Single-session apexification treatment with MTA is an alternative to the root-canal treatment of immature teeth. Since its results are far from ideal, research with MTA-derivative biomaterials continues; however, the number of studies is limited as of yet. This study aimed to compare the fragilities of in vitro-simulated immature teeth in single-session apexification with MTA and newly-developed calcium-silicate-based MTA derivatives. Two hundred seventy human permanent upper incisors were

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... mly divided into study (n = 180), positive control (Ca (OH)2) (n = 45), and negative control (NC-intact) (n = 45) groups. The study groups used ProRoot MTA (MTA-PR), MM-MTA, NeoMTA-Plus, and Biodentine (BD). Two-week, two-month, and one-year follow-ups data were recorded. A fracture resistance (FR) test was performed at the end of each period. The results of the biomaterials at the different follow-up timepoints were statistically analysed and compared. The two-week FR medians were significantly lower in MM-MTA, NEO, MTA-PR, and Ca (OH)2 groups (p<0.001, p<0.001, p=0.003, and p<0.001. respectively), compared to NC. The two-month FR medians were significantly lower in BD, MM-MTA, NEO, MTA-PR, and Ca (OH)2, (p=0.005, p<0.001, p<0.001, p<0.001, and p<0.001, respectively) compared to NC. The one-year FR medians were significantly lower in the BD, MM-MTA, NEO, MTA-PR, and Ca (OH)2 groups (p=0.002, p<0.001, p<0.001, p<0.001, and p<0.001, respectively) compared to NC. For all groups, FR at the one-year mark was significantly lower compared to the two-week and two-month marks (p<0.001, p<0.001). All groups were compared with each other regarding fracture resistance at two weeks, two months, and one year. Also, for each group follow-up data on fracture resistance were compared. Since FR was significantly higher at the two-week and the two-month mark compared to the one-year mark for each material, filling the root canal completely with biomaterials used in our study leads to tooth denaturation over time, with effects like Ca (OH)2.