To explore the key points of clinical diagnosis and treatment of three mesiobuccal root canals.

In the procedure of endodontic therapy for the upper left second molar with pulpitis, through root canal exploration under a dental microscope and cone beam CT (CBCT)-assisted imaging examination, it was confirmed that the left upper second molar contained 3 roots and 5 root canals, among which the third root canal existed in the mesiobuccal root. Combined with perfect root canal preparation, cleaning, disinfection, filling and minimally invasive inlay repair, the clinical symptoms were eliminated. The patients were followed up and the related literatures were reviewed.

One- and two-year follow-ups showed that the tooth had no discomfort and could be used normally. X-ray revealed that the filling was complete, and the periapical tissue was normal. The results of the literature review showed that the incidence of three mesiobuccal root canals in maxillary second molars was 0.11%-4.2%. It is difficult to find additional root canals only by X-ray imaging. Dentists should further determine the number and anatomical shape of root canals by CBCT and operating microscopy. When there are three mesiobuccal root canals in maxillary molars, dentists should avoid overpreparation. Healthy tooth tissue is the key to good prognosis.

During root canal therapy, clinicians should consider the anatomical variation of the root canal, should always be alert to the existence of an extra root canal, and should use CBCT, operating microscopy, ultrasound and various auxiliary instruments to locate and treat the variant root canal.

Metagenomic sequencing was used to explore the species composition and internal functional metabolic pathway of saliva and supragingival plaque microbial communities in healthy adults to provide a theoretical reference for the biological prevention and treatment of oral diseases.

Saliva and supragingival plaque samples were collected from healthy adults, total DNA was extracted, and a metagenomic library was constructed. The qualified library was sequenced via metagenomics, and the sequencing data were analyzed using bioinformatics and statistics.

The main bacterial phyla in healthy oral samples were Proteobacteria (32.51%), Bacteroidetes (30.81%), and Actinobacteria (16.23%), and the main bacterial species were Corynebacterium matruchotii (3.84%), Haemophilus parainfluenzae (2.91%), and Prevotella melaninogenica (2.76%). The alpha diversity of the supragingival plaque group was higher than that of the saliva group, and there was a significant difference in the composition of the microbial community between the two groups (P<0.05). At the species level, Prevotella melaninogenica, Fusobacterium periodonticum, and Prevotella intermedia were more abundant in saliva samples than in supragingival plaque samples, while Corynebacterium matruchotii, Propionibacterium acidifaciens, and Rothia dentocariosa were more abundant in supragingival plaque samples than in saliva samples (P<0.05). High-quality gene sets of saliva and supragingival plaque in healthy adults were constructed based on metagenomic sequencing. The results of KEGG pathway functional metabolic differences showed that starch and sucrose metabolism, leucine and isoleucine degradation, and arginine biosynthesis in salivary microorganisms were more abundant than in supragingival plaque, while glycolysis/gluconeogenesis and carbon metabolism in supragingival plaque were more abundant than in saliva.

There are significant differences in the species composition and functional gene metabolic pathways of saliva and supragingival plaque microecology in healthy adults. The sensitivity of dominant species in different microecological regions to the identification of oral diseases may be different. In the microbiological study of oral diseases, appropriate samples should be selected according to different diseases.

To investigate the distribution characteristics and functional genes of cariogenic bacteria in oral microorganisms of patients with type 2 diabetes mellitus and to improve the understanding of the relationship between type 2 diabetes mellitus and dental caries.

The experimental group included 10 patients with type 2 diabetes treated in the Department of Endocrinology, the First Affiliated Hospital of Air Force Medical University. The normal control group included healthy oral subjects without type 2 diabetes in the community population (10 cases). Samples of supragingival plaque from patients with type 2 diabetes mellitus and normal controls were collected and sequenced. Bioinformatics and statistical analysis of cariogenic bacteria such as Streptococcus mutans, Lactobacillus, Actinomyces viscosus and Candida albicans were carried out.

There were slightly fewer cariogenic bacteria such as Streptococcus mutans, Lactobacillus, Actinomyces viscosus and Candida albicans in supragingival plaque samples of type 2 diabetic patients than in normal controls, but the difference was not statistically significant (P＞0.05). The results of KEGG pathway functional metabolic differences showed that the metabolic pathways of D-arginine and D-ornithine metabolism, biofilm formation-Escherichia coli, carolactam degradation and arginine biosynthesis were more abundant in the T2DM group than in the normal control group, while metabolic pathways such as tyrosine metabolism, selenocompound metabolism and pyruvate metabolism showed the opposite trend.

There was no significant difference in the content of cariogenic microorganisms between type 2 diabetic patients and normal control group. The differential metabolic pathways of the functional genes indicated that an increase in the arginine metabolic pathway was beneficial to the maintenance of acid-base balance in the oral microecological environment.