Caspases-dependent Apoptosis in Human Melanoma Cell by Eugenol / 대한해부학회지

Malignant melanoma is a highly metastatic tumor, resistant to chemotherapy and radiotherapy. Recent studies have suggested that many therapeutic agents used against cancer mediate their effects by induction of apoptosis of the cancer cells. Eugenol enhances the generation of tissue-damaging free radicals and inflammation or allergic reactions. In particular, it is more cytotoxic against cancer cells compared with normal fibroblasts. This study was performed to investigate whether the cytotoxic effect of eugenol is associated with the induction of apoptosis and involves activation of caspase in the human melanoma G361 cells. Eugenol-induced apoptosis was confirmed by MTT assay, Hemacolor stain, Hoechst stain, DNA electrophoresis, and Western blot analysis. Eugenol had a significant dose- and time-dependent inhibitory effect on the viability of G361 cells. Eugenol treatment induced caspase-3 and -6 cleavage, and activation. The caspase-3 substrates PARP and DFF45 are cleaved during eugenol-induced apoptosis. It was found that the casapase-6 substrate lamin A was cleaved, whose cleavage has been reported to be necessary for complete condesation of DNA during apoptosis. These results suggest that eugenol may constitute a potential antitumor compound against melanoma occurring in the skin and oral mucosa.

The effect of sprue design on the internal porosity of titanium castings / 대한치과보철학회지

STATEMENT OF PROBLEM: The high melting temperature and chemical reactivity of titanium necessitates casting machines different from those used in conventional casting. Despite the new developments in Ti casting systems, inadequate mold filling and internal porosity are frequently observed casting defects. Therefore, the study on the fabrication technique including sprue design to solve these casting defects is still necessary. PURPOSE: The purpose of this study was to evaluate the effect of sprue design and cross sectional area of sprue on the internal porosity. MATERIALS AND METHODS: 30 simulated cast three units titanium crowns were prepared. 5 cast crowns for each with different sprue design(sinlge sprue, double sprue and plate sprue) of two cross sectional areas(small and large cross sectional areas) were fabricated. The sections of titanium castings were photographed in a microscope at x100 magnification to record internal porosities. RESULTS AND CONCLUSION: Within the limits of this study, the following conclusions were drawn: 1. There was a significantly lower in internal porosity of titanium castings for large cross sectional area of sprue group than the small group(P>.05). 2. There was no significant difference in internal porosity among sprue designs in similar cross sectional area of sprue(P>.05).

Effect of taper and surface area of inner crown on the retentive force of electroformed outer crown / 대한치과보철학회지

PURPOSE: With gold electroforming system for the double crown, the secondary crown is electroformed directly onto the primary crown. An even thick layer of high precision can be acquired. It is thought that the retention of electroformed outer crown is primarily acquired by the adhesive force (surface tension) through the saliva which is interposed between precisely fitted inner and outer crown. The purpose of this study was to investigate the effect of taper and surface area of inner crown on the retentive force of electroformed outer crown according to the presence of saliva. MATERIALS AND METHODS: 32 titanium inner crowns with cervical diameter of 8 mm and cone angles of 0, 2, 4, 6 degrees, which had same surface area by regulated height, were machined on a lathe. Another 32 titanium inner crowns with cone angles of 0, 2, 4, 6 degrees, which had doubled surface area by increased cervical diameter, were fabricated. Eight specimens of each group, for a total of 64 titanium inner crowns, were prepared. The electroformed outer crowns were fabricated directly on the inner crowns by using electroforming machine(GAMMAT free, Gramm Technik, Germany). The tertiary frameworks were waxed-up on the electroformed outer crown and cast using nonprecious alloy(Rexillium(R)III, Jeneric(R)/ Pentronh(R) Inc., USA). The cast metal frameworks were sandblasted with alubimium oxides and cemented using resin cement(Superbond C and B, Sun Medical Co., Japan) over the electroformed copings of each specimen. Then, artificial saliva(Taliva(R), Halim Pharm Co., Korea) was sprayed between the inner and outer crown, and they were connected under 5 kg force. The retentive force was measured by the universal testing machine(Tinius Olsen 1000, Tinius Olsen, USA) with a cross-head speed of 66.67 mm/sec. The direction of cross-head travel was exactly aligned with the path of removal of the respective specimens. This measurement procedures for retentive force of electroformed outer crown with artificial saliva were repeated in the same way without presence of artificial saliva. RESULTS AND CONCLUSION: The following conclusions were drawn: 1. The retentive force of electroformed outer crown was decreased according to increased taper of inner crown(P.05).

