Fracture resistance of endocrowns produced by 3D printing and CAD-CAM blocks: a comparative assessment

This study aimed to compare the fracture resistance of leucite reinforced glass ceramic (LRC), resin nanoceramic (RNC), lithium disilicate ceramic (LDS) blocks, and printable resin (PRM) used in the production of ferrulated and non-ferrulated endocrowns for mandibular molars. A total of 108 extracted mandibular molars with homogeneous dimensions and free of fractures, cracks, or caries were included. Root canal treatment was performed using the ProTaper Next rotary file system, and canals were obturated with gutta-percha and epoxy resin sealer by the lateral compaction technique. Specimens were divided into ferrule (F; 1-mm ferrule height), non-ferrule (NF), and control groups. Digital impressions were obtained with an intraoral scanner (Cerec Primescan), and restorations were designed in CAD software (inLab CAD SW 22.4). Based on restorative materials, groups were classified as follows: LRC, RNC, LDS, and PRM for both F and NF groups, in addition to a control group of intact teeth. Restorations were fabricated either by milling (LRC, RNC, LDS) or 3D printing (PRM), and surface conditioning was performed according to manufacturers’ instructions. All restorations were cemented using a universal adhesive system and dual-cure resin cement.Fracture resistance was tested in a universal testing machine (Instron, USA) at a crosshead speed of 1 mm/min until fracture occurred, and failure modes were classified as Type I (restoration fracture), Type II (restorable fracture involving tooth and restoration), or Type III (non-restorable fracture of tooth structure). Statistical analyses were performed using SPSS v23, with significance set at P < .05. Fracture resistance values varied significantly among restorative materials (P < .05); intact teeth exhibited the highest resistance, while LRC restorations showed the lowest. PRM, RNC, and LDS restorations demonstrated significantly higher resistance than LRC, and all endocrown groups exceeded maximum masticatory forces reported in the literature. Comparisons between ferrule and non-ferrule groups fabricated from the same material revealed no significant differences (P > .05). Although failure type distribution was not significantly different among groups, LRC restorations were mostly associated with type I fractures, RNC and PRM exhibited predominantly restorable fractures, and LDS showed the highest incidence of catastrophic failures. The RNC, PRM, and LDS groups showed higher fracture resistance than LRC, and while LRC and RNC/PRM mainly resulted in restorable fractures, LDS was associated with more catastrophic failures. Endocrowns used Leucite Reinforced Ceramic showed the lowest fracture resistance. In contrast, the fracture resistance values of all materials used are greater than the physiological chewing force value. At the same time, the presence of a ferrule did not affect the fracture resistance values.