ABSTRACT Calcium hydroxide apexification has been used in the treatment of immature teeth with pulp necrosis and apical periodontitis for more than 50 years. However, the guidelines of the European Academy of Paediatric Dentistry (EAPD) and the American Association of Endodontists (AAE) ‘Clinical recommendations for a regenerative procedure’ recommend against calcium hydroxide apexification. The American Association of Endodontists “Clinical considerations for a regenerative procedure” do not list calcium hydroxide apexification as a treatment option for immature teeth with pulp necrosis. This review analyses the strength of the science that led to calcium hydroxide no longer being recommended by the EAPD and AAE regenerative guidelines. Many differences in the studies and failure to include adequate controls have resulted in inconsistent outcomes between studies. Furthermore, prior in vitro studies have assessed narrow mechanical properties of teeth without a theoretical fracture mechanics model. Cvek's concerns regarding the thinness of the dentinal walls remain as a primary risk for tooth fracture with Class 3 root development fractured with an incidence of 77% compared to a fracture incidence of just 2% for mature teeth. This review develops a simple fracture mechanics approach to the phenomenon of transverse root fracture that provides a theoretical framework to why fragile roots are more likely to fracture when compared to mature teeth. Furthermore, the effect of the varying size access cavities has not been previously considered. Systematic reviews and clinical studies do attest to the success of all approaches for the treatment of immature teeth with pulp necrosis. Calcium hydroxide apexification is one of the recommended treatments in the International Association of Dental Traumatology guidelines. However, mineral trioxide aggregate (MTA) and hydraulic calcium silicate cements (HCSC's) may provide better outcomes and have the convenience for the patient of a shorter treatment time. Regenerative endodontic treatment (RET) is recommended when the tooth roots are very immature with Cvek Class 1–3 root development. However, the treatment of immature teeth with pulp necrosis remains a clinical challenge as does the risk of tooth fracture.