Quantification of periapical bone destruction in mice by micro-computed tomography

Zoledronic Acid Modulates Cytokine Expression and Mitigates Bone Loss during the Development of Induced Apical Periodontitis in a Mice Model

INTRODUCTION

Bisphosphonates are antiresorptive drugs used worldwide to treat systemic bone pathologies. This study aimed to assess the impact of zoledronic acid on the progression of induced apical periodontitis and the expression of cytokines interleukin (IL)-1β, IL-10, IL-6, and tumor necrosis factor alpha (TNF-α) in a mouse model.

METHODS

Sixteen female isogenic BALB/c mice 6 weeks of age were distributed into 2 groups: mice with induced apical periodontitis (the AP group, n = 8) and mice with induced apical periodontitis treated with zoledronic acid (the AP-ZA group, n = 8). The AP-ZA group received a dose of 125 μg/kg zoledronic acid diluted in sterile saline solution administered intraperitoneally once a week for 4 weeks before pulp exposure, whereas the AP group received only saline solution. Pulp exposures were performed on the maxillary first molars for the induction of apical periodontitis, and mice were euthanized after 7 and 21 days. The jaws were collected; scanned using micro-computed tomographic imaging; and processed for polymerase chain reaction analysis of IL-1β, IL-10, IL-6, and TNF-α. The Student t test was performed for parametric data, and Mann-Whitney U tests were used for nonparametric data. The level of significance was set at 5%.

RESULTS

Micro-computed tomographic imaging revealed higher bone resorption in the AP group compared with the AP-ZA group at both time points (P < .05). Real-time polymerase chain reaction demonstrated higher TNF-α expression in the AP group at both time points and higher IL-6 and IL-1β expression in the AP group at the 7- and 21-day time points, respectively, compared with the AP-ZA group (P < .05). No differences were observed regarding IL-10 expression between the groups.

CONCLUSIONS

Zoledronic acid had significant anti-inflammatory and antiresorptive effects on apical periodontitis in mice.

A novel experimental model to investigate fungal involvement shows expression of Dectin-1 in periapical lesion pathogenesis

BACKGROUND

Candida albicans is linked to persistent endodontic lesions. However, the recognition receptor that identifies it is not explored previously.

OBJECTIVES

The aim of this study was to (1) establish a zymosan-induced model of apical periodontitis in mouse, (2) observe the expression of Dectin-1 and its possible relationship with toll-like receptor (TLR) 2 and (3) observe relationship between Osteopontin (OPN) and inflammatory cytokines.

METHODS

A total of 138 Naval Medical Research Institute (NMRI) mice were randomly divided into; Experimental Group n = 69 and Zymosan Group n = 69. Periapical periodontitis was developed in right maxillary molar. The animals were sacrificed at 7, 21 and 42 days. Bone blocks containing the mesial root (n = 15 for qRT-PCR, n = 45 for enzyme-linked immune sorbent assay (ELISA)) were collected for mRNA expression and ELISA. While whole maxilla (n = 3 from each time interval) were used for histology and immunohistochemical analysis. One way analysis of variance (ANOVA) and Tuckey's posthoc was used for statistical analysis at p ≤ .05.

RESULTS

TLR-2, Dectin-1 and TLR4-positive cells was detected at all time intervals in both groups. A strong positive correlation was observed between TLR-2 and Dectin-1 in both lesions (regular r = .680, p = .015, zymosan (r = .861, p < .001)). A significant correlation was found between OPN and tumour necrosis factor-alpha (TNF-α) in zymosan lesion (r = .827, p = .001).

CONCLUSIONS

Immune cells of inflamed periapical tissue expressed Dectin-1 receptor in response to the microbial challenge from infected root canals and showed positive correlation with TLR-2 and OPN suggesting a possible receptor collaboration mediated by OPN. The expression of OPN and TNF-α showed positive correlation in response to fungal antigen, indicating a possible relationship.

