Study design and population

We performed a cross-sectional, descriptive study analysing patients who were diagnosed with TMD in Korea and utilised medical services at least once between January and December 2017. While previous studies have used the Research Diagnostic Criteria for TMD¹⁹ or self-reported surveys²⁰ to diagnose TMD, limited studies have used ICD codes in administrative data. In this study, our research team operationally defined TMD as cases with an International Statistical Classification of Disease and Related Health Problems, 10th revision (ICD-10) code of K07.6 (TMJ disorders) or S03.4 (sprain and strain of jaw) as the main diagnosis under outpatient care.

Claims data provided by the HIRA included raw data on treatment prescriptions for all patients who received medical services over the course of 1 year. The raw data did not contain personal and corporate information. Because the claims were submitted monthly, charges in the statement reflected up to 1 month of information. In other words, patients who had been hospitalised for >1 month would have been charged separately for each month. In such cases, errors such as overestimation of the number of inpatients and underestimation of medical expenses might occur when performing statistical analyses. Therefore, data on hospitalisation episodes, which involved collecting and calibrating several claims charged monthly for one consecutive medical practice, were used. In this study, separate claim forms of hospitalised patients were bundled into one hospitalisation episode. Variables used in the episode creating process included claims identification key, patient identification key, insurance type, main diagnostic code, treatment type, treatment start date and treatment end date.

Figure 1 shows the study participant selection process. Of the 35 765 claims of patients who visited the hospital with a K07.6 or S03.4 diagnostic code in 2017, a total of 11 608 claims whose secondary diagnostic code was not null were excluded. Additionally, 17 claims with zero total costs or missing cost data were also excluded, as well as 14 claims in which the number of days of visit was 0. Therefore, a total of 24 126 claims and 10 041 patients were included in the final analysis. Among 10 141 patients, there were only nine inpatient admissions, which were considered to be due to major injuries or invasive surgery. Because of such small sample size, these data might not accurately represent the actual number of TMD inpatients, so we did not analyse inpatient data in detail. Moreover, a single patient can be included as both inpatient and outpatient.

Participant flow diagram. ICD-10, International Statistical Classification of Disease and Related Health Problems, 10th revision; NPS, National Patient Sample; TMJ, temporomandibular joint.