Influence of tungsten carbide/carbon coating on the preload of implant abutment screws / 대한치과보철학회지

STATEMENT OF PROBLEM: In order to increase preload with reducing the friction coefficient, abutment screws coated with pure gold and Teflon as dry lubricant coatings have been introduced. But the reported data indicate that if screw repeated tightening and loosening cycle, an efficiency of increasing preload was decreased by screw surface wearing off. PURPOSE: This study was to evaluate the influence of tungsten carbide/carbon coating, which has superior hardness and frictional wear resistance, on the preload of abutment screws and the stability of coating surface after repeated closures. MATERIAL AND METHOD: The rotational values of abutment screws and the compressive forces between abutment and fixture were measured in implant systems with three different joint connections, one external butt joint and two internal cones. Moreover, the stability and the alteration of coating surface were examined by comparison of the compressive force and the removable torque values during 10 consecutive trials, observation with scanning electron microscope and analyzed the elemental composition with energy dispersive x-ray spectroscopy. RESULTS AND CONCLUSION: 1. Application of coating resulted in significant increase of compressive force in all implant systems(P.05). 3. Removable torque values were greater with non-coated screw than that with coated screw (P.05). 5. After repeated trials, the surface layer of coated screw was maintained relatively well. However, surface wearing and irregular titanium fragments were found in non-coated screw.

A study on the occlusal plane and the vertical dimension in Korean adults with natural dentition / 대한치과보철학회지

STATEMENT OF PROBLEM: Anatomic landmarks have been used in the orientation of occlusal plane and the determination of vertical dimension for edentulous patients. Such as labial vestibules of anterior region and hamular notches, retromolar pads of posterior region are very useful anatomic landmarks for fabrication of occlusion rim because they are to be identified on master casts. Therefore, if average distances between landmarks of maxillae and mandible in dentate subjects are measured and applied, not only occlusal plane but also vertical dimension can be established initially. PURPOSE: The purpose of this study is to measure vertical distances between anatomic landmarks and to present a guide to the orientation of occlusal plane and the determination of vertical dimension of edentulous patients. MATERIAL AND METHOD: Upper and lower border-molded casts were made in 93 Korean dentulous subjects, mean age 25 years. Incisal edges of central incisors, bottoms of labial vestibules, hamular notches and the half level of retromolar pads were marked on casts. Measurements of vertical distances from incisal edge of central incisor to the bottom of labial vestibule, between upper and lower bottoms of labial vestibules, from hamular notch to retromolar pad and from hamular notch to the occlusal plane established by the incisal edge of maxillary central incisor and mesiopalatal cusps of both maxillary first molars were made on each cast. RESULTS AND CONCLUSION: 1. The mean distance from the incisal edge of central incisor to the bottom of labial vestibule was 20.8mm(SD 1.7) on upper casts and 17.3mm(SD 1.4) on lower casts. 2. The mean distance between both bottoms of labial vestibules of upper and lower casts was 35.0mm(SD 2.7). 3. The mean distance from hamular notch to the half level of retromolar pad was 5.0mm(SD 1.3). 4. The mean distance from hamular notch to occlusal plane was 7.9mm(SD 1.5). 5. Distances from incisal edge of central incisor to labial vestibule on lower casts(p<0.01) and from hamular notch to retromolar pad(p<0.0001) were greater in male than in female.

