Objective: To investigate the etiology, diagnosis and treatment principles of inherited permanent tooth embryo necrosis caused by alveolar bone resorption due to severe periapical periodontitis of deciduous teeth, in order to provide a reference for clinical diagnosis and treatment Methods: The clinical data and related literature of a rare case of permanent tooth embryo necrosis were analyzed retrospectively. Results : This case was a 5-year-old girl. Physical examination and X-ray examination revealed chronic periapical inflammation in 75. X-ray showed that the periodontal bone of tooth 75 was extensively destroyed; additionally, the permanent tooth germ of tooth 35 was incomplete and the development was delayed compared to that of tooth 45 because of severe periapical periodontitis in the primary teeth. The initial diagnosis was that-- the embryo of tooth 35 stopped developing due to inflammation and was necrotic after tooth 75 was extracted. The postoperative pathological examination report showed that most bone around the embryos of tooth 35 was sequestrated. Through literature review and analysis, it was found that the degree of periapical lesions in the primary teeth and the developmental stage of the tooth embryo have a great impact on the formation of permanent tooth embryos. Conservative methods such as root canal therapy are usually adopted as treatment. Permanent tooth embryo necrosis caused by periapical periodontitis of deciduous teeth is rare in the clinic, so it is necessary to judge the degree of inflammatory infiltration and of tooth embryo damage as soon as possible according to the clinical symptoms and imaging manifestations; and to make a correct treatment plan. Conclusion There are no objective and clear diagnostic and treatment criteria for the clinical diagnosis of the pathological state of permanent tooth embryo, thus, methods such as etiology elimination and follow-up observation are usually adopted for abnormal permanent tooth embryo development. Future research should focus on prevention and finding addtional effective methods for diagnosis and treatment.

Recently, the dental application of nano materials has made progress in clinical treatment, such as implant surface modification as well as antibacterial, and controlled release. However, the active physical and chemical properties of nanomaterials may pose a potential safety risk in humans. Dental nanomaterials used for oral application can be released into the blood through a variety of mechanisms, and they can penetrate the blood-brain barrier and enter the central nervous system. Moreover, nanomaterials can also directly affect the central nervous system through the olfactory nerve and via sensory nerve terminal transport, causing organic and functional damage to central nerves, and even causing neurotoxicity during embryo development. Nanomaterials can interact with biomolecules such as cells, genes, and proteins in the body, and can produce neurotoxicity through the mechanisms of inducing oxidative stress, inflammatory responses, cell autophagy, apoptosis, genotoxicity, etc. Factors affecting the toxicity of nanomaterials include particle size, concentration, and solubility. Dental nanomaterials and their pathways into the central nervous system, as well as the mechanisms that may cause neurotoxicity, will be discussed on this review.

Bone tissue engineering, as an emerging method for the treatment of jaw defects caused by oral and maxillofacial trauma, inflammation, tumors and other diseases, has been a research hotspot due to its advantages of wide sources of materials, low risk of immune rejection and personalized treatment. However, due to functional activities such as chewing and expression in the oral and maxillofacial regions, the mechanical strength of scaffolds is highly required. A single component of scaffolds can not fully meet the requirements of oral and maxillofacial bone defect repair. In this paper, the methods of strengthening the mechanical strength of jaw bone tissue engineering scaffolds are summarized by summarizing the research on strengthening the mechanical strength of scaffolds in recent years. A review of the literature showed that, composite modification, crosslinking, coating, bionic scaffolding and other new processing methods have been used to enhance the mechanical strength of scaffolds. Among these studies, research on compound modification occurred the earliest. Although this process is simple, other substances have been introduced to increase the number of degradation products, and the compounding ratio needs to be adjusted. The crosslinking method has the risk of cytotoxicity due to the use of crosslinking agents; the coating method does not change the original structure and only changes the surface modification; however, it can be better utilized if the problem of stress concentration between interfaces is solved. Biomimetic scaffolds and microregulatory scaffolds are emerging technologies in recent years that can improve the internal molecular arrangement of materials, thus enhancing mechanical strength. Therefore, on the basis of perfecting the traditional method, future research will focus on new nanoscale materials, bionic scaffolds and new methods for the precise control of scaffold microstructure.

