Chinese Journal of Dental Research, 03/2021

Tooth eruption is closely linked to the normal development of dentition and proper establishment of occlusion. Disturbances in tooth eruption may affect oral physiological functions, facial contour and aesthetics; it is therefore important to understand the eruption process. This process is a complex biological event involving dynamic changes at the tissue and cellular levels. It is guided by anatomical structures as well as biological and molecular factors that result in the movement of the tooth to its final functional position in the oral cavity. Evidence increasingly suggests that stem cells contribute to tooth development and eruption. Multiple stem cell populations have been discovered in teeth and in their supporting tissues, such as dental follicle precursor cells, orofacial bone–/bone marrow–derived mesenchymal stem cells, periodontal ligament stem cells, stem cells from the apical papilla and dental pulp stem cells. These stem cells exhibit distinct differentiation capacities and are closely linked to alveolar bone remodelling, periodontium development and root formation during the eruption process. The present review summarises the current knowledge of the characteristics and functions of orofacial stem cells in tooth eruption, with a particular focus on recent discoveries concerning their lineage allocation and regulatory mechanisms. Keywords: alveolar bone, dental follicle, dental stem cells, motive force, osteoblasts, osteoclasts

Objective: To investigate the effects of ipriflavone (IPF), a synthetic isoflavone plant oestrogen with a structure similar to that of oestradiol, on the osteogenic differentiation of bone mesenchymal stem cells (BMSCs). Methods: BMSCs were derived from ovariectomised rats (rBMSCs-OVX) and then induced with or without IPF. Cell cytotoxicity, mineralisation in vitro and osteoblast-specific gene expression of BMSCs were studied. Results: IPF at a concentration of 10-8, 10-7 and 10-6 mol/l exhibited no cytotoxic effect on the proliferation of BMSCs but increased alkaline phosphatase activity and osteoblast-specific gene expression. Conclusion: IPF enhances osteogenic differentiation of rBMSCs-OVX partly in vitro, thus its use offers a potential strategy for the treatment of osteoporosis. Keywords: ipriflavone, mesenchymal stem cells, osteogenic differentiation, osteoporosis

Objective: To evaluate adhesives’ enamel bonding performance utilising the traditional microtensile bond strength test (µTBST) and a new double-sided microtensile bond strength test (DµTBST) to assess the suitability of the latter. Methods: A ‘tug-of-war’ direct encounter design was employed to compare the enamel bond strengths of two universal adhesives and their different application modes simultaneously under the same tensile load applied to double-sided bonded specimens. Clearfil Universal Bond (CU; Kuraray, Kurashiki, Japan) and Scotchbond Universal Adhesive (SB; 3M ESPE, St Paul, MN, USA) were applied in self-etch (S) and etch-and-rinse (E) mode on 110 human molar samples to perform two experiments. Experiment 1 compared the enamel bond strengths of the combinations of adhesive application modes utilising µTBST. The data were analysed using a Welch analysis of variance (ANOVA), followed by a Games-Howell test. Experiment 2 employed DµTBST to determine the suitability of the new double-sided bonded assembly and ascertain which of the adhesive application mode combinations was superior. The data were analysed using a Kaplan-Meier survival analysis, followed by pairwise comparisons with a Mantel-Cox log-rank test. The level of significance was set at P ˂ 0.05. Results: The µTBST results did not show significant differences for CUE vs CUS, SBE vs SBS, CUS vs SBS and CUS vs SBE (P ˃ 0.05); however, from DµTBST, the survival distributions for the interventions were statistically significantly different (χ2(3) = 145.130, P ˂ 0.0005), indicating the superiority of universal adhesive CU over SB and application mode E over S with certainty. Conclusion: DµTBST was able to add more discerning outcomes to the µTBST results, indicating that the new technique could become a valuable adjunct to the conventional method. Keywords: adhesives, dental bonding, dental enamel, microtensile bond strength test, new double-sided microtensile bond strength test

Objective: To analyse the subgingival microbiota of Stage I/II periodontitis, gingivitis with different degrees of severity, and periodontal health in subjects in a Chinese young adult population. Methods: Subgingival plaque samples were collected from 15 Stage I/II periodontitis patients, 38 gingivitis patients and 15 periodontally healthy individuals, all aged from 18 to 21 years. Gingivitis patients were divided into two subgroups according to the Bleeding Index (BI) of their sampled teeth: gingivitis with above median BI (G-HBI) and below median BI (G-LBI). The subgingival plaque samples were collected from teeth 16, 26, 36, 46, 11 and 31 according to FDI notation. The V3-V4 region of the 16S rRNA gene of all the samples was sequenced and analysed. Results: The Stage I/II periodontitis, gingivitis and periodontal health groups showed distinct subgingival microbiota profiles. When the gingivitis patients were stratified into two subgroups, the community structure of G-HBI showed no significant difference from early-stage periodontitis, but differed from G-LBI and the healthy group. Most periodontitis-related taxa were most abundant in Stage I/II periodontitis, followed by G-HBI, G-LBI and the periodontally healthy group. Porphyromonas gingivalis, Filifactor alocis, Tannerella forsythia, Saccharibacteria TM7 G-5 356, Lachnospiraceae G-8 500, Peptostreptococcaceae spp. and Syntrophomonadaceae VIIIG-1 435 were associated with Stage I/II periodontitis. Porphyromonas 275, Leptotrichia 417 and Saccharibacteria TM7 G-2 350 were associated with gingivitis. Porphyromonas gingivalis was significantly more abundant in G-HBI than in G-LBI. Conclusion: Within the limitations of this preliminary study, gingivitis and early-stage periodontitis were associated with an increased degree of dysbiosis in the subgingival microbiota in a Chinese young adult population. Keywords: gingivitis, microbiota, periodontitis, sequencing, young adults

