Comparative evaluation of the subtractive and additive manufacturing on the color stability of fixed provisional prosthesis materials

Purpose@#The purpose of this study is to compare the color stability of provisional restorative materials fabricated by subtractive and additive manufacturing. @*Materials and Methods@#PMMA specimens by subtractive manufacturing and conventional method and bis-acryl specimens by additive manufacturing were fabricated each 20. After immersing specimens in the coffee solution and the wine solution, the color was measured as CIE Lab with a colorimeter weekly for 4 weeks. Color change was calculated and data were analyzed with one-way ANOVA and the Tukey multiple comparisons test (α = 0.05). @*Results@#PMMA provisional prosthetic materials by subtractive manufacturing showed superior color stability compared to bis-acryl provisional prosthetic materials by additive manufacturing (P 0.05). @*Conclusion@#It is recommended to fabricate provisional restorations by subtractive manufacturing in areas where esthetics is important, such as anterior teeth, and consideration of the color stability will be required when making provisional prosthetic using additive manufacturing.

Relationship between inter-condylar width and inter-maxillary first molar width

PURPOSE@#The aim of this study was to evaluate the correlation between inter-condylar width and inter-maxillary first molar width to present the criteria for prosthetic reconstruction of dental arch width in maxillary and mandibular fully edentulous patients.@*MATERIALS AND METHODS@#120 Koreans (60 males and 60 females) who underwent the cone beam computerized tomography (Cone-beam CT) were selected. The Cone-beam CT images were analysed using Invivo 5.1. After reorientation of axis, inter-maxillary first molar width was measured by clicking both mesio-buccal cusp tip of maxillary first molar. And inter-condylar width was measured by clicking both middle points of condyles. The collected data were analysed with SPSS Version 20.0 and statistical significance of the correlation between inter-condylar width and inter-maxillary first molar width was verified by Pearson's correlation analysis.@*RESULTS@#The mean inter-condylar width of Korean was 105.9 mm, and that of male (108.3 mm) was statistically significantly wider than the female (103.4 mm). The inter-maxillary first molar width of Korean was 57.1 mm, and that of male (57.9 mm) was statistically significantly wider than the female (56.2 mm). Pearson's correlation analysis between inter-condylar width and inter-maxillary first molar width showed a Pearson correlation coefficient of 0.614 and statistically significantly positive correlation.@*CONCLUSION@#Inter-condylar width and inter-maxillary first molar width showed positive correlation and the average ratio of inter-condylar with and inter-maxillary first molar width was 1:0.54. Based on the results of this limited study, inter-condylar width can be used as a guide for setting up dental arch width in fully edentulous patient.

Evaluation of Bonwill triangle using cone beam computerized tomography in Korean

PURPOSE: The aim of this study was to evaluate the Bonwill triangle of Korean using the cone beam computerized tomography (Cone-beam CT). MATERIALS AND METHODS: 120 Koreans (60 males and 60 females) who visited Daejeon Dental College Hospital of Wonkwang University and who underwent the Cone-beam CT were selected. The Cone-beam CT images were analysed with Invivo 5.1 (Anatomage, San Jose, USA). After reorientation of axis, the intercondylar distance was measured by clicking both middle points of condyle. And the condyle-incisor distance was measured by clicking the middle point of condyle and contact point of the mandibular central incisor's incisal edge. The collected data were analysed using the SPSS Version 23.0 (IBM Inc., Armonk, USA) and statistical significance was verified by gender using independent t-test. RESULTS: The mean intercondylar distance of Korean was 105.9 mm, and the male (108.3 mm) was statistically significantly larger than the female (103.4 mm). The mean condyle-incisor distance of Korean was 105.2 mm, and the male (108.1 mm) was statistically significantly larger than the female (102.3 mm). CONCLUSION: The mean intercondylar distance of Korean in this study was 105.9 mm that was smaller than well-known 110 mm of Caucasian and the male was statistically significantly larger than the female. Within the limitations of this study, it would be necessary to use the articulator which can adjust the intercondylar distance according to the individual for prosthodontic treatment of Korean.

