Evaluation of the stress distribution in the external hexagon implant system with different hexagon height by FEM-3D / 대한치과보철학회지

PURPOSE: To analyze the stress distribution of the implant and its supporting structures through 3D finite elements analysis for implants with different hexagon heights and to make the assessment of the mechanical stability and the effect of the elements. MATERIALS AND METHODS: Infinite elements modeling with CAD data was designed. The modeling was done as follows; an external connection type Phi 4.0 mm x11.5 mm Osste(R) USII (Osstem Co., Pusan, Korea) implant system was used, the implant was planted in the mandibular first molar region with appropriate prosthetic restoration, the hexagon (implant fixture's external connection) height of 0.0, 0.7, 1.2, and 1.5 mm were applied. ABAQUS 6.4 (ABAQUS, Inc., Providence, USA) was used to calculate the stress value. The force distribution via color distribution on each experimental group's implant fixture and titanium screw was studied based on the equivalent stress (von Mises stress). The maximum stress level of each element (crown, implant screw, implant fixture, cortical bone and cancellous bone) was compared. RESULTS: The hexagonal height of the implant with external connection had an influence on the stress distribution of the fixture, screw and upper prosthesis and the surrounding supporting bone. As the hexagon height increased, the stress was well distributed and there was a decrease in the maximum stress value. If the height of the hexagon reached over 1.2 mm, there was no significant influence on the stress distribution. CONCLUSION: For implants with external connections, a hexagon is vital for stress distribution. As the height of the hexagon increased, the more effective stress distribution was observed.

Observation of the change of the dental implant stability and bone density evaluation methods / 대한치주과학회지

PURPOSE: The aim of this study was to examine the correlation of the subjective and the objective evaluation of edentulous ridge bone quality, and to evaluate the change of the dental implant stability in each bone density group for early healing period after implant installation. METHODS:Sixty-seven implants(Osstem implant(R), Seoul, Korea) were included in this study. We evaluated the bone density by 2 methods. The one was the subjective method which was determined by practitioner's tactile sense, the other was the objective bone type was based on Hounsfield units. The implant stability in each bone type group was assessed by resonance frequency analyzer(Osstell mentor(R)). Data were analyzed for the change of the implant stability, and they were compared to verify the difference of groups at the time of installation, 2, 6, 10, 14 weeks postoperatively. Spearman's correlation was used to demonstrate the correlation between the subjective and the objective evaluation of the bone density, and analysis of variance(ANOVA) was used to analyze the differences of implant stability at each time point. RESULTS: There was no close relation between the subjective and the objective evaluation of the bone density(r=0.57). In the subjective groups, there was statistically significant difference between the type 1 and 3 at 10 weeks and between the type 2 and 3 at 14 weeks. In the objective groups, there was no statistically significant difference between the D 1, 2, 3, 4, and 5 group with regard to RFA from baseline to 14 weeks(p>0.1). CONCLUSIONS: The implant stability increased over time during the study, and it was improved with bone density proportionally after 2weeks postoperatively. It is recommended that the decision of bone density is base on Hounsfield unit for implant loading time.

Accuracy of the impression technique using thermoforming polymethyl methacrylate tray / 대한치과보철학회지

STATEMENT OF PROBLEM: Use of the conventional dental impression procedure is problematic in patients who have difficulty opening their mouth, difficulty breathing through their nose or tendency to gag. PURPOSE: It is necessary to make individual trays more comfortable for patients during impression taking procedure. It was reported at the KAP Annual Meeting 2001 Seoul that an improved impression technique was suitable for this purpose. In this study, the accuracy of the improved dental impression method for implant was compared with the conventional dental impression method. MATERIAL AND METHODS: An oral simulator was made from clear acrylic resin block which had similar form of edentulous ridge. For setting up the standard, five fixtures were installed on it. Study casts were made using two kinds of impression techniques. One was the conventional method that was taken using silicone impression material and an individual resin tray under connection of inter-fixture relation. The other was the improved method in which was the connection of the impression coping and the thermoformed polymethyl methacrylate tray. In addition, two different study casts were made from the improved impression body. The coordinates of the fixture on the study model were measured by three-dimensional coordinate measuring equipment. Then the distances between each fixture were calculated and compared with that of oral simulator. Accuracy of the each impression method was also assessed. RESULTS: The differences of inter-fixture dimension between study casts and simulator in the improved impression technique showed 0.014+/-0.016mm and 0.017+/-0.022mm, respectively and that of the conventional method was 0.017+/-0.014mm. There was no significant difference between the improved impression technique and conventional method. CONCLUSION: The improved impression technique is useful for multiple support implants.

The comparative study of thermal inductive effect between internal connection and external connection implant in abutment preparation / 대한치과보철학회지

STATEMENT OF PROBLEM: The cement-type abutment would be needed for the reduction of its body in order to correct the axis and to assure occlusal clearance. In the case of intraoral preparation, there is a potential risk that generated heat could be transmitted into the bone-implant interface, where it can cause deterioration of tissues around the implant and failed osseointegration. PURPOSE: The purpose of this study was to assess the difference of the heat transmitting effect on external and internal connection implant types under various conditions. MATERIAL AND METHOD: For evaluating the effects of alternating temperature, the thermocoupling wires were attached on 3 areas of the implant fixture surface corresponding to the cervical, middle, and apex. The abutments were removed 1mm in depth horizontally with diamond burs and were polished for 30 seconds at low speed with silicone points using pressure as applied in routine clinical practice. Obtained data were analyzed using Mann-Whitney rank-sum test and Wilcoxon / Kruskal-Wallis Tests. PESULT: Increased temperature on bone-implant interface was evident without air-water spray coolant both at high speed reduction and low speed polishing (p<.05). But, the difference between connection types was not shown. CONCLUSION: The reduction procedure of abutment without using proper coolant leads to serious damage of oral tissues around the implant irrespective of external and internal connection type.

