A genome-wide association study of third molar agenesis in Japanese and Korean populations.

Tooth agenesis is the most common developmental anomaly of human dentition, occurring most often in the third molar (wisdom tooth). It is affected by genetic variation, so this study aimed to identify susceptibility genes associated with third molar agenesis. Examination of panoramic radiographs and medical history about third molar extraction were used to diagnose third molar agenesis. We then conducted a genome-wide association study of 149 cases with at least one-third molar agenesis and 338 controls from Japan and Korea using the Illumina HumanOmniExpress BeadChip. After rigorous quality-control filtering, approximately 550 000 single-nucleotide polymorphisms (SNPs) were analyzed in association tests with the status. We identified three SNPs showing evidence of association at P<1 × 10(-5) and 69 SNPs showing evidence of association at P<1 × 10(-4). SNP rs1469622, which maps to an intron of THSD7B (thrombospondin, type I, domain containing 7B) on chromosome 2, showed the strongest association (combined odds ratio=1.88, 95% confidence interval=1.43-2.47, P=7.5 × 10(-6)). The identified SNPs may be considered candidates for future replication studies in independent samples.

Lip sucking and lip biting in the primary dentition: two cases treated with a morphological approach combined with lip exercises and habituation.

Lip sucking and lip biting in the primary-dentition period can cause the upper incisors to tip labially and the lower incisors to collapse lingually with the lower lip wedged between the upper and lower anterior teeth. The resulting lip incompetence further aggravates maxillary protrusion. Thus, there is a causal relationship between lip sucking/lip biting and maxillary protrusion. Orofacial myologists provide lip training to activate the flaccid upper lip and raise the child's awareness to help stop the sucking or biting of the lower lip, sometimes using an oral screen. Two primary-dentition cases with lip sucking and lip biting were treated with a functional appliance (F.A.), resulting in the elimination of the habits in 5 to 6 months along with the improvement of the overjet, overbite and facial profile. The authors prioritize myofunctional therapy (MFT) when treating open bite cases with tongue thrust in the primary dentition. However, the treatment of maxillary protrusion due to lip sucking and lip biting is approached differently with priority given to morphological improvement to create an oral environment that makes lip sucking and lip biting difficult, which is complimented with lip exercises and habituation. This combined approach was found to be effective in breaking the lip-sucking and lip-biting habits.