Evaluation of interdental distance of natural teeth with cone-beam computerized tomography

PURPOSE: The aim of this study was to evaluate the interdental distances of anterior, premolar, and molar teeth at the cementoenamel junction (CEJ) and 2 mm below the CEJ in healthy natural dentition with cone-beam computerized tomography (cone-beam CT) in order to provide valuable data for ideal implant positioning relative to mesiodistal bone dimensions. MATERIALS AND METHODS: Two hundred patients who visited Dental Hospital, Wonkwang University, who had natural dentition with healthy interdental papillae, and who underwent cone-beam CT were selected. The cone-beam CT images were converted to digital imaging and communication in medicine (DICOM) files and reconstructed in three-dimensional images. To standardize the cone-beam CT images, head reorientation was performed. All of the measurements were determined on the reconstructed panoramic images by three professionally trained dentists. RESULTS: At the CEJ, the mean maxillary interdental distances were 1.84 mm (anterior teeth), 2.07 mm (premolar), and 2.08 mm (molar), and the mean mandibular interproximal distances were 1.55 mm (anterior teeth), 2.20 mm (premolar), and 2.36 mm (molar). At 2mm below the CEJ, the mean maxillary interdental distances were 2.19 mm (anterior teeth), 2.51 mm (premolar), and 2.60 mm (molar), and the mean mandibular interproximal distances were 1.86 mm (anterior teeth), 2.53 mm (premolar), and 3.01 mm (molar). CONCLUSION: The interdental distances in the natural dentition were larger at the posterior teeth than at the anterior teeth and also at 2 mm below the CEJ level compared with at the CEJ level. The distances between mandibular incisors were the narrowest and the distances between mandibular molars were the widest in the entire dentition.

Accuracy of spring-style and friction-style mechanical implant torque wrench / 대한치과보철학회지

PURPOSE: The aim of this study was to compare the accuracy of two different styles of mechanical implant torque wrenches before and after sterilization and repeated use. MATERIALS AND METHODS: Thirty new spring-style and friction-style mechanical implant torque wrenches from five different manufacturers were selected as subjects of study and assessed in terms of accuracy. Three manufacturers produced, spring-style (Dio, Neobiotech, Osstem) torque wrenches, and other three manufactures produced friction-style (Dentium, Osstem, Shinhung) torque wrenches. The procedure of target torque measurement was performed 10 times for each device and a digital torque gauge (MGT-12, Mark-10 Corp, USA) was used to record the measurements. All torque wrenches were used repeatedly for 20 times and then sterilized. This whole procedure was repeated 100 times and all torque wrenches were retested. The collected data was analyzed using a SPSS Statistics Analysis program to evaluate the accuracy of the torque wrenches and Mann-Whitney-U test was used for a comparative analysis. RESULTS: After sterilization and repeated use procedure, results did not show any significant difference between error values in the spring-style torque wrench group. However, the results demonstrated an increase in error values within the friction-style torque wrench group (P.05). There was significant difference between the accuracy of new friction-style torque wrenches before and after 100 cycles of sterilization and repeated use (P<.05). Within the limitation of this study, spring-style torque wrenches were more accurate than friction-style torque wrenches in delivering target torque values.

Combined application of roll flap and combination onlay-interpositional graft to enhance esthetics of maxillary anterior fixed partial denture: A case report

In the maxillary anterior region, reconstruction of the localized alveolar ridge defect is very important in enhancing the esthetics of fixed partial denture. A 40-year-old female patient presented with a chief complaint of the inconvenience and unesthetic problem of 3-unit maxillary anterior prosthesis due to alveolar ridge resorption. After removal of old prosthesis, intraoral examination revealed moderate (buccolingually 4 mm) ridge deficiency in missing tooth region, leading to the diagnosis of Class I alveolar ridge defect. One of the reconstruction techniques to overcome this problem might be a technique that combines two types of soft tissue augmentation techniques. The purpose of this paper was to demonstrate the new combined technique of roll flap and combination onlay-interpositional graft utilized to acquire sufficient dimension of recipient area by one time of operation and to present the esthetic improvement of fixed partial denture by using this procedure in case of maxillary anterior localized ridge defect.

