To observe the root and root canal morphology of mandibular second molars in Western Guangxi by CBCT, to provide a reference for clinical diagnosis and treatment.

In total, 564 patients' 1128 mandibular second molars that satisfy the inclusion criteria were analyzed with a planmecaromexis CBCT machine and its own image analysis software. The patients' gender, age and ethnic differences in the root and canal morphology and the symmetry of the bilateral root and canal were statistically analyzed.

Among the 1128 mandibular second molars, 662 were the Zhuang ethnic group and 384 were the Han ethnic group, and 82 were other ethnic groups; the double root type and C-shaped root type accounted for a relatively high proportion: 73.94% and 24.47%, respectively. The detection rates of the double root type were higher in males than in females (P < 0.05); the detection rates of the Cshaped root type were higher in females than in males (P <0.05); the root type of the teeth was mainly double-rooted in the Zhuang ethnic group (P＜0.01). The incidence of type Ⅳ in the mesial root of the double root type mandibular second molar was the highest (P < 0.01), and the incidence of type Ⅰ in the distal root was the highest (P < 0.01). The Cshaped root canal is more continuous at the mouth of the root canal, more downward corresponds to a worse continuity: in three different levels of root canal orifice, root middle and root apex, the root canal orifice is dominated by the C1 type, and both root middle and root apex are mainly C3-type (P < 0.01). The difference in symmetry of bilateral roots and root canals was statistically significant among different gender groups, age groups, and ethnic groups (P < 0.05): there were more males than females, the results in the 18-35-year-old group and the Zhuang ethnic group were higher.

The root and root canal morphology of mandibular second molars in western Guangxi people are complex and changeable. The roots are mainly double root type in the Han ethnic group and the Zhuang ethnic group. C-shaped roots are also common. The detection rate of C-shaped roots in the Zhuang ethnic group was higher, and the symmetry rate of bilateral roots and that of bilateral root canals was higher in the Zhuang ethnic group than in the Han ethnic group.

To investigate the outcomes of a novel direct pulp capping agent containing platelet-rich fibrin (PRF) and mineral trioxide aggregate (MTA).

A total of 32 New Zealand rabbits were randomly divided into 4 groups, namely, the PRF+MTA group (P+M group), PRF group (P group), MTA group (M group) and blank control group (BC group), with 8 rabbits per group. Dental pulp exposure and direct pulp capping were performed, and complete crown square sealing was performed on 2 mandibular central incisor teeth of each rabbit. Four rabbits from each group were euthanized after each observation period (7 and 28 days). The experimental teeth were subjected to HE staining. Inflammatory cell infiltration, calcified bridge formation and pulp tissue disorganization were observed and graded.

Inflammatory cell infiltration: on the 7^th day, group P+M and group M were lighter than group BC (P＜0.05); on the 28^th day, group P+M was lighter than group P and group BC (P＜0.05); group P+M and group M did not significantly differ (P＞0.05). Calcified bridge formation: on the 7^th and 28^th days, group P+M was lighter than group P, group M and group BC (P＜0.05); on the 28^th day, group M was higher than group BC (P＜0.05). Under microscope, the calcified bridge contained cellular components and was surrounded by odontoblast-like cells, sharing a structure resembled osteodentin; dentin tubule-like structure could not be observed in calcified bridge, and the calcified bridge resembled certain points of osteodentin. Pulp tissue disorganization: on the 7^th day, group P+M and group M were lighter than group BC (P＜0.05); on the 28^th day, group P+M was lighter than group P and group BC (P＜0.05). group P+M and group M did not significantly differ (P＞0.05).

The combination of PRF and MTA for direct pulp capping provided light inflammatory cell infiltration, stable pulp status and a strong ability of pulp tissue to form calcified bridge, and the calcified bridge resembled certain points of osteodentin.