ImportanceUntreated tooth decay is disproportionately present among low-income young children. While American Academy of Pediatrics (AAP) guidelines require pediatric clinicians to implement oral health care, the effectiveness of these oral health interventions has been inconclusive.ObjectiveTo test the effectiveness of multilevel interventions in increasing dental attendance and reducing untreated decay among young children attending well-child visits (WCVs).Design, Setting, and ParticipantsThe Pediatric Providers Against Cavities in Children’s Teeth study is a cluster randomized clinical trial that was conducted at 18 pediatric primary care practices in northeast Ohio. The trial data were collected between November 2017 and July 2022, with data analyses conducted from August 2022 to March 2023. Eligible participants included Medicaid-enrolled preschoolers aged 3 to 6 years attending WCVs at participating practices who were enrolled at baseline (WCV 1) and followed-up for 2 consecutive examinations (WCV 2 and WCV 3).InterventionsClinicians in the intervention group received both the practice-level (electronic medical record changes to document oral health) and clinician-level (common-sense model of self-regulation theory–based oral health education and skills training) interventions. Control group clinicians received AAP-based standard oral health education alone.Main Outcomes and MeasuresDental attendance was determined through clinical dental examinations conducted by hygienists utilizing International Caries Detection and Assessment System criteria and also from Medicaid claims data. Untreated decay was determined through clinical examinations. A generalized estimating equations (GEE) approach was used for both clinical examinations and Medicaid claims data.ResultsEighteen practices were randomized to either intervention or control. Participants included 63 clinicians (mean [SD] age, 47.0 [11.3] years; 48 female [76.2%] and 15 male [23.8%]; 28 in the intervention group [44.4%]; 35 in the control group [55.6%]) and 1023 parent-child dyads (mean [SD] child age, 56.1 [14.0] months; 555 male children [54.4%] and 466 female children [45.6%]; 517 in the intervention group [50.5%]; 506 in the control group [49.5%]). Dental attendance from clinical examinations was significantly higher in the intervention group (170 children [52.0%]) vs control group (150 children [43.1%]) with a difference of 8.9% (95% CI, 1.4% to 16.4%; P = .02). The GEE model using clinical examinations showed a significant increase in dental attendance in the intervention group vs control group (adjusted odds ratio, 1.34; 95% CI, 1.07 to 1.69). From Medicaid claims, the control group had significantly higher dental attendance than the intervention group at 2 years (332 children [79.6%] vs 330 children [73.7%]; P = .04) but not at 3 years. A clinically but not statistically significant reduction in mean number of untreated decay was found in the intervention group compared with controls (B = −0.27; 95% CI, −0.56 to 0.02).Conclusions and RelevanceIn this cluster randomized clinical trial, children in the intervention group had better dental outcomes as was evidenced by increased dental attendance and lower untreated decay. These findings suggest that intervention group clinicians comprehensively integrated oral health services into WCVs.Trial RegistrationClinicalTrials.gov Identifier: NCT03385629