Fracture resistance and marginal fidelity of zirconia crown according to the coping design and the cement type / 대한치과보철학회지

PURPOSE: The purpose was to compare the marginal fidelity and the fracture resistance of the zirconia crowns according to the various coping designs with different thicknesses and cement types. Material and METHODS: Zirconia copings were designed and fabricated with various thicknesses using the CAD/CAM system (Everest, KaVo Dental GmbH, Biberach., Germany). Eighty zirconia copings were divided into 4 groups (Group I: even 0.3 mm thickness, Group II: 0.3 mm thickness on the buccal surface and the buccal half of occlusal surface and the 0.6 mm thickness on the lingual surface and the lingual half of occlusal surface, Group III: even 0.6 mm thickness, Group IV: 0.6 mm thickness on the buccal surface and the buccal half of occlusal surface and the 1.0 mm thickness on the lingual surface and the lingual half of occlusal surface) of 20. By using a putty index, zirconia crowns with the same size and contour were fabricated. Each group was divided into two subgroups by type of cement: Cavitec(R) (Kerr Co, USA) and Panavia-F(R) (Kuraray Medical Inc, Japan). After the cementation of the crowns with a static load compressor, the marginal fidelity of the zirconia crowns were measured at margins on the buccal, lingual, mesial and distal surfaces, using a microscope of microhardness tester (Matsuzawa, MXT-70, Japan, x100). The fracture resistance of each crown was measured using a universal testing machine (Z020, Zwick, Germany) at a crosshead speed of 1 mm/min. The results were analyzed statistically by the two-way ANOVA and oneway ANOVA and Duncan's multiple range test at alpha= .05. RESULTS: Group I and III showed the smallest marginal fidelity, while group II demonstrated the largest value in Cavitec(R) subgroup (P .05). Panavia-F(R) subgroup showed significantly higher fracture resistance than Cavitec(R) subgroup in group I and II (P < .05). CONCLUSION: Within the limitation of this study, considering fracture resistance or marginal fidelity and esthetics, a functional ceramic substructure design of the coping with slim visible surface can be used for esthetic purposes, or a thick invisible surface to support the veneering ceramic can be used depending on the priority.

Fracture load and marginal fitness of zirconia ceramic coping by design and coloration / 대한치과보철학회지

PURPOSE: The purpose of this study was to compare the marginal fitness and fracture load of the zirconia copings according to the design with different thickness and coloration. MATERIAL AND METHODS: The evaluation was based on 80 zirconia copings. Zirconia copings were fabricated in design with different thicknesses using CAD/CAM system (Everset, KAVO dental GmbH, Biberach, Germany). The designs of copings were divided into four groups. The first group consisted of copings with uniform thickness of 0.3 mm. The thickness in the second group was 0.3 mm on the buccal surface and 0.6 mm on the lingual surface. The third group consisted of coping with uniform thickness of 0.6 mm. The thickness in the fourth group was 0.6 mm on the buccal surface and 1mm on the lingual surface. Each group consisted of 10 colored and 10 uncolored copings. Half of the copings (40) processed with a milling system according to the specific design were sent to be given a color (A3) through saturation in special dye by a manufacturing company. Just after sintering, the marginal discrepancies of copings were measured on the buccal, lingual, mesial and distal surfaces of metal die, under a Video Microscope System (sv-35, Sometech, Seoul, Korea) at a magnification of x100. It was remeasured after the adjusting of the inner surface. Next, all copings were luted to the metal dies using reinforced cement {GC FujiCEM (GC Corp. Tokyo, Japan)} and mounted on the testing jig in a Universal Testing Machine (Instron 4467, Norwood, MA, USA). The results were analyzed statistically using the one-way ANOVA test. RESULTS: The obtained results were as follow: 1. The measured value of marginal discrepancy right after sintering was the greatest in the contraction of the buccal area in all groups, except for group I2. 2. There was no significant difference of marginal fitness among the groups in the colored zirconia group (P.05), with no significance. CONCLUSION: There was difference in the marginal fitness according to the design and coloration of zirconia copings right after sintering, but it was decided that the copings may well be used clinically if the inner surface are adjusted. The copings should be thick enough for the reinforcement of fracture strength. But considering the esthetics of the visible surfaces (labial and buccal surface), the thickness of copings may be a little thin, without giving any significant effect on the fracture strength. This type of design may be considered when giving priority to preservation of tooth or esthetics.

