Micro-computed tomography for evaluating alveolar bone resorption induced by hyperocclusion

Effect of tension and compression on dynamic alveolar histomorphometry

Here, we tested the hypothesis that tensile and compressive stresses generated in the alveolar bone proper regulate site-specific cellular and functional changes in osteoclasts and osteoblasts. Thirty-two 13-week-old male mice were randomly divided into four groups: two experimental groups with vertical loading obliquely from the palatal side to the buccal side of the maxillary molar (0.9 N) 30 min per day for 8 or 15 days and unloaded controls (n = 8). Calcein and alizarin were administered 8 and 2 days before euthanization, respectively, to detect the time of bone formation. Undecalcified sections parallel to the occlusal plane were prepared on the palatal root and the surrounding alveolar bone in the middle of the root length. The alveolar perimeter was divided into 12 equal regions for site analysis, and the bone histomorphometric parameters were obtained for each region. Data from in vivo microfocus computed tomography were used to construct animal-specific finite element models. 2D stress distribution images were overlain on histology images obtained from the same location. Significant differences in the total perimeter between groups and between loading and unloading in each region were statistically analyzed (α = 0.05). Osteoclast counts and the alizarin label ratio were significantly higher in the loaded group than in the unloaded group in regions where the maximum von Mises and principal tensile stresses were the highest along the perimeter. The label ratio of calcein was significantly lower in the 8-day loaded group than in the unloaded group, indicating that the calcein-labeled surface was resorbed by osteoclasts that appeared during the loading period. The effect of loading was mitigated by an increase in the maximum principal compressive stress. We conclude that bone resorption and bone formation are functions of site-specific tension and compression in the alveolar bone proper, confirming our hypothesis. This finding is critical for the advancement of diagnosis and treatment planning in clinical dentistry.

The Effect of IFT80 Deficiency in Osteocytes on Orthodontic Loading-Induced and Physiologic Bone Remodeling: In Vivo Study

Osteocytes are the main mechanosensory cells during orthodontic and physiologic bone remodeling. However, the question of how osteocytes transmit mechanical stimuli to biological responses remains largely unanswered. Intraflagellar transport (IFT) proteins are important for the formation and function of cilia, which are proposed to be mechanical sensors in osteocytes. In particular, IFT80 is highly expressed in mouse skulls and essential for ciliogenesis. This study aims to investigate the short- and long-term effects of IFT80 deletion in osteocytes on orthodontic bone remodeling and physiological bone remodeling in response to masticatory force. We examined 10-week-old experimental DMP1 CRE+.IFT80f/f and littermate control DMP1 CRE-.IFT80f/f mice. After 5 and 12 days of orthodontic force loading, the orthodontic tooth movement distance and bone parameters were evaluated using microCT. Osteoclast formation was assessed using TRAP-stained paraffin sections. The expression of sclerostin and RANKL was examined using immunofluorescence stain. We found that the deletion of IFT80 in osteocytes did not significantly impact either orthodontic or physiologic bone remodeling, as demonstrated by similar OTM distances, osteoclast numbers, bone volume fractions (bone volume/total volume), bone mineral densities, and the expressions of sclerostin and RANKL. Our findings suggest that there are other possible mechanosensory systems in osteocytes and anatomic limitations to cilia deflection in osteocytes in vivo.

Inhibition of RANKL and Sema4D improves residual ridge resorption in mice

Residual ridge resorption (RRR) is a chronic and progressive bone resorption following tooth loss. It causes deterioration of the oral environments and leads to the pathogenesis of various systemic diseases. However, the molecular mechanisms and risk factors for RRR progression are still unclear and controversial. In this study, we developed a tooth extraction model using mice for analyzing long-term morphological and gene expression changes in the alveolar bone. We further applied ovariectomy to this model to elucidate the effects of osteoporosis on RRR progression. As a result, the alveolar bone loss was biphasic and consisted of rapid loss in the early stages and subsequently slow and sustained bone loss over a long period. Histological analysis indicated that ovariectomy prolonged the activation of osteoclasts in the alveolar bone. Furthermore, the expressions of Tnfsf11 and Sema4d kept increasing for a long time in OVX mice. Administration of neutralization antibodies for receptor activator of NF-κB ligand (RANKL) effectively suppressed RRR. Similarly, inhibition of Semaphorin 4D (Sema4D) also improved alveolar bone loss. This study demonstrated that reduced ovarian function may be a risk factor for RRR and that RANKL and Sema4D suppression are potential treatments.

