The dentigerous cyst is defined as a cyst arising from the retention of fluid between the recessed enamel epithelium and the crown of an unerupted tooth within the jaw, and then developing around its crown. It is classified as a developmental cyst by W. H. O. But since the permanent teeth are forming during childhood, we surmised that the development of dentigerous cysts may be associated with dental caries and periapical lesions of deciduous teeth.
To clarify the pathogenesis of the dentigerous cyst, the authors investigated 28 cases of dentigerous cysts in children, with special regard to the clinical and pathological findings. The results were as follows.
The ages of the patients were concentrated around the area of 10 years old. About 60% of the cysts occurred in the lower molar region and the characteristic findings were asymptomatic swelling in the alveolar region. In 22 cases, root canal treatment was performed on the primary predecessors. In 3 cases, the primary predecessors were affected and non vital. Pathological findings in all cases confirmed the presence of inflammation of the connective tissue of the cyst wall.
These results suggest that one of the pathogenetic factors in the occurrence of dentigerous cysts is inflammation caused by the periapical lesion of deciduous teeth.
18 cases were treated by marsupialization or extirpation after preoperative treatment using the irrigation method. The irrigation method was effective in reducing the size of the cyst cavity. Cyst cavity size and tooth axis influenced the eruption of permanent teeth after marsupialization. We considered that in cases where eruption is likely to be difficult, early orthodontic treatment is desirable.

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We report 6 cases of thyroglossal duct cysts in children, treated at our clinic from 1979 to 1994 and we did clinical studies of them.
Results were as follows:
1) In 6 cases, 4 males and 2 females, the thyroglossal duct cysts appeared between 5 nonths and 10.7 years old (mean age was 3.6 years old). One of them was a recurrence case.
2) The lesions, have no pain, being found in the midline neck region at or upon the level of the hyoid bone, and the measurements of the lesions were from 10 to 30 mm in diameter.
3) Imaginary diagnosis for MRI is very useful to get the information about the location, volume, expanse and so on, of the lesion.
4) Two cases were operated cystectomy with partial resection of the hyoid bone because of adhesion between the cyst and the hyoid bone, four cases were operated cystectomy or fistulectomy without resection of the hyoid bone, of which one had recurrence but has been well for 10 years since reoperation.
5) Histopathologically, the epitherium lining of the cysts were stratified squamous epithelium in 4 cases, ciliated columner in 2 cases. There are accessory organs in the cyst wall, such as mucous glands (lcase), thyroid tissue (lcase).

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When we treat growing patients with maxillofacial fractures, we should consider the development of the maxillofacial bone and the influence to development of the teeth. In our previous report, the long-term follow-up of pediatric alveolar bone fracture cases revealed malocclusions. Therefore, we investigated the histological changes after the pediatric alveolar bone fracture using Wister rats.
3-week-old female Wister rats were used for the experiment. We made the fracture of the alveolar bone in the mandible, using the dental turbine.
Histological observation of the healing was carried out immediately, 1 day, 3 days, 1 week, 3 weeks, 6 weeks, 10 weeks, 12 weeks, 15 weeks after the fracture.
3 days after the fracture, the fracture site was filled with fibrin and many neutrophil leukocytes were observed. 1 week after, neutrophil leukocytes infiltration was decreased and the new bone callus was formed. 3 weeks later, the fracture area was filled with the new bone callus. From 6 to 10 weeks after the fracture, a rapid bone formation was found, but there was less calcification area in the fracture site, which was cartilage-like. 12 weeks after, there was no immature bone and the fracture site was almost repaired.
In this experiment, long term histological change was observed after the alveolar fracture in children, and may influence the occlusion and the development of the maxillofacial bone.

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Clinico-statistical observation was performed on 141 pediatric patients under 15 years of age with supernumerary teeth at the Department of Maxillofacial Surgery I, Okayama University Dental Hospital during nine years (1985-1994).
The results are summarized as follows;
1) 190 supernumerary teeth were found in the 141 patients, that is, 94 patients with one supernumerary tooth, 45 patients with two, 2 patients with three.
2) The ratio of male to female was 3.4: 1.
3) Over 70% of the patients with supernumerary teeth were found in the 6-9 age group.
4) 87.4% of supernumerary teeth were impacted. The direction of eruption was normal (35.8%), inverted (53.7%) and horizontal (10.5%).
5) The most common locations were maxillary anterior area and palatal side.
6) 53.6% of the patients had problems with supernumerary teeth, of which 25 cases of diasthema were the most frequent.
7) 86.5% of supernumerary teeth were extracted during 1 month from the patient's first visit, and an operation was carried out with palatal side approach in 79.5% of the cases.

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We reported two cases of cemento-ossifying fibroma which occurred on the mandible of children, and discussed about their findings of several diagnostic imagings, including orthopantomogram, computed tomography (CT) and magnetic resonance imaging (MRI).
A10-year-old-girl (case 1) had orthopantomogram and MRI, and a 7-year-old-girl (case 2) had orthopantomogram and CT.
Preoperative orthopantomogram revealed a well-circumscribed, radiolucent lesion with mixed radiopacity in the mandibular body region. Dislocation of the tooth and mild root resorption were seen. After extirpation and bone currettage, we followed up the patients with orthopantomogram. When it recurred, orthopantomogram showed septum like structure and marked calcified foci in the well-circumscribed radiolucent area.
Preoperative CT examination revealed a large mass lesion in the body of the mandible which expanded bone cortex markedly, but did not destroy it. A few calcified foci were demonstrated in the lesion. CT which was taken for follow-up revealed soft tissue and water density mass that mixed calcified foci markedly in the body of the mandible.
On MRI, the recurrent tumor showed speckles of low signal intensity in isointense lesion on T1-weighted images. T2-weighted images showed to be in homogenous, low to high signal intensity mass in mandibular body to ramus region.

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Cleft lip and palate, a congenital malformation in the oral and maxillofacial region, is not necessarily corrected morphologically, functionally, cosmetically after primary surgery. Thus, patients with this disorder are treated with various therapies including secondary surgery, considering the patient's development, growth, age, general conditions and psychology. These treatments last long from infancy, in some cases, childhood, school days, adolescence to adulthood.
In the course of the long-term treatment, these children often face social difficulties such as being bullied.
In this study, we report a patient who underwent surgical correction of nasal deformity using hydroxy apatite porous block and closure of the cleft palate with particulate marrow and cancellous bone, and was followed up for a long time since childhood.

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Gingival hyperplasia is often presented as a symptom of systemic disease. We experienced a case of infant gingival hyperplasia with several congenital anomalies in which bimaxillary hyperplastic gingiva caused open bite.
The patient, a boy was born in July 1990 showing several congenital anomalies, for example, gargoyle-like facial features and hypertrichosis. In time he showed other various symptoms such as mental retardation, multiple tonic seizure, and marked gingival hyperplasia. Radiographic examination revealed morphological abnormality of teeth and hypoplasia of enamel and dentin. MRI showed progressive brain atrophy. These symptoms suggested metabolic disorder, however, it was denied by lysozomal examinations. Gingivectomy should be applied to hyperplastic gingiva, however, the poor general condition involving frequent dyspnea disturbs the performance of surgical procedures.

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We report one uncommon disease called “Opitz C syndrome”. This syndrome is characterized with cranial, facial, palatal and joint abnormalities. The previous reports have not been seen in the field of Oral and Maxillofacial Surgery. In this case report a 2-month-old boy who has Opitz C Syndrome with respiratory insufficiency was discussed. We also offer the intraoral finding of this syndrome, which has been well known, defined by Antely in 1985.

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