Objective. The aim of the study was to evaluate the association between psychosocial aspects of temporomandibular disorders (TMD) and oral health-related quality-of-life (OHRQoL) and, secondly, to investigate the gender differences in these associations using patient and non-patient groups. Materials and methods. The sample of the study consisted of 79 patients with TMD and 70 non-patients. The data was collected by Finnish versions of the RDC/TMD Axis II profile and Oral Health Impact Profile (OHIP-14) questionnaires. The associations between Axis II profile sub-scales and OHIP prevalence were evaluated using chi-square tests, as stratified by group status (TMD patients and non-patient controls) and by gender. The association between OHIP prevalence and Axis II profile sub-scales were evaluated using logistic regression analysis, adjusted by age, gender and group. Results. OHIP prevalence (those reporting at least one problem) was 90.9% in the patient group and 33.3% in the non-patient group (p < 0.001, chi-squared test). OHIP prevalence was higher among those scoring higher on all RDC/TMD Axis II profile sub-scales, i.e. graded chronic pain status, depression and non-specific physical symptoms with pain items included and with pain items excluded. The associations were significant in the non-patient group. Women showed statistically significant associations of OHIP prevalence with all Axis II sub-scales. Among men, OHIP prevalence associated with GCPS and somatization. The logistic regression analysis showed that OHIP prevalence associated significantly with somatization and depression. Conclusions. TMD associate with OHRQoL through multiple ways, linked with depression and somatization. These findings emphasize the importance of early and effective treatment of TMD.

Tooth development is a highly heritable process which relates to other growth and developmental processes, and which interacts with the development of the entire craniofacial complex. Abnormalities of tooth development are common, with tooth agenesis being the most common developmental anomaly in humans. We performed a genome-wide association study of time to first tooth eruption and number of teeth at one year in 4,564 individuals from the 1966 Northern Finland Birth Cohort (NFBC1966) and 1,518 individuals from the Avon Longitudinal Study of Parents and Children (ALSPAC). We identified 5 loci at P<5×10⁻⁸, and 5 with suggestive association (P<5×10⁻⁶). The loci included several genes with links to tooth and other organ development (KCNJ2, EDA, HOXB2, RAD51L1, IGF2BP1, HMGA2, MSRB3). Genes at four of the identified loci are implicated in the development of cancer. A variant within the HOXB gene cluster associated with occlusion defects requiring orthodontic treatment by age 31 years. Genome-wide association studies have been used to identify genetic variants conferring susceptibility to diseases, intermediate phenotypes, and physiological traits such as height, hair color, and age at menarche. Here we analyze the NFBC1966 and ALSPAC birth cohorts to investigate the genetic determinants of a key developmental process: primary tooth development. The prospective nature of our studies allows us to exploit accurate measurements of age at first tooth eruption and number of teeth at one year, and also provides the opportunity to assess whether genetic variants affecting these traits are associated with dental problems later in the life course. Of the genes that we find to be associated with primary tooth development, several have established roles in tooth development and growth, and almost half have proposed links with the development of cancer. We find that one of the variants is also associated with occlusion defects requiring orthodontic treatment later in life. Our findings should provide a strong foundation for the study of the genetic architecture of tooth development, which as well as its relevance to medicine and dentistry, may have implications in evolutionary biology since teeth represent important markers of evolution.

Twin and family studies indicate that the timing of primary tooth eruption is highly heritable, with estimates typically exceeding 80%. To identify variants involved in primary tooth eruption, we performed a population-based genome-wide association study of ‘age at first tooth’ and ‘number of teeth’ using 5998 and 6609 individuals, respectively, from the Avon Longitudinal Study of Parents and Children (ALSPAC) and 5403 individuals from the 1966 Northern Finland Birth Cohort (NFBC1966). We tested 2 446 724 SNPs imputed in both studies. Analyses were controlled for the effect of gestational age, sex and age of measurement. Results from the two studies were combined using fixed effects inverse variance meta-analysis. We identified a total of 15 independent loci, with 10 loci reaching genome-wide significance (P < 5 × 10⁻⁸) for ‘age at first tooth’ and 11 loci for ‘number of teeth’. Together, these associations explain 6.06% of the variation in ‘age of first tooth’ and 4.76% of the variation in ‘number of teeth’. The identified loci included eight previously unidentified loci, some containing genes known to play a role in tooth and other developmental pathways, including an SNP in the protein-coding region of BMP4 (rs17563, P = 9.080 × 10⁻¹⁷). Three of these loci, containing the genes HMGA2, AJUBA and ADK, also showed evidence of association with craniofacial distances, particularly those indexing facial width. Our results suggest that the genome-wide association approach is a powerful strategy for detecting variants involved in tooth eruption, and potentially craniofacial growth and more generally organ development.