Study on the role of pyroptosis in bone resorption induced by occlusal trauma with or without periodontitis

BACKGROUND AND OBJECTIVE

Occlusal trauma is considered to be a contributing factor to bone loss associated with inflammatory periodontal disease. We hypothesized that pyroptosis, a recently discovered inflammation-induced programmed cell death pathway, plays a role in occlusal trauma.

MATERIALS AND METHODS

The occlusal trauma model was established using a cemented 1-mm elevated computer-aided design and manufacturing (CAD/CAM) metal crown. The periodontitis model was established by periodontal wire ligation with lipopolysaccharide (LPS) injection. The rats were sacrificed at 1, 2, 3, and 4 weeks. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to analyze the expression of pyroptosis-, inflammation-, and osteoclast-related markers. Micro-computed tomography (micro-CT) was used to determine bone morphology parameters. Tissue morphology was evaluated using hematoxylin and eosin staining (H&E). Osteoclasts were identified using tartrate-resistant acid phosphatase (TRAP) staining. The expression and distribution of factors related to pyroptosis and inflammation were evaluated by immunohistochemistry (IHC). The colocalization of dead cells and cysteinyl aspartate-specific proteinase-1 (caspase-1)-positive cells was analyzed by immunofluorescence.

RESULTS

Quantitative real-time polymerase chain reaction and IHC results showed that occlusal trauma induced the expression of pyroptotic factors during the early stages, while occlusal trauma with periodontitis upregulated the expression of pyroptotic factors at the later stages. The results of qRT-PCR, TRAP staining, and micro-CT showed that occlusal trauma with periodontitis increased the production of proinflammatory cytokines, leading to severe bone loss. Glyburide, an NOD-like receptor pyrin domain containing protein 3 (NLRP3)inhibitor, reduced the expression of pyroptosis markers induced by occlusal trauma with periodontitis and reversed bone resorption.

CONCLUSIONS

Pyroptosis was involved in bone loss induced by occlusal trauma with or without periodontitis, while glyburide reversed inflammation and bone resorption.

Influence of hyperocclusion on the remodeling of gingival tissues

OBJECTIVE

The purpose of this study was to observe the effect of hyperocclusion on the remodeling of gingival tissues and detect the related signaling pathways.

DESIGN

Hyperocclusion models were established by tooth extraction in mice. The mice were sacrificed at 3, 7, 14, 28, or 56 days after the surgery, and the left mandibular first molars with gingival tissues were isolated and examinations were focused on the gingival tissues. Apoptotic cells were examined using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) technology. Proliferating cells, p65, inflammatory cytokines, and β-catenin were detected using immunohistochemical methods.

RESULTS

A series of apoptosis and proliferation responses were triggered in stressed gingival tissues. It was observed that the levels of p65, proinflammatory factors including interleukin-1β and tumor necrosis factor-α in extraction group were higher compared with those from mice with intact dentition, and peaked on days 14, 14 and 7 respectively. The expression of β-catenin was increased under hyperocclusion situations, peaked on day 14, and declined to the initial levels over time.

CONCLUSIONS

The results of this study suggest that hyperocclusion causes remodeling of the gingival tissues by activating a series of adaptive responses. Both nuclear factor kappa B and Wnt/β-catenin signaling pathways may be responsible for those adaptive responses though the exact mechanism is not clear.

Guidelines for Micro-Computed Tomography Analysis of Rodent Dentoalveolar Tissues

Micro–computed tomography (μCT) has become essential for analysis of mineralized as well as nonmineralized tissues and is therefore widely applicable in the life sciences. However, lack of standardized approaches and protocols for scanning, analyzing, and reporting data often makes it difficult to understand exactly how analyses were performed, how to interpret results, and if findings can be broadly compared with other models and studies. This problem is compounded in analysis of the dentoalveolar complex by the presence of four distinct mineralized tissues: enamel, dentin, cementum, and alveolar bone. Furthermore, these hard tissues interface with adjacent soft tissues, the dental pulp and periodontal ligament (PDL), making for a complex organ. Drawing on others' and our own experience analyzing rodent dentoalveolar tissues by μCT, we introduce techniques to successfully analyze dentoalveolar tissues with similar or disparate compositions, densities, and morphological characteristics. Our goal is to provide practical guidelines for μCT analysis of rodent dentoalveolar tissues, including approaches to optimize scan parameters (filters, voltage, voxel size, and integration time), reproducibly orient samples, define regions and volumes of interest, segment and subdivide tissues, interpret findings, and report methods and results. We include illustrative examples of analyses performed on genetically engineered mouse models with phenotypes in enamel, dentin, cementum, and alveolar bone. The recommendations are designed to increase transparency and reproducibility, promote best practices, and provide a basic framework to apply μCT analysis to the dentoalveolar complex that can also be extrapolated to a variety of other tissues of the body. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Relationship Between Crown to Root Ratio and Alveolar Bone Support in Patients With Unilateral Cleft Lip and Alveolus

