We performed a cross-sectional nationwide investigation of permanent tooth eruption timing and sequence in 30,825 children in Japan between the ages of 4 years and 18 years 11 months in order to assess changes in permanent tooth emergence. The following results were obtained :

1.Tooth emergence in boys occurred as follows. Tooth 1 emergence occurred between the ages of 5 Y 6 M and 7 Y 0 M, 6 between 5 Y 10 M and 7 Y 6 M, 1 between 6 Y 6 M and 7 Y 10 M, 2 between 6 Y 3 M and 8 Y 3 M, 6 between 5 Y 11 M and 8 Y 7 M, 2 between 7 Y 6 M and 9 Y 2 M, 3 between 9 Y 2 M and 11 Y 3 M, 4 between 9 Y 1 M and 11 Y 7 M, 4 between 9 Y 5 M and 11 Y 6 M, 3 between 9 Y 10 M and 12 Y 1 M, 5 between 10 Y 4 M and 13 Y 0 M, 5 between 10 Y 3 M and 13 Y 2 M, 7 between 11 Y 3 M and 13 Y 10 M,and 7 between 12 Y 1 M and 14 Y 5 M.

2.Tooth emergence in girls occurred as follows. Tooth 1 emergence occurred between the ages of 5 Y 5 M and 6 Y 7 M, 6 between 5 Y 6 M and 7 Y 0 M, 1 between 6 Y 3 M and 7 Y 7 M, 2 between 6 Y 3 M and 7 Y 8 M, 6 between 5 Y 10 M and 8 Y 4 M, 2 between 7 Y 2 M and 8 Y 8 M, 3 between 8 Y 8 M and 10 Y 5 M, 4 between 8 Y 11Mand11Y0M,4between9Y1M and11Y1M,3between9Y2M and11Y4M,5between 10 Y 1 M and 12 Y 11 M, 5 between 10 Y 2 M and 13 Y 1 M, 7 between 11 Y 2 M and 13 Y 10 M, and 7 between 11 Y 9 M and 14 Y 3 M.

3.The sequence of tooth eruption was not significantly different between boys and girls. The general eruption sequence was 6≒1 →2 →4 →3 →5 →7 for the maxilla and 1 →6 →2 →3 →4 →5 →7 for the mandible.

4.For boys, the eruption patterns of the first molar and central incisor were 77.2% for M type and 22.8% for I type in the maxilla, and 29.2% for M type and 70.8% for I type in the mandible. Those in girls were 73.4 % for M type and 26.6% for I type in the maxilla, and 36.7% for M type and 63.3% for I type in the mandible.

5.A comparison between boys and girls showed a significant difference regarding the eruption timing of 1, 1, 2, 2, 3, 3, 4, 4, and 6, as those erupted earlier in girls.

6.As compared to a previous report presented in Japan in 1988, eruption timing was significantly later for 4, 4, 5, 5, 6, and 6 in boys, and for 3, 4, 4, 5, 5, 6, and 7 in girls.

We investigated dental treatments received by intellectually disabled patients at the Department of Pediatric Dentistry of Hiroshima University Hospital during the fiscal year of 2015, and compared the findings with surveys conducted in 2004 and 2009. Since 2009, a total of 312 patients (214 males, 98 females) have received dental treatments, with 147 returning for follow-up examinations. Their age ranged from 1 to 42 years old, with those between 7 and 12 years of age comprising the largest percentage (35.5%).

The most common cause of intellectual disability was autism (41.9% of all patients), while no complications were noted in 34.6%) and Down syndrome was seen in 10.8%. The most common den tal treatment was professional mechanical tooth cleaning by a dental hygienist (34.8% of all). The numbers of fillings and crown restorations showed decreases over time. Physical restraint during dental treatment was used for 182 (58.1%) of all patients, while the most commonly adopted behavior management method was visual support. Annually, the number of patients requiring management has increased.

Cavities were prepared in 100 fresh pig mandibular molars, then measurements were conducted using Endodontic Meter SII (EM) and Osada Apit 15 (OA) devices to examine the applicability of use of a commercially available electronic apex locator for determining pulp exposure. The results showed that the value for cavities shown by OA with a certain value shown by EM uniformly increased in association with an increase in the EM value. Additionally, we observed a significant difference in mean OA value for cavities as compared to the displayed pulp exposure value determined using the EM. The range of OA values equivalent to EM values was also determined, indicating pseudo-exposure of pulp. Furthermore, molar measurements obtained with concomitant use of EM and OA in clinical pulpectomy cases during the process of access cavity preparation revealed values similar to experimental measurements obtained with porcine mandibular teeth. These results suggest the applicability of an OA device for use in pulp exposure examinations.

