Sachiko Hayashi-Sakai

Determination of fracture toughness of human permanent and primary enamel using an indentation microfracture method

The purpose of the present study was to examine the fracture toughness and Vickers microhardness number of permanent and primary human enamel using the indentation microfracture method. Crack resistance and a parameter indirectly related to fracture toughness were measured in 48 enamel specimens from 16 permanent teeth and 12 enamel specimens obtained from six primary teeth. The Vickers microhardness number of the middle portion was greater than the upper portion in primary enamel. The fracture toughness was highest in the middle portion of permanent enamel, because fracture toughness greatly depends upon microstructure. These findings suggest that primary teeth are not miniature permanent teeth but have specific and characteristic mechanical properties.

Eruption disturbances in Japanese children and adolescents

Abstract The aims of this report were to determine the nature of eruption disturbances and to establish the pattern of management for these teeth in a group of Japanese children and adolescents. Data were collected from the clinical records of patients in the Pediatric Dental Clinic of Niigata University Medical and Dental Hospital. There were 700 patients (364 males and 336 females) and 748 teeth (26 primary teeth and 722 permanent teeth) who were treated for eruption disturbances between 1979 and 2002. During this period, 17,365 new patients visited the clinic, of whom approximately 4% had eruption disturbances. The most frequently affected permanent teeth were the maxillary central incisors (38.6%), followed by the maxillary canines (15.4%). Of the permanent teeth, 52.5% were in males and 47.5% in females. Although there were more cases of maxillary central incisors in males than in females, the number of cases involving maxillary canines was higher in females. Whereas delayed eruption was noted in 76.7% of maxillary central incisors, 18.6% were impacted and 4.7% demonstrated abnormal direction/position which required treatment. In contrast, a higher percentage (64.8%) of maxillary canines that showed abnormal direction/position was treated. Eruption disturbances were found in 40% of the patients during routine examinations. This suggests that regular routine examinations are important for pediatric dentists to detect and treat eruption disturbances early.

Severe Impaction of the Primary Mandibular Second Molar Accompanied by Displacement of the Permanent Second Premolar

Tooth impaction is defined as any tooth that fails to erupt into a normal functional position and remains unerupted beyond the time at which it should normally erupt. Reports of impaction and eruption failure in primary teeth are relatively rare compared to permanent teeth. We report 2 rare cases where the second premolar was located on the occlusal side of the impacted mandibular second primary molar. In the first case, the succedaneous permanent tooth erupted after extraction of the primary tooth, fenestration, and traction. In the second case, the succedaneous permanent tooth erupted without fenestration or traction. Although the etiology of the tooth displacement was unknown in both cases, inhibition of the eruptive movement of the primary molar may have been associated with displacement of the succedaneous permanent premolar.

Classification of maxillary canine transpositions in Japanese children: A report of 10 cases

The aim of the present study was to examine the prevalence rate and treatment outcome of maxillary canine transposition in Japanese children according to the conventional standard and our new additional consideration of the classification. From 140 cases with ectopic canines diagnosed in the Pediatric Dental Clinic of Niigata University Medical and Dental Hospital, we selected 10 transposition cases as the present subjects. Out of 10 cases, 4 were males and 6 females. Six were classified into type A: the mesio-distal positional interchange of the canine and the first premolar, 2 cases into type B: the mesio-distal transposition of the canine and the lateral incisor, and the other 2 cases into type C: the present new classification that showed the vertical transposition of the canine and the first premolar within the developmental bone. The prevalence rate of types A and B resembled the previous papers regarding the ratio of sex and bilateral occurrence. Although 3 cases in type A, one case in type B and one case in type C could finally be aligned in the normal tooth order, every one of the types A and B cases were aligned in the reverse order. For every one case in types A and C, the transposed canines were extracted. It is recommended that pediatric dentists take an orthopantomogram during early mixed dentition as a routine practice in order to detect anomalies of tooth eruption, such as tooth transposition, as early as possible.

Occlusal guidance for unilateral scissors bite in primary dentition: A case report

A scissors bite is one of the more unusual malocclusions in primary dentition. The purpose of this report is to describe the unilateral scissors bite in primary dentition and the treatment outcome following the use of constriction appliances. A 5-year, 5-month-old boy developed a scissors bite in the left molar region due to the extended width of the maxillary dental arch. Two types of appliances were used to reduce the width of the maxillary dental arch; one was a removable type modified from a conventional expansion plate, and the other was a fixed type modified from a quad-helix appliance. The left maxillary primary molars were able to bite normally after the treatment using both appliances. As a result, the left first molars also could be guided to a normal occlusion and prevented from becoming a scissors bite. We suggest that improvement of the scissors bite in the primary dentition stage can prevent subsequent malocclusions in permanent dentition.

Hypophosphatasia: Evaluation of Size and Mineral Density of Exfoliated Teeth

OBJECTIVE Most cases of hypophosphatasia (HPP) exhibit early loss of primary teeth. Results of micro-computed tomography (micro-CT) analysis of teeth with HPP have not yet been reported. The purpose of the present study was to describe the size and mineral density distribution and mapping of exfoliated teeth with HPP using micro CT. STUDY DESIGN Seven exfoliated teeth were obtained from a patient with HPP. Exfoliated teeth sizes were measured on micro CT images and mineral densities of the mandibular primary central incisors were determined. RESULTS Partial dentures were fabricated for the patient to replace the eight primary teeth which had exfoliated. Most primary teeth sizes were within the normal range. The mean values of enamel and dentin mineral densities in teeth with HPP were 1.35 and 0.88 g/cm3, respectively, in the mandibular primary central incisors. CONCLUSION Mineral density distribution and mapping revealed that the values in teeth with HPP were lower than the homonymous teeth controls in all regions from the crown to apex. Furthermore, it was demonstrated that the differences between HPP and controls were larger on the crown side and the differences tended to converge on the apex side. These results suggested that the present patient showed mild hypomineralization in the primary dentition.