OBJECTIVES

To evaluate the tooth lengths, crown to root ratios (CRRs), and alveolar bone support (ABS) around cleft-adjacent maxillary central incisors (U1s) in patients with unilateral cleft lip and alveolus (UCLA) and to investigate the relationships between CRR and ABS.

DESIGN

This is a retrospective study.

SETTING

Cleft Lip and Palate Care Center of Shanghai Ninth People's Hospital, Shanghai, China.

PATIENTS

Fifty-eight Chinese patients with UCLA.

MAIN OUTCOME MEASURE

Cone beam computed tomography data from 58 nonsyndromic patients with UCLA (36 males, 22 females; mean age = 12.65 ± 3.64 years) were evaluated. Crown length and root length, alveolar bone thickness (ABT), and the distances between the cementoenamel junction and alveolar bone crest on 4 surfaces of cleft-adjacent U1 were measured and compared with those of noncleft side in the same patients. Crown to root ratio and frequency of dehiscence were calculated and comparisons were also made between cleft and noncleft sides. Regression analysis was performed to explore the association between CRR and ABS.

RESULTS

The CRR of cleft-adjacent U1 and alveolar bone crest heights (ACHs) on the 4 surfaces were significantly greater than those of noncleft side (P < .01). A 3 mm labial, all lingual, and apico-distal ABTs decreased on the cleft side (P < .01). A positive correlation was found between lingual ACH and CRR (R = 0.316, P < .05), between the 3 mm (R = 0.417, P < .05) and 6 mm labial (R = 0.448, P < .05) ABT and CRR. A negative correlation was found between the 3 mm and 6 mm labial ABTs and the root length.

CONCLUSIONS

It can be suggested that the CRR is related to ACH and ABT. The lingual ACH, the 3 mm, and 6 mm labial ABTs tend to increase with the increasing CRR.

Occlusion Heightened by Metal Crown Cementation is Aggressive for Periodontal Tissues

PURPOSE

To investigate the effect of experimental traumatic occlusion (ETO) induced by metal crowns on alveolar bone loss.

MATERIALS AND METHODS

Metal crowns were custom-made for the lower first molars with occlusal discrepancy of 0.4 and 0.7 mm from the maximum intercuspation. Thirty-six animals were randomly divided into three groups (n = 12 animals per group): 0.4-mm hyperocclusion group, 0.7-mm hyperocclusion group and the sham group (no metal crown). Twenty-eight days after crown cementation, the animals were euthanized and gingival tissue was collected to assess cytokine levels of IL-17, IL-6, and TNF-α using enzyme-linked immunosorbent assay (ELISA). Mandibles were stained with 1% methylene blue and alveolar bone levels were quantified. Western blotting was used to quantify the expression of receptor activator of nuclear factor κ B (RANK), and its ligand (RANKL), secreted osteoclastogenic factor of activated T cells (SOFAT) and TNF-α-converting enzyme (TACE). Also, mandibles were histologically processed and stained with hematoxylin and eosin, from which the presence of osteoclast-like cells, multinucleated cells containing ≥3 nuclei was counted at 100× magnification. The data were analyzed using one-way ANOVA and Tukey tests.

RESULTS

Experimental occlusal trauma for 28 consecutive days significantly increased alveolar bone loss and multinucleated cell counts (p < 0.05). RANK, RANKL, SOFAT, TACE, IL-6, and TNF-α were significantly higher in gingival tissues of ETO groups (p < 0.05). IL-17 titers were unchanged among the groups (p > 0.05).

CONCLUSION

Experimental traumatic occlusion activates and sustains bone resorption pathways in the periodontium inducing alveolar bone resorption. As the intensity of occlusal trauma increased, alternative osteoclastic pathways were activated, such as TACE and SOFAT.

