Dental anomalies such as enamel hypoplasia are associated to genetic disorder, however, only little is known about the responsible gene and molecular mechanism of dental anomalies. To date, non-ameloblast dental epithelial cell types; stratum intermedium, stellate reticulum, and outer enamel epithelium were not well characterized. Recently, the single-cell RNA-sequencing (scRNA-seq) technology was established as a novel transcriptome analysis. In this study, we performed scRNA-seq of dental cells from developing mouse incisor to characterize all stages- and all types-of dental cells. We found that secretory-stage of ameloblast were divided into two-subpopulations and showed distinct gene expression, indicating they have independent roles in tooth development. Furthermore, we identified Claudin-10 as a novel stratum intermedium marker gene from the scRNA-seq dataset. Interestingly, mutation of Claudin-10 causes Helix syndrome in human and the patients of Helix syndrome showed severe enamel attrition. By in vitro analyses, we found that Claudin-10 regulates the expression of alkaline phosphatase, which plays essential role in enamel mineralization. These findings contribute to identify marker genes of dental cell types and clarify the pathogenesis of dental anomalies.

Gram-positive Streptococcus mutans, a major pathogenic bacterium for human caries known to play an important role in biofilm formation, is exposed to drastic environment fluctuations, such as temperature and pH changes, nutrient availability, and invasion by foreign substances. This organism possesses a large number of transport proteins in the cell membrane for export and import of molecules, and its membrane transport function allows it to survive stress, as well as create conditions conductive for its growth and development. In addition, transport of nitrogen sources plays a major role in biofilm formation by S. mutans. Nitrogen is an essential nutrient for growth of Gram-positive bacteria and taken up into bacterial cells in various forms, with the nonessential amino acid glutamine, synthesized from ammonium, known to be a nitrogen source for biosynthesis of a variety of compounds. The present study focused on characterizing the glutamine membrane transporter (GlnP) with molecular biological methods.

Using S. mutans MT8148 as the parental strain, GlnP-deficient (GEMR) and complementary (compGEMR) strains were generated by molecular methods. In the logarithmic growth phase, the growth rate of MT8148 and comp-GEMR strains was decreased whereas that of the GEMR strain was not affected by glutamine. Furthermore, to confirm the relevance of membrane transport of glutamine in S. mutans, that was analyzed using fluorescent probes, which showed that fluorescence polarization of the GEMR strain was significantly decreased in a concentration-dependent manner. In addition, the structure of biofilm formed by the GEMR strains was coarser as compared to those associated with the MT8148 and comp-GEMR strains.

The present results indicate an important role for GlnP in regard to bacterial growth, membrane transport of glutamine, biofilm formation, and maintenance of biofilm structure.

For the prevention of accidents in childcare facilities, we investigated 695 cases of head, oral, and maxillofacial injuries in childcare facilities from 2017 to 2018, and determined the factors associated with the injuries. The following findings were observed.

1. The majority of injuries occurred in four-year-old children. The maximum average number of injuries per person was 3.85 in two-year-old children.

2. The most frequently injured sites were the frontal region in head injuries, the eye in facial injuries, and the lip in oral injuries.

3. Head, face, and oral cavity injuries occurred more frequently in the morning than in the afternoon. Children injured in the morning had a lower mean age than those injured in the afternoon.

4. Indoor injuries were more frequent than outdoor injuries. Most outdoor injuries occurred on the ground, while most indoor injuries occurred in the nursery room.

5. The children with indoor injuries had a lower mean age than those injured outdoors.

6. Bruising was the most common presentation in head, face, and oral cavity injuries.

7. Most injuries happened in March.

8. Oral injuries more frequently occurred outdoors than indoors. Furthermore, injuries were most common among three-year-old children.

These findings determined the most common age, time, place, and site for the occurrence of head, oral, and maxillofacial injuries in childcare centers. Based on the results of this survey, we believe that cooperation with childcare facilities is necessary to develop safety measures and educational activities for head, oral, and maxillofacial injuries.

