Statement of the problem: the restoration of weakened endodontically treated teeth with wide flared canal spaces and thin dentinal walls has presented several problems resulting from common insufficient sound coronal and radicular tooth structure. Materials and method: fifty maxillary-caries , cracks and fractures free-central insicors were endodontically treated, decoronated at M-D cementoenamel-junction and randomly distributed into five equal groups according to the intraradicular rehabilitation technique: group A: Coronal and intra-radicular cores using SDR (Dentsply, Weybridge, UK), group B : Coronal and intraradicular cores using Gradia Core (GC Corporation, Japan) and GC fiber post (GC Corporation, Japan), group C: Coronal and intraradicular cores using Xenious (StickTeck Ltd, Turku, Finland), group D: Coronal and intraradicular cores using flowable composite (Wave, SDI, Australia) and GC fiber post, and finally group E: Cast post and core. Which was cemented using resin cement (Rely X U 200, 3M ESPE, USA). Cr-Co copings were fabricated and cemented on all cores. All the specimens were thermocycled for 300 cycles and subjected to a compressive force at a 130º to the long axis of the tooth (Instron 8874; Instron Corp. Canton, Mass), until fracture. Results: group A scored the highest mean value of (739.15 N), followed by group D (510.29 N), then group B (422.92 N), group C came next (288.16 N), and the least results were registered in group E (285.03 N). In addition, the maximum record was in group A (1135.72 N) while the minimum appeared in group E, (153.40 N). There was also a statistical significant difference between groups A and C on one hand (p-value 0.016) and between groups A and E on the other (p-value 0.016). However, no noticeable difference was found among other groups. Conclusions: cast post should not be used to strengthen structurally compromised and weakened roots. Consequently, smart dentine substitute could be used alone to reinforce weakened roots or a combination of flowable composite resin and fiber post can also help in reinforcing frail roots. Key words: fracture resistance, intraradicular rehabilitation, smart dentine replacement.