The fracture resistance of heat pressed ceramics with wire reinforcement / 대한치과보철학회지

STATEMENT OF PROBLEM: Ceramics have been important materials for the restoration of teeth. The demands of patients for tooth-colored restorations and the availability of various dental ceramics has driven the increased use of new types of dental ceramic materials. Improved physical properties of theses materials have expanded its use even in posterior crowns and fixed partial dentures. However, ceramic still has limitation such as low loading capability. This is critical for long-span bridge, because bridge is more subject to tensile force. PURPOSE: The wire reinforced ceramic was designed to increase the fracture resistance of ceramic restoration. The purpose of this study was to evaluate the fracture resistance of wire reinforced ceramic. MATERIAL AND METHODS: Heat pressed ceramic (ingot No.200 : IPS Empress 2, Ivoclar Vivadent, Liechtenstein) and Ni-Cr wire (Alfa Aesar, Johnson Matthey Company, USA) of 0.41 mm diameter were used in this study. Five groups of twelve uniform sized ceramic specimens (width 4 mm, thickness 2 mm, length 15 mm) were fabricated. Each group had different wire arrangement. Wireless ceramic was used as control group. The experimental groups were divided according to wire number and position. One, two and three strands of wires were positioned on the longitudinal axis of specimen. In another experimental group, three strands of wires positioned on the longitudinal axis and five strands of wires positioned on the transverse axis. Three-point bending test was done with universal testing machine (Z020, Zwick, Germany) to compare the flexural modulus, flexural strength, strain at fracture and fracture toughness of each group. Fractured ceramic specimens were cross-sectioned with caborundum disc and grinded with sandpaper to observe interface between ceramic and Ni-Cr wire. The interface between ceramic and Ni-Cr wire was analyzed with scanning electron microscope (JSM-6360, JEOL, Japan) under platinum coating. RESULTS: The results obtained were as follows: 1. The average and standard deviation in flexural modulus, flexural strength and fracture toughness showed no statistical differences between control and experimental groups. However, strain was significantly increased in wire inserted ceramics (P < .001). 2. Control group showed wedge fracture aspects across specimen, while experimental groups showed cracks across specimen. 3. Scanning electron microscopic image of cross-sectioned and longitudinally-sectioned specimens showed no gap at the interface between ceramic and Ni-Cr wire. CONCLUSION: The results of this study showed that wire inserted ceramics have a high strain characteristic. However, wire inserted ceramics was not enough to use at posterior area of mouth in relation to flexural modulus and flexural strength. Therefore, we need further studies.

A study on the stress distribution of posterior fixed partial denture with various all-ceramic systems / 대한치과보철학회지

PURPOSE: The purpose of this study was to analyze stress distribution of all ceramic posterior fixed partial denture using a three dimensional finite element method. MATERIAL AND METHOD: A three dimensional finite element model was created to demonstrate all-ceramic posterior fixed partial denture and then this computer model measured the stress distribution of the all ceramic bridges which has a ceramic core materials such as Zirconia, IPS Empress 2, In-Ceram zirconia, Metal-Ceramic. Also the stress distribution was examined according to loading sites when force was applied to sites such as the central area of second premolar, the mesial connector of pontic, the central fossa of pontic, the distal connector of pontic, and the central fossa of second molar. RESULTS: 1. In all the materials of the core in this study, von Mises stress indicated that the stress increased as force was applied to loaded sites, just at those points, on the connector, and the margin in the area adjacent to the connectors. 2. The maximum principal stress was much higher in the lower part of the connectors than in any other region. 3. As the load was applied to the different locations, the research showed a consistent increase of stress in the lower connectors. The maximum value of the von Mises stress was two or three times greater when the load was applied directly to the connectors rather than indirectly through another stressed region. 4. In the case of In-Ceram zirconia, the stress in lower connectors was the highest of all the reference points, the stress showed 75% of all the maximum stress. Ziconia showed 72%, Metal-Ceramic 67% and IPS Empress 2 50%. 5. In the case of Ziconia, the stress was well dispersed in each reference point that the stress differences were smaller when compared to In-Cream ziconia.

