• The Journal of Korean Academy of Prosthodontics
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• v.42 no.1
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• pp.11-20
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• 2004

Problem : The several studies were reported to the effects of individual tooth tray with the parallel tooth, but not reported to the effect of individual tooth tray with severe undercut in impression making. Purpose : The purpose of this study is to examine the effect of individual tooth tray; 1) the accuracy of impression in terms of distance. 2) reproducibility of pocket. Material and methods : In this study, a metal model with 3 teeth including tooth prepared 30-degree undercut and gingival crevice of the depth 5mm, width 0.4mm was cast. Impressions of the metal model were taken in 5 times used 4 kinds of impression materials with individual tooth tray and another impression taking were made with conventional method without individual tooth, used same materials, procedure. The stone models were made. Distances between abutments were measured with a Micromeasurescoup-mm. Result : The following results were obtained ; 1. In the comparisonof inter-abutment distance between parallel tooth without individual tooth tray, 4elastomeric materials have not significant difference to the metal model(p>0.05). 2. In the comparisonof inter-abutment distance with undercut tooth without individual tooth tray, 4elastomeric materials have a significant difference to the metal model(p<0.05), especially polyether's dimensional change is large. 3. If individual tooth tray was used to take impression in abutment teeth with severe undercut, more stable results was achieved easily than conventional method. (p>0.05). 4. It is not true that the pressure of impression material with individual tooth tray increased to gingival sulcus. Conclusion : By the results, I knew the fact that individual tooth tray was useful impression method on the teeth with severe undercut for the dimensional stability. Also, I could not confirm the fact that individual tooth tray would increase the penetrating pressure into cervice.

• Journal of the korean academy of Pediatric Dentistry
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• v.34 no.2
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• pp.315-321
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• 2007

Removable appliance has many utilities in pediatric dentistry in the fields of space maintainance or occlusal guidance. In contrast to maxilla, many problems have occurred with mandible in using removable appliance such as deteriorated retention, inconvenience and patient's unwillingness to wear. It is probably due to adapting several retentive clasps at buccal side of the tooth, where there is actually little or no undercut especially in young children having the erupting teeth Moreover, acrylic base plate of conventional removable appliance is located at lingual parts, which leads to the conflict with alveolar crest undercut and sublingual soft tissues. Moreover, young children frequently do not follow the dentist's direction to elevate tongue properly during the impression taking process. Throughout this study, the position of clasps and acrylic baseplate was changed opposite to the traditional Hawley acrylic appliance in order to make a buccal acrylic appliance with buccal base plate and lingual clasp into primary dentition and early mixed dentition. This study was performed for the purpose of evaluating the buccal acrylic appliance in regards of patient compliance, retention and efficiency compared with traditional lingual acrylic appliance along with its merits and demerits. Buccal and lingual acrylic appliance were applied to 5 cases respectively which required space maintaining and tooth movement, and drew a comparison in relevance to patients' compliance, combination with the tongue's function and clinical effectiveness. According to this study, in every case buccal appliance was proved superior to lingual appliance in terms of retention and patients' compliance. Moreover, buccal appliance has shown to be similar to lingual appliance with respect to clinical effectiveness. Throughout this study, it was thought that, if removable appliance is to be applied to mandible, several drawbacks related to conventional lingual appliance shall be resolved. Conclusively, the buccal acrylic appliance is thought to be a good alternative in designing a mandibular appliance in young children and recommended to clinical applications.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.837-841
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• 1996

It is the eccentricity that determines most of the characteristics of the elliptic gears. Accoding to the theoretical tooth profiles, two pairs of the elliptic gears were manufactured by using CNC wire cutting machine. For harmonious rotating motion, it is necessaryto consider operating pressure angle and module not to generate undercut. The characteristics of vibration were investigated by analyzer.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.5
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• pp.85-92
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• 1998

