• Journal of Technologic Dentistry
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• v.35 no.1
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• pp.29-35
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• 2013

Purpose: The purpose of this study was to evaluate the validity of digital models fabricated by dental scannable stone. Methods: Twenty same cases of stone models(maxillary full arch) were manufactured. Intercanine distance, intermolar distance, two dental arch lengths(right, left), two diagonal of dental arch lengths(right, left) were measured for comparison. Each of ten stone models were measured by digital vernier calipers and scanned by dental scanner. Ten digital models were measured by CAD program. The mean(SDs) values were compared by a Mann-Whitney U test(${\alpha}$=0.05). Results: No statistically significant differences between the two groups were found at intermolar distance, dental arch length(right)(p>0.05). However, intercanine distance, dental arch length(left) and two diagonal of dental arch lengths(right, left) were statistically significant(p<0.05). Conclusion: Stone models fabricated by dental scannable stone showed larger than digital models.

• Journal of Technologic Dentistry
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• v.38 no.4
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• pp.263-272
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• 2016

Purpose: The purpose of this study is to measure and compare a degree of setting expansion of dental stone by time depending on the mixing methods and mixing ratios of dental stone, to compare the surface state of each specimen with the use of an optical camera with microscope, and thereby to provide a fundamental material for making dental prostheses. Methods: The test on setting expansion of dental stone is based on ISO 6873. With two different mixing ratios and three kinds of stone mixing methods, test groups were created, and a total of six types of specimens (N=30) were made. Based on the specimens, the setting expansion rate of each one was measured in each time slot of 24 hours, and the surface of the set stone was measured. Results: According to the analysis on setting expansion rate of stone, the setting expansion of the specimen that was created in the way of vacuum mixing at normal mixing ratio was 0.1944% at 120 minutes; the setting expansion of the specimen that was created in the way of vacuum mixing at the mixing ratio which was 40% higher than normal mixing ratio was 0.195% at 120 minutes; the setting expansion of the specimen that was created in the way of mixing with hands at normal mixing ratio and then removing bubbles in vacuum mixer was 0.196% at 120 minutes. Conclusion: The setting expansion rate of each dental stone specimen was significantly different with the lapse of time up to 24 hours(p<.001).

• The Journal of Korean Academy of Prosthodontics
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• v.40 no.2
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• pp.184-192
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• 2002

The purpose of this study was to investigate the abrasion resistance and surface roughness of conventional dental stones and improved dental stones and newly developed dental stones. Materials included in this study were several dental stones and newly developed dental stone; 2 type III. 6 type IV (including newly developed dental stone). 1 type V Ten specimens for each material, total ninety specimens were made. Each specimen was subjected to 50 complete cycle abrasion under constant load 0.42N at speed or 6mm per sec. The depth after abrasion test was measured for each specimen. Surface roughness before and after abrasion test was compared. The results were as follows ; 1. The resin containing die materials such as Tuff Rock and Resin Rock had superior abrasion resistance. 2. Type IV, V dental stone exhibited greater abrasion resistance than Type III dental stone. 3. The results or the surface roughness showed similar pattern with the abrasion resistance.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.1
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• pp.61-70
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• 2003

The purpose of this study was to investigate the contact angles and wettability of conventional dental stones and improved dental stones and newly developed dental stones on several impression materials. Materials included in this study were several dental stones and newly developed dental stone ; 2 type III stones (Snow Rock, New Diastone), 6 type IV stones(Crystal Rock, Vel Mix, Fuji Rock, Tuff Rock, Resin Rock and newly developed dental stone) and 1 type V stone (Die Keen). Contact angles on the impression materials were measured with contact angle measuring device. Ten specimens for each material, total 180 specimens were made on void entrapment model. The two impression materials (Handae, GC) were used to produce 9 groups of die stone casts form void entrapment model. Voids in the stone casts were counted under a stereoscopic microscope. The grad for the reproduction ability of each materials on the void entrapment model was calculated from the casts by one examiner. From the experiment, the following results were obtained : 1. The newly developed stones showed smallest contact angle. Type III dental stone had larger contact angles than type IV and V stones. Contact angle was much affected by the impression materials. 2. Resin containing die materials such as Tuff Rock and Resin Rock had smallest void number than any other groups. 3. In comparing reproduction parameters, Tuff Rock and Resin Rock presented superior results, while Vel Mix showed lowest reproduction ability.