Accuracy of stone cast produced by adjustable dental impression tray / 대한치과보철학회지

PURPOSE: This study was performed to measure the accuracy of adjustable dental impression trays by a scanning laser three-dimensional digitizer. MATERIALS AND METHODS: The metal stock, individual, and adjustable stock trays were used for 60 stone casts(10 casts each) duplicated a resin master model of mandible and maxilla. The type IV dental stone was poured in a vinyl polysiloxane impressions and allowed to set for one hour. The master model and the duplicated casts were digitized using an optical digitizer. The distance between the reference points were measured and analyzed on the graphic image of 3-D graphic software(CATIA version 5.0). The statistical significance of the differences between the groups was determined by a two-way ANOVA. RESULTS: There were no significant differences between the accuracies of the adjustable stock tray and the master model except only anterior arch width on the upper arch and the diagonal arch length and arch length on one side of the lower arch. CONCLUSION: The adjustable stock trays showed clinically acceptable accuracies of the study cast produced by them.

Geometrical analysis on the dentofacial composition of korean beautiful woman / 대한치과보철학회지

STATEMENT OF PROBLEM: The meaning of the beauty has a little different nature according to a time, culture, and nation. PURPOSE: This study was undertaken to estimate the geometric esthetic criteria for Korean woman by analysis of facial photograph in a smiling. MATERIAL AND METHODS: The facial photographs of 678 Korean beautiful woman were collected from Miss Korea candidates(from 1971 to 2003 year). The dento-facial composition was measured and analyzed geometrically on computer monitor using Adobe. Photoshop. 7.0. The statistical significance of the differences among the 4 decade groups was estimated by a chi2 test. RESULT: The Korean beautiful woman showed the geometric characteristics such as the 'coincidence'(83.0%) between facial midline and dental midline, the 'normal'(96.9%) alignment and arrangement of upper anterior teeth, the 'average'(79.1%) position and 'upward'(53.4%) curvature of upper lip, the 'parallel'(85.7%) relationship between the lower lip and upper anterior incisal curvature, the 'touching'(49.9%) and 'not-touching'(44.8%) relationship between upper anterior incisor and lower lip, the 'first premolar'(54.1%) and 'second premolar'(38.9%) displayed in a smile, and the 'symmetry'(89.4%) of smile. There was statistical significance among the 4 decades in the respect of the upper lip curvature, the relationship between upper anterior incisor and lower lip, and the most posterior teeth displayed in a smile (p<0.05). CONCLUSION: The Korean beautiful woman showed similar results to the western esthetic criteria in the some respects and the tendency that the Korean woman had more active smiling recently.

Perception assessment of esthetics of upper anterior teeth / 대한치과보철학회지

STATEMENT OF PROBLEM: The beauty has a little different meaning according to a time, culture, and nation. PURPOSE: This study was undertaken to determine the Korean perception of the altered upper anterior dental esthetics including the lack of symmetry, the midline deviation, the gingival exposure, the inclination of incisal plane, the type of incisal plane, and the type of gingival line. MATERIAL AND METHOD: 670 subjects were participated in this survey. A questionnaire accompanied by 12 sets of computer-manipulated images using 3D MAX 4.2 software was used to record the ranking of the geometric preference related to the anterior esthetic discrepancies in three or four degrees of alteration. The statistical significance of the differences between the groups was determined by a one-way ANOVA and a t-test. RESULTS: The results obtained were as follows: 1) The Korean perception of the anterior dental esthetics according to the subjects' occupation, sex, and age was most affected by occupation. 2) The masked image emphasizing the dentition and lips appeared stranger than the non-masked image at the same alteration. 3) The lack of symmetry, which was expressed as a unilateral discoloration of the tooth, showed incongruity in any teeth of the anterior dentition. The incongruity was more severe as the degree occurred closer to the midline. 4) The deviation of midline was showed more severe strangeness as the degree of deviation increased. However, more than half of the subjects did not perceive a deviation of 5mm. 5) During smiling, the exposure of the upper gingiva showed more severe incongruity as the degree of gingival exposure increased. 77% of the subjects perceived strangeness at the gingival exposure of 4.5mm. 6) The inclination of the incisal plane appeared stranger as the degree of inclination increased. 62% of subjects perceived strangeness at the 7.5.inclination of the incisal plane. 7) The type of incisal plane showed increasing trangeness in the order of convex/downward, straight/horizontal, and concave/upward. 80% of subjects perceived strangeness at concave/upward. 8) The type of gingival line was showed increasing incongruity in the order of the same, a little above, and a little under the zenith of the lateral incisor to the line joining the zenith of the central incisor and the canine. However, less than half the subjects did not perceive strangeness at any alteration of the gingival line. CONCLUSION: The Korean perception of the upper anterior dental esthetics was different to the westerner's perception in the some respects.

