• Journal of the korean academy of Pediatric Dentistry
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• v.35 no.2
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• pp.305-312
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• 2008

Crown-root fractures occur throughout both crown and root, and are defined as fractures involving enamel, dentin and cementum. The fractures may be grouped according to pulpal involvement into complicated and uncomplicated one. Crown-root fractures often occur on maxillary anterior teeth and comprise 5% of injuries affecting the permanent dentition and 2% in the primary dentition. To restore crown-root fractured tooth, biologic width must be maintained. For maintaining biologic width, such methods as gingivectomy following osteoplasty or orthodontic extrusion or surgical extrusion are available. Surgical extrusion is a method that extracts the tooth and replants the fractured tooth supragingivally. It is indicated when the length of the crown fragment is less than half the length of the clinical root. In these cases, root canal treatment and crown restoration using light-cured composite resin were performed after surgical extrusion. In following periodic examinations, favorable outcome was observed.

• Restorative Dentistry and Endodontics
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• v.28 no.4
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• pp.314-325
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• 2003

이 연구의 목적은 수종 상아질 접착 시스템과 복합 레진 및 resin-modified glass ionomer를 상아질 표면에 접착하여 재료 및 상아질내 위치에 따른 미세전단결합강도를 측정, 비교하는 것이다. 상아질 접착 시스템으로는, 3-step인 Scotchbond Multi-Purpose Plus, 2-step인 Single Bond와 자가 부식형 시스템인 Clearfil SE Bond를, 1-step인 Prompt L-Pop을 사용하였다. 이와 함께 hybrid type의 복합 레진인 Clearfil AP-X와 2250을 사용하였으며 resin-modified glass ionomer로는 Fuji II LC를 사용하였다. 상악 소구치를 치아의 근원심 중앙부를 절단하여 상아질면을 노출시켰다. 5개 실험군으로 분류하고 상아질면을 위치에 따라 치관부의 occlusal $\frac{1}{3}$, middle $\frac{1}{3}$, cervical $\frac{1}{3}$과 치근부로 구분지어 시편을 부착하였다. 미세전단결합강도측정는 Universal testing machine(EZ-test; Shimadzu, Japan)에서 측정하였다. Occlusal 1/3부위에서는 SE가 가장 높은 값을, SM과 SB간에는 유의차가 없었으며, PL, GI순으로, Middle 1/3부위에서는 $SM{\;}{\geq}{\;}SE{\;}{\geq}{\;}SB{\;}{\geq}{\;}PL{\;}{\geq}{\;}GI$순으로, cervical 1/3부위에서는 SM, SE, SB간에 유의차가 없었다. Root dentin에서는 SM이 가장 높은 값을 보였으며 SE, PL, GI간에 유의차가 없었다. SE만이 치관부 상아질에 비해 치근부에서 유의할만한 결합강도의 감소를 나타냈다(p<0.05). GI는 치관부 상아질에서는 다른 군에 비해 유의성 있게 낮은 결합강도를 보였으나 치근부에서는 SE, PL과 유의차가 없었다.

• The korean journal of orthodontics
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• v.34 no.3 s.104
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• pp.241-251
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• 2004

Previous studies have focused on the causes of root resorption after orthodontic treatment and treatment methods to reduce this phenomenon, and have been mainly associated with developed, mature roots. As parents become increasingly interested in their children's' dentition, orthodontists are performing fixed orthodontic treatment on patients of less than 10 years and before the completion of the immature root. Thus, the author evaluated the changes of root length and root form of maxillary immature incisors after orthodontic treatment, compared with those of mature teeth, and investigated the correlation according to gender, treatment duration, and displacement of incisors. The sample consisted of an immature root group of twenty-eight persons (between 8 and 10 years old) and a mature root group of thirty-one persons (between 11 and 15 years old). The crown and root length of the maxillary four incisors were measured with a periapical radiograph, changes in root length and crown-root ratio were calculated, and root form was classified according to a scoring system. The results were as follows. 1. The development of immature roots was not affected by orthodontic treatment and mostly showed normal root length and apical form. 2. Root length of immature teeth was sustained or became shorter, partially in long treatment duration or with open bite patients. Even though the teeth reached their normal root length, they demonstrated a blunt form. 3. Most of the mature roots showed mild resorption, and the form of mature roots was more blunt than the developed form of the immature roots (p<0.05). 4. The developed form of the immature roots was statistically related to treatment duration, while the form of the mature roots was significantly related to the displacement of incisors (p<0.05). 5. In contrast, other variables such as gender, classification of malocclusion, changes in overbite, and changes of U1 to SN showed no correlation with the root resorption of both groups.

