Chinese Journal of Dental Research, 04/2024

Tooth eruption is the process whereby the developing tooth moves to its functional position in the occlusal plane and it occurs concomitantly with formation of the tooth root, which is a critical component of the tooth anchored to surrounding alveolar bone through the periodontal ligament. Post-eruptive tooth movement ensues that once occlusion is achieved, the teeth maintain their alignment within the alveolar bone to facilitate proper bite function through periodontium remodelling. Tooth overeruption presents a clinically significant issue, yet the precise mechanisms by which alterations in occlusal forces are translated into periodontal remodelling remain largely unexplored. In this review, the present authors aim to outline the latest progress on the potential mechanisms governing tooth root formation and homeostasis during tooth eruptive and post-eruptive movement. Based on recent findings using various mouse models, we provide an overview of the collaborative intercellular interaction during root formation, including Hertwig’s epithelial root sheath, dental papilla and dental follicle. Moreover, we summarise the potential mechanism underlying post-eruptive movement mainly in view of the responses of periodontal tissues to vertical mechanical stimuli. In sum, the precise regulatory mechanisms during tooth eruption throughout life will shed light on disease treatment of tooth eruption defects and overeruption. Keywords: homeostasis, mechanotransduction, periodontium, tooth eruption, tooth root

Oral diseases not only greatly impact patients’ daily lives, but also pose a severe threat to their overall health. Due to the constant exposure of saliva to oral diseases, the former plays a vital role in their diagnosis and monitoring. Exosomes, nanosized bilayer lipid encapsulated nanovesicles, are widely present in saliva and can be released by any type of cell. Exosomes inherit features from their mother cells in both physiological and pathological conditions. The molecular characteristics and expression levels of exosomes depend on their cellular origin, and they can directly reflect the physiological state of the body and cells. This makes salivary exosomes a promising source for early detection and monitoring of oral diseases. As a result, researchers have been exploring the potential use of exosomes as biomarkers for diagnosing and predicting various oral diseases. This review provides an overview of the composition, separation and function of salivary exosomes. It also discusses their potential as diagnostic and prognostic markers for several oral diseases, including periodontitis, primary Sjögren’s syndrome, oral mucosal diseases, hand-foot-mouth disease and oral squamous cell carcinoma. By studying salivary exosomes, researchers hope to improve the early detection and monitoring of oral diseases, leading to better outcomes for patients. Keywords: diagnosis, liquid biopsy, oral disease, prediction, salivary exosomes

Objective: To assess the role of microtubule acetylation in the transportation of amorphous calcium phosphate (ACP)-containing vesicles that mediate the osteogenic differentiation process of rat bone mesenchymal stem cells (BMSCs). Methods: Rat BMSCs were cultured and transfected with sirtuin 2 (SIRT2) overexpression plasmids for an in vitro model. The microtubule acetylation-related protein levels were detected by western blots. The microtubule acetylation and the secretion rate of extracellular ACPcontaining vesicles were observed with immunofluorescence and live cell fluorescence imaging. The secretion of ACP was observed by transmission electron microscopy. The mineralised nodule formation was stained with Alizarin Red S staining and observed by microscopy. Results: Microtubule acetylation was increased during osteogenic differentiation of BMSCs, and microtubule transport efficiency was enhanced. Mechanically, microtubule acetylation is the key reason for the increased transportation rate of ACP-containing vesicles and enhanced osteogenic differentiation, as both were blocked after SIRT2-mediated microtubule acetylation inhibition. Conclusion: Microtubule acetylation mainly promotes the transportation and secretion of ACP vesicles, and ultimately promotes the osteogenic differentiation process. Keywords: biomineralization, intracellular transport, microtubule acetylation, osteogenic differentiation