Mechanical Properties Of Reused Lithium Disilicate Glass-Ceramic Of Ips Empress 2 System / 대한치과보철학회지

This investigation was designed to estimate the biaxial flexure strength and fracture toughness of lithium disilicate glass-ceramics of IPS Empress 2 system pressed with as-received ingots and their sprue buttons. Two groups of the lithium disilicate glass-ceramics were prepared as follows: group 1 is ingot-pressed group; group 2 is sprue button-pressed group. A ball-on-three-ball test was used to determine biaxial flexure strength (BFS) of disks in wet environment. Scanning electron microscopy(SEM) analysis was conducted to observe the microstructure of the ceramics. Unpaired t-test showed that there were no differences in the mean biaxial flexure strength (BFS) and KIC values between group 1 and 2 (p>0.05). Two groups showed similar values in the KIC and the strength at 5% failure probability. The SEM micrographs of the IPS Empress 2 glass-ceramic showed a closely packed, multi-directionally interlocking pattern of numerous lithium disilicate crystals protruding from the glass matrix. The lithium orthophosphate crystals could not be observed on the fracture surface etched. There was no a marked difference of the microstructure between group 1 and 2. Although there were no tests including color stability, casting accuracy, etc., the results of this study implied that we could reuse the sprue button of the pressed lithium disilicate glass-ceramic of IPS Empress 2 system.

A Clinical Study On The Occurrence Of Food Impaction / 대한치과보철학회지

The purpose of this study was to investigate the causes of food impaction and to explore solutions as well. For this study, 39 patients with food impaction wee selected. 77 contact areas in these patients were investigated mobility, tightness of contact area, gingival index, plaque index, attachment loss, alveolar bone loss, proximal caries, marginal ridge distance and occlusal relationships. The results were as follows ; 1. Teeth without distal support were found to be the most frequent site of food impaction (41.6%). Food impaction was found to be more frequent in the upper teeth (66.2%) than the lower teeth (33.8%). 2. Food impaction was found in tight contact cases (71.4%). Alveolar bone loss was not found in the early stage of food impaction (83.1%) 3. The distance between the marginal ridges of food impaction sites (mean=0.48mm) was shorter than that of the control group. (mean=0.77mm) (p<0.001) 4. In 18.2% of t he cases, proximal carries were found at the food impaction site. 5. Food impaction affected patient's occlusion with the following frequencies ; cusp to marginal ridge relationship (72.7%), cusp to fossa relationship (3.9%) and stepped relationship (23.4%).