Modulation of blood redox status by the progression of induced apical periodontitis in rats

This study aimed to investigate if apical periodontitis in different periods changes systemic levels of the antioxidant and pro-oxidant parameters in Wistar rats. Twenty-four rats were randomly allocated into healthy animals, apical periodontitis at 14 days (AP14) and apical periodontitis at 28 days (AP28). The first mandibular molars were accessed in the AP groups, and the pulp chamber was exposed to the oral environment, inducing the apical lesion. After 14 and 28 days, the animals were anesthetized, euthanized, and hemimandibles were collected for micro-computed tomography (micro-CT) analysis to measure lesion volume, bone volume (BV), percent of bone to total tissue volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), and trabecular space (Tb.Sp). A histological examination of the remaining bone was also performed. Finally, blood samples were collected for oxidative biochemistry analysis, investigating glutathione (GSH), Trolox equivalent antioxidant capacity (TEAC), and lipid peroxidation (TBARS). The lesion volume was greater at 28 than at 14 days, as shown by micro-CT. AP14 and AP28 had decreased BV and Tb.Th, but only AP28 showed a reduction in BV/TV. Tb.N and Tb. Sp were increased in apical periodontitis at 28 days. In the histopathological analysis, AP14 had focal regions of moderate mononuclear inflammatory infiltrate, and AP28 had an intense inflammatory infiltrate with bacterial colonies. In the biochemical evaluation, GSH, TEAC, and TBARS were increased after 14 days. However, GSH returned to control levels, TEAC was similar to AP14, and TBARS increased significantly after 28 days. Therefore, the oxidative biochemistry response was modulated according to the progression of periapical damage. After 14 days, the organism could still react to the injury. However, at 28 days, the antioxidant response decreased, associated with an increase in TBARS.

Micro-computed tomographic evaluation of endodontic ledge position in relation to canal curvatures

Background

Endodontic ledge (EL) formation is the most common complication of endodontic treatment. Although various etiological factors have been identified, canal curvature is the most significant variable correlated with EL formation. The aim of this micro-computed tomographic (micro-CT) study was to evaluate EL position in the mesial canals of the lower molars in relation to the degree of canal curvature.

Methods

Forty intact mandibular first molars with independent mesial canals with 20°–40° primary mesio-distal curvature, 10°–30° buccal-lingual canal curvature and 4 < r ≤ 8 mm main curvature radius were selected. Working length was measured with a K-File #10 and a high resolution pre-operative micro-CT analysis was performed. Ledges were created at the point of maximum canal curvature using stainless steel K-Files #30–35, alternating irrigation with 5% NaOCl and 10% EDTA. A post-operative high-resolution micro-CT analysis was then completed. Pre- and post-operative images were analyzed. The angle (α) formed between the vector passing through the geometric center of the EL and the center of the original canal lumen and the line joining the centers of the mesio-buccal and mesio-lingual canal orifices was calculated, and a descriptive statistical analysis was achieved. The α angle values were analyzed in relation to canal curvature using Kruskal-Wallis and post hoc Dunn’s tests. The level of significance was set at P < 0.05.

Results

The α angles appeared inversely proportional to canal curvatures in the buccal-lingual and mesio-distal projections. The mean α angle was 36.4° (standard deviation 10.64; 95% confidence interval 34.1–40.9).

Conclusion

Within the limitations of this study, endodontic ledges develop in the opposite direction to the three-dimensional canal curvature and their position is influenced by the degree of curvature. Clinically, the α angle values may be related to the recommended direction to manage endodontic ledges.

Trigeminal neurons control immune-bone cell interaction and metabolism in apical periodontitis

Abstract

Apical periodontitis (AP) is an inflammatory disease occurring following tooth infection with distinct osteolytic activity. Despite increasing evidence that sensory neurons participate in regulation of non-neuronal cells, their role in the development of AP is largely unknown. We hypothesized that trigeminal ganglia (TG) Nav1.8⁺ nociceptors regulate bone metabolism changes in response to AP. A selective ablation of nociceptive neurons in Nav1.8^Cre/Diphtheria toxin A (DTA)^Lox mouse line was used to evaluate the development and progression of AP using murine model of infection-induced AP. Ablation of Nav1.8⁺ nociceptors had earlier progression of AP with larger osteolytic lesions. Immunohistochemical and RNAscope analyses demonstrated greater number of macrophages, T-cells, osteoclast and osteoblast precursors and an increased RANKL:OPG ratio at earlier time points among Nav1.8^Cre/ DTA^Lox mice. There was an increased expression of IL-1α and IL-6 within lesions of nociceptor-ablated mice. Further, co-culture experiments demonstrated that TG neurons promoted osteoblast mineralization and inhibited osteoclastic function. The findings suggest that TG Nav1.8⁺ neurons contribute to modulation of the AP development by delaying the influx of immune cells, promoting osteoblastic differentiation, and decreasing osteoclastic activities. This newly uncovered mechanism could become a therapeutic strategy for the treatment of AP and minimize the persistence of osteolytic lesions in refractory cases.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00018-022-04335-w.

