Genetic, Psychological, and Behavioural Factors Associated with Subtypes of Pain-Related Temporomandibular Disorders

<b>Background:</b> This genetic association study investigated single nucleotide polymorphism (SNP) in interleukin-8 (<i>CXCL8</i>) and opiorphin (<i>OPRPN</i>) genes, as well as psychological characteristics and oral behaviours, between patients with pain-related temporomandibular disorders (TMDp) and healthy controls. The aim was to examine associations and predictive value of these factors for TMDp subtypes: arthralgia and myalgia. <b>Methods:</b> A total of 85 patients with TMDp (arthralgia and/or myalgia) and 85 pain-free controls were included. Diagnoses were established following the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD). All participants completed standardised self-report questionnaires assessing anxiety, depression, and oral behaviours. Buccal swabs were collected for DNA extraction, and SNP genotyping was performed using real-time PCR. Statistical analyses were conducted using dominant and recessive genetic models. Logistic regression models were applied to assess risk factors for each TMDp subtype. <b>Results:</b> Participants homozygous for the minor allele (CC genotype) of rs1387964 in <i>OPRPN</i> were significantly more prevalent in both arthralgia and myalgia groups compared to controls. Age and female sex predicted TMDp-arthralgia. Predictors of TMDp-myalgia included the CC genotype of rs1387964, age, female sex, anxiety, and depression. <b>Conclusions:</b> Genetic background and psychological characteristics were significant predictors of TMDp myalgia, highlighting a multifactorial profile for this TMDp subtype.