When the first milk molar is unilaterally lost at an early stage, a crown loop is a standard apparatus often used to maintain eruption space for the first molar. In this fundamental study, we investigated the effects of use of crown loop on periodontal tissue and also examined loop strength using the fol lowing methods. With placement of force onto the crown or a W- or U-shaped loop, stress in the periodontal ligament (PDL) of the milk canine and second milk molar was calculated using a finite element method. The alveolar bone and teeth were assumed to be rigid bodies, while the PDL was considered to be a nonlinear elastic film and the loop a linear elastic beam. Intrusive force was ap plied to the occlusal surface of the second milk molar or buccolingual force was applied to the buccal side of the loop. The following results were obtained.

1.When intrusive force was applied to the occlusal surface of the second milk molar, stress in the loop was nearly zero. In this case, the crown loop was scarcely affected by stress in the PDL of the second milk molar.

2.When intrusive force was applied to the buccal side of the loop, stress in the PDL of the second milk molar was increased by two to three times as compared to findings obtained when the same intrusive force was applied to the occlusal surface of the second milk molar. When buccolingual force was applied to the buccal side of a W-shaped loop, stress was produced in the PDL of both the second milk molar and milk canine.

Our results suggest that excessive occlusal force can produce a plastic deformation in the region soldered to the crown, leading to loop failure.

Oral health management has been provided for more than 45 years at our oral care center. For a better understanding of the oral conditions of recent child patients, data for age and gender, as well as dental caries in primary teeth, use of dental floss, and presence of interdental spaces and occlusal patterns were obtained from records of dental examinations performed from April 2016 to March 2017 and analyzed. There was a total of 273 patients (155 boys, 118 girls) examined during the study period, including 69 who were 2 years old (36 boys, 33 girls), 80 between 3 and 4 years old (49 boys, 31 girls), 74 between 4 and 5 years old (44 boys, 30 girls), and 50 aged 5 years (26 boys, 24 girls). Caries prevalence rates were 0.0%, 3.8%, 6.8%, and 8.0%, while dft indexes were 0.00, 0.04, 0.11,and 0.28, respectively, in those age groups. Both caries prevalence rates and dft indexes for all age groups were lower than in a Japan national survey of dental diseases, especially for the 4- and 5-year old patients, which were remarkably low. Additionally, dental floss usage rates were 33.3% (n＝23 people), 51.3% (n＝41), 59.5% (n＝44), and 62.0% (n＝31), respectively, in the age groups. The frequency of use dental floss was found to increase in the order of “occasionally”, “every day”, and “several times a week”. We found that 100% of the patients with decayed and filled primary teeth in the 4- and 5-year-old groups used floss. Dental floss usage by patients without dental caries increased with age.

Closed dentition was observed in 45.0% of all patients, with a prevalence ranging from 53.8% to 56.5% in those aged from 2 to 3 years and from 32.4% to 34.0% in the 4- and 5-year-old children. As for occlusal patterns, normal occlusion was the most common seen in all age groups, with prevalence ranging from 42.5% to 48.6% in patients aged 2-4 years and 64.0% in those aged 5 years. Deep overbite was the most common malocclusion category in this cohort and showed a decreasing trend with age, as it was seen in 39.1%, 41.3%, 32.4%, and 20.0% of our 2-, 3-, 4-, and 5-year-old patients, respectively. On the other hand, the incidence of anterior end-to-end bite increased with age and reached 10.0% in the 5-year-old group.

The aim of the present study was to investigate the tendency of supernumerary teeth in patients examined at a university hospital pediatric dentistry clinic so as to develop treatment guidelines from the perspective of a higher order medical institution. We conducted a survey of 620 children (787 teeth) under 15 years old who were diagnosed with supernumerary teeth at our hospital over a 7-year period from December 2010. The following findings were obtained.

1.The ratio of males to females was approximately 3 : 1.

2.Supernumerary teeth most often occurred as maxillary incisors. As for the direction of tooth eruption, 50.1% of supernumerary teeth were normally directed, 40.2% were inverted, and 9.7% were horizontal. Impacted teeth occurred at a rate of 70.4% and erupted teeth at 29.6%.

3.During the study period, 84.8% of the patients were referred from another dental clinic.

4.The mean age at diagnosis was 7.1 years.

5.More than half (54.0%) of the patients were examined using a combination of intraoral radiography and cone beam computed tomography (CBCT).

6.The mean age at tooth extraction was 7.6 years (n＝500, 620 teeth).