Shear bond strength of veneering ceramic to electroformed gold with three different surface treatment / 대한치과보철학회지

PURPOSE: The success of the bonding between electroformed gold and ceramic is dependent on the surface treatment of the pure gold coping. The purpose of this study was to evaluate the bonding strength between the electroformed gold and ceramic with varying surface treatment. MATERIALS AND METHODS: A total of 32 disks, 8 were using conventional ceramometal alloy, 24 were using electroforming technique as recommended by manufacturer, were prepared. 24 electroformed disks were divided 3 groups according to surface treatment, i.e. 50 microns aluminium oxide sandblasting(GES-Sand), gold bonder treatment(GES-Bond) and Rocatec(TM) system(GES-Rocatec). For control group of conventional alloy 50 microns aluminium oxide treatment was done(V-Supragold). Energy dispersive x-ray analysis and scanning electron microscope image were observed. Using universal testing machine, shear bond strength and bonding failure mode at metal-porcelain interface were measured. RESULTS AND CONCLUSION: The following conclusions were drawn: 1. In the energy dispersive x-ray analysis, the Au was main component in electroformed gold(99.9wt%). After surface treatment, a little amount of Al2O3(2.4wt%) were found in GESSand, and SiO2(4wt%) in GES-Bond. In GES-Rocatec, however, a large amount of SiO2(17.4wt%) were found. 2. In the scanning electron microscopy, similar pattern of surface irregu larities were observed in V-Supragold and GES-Sand. In GES-Bond, surface irregularities were increased and globular ceramic particles were observed. In GES-Rocatec, a large amount of silica particles attached to metal surface with increased surface irregularities were observed. 3. The mean shear bond strength values(MPa) in order were 22.9+/-3.7 (V-Supragold), 22.1+/- 3.8(GES-Bond), 20.1+/-2.8(GES-Rocatec) and 13.0+/-1.4 (GES-Sand). There was no significant difference between V-Supragold, GES-Bond, and GES-Rocatec.(p>0.05) 4. Most bonding failures modes were adhesive type in GES-Sand. However, in V-Supragold, GESBond and GES-Rocatec, cohesive and combination failures were commonly observed. From this result, with proper surface treatment method electroformed gold may have enough strength compare to conventional ceramometal alloy.

A study of precise fit of the CAM zirconia all-ceramic framework / 대한치과보철학회지

STATE OF PROBLEM: Zirconia all-ceramic restoration fabricated with CAM system is on an increasing trend in dentistry. However, evaluation of the marginal and internal fits of zirconia bridge seldomly have been reported. PURPOSE: This study was to evaluate the fit of margin and internal surface in posterior 3-unit zirconia bridge framework fabricated with CAM system(DeguDent, Germany). MATERIAL AND METHOD: Preparations of secondary premolar and secondary molar on artificial resin model were performed for fabrication of 3-unit posterior bridge framework. Fits of 5 zirconia bridge framework were compared with 5 precious ceramo-metal alloy framework(V-GnathosPlus, Metalor, Switzerland), and prepared margins were designed to chamfer and shoulder finishing line. Each framework was cemented to epoxy resin model with reinforced glass ionomer(FujiCEM, GC Co., Japan), embedded in acrylic resin and sectioned in two planes, mesiodistal and buccolingual. Samples were divided into six pieces by sectioning and had two pieces of each surface(i.e. mesial, distal, buccal and lingual surface) per abutment, so there were eight measuring points in each abutment. External gap was measured at the margin and internal gaps were measured at the margin, axial and occlusal surface. Gaps were observed under the measuring microscope(Compact measuring microscope STM5; Olympus, Japan) at a magnification of * 100. T-test were used to determine the statistic significance of the different gaps between zirconia and metal framework. RESULTS AND CONCLUSION: 1. External and internal marginal gaps of zirconia and metal framework were in clinically acceptable range. External marginal gaps were not different significantly between zirconia(81.9 micrometer) and metal(81.3 micrometer) framework and internal marginal gaps of zirconia(44.6 micrometer) were smaller than those of metal framework(58.6 micrometer). 2. Internal axial gaps of zirconia framework(96.7 micrometer) were larger than those of metal framework(78.1 micrometer) significantly and adversely, internal occlusal gaps of zirconia framework(89.4 micrometer) were smaller than those of metal framework(104.9 micrometer) significantly. 3. There were no significant differences in external and internal marginal gaps between chamfer and shoulder finish line when zirconia frameworks were fabricated.

