• The Journal of Korean Academy of Prosthodontics
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• v.42 no.1
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• pp.58-72
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• 2004

Statement of problem : Clinically, maxillary first premolar has a high risk of fracture. This is thought to be caused by the susceptible figure which the maxillary first premolar has In other words, sharp cusp angles of the premolar is thought to influence this situation. Purpose : This study was to know stress distribution of all-ceramic crown according to the cusp angle. Material and Method : It was manufactured a three dimensional finite element model simplified maxillary first premolar, and then analyzed stress distribution when cusp angle was each $80^{\circ}$, $90^{\circ}$, $100^{\circ}$, $110^{\circ}$ and $120^{\circ}$. Results and conclusion : 1. The von Misses stress showed that stress decreases as cusp angle increases in the central groove of the occlusal surface. 2. It showed that maximum principal stress was centered at the region of the central groove of the occlusal surface and a region which the force was inflicted. And also it appeared high on the lingual and buccal side of finish line. 3. The X axis of normal stress was focused in the central groove of the occlusal surface. The Y axis normal stress appeared high in the central groove of the occlusal surface, buccal and lingual side. 4. The Stress near the finish line showed a low value compared with stress in the region of the central groove of the occlusal surface. 5. It shows that the most dangerous angle for tooth fracture was on $80^{\circ}$ of the cusp angle and low on $120^{\circ}$ of its.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.15-19
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• 1996

The cusp height in ball end milling, flat end milling and filleted end milling according to various surface inclination angle was calculated. The calculation result shows that, for each kind of tools, there exists certain range of inclination angle in which cusp height characteristics favorable. From machining time calculation, filleted end mill found to be superior to flat end mill in rough machining of sculptured surface.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.944-947
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• 2000

Sculptured surface machining plays a vital role in the process of bring new products to the market place. A great variety of products rely on this technology for the production of the dies and moulds used in manufacturing. And, the use of CNC machines and CAD/CAM system has become a vital parts of product development process. The propose of this study is to investigate the effect of cutting parameters on the machinability such as surface roughness and cusp generated in the machining of sculptured surface on a three-axis CNC machining center using the CAD/CAM system. Experimental result showed that: In step down cutting, as the inclined angle of surface became smaller, the cusp height appeared higher. On the other hand, in step over cutting, as the inclined angle of surface became larger, the cusp height appeared higher. In the point of precision machining, step over cutting was more effective. For the minimization of cusp height, step down cutting was effective in larger inclined surface, but step over cutting in smaller inclined surface.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.826-830
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• 2000

Sculptured surface machining plays a vital role in the process of bring new Products to the market place. A great variety of products rely on this technology for the production of the dies and moulds used in manufacturing. And, the use or CNC machines and CAD/CAM system has become a vital parts or product development process. But, cusp is inevitable by-product in sculptured surface machining, and it is very difficult to calculate the cusp height correctly. In this study, an analytical cusp height model is proposed considering the radius of the ball end mill, radius of machined workpiece and the inclined angle of convex or concave circular surface. Experiments were performed to check the validity of this proposed model and experimental results showed that the proposed cusp model were very effective.

• Journal of the korean academy of Pediatric Dentistry
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• v.38 no.4
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• pp.337-347
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• 2011

The basic structure of the primary crowns usually resemble their succeeding permanent teeth. However, maxillary second primary molars resemble ipsilateral first permanent molars. Accordingly in this study, odontometric data of the two teeth was obtained, then analyzed to verify the morphological relationship and sex difference between the two teeth. Dental study casts were examined for their mesiodistal and buccolingual width of the crowns, diameter of each cusps, and intercuspal distances. Photographs of the crowns were taken to measure the angles between each cusp tip. The results are as follows : 1. In boys, PrI, PaI, DBC angle, and MBC angle did not show any statistically significant difference between the two teeth(p>0.05), and moderate level of correlations were observed. 2. In girls, crown index, DBC angle, and MBC angle of the two teeth did not show any statistically significant difference(p>0.05), and moderate level of correlations were recognized. 3. Measurements that did not show statistically significant difference between the two teeth in both boys and girls were DBC angle and MBC angle(p>0.05). In DLC angle, however, statistically significant difference was observed(p<0.01). 4. Most of the measurements showed sex differences, except DBC angle, which did not show any sex difference in both teeth(p>0.05).

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1255-1265
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• 1992

Under uniform heat flow, the thermal stress intensity factors for the interfacial crack on a rigid cusp-type inclusion are determined by Hilbert problem expressed with complex variable. The thermal stress intensity factors are expressed in terms of the periodic function of heat flow angle. When the tip of the interfacial crack meets that of the cusp crack, the thermal stress intensity factors have singularities. The thermal stress intensity factors at the interfacial crack tip located in the distance from the cusp crack tip vary with the location of the interfacial crack tip. From the results of the analysis, the complex potential functions and the thermal stress intensity factors for the cusp-type inclusion without the interfacial crack are derived under the cusp surface boundary conditions insulated or fixed to zero relative temperature.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.2
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• pp.242-255
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• 1999

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 height 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 molar 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 2of 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.

