• Journal of the korean academy of Pediatric Dentistry
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• v.42 no.2
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• pp.197-202
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• 2015

Numerous challenges in treating permanent dentition are encountered, especially in treating immature teeth with pulp necrosis. Historically, calcium hydroxide application during long periods of time was used to induce the formation of a calcific barrier across the open apex. In 2004, a new treatment modality for the management of the open apex was introduced. This treatment was named as 'revascularization' and gained acceptance among dentists. The protocol was different from the traditional apexification techniques in that the canal was irrigated and disinfected with a combination of three antibiotics (ciprofloxacin, metronidazole and minocycline). At the next appointment, bleeding was induced and the canal was sealed with MTA. Successful regenerative endodontic treatment of necrotic immature permanent teeth can provide continued root development, increased thickness in the dentinal walls and apical closure. These developments of a functional pulp-dentin complex have a promising impact on retaining the natural teeth, the goal of the dental health care.

• Journal of the korean academy of Pediatric Dentistry
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• v.25 no.3
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• pp.555-561
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• 1998

Hypophosphatasia is a rare metabolic disorder which manifests characteristics such as abnormal mineralization of bone and dental tissues, diminished serum and tissue alkaline phosphatase, and increased urinary secretion of PEA. It inherited as an autosomal recessive or dominant trait and occurs in all races. In general, hypophosphatasia can be classified in 4 subtypes which are the perinatal, infantile, childhood, adult type depending upon the age at presentation and severity. In young children with Hypophosphatasia the long bones show irregular defects, and the skull showes poor calcification. In older children with premature closure of the skull sutures there may be multiple lucent area called gyral or convolutional markings, described as resembling beaten copper, presumably resulting from increased intracranial pressure. Examination of the jaws reveals a generalized lucency of the maxilla and mandible. the cortical bone and lamina dura are thin, and the alveolar bone may be deficient. Clinical features of Hypophosphatasia include premature loss of deciduous teeth, especially incisors, hypoplasia or aplasia of root cementum, enamel hypoplasia, irregular calcification of dentin, large pulp chamber, and resorption of marginal alveolar bone and roots. Our report involves a patient with a chief complaint of early loss of both Mx. and Mn. deciduous incisors. After conducting a through clinical and radiographic examination this patient was referred to pediatrics under the suspicion of hypophosphatasia, the diagnosis proved to be correct and successful results were accomplished through a denture made to improve esthetics and function.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.27 no.2
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• pp.75-81
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• 2018

The aim of this study was to evaluate the biomechanical behavior and long-term safety of high performance polymer PEKK as an intraradicular dental post-core material through comparative finite element analysis (FEA) with other conventional post-core materials. A 3D FEA model of a maxillary central incisor was constructed. A cyclic loading force of 50 N was applied at an angle of $45^{\circ}$ to the longitudinal axis of the tooth at the palatal surface of the crown. For comparison with traditionally used post-core materials, three materials (gold, fiberglass, and PEKK) were simulated to determine their post-core properties. PEKK, with a lower elastic modulus than root dentin, showed comparably high failure resistance and a more favorable stress distribution than conventional post-core material. However, the PEKK post-core system showed a higher probability of debonding and crown failure under long-term cyclic loading than the metal or fiberglass post-core systems.

• Journal of the korean academy of Pediatric Dentistry
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• v.50 no.4
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• pp.443-451
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• 2023

The purpose of this study was to evaluate whether the newly introduced calcium silicate-based materials with fast-setting properties could be appropriately used as basement materials in indirect pulp treatment (IPT). This was performed by quantifying the durability of adhesion between the material and composite resin, measured by the shear bond strength (SBS). Five calcium silicate-based materials, TheraCal LC^® (TLC), TheraCal PT^® (TPT), TheraBase^® (TB), Well-Root^TM PT (WPT), and Endocem^® MTA (EMTA), as well as two glass ionomer-based materials, Fuji II and Fuji II LC, were included. Specimens containing these materials were manufactured and bonded to composite resin with a universal adhesive applied in self-etch mode. The SBS values and failure modes were recorded, and the mean SBSs of the materials were compared. Both TPT and TB exhibited SBS values that were similar to TLC, while both WPT and EMTA appeared to have statistically lower SBS values. Mixed failure was commonly observed in TLC and TPT, while all WPT and EMTA samples showed cohesive failure. In comparison with TLC and TPT, more samples with cohesive failure were observed in TB, implying that this material forms a stronger bond with composite resin. Together with the ability of TB to chemically bind to dentin due to its 10-methacryloyloxydecyl dihydrogen phosphate component, TB seems to be a promising material for IPT within the limitations of this in vitro study.