• The Journal of Advanced Prosthodontics
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• v.10 no.5
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• pp.335-339
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• 2018

PURPOSE. The purpose of the present study was to compare scanning trueness and precision between an abutment impression and a stone model according to dental computer-aided design/computer-aided manufacturing (CAD/CAM) evaluation standards. MATERIALS AND METHODS. To evaluate trueness, the abutment impression and stone model were scanned to obtain the first 3-dimensional (3-D) stereolithography (STL) file. Next, the abutment impression or stone model was removed from the scanner and re-fixed on the table; scanning was then repeated so that 11 files were obtained for each scan type. To evaluate precision, the abutment impression or stone model was scanned to obtain the first 3-D STL file. Without moving it, scanning was performed 10 more times, so that 11 files were obtained for each scan type. By superimposing the first scanned STL file onto the other STL files one by one, 10 color-difference maps and reports were obtained; i.e., 10 experimental scans per type. The independent t-test was used to compare root mean square (RMS) data between the groups (${\alpha}=.05$). RESULTS. The $RMS{\pm}SD$ values of scanning trueness of the abutment impression and stone model were $22.4{\pm}4.4$ and $17.4{\pm}3.5{\mu}m$, respectively (P<.012). The $RMS{\pm}SD$ values of scanning precision of the abutment impression and stone model were $16.4{\pm}2.9$ and $14.6{\pm}1.6{\mu}m$, respectively (P=.108). CONCLUSION. There was a significant difference in scanning trueness between the abutment impression and stone model, as evaluated according to dental CAD/CAM standards. However, all scans showed high trueness and precision.

• The Journal of Korean Academy of Prosthodontics
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• v.9 no.1
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• pp.23-27
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• 1969

The purpose of this studies is to determine the surface hardness of dental stone and to investigate the methods which increase the surface hardness of dental stone using the dissolved solution of various synthetic resin, the obtained results of hardness value calculated Rockwell Hardness Number by means of Rockwell Hardness Tester. 1) In this experiment, 10% polystyrene dissolved in 100cc amylacetate is excellent solution which provides the surface hardness of dental stone after setting of specimen, and there is no effective way that stone specimen is immersed into polystyrene in amylacetate, polystyrene in benzene and polystyrene in butylacetate above 1 hour. 2) When the stone specimen is immersed into acrylic resin in benzene and melamin resin in amylacetate at least 1 hour to 3 hours, the hardening effect of stone surface is valuable. 3) The stone specimen immersing into urea resin in butylacetate, the surface hardness of the stone specimen decreased within 1 hour, but increased after 3 houre. 4) For the separating medium, the easyfoil is superior to the olive oil in the aspect of improving the hardening effect of the immersed specimen.

• Journal of Technologic Dentistry
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• v.34 no.3
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• pp.227-235
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• 2012

Purpose: This study compared the surface hardness (Vickers) and microstructural characteristics between a type IV stone with and without die hardening treatment, a polyurethane die material. Methods: Materials used were a type IV stone(MG Crystal Rock), two die hardeners (Hardening bath, Epox-it), and a polyurethane resin material(Polyluck). Six specimens per group were prepared according to manufacturer's directions. The prepared specimens were tested by means of hardness test, one-way ANOVA analysis, scanning electron microscopic(SEM) observations and energy dispersive spectroscopic(EDS) analysis. Results: In the hardness test and its statistical analysis, there was no significant difference in the surface hardness between a type IV stone and type IV stone with die hardener coating, type IV stone mixed with an epoxy like material instead of water. In contrast, polyurethane resin material exhibited significantly greater surface hardness than other specimen groups (p<0.05). Conclusion: By considering the results of the hardness test, SEM observations and EDS analysis, although the die hardeners on type IV stone did not show remarkable improvement in surface hardness, the die hardener coating on the surface of type IV stone material did show decrease of microporous and improvement of surface defects.

