• The Journal of Korean Academy of Prosthodontics
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• v.37 no.2
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• pp.143-166
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• 1999

The success of porcelain laminate veneer depends on the bond strength between tooth structure and ceramic restoration and the design of tooth preparation. In particular, incisal coverage and incisal finish line are the two most important factors in long-term fracture resistance. Although the majority of clinicians are practicing incisal coverage and there are various opinions on the geo-metrical ratio between the clinical crown length of the remaining tooth structure and the length of incisal extension in porcelain laminate veneer and the optimal incisal finish lines. scientific evidence still loaves much to be desired. The purpose of this study was to determine the effects of the amounts of incisal coverage and the types of incisal finish line on the stress distribution in maxillary anterior porcelain laminate veneers under two different loading conditions. Three-dimensional finite element models of a maxillary anterior porcelain veneer with differ-ent amounts of incisal coverage ; 0, 1, 2, and 3mm and different incisal finish lines feathered edge, incisal bevel, reverse bevel and lingual chamfer with various amounts of lingual extension were developed. 300N force was applied at the point 0.5mm cervical of the linguoincisal edge in two loading conditions ; A) 125 degrees, B) 132 degrees. Tensile and compressive stress in ceramic and shear stress in the resin cement layer were analyzed using three-dimensional finite element method. The results were as follows : 1. The types of incisal finish line had more influence on the stress distribution in porcelain laminate veneer than the amounts of incisal coverage. 2. In case of no incisal coverage, incisal beveled laminate exhibited more evenly distributed tensile stress than feathered edged laminate. And in case of incisal coverage, reverse beveled laminate and lingual chamfered laminate with 1mm lingual extension exhibited more evenly distributed tensile stress than lingual chamfered laminates with 2mm and 3mm lingual extension. 3. As long as the lingual chamfer goes, less tensile stress was found at the incisal edge, while much more tensile stress was found at the lingual margin area in proportion to the length of lingual extension. 4. Under 125 degree load, tensile stress in porcelain laminate veneer had increased compared with that under 132 degree load and the difference exhibited by the change of the amount of tooth support was larger. 5. The types of incisal finish line and the distance from the incisal finish line to the loading point had more influence on the shear stress distribution in the resin cement layer than the amounts of incisal coverage. In contrast loading condition had little influence.

• The Journal of Advanced Prosthodontics
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• v.10 no.6
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• pp.401-407
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• 2018

PURPOSE. When performing an occlusal procedure, it is recommended that the patient should be sitting straight with the head in a natural position. An inappropriate mandibular position caused by an incorrect occlusal record registration or occlusal adjustment can result in damaged teeth and cause functional disorders in muscles and temporomandibular joints. The purpose of this study was to clarify the influence of horizontal cephalic rotation on mandibular position by investigating the three-dimensional positions of condylar and incisal points. MATERIALS AND METHODS. A three-dimensional jaw movement measurement device with six degrees of freedom (the WinJaw System) was used to measure condylar and incisal points. The subjects were asked to sit straight with the head in a natural position. The subjects were then instructed to rotate their head horizontally $0^{\circ}$, $10^{\circ}$, $20^{\circ}$, $30^{\circ}$, $40^{\circ}$, $50^{\circ}$and $60^{\circ}$ in the right or left direction. RESULTS. The results indicated that horizontal cephalic rotation made the condyle on the rotating side shift forward, downward, and toward the inside, and the condyle on the counter rotating side shift backward, upward, and toward the outside. Significant differences in deviations were found for angles of rotation higher than $20^{\circ}$. The incisal point shifted in the forward and counterrotating directions, and significant differences were found for angles of rotation higher than $20^{\circ}$. CONCLUSION. The mandibular position was altered by horizontal cephalic rotations of more than $20^{\circ}$. It is essential to consider the possibility of deviation of the mandibular position during occlusal procedures.