Early diagnosis of tooth agenesis in childhood enables clinicians to improve occlusion in the patient. In addition to patient age, we speculated that the developmental stage of adjacent teeth could assist with tooth agenesis diagnosis. In the present study, development of the mandibular second premolar (P2) was compared with that of adjacent teeth, including the mandibular first premolar (P1) and first molar (M1) in 238 patients aged 3-8 years old, by examining the formation stages of each tooth shown by panoramic and dental radiographic imaging.

Our findings showed that when P2 was in the initial mineralization (Ci) stage, P1 was between the cusp outline complete (Coc) and crown half completed with dentine formation (Cr1/2) stages, while M1 was between the crown three-quarters completed (Cr3/4) and initial root formation with diverge edges (Ri) stages. Agenesis of P2 could be readily determined after P1 had reached the crown threequarters completed (Cr3/4) stage and M 1 when the root length was less than the crown length (R1/4) stage. The average age in which a P2 tooth germ could be confirmed in the mandible was 3.70±0.73 years (males : 3.82±0.89, females : 3.52±0.47 years), with a median value of 3.58 years (males :3.58, females : 3.41 years). In addition to patient age, information regarding tooth germ development in adjacent teeth may help to facilitate early diagnosis of congenital absence of P2, which would help clinicians with early implementation of appropriate management strategies to achieve healthy permanent occlusion.

The purpose of this study was to use clinical testing for verification of the plaque removal efficacy of a new child's toothbrush (NT), which is mainly composed of soft materials, and a conventional toothbrush (CT), composed of only hard materials. The following results were obtained.

1.Plaque removal efficacy for all teeth for the NT was 27.7±12.8% and for the CT was 28.7± 13.5%, which was not a significant difference (variance analysis, t­test, Mann­Whitney's U test).

2.A bending test was also conducted. The amount of deflection in both vertical and lateral directions was significantly greater for the NT as compared to the CT. Furthermore, deflection in lateral di­ rections for the NT was significantly greater than in vertical directions. In addition, as the loading weight increased, the deflection amount increased.

These results suggest that the NT, mainly composed of soft materials, is useful for reducing oral trauma and improving plaque removal efficacy when used with young children.

Background. Permanent tooth stainless steel crowns (SSCs) are utilized in the field of pediatric dentistry for interim restoration of permanent teeth in young patients that require full coverage restoration.

Aim. We investigated permanent tooth SSC longevity and evaluated treatment effectiveness when used for interim restoration of young permanent teeth.

Design. A retrospective examination was performed of dental records of patients who visited the Pediatric Dental Clinic at Nagasaki University Hospital from January 2018 to May 2018 and had a permanent tooth SSC restoration placed by a pediatric dentist. Fifty-seven individual SSCs were evaluated with regard to patient age at time of restoration placement, diagnosis, and duration of crown service, with the latter further divided into requiring replacement and continuing use.

Results. Of the 57 permanent tooth SSC restorations performed during the survey period, the average service period was 46 months. Furthermore, 36 were considered functioning uneventfully for an average service period of 45.6 months, while 21 required replacement.

Conclusion. A permanent tooth SSC is a viable option for interim restoration of a permanent tooth in a young patient requiring full coverage restoration. It should be replaced with a cast crown at the appropriate time after completion of patient growth and development.

X-ray imaging at a local dental clinic revealed a supernumerary tooth and hard tooth-like tissue in the upper anterior tooth area in a female child patient, who was then referred to our department. The patient age at the initial examination was 4 years 8 months, and there was no significant systemic or family history. Hellman's dental stage was II A and the terminal plane was vertical. Our initial examination showed that part of the upper right deciduous central incisor had erupted and was distally inclined, which had delayed full eruption. In follow-up visits, malpositioning and eruption disturbance of the upper central incisor during the incisor exchange phase were confirmed in X-ray and threedimensional cone beam CT findings. Extraction of the supernumerary tooth and removal of the hard tooth-like tissue, which was shown to be an odontoma, were performed. In postoperative follow-up examinations, prognosis has been favorable, though long-term observations are considered necessary.