Objective: To assess the prevalence, location, diameter, course and anastomosis of the lateral lingual foramina (LLF) and canals (LLCs) in a northern Chinese population using CBCT. Methods: CBCT images of 506 patients (181 male and 325 female, mean age 21.03 ± 8.11 years) were collected. The prevalence, location, diameter, length, angle and anastomosis of the LLF and LLCs were assessed. The measurement variables were analysed by sex and age. Statistical analysis was performed using SPSS (v. 25, IBM, Armonk, NY, USA). Results: A total of 461 LLF were detected in 307 (60.7%) subjects, 175 (57.0%) of whom had unilateral LLF and 132 (43.0%) of whom had bilateral LLF, with each lateral having one to four LLF. The majority of LLF (375/461, 81.3%) were located below the premolars, particularly the first premolar. The mean diameter of the LLF was 0.58 ± 0.20 mm. The mean vertical distance from the LLF to the inferior border and the alveolar crest was 6.68 ± 1.43 mm and 23.65 ± 2.89 mm, respectively. In total, 197 LLCs were visible in the cancellous bone and evaluated. The mean length of LLCs was 6.26 ± 1.29 mm, and the mean angle of LLCs was 140.64° ± 17.29°. The overwhelming majority (93.4%) of LLCs communicated with the mandibular incisive canal and the rest connected with the mandibular canal. Conclusion: The prevalence of LLCs was high in the northern Chinese population. The presence of LLCs is a significant predictor of communication with the mandibular incisive canal. Keywords: CBCT, lateral lingual canals, lateral lingual foramina, mandible

Objective: To evaluate the clinical performance of direct composite restorations using the modified stamp technique (MST) in vivo. Methods: A total of 30 posterior teeth with undermining caries were randomly divided into two groups and then restored using the MST and conventional technique (CT), respectively. 3D images of the occlusal surface were obtained using an intraoral scanner (CEREC Omnicam, Dentsply Sirona, Charlotte, NC, USA) before and after treatment and the differences between these two 3D images were analysed with reverse engineering software. Statistical analysis was performed using a one-way analysis of variance (ANOVA) combined with a least significant difference (LSD) post hoc test using SPSS 20.0 software (IBM, Armonk, NY, USA). Results: The statistical analysis revealed that the average root mean square (RMS) values of best fit alignment errors were significantly different between groups (P < 0.01). The average RMS values in the MST and CT groups were 0.0738 ± 0.0279 and 0.1638 ± 0.0682, respectively. The LSD post hoc test revealed that the value was significant smaller in the MST group than in the CT group. Conclusion: The MST was effective in direct composite restoration. The morphological consistency of the occlusal surface using the MST was better than with the CT. Keywords: caries, conventional technique, direct composite restorations, modified stamp technique

Objective: To investigate various factors affecting the clinical outcome of nonsurgical periodontal treatment and evaluate the treatment effects of adjunctive amoxicillin and metronidazole (AMX + MET) in patients with generalised aggressive periodontitis (GAgP). Methods: Forty-two patients with GAgP were recruited and randomly assigned to three groups: scaling and root planing (SRP) only, AMX + MET after SRP, and AMX + MET during SRP. The patients were assessed every 2 months post-therapy. Periodontal clinical and subgingival microbiological parameters were analysed at baseline and 6 months post-therapy. The impacts of different covariates on pocket probing depth (PD) reduction were evaluated. Results: A multilevel analysis revealed that 58% of the variability in PD reduction was attributed to site-level parameters, 27.3% to patient-level parameters and 18.7% to tooth-level parameters. Greater PD reduction can be expected at initially deeper PD sites and sites with intrabony defects, and in patients with adjunctive use of AMX + MET. Persistent Tannerella forsythia infection and tooth mobility after treatment were negatively associated with PD reduction. Conclusion: The clinical outcomes of nonsurgical periodontal treatment were mainly influenced by site-level parameters, and adjunctive use of AMX + MET can lead to better clinical results in patients with GAgP in a short time. Keywords: aggressive periodontitis, drug therapy, multilevel analysis, periodontal debridement, root planing

Gemination and fusion are developmental conditions affecting the shape of teeth in both primary and permanent dentition. A 12-year-old girl presented for clinical assessment and the examination revealed an unusually shaped mandibular right second molar with irreversible pulpitis. Correlation of the intraoral and radiological appearance of this tooth suggested a diagnosis of either double gemination or fusion. The favourable position of the developing third molar supported early extraction of the abnormal second molar. The present report documents the clinical and radiological presentation of a mandibular second molar with an unusual developmental alteration in shape. Well-timed extraction therapy and good communication may reduce the need for unnecessary, complex treatment. Keywords: dental anomalies, fusion, gemination, oral surgery, permanent molar