• Restorative Dentistry and Endodontics
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• v.27 no.4
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• pp.432-440
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• 2002

The purpose of this study is to identificate root canal system including ideal access placement, root curvature, canal configuration, incidence of isthmus in mandibular incisors for success of endodontic treatment. 200 mandibular incisors were selected. The ideal access placement was determimed as follows. The teeth there radiographed from mesiodistal and buccolingual views using intraoral dental film. The image was divided into coronal, middle and apical third using the proximal film. Straight line access was determined by measuring the faciolingual canal width and placing points at midway point between the buccal and lingual wall at the junction of the middle and apical third and at the juntion of coronal and middle third of the root canal. A line was drawn connecting these two points extending through the crown of the tooth. The point at which the line crossed the external crown surface was recorded as facial, incisal, lingual. Degree of root curvature was determined by Schneider Protractor Method. Both section method and clearing method were used in this study. By section method, 100 mandibular incisors were embedded in clear resin and transeverse serial sectioned at 0.5, 1.0, 2.0, 3.0, 4.0, 5.0mm level from root apex. The resected surfaces were stained by methylene blue and examined under $\times$40 magnification with a stereomicroscope. By clearing method, 100 mandibular incisors were cleared in methysalicylate after decalcification with 10% nitric acid and evaluated under $\times$18 magnification with a stereomicroscope. The results were as follows ; 1. 29% had the center of the plotted straight-line access facial to incisal edge, whereas 71% had straight-line access at the incisal edge. When incisal wear classified as extensive, the straight-line access was plotted on the incisal edge 95.5%. When incisal wear classified as slight/none, the straight-line access was plotted on the facial 65.9%. 2. Degree of curvature of main canal was straight or almost straight, and only 10% in buccolingual direction had a degree of curvature greater than 20 degrees and 5.5% in mesiodistal direction had. 3. In section method, canal configuration analysis showed that 51% of the specimen classified as type I, 27% as type II, 12% as type III, 10% as type IV. For theses setions with two canals, the incidence of an isthmus was 36.7%, 64.3%, 79.2%, 96.3%, 97.4%, 97.6% at each level and highest in 3~5mm sections. 4. In clearing method, canal configuration analysis showed that 74% of the specimen classified as type I, 11% as type II, 6% as type III, 9% as type IV. These results suggested that traditional access from lingual should be moved as far toward the incisal as possible to locate and debride the lingual canal and root canal system should be cleaned, shaped completely and obturated three dimensionally for successful endodontic treatment.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.4
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• pp.443-457
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• 2004

Purpose: The purpose of this study was to analyze and estimate whether each company may produce the color of artificial teeth as it stands, in the standard of vita classical shade guide using ShadeScan$^{TM}$ System. Material and methods: we chose the products of 6 companies -EFUCERA, IVOCLAR, ENDURA, TRUBYTE, DURADENT, and DURACROSS- estimated the shade value of each fixed point(cervical, body, and incisal area) of artificial tooth, and verified the equality among the samples from the same company. Results: First, the variation appeared significant at cervical and incisal area. It means that there were significant differences between cervical and incisal area although the most similar artificial teeth to the patients’natural teeth were provided. Second, the results in the body area showed that the variation between artificial and natural teeth was finite(p<0.05) in that area. Conclusion: it shows that the reproduction of colors of artificial teeth might be successful regarding the body is the most important part for a determination of the color of artificial teeth. However, more complements are necessary for the better reproduction of the color of artificial teeth between cervical and incisal area.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.4
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• pp.405-420
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• 2003

Purpose : The purpose of this study was to compare the fracture resistance of the IPS Empress ceramic crown with 1.0mm width rounded shoulder, which is usually recommended in all ceramic crown. and 0.5mm width chamfer finish lines on the maxillary central incisor. Material and method : After 15 metal dies were made for each group, the IPS Empress all ceramic crowns were fabricated and cemented with resin cement(Bistite resin cement, Tokuyama Soda Co. LTD., Japan) on the metal die. The cemented crowns were mounted on the positioning jig and the universal testing machine(Zwick Z020, Zwick Co. Germany)was used to measure the fracture strength with loading on the incisal edge. And also, three-dimensional finite element stress analysis was used to measure the stress distribution with the various types of the finish lines(1.0mm width rounded shoulder, 0.5mm width chamfer), the loading site(incisal edge, incisal $\frac{1}{3}$) and the type of loading(concentration loading, distribution loading). Results and conclusion : 1. In the fracture resistance experiment according to the finish line, the mean fracture strength of rounded shoulder(876N) and the mean fracture strength of chamfer(882N) did not skew any significant difference between each other(p>0.05). 2. The stress distribution of all ceramic crown in three dimensional finite element analysis showed concentration aspect at loading point and cervical area or labial surface. 3. In metal die, there were no differences in stress distribution between finish lines, but in natural teeth model, chamfer finish line showed higher stress than rounded shoulder finish line. 4. When force was loaded on the incisal edge the stress was concentrated on the incisal edge and the cervical area of labial surface. When force was loaded on the incisal $\frac{1}{3}$, the stress concentrated on the cervical area of labial surface and the cingulum area. 5. Generally, natural teeth model showed higher and various stress than the metal die.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.3
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• pp.121-140
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• 1991

