Examination of the Relationship between Oral Health and Arterial Sclerosis without Genetic Confounding through the Study of Older Japanese Twins

Tooth Loss and Carotid Intima-Media Thickness in Relation to Functional Atherosclerosis: A Cross-Sectional Study

Structural arterial stiffness can be evaluated with carotid intima-media thickness (CIMT). Functional arterial stiffness can be evaluated with cardio-ankle vascular index (CAVI). A positive association between CIMT and tooth loss has been reported, but no studies have evaluated the association between CIMT and tooth loss in relation to functional arterial stiffness (functional atherosclerosis). A cross-sectional study of 1235 Japanese individuals aged 40–89 years was conducted. Tooth loss was defined as being in the lowest tertile for the number of remaining teeth (≤20 in men and ≤19 in women). Functional atherosclerosis was defined as CAVI ≥ 9.0. Independent of known confounding factors, CIMT was positively associated with tooth loss only in participants without functional atherosclerosis. Adjusted odds ratios for tooth loss and a 1 standard deviation increment in CIMT were 1.27 (1.04–1.55) for participants without functional atherosclerosis and 0.99 (0.77–1.26) for participants with functional atherosclerosis. CIMT and functional atherosclerosis had a significant effect on tooth loss; the fully adjusted p-value for the interaction on tooth loss was 0.019. Independent of known confounding factors, CIMT is positively associated with tooth loss only in participants without functional atherosclerosis. This finding helps clarify the influence of the progression of arterial stiffness on tooth loss because the progression of structural atherosclerosis might have a beneficial influence on the maintenance of the microcirculation.

Factors Influencing the Localization of Mandibular Third Molars in Twins

PURPOSE

The aim of the present study was to evaluate the genetic and environmental factors influencing the localization of mandibular third molars by analyzing the panoramic radiographs of twins. We examined the mandibular third molars of Japanese monozygotic (MZ) and dizygotic (DZ) twins recruited by the Osaka University Center for Twin Research.

MATERIALS AND METHODS

The present study included 49 pairs (98 participants) of MZ twins and 11 pairs (22 participants) of DZ twins. Using panoramic radiography, we evaluated the degree of eruption of mandibular third molars according to the height of the alveolus bone and the third molar space/crown width ratio. Using co-twin control analysis and a generalized linear mixed model, we evaluated the effects of various factors, including gender, age, body height, number of teeth, length of the lower dental arch, existence of a second molar, bruxism, and previous orthodontic therapy.

RESULTS

Body height, third molar space/crown width ratio, and length of the mandibular dental arch were related to the degree of mandibular third molar eruption and were strongly influenced by genetic factors rather than common or unique environmental factors.

CONCLUSIONS

The degree of third molar eruption was more similar among MZ twins than among DZ twins; therefore, genetic factors can be expected to have more significant influence than will environmental factors. These results can help identify the trend of third molar eruption from a young age, allowing us to advise the early extraction of mandibular third molars for patients with a short stature, narrow retromolar space, or short mandibular dental arch. In addition, if the genes that influence the degree of eruption were identified, we would be better equipped to predict an individual's risk of impaction, and indications for extraction might change.

Update on Osaka University Twin Registry: An Overview of Multidisciplinary Research Resources and Biobank at Osaka University Center for Twin Research

The Osaka University Twin Registry was originally established as a registry of older twins but was subsequently expanded to include twins of all ages. The Center for Twin Research at Osaka University Graduate School of Medicine has been managing this registry, as well as collecting research information and bioresources from twin participants. Based on the resources, multidisciplinary research projects have been conducted in collaboration with researchers from institutions both inside and outside Japan. One of the main aims of the center is to collect research information as well as biological resources from registered twins, and to establish a biobank and databases of these data and bioresources. Although data availability may vary, the following data have been collected: physical data (e.g., height, body weight, blood pressure, theoretical visceral fat, pulse wave velocity and bone density); epidemiological data (e.g., medical history, lifestyle, quality of life, mood status, cognitive function and nutritional status); electrocardiography, ultrasonography (carotid artery and thyroid); dentistry, dermatological assessment; positron emission tomography; magnetoencephalographam; brain magnetic resonance imaging (MRI); and functional MRI. In addition to these in-person survey data, microbiome data have been collected from some participants. As for bioresources, peripheral blood is obtained from the participants for isolation of serum and extraction of DNA and RNA, then stored in deep freezers for further analyses. A variety of research projects are in progress and more are on the way both in Japan and internationally using these data.