• The Journal of Korean Academy of Prosthodontics
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• v.46 no.1
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• pp.22-30
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• 2008

Purpose: The purpose of this study is to compare three different CAD/CAM systems through the fracture strength of zirconia core and to evaluate the clinical availability of each system. Material and methods: The following three groups of 30 maxillary mesial incisor core for all-ceramics(each group 10) were fabricated as follows: group 1. $Adens^{(R)}$ CAD/CAM system, group 2. $Cerasys^{(R)}$ CAD/CAM system, group 3. 3M $Lava^{(R)}$ CAD/CAM system. All specimens were manufactured consistently thickness 0.5mm and relief $40{\mu}m$. Specimens were subjected to compressive loading on the lingual area by Z250/$SN5S^{(R)}$. Each group's mean and standard deviation were calculated and Kruskal Waillis test, Wilcoxon Rank Sum test were utilized to find out the relationship among the groups. Results: The results were as follows: 1. The mean fracture strength of $Adens^{(R)}$ system was $615.89{\pm}156.1N$, the $Cerasys^{(R)}$ system was $863.98{\pm}151.5N$, and the 3M $Lava^{(R)}$ system was $1143.1{\pm}286.6N$. 2. The fracture strength of the systems showed the significant statistical differences in order of 3M $Lava^{(R)}$ system, $Cerasys^{(R)}$ system, $Adens^{(R)}$ system. Conclusion: In this study, in spite of the differences among the groups, every group showed clinically useful results. It is necessary to study further clinical experiments on a long term basis.

• The Journal of Advanced Prosthodontics
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• v.9 no.4
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• pp.244-251
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• 2017

PURPOSE. The purpose of this study was to determine fracture resistance and failure modes of three-unit fixed dental prostheses (FDPs) made of lithium disilicate pressed on zirconia (LZ), monolithic lithium disilicate (ML), and monolithic zirconia (MZ). MATERIALS AND METHODS. Co-Cr alloy three-unit metal FDPs model with maxillary first premolar and first molar abutments was fabricated. Three different FDPs groups, LZ, ML, and MZ, were prepared (n = 5 per group). The three-unit FDPs designs were identical for all specimens and cemented with resin cement on the prepared metal model. The region of pontic in FDPs was given 50,000 times of cyclic preloading at 2 Hz via dental chewing simulator and received a static load until fracture with universal testing machine fixed at $10^{\circ}$. The fracture resistance and mode of failure were recorded. Statistical analyses were performed using the Kruskal-Wallis test and Mann-Whitney U test with Bonferroni's correction (${\alpha}=0.05/3=0.017$). RESULTS. A significant difference in fracture resistance was found between LZ ($4943.87{\pm}1243.70N$) and ML ($2872.61{\pm}658.78N$) groups, as well as between ML and MZ ($4948.02{\pm}974.51N$) groups (P<.05), but no significant difference was found between LZ and MZ groups (P>.05). With regard to fracture pattern, there were three cases of veneer chipping and two interfacial fractures in LZ group, and complete fracture was observed in all the specimens of ML and MZ groups. CONCLUSION. Compared to monolithic lithium disilicate FDPs, monolithic zirconia FDPs and lithium disilicate glass ceramics pressed on zirconia-based FDPs showed superior fracture resistance while they manifested comparable fracture resistances.

• Journal of Periodontal and Implant Science
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• v.46 no.6
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• pp.372-381
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• 2016