FLEXURE STRENGTH AND MICROSTRUCTURE OF IPS EMPRESS 2 GLASS-CERAMIC ON HEAT PRESSING AND HEAT TREATMENTS / 대한치과보철학회지

This investigation was designed to determine whether heat-pressing and/or simulated heat treatments affected the flexure strength and the microstructure of the lithium disilicate glassceramic in the IPS Empress 2 system. Four groups of the specimens were prepared as follows group 1 - as-received material ; group 2 - heat-pressed material ; group 3 - heat pressed and simulated initial heat-treated material ; group 4 - heat-pressed and the simulated heat-treated material with full firings for a final restoration. The three-point bending test and the scanning electron microscope (SEM) analysis was conducted for the purpose of this study. The flexure strength of group. 2 was significantly higher than that of group 1. However, there were no significant differences in strength among group 2, 3, and 4, and between group 1 and 4. The SEM micrographs of the lithium disilicate glass-ceramic showed the closely packed, multi-directionally interlocking microstructure of numerous lithium disilicate crystals protruding from the glass matrix. The crystals of the heat-pressed materials (group 2, 3, and.4) were a little denser and about two times bigger than those of the as-received material (group 1). This change of microstructure is more obviously exhibited particularly between group 1 and 2. However, there was no a marked difference among group 2, 3, and 4 after the heat pressing procedure. Although there were significant increase of the strength and some changes of the microstructure after the heat-pressing operation, the conr bination of the heat-pressing and the simulated subsequent heat treatments did not produce the increase of strength of IPS Empress 2 glass-ceramic.

FRACTURE STRENGTH OF THE IPS EMPRESS CROWN:THE EFFECT OF OCCLUSAL DEPTH AND AXIAL INCLINATION ON UPPER FIRST PREMOLAR CROWNS / 대한치과보철학회지

The purpose of this study was to compare the fracture strength of the IPS Empress ceramic crown according to the occlusal depth (1.5mm, 2.0mm, 2.5mm) and axial inclination (4degree, 8degree, 12degree) of the upper first premolar. After 10 metal dies were made for each group, the IPS Empress ceramic crowns were fabricated and each crown was cemented on each metal die with resin cement. The cemented crowns mounted on the testing jig were inclined 30 degrees and a universal testing machine was used to measure the fracture strength. The results were : 1. The fracture strength of the ceramic crown with 2.5mm depth and 12degreeinclination was the highest (630N). Crowns of 1.5mm depth and 4degreeinclination had the lowest strength(378N). There were no significant differences of the fracture strength by axial inclination in same occlusal depth group. 2. The fracture mode of the crowns was similar. Most of fracture lines began at the loading area and extended through proximal surface perpendicular to the margin, irrespective of occlusal depth.

A STUDY ON MORPHOLOGY AND SIZE OF CLINICAL CROWN OF PERMANENT MANDIBULAR MOLAR IN KOREAN ADULT / 대한치과보철학회지

The purpose of this study was to estimate the morphology and the size of permanent mandibular molar in Korean Adult. The 100 dental college students with a normal dentition and without any dental prosthesis and severe caries were selected for this study. The subjects were taken impression to make study model. On the study model, the 5 dentists measured those sizes and estimated morphological structures with a calipers, a Boley gauge and a protractor. The results were as follows : 1. The clinical crown height, width, thickness and the other anatomical structures had symmetrical relationship between the left and right mandibular molar. 2. In the clinical crown heights aspect, the buccal crown heights always were higher than the lingual crown height. The heights of the each surface, the buccal or lingual surface, were gradually decreased from the 1st molar to the 2nd molar and the difference on the buccal surface was higher than that on the lingual surface. 3. In the clinical crown width aspect, the mesiodistal measurement of the mandibular 1st molar was higher than that of the mandibular 2st molar. 4. In the clinical crown thickness aspect, the mesial buccolingual measurement was highest on the mandibular 1st molar and the distal buccolingual distance was lowest on the mandibular 2nd molar. This distal thickness of the mandibular molar always was higher than that of the mesial half. 5. The well-developed mesiobuccal groove of the 1st mola was observed more often than that of the 2nd molar. The buccal pit was also observed more frequently at the 1st molar, but the frequency(35%) was not high. 6. The occlusal type according to the number of cusp was almost 5-cusp(98%) in the 1st molar and was also 5-cusp(63%) in the 2nd molar. The frequency of the 6th cusp was 31% in the 1st molar and was 22% in the 2nd molar. The frequency of the 7th cusp was below 2% in the both teeth. 7. In the buccolingual intercuspal distance aspect of the mesial and distal half, the intercuspal distance of distal half was higher than that of the mesial half on the 1st and 2nd molar, but the difference on the 1st molar was higher than that on the 2nd molar. 8. The difference between the widths of the buccal and lingual half was 1.5mm in the 1st molar and 0.8mm in the 2nd molar. Therefore the lingual convergency of the occlusal surface was more higher in the 1st molar. 9. On the mandibular 1st and 2nd molar, the distobuccal external angle was more acute than the mesiobuccal external angle. But the mesiobuccal internal angle was more acute than the distobuccal internal angle. 10. When the mandibular molar was a 5-cusp type, the development of the distal cusp on the 1st molar was better than that on the 2nd molar. The difference between the cusps was around 0.4mm.

