Causes and consequences of temporomandibular joint diseases

Sammanfattning: Temporomandibular joint disorders (TMJD), a subgroup of Temporomandibular disorders (TMD), has a multifactorial etiology with still largely unknown pathophysiology. Although many risk factors have been proposed, few population-based studies have been conducted. There are known associations between TMJD and mental and behavioral disorders (MBD) and musculoskeletal diseases (MSD). MBD and MSD cause high work disability and are the leading causes for sick leave (SL) and disability pension (DP) both globally and in Sweden. However, no studies have investigated work disability among patients with TMJD (pwTMJD) or the effect of MBD and MSD comorbidity on work disability among pwTMJD. This thesis includes all Swedish citizens aged ≥18 registered between 1998 and 2016 in the National Patient Registry with a TMJD diagnosis or TMJD surgical procedure code. These pwTMJD (n=33 316) were matched to a comparison cohort (n=333 160) from the Total Population Registry. pwTMJD were categorized depending on whether they had received surgical treatment or not, and on the number of surgical procedures. Study I shows that pwTMJD have 2–3 times more mean annual days of SL and DP than the general population and that patients who had undergone several surgical treatments were most dependent on these benefits. The increased work disability among pwTMJD was noticeable as early as five years before first time diagnosis or treatment. Study II and Study III investigate the probability of developing TMJD among individuals with and without MBD/MSD. Study II shows that many MBD increase the probability of TMJD and that individuals with MBD had a higher risk of needing repeated surgical procedures compared to individuals with no MBD. Study III shows that virtually all MSD increase the probability of TMJD, especially TMJD that require repeated surgical procedures. Study IV further examines the impact of MBD and MSD comorbidity on mean annual days of SL and DP among pwTMJD compared to the general population, by using strata of comorbidity. The results show that both MBD and MSD comorbidity by themselves have a large impact on the use of social insurance benefits but that combined MBD/MSD comorbidity had the largest impact on SL and DP. Regardless of comorbidity, pwTMJD displayed the highest mean annual days of SL and DP in almost all strata of comorbidity. In conclusion, the results in this thesis show that MBD and MSD are strong predictors for the development of TMJD. The results also show that pwTMJD have more work disability than the general population, and that this increased dependence on social insurance benefits is strongly influenced by comorbidities. These findings emphasize how pwTMJD are suffering from their condition and that a multimodal approach is warranted, preferably steered by national guidelines designed by specialists in orofacial pain and function, oral and maxillofacial surgeons, and colleagues from the medical field.