Purpose: The aim of this study was to determine the relationship between buccal bone thickness and gingival thickness by means of a noninvasive and relatively accurate digital registration method. Methods: In 20 periodontally healthy subjects, cone-beam computed tomographic images and intraoral scanned files were obtained. Measurements of buccal bone thickness and gingival thickness at the central incisors, lateral incisors, and canines were performed at points 0-5 mm from the alveolar crest on the superimposed images. The Friedman test was used to compare buccal bone and gingival thickness for each depth between the 3 tooth types. Spearman's correlation coefficient was calculated to assess the correlation between buccal bone thickness and gingival thickness. Results: Of the central incisors, 77% of all sites had a buccal thickness of 0.5-1.0 mm, and 23% had a thickness of 1.0-1.5 mm. Of the lateral incisors, 71% of sites demonstrated a buccal bone thickness <1.0 mm, as did 63% of the canine sites. For gingival thickness, the proportion of sites <1.0 mm was 88%, 82%, and 91% for the central incisors, lateral incisors, and canines, respectively. Significant differences were observed in gingival thickness at the alveolar crest level (G0) between the central incisors and canines (P=0.032) and between the central incisors and lateral incisors (P=0.013). At 1 mm inferior to the alveolar crest, a difference was found between the central incisors and canines (P=0.025). The lateral incisors and canines showed a significant difference for buccal bone thickness 5 mm under the alveolar crest (P=0.025). Conclusions: The gingiva and buccal bone of the anterior maxillary teeth were found to be relatively thin (<1 mm) overall. A tendency was found for gingival thickness to increase and bone thickness to decrease toward the root apex. Differences were found between teeth at some positions, although the correlation between buccal bone thickness and soft tissue thickness was generally not significant.

• Journal of Periodontal and Implant Science
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• v.47 no.6
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• pp.372-380
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• 2017

Purpose: The aim of this prospective pilot study was to compare alveolar ridge preservation (ARP) procedures with open-healing approach using a single-layer and a double-layer coverage with collagen membranes using radiographic and clinical analyses. Methods: Eleven molars from 9 healthy patients requiring extraction of the maxillary or mandibular posterior teeth were included and allocated into 2 groups. After tooth extraction, deproteinized bovine bone mineral mixed with 10% collagen was grafted into the socket and covered either with a double-layer of resorbable non-cross-linked collagen membranes (DL group, n=6) or with a single-layer (SL group, n=5). Primary closure was not obtained. Cone-beam computed tomography images were taken immediately after the ARP procedure and after a healing period of 4 months before implant placement. Radiographic measurements were made of the width and height changes of the alveolar ridge. Results: All sites healed without any complications, and dental implants were placed at all operated sites with acceptable initial stability. The measurements showed that the reductions in width at the level 1 mm apical from the alveolar crest (including the bone graft) were $-1.7{\pm}0.5mm$ in the SL group and $-1.8{\pm}0.4mm$ in the DL group, and the horizontal changes in the other areas were also similar in the DL and SL groups. The reductions in height were also comparable between groups. Conclusions: Within the limitations of this study, single-layer and double-layer coverage with collagen membranes after ARP failed to show substantial differences in the preservation of horizontal or vertical dimensions or in clinical healing. Thus, both approaches seem to be suitable for open-healing ridge preservation procedures.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.3
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• pp.480-487
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• 2001

In children and adolescents, oral and maxillofacial trauma is one of the most common causes of dental and periodontal damage, which often induces crown fracture of the permanent anterior teeth. Frequently, these traumatized teeth lose their vitality, and require routine endodontic treatment if their root apices are closed. However if their apices are not fully closed, further root formation should be promoted by apexification or apexogenesis. Calcium hydroxide is a biocompatible & bacteriostatic material, and is widely used for apexification. However it has several disadvantages which include the need for multiple visits and patient cooperation, low strength and technical sensitivity in a broad apex. In one-visit apexification using IRM or SuperEBA, patient's visits can be minimized. However, their biocompatibility is questionable. Mineral trioxide aggregate(MTA) is a relatively new material. It is considered biocompatible with periapical hard tissue and has good marginal sealing ability. MTA is also known to help facillitate the growth of the cementum around it. In this case report, apexification with MTA was attempted on traumatized maxillary central incisors with immature root apices, and favorable clinical results were achieved.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.3
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• pp.355-362
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• 2001

Data derived from odontometric studies are useful in many areas. Especially crown diameter of primary teeth is important in not only anthropology but also clinical dentistry. The purposes of this study were to compare diameters of primary molars of Korean children with those of preformed stainless steel crown, and examine racial characteristics of primary molars of Korean children. The mesiodistal and buccolingual diameters of primary molars were measured on dental casts taken from 235 children(male 105, female 131), with digital calipers. And the data were compared with those of preformed stainless steel crowns. The results were as follows; 1. No significant difference was observed between the right and left members of antimeric teeth and all primary molars of male were larger than those of female. 2. The diameters of primary molars of Korean are smaller than those of Austrailian aborigines and there was significant difference between diameters of primary molars of Korean and those of other populations. 3. There were size differences between diameters of maxillary, mandibular first molar and preformed stainless steel crown than other primary molars, relatively.

• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.4
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• pp.581-585
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• 2002

Focal epithelial hyperplasia(FEH) is Human papilloma virus - induced, localized proliferation of oral squamous epithelium. FEH usually occurs in the childhood, but occasionally affects the young and middle-aged adults. Sites of the greatest involvement include the labial, buccal and lingual mucosa, but lesions of gingiva or tongue have also been reported. This disease is typically characterized by multiple soft, non-tender flattened papules and plaques. Occasional lesions show a slight papillary surface change. Individual lesions are small, discrete and well demarcated. The histopathologic hallmark of FEH is acanthosis of the oral epithelium. Cells demonstrating viral cytopathic changes including koilocytes or mitosoid cells may be present. The 5-year-old female of this case visited Department of Pediatric Dentistry, College of Dentistry, Yonsei University with a chief complaint of exophytic lesions on gingiva. Sessile papillary papules were detected by clinical examination on buccal gingiva at the maxillary left and right second deciduous molars. The patient did not complain of pain by palpation. An excisional biopsy was carried out for a histological examination and acanthosis was observed. The lesions were diagnosed as FEH. FEH would regress spontaneously after several months or years. Conservative excision may be performed for diagnostic or esthetic purpose. The risk of recurrence after this therapy is minimal, and there is no malignant transformation.

• Journal of the korean academy of Pediatric Dentistry
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• v.27 no.2
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• pp.344-350
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• 2000

Incidence of crown-root fracture due to traumatic injury, have been reported 3% in the permanent dentiton, 2% in the deciduous dentition. There are two treatment methods for crown-root fractured teeth with pulp exposure, when the fracture line was located under the alveolar crest. One way is the extrusion by orthodontic force the other way is intra-alveolar transplantation which occlusally repositioning of apical fragment in the alveolar socket. Since intra-alveolar transplantation has introduced in 1970s, it was practiced as alternative to orthodontic extrusion. As the result, this method may thoughted that had a good prognosis. As a result of trauma, completely crown-root fracture was occured in the maxillary right central incisor in this case. We couldn't reposition the deepest fracture line above the alveolar crest by the conventional surgical extrusion, because apical fragment was too short. Thus, after extraction of apical fragment, we repositioned it to the socket following demineralized freezed dried bone graft, which possible to support the apical fragment. At the 15-month recall examination, the root still showed normal mobility and there was not observed any in flammatory or replacement root resorption in the periapical radiograph.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.3
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• pp.429-437
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• 2006

The purpose of this study was to evaluate the shade of primary incisors. One hundred and nineteen children 394 maxillary anterior primary incisors were assessed. Digital shade analysing system ($ShadeScan^{TM}$, Cynovad, Canada) was used for measuring the shades This system enabled to improve the accuracy and objectivity The images of the teeth were taken with $ShadeScan^{TM}$ and shade maps of the teeth were obtained with $ShadeScan^{TM}$ software. The shades of three regions (cervical third middle third, incisal third) of the teeth were evaluated. The results were as follows : 1. In cervical third of primary incisors, D2 and D3 were the major shades and D2 was the most frequent shade. 2. In middle third of primary incisors, C1, D2, and B1 were the major shades and C1 was the most frequent shade. 3. In incisal third of primary incisors, A2 was the most frequent shade and D2 shade followed.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.3
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• pp.522-528
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• 2006

When tooth is displaced within the alveolar bone, it could apply pressure and rupture the apical vessels. Pulpal reaction in such case is affected by the stage of root formation, amount of intrusion and pulpal infection. Determining the need of pulp treatment depends on the pulp vitality. Therefore, periodic vitality tests, coronal color changes and radiographic root resorption signs should be observed through periodic post-trauma follow-up. Pulp necrosis, pulp canal obliteration, external root resorption, root ankylosis and marginal bone loss could result from periodontal injuries. Negative sign changes from positive signs of vitality tests suggest pulp necrosis. In this case, pulp treatment should be held before root resorption occurs. By comparing the following two cases, complications of intrusion and factors producing them could be confirmed, thus we propose to report these two cases.