Comparative studies of retentive forces in maxillary overdenture bar attachments / 대한치과보철학회지

STATEMENT OF PROBLEM: It could be hypothesised that attachments, which provide more retention against vertical and horizontal dislodgement, will be associated with more favorable parameters of oral function. PURPOSE: This study was to provide data of initial retentive force and retention loss of different bar attachment systems recommended for use with maxillary implant overdentures. MATERIAL AND METHOD: 4 implants were placed in the anterior region of edentulous maxilla, five different systems of bar attachment were fabricated as follows: cantilevered Hader bar using clips (Type 1), Hader bar using clips without cantilever (Type 2), Hader bar using clip and ERA attachment orange male (Type 3), Hader bar using clip and ERA attachment white male (Type 4), and Bar using magnets (Type 5). Each samples were placed in the universal testing machine for determination of retentive forces(at initial and after every 200 cycles up to 1,000 cycles). Results and Conclusion 1. Attachment type 1 showed the biggest initial retentive force followed by type 3, type 2, type 4, and lastly type 5( p<0.001). 2. After 1,000 cycles of repeated removals of attachments, significant loss of retentive forces was taken place except for attachment type 5. 3. After 1,000 cycles of repeated removals, the loss of retentive force between type 1 and type 2, which used Hader bar and clip attachments, was greater in type 1 that had wider clip formation. And between type 3 and type 4, which used ERA attachments, the loss of retentive force was greater in type 4 that had white male attached (p<0.001). 4. After 1,000 cycles of repeated removals, attachment type 3 showed the biggest retentive force followed by type 2, type 4, type 1 and lastly type. 5. There was no significant difference between attachment type 3 and 4, and type 4 and 1(p<0.001).

Effect of surface treatments of zirconia ceramic on the bond strength of resin cements / 대한치과보철학회지

STATEMENT OF PROBLEM: It is not clear how to make a stable bonding between zirconia ceramic and resin cement. And the study about surface treatment of zirconia ceramic or bonding resin cement are not enough. PURPOSE: To measure and compare the shear bond strength of some resin cements on zirconia ceramic after different surface treatments. MATERIAL AND METHOD: 48 ceramic discs were made of 3 ceramic materials, zirconia ceramics Zi-Ceram), heat-pressed ceramics (IPS Empress 2) and slip cast alumina ceramics (In-Ceram). According to the surface treatments of ceramic specimens and resin cements, specimens were classified into 6 groups and each group was composed of 8 specimens. For the surface treatment of Zi-Ceram group (test group), sandblasting and diamond bur preparation were applied and Superbond C&B and Panavia F were bonded respectively. For IPS Empress 2 group (control group), Variolink II was bonded after sandblasting, acid etching, silanization and for In-Ceram ALUMINA group (control group), Panavia F was bonded after sandblasting. After storing specimens in distilled water for 24 hours, the shear bond strength was measured by the universal testing machine. RESULTS AND CONCLUSION: 1. Zi-Ceram group with Superbond C&B cement showed higher bond strength than with Panavia F cement regardless to the surface treatments (p0.05). 3. Zi-Ceram group with sandblasting and Superbond C&B cement (12.1MPa) showed the highest bond strength. The bond strength of this group was not significantly different from In-Ceram ALUMINA group (10.4MPa) (p>0.05) and lower than IPS Empress 2 group (15.9MPa) (p<0.05).

Effect of anchorage systems and palatal coverage of denture base on load transfer with maxillary implant-supporting overdentures : A three-dimensional photoelastic stress analysis / 대한치과보철학회지