Effects of Anti-RANKL Antibody and Zoledronic Acid on Periapical Lesion Development in Mice

INTRODUCTION

Anti-resorptive drugs are widely used to treat osteoporosis and other systemic bone diseases, though their efficacy for local bone resorption following localized inflammation has not been fully elucidated. We examined the effects of an anti-receptor activator of nuclear factor-κB ligand (RANKL) antibody and the bisphosphonate zoledronic acid (ZOL) on periapical lesion (PL) development in mice.

METHODS

Dental pulps of lower first molars in mice were removed, with the exposed dental pulp chambers left open to the oral environment to induce apical periodontitis. An anti-RANKL antibody or ZOL was intraperitoneally injected once per week until postoperative day 21, then micro-computed tomography and histological analyses were performed.

RESULTS

PL enlargement was inhibited by both the anti-RANKL antibody and ZOL in a dose-dependent manner and reduction of inflammatory cell infiltration in apical tissues inhibited periapical bone resorption. The anti-RANKL antibody decreased the number of osteoclasts in periapical tissues, while ZOL suppressed periapical bone resorption with osteoclast numbers maintained. While administration of each of the anti-resorptive drugs increased femoral bone mass, femoral bone mineral density in the PL group was lower as compared to the sham-operated group.

CONCLUSIONS

These results suggest that an anti-resorptive drug administered systemically is distributed to areas of local inflammation in the jaw and can prevent PL development.

Accuracy of radiographic pixel linear analysis in detecting bone loss in periodontal disease: Study in diabetic rats

Introduction

Periodontitis, a complex infectious disease that may lead to irreversible loss of periodontium, is considered a predisposing agent for developing insulin resistance due to the release of inflammatory mediators, showing a bilateral relationship with diabetes mellitus. The investigation of periodontal disease requires a clinical approach and complete intraoral radiographs, even with increasing concerns about radiation exposure. Thus, this study assesses pixel linear analysis accuracy using digital radiography via Digora® in detecting alveolar bone destruction in diabetic rats with periodontal disease.

Methodology

40 rats were divided into groups (n = 10): control (C), rats with periodontal disease (PD), experimental diabetic rats (ED), experimental diabetic rats with periodontal disease (ED-PD). Diabetes was induced by streptozotocin and periodontal disease by periodontal ligature. After 30 days, maxillae bone destruction was obtained by linear analysis of vertical bone loss using digital radiography and then assessed by micro-CT and histology. Data were analyzed by ANOVA and Tukey’s test (p < 0.05).

Results

Radiographic, micro-CT and histological analysis presented accurate and similar results. PD and ED-PD groups showed higher bone destruction than C and ED groups (p < 0.05). Moreover, the ED-PD group had higher bone loss than the PD group (p < 0.05).

Conclusion

The pixel linear analysis via digital radiography was an accurate, low-cost alternative in detecting alveolar bone loss in this rat model. Micro-CT and histological analysis may also be used to obtain linear measures to assess and compare periodontal bone destruction in diabetic rats.

X-ray microtomography-based atlas of mouse cranial development

BACKGROUND

X-ray microtomography (μCT) has become an invaluable tool for non-destructive analysis of biological samples in the field of developmental biology. Mouse embryos are a typical model for investigation of human developmental diseases. By obtaining 3D high-resolution scans of the mouse embryo heads, we gain valuable morphological information about the structures prominent in the development of future face, brain, and sensory organs. The development of facial skeleton tracked in these μCT data provides a valuable background for further studies of congenital craniofacial diseases and normal development.

