The role of polymorphisms associated with early tooth eruption in dental and occlusal traits in East Asian populations.
OBJECTIVE
A recent study suggested that rs6504340, a polymorphism within the homeobox B (HOXB) gene cluster, is associated with the susceptibility for malocclusions in Europeans. The resulting malocclusions require orthodontic treatment. The aim of this study was to investigate the association of rs6504340 and other dentition-implicated polymorphisms with dental and occlusal traits in Korean and Japanese populations.


METHODS
The study participants included 223 unrelated Koreans from the Busan area and 256 unrelated Japanese individuals from the Tokyo metropolitan area. DNA samples were extracted from saliva specimens. Genotyping for rs6504340 and four single nucleotide polymorphisms (SNPs) that have been shown to be associated with the timing of first tooth eruption and the number of teeth at 1 year of age (rs10506525, rs1956529, rs9674544, and rs8079702) was performed using TaqMan assays. The Index of Orthodontic Treatment Need (IOTN), overjet, overbite, arch length discrepancy, crown sizes, and length and width of the dental arches were measured. Spearman's correlation coefficients were calculated to evaluate relationships between rs6504340 and these dental/occlusal traits.


RESULTS
We evaluated the aesthetic components and dental health components of the IOTN in the Korean and Japanese populations and found that neither rs6504340 nor the other four SNPs showed any association with dental and occlusal traits in these East Asian populations.


CONCLUSIONS
These negative results suggest that further research is needed to identify the genetic determinants of malocclusions in order to reach a consensus.
Department of Orthodontics, School of Dentistry, Showa University, Tokyo, Japan.
Tetsutaro
T
Yamaguchi
Department of Human Biology and Anatomy, Graduate School of Medicine, University of the Ryukyus, Okinawa, Japan.
Akira
A
Kawaguchi
Department of Orthodontics, School of Dentistry, Pusan National University, Biomedical Research Institute, Pusan National University Hospital, Busan, Korea.
Yong-Il
YI
Kim
Department of Orthodontics, School of Dentistry, Showa University, Tokyo, Japan.
Shugo
S
Haga
Department of Orthodontics, School of Dentistry, Showa University, Tokyo, Japan.
Koshu
K
Katayama
Department of Human Biology and Anatomy, Graduate School of Medicine, University of the Ryukyus, Okinawa, Japan.
Hajime
H
Ishida
Department of Orthodontics, School of Dentistry, Pusan National University, Biomedical Research Institute, Pusan National University Hospital, Busan, Korea.
Soo-Byung
SB
Park
Department of Orthodontics, School of Dentistry, Showa University, Tokyo, Japan.
Koutaro
K
Maki
Department of Human Biology and Anatomy, Graduate School of Medicine, University of the Ryukyus, Okinawa, Japan.
Ryosuke
R
Kimura
Genetics; Orthodontic index; Tooth size