• International Journal of Oral Biology
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• v.49 no.2
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• pp.48-52
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• 2024

This study explores the histological features and Bmp4 expression patterns in the replaced tooth germ of Xenopus laevis. Tooth germ formation starts from the dental placode through epithelial-mesenchymal interactions, involving various signaling pathways such as Fgf, Shh, Bmp, and Wnt. In mice, Bmp4 expression in the dental placode inhibits Pax9 expression in the dental mesenchyme. Although absent in the presumptive dental lamina of birds and toothless mammals, Bmp4 remains conserved in reptiles and fish owing to gene duplication. However, its expression in amphibian tooth germs is poorly understood. Three-month-old X. laevis were employed in this study. Initially, samples underwent paraffin embedding and were sectioned into 5 or 12 ㎛ ribbons for H&E staining and in situ hybridization, respectively. Results revealed teeth appearing in two maxillary rows: the labial side, with prefunctional and functional teeth, and the lingual side, with replaced tooth germs behind functional teeth. Enameloid was observed between the inner dental epithelium and dental mesenchyme at the cap or early bell stages, whereas enamel and dentin formed during the late bell or mineralization stages from the replaced tooth germ. Bmp4 expression was evident in the inner dental epithelium (ameloblasts), dental papilla (odontoblasts), stellate reticulum, and Hertwig's epithelial root sheath. Overall, these findings highlight the conservation of Bmp4 expression in X. laevis tooth development.

• Restorative Dentistry and Endodontics
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• v.32 no.1
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• pp.47-60
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• 2007

The purpose of this study is to compare and to evaluate the effect of pH and lactic acid concentration on the progression of artificial root caries lesion using polarizing microscope, and to evaluate the morphological changes of hydroxyapatite crystals of the demineralized area and to investigate the process of demineralization using scanning electron microscope. Artificial root caries lesion was created by dividing specimens into 3 pH groups (pH 4.3, 5.0, 5.5), and each pH group was divided into 3 lactic acid concentration groups (25 mM, 50 mM, 100 mM). Each group was immersed in acid buffer solution for 5 days and examined. The results were as follows : 1. Under polarized microscope, the depth of lesion was more effected by the lactic acid concentration rather than the pH. 2. Under scanning electron microscope, dissolution of hydroxyapatite crystals were increased as the lactic acid concentration increased and the pH decreased. 3. Demineralized hydroxyapatite crystals showed peripheral dissolution and decreased size and number within cluster of hydroxyapatite crystals and widening of intercluster and intercrystal spaces as the pH decreased and the lactic acid concentration increased. 4. Under scanning electron microscope evaluation of the surface zone, clusters of hydroxyapatite crystals were dissolved, and dissolution and reattachment of crystals on the surface of collagen fibrils were observed as the lactic acid concentration increased. 5. Under scanning electron microscope, demineralizatlon of dentin occurred not only independently but also with remineralization simultaneously. In conclusion, the study showed that pH and lactic acid concentration influenced the rate of progression of the lesion in artificial root caries. Demineralization process was progressed from the surface of the cluster of hydroxyapatite crystals and the morphology of hydroxyapatite crystals changed from round or elliptical shape into irregular shape as time elapsed.

• Restorative Dentistry and Endodontics
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• v.32 no.4
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• pp.356-364
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• 2007

The purpose of this study was to assess the background color-interceptive ability ana opacity of opaque shade composites (Universal composite, Filtek Z350, Charisma, Clearfil ST, Palpaque Estelite, Esthet-X, and Metafil Flo). Twenty four background specimens (diameter 5.5 mm, thickness 3.0 mm) with Root dentin Mustard (Bisco, Schaumburg, IL, USA) were made. The CIE $L^*a^*b^*$ value of background specimens was measured by a spectrophotometer (Spectrolino, GretagMacbeth, Regensdorf, Switzerland). Three specimens in every group were filled on the background specimens. The surface color of samples was measured by a spectrophotometer in 3.0 mm and every thickness to 0.5 mm while grinding. The color difference in the background color along with 3.0 mm specimen gauged the masking effect in each thickness while grinding and polishing. The opacity was calculated in 1 mm thick specimens. The opacity was in the decreasing order of Clearfil ST, Metafil Flo, Filtek Z350, Palpaque Estelite, Universal composite, Charisma, and Esthet-X (p < 0.05). As the thickness get reduced, $L^*$ value showed decreasing, $a^*$ increasing tendency. The surface color difference between pair of the 3.0 mm thick specimen and after grinding in same opaque resin was above 3.3 except Clearfil ST and Metafil Flo. The color difference (${\Delta}E^*$) between pair of background specimen and opaque resin built-up specimen showed more than 10.0 regardless kinds and thickness. The variance in opacity characteristics and color of the opaque composites is dependent upon manufacturer. When using the opaque resin, the optical properties of each material must be considered as well as cavity.

