• 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%.

• The korean journal of orthodontics
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• v.29 no.5 s.76
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• pp.613-625
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• 1999

The purpose of this study was to compare the bracket shear bond strengths of the crystal growth solutions with those of the $37\%$ phosphric acid etch technique. The 4 crystal growth solutions were made experimentally in the lab, that is, (1) $30\%$ polyacrylic acid solution containing 0.3 M sulfuric acid (ES 1), (2) $30\%$ polyacrylic acid solution containing 0.6M sulfuric acid (ES 2), (3) $30\%$ polyacrylic acid solution containing 0.3 M sulfuric acid and 0.6 M lithium sulfate(ES 3), and (4) $30\%$ polyacrlic acid solution containing 0.3 M sulfuric acid and $5\%$ phosphoric acid(ES4). The $37\%$ phosphoric acid solution used as a control. Bovine lower incisor tooth enamel was treated by the above solutions for 60 sec, washed out for 20 sec with slow water stream, and bonded lower anterior edgewise bracket with the light curing orthodontic composite resin adhesives. The teeth bonded brackets were stored in the distilled water at room temperature for 24 h, and followed to test the bracket shear bond strength. The acid etch technque showed 177.6 kg/$cm^2$ of mean shear bond strength which was the highest among the enamel treatment solutions. ES 1 shown 58.4 kg/$cm^2$ of mean shear bond strength and that of ES 4 showed 66.5 kg/$cm^2$. There was no significant difference between the two(p>0.05). ES2 showed 110.6kg/$cm^2$ of mean shear bond strength which was $62.3\%$ of that of acid etch technique. ES 3 showed 131.1 kg/$cm^2$ of mean shear bond strength which was the highest among experimental crystal growth solutions and which was $74\%$ of that of acid etch technique. The shear bond strengths of the crystal growth solutions were significantly lower that that of acid etch technique(p<0.05). The results sugest that although bracket shear bond strength of $30\%$ polyacrylic acid solution containing 0.3M sulfuric acid and 0.6 M lithium sulfate were showed the highest, it is low for the clinical application of this solution.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.1
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• pp.119-125
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• 2009

Fusion and gemination are irregularities in tooth development. It is often difficult to differentiate between gemination and fusion and it is common to refer to these anomalies as 'double teeth'. The deciduous teeth are most commonly involved, but in 0.1% of cases permanent teeth are affected, in which case aesthetic, funtional and periodontal problems can result. Double teeth present great difficulties in management and required a multidisciplinary approach. The central groove on the labial and palatal surfaces of a double tooth is extremely prone to caries, therefore early 'fissure sealing' is essential. In permanent dentition, surgical separation of fused teeth may be possible with subsequent orthodontic alignment and restorative treatment as needed to reshape the crown. Reshaping or reduction of a double tooth with a single canal may be attempted by modifying the appearance of the labial groove and the use of composite tints but is often impossible and extraction may be the only alternative. Orthodontic treatment and prosthetic replacement is then required. Implants may be an option for adolescents. The present study describes three clinical cases of double teeth in the position of the maxillary permanent incisors. The first case demonstrates an example of multidisciplinary care including surgical intraoral hemisection, root canal therapy, restorative and orthodontic treatment. The second and third cases describe the external and internal morphology of the two fused teeth by means of three dimensional dental computer tomography.

• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.4
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• pp.632-640
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• 2002