Self-Esteem and Oral Condition of Institutionalized Abused Children in Japan

OBJECTIVE Abused children have been reported to have low self-esteem. The aim of this study was to investigate the effects of dental intervention on self-esteem, oral condition, and concern for oral health in abused children admitted to a child protection service facility. STUDY DESIGN We examined the oral condition of 65 children (34 boys, 31 girls; aged 2-15 years), instructed them in tooth-brushing. Self-esteem was examined using Popes five-scale test for children. Before discharge, the children completed questionnaires on concern about their oral health. RESULTS The findings revealed the reasons for admission were child abuse and neglect (n=45), domestic violence against the mother (n= 20), special needs (n=11), delinquency (n=7), school refusal (n=2), and other reasons (n=3). Thirty-five of the 65 residents (54%) needed treatment for caries. Of these, 24 (69%) were abused children and 11 (31%) were admitted due to other reasons. Mean self-esteem score differed significantly between the resident children (n=43) and an outpatient control group (n=102) (59.16±14.54 vs 73.92±16.81, respectively; p<0.01). CONCLUSION Although the abused children had low self-esteem, after dental intervention, positive answers regarding oral health were obtained. The findings suggest that dental interventions might be effective for helping to improve the self-esteem of abused children.

Clinical and Radiographic Findings and Usefulness of Computed Tomographic Assessment in Two Children with Regional Odontodysplasia

Regional odontodysplasia is a rare, severe, and nonhereditary developmental disorder in tooth formation and involves epithelial and mesenchymal-derived dental tissue. On radiographs, affected teeth have an abnormal morphology, a hypoplastic crown, and only a faint outline of hard tissue, a condition termed “ghost teeth.” We report clinical and radiographic findings from two children with regional odontodysplasia. Using computed tomography (CT), we calculated attenuation coefficients (i.e., Hounsfield units) for affected teeth and assessed the condition of dental follicles. To measure density, regions of interest were delimited and CT values were calculated. In our two patients, the CT values for enamel were lower in affected teeth than in sound teeth, while CT values for dentin were similar for affected and sound teeth. The average CT value for dental follicles in affected teeth was about 65 to 120, which suggests that dense fibrous connective tissues or hard tissue-like structures might be present in dental follicles. Analysis of CT values may be quite useful in the diagnosis and treatment of regional odontodysplasia.

Severe cases of ectopically erupting maxillary canine with excessive mesial angulation

The aim of the present study was to examine retrospectively how best to treat severe cases of ectopically erupting maxillary canines with mesial angulation exceeding 50 degrees. From the ectopically erupting canines diagnosed at the Pediatric Dental Clinic of Niigata University Hospital, we selected for our study 14 severe cases in which mesial angulation exceeded 50 degrees. Nine ectopically erupting canines could be aligned within the arch after traction, and two canines are in the course of treatment, while three canines were removed. In the removed canines, the vertical length from the occlusal line of the crown top was shorter than that in the aligned canines with similar initial condition. This means that the vertical length to the occlusal line of the impacted canine influences the treatment complexity. In four similar ectopically erupting canines in which mesial inclination was nearly 80 degrees or greater and vertical length was over 30 millimeters with Sector 1 or 2 positioning distal to the midline of the root of its adjacent lateral incisor, the initial disruptive conditions were improved after extraction of the predecessor and/or fenestration of the affected canine. It is concluded that traction should be postponed until a few months after extraction of the predecessor if the ectopically erupting canine is located far away from the occlusal line (over 30 millimeters) and its mesial inclination is more than nearly 80 degrees; also that this treatment plan should be limited to cases in which the crown top belongs to Sector 1 and 2.

The clinical oro-facial findings of an 11-year-old Japanese boy with 47, XYY: A case report

Abstract 47, XYY is a sex chromosome-number disorder occurring in males. Pediatric dentists seldom report encountering 47, XYY males, probably because there are no overt signs of the disease. The purpose of this report is to present the clinical oro-facial findings of the case of a 47, XYY boy based on cephalometric analysis and study model examinations as well as micro-CT measurement of tooth mineralization. An 11-year-old Japanese boy was referred to our clinic for extraction of primary teeth because of their prolonged retention. He had 47, XYY disorder, pulmonary hypertension, and slight mental retardation. Cephalometric analysis and study model examinations that included a comparison of tooth size and arch assessments were performed. A further attempt was made to demonstrate the degree of dentin mineralization in primary molars. The boys height and weight were normal but his head circumference had exceeded the 94th percentile since 2 years of age. The cephalometric analysis showed an increase in the lower facial height and bimaxillary protrusion with a longer mandible. Study model examination revealed that the mesio-distal crown widths of all erupted primary and permanent teeth were larger than the standard values, except for the mandibular permanent canines. The degree of dentin mineralization was almost normal in the crown and root areas. A profilogram showed an increase in the lower facial height and bimaxillary protrusion with a longer mandible. The dental arch showed a remarkably contracted width but an extended length. The crown width was larger than the standard values, but the distribution of the degree of dentin mineralization differed little from normal.