FINDINGS

In this work, reusable tomographic data from 7 full 3D scans of mouse embryo heads are presented and made publicly available. The ages of these embryos range from E12.5 to E18.5. The samples were stained by phosphotungstic acid prior to scanning, which greatly enhanced the contrast of various tissues in the reconstructed images and enabled precise segmentation. The images were obtained on a laboratory-based μCT system. Furthermore, we provide manually segmented masks of mesenchymal condensations (for E12.5 and E13.5) and cartilage present in the nasal capsule of the scanned embryos.

CONCLUSION

We present a comprehensive dataset of X-ray 3D computed tomography images of the developing mouse head with high-quality manual segmentation masks of cartilaginous nasal capsules. The provided μCT images can be used for studying any other major structure within the developing mouse heads. The high quality of the manually segmented models of nasal capsules may be instrumental to understanding the complex process of the development of the face in a mouse model.

Histologic, Radiographic, and Micro-Computed Tomography Evaluation of Experimentally Enlarged Root Apices in Dog Teeth with Apical Periodontitis after Regenerative Treatment

Background

Blood clot (BC) and platelet-rich fibrin (PRF) has been successfully used to biologically treat immature roots. It is nowadays considered the treatment of choice.

Objective

This study aimed to determine the ability of PRF and BC scaffolds to enhance regeneration of disinfected root canals and healing of apical periodontitis within experimentally enlarged canal apices of dog teeth.

Methods

Forty-eight root canals in 28 mandibular premolars from 4 healthy adult dogs were experimentally infected and developed apical periodontitis. The teeth were randomly divided into a control (untreated) group, a disinfection only group, a group that received disinfection and a BC scaffold, and a group that received disinfection and a BC + PRF scaffold. Healing of the apical radiolucency was evaluated by conventional radiography, micro-computed tomography, and histology after 3 months. The data were analyzed by χ² test.

Results

Healing was achieved in 49% of roots as seen on radiograph and 43% as seen on micro-computed tomography. There was no significant between-group difference in the presence or absence of periapical radiolucency in the mesial roots when seen on conventional images (P = 0.255), but there was a significant difference in the distal roots (P = 0.001); similarly, on micro-computed tomography, there was no significant between-group difference in the mesial roots (P = 0.174) but there was a significant difference in the distal roots (P = 0.001). Histologically, apical closure was significantly not greater in the BC + PRF scaffold group than in the BC scaffold group (P = 0.001).

Conclusions

A mix of BC + PRF scaffold did not improve tissue regeneration in experimentally enlarged dog teeth. (Curr Ther Res Clin Exp. 2021; 82:XXX–XXX) © 2021 Elsevier HS Journals, Inc.

Immunomodulation Mediated by Azithromycin in Experimental Periapical Inflammation

INTRODUCTION

The purpose of the present study was to compare the immunomodulatory effect of azithromycin (AZM), ampicillin (AMP), amoxicillin (AMX), and clindamycin (CLI) in vitro and AZM on preexisting periapical lesions compared with AMP.

METHODS

The susceptibility of 4 common human endodontic pathogens (Parvimonas micra, Streptococcus intermedius, Prevotella intermedia, and Fusobacterium nucleatum) to AZM, AMP, AMX, and CLI was confirmed by agar disk diffusion assay. Preexisting periapical lesions in C57BL/6J mice were treated with AZM, AMP, or phosphate-buffered saline (PBS). Periapical bone healing and the pattern of inflammatory cell infiltration were evaluated after a 10-day treatment by micro-computed tomographic and histology, respectively. Besides, the effect of antibiotics in pathogen-stimulated nuclear factor kappa B activation and the production of interleukin 1 alpha and tumor necrosis factor alpha was assessed in vitro by luciferase assay and enzyme-linked immunosorbent assay.

RESULTS

All examined endodontic pathogens were susceptible to AZM, AMP, AMX, and CLI. AZM significantly attenuated periapical bone loss versus PBS. PBS resulted in widely diffused infiltration of mixed inflammatory cells. By contrast, AZM brought about localized infiltration of neutrophils and M2 macrophages and advanced fibrosis. Although the effect of AMP on bone was uncertain, inflammatory cell infiltration was considerably milder than PBS. However, most macrophages observed seemed to be M1 macrophages. AZM suppressed pathogen-stimulated nuclear factor kappa B activation and cytokine production, whereas AMP, AMX, and CLI reduced only cytokine production moderately.