The objective of the study was to apply the vibration technique to reduce the viscosity of bonding adhesives and thereby compare the bond strength and resin penetration into dentinal tubules achieved with those gained using the conventional technique. Eighty-eight noncarious extracted human permanent molar teeth were sectioned to remove the coronal enamel and were embedded in 1-inch PVC pipe with acrylic resin. The occlusal surfaces were placed so that the tooth and the embedding medium were at the same level to form one flat surface, and the samples were subsequently polished with silicon carbide abrasive papers. The samples were randomly assigned to 4 groups(n=22). On Group 1 and 2, Single Bond(3M-ESPE, St. Paul, USA) was used, and on Group 3 and 4, One-Step(Bisco Inc., Schaumburg, USA) was used, and each was applied according to its manufacturer's instructions. For Group 2 and Group 4, vibration was applied with ultrasonic scaler for 10 seconds, and the adhesive was light-cured for 10 seconds. Resin composite was condensed on to the prepared surface in two increments using a mold kit(Ultradent Products Inc., USA) and each was light-cured for 40 seconds. After 24 hours in tap water at room temperature the specimens were thermocycled, and shear bond strengths were measured with a universal testing machine(Instron 4465, Canton, USA). To investigate infiltration patterns of the adhesive materials, the surface of specimen was examined with scanning electron microscope. The results were as follows. 1. The shear bond strengths of vibration groups(Group 2, Group 4) were significantly greater than those of the non-vibration groups(Group 1, Group 3)(p<0.05). 2. The shear bond strengths of Single Bond and One-Step were not significantly different (p>0.05). 3. The vibration groups showed greater number of resin tags in tubules and lateral branches under SEM.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.3
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• pp.328-334
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• 2009

Statement of problem: Pier abutments act as a Class I fulcrum lever system when the teeth are incorporated in a fixed partial denture with rigid connectors. Therefore non-rigid connector incorporated into the fixed partial denture might reduce the stresses created by the leverage. Purpose: The purpose of this study was to evaluate, by means of finite element method, the effects of non-rigid connectors and supporting alveolar bone level on stress distribution for fixed partial dentures with pier abutments. Material and methods: A 2-dimensional finite element model simulating a 5-unit metal ceramic fixed partial denture with a pier abutment with rigid or non-rigid designs, the connector was located at the distal region of the second premolar, was developed. In the model, the lower canine, second premolar, and second molar served as abutments. Four types of alveolar bone condition were employed. One was normal bone condition and others were supporting bone reduced 20% height at one abutment. Two different loading conditions, each 150 N on 1st premolar and 1st molar and 300N on 1st molar, were used. Results: Two types of FPD were displaced apically. The amount of displacement decreased in an almost linear slope away from the loaded point. Non-rigid design tended to cause the higher stresses in supporting bone of premolar and molar abutments and the lower stresses in that of canine than rigid design. Alveolar bone loss increased the stresses in supporting bone of corresponding abutment. Conclusion: Careful evaluation of the retentive capacity of retainers and the periodontal condition of abutments may be required for the prosthetic design of fixed partial denture with a pier abutment.

• Restorative Dentistry and Endodontics
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• v.31 no.3
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• pp.147-152
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• 2006

The purpose of this study was to evaluate the influence of the AH-26 root canal sealer on the shear bond strength of composite resin to dentin. One hundred and forty four (144) extracted, sound human molars were used. After embedding in a cylindrical mold, the occlusal part of the anatomical crown was cut away and trimmed in order to create a flat dentin surface. The teeth were randomly divided into three groups; the AH-26 sealer was applied to the AH-26 group, and zinc-oxide eugenol (ZOE) paste was applied to the ZOE group. The dentin surface of the control group did not receive any sealer. A mount jig was placed against the surface of the teeth and the One-step dentin bonding agent was applied after acid etching. Charisma composite resin was packed into the mold and light cured. After polymerization, the alignment tube and mold were removed and the specimens were placed in distilled water at $37^{\circ}C$ for twenty four hours. The shear bond strength was measured by an Instron testing machine. The data for each group were subjected to one-way ANOVA and Tukey's studentized rank test so as to make comparisons between the groups. The AH-26 group and the control group showed significantly higher shear bond strength than the ZOE group (p<0.05). There were no significant differences between the AH-26 group and the control one (p>0.05). Under the conditions of this study, the AH-26 root canal sealer did not seem to affect the shear bond strength of the composite resin to dentin while the ZOE sealer did. Therefore, there may be no decrease in bond strength when the composite resin core is built up immediately after a canal filling with AH-26 as a root canal sealer.