This present paper describes a mathematical model of profile shifted elliptical gears, and this model is based on the concepts of envelope theory and conjugate geometry between the blank and the straight-sided rack cutter. The geometric model of the rack cutter includes working regions generating involute curves and fillets for trocoidal curves, and furthermore the addendum modified coeff. is considered for avoiding undercutting. The addendum modified coeff. is changed linearly along with pitch curves and must be the same absolute value at both major semi-axis and minor semi-axis. If undercutting is at all pronounced, the undercut tooth not only are weakened in strength, but lose a small portion of the involute adjacent to the base circle, then this loss of involute may cause a serious reduction in the length of contact. A very effective method of avoiding undercutting is to use the so-called profile shifted gearing. Non-undercutting condition is examined with the change of eccentricity and addendum modified coeff. in elliptical gears and then the minimum number of tooth is proposed not to gernerate undercutting phenomenon.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.572-577
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• 1997

This present paper describes a mathematical model of profile elliptical gears, and this model is based on the concepts of envelop theory and conjugate geometry between the blank and the straight-sided rack cutter. The geometric model of the rack cutter includes working regions generating involute curves andd fillets for trocoidal curves, and furthermore the addendum modified coeff,is considered for avoiding undercutting. The addendum modified coeff, is changed linearly along with pitch curves and must be the must be the same absolute value at both major semi-axis and minor semi-axis. If undercutting is at all pronounced, the undercut tooth not only are weakened in strength, but lose a small portion of the involute adjacent to the base circle, then this loss of involute may ncause a serios reduction in the length of contact. A very effective method of avoiding undercutting is to use the so-called profile shifted gearing. Non-undercutting conditon is examined with the change of eccentricity and addendum modefied coeff. in elliptical gears and then the minimum number of tooth is proposed not to gernerate undercutting phenomenon.

• Journal of the korean academy of Pediatric Dentistry
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• v.26 no.2
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• pp.207-217
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• 1999

The purpose of this study was to compare the retentive forces of various types of clasps for removable orthodontic appliances for primary and mixed dentition. Seven metal models of a single tooth and two teeth were made, including maxillary left primary canine, first primary molar, second primary molar and first molar. Retentive forces of Adams clasp, circumferential clasp(C clasp), Jackson clasp, Duyzing clasp, arrowhead clasp, ball clasp, eyelet clasp, and triangular clasp were measured by Universal Testing Machine(Zwick Z020, Germany). The obtained results were as follows. 1. Jackson clasp and Adams clasp showed the highest retentive force among single tooth clasps. 2. C clasp showed the lowest retentive force, and there was no statistically significant difference in retentive force between mesial end C clasp and distal end C clasp. 3. Eyelet clasp showed the highest, and ball clasp showed the lowest retentive farce among clasps for interdental undercut. 4. Triangular clasp showed higher retentive force than ball clasp.

• The Journal of Korean Academy of Prosthodontics
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• v.35 no.3
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• pp.470-485
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• 1997

A fundamental principle in clasp selection for a specific abutment is the reduction of the transmission of excessive forces to the abutment tooth. Those forces include tilting, tipping, and stress on the abutment tooth. The flexibility of a clasp was believed to directly affect the reduction of such forces. Opinions have been expressed concerning the proper type of clasp to be used to prevent stress on periodontium. In order to evaluate and compare the various designs of a clasp system, it is necessary to measure these forces. This study compared the average measurements of forces required to dislodge three kinds of circumferential clasps having different amount of undercuts : the first with a round retentive arm, the second with a half round retentive arm, the third with a wrought wire retentive arm under tensile load. Three commonly used undercuts( 0.01, 0.02, 0.03 inch) were created on nine cast crowns, premolars and molars. The test was run six times for a same clasp. The means of tensile load required to dislodge each of the different clasps were compared statistically using the ANOVA test and multiple range test (Duncan test). The results were as follows. 1. The amount of tensile load of the wrought wire clasp was significantly different from the cast round or half round clasp (p<0.05). 2. The more amount of the undercut, the more tensile load was needed to dislodge the clasps. There were significant differences among them (p<0.05). 3. The molar showed higher tensile load than the premolar, and there was significant difference (p<0.05). 4. The means of tensile load according to clasp types showed significant differences at the molar between wrought wire clasp and cast clasp (p<0.05), but did not at the premolar.

