Abstract: Objective: To investigate the effect of apical foramen sizes on pulp tissue regeneration and teeth compressive strength. Methods: Single root premolars with complete root development and without tooth root fracture were collected after orthodontic extraction. Twelve millimeter tooth roots were preserved after de-crowned, and randomly divided into 5 groups with 25 teeth in each group. The root canals were prepared to 30#, 40#, 60#, 80#, and 100# main files, respectively, in which 30# main file group was used as the control group. Human dental pulp stem cells were cultured in vitro and inoculated into 0.25% hydrogel scaffolds and then injected into the root canals of different groups. Five teeth were taken from each group and were cultured in Transwell chamber for 14 days, 21 days, and 28 days. Then, the total RNA of the cells was extracted, the expression of DSPP and DMP 1 were detected by real-time PCR. The remaining 10 teeth in each group were implanted subcutaneously into the nude mice. After 28 days, 5 teeth were used for histological examination and 5 samples were used for static load test. Results: After 28 days, the expression of DSPP and DMP1 in the experimental groups were higher than those in the control group (P<0.05), and the expression of 40 # main file group was higher than that in the experimental groups (P<0.05). Histological analysis showed that there was no continuous pulp like tissue formation in the 30#, 40#, and 60# main file groups. The tissue formation in the 80 # and 100 # main file group could be seen, but no typical pulp like tissue structure was found. The static load test showed that the average compressive load of 40 # main file group was not different from that of the control group, while the other experimental groups were lower than the control group (P<0.05). Conclusion: The size of apical foramen has no significant effect on pulp tissue regeneration within size of 100# (1 mm), but the compressive strength of apical foramen is obviously decreased when the apical foramen is prepared more than 40#.

Key words: Apical foramen size, Pulp regeneration, Dental pulp stem cells, Teeth compressive strength