• The Journal of Korean Academy of Prosthodontics
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• v.57 no.2
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• pp.127-133
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• 2019

Purpose: The purpose of present study was to investigate fracture strength and mode of failure of endodontically treated teeth restored with metal cast post-core system, prefabricated fiber post system, and newly introduced polyetherketoneketone (PEKK) post-core system. Materials and methods: A total of 21 mandibular premolar were randomly grouped into 3 groups of 7 each according to the post material. Group A was for metal cast post core; Group B for prefabricated glass fiber post and resin core; and Group C for milled PEKK post cores. All specimens were restored with metal crown. The fracture strength of each specimen was measured by applying a static load of 135-degree to the tooth at 2 mm/min crosshead speed using a universal testing machine. After the fracture strength measurement, the mode of failure was observed. The results were analyzed using Kruscal-Wallis test and post hoc Mann-Whitney U test at confidence interval ${\alpha}=.05$. Results: Fracture resistance of PEKK post core was lower than those of cast metal post and fiber reinforced post with composite resin core. In the aspect of fracture mode most of the root fracture occurred in the metal post core, whereas the post detachment occurred mainly in the fiber reinforced post. In the case of PEKK post core, teeth and post were fractured together. Conclusion: It is necessary to select appropriate materials of post for extensively damaged teeth restoration and clinical application of the PEKK post seems to require more research on improvement of strength.

• Journal of dental hygiene science
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• v.4 no.3
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• pp.103-109
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• 2004

The present study prepared 72 test samples - 24 made of amalgam alloy, 24 of Verabond (Ni-Cr alloy) for crown and 24 of Talladium $^{TM}alloy$ for denture - according to the manufacturers' manuals and general method in consideration of the width of the mesial-distal dental crown of the lower $1^{st}$ molar and MOD cavity in clinics, put them in a 200 ml beaker containing 80 ml of artificial saliva, and measured their galvanic corrosion at distances of 0 mm, 7 mm and 40 mm after 7 days. Isolated metals in the electrolyte such as Cu, Ag, Ni, Cr, Sn, Zn and Hg were quantitatively analyzed with Inductively Coupled Plasma - Atomic Emission Spectrometer (ICP-AES, JY-50P, VG Elemental Co. France), and from the results were drawn conclusions as follows. First, Cu, Sn, Ag, Hg and Zn were highly advantageous when amalgam contacted gold alloy compared to Ni-Cr alloy for crown and Talladium alloy for denture. In addition, although gold alloy was finest in terms of oral tissue and biocompatibility, it was most disadvantageous when it was with amalgam. Second, when amalgam contacted gold alloy, heavy metals such as Ni and Cr were not isolated at all because gold alloy did not contain such elements but Sn was isolated as much as $227.1{\pm}18.0035{\mu}g/cm^2$ although it was not included in the composition either. Hg was also isolated. These elements are assumed to have been isolated from amalgam itself. Third, when amalgam alloy was apart from gold alloy 0 mm, 7 mm and 40 mm, Cu and Ag showed significance but Hg did not. This suggests that gold alloy must not be used together with amalgam, and must not be used between dissimilar prostheses regardless of distance. Fourth, when amalgam alloy contacted Ni-Cr alloy for crown, Ag was not isolated from the amalgam, but Zn, Ni, Sn, Hg and Cu were isolated in order of quantity. Significance was observed according to distance - 0 mm, 7 mm and 40 mm. Hg was not isolated but heavy metals Ni and Cr were isolated. If amalgam alloy was in the opposite arch or it was apart from Ni-Cr alloy for crown, the isolation Hg was less than that when amalgam alloy contacted Ni-Cr alloy for crown. Fifth, when amalgam alloy contacted Talladium alloy for denture, significance was observed at distances of 0mm, 7 mm and 40 mm. Hg was not isolated but heavy metals Ni and Cr were isolated. If amalgam alloy was in the opposite arch or it was apart from Talladium alloy for denture, the isolation Hg was less than that when amalgam alloy contacted Talladium alloy for denture. Sixth, according to the result of ICPES test on Cu, Sn, Ag, Hg, Zn, Ni and Cr of amalgam alloy, gold ally, Verabond and Talladium alloy when these alloys contacted artificial saliva, significance was observed in Cu and Hg. Seventh, when amalgam alloy contracted two non-precious metals Ni-Cr alloy for crown and Talladium alloy for denture in artificial saliva, significance was observed in the isolated by-products of Hg, Ni and Cr according to distance.