Takuro Yonezu

Tooth size-arch length relationships in the deciduous dentition: a comparison between contemporary and historical samples ☆

In a recent study, it was reported that maxillary and mandibular arch lengths were significantly shorter in a sample of contemporary children in the deciduous dentition compared with a historical sample from about 50 years earlier. The purpose of this study was to describe secular changes that might have occurred in tooth sizes and tooth size-arch length relationships in the same cohorts of contemporary and historical North American white children in the deciduous dentition. The 2 samples were similar in terms of geographic location, racial and ethnic backgrounds, and socioeconomic status. Both samples were restricted to white children with a normal overjet (<4 mm) and a normal anteroposterior molar relationship, no anterior open bite, and no crossbite. In addition, subjects were excluded if any permanent teeth were erupted. Measurements of mesiodistal tooth sizes and arch lengths of maxillary and mandibular arches were made, and tooth size-arch length discrepancies (TSALD) were determined. The results indicated that tooth sizes were generally similar in the 2 cohorts but slightly larger in contemporary children. Crowding, as measured by TSALD, was found to be common in the mandibular arch for contemporary children in the deciduous dentition of both boys and girls. Moreover, crowding was much more common and severe in contemporary children compared with children in the historical cohort. Further research is needed to determine whether the increase in mandibular crowding in the deciduous dentition will continue to be observed in the mixed and permanent dentitions and to further establish these possible secular trends.

Effects of prolonged breast- and bottle-feeding on occlusal characteristics in the primary dentition

The purpose of this study was to assess the effects of prolonged breast- and bottle-feeding on the growing primary dentition. This longitudinal study was conducted through a survey questionnaire and clinical examination of 592 children from 18 months to 36 months of age. Selected occlusal characteristics were compared among groups of children with different durations of breast- or bottle-feeding. The prevalence of breast-feeding at 18 months, 24 months and 36 months of age was 9.3%, 3.2% and 0.2% respectively. Prevalence of bottle-feeding was 14.4%, 2.9% and 0.7% respectively. Deepbite showed tendencies towards increasing prevalence with increased bottle-feeding duration. One third of the children who continued bottle-feeding at 24 months of age exhibited deepbite. Anterior crossbite were significantly more prevalent among those with continued breast-feeding at 18 months but ceased by 24 months (28.0%) than for that in the habit-free group (11.7%). However, anterior crossbite showed tendencies towards decreasing prevalence with increased breast-feeding duration. The prevalence of anterior crossbite was 6.7% in the children who continued breast-feeding at 24 months of age. However, the study suggests that spontaneous change in the occlusion following feeding discontinuation, although longer-term longitudinal studies are needed to demonstrate such changes directly.

Development of Jaw and Deciduous Teeth in Japanese Children —Comparing Size of Crown and Alveolar Area between Today and 40 Years Ago—

The purpose of the present study was to investigate change in the size of the jaw and deciduous teeth in Japanese children over the past 40 years by performing measurements on plaster models of the dental arch obtained from children born between 2007 and 2009 (2000s group) and children born between 1968 and 1974 (70s) group. A total of 61 children were enrolled in the 2000s group, comprising 25 boys (average age, 4 years 5 months) and 36 girls (average age, 4 years 4 months), and 93 children in the 70s group, comprising 45 boys (4 years 6 months) and 48 girls (4 years 4 months). The mesiodistal width of the crown, dental arch width, dental arch length, dental arch height, and available arch length in these groups were measured using a 3D measurement system and the sums of the mesiodistal width of the crown and tooth size-arch length discrepancies calculated. The results of the two groups were statistically compared and the following conclusions reached: the size of deciduous teeth has not changed statistically over the last 40 years; the size of the dental arch has decreased in boys (p<0.01), while remaining approximately the same in girls; and the tooth size-arch length discrepancy has decreased, especially in boys (p<0.01). These results indicate that the interdental spaces of the deciduous dentition have decreased, increasing the risk of crowding in Japanese children.

Alveolar Growth in Japanese Infants : A Comparison between Now and 40 Years ago

To investigate differences in alveolar growth during the primary dentition period among different age groups, dental arch width, length, and height were measured in 93 dental arch plaster models obtained from 4-year-olds born between 1968 and 1974, 88 from 5-year-olds born between 1968 and 1974 (70s group), 61 from 4-year-olds born between 2007 and 2009, and 56 from 5-year-olds born between 2006 and 2008 (2000s group). A comparison was also performed to determine whether there was any difference in change between 4 and 5 years of age. The results showed age- and sex-dependent differences in growth patterns in primary dental arch width, length, and height. The amount of change was greater in the 2000s group than in the 70s group, suggesting that yearly growth between 4 and 5 years of age has increased over the last 40 years.

Relationship between Interdental Spacing and Colonization by Streptococcus mutans in Children

The purpose of this study was to investigate the relationship between interdental spacing in the upper incisors and other associated factors with colonization by Streptococcus mutans in children. A total of 47 children aged between 24 and 36 months with no decayed cavities were enrolled in the study. Models were obtained to evaluate interdental spacing in the upper anterior region. The relationships between S. mutans colonization and number of erupted teeth, interdental spacing, diet, and oral hygiene behavior were investigated. S. mutans was detected in the saliva of 14 children (29.8%). No sociodemographic variable was associated with colonization by S. mutans. Neither number of erupted teeth nor childrens age showed an influence on colonization by S. mutans. However, children with interdental spacing in the upper incisors were less likely to show colonization by S. mutans (15.8%) than those without (39.3%). Furthermore, children who ceased breast-and/or bottle-feeding by 15 months of age were less likely to show colonization by S. mutans (22.7%) than those who continued feeding until 19 months of age or more (46.2%).