An in-vitro wear study of indirect composite resins against human enamel / 대한치과보철학회지

STATEMENT OF PROBLEM: Second-generation indirect composite resins have been improved flexural strength, compressive strength, hydrolytic degradation resistance, wear resistance compared to first-generation indirect composite resins, but there are still some problems as hydrolysis and low wear resistance. Some manufacturers claim that wear resistance of their materials has been improved, but little independent study has been published on wear properties of these materials and the properties specified in the advertising materials are largely derived from in-house or contracted testing. PURPOSE: This study was to evaluate the wear of indirect composite resins (SR Adoro, Sinfony, Tescera ATL) and gold alloy against the human enamel. MATERIAL AND METHOD: Extracted human incisors and premolars were sectioned to 2*2*2mm cube and embedded in the clear resin and formed conical shaped antagonist to fit the jig of pinon-disk tribometer. Total 20 antagonists were stored in distilled water. Five disk samples, 24mm in diameter and 1.5mm thick, were made for each of three groups of indirect composite resins and gold alloy group, and polished to #2,000 SiC paper on auto-polishing machine. Disk specimens were tested for wear against enamel antagonists. Wear test were conducted in distilled water using a pin-on-disk tribometer under condition (sliding speed 200rpm, contact load 24N, sliding distance 160m). The wear of the enamel was determined by weighing the enamel antagonist before and after test, and the weight was converted to volumes by average density. The wear tracks were analyzed by scanning electron microscopy and surface profilometer to elucidate the wear mechanisms. Statistical analysis of the enamel wear volume, wear track depth and wear tract width of disk specimens were accomplished with one-way ANOVA and the means were compared for significant differences with Scheffe's test. RESULTS: 1. The enamel wear was most in gold alloy, but there were no statistically significant differences among all the groups (P>.05). 2. In indirect composite resin groups, the group to make the most shallow depth of wear tract was Sinfony, followed by Tescera ATL, SR Adoro (P.05). 3. The width of wear tract of SR Adoro was larger than the other groups (P.05). 4. SEM analysis revealed that Sinfony and gold alloy showed less wear scars after test, Tescera ATL showed more wear scars and SR Adoro showed the most. CONCLUSION: Within the limits of this study, Sinfony and gold alloy showed the least wear rates and showed similar wear patterns.

Fracture strength of zirconia monolithic crowns and metal-ceramic crowns after cyclic loading and thermocycling / 대한치과보철학회지

PURPOSE: The purpose of this study was to compare the fracture strength of the zirconia monolithic all-ceramic crowns according to the thickness (0.5mm, 0.8mm, 1.1mm) and metal-ceramic crowns (1.0mm, 1.5mm). MATERIAL AND METHOD: Twelve crowns for each of 3 zirconia crown groups were fabricated using CAD/CAM system (Kavo, Germany) and twelve crowns for each of 2 metal-ceramic crown groups were made by the conventional method. All crowns were luted to the metal dies using resin cement. Half of the specimens were exposed to thermocycling (5-55degrees C, 1 Hz) and cyclic loading (300,000 cycles, 50N). Subsequently, all crowns were mounted on the testing jig in a universal testing machine. The load was directed at the center of crown with perpendicular to the long axis of each specimen until catastrophic failure occurred. Analysis of variance and Tukey multiple comparison test (P<.05) were used for statistical analysis of all groups, and paired t-test (P<.05) was followed for statistical comparison between each groups'fracture load before and after cyclic loading. RESULTS: 1. The fracture strength of the zirconia monolithic crowns and the metal-ceramic crown increased as thickness increased (P<.05). 2. The cyclic loading and thermocycling significantly decreased the fracture strength of the zirconia monolithic crowns (P<.05). 3. The standard deviation of fracture strength of the zirconia monolithic crowns was very low. CONCLUSION: The fracture strength of the zirconia monolithic crowns for the posterior area tends to be higher with thickness increased and 0.8mm or over in thickness is recommended to have similar or over the fracture strength of metal-ceramic crowns.

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).

Fracture strength of zirconia monolithic crowns / 대한치과보철학회지

PURPOSE: The purpose of this study was to compare the fracture strength of the zirconia monolithic all-ceramic crowns according to the thickness(0.5 mm, 0.8 mm, 1.1 mm) and IPS Empress II ceramic crown of 1.5 mm thickness. MATERIAL AND METHOD: Eight crowns for each of 3 zirconia crown groups were fabricated using CAD/CAM system(Kavo, Germany) and eight Empress II crowns were made from silicone mold and wax pattern. Each crown group was finished in accordance with the specific manufacturer's instruction. All crowns were luted to the metal dies using resin cement and mounted on the testing jig in a universal testing machine. The load was directed at the center of crown with perpendicular to the long axis of each specimen until catastrophic failure occurred. Analysis of variance and Tukey multiple comparison test(p<.05) were applied to the data. RESULTS AND CONCLUSION: 1. The fracture strength of the zirconia monolithic all-ceramic crown was higher thickness increased(p<.05). 2. The fracture strength of 1.1 mm thickness zirconia monolithic all-ceramic crown was higher than the fracture strength of 1.5 mm thickness IPS Empress II crown(p<.05). 3. The fracture strength of 0.5 mm thickness zirconia monolithic all-ceramic crown exceeded maximum occlusal forces.

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.

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.

Stability of simultaneous implantation with autogenous iliac bone graft in the severely atrophic maxilla

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).