Relaltionship Between The Depth Access Hole And Prosthetic Components In Screw Retained Implants / 대한치과보철학회지

A total of 605 implant fixture prosthesis delivered by 3 clinics and 2 laboratories were examined in this study. The object of this study was to determine the proper length of screw head. The depth of access hole were measured and compared to the type of fixture, abutment, gold screw and prosthesis. The results were as follows: 1. The average number of fixtures per patient were 2.97. 2. The number of fixture installed in the lower posterior area are 327(55.56 %), the upper posterior area 171(28.25%). 3. The depth of access hole is 4.23 mm in shallow area, and 5.46 mm in deep area and the differences were 1.23 mm. 4. The average depth of the aceess hole of the UCLA abutment were 5.02 mm. 5. The number of 4-5 mm access hole depth were 60(22.39%)in abutment screw level and the number of 4-5 mm depth in fixture level were 101(29.19%). 6. In the shape of screw head, hexed type were 576(95.21%), slotted type were 29(4.79%).

ANALYSIS OF OPTICAL TRANSMISSION CHARATERISTICS BY VISIBLE LIGHT INTO SHADE GUIDES / 대한치과보철학회지

The purpose of this study was the evaluation of spectral transmission of the commercial three shade guides and the relationship of hue, value, and chroma according to the transmission rate. The spectral transmittance of three shade guides - Vita Lumin Shade Guide, Vintage and Unibond Shade Guide, and Vitapan 3D-Master Shade Guide - were measured. For direct transmission measurements, each shade tabs were placed at the entrance port of the 1mm diameter intergrating sphere. The intensity of the light source passing through the shade tabs to the right angle was continuously recorded for wavelength from 400 to 700 nm. A transmission spectrum and digital data were obtained for each measurement and they were evaluated using Microcal Origin program. The obtained results of this study were as follows 1. In Vita Lumin Shade Guide, sum of the transmission rate of the shade tabs at the wavelength 400-700nm was decreased in agreement with the arrangement order at each A, B, C, D group, except D4 shade tab. However, there were no relationships between the transmission rate of the shade tabs and the value-oriented. 2. In Vintage and Unibond Shade Guide, sum of the total transmission rate of the shade tabs was decreased in agreement with the arrangement order at each A, B, C, D group. When all shade tabs arranged in value-oriented, transmission rate was accord with the order, except D4 shade tab. 3. When shade tabs of the Vitapan 3D-Master Shade Guide have the same value and hue, sum of their total transmission rate decreased in accordance with the chroma-oriented. When the shade tabs have the same value and chroma, there were no differences from the order of the transmission rate to the various hue type. However, in the "R" tabs of reddish hue type, the transmission rate increased at the long wavelength range area. In conclusion, we need the quantitative analyzing instruments in transmission determination. Vitapan 3D-Master Shade Guide covers the tooth color space taking into account the parameters of the systematic value, chroma, hue oriented, and the transmission rate relatively accorded with that sequence.

Tensile Bond Strength Between Non-Precious Dental Alloy and Veneering Reinforced Composite Resins / 대한치과보철학회지

Recently the 2nd generation laboratory composite resins were introduced. Although the mechanical properties of these composite resins have been improved, there were some disadvantages such as discoloration, low abrasion resistance and debonding between metal and resin. The purpose of this study was to evaluate the tensile bond strength between non-pecious dental alloy(verabond) and four veneering reinforced composite resins: Targis(Ivoclar Co.,U.S.A.), Artglass(Kulzer CO., Gemany). Sculpture(Jeneric Pentron Co., U.S.A.), and Estenia(Kurary Co., Japan). All test metal specimens were polished with #1,000 SiC paper, and sandblasted with 250micrometer aluminum oxide. After then, according to manufacturer's instructions metal adhesive primer and veneering resins were applied. All test specimens were divided into two groups. One group was dried in a desiccator at 25degrees C for 3 days, the other group was subjected to thermal cycling(2,000x) in water(5/55degrees C). Tensile bond strength was measured using Instron Universal Testing machine and the fractured surface was examined under the naked eyes and scanning microscope. Within the limitations imposed in this study, the following conclusions can be drawn: 1. in no-thermal cycling groups, there were no significant differences between Estenia and VMK68 but there were significant differences between Targis, Artglass, Sculpture and VMK68(p<0.05). 2. in no-thermal cycling resin groups, the highest tensile bond strength was observed in Estenis and there were significant differences between Estenia and the other resins(p<0.05). 3. Before and after thermal cycling, there were significant differences in tensile bond strength of Targis and Artglass(p<0.05). The tensile bond strength of Artglass was decreased and that of Targis was increased. 4. in no-thermal cycling groups, Artglass showed mixed fracture modes(95%), but after thermal cycling, Artglass showed adhesive fracture modes(75%).