The effect of heat treatment of the TI6AL4V specimen fabricated by selective laser melting method on the crystalline structure and chemical compositions / 대한치과재료학회지

In this study, the Ti6Al4V specimens were fabricated using selective laser melting (SLM) method (Ti6Al4V-AS group). These specimens were performed to heat treatment at 950℃ and 550℃ using vacuum electric furnace (Ti6Al4V-HT group). The mechanical properties, metallographic shape, crystalline structure, and chemical compositions of the alloy specimens before and after heat treatment were analyzed. The Ti6Al4V-AS group showed ultimate tensile strength (UTS) and low elongation values. Acicular crystal grains were observed in metallographic image and the α'-Ti phase was dominant. After heat treatment (Ti6Al4V-HT group), the UTS was lowered and the elongation was increased. In addition, a lamellar structure in which columnar crystal grains are arranged was observed, α+β-Ti phase was formed, and crystallinity increased. As a result of analyzing the chemical composition, the Ti6Al4V-AS specimen contained a higher carbon content than the Ti6Al4V-HT specimen. This high carbon content could be related to the formation of α'-phase, high strength and low elongation of the Ti6Al4V-AS specimen. Ti6Al4V-HT specimen showed that the overall carbon content was low, but the carbon content was locally high in the α-Ti phase region. Therefore, it is necessary to control effectively the incorporation of carbon gas in the production of Ti6Al4V specimens using SLM.

A study on coating of collagen-containing hydroxyapatite on titanium using electrochemical deposition method / 대한치과재료학회지

In this study, a biomimetic coating in which hydroxyapatite (HAp) and collagen (Col), the major components of bone, were coated together on titanium was performed using the ECD method. The polished CP-Ti (commocially pure–titanium) disks (Ti-As), and the roughened CP-Ti disks (Ti-R) fabricated by anodic oxidation method were prepared. An electrolyte (E) was prepared by mixing Ca(NO 3 ) 2 and NH 4 H 2 PO 4 . Collagen-contaiing electrolyte (ECol) was prepared by adding collagen (Type-I) to E electrolyte. A pulse-type negative electric current of -5 mA, -10 mA, and -15 mA was applied to the titanium specimens, respectively.The temperature of electrolyte solution was maintained at 37℃. The fabricated specimens were named to Ti-As-E-5, Ti-As-E-10, Ti-As-E-15, Ti-As-ECol-5, Ti-As-ECol-10, Ti-As-ECol-15, Ti-R-E-5, Ti-R-E-10, Ti-R-E-15, Ti-R-ECol-5, Ti-R-ECol-10, and Ti-R-ECol-15, respectively. The nanorod-shaped crystallites were evenly formed on the surface of Ti-As-E groups. The length of nanorods on Ti-As-ECol groups was shorter than that on Ti-As-E groups. A low crystalline HAp structure was detected in X-ray diffraction (XRD) patterns of Ti-As-E groups. For Ti-As-ECol groups, the HAp structure was confirmed by analysis of the selected area electron diffraction (SAED) patterns obtained from a transmission electron microscope (TEM). Fourier-transform infrared spectroscopy (FT-IR) spectra of Ti-As-ECol groups showed the amide peaks assigned to collagen and related to carbonate apatite. Similarly to the Ti-As specimens, HAp crystallites were coated on Ti-R-E and Ti-R-ECol groups and their surface roughness was maintained. It is expected that the results of this study could be applied to the development of a biomimetic surface treatment method for titanium implants.

A study on the formation of bovine serum albumin-containing hydroxyapatite on titanium using electrochemical deposition method / 대한치과재료학회지

In this study, the hydroxyapatite (HAps) containing bovine serum albumin (BSA) were coated on titanium using the electrochemical deposition (ECD) method. Negative electric current pulses were applied to titanium specimens at 37 ℃ using a Ca- and P-containing electrolyte in which BSA was added E-BSA-10, E-BSA-15, and E-BSA-20 groups were prepared by changing the electric current to –10 mA, –15 mA, and –20 mA, respectively. As a comparative group, an E-15 specimen was prepared by applying a current of -15 mA to the specimen in Ca- and P-containing electrolyte without BSA. A coating film composed of nanosheet-shaped crystals was observed on the surface of each specimen, and the size of the nanocrystals on the BSA-containing groups was larger than that of the E-15 group. These crystals were smaller in size and higher in density as the applied current values were increased. All specimens had HAp crystalline structure. BSA-containing specimens showed a tendency of preferential growth of HAp crystals in c-axis orientation, and this tendency decreased as the applied current values were increased. In the FT-IR spectrum, amide peaks that corresponds to BSA were identified. As a result of soaking the BSA-containing group specimens in phosphate-buffered saline (PBS) for 60 hours, it was observed that the crystal structure aligned with the c-axis was disordered, and BSA was released slowly with the decomposition of HAp. This study is expected to be applied to the development of a surface treatment method for coating titanium implants with HAp containing various biological factors in the future.