PURPOSE: The purpose of this study was to determine the effect of anchorage systems and palatal coverage of denture base on load transfer in maxillary implant-supported overdenture. MATERIAL AND METHODS: Maxillary implant-supported overdentures in which 4 implants were placed in the anterior region of edentulous maxilla were fabricated, and stress distribution patterns in implant supporting bone in the case of unilateral vertical loading on maxillary right first molar were compared with each other depending on various types of anchorage system and palatal coverage extent of denture base using three-dimensional photoelastic stress analysis. Two photoelastic overdenture models were fabricated in each anchorage system to compare with the palatal coverage extent of denture base, as a result we got eight models : Hader bar using clips(type 1), cantilevered Hader bar using clips(type 2), Hader bar using clip and ERA attachments(type 3), cantilevered milled-bar using swivel-latchs and frictional pins(type 4). RESULT: 1. In all experimental models, the highest stress was concentrated on the most distal implant supporting bone on loaded side. 2. In every experimental models with or without palatal coverage of denture base, maximum fringe orders on the distal ipsilateral implant supporting bone in an ascending order is as follows; type 3, type 1, type 4, and type 2. 3. Each implants showed compressive stresses in all experimental models with palatal coverage of denture base, but in the case of those without palatal coverage of denture base, tensile stresses were observed in the distal contralateral implant supporting bone. 4. In all anchorage system without palatal coverage of denture base, higher stresses were concentrated on the most distal implant supporting bone on loaded side. 5. The type of anchorage system affected in load transfer more than palatal coverage extent of the denture base. CONCLUSION: To the results mentioned above, in the case of patients with unfavorable biomechanical conditions such as not sufficient number of supporting implants, short length of the implant, and poor bone quality, selecting a resilient type attachment or minimizing the distal cantilevered bar is considered to be an appropriate method to prevent overloading on implants by reducing cantilever effect and gaining more support from the distal residual ridge.

The fit of zirconia core fabricated with CAD/CAM system / 대한치과보철학회지

STATEMENT OF PROBLEM: The use of zirconia prostheses fabricated with CAD/CAM system is on an increasing trend in dentistry. However, evaluation of the fit related to internal relief and marginal reproducibility of zirconia has not been reported. PURPOSE: This study was to evaluate the fit related to internal relief and marginal reproducibility of zirconia core fabricated with CAD/CAM system. Materials and methods: The evaluation was based on 30 zirconia cores and 5 IPS-Empress2 cores. Zirconia cores were fabricated in different conditions of internal relief(0, 10, 20, 30, 40 and 50 micrometer), and IPS-Empress2 cores were fabricated in accordance with the manufacturer's instructions. Before cementation, the marginal discrepancies of cores were measured on metal die. And then, each core was cemented to stone die, embedded in an acrylic resin and sectioned in two planes(mesiodistally and labiopalatally). The internal gaps were measured at the margin and axial surface. Measurements for the marginal discrepancies, the internal marginal gaps and the internal axial gaps were performed under a measuring microscope(Compact measuring microscope STM5; Olympus, Japan) at a magnification of *100. In addition, the marginal configurations of metal die, zirconia core and IPS-Empress2 core were examined with SEM(S-2700, Hitachi, Japan). RESULTS: Within the limits of this study the results were as follows. 1. Compared with IPS-Empress2 cores, the marginal discrepancies of zirconia cores had no significant differences, the internal marginal gaps were statistically smaller and the internal axial gaps were statistically larger in each condition of internal relief. 2. The marginal discrepancies and the internal marginal gaps of zirconia cores had no significant differences related to the conditions of internal relief(P>0.05). 3. The internal axial gaps of zirconia cores with 0.20micrometer for internal relief were significantly larger than that with 50micrometer(P<0.0001). 4. SEM micrographs showed favorable marginal reproducibility of zirconia core and smooth texture on the milling surface. CONCLUSION: The marginal discrepancy and the internal gaps of zirconia core were clinically acceptable and the milling surface was showed smooth texture. For fabrication of the durable esthetic restoration, further investigations on complex design of core, milling accuracy, compatability of enamel porcelain and porcelain firing seems to be needed.