A STUDY ON THE MICROSTRUCTURE OF IPS EMPRESS CERAMICS ACCORDING TO THE HEAT TREATMENT AND SPRUE TYPE / 대한치과보철학회지

This study was undertaken to clarify the microstructure of the different IPS Empress ingots by etching and to observe the change of leucite crystal structure according to subsequent heat treatment and the crystal distribution according to sprue types(0 2.8mm, single sprue; 0 1.8mm, double sprue) by scanning electron microscopy. IPS Empress T1, O1 ingots used for staining technique, and Dentin(A2) ingots used for layering technique were selected for this study. To observe the microstructures of these ingots before pressing, the specimens were prepared in splinters(3x3x3mm) taken from the original ingots. And to estimate crystal distribution and microstructural change by sprue type and subsequent heat treatment, the specimens(3x3x3mm) were heat-pressed through the two types of sprues with different diameters and numbers, and all specimens were fired according to the recommended firing schedule. The observed surface was ground with waterproof papers(#800~#1800) on the grind polisher and was cleaned ultrasonically. All specimen were etched with 0.5% hydrofluoric acid. After etching, the surface was treated by ion sputter coating for SEM observation at an accelerating voltage of 20kV. In all specimens, the central area of ground surface was observed because there was less difference in microstructure between the peripheral area and the central area. The results were as follows ; 1. In the microstructure according to the ingot type, there was a wide difference between the staining (T1,O1) and layering(Dentin A2) ingots, but there was not a considerable difference between the T1 ingot and the O1 ingot for staining technique. 2. In all specimens, the crystal dispersion of IPS Empress ceramic using double sprue was significantly more scattered than that of IPS Empress ceramic using single sprue. The degree of scattering was strongest in the Dentin(A2) specimen and weakest in the O1 ingot. 3. In the microstructural change according to the subsequent heat treatment, all of ingots had some microcracks in the inside of the leucite crystal and the glass matrix after pressing. The inner splinters of the leucite crystal became smaller, and more microcracks occurred in the glass matrix due to increasing heat treatment times. 4. The size of leucite crystals varied from 1micrometerto 5micrometer. The mean size of mature crystals was about 5micrometer. The form of the crystal was similar to a circle when it was smaller and similar to an ellipse when it was larger.

A STUDY ON THE WEAR OF DENTAL RESTORATIVE MATERIALS / 대한치과보철학회지

The purpose of this study was to compare the wear characteristics of Type III Gold Alloy (Degular C; Degussa AG), VMK 95 (Vita Zahnfabrik), Vitadur Alpha (Vita Zahnfabrik), IPS Empress (Ivoclar-Vivadent) and Targis (Ivoclar-Vivadent). Ten samples of each material were abraded against enamel of extracted incisors for 160,000 cycles on the wear machine. The depth of wear scars on enamel was analized with profilometer (Alpha-step 200; Tencor). And the wear of material specimen was determined with micrometer (PB-1B; Mitutoyo Co. Japan). The results obtained were as follows : 1. Type III gold alloy (2.47micrometer) and Targis (5.89micrometer) caused less wear of enamel specimens compared to VMK 95 (75.59micrometer), IPS Empress (78.60micrometer) and Vitadur Alpha (78.89micrometer) (p<0.05). 2. The wear of material specimen when opposing enamel was the lowest in type III gold alloy (3.0micrometer), followed by Targis (69.8micrometer), IPS Empress (148.4micrometer). VMK 95 (298.0micrometer) and Vitadur Alpha (300.8micrometer) exhibited the most severe wear against enamel (p<0.05).