Effect of compositional variation of dental MTA cements on setting time / 대한치과재료학회지

The long setting time of dental MTA (Mineral Trioxide Aggregate) cement is a major disadvantage in clinical use. In this study, the setting time (ST) of nine commercial MTA cements was tested according to the ISO 6876:2012 standard (n = 5).Materials evaluated were ProRoot MTA (PR), Ortho MTA (Ortho), Retro MTA (Retro), Endocem MTA (Endocem), Endoseal MTA (Endoseal), One-Fil (OF), MTA Cem (MC), EZ-Seal (EZ), and Biodentine (BD). XRD and XRF analysis were performed to evaluate the effect of composition on ST. Kruskal-Wallis test as a non-parametric ANOVA followed by Duncan’s post hoc test was used for statistical analysis. The ST was PR > EZ > OF > Ortho > Retro > MC > Endoseal > BD > Endocem in decreasing order (p < 0.001). PR showed the longest (369.4 min) and Endocem showed the shortest (2.4 min) ST. Endocem (2.4 min), BD (16.0 min) and Endoseal (47.0 min) contained calcium carbonate. MC (48.8 min), Retro (43.6 min), Ortho (65.0), and OF (165.4 min), which had the next short setting time, contained dicalcium aluminate. In EZ (182.4 min), dicalcium silicate was the main crystalline phase rather than tricalcium silicate, which contributes to the early strength, and it contained calcium sulfate. Endocem, which showed the shortest setting time, showed the smallest d90 particle size of 6.12 µm. The information obtained from this study would be helpful in developing a composition for controlling the setting time of MTA cement and selecting a product with a setting time suitable for each clinical case.

A study on the formation of bovine serum albumin-containing hydroxyapatite on titanium using electrochemical deposition method / 대한치과재료학회지

In this study, the hydroxyapatite (HAps) containing bovine serum albumin (BSA) were coated on titanium using the electrochemical deposition (ECD) method. Negative electric current pulses were applied to titanium specimens at 37 ℃ using a Ca- and P-containing electrolyte in which BSA was added E-BSA-10, E-BSA-15, and E-BSA-20 groups were prepared by changing the electric current to –10 mA, –15 mA, and –20 mA, respectively. As a comparative group, an E-15 specimen was prepared by applying a current of -15 mA to the specimen in Ca- and P-containing electrolyte without BSA. A coating film composed of nanosheet-shaped crystals was observed on the surface of each specimen, and the size of the nanocrystals on the BSA-containing groups was larger than that of the E-15 group. These crystals were smaller in size and higher in density as the applied current values were increased. All specimens had HAp crystalline structure. BSA-containing specimens showed a tendency of preferential growth of HAp crystals in c-axis orientation, and this tendency decreased as the applied current values were increased. In the FT-IR spectrum, amide peaks that corresponds to BSA were identified. As a result of soaking the BSA-containing group specimens in phosphate-buffered saline (PBS) for 60 hours, it was observed that the crystal structure aligned with the c-axis was disordered, and BSA was released slowly with the decomposition of HAp. This study is expected to be applied to the development of a surface treatment method for coating titanium implants with HAp containing various biological factors in the future.

Effect of compositional variation of dental MTA cements on setting time / 대한치과재료학회지

