Purpose: The purpose of the present study was to evaluate the individual susceptibility of four different types of OXIS contact areas (open [O], point [X], straight [I], and curved [S]) to approximal caries in children. Methods: A retrospective cohort study was performed using clinical photographs and cone-beam computed tomography images of children, available from January 1, 2014, to August 31, 2015, showing the presence of at least one caries-free contact area between the primary molars. A single calibrated examiner scored 1,102 selected contacts using OXIS criteria from the occlusal view and subsequently evaluated the same contacts with a minimum follow-up period of one year for the presence of approximal caries. Results: Of the 1,102 contacts, 259 (23.5 percent) were found to be carious or restored due to approximal caries. Multivariate logistic regression analysis showed that only the type of contact played a significant role in caries prevalence (P<0.05). The odds ratios of OXIS contacts for the development of approximal caries were: S contact-147.4 (95 percent confidence interval [95% CI] equals 19.7 to 1101.7); I contact-24.5 (95% CI equals 3.4 to 177.9); X contact-1.1 (95% CI equals 1.0 to 12.5); and O contact-1.00 (reference). Conclusions: Among the OXIS contacts, the S type was most susceptible to approximal caries due to its complex morphology. The broad contact areas, namely, I and S types, are at greater risk for approximal caries in primary molars than O and X contacts.