Orthodontics at a Pivotal Point of Transformation

Effect of orthodontic treatment on traumatized teeth treated by regenerative endodontic procedure

OBJECTIVES

To evaluate the effect of orthodontic movement on traumatized teeth treated with the regenerative endodontic procedure (REP).

MATERIALS AND METHODS

The increase of the radiographic root area (RRA) of each REP tooth was measured at each follow-up visit after the end of orthodontic treatment. The study included two experimental groups of patients aged 7-17 with REP-treated teeth. The Ortho REP group consisted of eight patients who underwent orthodontic treatment, whereas the second group (no Ortho REP group) included seven patients who did not receive orthodontic treatment. The control groups comprised the same patients and their homologous or adjacent healthy teeth that did not undergo REP treatment.

RESULTS

Orthodontic treatment did not negatively affect root development of immature, traumatized REP-treated teeth during the treatment or retention periods. Additionally, the increase in RRA in regenerated teeth was age-dependent, with the greatest RRA increase in young patients.

CONCLUSIONS

Close collaborative endodontic-orthodontic follow-up is recommended to ensure favorable results. The findings suggest that REP-treated teeth may undergo orthodontic treatment without adverse effects.

The role of biophysical cues and their modulated exosomes in dental diseases: from mechanism to therapy

Dental diseases such as caries and periodontitis have been common public health problems. Dental disease treatment can be achieved through stem cell-based dental regeneration. Biophysical cues determine the fate of stem cells and govern the success of dental regeneration. Some studies have manifested exosomes derived from stem cells could not only inherit biophysical signals in microenvironment but also evade some issues in the treatment with stem cells. Nowadays, biophysical cue-regulated exosomes become another promising therapy in dental regenerative medicine. However, methods to improve the efficacy of exosome therapy and the underlying mechanisms are still unresolved. In this review, the association between biophysical cues and dental diseases was summarized. We retrospected the role of exosomes regulated by biophysical cues in curing dental diseases and promoting dental regeneration. Our research also delved into the mechanisms by which biophysical cues control the biogenesis, release, and uptake of exosomes, as well as potential methods to enhance the effectiveness of exosomes. The aim of this review was to underscore the important place biophysical cue-regulated exosomes occupy in the realm of dentistry, and to explore novel targets for dental diseases.

Predictability of rotational tooth movement with orthodontic aligners comparing software-based and achieved data: A systematic review and meta-analysis of observational studies

OBJECTIVE

To evaluate all available evidence on the prediction of rotational tooth movements with aligners.

DATA SOURCES

Seven databases of published and unpublished literature were searched up to 4 August 2020 for eligible studies.

DATA SELECTION

Studies were deemed eligible if they included evaluation of rotational tooth movement with any type of aligner, through the comparison of software-based and actually achieved data after patient treatment.

DATA EXTRACTION AND DATA SYNTHESIS

Data extraction was done independently and in duplicate and risk of bias assessment was performed with the use of the QUADAS-2 tool. Random effects meta-analyses with effect sizes and their 95% confidence intervals (CIs) were performed and the quality of the evidence was assessed through GRADE.

RESULTS

Seven articles were included in the qualitative synthesis, of which three contributed to meta-analyses. Overall results revealed a non-accurate prediction of the outcome for the software-based data, irrespective of the use of attachments or interproximal enamel reduction (IPR). Maxillary canines demonstrated the lowest percentage accuracy for rotational tooth movement (three studies: effect size = 47.9%; 95% CI = 27.2-69.5; P < 0.001), although high levels of heterogeneity were identified (I2: 86.9%; P < 0.001). Contrary, mandibular incisors presented the highest percentage accuracy for predicted rotational movement (two studies: effect size = 70.7%; 95% CI = 58.9-82.5; P < 0.001; I2: 0.0%; P = 0.48). Risk of bias was unclear to low overall, while quality of the evidence ranged from low to moderate.

CONCLUSION

Allowing for all identified caveats, prediction of rotational tooth movements with aligner treatment does not appear accurate, especially for canines. Careful selection of patients and malocclusions for aligner treatment decisions remain challenging.

Suppressing ROS generation by apocynin inhibited cyclic stretch-induced inflammatory reaction in HPDLCs via a caspase-1 dependent pathway

It has been reported that cyclic stretch could induce inflammatory reaction in human periodontal ligament cells (HPDLCs). Though reactive oxygen species (ROS) has been reported to be involved in pathogen-induced periodontal inflammatory reaction, its role in the force-related periodontal diseases has not been well clarified. This study inspected the role of ROS in the cyclic stretch-induced inflammatory reaction in HPDLCs and studied the inhibitory effect of antioxidant apocynin on this inflammatory reaction. Results confirmed that cyclic stretch induced inflammatory reaction and production of ROS in HPDLCs. This inflammatory reaction was inhibited by apocynin through blocking the production of ROS. The cyclic stretch also induced the expression of caspase-1 and NLRP3 inflammasome, which could also be inhibited by apocynin. Moreover, the cyclic stretch-induced inflammatory reaction was inhibited by caspase-1 inhibitor. Collectively, it is the first time that increased intracellular ROS was proved to play as an intermediate signal in the cyclic stretch-induced inflammatory reaction in HPDLCs, via a caspase-1-dependent pathway. The inhibitory effect of apocynin on the cyclic stretch-induced inflammatory reaction in HPDLCs shows the potential of antioxidants in the treatment of force-related periodontal inflammatory diseases.