Fifteen dental college students of Chosun University without the abnormal occlusion, the history and symptom of temporomandibular dysfunction(TMD), and who had all permanent teeth except third molar and the fifteen moderate group and the fifteen severe group classified according to Helkimo's dysfunction index among patients on the basis of the symptom of TMD were selected. The occlusal contact, occlusal force and occlusal interference in eccentric movement was studied and analyzed using T-Scan system. The result were as follows : 1. The TLR centering around midsagittal axis was located at $1.42{\pm}0.82mm$ in control group, $3.36{\pm}1.45mm$ in severe group, and as TMD was heavier, occlusal contact was located at the farther point from midsagittal axis. 2. The PLR from the first contact to the fifth contact centering around midsagittal axis was located at $1.73{\pm}1.78mm$ in control group, $3.36{\pm}1.41mm$ in moderate group, and $5.39{\pm}4.32mm$ in severe group, and as TMD was heavier, occlusal contact was located at the farther point from midsgittal axis. 3. The TFB, PFB, RFB and LFB of occlusal contact centering around incisal axis had no significant difference statistically among control group, moderate group, and severe group, and it was located at first molar. 4.The LF and RF was smaller in TMD group than in control group. 5. The LR moment of occlusal force centering around midsagittal axis was located at $178.51{\pm}139.81N.mm$ in control group, $466.25{\pm}296.47N.mm$ in moderate group, and $749.18{\pm}588.18N.mm$ in severe group. And as TMD was heavier, it was located at the farther point from midsagittal axis. 6. The RL and LL of occlusal force centering around incisal axis had not-significance statistically among control group, moderate group, and severe group, and it was at the first molar. 7. The number of occlusal interference of the eccentric movement was increased in the patients of TMD.

• The Journal of Korean Academy of Prosthodontics
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• v.17 no.1
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• pp.61-66
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• 1979

To investigate the variation of the mandibular rest position according to time, the mandibular rest position was induced by combination of relaxation and swallowing method. The displacement of the incisal point was recorded with the pinpointed miniature lamp luminograph in three dimensions immediately, 30 seconds, and 60 seconds after induction of the mandibular rest position. The Results obtained were as follows 1. Intermaxillary vertical distance measured immediately after induction of mandibur rest position ranged from 1.0mm to 3.9mm And it varied irregularly with time, ranging from 0.1mm to 1.1mm Anteroposterior variance with time ranged irregularly from 0.2mm to 0.8mm 2. The mandibular rest position observed in the frontal plane varied with time to right or left direction, ranging from 0.2mm to 0.5mm from the centric occlusion 3. the mandibular rest position wos not placed definite position but varied spatially in certain range with time.

• Restorative Dentistry and Endodontics
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• v.37 no.4
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• pp.240-244
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• 2012

Crown reattachment is the most conservative treatment which can be used to restore fractured tooth, presumably with sufficient strength, while maintaining original contour, incisal translucency, and reducing chair time and cost. However, in case of crown fracture with pin-point pulp exposure, we should cautiously minimize the irritation to the pulp and consider pre-treatment pulpal status, choice of pulp capping materials, choice of bonding system and treatment sequence during crown reattachment procedures. This case reports the considerations while crown reattachment with direct pulp capping using calcium hydroxide (Dycal, Dentsply Caulk).