Objective: To establish precise positional references for orthognathic surgery by examining the relative positioning of the infraorbital foramen (IOF) in relation to the anterior nasal spine (ANS) and the mental foramen (MF) in relation to the pogonion (Pog). Methods: A cohort of 115 patients with CBCT images was randomly selected for analysis. Distances and positional relationships between the IOF and ANS, as well as the MF and Pog, were measured using 3D reconstruction images. Results: On average, the ANS was situated 21.40 mm below the IOF, with a horizontal distance of 26.42 mm. The horizontal and vertical distances between the MF and Pog were 23.57 and 9.71 mm, respectively. Scatter plots centred on the ANS indicated that 83% (191/230) of the IOF were distributed in a 30- to 45-degree fan shape, the radius of which ranged from 30 to 40 mm. Similarly, 98% (226/230) of the MF occupied a 45-degree fan shape within a 20 to 30 mm radius in the bilateral superior quadrant centred on the Pog. Conclusion: During maxillary osteotomy, there is a potential risk of damaging the infraorbital neurovascular bundle located 21.40 mm above the ANS. To mitigate the risk of IOF injury, caution is advised, particularly when retracting the flap below a 30-degree fan shape within a 30 to 40 mm radius centred on the ANS and a 45-degree fan shape within a 20 to 30 mm radius centred on the Pog. Special attention is warranted during flap elevation in this specified area. Keywords: CBCT, infraorbital foramen, mental foramen, orthognathic surgery

Objective: To compare accuracy, duration of drilling and accumulation of bone chips between low-speed drilling and conventional drilling in freehand implant placement surgery. Methods: The implant surgery procedures were performed using identical drill bits on pig ribs in the low-speed drilling group and the conventional drilling group. CBCT images of the preoperative implant design and postoperative implant positions were compared by using the space vector formula to calculate the angular deviation of the implants between the two groups, as well as the horizontal and vertical deviations of the implant necks and roots. The duration of the procedure was recorded, and the bone chips were collected and compared using a screening method and scanning electron microscopy. Results: There were no significant differences in any of the four primary outcome variables relating to accuracy between the low-speed and conventional drilling methods. However, the results revealed that the length of the procedure differed significantly between the two groups and more large bone fragments could be collected when performing low-speed drilling. Conclusion: Low-speed drilling does not affect the accuracy of implant nest preparation, but it can harvest large bone chips which may have better osteogenic activity. Low-speed drilling could be an alternative to conventional drilling. Keywords: bone graft, dental implant, low-speed drilling, surgical procedure

Objective: To investigate the prevalence and characteristics of taurodontism in patients with cleft lip and palate (CLP) and clarify the relationship between CLP and the frequency and severity of taurodontism. Methods: CBCT scans of 30 patients with bilateral CLP (BCLP), 70 with unilateral CLP (UCLP) and 70 healthy individuals were taken for investigation. In each group, the first and second molars were assessed for the presence of taurodontism. In taurodontic teeth, the severity of taurodontism was measured and classified based on the taurodontic index (TI). The frequency and severity of taurodontism were compared between the three groups. Results: Taurodontism was significantly higher in patients with CLP (P < 0.001), and its prevalence was significantly higher in patients with BCLP than those with UCLP (P = 0.003) and the control group (P < 0.001). There was no difference among the three groups regarding the severity of taurodontism. Additionally, the frequency of taurodontism in the second molars was significantly higher than that in the first molars in the control group (P = 0.019). Conclusion: Based on this investigation, clinicians should be aware of the possible complications that may occur when performing dental procedures on patients with BCLP and UCLP due to the higher incidence of taurodontism in these patients. Keywords: CBCT, cleft lip and palate, taurodontism

Impaction of mandibular second molars should be resolved as soon as possible once diagnosed, since it may lead to many functional, periodontal, hygienic and endodontic problems. Treatment options for impacted second molars include orthodontic-assisted eruption following surgical exposure, surgical uprighting and, in some cases, surgical extraction with possible subsequent implant placement if the tooth is deemed non-restorable or the patient prefers an implant restoration. This case report describes the orthodontic treatment of a 21-year-old woman with maxillomandibular protrusion and impacted bilateral mandibular second molars. The Physiologic Anchorage Spee-wire System (PASS) was adopted due to its innovative strategy of physiological anchorage control and unique design involving the multilevel low-friction (MLF) bracket and cross buccal tube (XBT). After 22 months of treatment, a well-aligned dentition, a normal functional occlusion and a harmonious facial profile were obtained, and impaction of the bilateral mandibular second molars was finally resolved. This case report demonstrates a simple and efficient solution to dental impaction. The PASS technique is superior to other preadjusted straight wire appliances in the treatment of maxillomandibular protrusion cases without auxiliary anchorage devices, and the mandibular buccal tube involved in the PASS technique can assist in uprighting the impacted mandibular second molars with NiTi round wire and minimising oral discomfort for the patient. Keywords: anchorage, maxillomandibular protrusion, molar impaction, physiological anchorage, Spee-wire system