Cyclic tensile forces enhance the angiogenic properties of HUVECs by promoting the activities of human periodontal ligament cells

BACKGROUND

This study aimed to investigate whether human periodontal ligament (PDL) cells secrete pro-angiogenic factors that induce the vascularization of surrounding bone tissue under tensile stress.

METHODS

Quantitative real-time PCR and Western blotting were used to analyze the mRNA and protein expression levels of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), Angiopoietin-I (Ang-I), connective tissue growth factor （CTGF）, and macrophage colony-stimulating factor (M-CSF) in PDL cells after tensile force treatments of different durations. Enzyme-linked immunosorbent assay was used to measure the VEGF concentration in the supernatants of cell cultures. Cell viability assay, wound healing assay, and tube formation assay were performed to evaluate the angiogenic behaviors of human umbilical vein endothelial cells (HUVECs).

RESULTS

The mRNA expression and protein expression of VEGF, bFGF, Ang-I, and M-CSF was increased in the cells that received 6 to 48 hours of tensile force treatment. And, the VEGF level in the supernatant significantly increased in the human PDL cell cultures stressed for 6 to 48 hours. The abilities of HUVECs to proliferate, migrate, and form tubes were enhanced in media conditioned with tensile-stressed human PDL cells. Hence, tensile force induced human PDL cells to express and release pro-angiogenic factors enhancing the proliferation, migration, and angiogenic capacity of HUVECs.

CONCLUSION

Tensile stress induced human PDL cells to express and release pro-angiogenic factors, including VEGF, bFGF, Ang-I, and M-CSF, thereby enhancing the proliferation, migration, and angiogenic capacity of HUVECs.

Effect of hyperglycaemic conditions on the response of human periodontal ligament fibroblasts to mechanical stretching

Objectives

The aim of the present study was to investigate the impact of high glucose concentration on the response of human periodontal ligament fibroblasts (PDLFs) to cyclic tensile strain.

Materials and Methods

Human PDLFs were incubated under normal or high glucose conditions, and then were subjected to cyclic tensile stretching (8 per cent extension, 1 Hz). Gene expression was determined by quantitative real-time polymerase chain reaction. Intracellular reactive oxygen species (ROS) were determined by the 2’,7’-dichlorofluorescein-diacetate assay, activation of mitogen-activated protein kinase (MAPK) was monitored by western analysis and osteoblastic differentiation was estimated with Alizarin Red-S staining.

Results

Cyclic tensile stretching of PDLF leads to an immediate activation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), as well as to the increased expression of the transcription factor c-fos, known to regulate many osteogenesis-related genes. At later time points, the alkaline phosphatase and osteopontin genes were also upregulated. Hyperglycaemic conditions inhibited these effects. High glucose conditions were unable to increase ROS levels, but they increased the medium’s osmolality. Finally, increase of osmolality mimics the inhibitory effect of hyperglycaemia on MAPK activation, c-fos and osteoblast-specific gene markers’ upregulation, as well as osteogenic differentiation capacity.

Conclusion

Our findings indicate that under high glucose conditions, human PDLFs fail to adequately respond to mechanical deformation, while their strain-elicited osteoblast differentiation ability is deteriorated. The aforementioned effects are most probably mediated by the increased osmolality under hyperglycaemic conditions.

Early responses of human periodontal ligament fibroblasts to cyclic and static mechanical stretching

Objective

To compare the mechanotransduction caused by cyclic and static mechanical strains in human periodontal ligament fibroblasts (hPDLFs) cultured under identical conditions.

Materials and methods

hPDLFs, originating from the same donors, were exposed either to cyclic or to static tensile strain using specially designed devices and under identical culture conditions. Activation of all members of mitogen-activated protein kinases (MAPKs) was monitored by western immunoblot analysis. Expression levels of immediate/early genes c-fos and c-jun were assessed with quantitative real-time polymerase chain reaction.

Results

Time course experiments revealed that both types of stresses activate the three members of MAPK, that is ERK, p38, and JNK, with cyclic stress exhibiting a slightly more extended activation. Further downstream, both stresses upregulate the immediate/early genes c-fos and c-jun, encoding components of the activator protein-1 (AP-1), a key transcription factor in osteoblastic differentiation; again cyclic strain provokes a more intense upregulation. Six hours after the application of both strains, MAPK activation and gene expression return to basal levels. Finally, cells exposed to cyclic stress for longer periods are distributed approximately perpendicular to the axis of the applied strain, whereas cells exposed to static loading remain in a random orientation in culture.

Conclusion

The findings of the present study indicate similar, although not identical, immediate/early responses of hPDLs to cyclic and static stretching, with cyclic strain provoking a more intense adaptive response of these cells to mechanical deformation.

Periodontal Ligament and Alveolar Bone in Health and Adaptation: Tooth Movement

The periodontal ligament (PDL) and alveolar bone are two critical tissues for understanding orthodontic tooth movement. The current literature is replete with descriptive studies of multiple cell types and their matrices in the PDL and alveolar bone, but is deficient with how stem/progenitor cells differentiate into PDL and alveolar bone cells. Can one type of orthodontic force with a specific magnitude and frequency activate osteoblasts, whereas another force type activates osteoclasts? This chapter will discuss the biology of not only mature cells and their matrices in the periodontal ligament and alveolar bone, but also stem/progenitor cells that differentiate into fibroblasts, osteoblasts and osteoclasts. Key advances in tooth movement rely on further understanding of osteoblast and fibroblast differentiation from mesenchymal stem/progenitor cells, and osteoclastogenesis from the hematopoietic/monocyte lineage.