Chinese Journal of Dental Research, 01/2023

In recent years, as the number of adults seeking orthodontic treatment has increased, so too has the number of periodontal tissue problems, particularly regarding the impact on periodontal tissue of receiving orthodontic treatment. Orthodontic treatment improves the occlusion and appearance of teeth by moving the teeth appropriately. These movements have a significant impact on the interactions between the teeth and periodontal tissues. Orthodontic treatment can also recover tooth alignment for patients with tooth displacement caused by periodontitis; however, orthodontic treatment also often has adverse effects on periodontal soft tissue, such as gingivitis, gingival enlargement and gingival recession. The purpose of this review is to summarise the current evidence and solid knowledge of periodontal soft tissue problems in orthodontic treatment and outline some prevention strategies. Keywords: orthodontic treatment, periodontal tissue health, principle of treatment

Objective: To explore whether hydrogen sulphide (H2S) could protect human periodontal ligament stem cells (PDLSCs) from senescence and the possible underlying mechanisms. Methods: Cell cycle assay and Ki-67 assay were used to measure proliferation of PDLSCs. Real-time polymerase chain reaction (PCR) was used to measure cellular senescence–related p16 and p21. Calcium influx was detected by measurement of Ca2+ imaging. In addition, we analysed the possible mechanisms underlying H2S acting on PDLSCs by microarray. Results: The cell proliferation rate of aging PDLSCs decreased significantly. The expression of cellular senescence–related p16 and p21 significantly increased in aging PDLSCs. H2S donor (GYY4137) treatment increased the proliferation rate of senescence PDLSCs. Furthermore, the donor of H2S treatment effectively prevented cell cycle arrest of PDLSCs during the aging process and inhibited the expression of cellular senescence–related markers. Mechanically, H2S donor treatment could activate the calcium influx in PDLSCs. Moreover, pretreatment with TRPV4 inhibitors significantly attenuated the calcium influx induced by H2S donor treatment in PDLSCs. It also alleviated the protective effect of H2S on the senescence of PDLSCs. Conclusion: H2S alleviated the senescence of human PDLSCs by TRPV4 channel mediated calcium flux. These results provide a potential strategy to deal with cell aging and may facilitate cell therapy for oral diseases. Keywords: calcium flux, cell senescence, hydrogen sulphide, periodontal ligament stem cells, transient receptor potential cation channel subfamily V member 4

Objective: To evaluate the extension of canalis sinuosus (CS) into the alveolar crest for surgical reference in the anterior maxilla. Methods: In this cross-sectional study, 485 CBCT images were evaluated in three orthogonal planes (axial, coronal and sagittal). The type of extension of CS into the alveolar ridge in the anterior maxilla was evaluated. The alveolar ridge was divided into four equal parts in a vertical and horizontal direction. In a vertical direction from apical to incisal and in a horizontal direction from labial to palatal, the four parts were designated as types 0, I, II and III, respectively. The extension of CS into the alveolar ridge was then traced. Results: CS was present in 380 subjects (78.35%), and the extension type was unilateral in 217 of them (57.11%) and bilateral in 163 of them (42.89%). There was no significant relationship between incidence of CS and sex. Regarding the distribution of vertical and horizontal types, type II (the third quadrant of the ridge from apical to incisal and from labial to palatal, respectively) was significantly more prevalent than other types. Conclusion: The most common location of CS into the alveolar ridge in both horizontal and vertical directions was type II (which is not close to the cortex). Awareness about the presence and possible locations of CS helps to reduce the risk of unjustifiable postoperative complications. Keywords: alveolar process, CBCT, incidence, maxilla

Objective: To analyse the effects of premolar extraction on the upper airway in adult and adolescent orthodontic patients using CBCT. Methods: The Embase, Web of Science, Cochrane Library and Medline (via PubMed) databases were searched with no language restrictions. Longitudinal studies in which CBCT was applied to assess the effects of tooth extraction on the upper airway were included in the analysis. Two authors performed the study selection, methodological quality assessment, data extraction and data synthesis independently. Results: A total of 12 studies were included, six of which were eligible for quantitative synthesis. In the adult group, the nasopharynx and oropharynx volume showed no significant change, and the minimum cross-sectional area of the upper airway demonstrated a non-significant decrease compared to the non-extraction group. In the adolescent group, the nasopharynx volume, oropharynx volume and minimum cross-sectional area of the upper airway increased in a non-significant manner. Conclusion: The currently available evidence indicates that tooth extraction does not increase the risk of airway collapse in adult and adolescent patients. The present findings should be interpreted with caution and evaluated in further high-quality studies. Keywords: airway, extraction, meta-analysis, orthodontic

Objective: To investigate the efficacy of different obturation techniques on sealer penetration in teeth with internal root resorption using confocal laser microscopy. Methods: An artificial internal resorption cavity (3 mm deep and 1.2 mm in diameter) was formed in the round-shaped root canals of 45 single-rooted teeth at a distance of 7 mm from the apex, then roots were instrumented (size 40/.06). The samples were divided into three groups (n = 15) according to the obturation technique: lateral compaction (LC), warm vertical compaction (WVC) and carrier-based (CB). Results: In the resorption regions, the sealer penetration depth in the CB and LC groups was significantly higher than that in the WVC group (P < 0.05). Conclusion: Within the limitations of this study, the penetration depth of the sealer in the resorption region was higher in the CB and LC groups as compared to that in the WVC group. Keywords: carrier‐based technique, internal root resorption, sealer penetration, warm vertical compaction

Intentional replantation involves a combination of periodontics, endodontics, prosthodontics and oral surgery. Crown-root fracture management is still complicated nowadays. A fracture line extending longitudinally to the subgingival area and intruding bioogical width could affect infection control, gingival health and crown restoration. In the present study, we present two cases. Case 1 involved a 23-year-old man who presented at our hospital with crown-root fracture of the maxillary left central incisor. A radiographic image of the tooth revealed a fracture line under the alveolar crest. The fractured tooth was treated with intentional replantation with 180-degree rotation, root canal treatment and veneer restoration. The patient was followed up for 60 months. The replanted tooth functioned well, and no symptoms of resorption or ankylosis were observed by radiographic examination. Case 2 involved a 20-year-old woman who was referred to our hospital for crown-root fracture of her maxillary teeth. A radiographic examination revealed complicated crown-root fracture of the maxillary right lateral incisor and both maxillary central incisors. The central incisors were treated with intentional replantation with 180-degree rotation. At the 48-month follow-up, the fractured teeth were found to have regained normal function based on clinical and radiographic examination. Limited case reports are available on a long-term follow-up of intentional replantation with 180-degree rotation. These two cases, particularly case 2, presented optimal healing after 4 years with unideal crown–root ratios. This case report suggests that this old method of preserving teeth with crown-root fractures can be used as a last resort to save teeth owing to its timesaving and microinvasive procedure. Keywords: 180-degree rotation, crown-root fracture, intentional replantation