Interactive study blocks for hydraulic cement research in endodontics

Background: Hydraulic cements used in endodontic therapy interact with the clinical environment. In vitro testing requires the use of extracted human teeth to mimic the clinical environment. This introduces bias, ethical restrictions and a limited supply of natural teeth, so an alternative tooth replica is required to mimic the microstructure, morphology and the mineral content of natural dentine. 

Methods: A slip-casting method was chosen to produce a tooth replica from a slurry of hydroxyapatite, porogen, binding and dispersing agent. μ-CT scanning was used to create an accurate 3D model of the root canal anatomy of extracted teeth. Plaster moulds were produced to accommodate the slip-casting process, and samples of variable hydroxyapatite-to-porogen ratio were created to study the effect of this ratio on the resulting microstructure and hardness and whether these values were comparable to natural dentine. All three compositions were analysed using a scanning electron microscope for the microstructural assessment and a Vickers indenter to determine the microhardness. 

Results: All the tested compositions closely matched the pore diameter of that of the coronal and middle thirds of natural teeth while demonstrating significantly bigger pore diameters compared to the apical section except composition 3 which showed significantly bigger pore diameters compared to both middle and apical sections. Varying the wt.% of the constituent materials did not significantly affect the pore density/mm² (ranging from 8787 to 11,813). All compositions revealed hardness values higher than natural dentine, which shows potential as a suitable tooth substitute in research. 

Conclusions: The slip casting method to manufacture hydroxyapatite tooth replicas is promising but requires further research to assess its suitability to test hydraulic cements in endodontics.