• The Journal of Advanced Prosthodontics
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• v.11 no.2
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• pp.138-146
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• 2019

PURPOSE. Comparing the accuracy of casts produced from digital workflow to that of casts produced from conventional techniques. MATERIALS AND METHODS. Whole arch alginate (ALG) and polyvinyl siloxane (PVS) impressions were taken with stock trays and custom trays, respectively. The ALG impressions were poured with type III dental stone, while the PVS impressions were poured with type IV dental stone. For the digital workflow, IOS impressions were taken and physical casts were produced by 3D printing. In addition, 3D printed casts were produced from images obtained from a laboratory scanner (LS). For each technique, a total of 10 casts were produced. The accuracies of the whole arch and separated teeth were virtually quantified. RESULTS. Whole arch cast accuracy was more superior for PVS followed by LS, ALG, and IOS. The PVS and ALG groups were inferior in the areas more susceptible to impression material distortion, such as fossae and undercut regions. The LS casts appeared to have generalized errors of minor magnitude influencing primarily the posterior teeth. The IOS casts were considerably more affected at the posterior region. On the contrary, the IOS and LS casts were more superior for single tooth accuracy followed by PVS and ALG. CONCLUSION. For whole arch accuracy, casts produced from IOS were inferior to those produced from PVS and ALG. The inferior outcome of IOS appears to be related to the span of scanning. For single tooth accuracy, IOS showed superior accuracy compared to conventional impressions.

• The korean journal of orthodontics
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• v.27 no.1
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• pp.157-171
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• 1997

This study was conducted to see the effect of TiN ion-plating on the bond strength of orthodontic bracket. Three stainless-steel brackets with different base types were chosen; when TiN ion-plated brackets and non iorrplated brackets were bonded to the teeth, initial and long-term bond strength were measured, The observations oi bonding surface and failure sites through the scanning electron microscope were analysed and compared. The summary of this study was as follows; ${\cdot}$ When TiN ion-plating was not applied, the Micro-Loc type was the highest in bond strength atter 24 hours as $5.89{\pm}1.77$ MPa, followed by $4,27{\pm}1.12MPa$ for Foil Mesh type and $2.64{\pm}0.58MPa$ for Undercut type(P<0.05). ${\cdot}$ Under TiN ion-plating, the bond strength after 24 hours showed: Micro-Loc type $-6.26{\pm}1.51MPa$, Foil Mesh type $-7.45{\pm}2.01MPa$, Undercut type $-2.93{\pm}0.84MPa$. Unlike in the case of non ion-plating, Foil Mesh type showed a higher strength than Micro-Loc type, with Undercut type still showing the lowest bond strength(P<0.05). The bond strength, after 24 hours, increased in case of ion-plated in all 3 types, but a significant increase was shown only in Foil Mesh type(P<0.001). ${\cdot}$ Under a long-term immersion, regardless of ion or non ion-plating, bond strength in general increased over the initial bond strength(one day), with more stability. ${\cdot}$ Through scanning electron microscopic observation of bonding surface, it was found that, regardless of the bracket base type or the application of ion-plating, the resin was thoroughly spreaded into bracket base to form a solid bonding surface between the bracket and the tooth. This was also true in case of a long-term immersion. ${\cdot}$ The scanning electron microscopic observation of failure sites revealed diverse failure patterns.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.2
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• pp.283-289
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• 2012

Cam rack pinion (CRP) system which consists of cam rack and roller pinion transforms the rotation motion into linear one. The roller pinion has the plurality of rollers and meshes with its conjugated cam rack. The exact tooth profile of the cam rack and the non-undercut condition to satisfy the required performance have been proposed by introducing the profile shift coefficient. The load stress factors are investigated by varying the shape design parameters to predict the gear surface fatigue limit which is strongly related to the gear noise and vibration at the contact patch. The results show that the pitting life can be extended significantly by increasing the profile shift coefficient.