A Study on the Bond Strength of Reline Resin to Pressure Injection Type Thermoplastic Denture Base Resin / 대한치과보철학회지

The purpose of this study was to evaluate the bond strength of reline resin to pressure injection type thermoplastic denture base resin.The denture base resins used in this study were Hipolycarbonate(High Dental Co.,Japan),Acetal dental(Pressingdental s.r.l.,Repubblica di San Marino)of thermoplastic resin and Acron MC(GC Dental Industrial Co.,Japan)of heatcured resin.The reline resins used were Lucitone 199(Dentsply international Inc.,USA),Tokuso rebase(Tokuyama Corp.,Japan),and Lightdon-U(Dreve-Dentamid-Gmbh,Germany).The reline resins are representative of heat-cured,self-cured,and light-cured resin respectively.Bond strength was examined by use of a three-point transverse flexural strength test. The results were as follows: 1.The bond strength of Lucitone 199 to Acron MC was the highest. 2.The bond strengths of Lucitone 199 and Tokuso rebase to Hi-polycarbonate resulted in a value of approximately one half that of Lucitone 199 to Acron MC,and there were no significant differences between these and the bond strength of Tokuso rebase to Acron MC(p<0.05). 3.The bond strengths of reline resins to Acetal dental were lower than those of reline resins to Hi-polycarbonate. 4.For all base resins Lightdon-U showed lower bond strength than the other reline resins.

Shear Bond Strengths between Abrasion-Resistant Denture Teeth and Composite Resins / 대한치과보철학회지

This study investigated the shear bond strengths between abrasion-resistant denture teeth and composite resins according to surface treatments. Denture teeth for this study were Trubyte IPN teeth(Dentsply Inc.,USA)with interpenetrating polymer network and Endura Posterio(Shofu Inc.,Japan)of composite resin teeth,and restorative composite resins were Clearfil FII (Kuraray,Japan)of the self-cured composite resin and Z100(3M Dental Product,USA)of the light-cured composite resin.Five different surface treatments were evaluated:(1)50 mu m Al2O3 sandblasting;(2)#100 carbide paper;(3)chloroform;(4)retentive holes;and (5)no treatment. after surface treatments,denture teeth were examined by scanning electron microscopy(SEM), and the maximum shear bond strengths between abrasion-resistant denture teeth and composite resins were measured using Instron. The results were as follows; 1.IPN teeth treated with sandblasting had the highest shear bond strength,and Endura treated with sandblasting and carbide paper had significantly greater shear bond strength than with any other surface treatment. 2.Regardless of composite resins,the shear bond strength on Endura was greater than on IPN teeth. 3.Regardless of denture teeth,the shear bond strength of Clearfil FII was greater than of Z100. 4.In appearance of SEM,IPN teeth treated with sandblasting showed generalized roughness on the all of surface,however,carbide paper treatment resulted in partly rough.Endura treated with sandblasting and carbide paper showed similar surface characteristics.Wetting denture teeth surface with chloroform removed the debris and created a particle-free and smooth surface.

Effects Of Current Density And Etching Time On Etching Depth And Surface Roughness Of Ni-Cr-Be Alloy / 대한치과보철학회지

The purpose of this study is to investigate which current densities and etching times will result in an optimal etching depth and surface roughness when an Ni-Cr-Be alloy is etched with 30% perchloric acid(HClO4 ). For this study,observations were made by means of an optical three-dimen-sional surface roughness measuring machine and a scanning electron microscope. The etchings took place under the following conditions using current densities of 300mA/cm2, 450mA/cm2, 600mA/cm2 and 750mA/cm2, and using etching time of three, five, six, seven and nine minutes. Under the conditions, the experiments reached the following conclusions. 1. When the current density is above 450mA/cm2 and the etching time is longer than five min-utes, the etching depth increased as the current density and etching time increased. And the surface roughness was significantly influenced by the interaction of the current density and etching time. 2. Under the etching conditions of 600mA/cm2 and five minutes, the optimal etching depth for a resin cement space and the highest surface roughness for mechanical retention were obtained. The etching depth and surface roughness were 32.86 micrometer and 7.90 micrometer, respectively. 3. Observations under the scanning electron microscope showed that both the corrosion at the grain boundary and the corrosion within the grain occurred on the etched surface. It was also observed that the corrosion at the grain boundary became more severe as the current density and etching time increased. In addition, at higher current densities and longer etching times, general corrosion appeared.