• 대한치과보철학회:학술대회논문집
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• 2004.11a
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• pp.58-58
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• 2004

• Journal of the korean academy of Pediatric Dentistry
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• v.48 no.3
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• pp.352-358
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• 2021

Molar-incisor malformation (MIM) is characterized by malformation in the root with a normal crown. While MIM mostly occurs in the permanent first molar, it has also been reported in the maxillary central incisor and the primary second molar (PSM), but anatomical analysis of the primary teeth with MIM has not been studied to date. In this case report, a patient with MIM was reported, and an extracted PSM with MIM was analyzed with micro computed tomography (CT). A cervical constriction morphology of the cementoenamel junction (CEJ) can be observed in extracted PSM. In micro CT analysis, characteristics such a mineralized plate (cervical mineralized diaphragm) in the CEJ area, complex root canal morphologies, a calcified mass inside the pulp chamber, and constricted pulp chamber of crown portion were observed.

• Journal of the korean academy of Pediatric Dentistry
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• v.32 no.3
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• pp.576-583
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• 2005

Tooth formation is a complex developmental process that is mediated through a series of reciprocal epithelial-mesenchymal interactions. Several signal pathways and transcription factors have been implicated in regulating molar crown development, but relatively little is known about the regulation of root development. It was reported that NFI-C knockout mice showed abnormal root formation with normal crown. The aims of this study are to elucidate how the NFI-C regulate the determine of root shape and odontoblasts differentiation. We carried out immunohistochemistry using cytokeratin to investigate the role of Hertwig's epithelial root sheath and DSPP mRNA in-situ hybridization to conform the nature of root dentin during root development in NFI-C knockout mice. Cytokeratin reacted with all the HERS cells and the continuity of cytokeratin positive cells between the HERS cells and enamel epithelium was lost in the cervical region both wild and K/O types. After root dentin deposition cytokeratin positive-HERS cells showed irregularity and loss of polarity in the cervical region in K/O type. DSPP mRNA was strongly expressed in odontoblasts of crown and root dentin in wild type mice, whereas expression of DSPP mRNA was restricted in odontoblast of crown dentin in the K/O type. During root formation in NFI-C knockout mice, HERS normally grow out of the crown but fail to induce odontoblast differentiation in root portion. These results suggest that NFI-C may play important roles in odontoblast differentiation during root dentin formation.

• The korean journal of orthodontics
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• v.34 no.1 s.102
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• pp.47-61
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• 2004

Although the purpose of orthodontic treatment is to increase the function and esthetics of the jaws along with increasing stability, there are many side effects during the treatment itself, such as root resorption and alveolar bone resorption. Such resorption of the apical root Is unpredictable, and may even proceed into the dentin layer. Once the process has begun, it is irreversible. By evaluating the effect of many oral habits, especially that of nail biting, in correlation with the root and the periodontal tissues, the appropriate biomechanics for orthodontic treatment can be taken into consideration, along with the possibility of root resorption and alveolar bone loss during orthodontic treatment, and any legal problems that might occur. Among the male and female patients of the ages $10\~15$ without skeletal deformity, 63 were chosen as the experiment group with known nail biting habits at time of examination, and within the same age group without nail biting habits as the control. After the orthodontic treatment, number of the experiment group was 31 and the control group was 22. The periapical radiographies of anterior teeth were taken and the assesment of the root length and alveolar bone level were taken before(T1) and after(T2) the orthodontic treatment. The results from this study were as follows : 1. Before the orthodontic treatment, average crown-to-root ratio of the experimental group showed noticeably high values in 4 maxillary incisors and mandibular right central incisor. 2. Before the orthodontic treatment, comparing the root length, maxillary and mandibular right central incisors and both mandibular incisors had a smaller value in the experimental group. 3. Before the orthodontic treatment, comparing and evaluating the alveolar bone loss measured from the cemento-enamel junction to the alveolar bone crest, some crestal bone of the experiment group showed greater loss than the control. 4. After the orthodontic treatment, there was shortening of the root length and loss of the crestal bone in both groups. 5. After the orthodontic treatment, the changes of C/R ratio and the shortening of root length were significantly high in the experimental group. 6. After the orthodontic treatment, the level of alveolar crestal bone showed greater loss in the experimental group.