The long setting time of dental MTA (Mineral Trioxide Aggregate) cement is a major disadvantage in clinical use. In this study, the setting time (ST) of nine commercial MTA cements was tested according to the ISO 6876:2012 standard (n = 5).Materials evaluated were ProRoot MTA (PR), Ortho MTA (Ortho), Retro MTA (Retro), Endocem MTA (Endocem), Endoseal MTA (Endoseal), One-Fil (OF), MTA Cem (MC), EZ-Seal (EZ), and Biodentine (BD). XRD and XRF analysis were performed to evaluate the effect of composition on ST. Kruskal-Wallis test as a non-parametric ANOVA followed by Duncan’s post hoc test was used for statistical analysis. The ST was PR > EZ > OF > Ortho > Retro > MC > Endoseal > BD > Endocem in decreasing order (p < 0.001). PR showed the longest (369.4 min) and Endocem showed the shortest (2.4 min) ST. Endocem (2.4 min), BD (16.0 min) and Endoseal (47.0 min) contained calcium carbonate. MC (48.8 min), Retro (43.6 min), Ortho (65.0), and OF (165.4 min), which had the next short setting time, contained dicalcium aluminate. In EZ (182.4 min), dicalcium silicate was the main crystalline phase rather than tricalcium silicate, which contributes to the early strength, and it contained calcium sulfate. Endocem, which showed the shortest setting time, showed the smallest d90 particle size of 6.12 µm. The information obtained from this study would be helpful in developing a composition for controlling the setting time of MTA cement and selecting a product with a setting time suitable for each clinical case.

Fabrication of rough surface on titanium using electrochemical treatment in NaCl electrolyte / 대한치과재료학회지

It is difficult to get sufficient roughness on titanium implant surface using traditional electrochemical treatments. In this study, we have developed a new method which provides a hybrid structured titanium surface having micro/nano roughness using electrochemical treatment in NaCl electrolyte and hydrothermal treatment. Titanium disks were anodically oxidized (ANO) in 0.15M NaCl electrolyte by applying positive electric pulses. The oxide compounds loosely attached to the surface were removed by ultrasonic cleaning (ANO group). These specimens were hydrothermally (HT) treated in an alkaline solution (ANO-HT group). ANO group showed the dimpled grain surfaces with a diameter of approximately 30 µm, and its roughness (Ra) was about 2.4 µm. The nano-sized crystallites which had an anatase TiO₂ crystalline structure were uniformly distributed on the surface of ANO-HT group. This group still retained high roughness (~2.7 µm) similar to ANO group and showed high hydrophilicity. Titanium surface with high roughness and hydrophilicity was fabricated using new electrochemical treating method and hydrothermal treatment. This surface modification method could be used for enhancing the osteoconductivity of the titanium implants.

Surface characterization of calcium phosphate coating formed on chitosan and alkali-treaDted titanium metal / 대한치과재료학회지

The calcium phosphate coating on various pretreated metals was prepared by soaking in modified simulated body fluid (m-SBF) solution. The coating structure and its surface morphologies were determined by x-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The results revealed significant differences in morphology and composition of the calcium phosphate coatings with and without chitosan and NaOH-pretreated commercially pure titanium (cp-Ti) substrate. The calcium phosphates formed on chitosan coated-Ti pretreated with NaOH were ~ 350 nm-sized resulting in strong bonding of the apatite layer with the substrates and a uniform gradient of stress transfer from coating materials to the Ti-substrate. After NaOH pretreatment, the hydroxyl groups bind to Ca²⁺ to attract PO₄³⁻ anions, eventually resulting in a continuous layer of calcium phosphate on chitosan coated-Ti substrate during immersion in m-SBF solution. The chitosan coated-Ti showed hydrophobic surface while NaOH pretreatment resulted in maximum hydrophilicity to the Ti substrate. Due to improved wettability of Ti by NaOH pretreatment before chitosan coating, aggregation of calcium phosphate was prevented and size-controlled composite materials were obtained.

Hydroxyapatite Coatings on Titanium Using Electrochemical Deposition Method at Body Fluid Temperature / 대한치과재료학회지

In this study, hydroxyapatite (HAp) was coated on titanium using electrochemical deposition (ECD) method at body fluid temperature. The titanium specimens for ECD were prepared by chemically etching treatment using 5M NaOH solution. The electrolyte mixed with 5 mM Ca(NO³)² and 2 mM NH⁴H²PO⁴ which has pH 5 (E2) was adjusted to pH 3 (E1) and pH 6 (E3). The different electric pulses of −10, −15, −30 mA were applied to each specimen. The temperature of electrolytes was kept at 37℃. E1-10, E1-15, E1-30, E2-10, E2-15, E2-30, E3-10, E3-15, and E3-30 groups were prepared for this study. Scanning electron microscope (SEM) images showed that E1-10 and E1-15 groups were not coated and the powder-shaped compounds were formed on E3-15 and E3-30 groups. The cracks were observed on the surface of E1-30 and E2-30 groups. The evenly and stable coated layer was deposited on E2-10, E2-15 and E3-10 groups. The layer coated on titanium surface had an HAp crystalline structure. E1-30 and E2-30 groups had low crystallinity, even though they had thick layer. HAp layer on for E2-10 group was well deposited on the surface because it more aligned to c-axis compared with other groups.

