The aim of the study: Study of the effect of the core building-up material quality of three different materials on the location of fracture for a group of lower premolars after treating the core and restoring them with fiberglass posts.

Research materials and methods: The research sample consisted of (30) lower first laughs, as these teeth were extracted in the course of orthodontic treatment (free from any defects) and stored with distilled water. The clinical crowns of these teeth were cut so that a coronary tissue was kept 2mm high above the enamel-cemento junction. These teeth were treated with pulp and restored with fiberglass posts. The research sample was divided into three groups, each consisting of (10) premolars, according to the type of core building-up material.

1. Composite Resin (IVOCLAR, T-Econom, Liechtenstein) Group T.

2. Flow composite resin (IVOCLAR, Titric N-Flow, Liechtenstein) Group F.

3. Resin Reinforced Glass Ionomer Cement (3M ESPE, Vitermer, USA) Group G.

The teeth were crowned with Nickel-Chrome crowns and then an oblique force was applied at an angle of 45 to the tooth axis using a general mechanical testing device at a speed of 1mm / min until failure occur.

Results: It was found that group T premolars restored with composite resin had nine Cervical Fracture states and once in middle while the locations of fracture fore premolars restored with Flow resin had eight Cervical Fracture states and twice in Middle, and locations of fracture for premolars Restored with Glass ionomer cement had ten Cervical Fracture, and significant differences were observed between groups (P =1).

Conclusion: As it turns out, there is no correlation to the core building-up material in the failure model.