• Journal of the korean academy of Pediatric Dentistry
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• v.33 no.4
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• pp.643-652
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• 2006

The purpose of this study was to elucidate the size and morphologic characteristics of maxillary primary first molars in Korean children using three-dimensional laser scanner and compare three-dimensional image with preformed stainless steel crown. Scanned three-dimensional images of dental cast taken from 132 children(male 62, female 70) by three-dimensional laser scanner(Breuckmann opto-Top HE100, INUS, Korea) were used. Mesiodistal diameter, buccolingual diameter, occlusogingival height and crown shape of each image were calculated by Rapidform 2004 program(INUS, Korea). The values were statistically compared by independent samples t-test with 95% of significant level. The results were as follows : 1. No significant difference in crown size was found between left and right maxillay primary first molar(p>0.05). 2, Significant difference in mesiodistal diameter, buccolingual diameter, buccal occlusogingival height was found between male and female (p<0.05), and crown size of male was bigger than that of female. 3. Average image of maxillay primary first molar was shaped three-dimensionally and measured. In comparison with 3M stainless steel crown, this image was similar with No.4 or No.5 SS crown in male, No.4 in female. In comparison with ILSUNG SS crown, this image was similar with No.5 in male, No.4 in female. 4 Mesiolingual line angle area, distolingual line angle area and buccogingival ridge were more obvious in average image than 3M stainless steel crown. ILSUNG SS crown was more square and had longer mesiodistal diameter than average 3D image.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.5
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• pp.479-489
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• 2008

Statement of the problem: Under anatomical limitations on maxillary posterior region, a poor crown-to root ratio acting on dental implants can result in undesirable stress in surrounding bone, which in turn can cause bone defects and eventual failure of implants. Purpose: The purpose is to compare stress distribution due to different crown-root ratio and effect of splinting between natural teeth and implants in maxillary molar area under different loads. Material and methods: Analysis of stress arising supporting bone of the natural teeth and the implant was made with 3-dimensional finite element method. The model simulated naturel teeth was made with 2nd premolar and 1st molar in the maxillary molar region (Model T). The model simulated implants placed on same positions with two parallel implants of Straumann Dental Implant cemented abutment (Model I). Each model was designed in different crown-root ratio (0.7:1, 1:1, 1.25:1) and set cement type gold crown to make it non-splinted or splinted. After that, 300 N force was loaded to each model in five ways (Load 1: middle of occlusal table, Load 2: middle of buccal cusp, Load 3: middle of lingual cusp, Load 4: horizontal load to buccal cusp of anterior abutment only, Load 5: horizontal load to middle of buccal cusp of each abutment), and stress distribution was analyzed. Results and conclusion: On all occasions, stress was concentrated at the cervical region of the implant. Under load 1, 2 and 3, stress was not increased even when crown-root ratio increases, but under load 4 and 5, when crown-root ratio increases, stress also increased. There was difference in stress values between natural teeth and implants when crown-root ratio gradually increases; In case of natural teeth, splinting decreased stress under vertical and horizontal loads. In case of implants, splinting decreased stress under vertical loads 1,2 and 3, but increased maximal stress under loads 2 and 3. Under horizontal loads, splinting decreased stress, however the effect of splinting decreased under load 5 than load 4. Furthermore, the stress was increased, when crown-root ratio is 1.25:1. Clinical implications: This limited finite element study suggests that the stress on supporting bone may be increased under non-axial loads and poor crown-root ratio. Under poor crown-root ratio, excessive stress was generated at the cervical region of the implant, and decreased splinting effect for stress distribution, which can be related to clinical failure.

• Journal of the korean academy of Pediatric Dentistry
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• v.42 no.2
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• pp.172-179
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• 2015

The developmental mechanism of root formation is a complex process. Hereditary and environmental factors may affect the morphology of the developing root. A total of 12 cases was presented with permanent first molars with abberant root morphology. Clinically, these teeth appeared as a normal crown. However, radiographically, the root was slender, twisted and characterized by irregular lengths. In addition, root trunk length was shorter and pulp chamber was obliterated. In these cases, periapical radiolucency and loss of lamina dura were often observed. In 6 cases, an abnormal root of the primary second molars were also present, as well as root malformation of permanent first molars. In 3 cases, permanent central incisors also had a dysmorphic crown. These cases almost all had medical history, such as premature birth, brain infection or congenital heart disease in infants. The present paper describes cases of permanent first molars with an abnormal root that are rarely reported in literature. This case may intensify the variation in the permanent first molar and is intended to reinforce the clinician's awareness of rare morphology of the roots.