• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.1
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• pp.277-283
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• 2020

In a concentric magnetic gear, which replaces the teeth of a mechanical gear with a permanent magnet, the polar ratio of the magnet that determines the reduction ratio affects the behavior of the magnetic gear dramatically. This study analyzed the density of transmission torque, the efficiency of torque considering the solid loss, and the torque quality, including the cogging characteristics using finite element analysis. When the pole number on the driving side was changed from two to five, it was confirmed that there was an optimal pole ratio, in which the transmission torque was maximized. Because eddy current generation density is proportional to the magnetic field, the transmission efficiency also shows a similar tendency to the transmission torque density, and the efficiency is more than 95% at a low gear ratio. The cogging characteristics due to the interaction of the permanent magnets with the limited number of poles are inversely proportional to the least common multiple between the number of magnets on the drive side and the number of modulator teeth. A test model was built for the transmission torque evaluation.

• Restorative Dentistry and Endodontics
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• v.7 no.1
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• pp.139-144
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• 1981

Eighty four human maxillary first premolars were injected with china ink, decalcified, cleared and used in study, in vitro, to determine the number of root canals, the frequency and location of lateral canals, the frequency and location of transverse anastomoses, the curvature of root canals, the location of apical foramens, and the frequency of apical deltas. The results were as follows: 1. Most of the teeth demonstrated two canals, but 20.2% of the teeth were found to have one canal. 2. Of the 151 canals studied, 38.4% of the canals were found to have lateral canals and these ramifications were usually located in the apical third of the root. 3. Of the two root canals in one root, 35.7% of the canals were found to have transverse anastomoses and were usually located in the middle third of the root. 4. 15.2% of apical foramens were located directly on the root apex and 84.8% of them laterally, and 52.3% of canals showed distal curvature.

• The korean journal of orthodontics
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• v.17 no.1
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• pp.85-91
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• 1987

The aim of this study was to clarify whether bonding/debonding procedure will affect the occurance of enamel crack. The frequency of enamel crack was compared between before-bonding and after-debonding on 200 human extracted teeth. Each facial surface of the tooth was divided in 9 fragments. A presence of crack, which was classified by its direction as vertical, horizontal and oblique crack, was surveyed in each fragment. Number of all cracks in facial surface was 1355 at before-bonding, and 1605 at after-debonding, so it revealed significant increase rate of $18.5\%$, but compared by fragment, cracks were significantly Increased in OC, OD, CC and GC fragments. All kinds of cracks were significantly increased, especially increase rate of oblique crack reached $54.9\%$. The increase rate of cracks was not superior at any fragment or region, but some evidence was seen in CC fragment. Judging from the above, increase of crack is unavoidable with bonding/debonding procedures.

• The Journal of the Korean dental association
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• v.22 no.5 s.180
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• pp.423-427
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• 1984

A total of 114 extracted human mandibular first molars were used to study the configuration of the floor of the chamber. The specimens were ground and the pulp chamber was examined with a magnifier and explored with sharp explorer. The study showed the shape of the pulp chamber, number of root canals, and the type of canal orifice. The results were as follows; 1. In so far as observing the shape of the pulp chamber of the teeth, 58.8% of the teeth were square, 34.2% were triangle and 7.0% were ovoid shape. 2. 58.8% of the specimens have 4 root canal orifices, 34.2% have 3 root canal orifices, 7.0% have 2 root canal orifices. 3. 41.2% of the specimens show 'H' shape, 17.6% show 'Square' shape, 31.6% show 'T' shape, 2.0% show 'reverse-T' shape and 7.0% show 'I' shape.

• Restorative Dentistry and Endodontics
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• v.12 no.1
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• pp.165-169
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• 1986

A total of 114 extracted human mandibular 2nd molars were used to study the configuration of the floor of the chamber. The specimens were ground and the pulp chamber was examined with a magnifier and explored with sharp explorer. The study showed the shape of the pulp chamber, number of root canals, and the type of canal orifice. The results were as follows, 1. In so far as observing the shape of the pulp chamber of the teeth, 47.4% of the teeth were square, 42.9% were triangle and 9.7% were ovoid shape. 2. 35% of the samples had 2 root canal orifices, 62% had 3 root canal orifices, 3% had 4 root canal orifices. 3. 3% of the specimens showed 'H' shape, 5% showed 'Square' shape, 51% showed 'T' shape, 1% showed 'reverse-T' shape, 35% showed 'I' shape and 5% showed the specific 'C' shape.

