions (NCCLs). Thirty-nine healthy adults who had at least 2 NCCLs in their premolar areas were included in this study. One hundred and fifty teeth were equally assigned to six groups: (A) Scotchbond Multi-Purpose (SBMP, 3M ESPE, St. Paul, MN, USA, 4th generation bonding system) without retention grooves; (B) SBMP with retention grooves; (C) BC Plus (Vericom Co., Anyang, Gyeonggido, Korea, 5th generation bonding system) without retention grooves; (D) BC Plus with retention grooves; (E) Adper Prompt (3M ESPE, Seefeld, Germany, 6th generation bonding system) without retention grooves; (F) Adper Prompt with retention grooves. All cavities were filled with a hybrid composite resin. Denfil (Vericom Co., Anyang, Gyeonggido, Korea) by one operator. Restorations were evaluated at baseline and at 6-month recall, according to the modified USPHS (United States Public Health Service) criteria. Additionally, clinical photographs were taken and epoxy resin replicas were made for SEM evaluation. At 6-month recall, there were some differences in the number of alpha ratings among the experimental groups. But, despite the differences in the number of alpha ratings, there was no significant difference among the 3 adhesive systems (p < 0.05). There was also no significant difference between the groups with or without mechanical retention (p < 0.05). Follow-ups for longer periods than 6 months are needed to verify the clinical performance of different bonding systems and retention grooves.