• The korean journal of orthodontics
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• v.21 no.2 s.34
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• pp.259-272
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• 1991

Orthodontic traction has been suggested as the treatment of choice for intrusive luxation injuries. Prior research has shown orthodontic forces to be ineffective in the presence of ankylosis or in cases with zero mobility following the injury. If orthodontic traction is to be effective, it must be initiated prior to the onset of ankylosis. The purpose of this study was to describe the effects of intrusive luxation at various times following the injury, and to determine the time of the onset of ankylosis, and to examine what effect immediate partial luxation has on the onset of ankylosis. Eight young mongrel dogs were utilized for this study. Intrusive luxation was produced with an axial impact using a gravity hammer and a specially designed holding device on 4 teeth (2 max. and 2 man. first premolars) in each dog. The teeth were intruded approximately 3-4mm in an axial direction. One maxillary and one mandibular premolars were partially luxated with the other two teeth being untouched. Pre and posttrauma tooth position was documented with plaster models and radiographs taken with an individualized X-ray jig. Dogs were sacrificed immediately following the injury and at 1, 2, 4, 7, 10, 14 and 21 days respectively. Tetracycline was administered as a vital bone marker 24 hours before sacrifice. Block sections of the tooth and alveolus were prepared for decalcified and non decalcified histologic sections. The effects of traumatic intrusion were analyzed by means of model casts, radiographs, tetracycline bone marking and histologic preparations. The results obtained were as follows: 1. The animal sacrificed immediately following the injury displayed alveolar fractures, torn periodontal ligaments, and areas of direct tooth-bone contact. 2. The odontoblastic layer of the pulp was disorganized as early as 24 hours after the injury. 3. Bony remodeling was noted at 4 days along with active surface resorption. 4. Ankylosis was first seen 7 days after the injury. 5. Osteogenesis in the dentin (thick tetracycline bands) was observed 7 days after the injury. 6. There was no progressive root resorption and ankylosis where the periodontal ligament has been healed. 7. The Luxated group showed significantly more root resolution and ankylosis than the Nonluxated group with increased observation periods. The results suggest that ankylosis may occur within the first week following the injury, and hence orthodontic traction should be initiated as soon after the injury as possible.

• Journal of the korean academy of Pediatric Dentistry
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• v.38 no.3
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• pp.276-283
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• 2011

Recently, undifferentiated stem cells which exist in dental papillae of immature permanent teeth were newly discovered and these stem cells appear to be the origin of ameloblasts associated with the formation of root dentin. When treating immature permanent teeth, the preservation of these stem cells induce the continuous formation of the root. Therefore, it is reported that minimal invasion to periapical region in immature permanent teeth with periapical inflammation resulted in good-healing pattern in clinical and radiographic examination. In this case, a 10 year-old boy(mandibular right premolar) and a 8 year-old girl(maxillary left premolar) who visited the department of pediatric dentistry at Chosun University Dental Hospital were diagnosed with pulp necrosis and periapical abscess in clinical and radiographic examination. Endodontic instrumentation to the periapical region was limited and MTA(Mineral Trioxide Aggregate) was applied into the pulp canal. The periodic checks showed healing of periapical abscess and the development and growth pattern of roots. In permanent teeth with pulp necrosis and periapical abscess, preservation of pulp and dental papillae in the periapical region showed good prognosis during the periodic examinations. Therefore, a lot of clinical examination and long-term evaluation of conservative pulp treatment in immature permanent teeth are expected to be necessary.

• Journal of the korean academy of Pediatric Dentistry
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• v.39 no.4
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• pp.397-403
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• 2012

The vitality of immature tooth could be lost by dental caries, trauma and fracture of malformed tooth. The vitality loss might lead to halt of the development of the root. The recommended endodontic treatment for a non-vital immature permanent tooth is apexification. Apexification is a method of inducing apical closure through the formation of mineralized tissue in the apical pulp region. Calcium hydroxide is the material of choice for apexification. Long-term exposure to calcium hydroxide may form the apical hard tissue, but weaken the dentin due to its alkaline nature and thus make the roots more susceptible to fracture. It is important to preserve any weakened tooth, so a permanent restoration is needed to reinforce teeth that are prone to fracture. The purpose of this case report was to describe the treatment for reinforcing immature teeth treated with long-term calcium hydroxide. In these cases, the apexes of teeth were sealed with MTA plugs and the root canals were restored with composite resin and fiber post.