Effects on the incidence of dentinal microcracks in curved root canal preparation with ProTaper Universal and ProTaper Gold / 口腔疾病防治

Objective@#This study aims to compare the incidence of dentinal microcracks produced by ProTaper Universal (PTU) and ProTaper Gold (PTG) file systems during root canal procedures in different curved canals using a dyeing technique.@*Methods@#Sixty extracted human molars were divided into 3 groups of 20 samples each in terms of root curvature (mild bending group, 10 °-19 °; moderate bending group, 20 °-29 °; severe bending group, 30 °-39 °). Ten samples of each group were then randomly allocated to the PTU and PTG file systems. After preparation, all roots were stained using a dyeing method and sectioned at the most curved plane and 2 mm below and above the most curved plane with a low-speed saw under cold water. A stereomicroscope was used to inspect dentinal microcracks at 60 × magnification, and differences between these three instrument groups were analyzed using the chi-square test.@* Results @# The PTG file system induced significantly fewer dentinal microcracks for total, incomplete and complete cracks (P < 0.05), and the effect was more obvious with increasing canal curvature.@*Conclusion @# With the limitations of this in vitro study, it can be concluded that ProTaper Gold can result in fewer dentinal microcracks than ProTaper Universal.

Study of root canal isthmus dentin structure and mineral content and microhardness / 口腔疾病防治

Objective@#To investigate the differences in dentin structure, mineral content and microhardness of single premolar roots with or without an isthmus.@*Methods @#Thirty single-root premolars with a canal isthmus (experimental group) and thirty single-root premolars without a canal isthmus (control group) were collected and analyzed by scanning electron microscopy, X-ray energy spectrometry and a Vickers microhardness tester. Structure, mineral content and microhardness were compared. Results In the experimental group, the dentinal tubules were not obvious, and the structure was disordered. In the control group, the dentin tubules of the root canal wall were arranged regularly, and the lumen opening was clear. The Ca and P contents and Ca/P ratio of the experimental group were lower than those of the control group (P < 0.05). The microhardness of the experimental group was less than that of the control group (P < 0.05).@* Results@# In the experimental group, the dentinal tubules were not obvious, and the structure was disordered. In the control group, the dentin tubules of the root canal wall were arranged regularly, and the lumen opening was clear. The Ca and P contents and Ca/P ratio of the experimental group were lower than those of the control group (P < 0.05). The microhardness of the experimental group was less than that of the control group (P < 0.05).@*Conclusion@#The dentin structure of the root canal isthmus was changed, and the Ca, P contents and microhardness were low. The root canal isthmus was a weak link in the root, which could weaken the resistance of the hard tissue of the root tooth, which may be one of the important factors that could cause vertical root fracture.