Enterococcus faecalis has been confirmed to be closely related to dental pulp and periapical disease in recent years. Enterococcus faecalis is one of the important bacteria causing persistent or secondary root canal infection and root canal treatment failure. Traditional root canal disinfection drugs such as sodium hypochlorite, chlorhexidine and calcium hydroxide can not completely remove Enterococcus faecalis in the root canal because of the concentration limitation of the drug and the complexity of the root canal system. Therefore, how to effectively resist the Enterococcus faecalis infection in the root canal has become one of the important research directions in the treatment of periodontal pulp periapical disease. In recent years, some new antimicrobial agents and disinfection methods have emerged due to the drug resistance and pathogenicity of Enterococcus faecalis, such as laser, photodynamic, ultrasonic irrigation and ozone therapy. Their combination with traditional root canal irrigation drugs can significantly enhance the ability of traditional drugs to remove Enterococcus faecalis in the root canal. In addition, the emergence of new disinfection methods such as chlorine dioxide, nano-magnesia, superoxidized water and N-acetylcysteine have been shown to have a unique killing effect on Enterococcus faecalis in root canals. At present, most of the new disinfection methods described above are in the in vitro experimental stage, and their stimulation and damage to normal tissue still lack relevant clinical data support; thus, these outcomes need to be further studied.

In recent decades, although great progress has been made on the diagnosis and treatment of oral squamous cell carcinoma (OSCC), its 5-year survival rate has not been significantly improved. The basic reason is the unclear pathogenesis, lack of effective molecular markers for assessing invasion, metastasis, and recurrence as well as therapeutic targets. The present view is that genetic and epigenetic abnormalities are related to the occurrence and development of OSCC. Epigenetic inheritance is a biological behavior that can be regulated and reversed, and it plays an important role in the occurrence and development of malignant tumors. First, this review will describe the role of epigenetic modifications in the development of OSCC in combination with our research and the latest research progress of epigenetics, including DNA methylation, RNA methylation, short noncoding RNAs (miRNAs, etc.), long noncoding RNAs, circular RNAs, histone modifications (acetylation and methylation), chromatin remodeling and genomic imprinting. Then, we will analyze the value of epigenetic studies in the prevention, diagnosis, and targeted therapy of OSCC.

Eye tracker is an instrument that can record the characteristics of eye movement when people process visual information. This instrument is important for basic psychological research. In the study of dental aesthetics, an eye tracker reflects the observer′s objective eye movement pattern and reveals the underlying aesthetic psychology. This paper summarizes the major research methods of dental aesthetics while focusing on eye-tracking studies in oral aesthetics. Eye tracking studies show that different population has different eye movement patterns when observing the same faces, while the same population can have different eye movement patterns when observing the faces of dental patients and normal people. This finding reveals that the personal characteristics and experience, the social environment and the featured facial structure of the observed individuals can influence eye movement patterns. This study also shows the factors that cause the aesthetic differences among different individuals and groups, as well as the psychological mechanisms.

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.

Objective: To analyze the impact of the activation mode on the results of space closure in the mandibular arch using a double keyhole loop (DKHL) with a typodont model and reverse engineering technique to provide guidance for clinical treatment. Methods: Nine normal mandibular typodont models after leveling were randomly divided into 3 groups, which then underwent three types of DKHL activation for space closure. Each model was assessed at the initial stage and after the warm water bath, and the images were superimposed to measure the displacement of special crown and root mark points. All statistical analysis of the data was performed using SPSS 19.0 Results: After equal activation times, the root retraction of anterior teeth and the crown forward position of posterior teeth in groups activated at the distal loop (conditions 2 and 3) were much greater than those in the group activated horizontally (condition 1). Activation between mesial and distal loops (condition 3) induced significant anterior tooth intrusion, together with elongation and buccal inclination of posterior teeth. The displacement of mark points among the three conditions showed a statistically significant difference. Conclusion The movement of mandibular anterior and posterior teeth could be flexibly controlled through different DKHL activation modes, which should be chosen carefully according to individual conditions.