The characteristics of disabilities and illnesses are gradually being understood end the social environment and welfare system for them are improving. However, the environment of dental care at the dental clinic for the children with disabilities and illnesses is not yet sufficient, and urgent environmental improvement is required. Therefore, to clarify the problems of dental situation for those patients, we investigated first-visit patients with disabilities and illness who visited our department from 2013 to 2018. Of the 1,301 first-visit patients, the percentage of children with disabilities and illnesses was 49%. In this study, the disabilities and illnesses were categorized with physical disabilities, sensory disorders, internal disorders, developmental disorders, seizure disorders, congenital malformations, chromosomal abnormalities, and genetic abnormalities. The 323 patients included 4% with physical disabilities, 11% with sensory disorders, 15% with internal disorders, 34% with developmental disorders, 8% with seizure disorders, 14% with congenital malformations, 8% with chromosomal abnormalities, and 6% with genetic abnormalities were further investigated. Caries was the most common complaint (31%) followed by cleft lip and palate (17%), dental check-up (14%), surgical treatment (11%), denture guidance (8%), trauma (4%), and swallowing (3%). Ninety-three percent of the patients brought a letter of referral and 7% did not. The number of patients by residential area was highest in Tokushima City (37%), where our hospital is located. This was followed by Anan City (10%) and Naruto City (8%). Nine percent of the patients came from outside Tokushima Prefecture. The dental needs of children with disabilities and illness, as well as the environment and system surrounding them, should be analyzed from the standpoint of both the patient and the medical personnel, so that the needs of both parties can be met.

Cayler cardio-facial syndrome is associated with an asymmetric crying face and congenital heart disease. The asymmetric crying face is due to congenital hypoplasia of the depressor angulioris muscle. Asymmetry of the lower lip is especially evident during mouth opening or crying. There are no reports on oral findings in patients with Cayler cardio-facial syndrome. We experienced a child with Cayler cardio-facial syndrome, and report on our examination including oral findings.

The child with Cayler cardio-facial syndrome was a boy aged 3 years and 3 months at the first visit. He was diagnosed with a ventricular septal defect at birth, but it closed spontaneously at one year old. His face appeared symmetrical when resting, but left-right asymmetry was observed during mouth opening and crying. He had no problems with functions such as pronunciation, predation, chewing, and swallowing. His terminal plane was efferent on the left and vertical on the right, with deciduous canine occlusion type I and he had a clinically normal occlusion. His dental arch width did not show a clear laterality. He also had facial asymmetry in mouth opening at 7 years old. He did not need special care in dental treatment because the ventricular septal defect closed spontaneously.

One-sided hypoplasia or deficiency of the depressor angulioris muscle in Cayler cardio-facial syndrome is considered to have no effect on the oral cavity. However, if the dentist finds a patient with an asymmetric crying face, it is considered that the dentist should ask about the presence or absence of heart disease.

Supernumerary teeth in the anterior region affect the eruption of permanent teeth and are frequently encountered in clinical pediatric dentistry. Here, we report two rare cases of recurrence of impacted maxillary anterior supernumerary teeth at the same site.

Case 1:A 6-year-and-two-month-old boy presented with anomalous eruption of the permanent anterior teeth because of the recurrence of impacted supernumerary teeth. Previously, two supernumerary teeth had been extracted from the same site under general anesthesia. The eruption status of the anterior teeth was continuously evaluated. One impacted supernumerary tooth was observed at the same site 24 months after treatment. It was extracted under general anesthesia. Considering the difficulty in spontaneous eruption of the left central maxillary incisor, we performed fenestration and traction. Currently, the patient is under continuous management to attain proper occlusion of permanent teeth.

Case 2:A 4-year-and-eight-month-old boy presented with an erupted supernumerary tooth and confirmed torsion of the maxillary central incisor tooth germ. The tooth was extracted under normal conditions, and regular dental check-ups continued. Twenty-four months after the procedure, two impacted supernumerary teeth were found at the same site. These were extracted under general anesthesia. Following this, we observed spontaneous eruption of the permanent anterior teeth.

Although the occurrence of multiple supernumerary teeth has been extensively reported, there are few reports on supernumerary teeth recurring at the same site. Hence, we believe these two cases are extremely rare. In both cases, eruption of the permanent tooth was affected owing to the recurrence of supernumerary teeth two years after extraction from the same site. Therefore, it is necessary to confirm the eruption state of the teeth and obtain radiographs, as appropriate, to check the course over a long period of time even after extraction of supernumerary teeth.