The association between orthodontic treatment and temporomandibular disorders diagnosis and disease characteristics

BACKGROUND

The association between orthodontic treatment and temporomandibular disorders (TMD) has been contentious in the literature.

OBJECTIVES

To analyse the associations between orthodontic treatment and TMD diagnosis and diseases characteristics.

METHODS

This case-control study included 291 individuals, 192 TMDs and 99 controls. All patients underwent assessment based on a questionnaire and a clinical examination according to Axis I of the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD). Differences in orthodontic treatment between TMDs and controls, as well as across different TMD diagnoses within the TMD group were analysed. Patients who underwent orthodontic treatment were compared to those who did not, regarding their trauma history, bruxism, aggressive teeth brushing, level of oral hygiene, pain scores, muscle tenderness scores and subjective sleep quality.

RESULTS

Of the 291 participants, 119 (40.9%) underwent orthodontic treatment and 172 (59.1%) had no orthodontics experience. Orthodontic treatment included: mandibular orthodontic treatment (102 subjects) and maxillary orthodontic treatment (113 subjects) of those 47 used a headgear. Following multivariate analysis among TMDs, orthodontic treatment was associated with a good level of oral hygiene versus poor (Odds ratio [OR]: 5.17 [1.04-25.59]), lower number of tender muscles [OR = 0.84 (0.74-0.96)] and lower (better) Pittsburgh Sleep Quality Index (PSQI) scores (OR = 0.86 [0.76-0.97]). None of the studied parameters maintained a statistically significant association with orthodontic treatment in the multivariate analysis among the entire study population.

CONCLUSIONS

Utilising a holistic approach, this study supports the main hypothesis that orthodontic treatment is not associated with TMD diagnosis and disease characteristics.

The labiopalatal impacted canine: Accurate diagnosis based on the position and size of adjacent teeth: A cone-beam computed tomography study

INTRODUCTION

Labiopalatal impacted canines (L-PICs) occur when the canines lie between central and lateral incisors, with their tip palatal to the central incisor and part of their crown labial to the lateral incisor. Because of their unusual position, they are often misdiagnosed, and their orthodontic resolution fails. This study aims to provide clinicians with pathognomonic features for early and accurate positional diagnosis of L-PICs.

METHODS

The L-PIC sample included 21 subjects with full diagnostic records. The control group of normally erupted canines was taken from a previous study. Clinical photographs, 2-dimensional radiographs, and cone-beam computed tomography were used to evaluate the positions of the adjacent incisors and first premolars, the canine incisor index, and the mesiodistal width of the lateral vs central incisors.

RESULTS

Central incisors adjacent to L-PICs showed significant mesial root angulation, labial root inclination, and mesiolabial crown rotation, whereas lateral incisors presented significant distal root angulation, palatal root inclination, and mesiolabial crown rotation, in comparison to controls. The roots of the central and lateral incisors were divergent, in contrast to the controls, in which they were slightly convergent. The first premolar positions were not affected. The mean canine incisor index was significantly bigger in L-PICs vs the controls, suggesting a palatal canine. The lateral incisor widths were similar between the groups.

CONCLUSIONS

This study provides the orthodontist with evidence-based clinical and radiographic red flags for diagnosing L-PIC, which may allow timely initiation of orthodontic treatment and correct planning of mechanotherapy.

Resolvin D1 shows osseous-protection via RANK reduction on monocytes during orthodontic tooth movement

The study aimed to investigate the role of RvD1 in acute and prolonged sterile inflammation and bone remodeling. A mouse model of sterile inflammation that involves bone resorption was used to examine endogenous RvD1 kinetics during inflammation. Application of exogenous RvD1 significantly inhibited bone remodeling via osteoclast reduction, alongside an anti-inflammatory secretome shift, increased macrophages recruitment and reduction of T-cytotoxic cells. In vitro and in vivo, RvD1 led to significant reduction in RANK expression which reduce osteoclastogenesis in a dose-dependent manner. Taken together, the data shows a dual role for RvD1, as a potent immunoresolvent agent alongside an osteoresolvent role, showing a potential therapeutic agent in bone resorption associated inflammatory conditions.

