Although preventable, dental disease is one of the most common chronic diseases in the United States and exacts a substantial personal and societal toll. It is closely linked to low oral health literacy and poor oral hygiene behaviors (OHBs). Using the high prevalence and burden of dental disease as a proxy, there is a large gap between knowledge about quality oral hygiene routines and what is practiced by individuals. The causes are many but ultimately distill down to a systemic failure to communicate oral hygiene instructions (OHIs) effectively or to engage and motivate patients in their own oral self-care. To address the know-do gap, we begin by distilling desired brushing behaviors into a simple 2x2x4 OHI (brushing 2 times a day, for 2 minutes each time, all 4 dental quadrants). We will leverage tracking capabilities of our innovative eBrush platform to remotely monitor tooth-brushing activities in home settings. Using the 2x2x4 OHI and eBrush as foundational elements, we will develop and evaluate the effectiveness of personalized Digital Oral Health Interventions (DOHI) for promoting ideal OHBs in at-risk individuals. In the UG3 phase, we will build out the technologic infrastructure for collecting brushing data and delivering the DOHI. Then, we will engage target end-users in the co-design of an app for oral self-care and establish the usability and feasibility of the system. In the UH3 phase, we will build and validate computational models to infer the quality of OHBs from brushing data and personalize the DOHI. Using a cohort of 130, we will conduct a 10-week Micro-Randomized Trial to optimize the adaptive tailoring of engagement strategies. Finally, we will evaluate effectiveness of the computationally-driven, adaptive DOHI in promoting sustained engagement in the 2x2x4 OHB. We hypothesize that a dynamic and personalized DOHI will be more effective than traditional, static, clinician-delivered OHI in improving oral health and adherence to 2x2x4 OHBs. We will test our hypothesis through a 6-month, pragmatic, randomized, controlled, parallel-group clinical trial. Eligible adults from safety-net dental clinics will be equipped with an electronic toothbrush and the smartphone app for tracking brushing data. After a run-in period (4 weeks) to ensure technical proficiency and establish baseline OHBs, 260 at-risk subjects will receive a clinician-delivered 2x2x4 OHI and randomized to either: (a) an intervention arm where subjects receive ongoing, personalized DOHIs at opportune times; or (b) a control arm where subjects lack such feedback. Subjects will be followed for 20 weeks. Trained dental examiners will conduct assessments at each visit (baseline, randomization and after 20 weeks). Primary outcomes are changes in dental health from baseline (Modified Gingival Index and Plaque Index). Secondary outcome is the quality of adherence to the 2x2x4 OHI. We will explore subject-level features that predict the magnitude of response to the DOHI. Ou...