Berberine Promotes the Proliferation and Osteogenic Differentiation of Alveolar Osteoblasts through Regulating the Expression of miR-214

INTRODUCTION AND OBJECTIVE

Alveolar osteoblasts have critical functions during alveolar bone regeneration. Berberine (BBR) and microRNAs (miRNAs) are considered to play important roles in regulating osteoblast differentiation. The study aimed to investigate the role and mechanisms of BBR in osteogenic differentiation of human alveolar osteoblasts (HAOBs) and determine miR-214 expression in the process.

METHODS

Healthy human alveolar bones were cultured in vitro and prepared for morphological observation and alkaline phosphatase (ALP) staining. The third generation of HAOBs was used for cell transfection and treated by different concentrations of BBR. Cell Counting Kit-8 was used to detect the effect of BBR and increased miR-214 on the proliferation of HAOBs. qRT-PCR and Western blot were used to detect the expression of osteogenic differentiation-related genes and miR-214 level, respectively.

RESULTS

The ALP staining results were positive, indicating that cultured cells were HAOBs. Different concentrations of BBR significantly promoted the proliferation of HAOBs and increased the expression levels of ALP, osteocalcin (OCN), collagen type I alpha 1 (COL1A1), runt related transcription factor 2 (RUNX2), and osterix (OSX). Moreover, the expression of miR-214 was reduced as BBR concentrations increased, and the increase of miR-214 reversed the BBR-induced proliferation and osteogenic differentiation of HAOBs.

CONCLUSION

BBR could promote the proliferation and osteogenic differentiation of HAOBs through downregulating the expression of miR-214.

Dental pathology of the wild Iberian wolf (Canis lupus signatus): The study of a 20th century Portuguese museum collection

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Dental pathology of wild Iberian wolf was studied in 61 complete skulls and 4 mandibles from a museum collection.

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Museum collections can provide crucial information about wild elusive species.

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The most frequent observed abnormalities were tooth wear, periodontitis and tooth fractures.

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Dental radiography is of a great importance for the diagnose and classification of the dental and periodontal conditions.

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Dental radiography can be useful for the age estimation of archaeological Canis.

For some wild canids, such as the Iberian wolf, there is a lack of in-depth knowledge about dental pathology. We aimed to evaluate it, in a standardized manner, in specimens from a Portuguese museum collection.

Sixty-five deceased specimens of wild Iberian wolves, 61 complete skulls and 4 mandibles, collected in Portugal between 1977 and 1995, were analyzed. Sample comprised 18 females, 24 males and 23 individuals of undetermined sex. Teeth were evaluated by visual observation and dental radiography for tooth wear, periodontitis, fractures and other dental lesions.

We have found several causes for teeth absence: artefactual, secondary to periodontitis and agenesia. About 30% of the teeth showed signs of wear. Only a small (<13%) fraction of maxillary and mandibular teeth did not show periodontitis. The tooth 308 showed periodontitis in all males (p = 0.017) and the tooth 104 was significantly affected by this condition in females (p = 0.020). A significant relationship was found between females and tooth wear in three teeth. Periodontitis showed a significant association with tooth wear (p < 0.001) and fractures (p = 0.027). Tooth fractures were more frequent in the maxilla than in the mandible. Seven periapical lesions, seven root fusions and three specimens with malocclusion were identified in the collection. Results are discussed integrating information from diet, habitat, genetic and spatial behavior.

Dental radiography is here proposed as an approach for the age estimation in archaeological canids. This research contributes to the knowledge of the dental disease in the largest wolf population in Western Europe, a target subspecies of multiple conservation measures.

Mechanoadaptive Responses in the Periodontium Are Coordinated by Wnt

Despite an extensive literature documenting the adaptive changes of bones and ligaments to mechanical forces, our understanding of how tissues actually mount a coordinated response to physical loading is astonishingly inadequate. Here, using finite element (FE) modeling and an in vivo murine model, we demonstrate the stress distributions within the periodontal ligament (PDL) caused by occlusal hyperloading. In direct response, a spatially restricted pattern of apoptosis is triggered in the stressed PDL, the temporal peak of which is coordinated with a spatially restricted burst in PDL cell proliferation. This culminates in increased collagen deposition and a thicker, stiffer PDL that is adapted to its new hyperloading status. Meanwhile, in the adjacent alveolar bone, hyperloading activates bone resorption, the peak of which is followed by a bone formation phase, leading ultimately to an accelerated rate of mineral apposition and an increase in alveolar bone density. All of these adaptive responses are orchestrated by a population of Wnt-responsive stem/progenitor cells residing in the PDL and bone, whose death and revival are ultimately responsible for directly giving rise to new PDL fibers and new bone.