BACKGROUND:Previous studies show that the fracture resistant force of endodonticaly treated teeth can be improved by post. But this idea has been controversial in recent years. Many scholars believe that the root canal preparation might weaken dental root the post increases the risk of tooth fracture. OBJECTIVE: To evaluate the fracture resistance ability of severe wedge-shaped-defect premolar to oblique loading, which was restored with fiber reinforced composite posts by different therapy methods. METHODS:A total of 50 human maxilary premolars were randomly divided into five groups, with ten teeth in each group. They were given folowing treatments: Group A: 10 untreated premolars; Rest 40 premolars of Groups B, C, D and E were prepared 1/3 bucco-lingual distance for artificial severe wedge-shaped defects at the buccal cervix. Group B: untreated severe wedge-shaped defects premolars; Group C: severe wedge-shaped defects premolars were endodonticaly treated, remaining dentin over hang above the wedge shaped defect, LuxaPost posts reinforced in buccal canal and lingual canal, LuxaCore composite resin restored dentin defect; Group D: severe wedge-shaped defects premolars were endodonticaly treated, LuxaPost posts reinforced in buccal canal and lingual canal, LuxaCore composite resin restored dentin defect, and then covered with ful metal crown; Group E: severe wedge-shaped defects premolars were endodonticaly treated, removing dentin over hang above the wedge shaped defect, LuxaPost posts reinforced in buccal canal and lingual canal, restored with LuxaCore composite resin, and then covered with ful metal crown. Fracture resistance of each specimen was measured in each group. RESULTS AND CONCLUSION: The fracture strength of each group were Group A (1 002.69±147.62) N, Group B (439.28±66.34) N, Group C (958.30±101.23) N, Group D (1 207.09±143.48) N, and Group E (1 056.44±139.30) N. Group D had the highest fracture strength (P < 0.01), while Group B had the lowest fracture strength (P < 0.01). There were no significant difference among the fracture strength of Group A, Group C and Group E. Our findings indicated that the fracture resistance of the severe wedge-shaped defected premolar can be improved by fiber reinforced composite post and dentin above wedge shaped defect remained.

The clustered regularly interspaced short palindrome repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system is a versatile genome editing tool with high efficiency. A guide sequence of 20 nucleotides (nt) is commonly used in application of CRISPR/Cas9; however, the relationship between the length of the guide sequence and the efficiency of CRISPR/Cas9 in porcine cells is still not clear. To illustrate this issue, guide RNAs of different lengths targeting the EGFP gene were designed. Specifically, guide RNAs of 17 nt or longer were sufficient to direct the Cas9 protein to cleave target DNA sequences, while 15 nt or shorter guide RNAs had loss-of-function. Full-length guide RNAs complemented with mismatches also showed loss-of-function. When the shortened guide RNA and target DNA heteroduplex (gRNA:DNA heteroduplex) was blocked by mismatch, the CRISPR/Cas9 would be interfered with. These results suggested the length of the gRNA:DNA heteroduplex was a key factor for maintaining high efficiency of the CRISPR/Cas9 system rather than weak bonding between shortened guide RNA and Cas9 in porcine cells.
Base Sequence ; Complement System Proteins ; CRISPR-Cas Systems ; DNA ; Genome ; Nucleotides ; RNA, Guide ; Swine