Project Summary/Abstract (30 lines) We seek to understand what if any relationship exists between initiation of transmucosal buprenorphine and poor dental outcomes in a retrospective study among a cohort of patients followed at the VA with a diagnosis of opioid use disorder. Prior data suggest that dental problems have arisen after initiation of buprenorphine, however a simple pre-post evaluation of buprenorphine initiation would be insufficient to answer the question of an association, due to confounding. Dental disease worsens with age and over time, an example of time- varying confounding, and patients with OUD, once in treatment, may be more likely to seek routine healthcare that was deferred due to active addiction, an example of healthy user or adherer bias. As a result, we seek to use Aim 1 to characterize longitudinal patterns of MOUD prescribing, as well as patterns of preventive and acute dental care services over time. To rigorously understand the association of transmucosal buprenorphine and poor dental outcomes, we will require an adequate control group with minimal confounding. To achieve this, in Aim 2 we will compare patients with OUD on transmucosal buprenorphine (our main exposure group) to patients with OUD receiving injectable or implantable buprenorphine, methadone, and naltrexone using negative control outcomes. Once we have determined appropriate control groups based on our analyses from Aim 2, in Aim 3 we will report the cumulative risk and risk difference of poor dental outcomes among patients on transmucosal buprenorphine as compared to other MOUD. We will use the VA Corporate Data Warehouse to obtain both prescribing and dental data among patients with OUD diagnosis between 2001 and 2021. Our study team is uniquely suited to employ our proposed methodologies. Drs. Durkin and Roy (Co-PIs) have experience using large prescription datasets to understand trends in utilization. Dr. Butler (Co-I) has extensive expertise in the use of negative control outcomes to reduce bias in comparative effectiveness studies. Dr. Suda (Co-I) has expertise in the VA Corporate Data Warehouse and the use of large datasets to understand dental healthcare utilization patterns. Without rigorous study, the FDA warning may have the unintended consequence of deterring patients from initiation of buprenorphine. In light of the opioid overdose epidemic and known benefits of MOUD, every effort must be made to reduce barriers to initiating buprenorphine. This study will be the first step in understanding the association between transmucosal buprenorphine and dental outcomes.