This study was conducted to assess caries treatment thresholds among Japanese dentists and to identify characteristics associated with their decision to intervene surgically in proximal caries lesions within the enamel. Participants (n = 189) were shown radiographic images depicting interproximal caries and asked to indicate the lesion depth at which they would surgically intervene in both high- and low-caries-risk scenarios. Differences in treatment thresholds were then assessed via chi-square tests, and associations between the decision to intervene and dentist, practice, and patient characteristics were analyzed via logistic regression. The proportion of dentists who indicated surgical intervention into enamel was significantly higher in the high-caries-risk scenario (73.8%, N = 138) than in the low-caries-risk scenario (46.5%, N = 87) (p < 0.001). In multivariate analyses for a high-caries-risk scenario, gender of dentist, city population, type of practice, conducting caries-risk assessment, and administering diet counseling were significant factors associated with surgical enamel intervention. However, for a low-caries-risk scenario, city population, type of practice, and use of a dental explorer were the factors significantly associated with surgical enamel intervention. These findings demonstrate that restorative treatment thresholds for interproximal primary caries differ by caries risk. Most participants would restore lesions within the enamel for high-caries-risk individuals (Clinicaltrials.gov registration number NCT01680848). © 2012 International & American Associations for Dental Research.