Osteoblastic behavior to zirconium coating on Ti-6Al-4V alloy

PURPOSE: The purpose of this study was to assess the surface characteristics and the biocompatibility of zirconium (Zr) coating on Ti-6Al-4V alloy surface by radio frequency (RF) magnetron sputtering method. MATERIALS AND METHODS: The zirconium films were developed on Ti-6Al-4V discs using RF magnetron sputtering method. Surface profile, surface composition, surface roughness and surface energy were evaluated. Electrochemical test was performed to evaluate the corrosion behavior. Cell proliferation, alkaline phosphatase (ALP) activity and gene expression of mineralized matrix markers were measured. RESULTS: SEM and EDS analysis showed that zirconium deposition was performed successfully on Ti-6Al-4V alloy substrate. Ti-6Al-4V group and Zr-coating group showed no significant difference in surface roughness (P>.05). Surface energy was significantly higher in Zr-coating group than in Ti-6Al-4V group (P<.05). No difference in cell morphology was observed between Ti-6Al-4V group and Zr-coating group. Cell proliferation was higher in Zr-coating group than Ti-6Al-4V group at 1, 3 and 5 days (P<.05). Zr-coating group showed higher ALP activity level than Ti-6Al-4V group (P<.05). The mRNA expressions of bone sialoprotein (BSP) and osteocalcin (OCN) on Zr-coating group increased approximately 1.2-fold and 2.1-fold respectively, compared to that of Ti-6Al-4V group. CONCLUSION: These results suggest that zirconium coating on Ti-6Al-4V alloy could enhance the early osteoblast responses. This property could make non-toxic metal coatings on Ti-6Al-4V alloy suitable for orthopedic and dental implants.

Cytotoxicity and physical properties of tricalcium silicate-based endodontic materials

OBJECTIVES: The aim of this study was to evaluate the cytotoxicity, setting time and compressive strength of MTA and two novel tricalcium silicate-based endodontic materials, Bioaggregate (BA) and Biodentine (BD). MATERIALS AND METHODS: Cytotoxicity was evaluated by using a 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-((phenylamino)carbonyl)-2H-tetrazolium hydroxide (XTT) assay. Measurements of 9 heavy metals (arsenic, cadmium, chromium, copper, iron, lead, manganese, nickel, and zinc) were performed by inductively coupled plasma-mass spectrometry (ICP-MS) of leachates obtained by soaking the materials in distilled water. Setting time and compressive strength tests were performed following ISO requirements. RESULTS: BA had comparable cell viability to MTA, whereas the cell viability of BD was significantly lower than that of MTA. The ICP-MS analysis revealed that BD released significantly higher amount of 5 heavy metals (arsenic, copper, iron, manganese, and zinc) than MTA and BA. The setting time of BD was significantly shorter than that of MTA and BA, and the compressive strength of BA was significantly lower than that of MTA and BD. CONCLUSIONS: BA and BD were biocompatible, and they did not show any cytotoxic effects on human periodontal ligament fibroblasts. BA showed comparable cytotoxicity to MTA but inferior physical properties. BD had somewhat higher cytotoxicity but superior physical properties than MTA.

Surface characteristics of thermally treated titanium surfaces

PURPOSE: The characteristics of oxidized titanium (Ti) surfaces varied according to treatment conditions such as duration time and temperature. Thermal oxidation can change Ti surface characteristics, which affect many cellular responses such as cell adhesion, proliferation, and differentiation. Thus, this study was conducted to evaluate the surface characteristics and cell response of thermally treated Ti surfaces. METHODS: The samples were divided into 4 groups. Control: machined smooth titanium (Ti-S) was untreated. Group I: Ti-S was treated in a furnace at 300degrees C for 30 minutes. Group II: Ti-S was treated at 500degrees C for 30 minutes. Group III: Ti-S was treated at 750degrees C for 30 minutes. A scanning electron microscope, atomic force microscope, and X-ray diffraction were used to assess surface characteristics and chemical composition. The water contact angle and surface energy were measured to assess physical properties. RESULTS: The titanium dioxide (TiO2) thickness increased as the treatment temperature increased. Additional peaks belonging to rutile TiO2 were only found in group III. The contact angle in group III was significantly lower than any of the other groups. The surface energy significantly increased as the treatment temperature increased, especially in group III. In the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, after 24 hours of incubation, the assessment of cell viability showed that the optical density of the control had a higher tendency than any other group, but there was no significant difference. However, the alkaline phosphatase activity increased as the temperature increased, especially in group III. CONCLUSIONS: Consequently, the surface characteristics and biocompatibility increased as the temperature increased. This indicates that surface modification by thermal treatment could be another useful method for medical and dental implants.