• The korean journal of orthodontics
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• v.27 no.2
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• pp.297-313
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• 1997

The purposes of this study were to compare the soft tissue changes following hard tissue change after surgery between the one jaw and two-jaw surgery in skeletal class III patients and to get the reference of the incisal inclination at presurgical orthodontics. For this study 24 patients for the two-jaw surgery group and 18 patients for one jaw surgery group were selected. Lateral cephalograms were taken at pretreatment, after presurgical orthodontic treatment, immediately after surgical treatment and at least 6 months after surgery. They were traced and analyzed on skeletodental structure and soft tissue. The results were as follows: 1. After surgery, maxilla, maxillary incisors and upper lip were moved anteriorly and superiorly in two-jaw surgery group. Mandible and mandibular incisors were moved posteriorly and superiorly, and thickness of lower lip was increased in both group but there were no statistically significant difference. Anterior facial height was more decreased in two-jaw surgery group (p<0.05). At least 6 months after surgery, by the postorthodontic treatment, maxillary incisors were moved labially 1.44mm, mandible and mandiibular incisors were moved lingually 1.43mrn, 1.26mm respectively in one jaw surgery group. But there was no statistically significant changes of hard tissue in two :jaw surgery group. 2. The correlation coefficients of maxillary hard and soft tissue horizontal changes were high in two jaw surgery group and the ratios for soft tissue to A point were 19% at Sri, 80% at SLS, 82% at LS. The ratios for soft tissue to B point were 92% at LI, 104% at ILS in one jaw surgery group, 89% at LI, 101% at ILS in two-jaw surgery group. 3. The correlation coefficients and change ratios of mandibular incisors and LL HS on lower lip horizontal changes were 0 0.89 and 75%, 85% in one jaw surgery group, 0.93, 0.90 and 76%, 87% in two-jaw surgery group. The correlation coefficients of maxillary incisors and Sn, SLS and LS on upper lip horizontal changes were 072, 0.76 and 0.75 in two jaw surgery group and ratios of changes were 57%, 58% and 59%. 4. The regression equations between skeletal horizontal discrepancy and incisal inclinaton were taken in one jaw surgery group. Those were FMIA=57.48-2.17ANB, U1-SN=-75.02+2.17SNB and $R^2$ were 0.63, 063 respectively. So if there is skeletal horizontal discrepancy by mandibular prognathism in one jaw surgery case, we consider attaining more labial inclination of maxillary incisors than normal and more lingual inclination of mandibular incisors than normal. But correlation coefficient of the regression equations in two jaw surgery group was low, so, that equation was not reliable.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.2
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• pp.175-184
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• 2008

Purpose: This study was designed to investigate the fitness of adjustable dental impression trays on the Chinese and the Japanese. Material and methods: Initial design of the adjustable dental trays was developed from the results of the dental arch size of Korean adults. This design was applied to the CAD-CAM process in order to create tray model samples. Simple silicon-base molds were then replicated based on these sample models. Polyurethane injection into the silicon- base molds completed the process of creating a large number of test products. 60 Chinese dental students (male:30, female:30) from the Shanghai Second Medical University and 60 Japanese alumni from the Kumamoto high school (male:30, female:30) were selected for taking irreversible hydrocolloid impression with these trays. The width and length of the impression body were measured on several measuring points by Vernier caliper. The results were analyzed statistically to evaluate the fitness of the trays. Results: 1. Uniform impression material thickness was achieved on the Chinese and Japanese by controlling the width of the tray using stops and beveled guides. The material thickness was generally within the range of 3 mm to 6 mm. 2. In the maxillary tray of the Chinese, average thickness of the impression material of the labial vestibule of the incisal teeth was 6.2 mm, the canine was 5.9 mm and the midpalatal part 10.5 mm and the posterior palatal part 9.7 mm. These were relatively large values. 3. In the mandibular tray of the Chinese, average length of the impression material of the lingual vestibule of first, second premolar contact point was 8.9 mm, the incisal teeth was 7.8 mm and thickness of the labial part of canine was 6.8 mm and premolars 7.0 mm. These were relatively large values. 4. In the maxillary tray of the Japanese, average thickness of the impression material of the labial vestibule of the incisal teeth was 7.4 mm, the canine was 7.7 mm and the midpalatal part 9.1 mm. These were relatively large values. 5. In the mandibular tray of the Japanese, average thickness of the impression material of the labial vestibule of first, second premolar contact point was 8.4 mm, and thickness of the labial part of canine was 7.4 mm. These were relatively large values. Conclusion: This adjustable dental tray shows good accuracy to Korean because it was designed by the analysis of the dental arch size of Korean adult model. With this result, it can be applied to Chinese and Japanese, we can take more easy and accurate dental impressions.