γδ T Cells Differentially Regulate Bone Loss in Periodontitis Models

γδ T cells are nonclassical T lymphocytes representing the major T-cell population at epithelial barriers. In the gingiva, γδ T cells are enriched in epithelial regions adjacent to the biofilm and are considered to regulate local immunity to maintain host-biofilm homeostatic interactions. This delicate balance is often disrupted resulting in the development of periodontitis. Previous studies in mice lacking γδ T cells from birth (Tcrd^-/- mice) examined the impact of these cells on ligature-induced periodontitis. Data obtained from those studies proposed either a protective effect or no impact to γδ T cells in this setting. Here, we addressed the role of γδ T cells in periodontitis using the recently developed Tcrd-GDL mice, enabling temporal ablation of γδ T cells. Specifically, the impact of γδ T cells during periodontitis was examined in 2 modalities: the ligature model and the oral infection model in which the pathogen Porphyromonas gingivalis was administrated via successive oral gavages. Ablation of γδ T cells during ligature-induced periodontitis had no impact on innate immune cell recruitment to the ligated gingiva. In addition, the number of osteoclasts and subsequent alveolar bone loss were unaffected. However, γδ T cells play a pathologic role during P. gingivalis infection, and their absence prevented alveolar bone loss. Further analysis revealed that γδ T cells were responsible for the recruitment of neutrophils and monocytes to the gingiva following the exposure to P. gingivalis. γδ T-cell ablation also downregulated osteoclastogenesis and dysregulated long-term immune responses in the gingiva. Collectively, this study demonstrates that whereas γδ T cells are dispensable to periodontitis induced by the ligature model, they play a deleterious role in the oral infection model by facilitating pathogen-induced bone-destructive immune responses. On a broader aspect, this study highlights the complex immunopathologic mechanisms involved in periodontal bone loss.

Natural size variation among embryos leads to the corresponding scaling in gene expression

Xenopus laevis frogs from laboratory stocks normally lay eggs exhibiting extensive size variability. We find that these initial size differences subsequently affect the size of the embryos prior to the onset of growth, and the size of tadpoles during the growth period. Even though these tadpoles differ in size, their tissues, organs, and structures always seem to be properly proportioned, i.e. they display static allometry. Initial axial patterning events in Xenopus occur in a spherical embryo, allowing easy documentation of their size-dependent features. We examined the size distribution of early Xenopus laevis embryos and measured diameters that differed by about 38% with a median of about 1.43 ​mm. This range of embryo sizes corresponds to about a 1.9-fold difference in surface area and a 2.6-fold difference in volume. We examined the relationship between embryo size and gene expression and observed a significant correlation between diameter and RNA content during gastrula stages. In addition, we investigated the expression levels of genes that pattern the mesoderm, induce the nervous system and mediate the progression of ectodermal cells to neural precursors in large and small embryos. We found that most of these factors were expressed at levels that scaled with the different embryo sizes and total embryo RNA content. In agreement with the changes in transcript levels, the expression domains in larger embryos increased proportionally with the increase in surface area, maintaining their relative expression domain size in relation to the total size of the embryo. Thus, our study identified a mechanism for adapting gene expression domains to embryo size by adjusting the transcript levels of the genes regulating mesoderm induction and patterning. In the neural plate, besides the scaling of the expression domains, we observed similar cell sizes and cell densities in small and large embryos suggesting that additional cell divisions took place in large embryos to compensate for the increased size. Our results show in detail the size variability among Xenopus laevis embryos and the transcriptional adaptation to scale gene expression with size. The observations further support the involvement of BMP/ADMP signaling in the scaling process.

Bovine Bone Promotes Osseous Protection via Osteoclast Activation

The current study aimed at investigating the long-term biological mechanisms governing bone regeneration in osseous defects filled with bovine bone (BB). Tooth extraction sockets were filled with BB or left unfilled for natural healing in a C57BL/6 mouse alveolar regeneration bone model (n = 12). Seven weeks later, the alveolar bone samples were analyzed histologically with hematoxylin/eosin and tartrate-resistant acid phosphatase staining. A separate group (n = 10) was used for RNA sequencing. Osteoclast inhibition was induced by zoledronic acid (ZA) administration at 2 wk postextraction in a third group (n = 28) for examination of osseous changes and cellular functions with micro-computed tomography and quantitative reverse transcription polymerase chain reaction, respectively. Histological and radiological osseous healing was observed in both BB-filled and normal-healing sockets. However, BB regenerated bone showed significant robust expression of genes associated with bone homeostasis and osteoclasts' function. Osteoclasts' inhibition in BB-filled sockets led to decreased bone resorption markers and reduced bone formation to a greater extent than that observed in osteoclasts' inhibition with natural healing. BB displays long-term biologically active properties, despite a naive osseous histological appearance. These include activation of osteoclasts, which in turn promotes osseous remodeling and maturation of ossified bone.