7.For the extraction procedure, 44.6% were performed under normal dental examination conditions (mean age, 7.8 years), while 44.0% were extracted under general anesthesia (mean age, 7.4 years).

8.Following extraction, 60.0% of the patient were followed at the referring dental clinic, most of which were general dental clinics (n＝243).

The present results suggest that supernumerary teeth cases are commonly referred to a university hospital because of the diverse conditions and requirement of specialized care. Timing of extraction and associated dental treatment were decided after analysis of the conditions of the supernumerary and neighboring permanent teeth noted in radiographic examinations such as CBCT, as well as in consideration of mental and physical stress potentially encountered by the patient during extraction. In addition when considering the influence on permanent teeth, we strongly encourage regular follow-up and management after extraction of supernumerary teeth to consider their effects on permanent dentition.

Radiolucent lesions within intracoronal dentin located adjacent to the amelodentinal junction of unerupted developing teeth is a rare phenomenon, with most cases noted in molars and premolars, and more often in mandibular as compared to maxillary teeth. The majority of affected teeth are as ymptomatic, with the lesions incidentally discovered during a routine radiographic examination in bitewing and panoramic radiographs and the finding is often erroneously referred to as “pre-erupted caries”. Several theories for development of pre-eruptive intracoronal radiolucency (PEIR) have been proposed, though it is currently widely accepted that PEIR is resorptive in nature, while the etiology remains unclear.

We describe three teeth with PEIR due to idiopathic resorption, a maxillary second premolar, man dibular first premolar, and mandibular second premolar in three 9-year-old girls. The defects were lo calized within dentin without lesion progression until eruption. Removal of intact enamel on occlusal surfaces and empty defects with soft, grayish, and flaky dentin was performed with an excavator until hard dentin was reached. The defects were then treated by indirect pulp capping with calcium hydrox ide, glass ionomer lining, and composite resin restoration. Affected teeth remained asymptomatic with continued root development.

It appears that the dentin defects in our patient were due to the resorptive process, though the etiol ogy of the idiopathic pre-eruptive intracoronal resorption is unknown. In the present cases, the lesions were incidentally discovered in radiographic imaging conducted prior to their eruption into the oral cavity, though were missed in the initial radiographs.

We consider that practitioners may not notice the initial signs, especially with small lesions. Thus,it is important to examine radiographic images for abnormalities in regard to number, size, shape, and position of unerupted permanent teeth, as well as PEIR.

The prevalence of supernumerary teeth has been estimated to range from 1-5% and those frequently occur in the maxillary incisor region. A previous report found that it is rare for monozygotic twins to have different numbers of supernumerary teeth. We examined monozygotic twin brothers and found that the number of supernumerary teeth in them was different. The patients had their initial examination for an extra tooth at the age of 6 years 0 months old. The older brother was seen first, then two days later the younger brother came to our hospital for an examination. Panoramic radiography findings showed that the older brother had three supernumerary teeth, while the younger had two. Following diagnosis, we decided to extract the teeth in each patient under nitrous oxide inhalation sedation with local anesthesia. The postoperative course of each patient was uneventful. Since the patients were monozygotic twins, involvement of environmental and genetic factors was considered. We concluded that the differences in number, form, situation, and direction of the affected teeth may have been the result of not only genetic and environmental, but also epigenetic factors.

A rhabdomyosarcoma is a highly malignant soft tissue tumor originating in skeletal muscle cells that have failed to completely differentiate and typically occurs during childhood. This report highlights the case of a 7-year-old girl who developed dysodontiasis as a result of treatment for a rhabdomyosarcoma. The patient was diagnosed with a rhabdomyosarcoma of the right orbit (Stage I) at the age of 2 years 6 months and was treated by removal of 80% of the conjunctiva of the rapidly enlarged tumor. Subsequently, chemotherapy was given from the age of 2 years 7 months to 4 years 6 months, while radiotherapy (total dose 45 Gy) was also administered to parts along the right side of the orbit to the maxillary sinus from the age of 2 years 8 months to 2 years 9 months. Dental orthopantomograph findings revealed microdontia of the maxillary right first premolar and mandibular left second premolar, absence of dental germs of the mandibular and maxillary right second premolars,root hypoplasia of the maxillary right and left central incisors, right lateral incisor, right canine, right first premolar, and right first molar, root dysplasia of the maxillary left lateral incisor, and hypoplasia of the maxillary right alveolar bone. Based on these findings, we consider that the remarkable tooth dysplasia and maxillary development abnormalities in this case were caused by chemotherapy and radiotherapy treatments performed for the rhabdomyosarcoma in early childhood.