Although a series of studies on OXIS contacts have been performed, studies regarding changes in OXIS contacts over time are lacking. Therefore, this study aimed to evaluate the change in contact type between primary molars after 3 years in children aged 3–7 years.

This longitudinal study was conducted using 2922 sectional die models of 926 children. At baseline (T0), the contact type between the primary molars was scored using replication via the sectional die model method according to the OXIS criteria. After 3 years, the sectional die models of the same children were scored using the same criteria (T1).

McNemar’s tests revealed a significant change in contacts from baseline to 3 years. The post hoc test explained specific changes in the contacts that were observed to be significant. These were O to X (p < 0.001), O to I (p < 0.001), O to S (p = 0.035), and I to X (p < 0.001).

A significant change in OXIS contact over time was observed. The O-type contact underwent the maximum change. The least and most stable contacts are the “O” and “I” types, respectively. This change in contact type with age may alter the risk of caries in children.