Expression of the ALK1 family of type I BMP/ADMP receptors during gastrula stages in Xenopus embryos

Multiple members of the transforming growth factor beta (TGFβ) family of secreted factors play central inductive and patterning roles during embryogenesis. During gastrulation in vertebrates, the bone morphogenetic protein (BMP) sub-family is linked to formation of the embryonic organizer, Spemann's organizer in Xenopus, and dorsal-ventral mesoderm patterning. Our knowledge regarding the BMP receptors mediating this signaling is still very incomplete. The BMPR1A (ALK3) and BMPR1B (ALK6) receptors are known to mediate the BMP4 signal. These receptors belong to the ALK1 subfamily of type I receptors that also includes ACVR1 (ALK2), and ACVRL1 (ALK1). We studied by qPCR and in situ hybridization the spatio-temporal expression patterns of ALK2 and ALK1 and compared them to ALK3 and ALK6, and to the main BMPs expressed during gastrulation, i.e., BMP4, BMP7, BMP2, and ADMP, in an attempt to establish a link between ligands and receptors. There is extensive overlap between BMP4, and ALk3 and Alk6 expression, supporting their functional interaction. Robust Alk6 expression was observed from mid-gastrula. Animal region expression of both receptors shows co-expression with BMP4 and BMP7. Alk2 transcripts were detected within the organizer, overlapping with its proposed ligand, ADMP, suggesting a probable function within the organizer. Alk1 is very weakly expressed during gastrula, but its transcripts were localized to the lateral marginal zone flanking the organizer domain. No receptor closely matched the maternal BMP2 expression, although Alk2, Alk3, and Alk6, have transcripts of maternal origin. Our analysis shows that the BMP ligands and their receptors exhibit dynamic expression patterns during gastrula stages.

ADMP controls the size of Spemann's organizer through a network of self-regulating expansion-restriction signals

BACKGROUND

The bone morphogenetic protein (BMP) signaling gradient is central for dorsoventral patterning in amphibian embryos. This gradient is established through the interaction of several BMPs and BMP antagonists and modulators, some secreted by Spemann's organizer, a cluster of cells coordinating embryonic development. Anti-dorsalizing morphogenetic protein (ADMP), a BMP-like transforming growth factor beta ligand, negatively affects the formation of the organizer, although it is robustly expressed within the organizer itself. Previously, we proposed that this apparent discrepancy may be important for the ability of ADMP to scale the BMP gradient with embryo size, but how this is achieved is unclear.

RESULTS

Here we report that ADMP acts in the establishment of the organizer via temporally and mechanistically distinct signals. At the onset of gastrulation, ADMP is required to establish normal organizer-specific gene expression domains, thus displaying a dorsal, organizer-promoting function. The organizer-restricting, BMP-like function of ADMP becomes apparent slightly later, from mid-gastrula. The organizer-promoting signal of ADMP is mediated by the activin A type I receptor, ACVR1 (also known as activin receptor-like kinase-2, ALK2). ALK2 is expressed in the organizer and is required for organizer establishment. The anti-organizer function of ADMP is mediated by ACVRL1 (ALK1), a putative ADMP receptor expressed in the lateral regions flanking the organizer that blocks expansion of the organizer. Truncated ALK1 prevents the organizer-restricting effects of ADMP overexpression, suggesting a ligand-receptor interaction. We also present a mathematical model of the regulatory network controlling the size of the organizer.

CONCLUSIONS

We show that the opposed, organizer-promoting and organizer-restricting roles of ADMP are mediated by different receptors. A self-regulating network is proposed in which ADMP functions early through ALK2 to expand its own expression domain, the organizer, and later functions through ALK1 to restrict this domain. These effects are dependent on ADMP concentration, timing, and the spatial localization of the two receptors. This self-regulating temporal switch may control the size of the organizer and the genes expressed within in response to genetic and external stimuli during gastrulation.