The effects of short-term application of calcium hydroxide on dentin fracture strength / 대한치과보존학회지

OBJECTIVES: This in vitro study investigated whether short-term application of calcium hydroxide in the root canal system for 1 and 4 wk affects the fracture strength of human permanent teeth. MATERIALS AND METHODS: Thirty two mature human single rooted mandibular premolars in similar size and dentin thickness without decay or restorations were hand and rotary instrumented and 16 teeth vertically packed with calcium hydroxide paste and sealed coronally with caviton to imitate the endodontic procedure and the other 16 teeth was left empty as a control group. The apicies of all the samples were sealed with resin, submerged in normal saline and put in a storage box at 37degrees C to mimic the oral environment. After 1 and 4 wk, 8 samples out of 16 samples from each group were removed from the storage box and fracture strength test was performed. The maximum load required to fracture the samples was recorded and data were analysed statistically by the two way ANOVA test at 5% significance level. RESULTS: The mean fracture strengths of two groups after 1 wk and 4 wk were similar. The intracanal placement of calcium hydroxide weakened the fracture strength of teeth by 8.2% after 4 wk: an average of 39.23 MPa for no treatment group and 36.01 MPa for CH group. However there was no statistically significant difference between experimental groups and between time intervals. CONCLUSIONS: These results suggest that short term calcium hydroxide application is available during endodontic treatment.

Physical and chemical properties of experimental mixture of mineral trioxide aggregate and glass ionomer cement / 대한치과보존학회지

OBJECTIVES: The purpose of this study was to determine the setting time, compressive strength, solubility, and pH of mineral trioxide aggregate (MTA) mixed with glass ionomer cement (GIC) and to compare these properties with those of MTA, GIC, IRM, and SuperEBA. MATERIALS AND METHODS: Setting time, compressive strength, and solubility were determined according to the ISO 9917 or 6876 method. The pH of the test materials was determined using a pH meter with specified electrode for solid specimen. RESULTS: The setting time of MTA mixed with GIC was significantly shorter than that of MTA. Compressive strength of MTA mixed with GIC was significantly lower than that of other materials at all time points for 7 days. Solubility of 1 : 1 and 2 : 1 specimen from MTA mixed with GIC was significantly higher than that of other materials. Solubility of 1 : 2 specimen was similar to that of MTA. The pH of MTA mixed with GIC was 2-4 immediately after mixing and increased to 5-7 after 1 day. CONCLUSIONS: The setting time of MTA mixed with GIC was improved compared with MTA. However, other properties such as compressive strength and pH proved to be inferior to those of MTA. To be clinically feasible, further investigation is necessary to find the proper mixing ratio in order to improve the drawbacks of MTA without impairing the pre-existing advantages and to assess the biocompatibility.

The Effect of Occlusion on the Reorganization of Periodontal Fibers during Retention Periods after Tooth Movement in Rats / 대한치과교정학회지

The purpose of this study was to evaluate the effect of occlusion on the mechanical strength of periodontal fibers during retention periods after experimental tooth movement. In the Sprague-Dawley male rats weighing 200 g or more, the intraoral elastics were inserted into the both right and left interproximal space between upper first and second molars for tooth movement. After 4 days later, the left lower first, second, and third molars were extracted for differentiating the non-occlusal side from the occlusal side in the same mouth. At the same time the elastics were removed and then light cured resin was placed in the space between upper first and second molars following undercut was made for retention bilaterally. From the beginning of retention, 7 rats were sacrificed at 0, 4, 8, 12, 16, 20 days respectively. For evaluating of magnitude on the mechanical strength of periodontal tissue, the maximal shear load of the upper first molars were measured bilaterally during extraction using Instron Universal Testing Machine. The results of this study were obtained as follows : 1. In the occlusal side, the maximal shear load was increased from no retention to retention 20 days group as time was going and statistically difference was shown from retention 12 days group (p 0.05). 3. The result compared with the maximal shear load between occlusal and nonocclusal side showed no statistically difference until retention 8 day group (p > 0.05), but showed statistically difference from retention 12 day to 20 day group (p < 0.05). These results show that occlusion had an effect on mechanical strength of the periodontal fibers during retention periods after experimental tooth movement; therefore, it is suggested that occlusion should be considered while the retainer types and retention period are planned.