MARGINAL DISCREPANCY AND RETENTION FORCE OF CONICAL TELESCOPE OUTER CROWN WITH CO-CR-TI ALLOY / 대한치과보철학회지

The purpose of this study was to investigate the effects of investing conditions on the marginal discrepancy of conical telescope outer crown with Co-Cr-Ti alloy(Dentitan) and to compare the marginal discrepancy and the retention force of outer crowns using different pattern materials (plastic foil, casting wax, pattern resin). To evaluate the effects of investing conditions on the marginal discrepancy, patterns with plastic foil were invested under three different liquid/powder ratio conditions using phosphate bonded investment (Univest-nonprecious): standard, 10% decreased and 10% increased. At each liquid/powder ratio condition, metal ring was lined with single or double layers of ceramic ring liner. The marginal discrepancy of outer crown at different investing conditions was measured by x 100 compact measuring microscope(STM5, Olympus, Japan). For measurement of the marginal discrepancy and the retention force of outer crown using different pattern materials, the investing condition of 10% decreased liquid/powder ratio and double layers of ring liner was selected because this investing condition resulted in the best fit of outer crown. Marginal discrepancy was measured in the same way above and retention force on universal testing machine. Under the conditions of this study, the following conclusions were drawn: 1. The thickness of ring liner had more influence on the marginal discrepancy of outer crown than the liquid/powder ratio, and the acceptable marginal fitness could not be expected at the investing condition directed by investment manufacturer. 2. There were no differences in the marginal discrepancy of outer crown among three different pattern materials 00.05). 3. Casting wax showed the greatest retention force(1640g) of outer crown, followed by pattern resin(1110g), plastic foil(820g). However, there was no significant difference between plastic foil and pattern resin(p>0.05). 4. Plastic foil showed the least variation in marginal discrepancy and retention force.

Effect of Degassing Condition on Ceramic Bond Strength of Ni-Cr Alloys / 대한치과보철학회지

This study evaluated the effect of dagassing on the ceramic bond strength of two Ni-Cr alloys under varying holding time at the upper limit temperature and atmospheric conditions. Metal specimens were divided into 5 groups for each alloy according to degassing conditions prior to porcelain application : no degassing, degassing under vacuum without hold, degassing under vacuum with hold for 5min. and 10 min. respectively at the upper limit temperature and degassing in air. Total number of metal ceramic specimens was eighty and each group had eight specimens : The ceramic bond strength was measured by four-point flexural test using Instron and the fractured surface was examined under SEM. The results obtained were as follows. 1. Degassing in air improved the ceramic bond strength of Ni-Cr alloys. 2. in degassing under vacuum, hold at the upper limit temperature was advantageous to the ceramic bonding of Ni-Cr alloys. 3. After ceramic metal bond test, metal surfaces were partially covered with the thin porcelain layer, and the cohesive failures in porcelain were predominant in groups showing higher ceramic bond strength.

COLORIMETRIC ANALYSIS OF COLOR DIFFERENCES BETWEEN DENTIN PORCELAINS / 대한치과보철학회지

The purpose of this study is to evaluate the color differences that can exist between differnet brands of dentin porcelain having identical shade designations. The instrumental colorimetric technique was used to determine these differences. The three brands of dentin porcelain used were Vita VMK-68, Shofu Vintage, and Ceramco II. The three shades selected were the Vita Lumin shades A2, B2, and C2. The color difference values were compared with each other using L*, a*, b*, three variables of the CIELAB color system, and E. The results of this study were as follows: 1. Corresponding shades of different brands of dentin porcelain produced different L*, a*, b* values. 2. The greatest E value in corresponding shade was found to exist between Ceramco II and Shofu Vintage, followed by between Vita VMK-68 and Ceramco II, and then between Vita VMK-68 and Shofu Vintage. 3. The E values in shade C2 were mainly influenced by L* value ; however none of L*, a*, b* values had greater influence on E values than the others in shade A2, B2. 4. Shofu Vintage had the highest b* value, followed by Vita VMK-68, and then Ceramco II.

