Abstract : The treatment of immature necrotic teeth is challenging in terms of achieving good apical seals, apexification with MTA is a common treatment option many in cases. Despite the good biocompatibility of MTA and its ability to form a calcified apical barrier, its extrusion to the periapical tissues could reduce the success rates of the treatment. Several materials were used as internal matrix to prevent over extrusion of MTA to obtain better results. Therefore, this study aimed to evaluate absorbable collagen membrane as an internal matrix on limiting MTA over extrusion in 3D printed open apex tooth replicas. The study sample included 40 3D printed open apex tooth replicas made by the 3D printer from a model designed based on data taken from a CBCT scan of a single-canal tooth. All 3D printed open apex tooth replicas were divided into two equal groups: Gorup 1 (Experminteal, n=20) MTA plug after application absorbable collagen matrix, and Gorup 2 (Control, n=20) MTA plug alone without application absorbable collagen matrix. The replicas were immersed in saline soaked oasis, then 4mm thickness apical plugs were made in each group and left 48 hours to set. Periapical radiographs were taken to evaluate the apical plug extrusion. The results showed that there were no statistically significant differences in the MTA over extrusion with or without the application absorbable collagen matrix (p = 0.937). The use of collagen internal matrix didn’t prevent MTA over extrusion during apexification procedures.