• Restorative Dentistry and Endodontics
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• v.6 no.1
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• pp.105-107
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• 1980

A total of 125 extracted maxillary first molars were used to study the configuration of the floor of the pulp chamber. The specimens were ground and the pulp chamber was examined with a magnifying glass and explored with sharp explorer. The study showed the shape of the pulp chamber, number of root canals, and type of canal orifice. The results were as follows; 1. In so far as observing the shape of the pulp chamber of the teeth, 50.4% of the teeth were trapezoid, 20.8% were inverted trapezoid, 18.4% were rectangle and 10.4% were triangle shape. 2. 71.2% of the specimens have 3 root canal orifices, and 28.8% have 4 root canal orifices. 3. 71.2% of the specimens have 1 mesiobuccal canal orifice, 23.2% have 2 mesio-buccal canal orifices joined by a groove, and 5.6% have 2 mesio-buccal canal orifices seperated each other.

• Restorative Dentistry and Endodontics
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• v.4 no.1
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• pp.23-27
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• 1978

Fifty two mandibular permanent canines were chosen to study the anatomy of the root canal. The experimental teeth were injected with China ink, decalcified, cleared and observed to investigate the number of root canals, frequency and location of lateral canals, the location of apical foramens, the frequency of apical deltas, and the curvature of root canals. The results were as follows: 1) all of the experimental teeth demonstrated single canal. 2) of the 52 canals, 9.6% of the canals were found to have lateral canals and the locations of the lateral canals were in the apical third of the roots 3) Thirty three apical foramens were located laterally on the root apices and nineteen foramens were located on the centers of the root apices. 4) 37 canals showed straight curvature, 12 canals distal curvature. 3 canals labial curvature.

• Restorative Dentistry and Endodontics
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• v.10 no.1
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• pp.183-186
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• 1984

Thirty maxillary lateral incisors were injected with china ink, decalcified, cleared and used in an in vitro study to determine the number of root canals, the frequency and location of lateral canals, the location of apical foramens, the frequency of apical deltas, and the curvature of root canals. The results were as follows: 1. Most of the teeth demonstrated single canal, but 6.7% of the teeth were found to have bifurcated canals. 2. Of the 32 canals studied, 37.5% of the canals were found to have lateral canals and these ramifications were usually located in the and apical third of the root. 3. 9 apical foramens were located directly on the root apex and 21 foramens laterally. 4. 3 canals showed mesial curvature, 20 canals distal curvature, 4 canals labial curvature, and 3 canals palatal curvature.

• Restorative Dentistry and Endodontics
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• v.3 no.1
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• pp.12-16
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• 1977

One hundred human maxillary first molars were injected with china ink, decalcified, cleared, and used in vitro study to determine the number of root canals, the frequency and location of lateral canals, canals per root, and frequency of apical deltas. The results were as follows; 1. The mesiobuccal root was found to contain a single primary canal in 53% of the teeth studied and two canals in 47 % of the teeth studied. 2. In mesiobuccal roots with two canals, the seperated apical foramen appeared 32% of the specimens and the common apical foramen 15% of the specimens. 3. Of the 347 canals studied, 26.9% of the canals were found to contain lateral canals and these ramifications were mainly located in the apical third of the root.

• Restorative Dentistry and Endodontics
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• v.9 no.1
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• pp.121-125
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• 1983

Thirty eight mandibular second premolars were injected with china ink, decalcified, cleared and used in an in vitro study to determine the number of root canals, the frequency and location of lateral canals, the location of apical foramens, the frequency of apical deltas, and the curvature of root canals. The results were as follows: 1. Most of the teeth demonstrated single canal, but 5.3% of the teeth were found to have bifurcated or trifurcated canals. 2. Of the 40 canals studied, 52.5% of the canals were found to have lateral canals and these ramifications were usually located in the apical third of the root. 3. 7 apical foramens were located directly on the root apex and 31 foramens laterally. 4. 4 canals showed mesial curvature, 20 canals distal curvature, 11 canals buccal curvature, and 8 canals lingual curvature.