A STUDY FOR SETTING AND THERMAL EXPANSION OF DENTAL SOLDERING INVESTMENTS / 대한치과보철학회지

The purpose of this study was to investigate setting and thermal expansion of dental soldering investments. In order to compare expansion rates and to investigate the effect of water/powder ratio on expansion, setting and thermal expansion of four dental soldering investments were measured under three different water/powder ratio conditions: standard, 20% decreased and 20% increased. Setting expansion of investments was measured by use of dialgauge method. Each measurement was started two minutes later from the beginning of spatulation and recorded every one minute for one hour. Thermal expansion of cylindrical test specimens, 10mm diameter, 50mm length, was recorded in a Thermodilatometer at heating rate of 10degrees C per minute from 25degrees C to 700degrees C. The results of this study were obtained as follows: 1. Setting expansion rates under the standard water/power ratio condition were 0.198% in Speed-E, 0.090% in Deguvest, 0.080% in CM and Hi-temp. Setting expansion of Speed-E was significantly different from those of CM, Deguvest and Hi-temp, and setting expansion of Deguvest was significantly different from those of CM and Hi-temp(p<.05). 2. Under the decreased water/powder ratio condition, there was significant increase in setting expansion of 4 dental soldering investments(p<.05). 3. There were no significant differences in setting expansions of investments except Hi-temp between standard and increased water/powder ratio condition(p<.05). 4. Thermal expansion rates under the standard water/powder ratio condition were 1.923% in Deguvest, 1.629% in Speed-E, 1.619% in Hi-temp and 1.580% in CM. No significant difference in thermal expansions under the standard water/powder ratio condition existed only between Speed-E and Hi-temp(p<.05). 5. Under the decreased water/powder ratio condition, there was significant increase in thermal expansion of CM and Deguvest but decrease in thermal expansion of Speed-E(p<.05). 6. Under the increased water/powder ratio condition, there was significant decrease in thermal expansion of CM, Deguvest and Speed-E but decrease in thermal expansion of Hi-temp(p<.05).

THE INFLUENCE OF WATTAGE AND CURING TIME OF MICROWAVE ENERGY ON PHYSICAL PROPERTIES OF THE DENTURE BASE RESIN / 대한치과보철학회지

The purpose of this study was to evaluate the effect of wattage and curing time on surface hardness, three-point bending strength and internal porosity of microwave curing denture base resin. Two sizes of resin spicimens were made of Acron MC ; 3.5x10x60mm for surface hardness and three-point bending strength measurement and 5x12x60mm for internal porosity measurement. They were cured by microwave energy at varing wattages(500W, 700W) and curing times(2min., 3min., 4min.) to determine if a certain wattage/curing time combination would improve physical properties. Surface hardness was measured with Vikers hardness tester, three-point bend-ing strength with universal testing machine and internal porosity was calculated by measuring the weight in air and in water. The results obtained were as follows : 1. There was no significant difference in percent porosity among experimental groups(p>0.05). 2. 500W/3min, group showed the higher surface hardness than 700W/2, 3, 4min. groups(p0.05). 3. 500W/3min. group yielded the higher value of bending strength than 500W/2min., 700W/3, 4min. groups(p0.05).

A MEASUREMENT OF DISPLACEMENTS OF CAST FRAMEWORK BY TORCH SOLDERING AND ELECTRIC SOLDERING TECHNIQUES / 대한치과보철학회지

The purpose of this study was to investigate the displacements of cast framework by torch soldering and electric soldering techniques. Specimen had two cylinders and connecting bar that had sectioned with 0.3mm gap at mid point. 10 of total specimens were divided into two groups. In torch soldered group, soldering investment block was made and conventional torch soldering procedure was carried out. In electric soldered group, electric soldering was carried out on the master cast without soldering investment block by using electric soldering machine(Dentapunkt DP 7, Kulzer, Germany). After soldering procedure, three dimensional coordinates of two centroids of each cylinder were measured by three dimensional coordinate measuring machine. The intercentroidal displacement and global displacement were calculated and then, these values were compared and evaluated. The results were obtained as follows: 1. Intercentroidal distances of specimens decreased after both soldering procedures, and the decrease in intercentroidal distance was greater for torch soldered group than for electric soldered group 2. Global displacements of torch soldered group were greater than those of electric soldered group