• Journal of Dental Rehabilitation and Applied Science
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• v.16 no.2
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• pp.79-92
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• 2000

The purpose of this study was to estimate the morphology and the size of permanent maxillary 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, authour three times measured those sizes and estimated morphological structures with a calipers, a Boley gauge and a protractor. The results were as follows; 1. In the maxilary first molar's clinical crown height, mesiolingual cusp height was 6.34mm, mesiobuccal cusp height was 6.05mm, distobuccal cusp height was 5.20mm. And in the maxillary second molar's clinical crown height, mesiobuccal cusp height was 5.85mm, mesiolingual cusp height was 5.71mm, distobuccal cusp height was 5.51mm, distolingual cusp height was 3.53mm. This result considered that the maxillary first molar inclined to distobuccal, and the maxillary second molar more upright than the maxillary first molar. 2. In the width of clinical crown, the maxillary first molar was 10.43mm, the maxillary second molar was 10.20mm, and the difference between the first molar's width and the second molar's width was 0.23mm. 3. The crown thickness was measured divided into mesial buccolingual half and distal buccolingual half. The mesial buccolingual half was 11.14mm, and distal buccolingual half was 10.35mm in the maxillary first molar, and in the maxilary second molar, mesial buccolingual half was 11.25mm, and distal buccolingual half was 9.72mm. This result considered that height of convergency located in mesial half of crown. 4. In the buccal groove length, total length and ratio, the maxillary first molar was 52.5%, the maxillary second molar was 50%. And the development of buccal groove in the maxillary first molar was 59% in case of the well developed buccal groove and 41% in case of the weak developed one. And frequency of buccal pit of the maxillary first molar was 12.5%. Whereas, the frequency of buccal of the well developed buccal groove in the maxillary second molar was 37% and that of the weak developed one was 63%. And frequency of buccal pit of the maxillary second molar was not seen. 5. The 3 cusp type tooth cannot be found in the maxillary first molar and the frequency of 3 cusp type tooth in the maxillary second molar was as small as 6% 6. In the case of 4 cusp type tooth, the size of distal lingual cusp molar was difference between in the maxillary first molar and in the maxillary second molar by about 1mm. 7. The intercuspal distance was similar in the maxillary first premolar and second molar. And intercuspal distanc of mesial half of the maxillary first molar and the maxillary second molar was silmillar, too. 8. The an measurement of occlusal surface in 4 cusp type tooth showed that the angle of occlusal surface between the distobuccal and mesiolingual was an obtuse angle, and the angle of occlusal surface between mesiobuccal and distolingual was an acute angle in the both cases of maxillary first and second molar. 9. The measurements of the development of Carabelli cusp showed that the frequency of the well developed one was 7% and that of the weak developed one was 56% in the maxillary first molar. And there cannot be found the well developed one and can be found 2.5% only in the case of the weak developed one in the maxillary second molar. 10. The well developed oblique ridge in the maxillary first molar showed the 100% frequency and that in the maxillary second molar showed the 85.5% frequency. The frequency of mesiomarginal ridge tubercle in the maxillary first molar was 82% and that in the maxillary second molar was 30.5%. And the frequency of distal accessory tubercle in the maxillary first molar can be seen about 19% and that in the maxillary second molar can be seen about 12%.

• Journal of Technologic Dentistry
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• v.11 no.1
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• pp.65-70
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• 1989

The development of the lobe pattern in the human dentition plays a part in the form and function of each individual teeth. In order to determin the morphological categories used to describe the occlusal surfaces of the maxillary and mandibular molars, the variation of the developmental grooves which separate each lobe in the molars was examined and analysed. The obtained conclusions were as follow. 1. Most of the maxillary first molars with more distinct and more developmental grooves than the other molars but in most cases of the third molar, a heart-shaped outline due to poorly developed or abscent distolingual cusp was most frequent and in this case the third molar had the 3 cusps separated by the central developmental groove and the buccal developmental groove. 2. In most cases, the mandibular first molar had the 5-cusp type that the groove patter resembles a Y, the second molar the 4-cusp type arranged in such a way that the buccal and lingual developmental grooves meet the central developmental groove at right angle on the occlusal surface and many instances of the mandibular third molars had the 5-cusp thpe with a+groove pattern which separatess the mesiolingual cusp from the distobuccal cusp and the 4-cusp type with a+groove pattern. 3. The maxillary and mandibular third molar were most variable in the developmental groove.

• Imaging Science in Dentistry
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• v.39 no.2
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• pp.89-92
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• 2009

Purpose: To assess the angle between mandibular canal and occlusal plane at each posterior tooth region and location of mental foramen on the panoramic radiographs. Materials and Methods: This study analysed 46 half-mandibles of panoramic radiographs. Inferior border of mandibular canal was traced. Occlusal plane was drawn from lingual cusp tip of the first premolar to distolingual cusp tip of the second molar. Perpendicular line from occlusal plane was drawn at each tooth region and then tangential lines were drawn from the crossing points at canal. the angle between occlusal plane and tangential line was measured. The location of mental foramen was also studied. According to the location of mental foramen, radiographs were divided into M (mesial) group and D (distal) group on the basis of the second premolar. and then inter-group analysis about mandibular canal angle was done. Results: The angles of mandibular canals were -17.7$^{\circ}$, -9.5$^{\circ}$, 8.2$^{\circ}$, 22.3$^{\circ}$, and 39.2$^{\circ}$at first premolar, second premolar, first molar, second molar, and third molar, respectively. The commonest position of the mental foramen was distal to the second premolar. Inter-group comparison showed statistically significant difference at the second premolar and the first molar(p<0.001). Conclusion: The knowledge of mandibular canal angle and location of mental foramen can help understanding the course of mandibular canal. (Korean J Oral Maxillofac Radiol 2009; 39: 89-92)