Bleaching effect of carbamide peroxide gel on discolored nonvital teeth / 대한치과보존학회지

The bleaching of discolored nonvital teeth is conservative treatment that satisfy the cosmetic desire. The most common method for this treatment, walking bleaching, is using 30% hydrogen peroxide and sodium perborate. Many alternatives are suggested for preventing the external cervical root resorption that is the common complication of the nonvital teeth bleaching with 30% hydrogen peroxide. The same extent of oxidation reactions as that resulted by the bleaching with the application of 30% hydrogen peroxide and sodium perborate can also be acquired more safely by materials that contain 10% carbamide peroxide, used primarily for the bleaching of vital teeth. Therefore, this study was performed to evaluate the efficacy of 10% and 15% carbamide peroxide bleaching gel in nonvatal teeth bleaching. The internal bleaching of intentionally discolored teeth was performed in vitro with 10% carbamide peroxide (Group 1), 15% carbamide peroxide (Group 2), mixture of distilled water and sodium perborate (Group 3), and mixture of 30% hydrogen peroxide and sodium perborate (Group 4). The bleaching materials were refreshed following 3, 6, 9 and 12 days. To evaluate the bleaching effect, the color change of the crowns was measured at 1, 2, 3, 4, 7 and 15 days of bleaching using the colorimeter. The results were as follows : 1. L* and DeltaE* values were increased with time in all bleaching agents(p<0.01). 2. There was no significant difference in L* and DeltaE* value among bleaching agents. 3. DeltaE* value higher than 3 was shown after 3 days of bleaching with 10% carbamide peroxide gel, 1 day with 15% carbamide peroxide gel, 4 days with mixture sodium perborate and distilled water and 4 days with mixture sodium perborate and 30% hydrogen peroxide, respectively. These results revealed that the use of 10% and 15% carbamide peroxide bleaching gel in non-vital teeth bleaching is as effective as mixture of distilled water and sodium perborate and mixture of 30% hydrogen peroxide and sodium perborate. Accordingly, carbamide peroxide could be used clinically to bleach discolored non-vital teeth.

EFFECT OF GOLD ELECTRODEPOSIT ON THE BOND STRENGTH BETWEEN ALLOYS AND VENEERED RESIN / 대한치과보철학회지

The purpose of this experiment was to determind whether the gold electrodeposit on Pd-Ag and Ni-Cr alloys influences on the shear bond strength between veneering resin and silicoated metal surface. All the metal specimens were sandblasted with 250microneter aluminum oxide and followed by silicoating and resin veneering. According to the metal surfaces to be veneered, experimental groups were divided into five. Group Prec : Gold alloy without gold coating Group Semi : Pd-Ag alloy without gold coating Group Base : Ni-Cr alloy without gold coating Group Semi-G : Pd-Ag alloy with gold coating Group Base-G : Ni-Cr alloy with gold coating All specimens were thermocycled 1,000 times at temperature of 5degrees C to 55degrees C. The effects of gold electrodeposit on the shear bond strength between resin and metal interface were measured and fractured surface of the resin veneered metal was examined under the scaning electron microscope. The following results were obtained 1. The shear bond strength between resin and metal was 64.51+/-11.11Kg/cm2in Prec group, 62.77+/-11.23Kg/cm2in Base group and 58.97+/-9.20 Kg/cm2in Semi Group. There was no significant difference among the groups. 2. The bond strength in groups Semi-G and Base-G decreased about 17%, compared to the non-gold-electrodeposit groups(Semi, Base). 3. In groups of non electrodeposit(Prec, Semi, Base), fracture occurred at the interface between alloy and resin, while fracture interface was observed between gold coating and resin in group Semi-G, and between metal substrate and gold coating in group Base-G resp[ectively.

Effect of screw number and length on internal fixation of mandibular fractures

This study was performed to evaluate the effect that screw number and length have on the ability of two types of plate to resist vertical masticatory force. Five trials were done with two, four, or six screws, using screws 4 mm, or 12 mm in lenght and mini bone plates or mini compression plates. The fractured ribs were subjected to increasing weights until failure. With the mini bone plate, increasing the number of screws increased the weight resisted than screw length. For the mini compression plate, increasing screw length and the number of screws increased weight resisted.