Objective: To evaluate the impact of various access cavity designs and the amount of remaining tooth structure (traditional access, truss access &conservative access) on the fracture strength of upper first premolars. Materials and methods: forty-two intact maxillary premolars with two roots were anatomically distributed among four main groups: Control group: 6 intact sound premolars. Traditional access cavity group (TAC): (n=12),Truss group (TREC)(n=12) and Conservative access group (CEC):(n=12). The three access cavity test groups were further subdivided into 2 subgroups 6 teeth each according to the number of remaining residual walls either 3 or 2 residual walls. During access cavity preparation, Cone Beam Computed Topography (CBCT) was utilized as a guide tool to detect canal orifices while maintaining the integrity of the pericervical dentin. The teeth were embedded in self-curing acrylic resin 2 mm below the cementoenamel junction after access cavity preparation. After that, the specimens were loaded in a universal loading machine (Instron model 3345) until they fractured, and the fracture values were recorded in newtons. Tukey post hoc analysis was used for multiple comparisons (P <.05) and 2-way analysis of variance was used to analyze the data. R statistical analysis software, version 4.3.1 for Windows, was used to conduct the statistical analysis. Results: Only the remaining tooth structure had a significant effect on the teeth's fracture resistance, and the loss of the mesial and distal marginal ridges significantly reduced the teeth's strength. .That truss access cavity did not significantly improve the fracture resistance in the 3 remaining wall groups.