• Journal of Technologic Dentistry
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• v.34 no.2
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• pp.121-128
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• 2012

Purpose: The aim of this study was to determine the reliability and accuracy of measurements in digital models(CEREC$^{(R)}$ AC) compared to stone models. Methods: A master model(500B-1, Nissin Dental Product, Japan) with the prepared upper full arch tooth was used. Conventional impression and then stone model(n=10) were produced from this master model, and on the other hands, digital impressions were made with the CEREC$^{(R)}$ AC intra-oral scanner(n=10). One examiner measured two times the intercanine, intermolar distance, dental arch length. The stone model were measured using a digital caliper. The t-student test for paired samples and intraclass correlation coefficient(ICC) were used for statistical analysis. Results: The measurement of two methods showed very good reliability. At the intra-examiner reliability of measurement, ICC at the stone and CEREC$^{(R)}$ AC model were 0.81 and 0.94. The mean difference between measurements made directly on the stone models and those made on the CEREC$^{(R)}$ AC model was 0.20~0.28mm, and was statistically significant(P=0.001). Conclusion: These in vitro studies show that accuracy of the digital impression is similar to that of the conventional impression. These results will have to be confirmed in further clinical studies.

• Journal of Technologic Dentistry
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• v.36 no.2
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• pp.91-96
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• 2014

Purpose: The purpose of this study was evaluate the validity of polyurethane model fabricated by intra oral scanning method. Methods: Ten sam cases of stone models were manufactured from master model, and polyurethane models were made with the intra oral scanning and CNC milling method. One examiner individually measured 6 distances(intercanine distance, intermolar distance, two dental arch lengths(right, left) and two diagonal of dental arch lengths(right, left) on the stone models and the polyurethane models. The Mann-Whitney U test(${\alpha}$=0.05) were used for statistical analysis. Results: The mean difference between measurements made directly on the stone models and those made on the polyurethane models was 0.31-0.38mm. No statistically differences between the two groups were founded 4 distances(p>0.05), but 2 distances were statistically significant(p<0.05). Conclusion: Stone models showed larger than polyurethane models fabricated by intra oral scanning method.

• Journal of Technologic Dentistry
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• v.40 no.1
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• pp.33-40
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• 2018

Purpose: The purpose of this study was to investigate the influence of mechanical properties of various ultra-dental stone by setting methods. Methods: 240 cylinder specimens($10mm{\times}20mm$) were prepared from three ultra-dental stones(Gemma, Die keen and Fuji rock; n = 80) in accordance with the manufacturers' recommendations. Half of the specimens of each stone(n = 40) were dried in open air within a room temperature; the other half(n = 40) underwent in a silicone rubber mold in open air for 30 minutes and then were dried in a microwave oven for 10 minutes to 600W. Compressive strength(CS), compressive modulus(CM) and diametral tensile strength(DTS) conducted until fracture using Instron 5966 at each of the following periods: 1 and 24 hours from mixing. One-way analysis of variance and Scheffe's post hoc test were performed for statistical comparisons at a significance level of P<.05. Results: The CS and CM values in all dental stone indicated highest after 24h(54.25 MPa < ) than the values for specimens dried in microwave method. The DTS values revealed the highest microwave method. However, in 24h, FJ(Fu-ji rock) and GM(Gemma) had lower mechanical properties than air. Conclusion : Within the limitations of this study, CS did not influence by microwave method but DTS affected according to the setting.