Objective : To investigate the effect of the clinical application of molar uprighting in the treatment of impacted mandibular second molars. Methods: A total of 16 cases of impacted mandibular second molars were chosen, and the impacted molars were treated with straight wire appliances and molar uprighting. Before and after treatment, the vertical angle of the molar, the height of the distal buccal tip, the height of the distal buccal tip of the anchorage molar, the depth of the periodontal pocket and the height of the alveolar bone were measured. Moreover, the treatment cycles of the third molar extraction group, the premolar group and the nonextraction group were compared. Results : All impacted molars responded well to treatment. The vertical time of impacted molars was (1.34 ± 0.45) months, (2.20 ± 0.57) months, and (2.30 ± 0.45) months in the third molar extraction group, the premolar extraction group and the nonextraction group, respectively. The treatment time of the third molar extraction group was shorter than that of the other two groups, and the difference was statistically significant (P < 0.05). After treatment, the inclination of impacted second molars increased by (25.94 ± 8.85)°, the elongated distal buccal tip was depressed by (1.00 ± 1.48) mm, the depth of the proximal and middle periodontal pocket of impacted molars decreased by (1.21 ± 1.03) mm, and the height of the alveolar bone of the proximal and middle adjacent surfaces of impacted second molars increased by (4.57 ± 1.45) mm; these differences were statistically significant (P < 0.05). There was no significant difference in the height of the distal buccal tip of the first molar before and after treatment (P > 0.05). Conclusion Molar uprighting is an efficient, reliable, and convenient method that can shorten the treatment period. Extraction of crowded third molars is beneficial for the vertical and periodontal health of impacted second molars.

Objective: Through a pain study of buccal gingival mucosa sensitivity of the mandible, the corresponding sensitive area of pain was determined, which provided the basis for reducing the pain and discomfort of oral diagnosis and treatment. Methods: 400 patients with mandibular tooth extraction in the outpatient department of stomatology were selected. During tooth extraction, articaine epinephrine injection was used for infiltration anesthesia. The injection needle size was 0.3 mm × 21 mm, and the injection site was about 5 mm away from the buccal gingival margin. The pain degree of the patients was recorded. The data were statistically analyzed using the modified International pain classification method. Results : Among the 400 patients who underwent mandible extraction, 75% (300 patients) graded their pain from painless to moderate, and 25% (100 patients) reported moderate to severe and severe pain. Of those in the moderate to severe and severe groups, 50% and 42% reported pain in the central and lateral incisors, respectively, and 38% were in the canine group. When comparing the moderate to severe and the severe groups, 16% and 10% were in the bicuspid group, 16% and 12% and 16% were in the molar group, respectively . There were significant differences in the pain sensitivity of different teeth positions (χ2=54.203, P < 0.001). The proportion of moderate to severe and severe pain in the anterior teeth group was higher than it was in the posterior teeth group (χ2=55.555, P < 0.001). There were significant differences in the pain sensitivity of different ages (χ2=96.501, P=0.000), and there was a positive correlation between pain and age (r=0.465, P < 0.001). The proportion of women with at least a moderate degree of pain was higher than that of men (χ2=12.298, P=0.031). Conclusion The sensitivity of the buccal gingival mucosa to pain is different in different positions of the mandible. The sensitivity of the anterior gingiva is higher than that of the posterior gingiva. Age is positively correlated with the degree of pain. Further, compared with men, women are more sensitive to pain.