CONCLUSIONS

This study showed that AZM led to the resolution of preexisting experimental periapical inflammation. Our data provide a perspective on host response in antibiotic selection for endodontic treatment. However, well-designed clinical trials are necessary to better elucidate the benefits of AZM as an adjunctive therapy for endodontic treatment when antibiotic therapy is recommended. Although both AZM and AMP were effective on preexisting periapical lesions, AZM led to advanced wound healing, probably depending on its immunomodulatory effect.

Effects of alcohol and nicotine consumption on the development of apical periodontitis in rats: a correlative micro-computed tomographic, histological and immunohistochemical study

AIM

To evaluate the effects of alcohol and nicotine, when used alone or simultaneously, in the development of apical periodontitis induced in rats, using a correlative analytic approach with micro-CT, histological and immunohistochemical analysis.

METHODOLOGY

Twenty-eight male Wistar rats were arranged into four groups: Control, Nicotine, Alcohol and Alcohol + Nicotine. The alcohol groups were exposed to self-administration of a 25% alcohol solution, whilst the other groups drunk only filtered water. The nicotine groups received daily intraperitoneal injections of a solution with 0.19 μL of nicotine per mL, whilst the other groups received saline solution. The pulps of the left mandibular first molars were exposed for 28 days to induce periapical lesions. Throughout the experiment, drug administration was maintained, and the animals had their weight and solid and liquid consumption measured. After euthanasia, the mandibles were removed and the area, volume and major diameter of the periapical lesions were measured using micro-computed tomography images. The samples were submitted to histopathological evaluation and immunohistochemistry for RANKL and PTHrP. Statistical analysis was undertaken with a significance level of 5%. Nonparametric data were analysed using the Kruskal-Wallis test followed by Dunn's test, whilst one-way anova followed by Tukey's test was performed for parametric data.

RESULTS

The alcohol groups had lower solid and liquid consumption and gained less weight when compared to the nonalcohol groups (P < 0.05). The Alcohol + Nicotine group had lesions with significantly larger volume and area when compared to the other groups (P < 0.05), whilst the Alcohol or Nicotine groups had significantly larger lesions than the control group (P < 0.05). There was no significant difference in the largest diameter of the lesions amongst groups (P > 0.05). The experimental groups had greater inflammatory response scores than the control group (P < 0.05), and the representative samples had more pronounced immunoreaction against RANKL and PTHrP antibodies.

CONCLUSIONS

Alcohol and nicotine consumption exacerbated the inflammatory response and the development of periradicular lesions in rats. The association of both substances enhanced their harmful effects.

Association between Increased Inducible Costimulator/Inducible Costimulator Ligand Expression with Bone Destruction in Apical Periodontitis

INTRODUCTION

The aim was to assess the association of inducible costimulator (ICOS) and ICOS ligand with bone destruction in apical periodontitis (AP).

METHODS

Specimens from patients presenting with AP were obtained during apicoectomy and subjected to histopathologic analysis and molecular assessment of ICOS/ICOS ligand. In addition, the experimental AP was induced by exposing the pulp of first mandibular molars of rats. Histologic and radiographic examinations were performed to validate the periapical lesions. The immunolocalization and messenger RNA expression of ICOS/ICOS ligand were evaluated by immunofluorescence staining and quantitative real-time polymerase chain reaction. The osteoclastic activities in periapical lesions, including the lesion size and the expression of tartrate-resistant acid phosphatase and the receptor activator of nuclear factor kappa B ligand, were recorded and followed by correlation analysis with ICOS/ICOS ligand expression.

RESULTS

In excisional specimens from AP patients, a significantly increased expression of ICOS/ICOS ligand was found compared with the healthy control. In the experimental AP samples, the expression of ICOS/ICOS ligand, tartrate-resistant acid phosphatase, and receptor activator of nuclear factor kappa B ligand was significantly elevated in inflamed periapical tissues (AP group) when compared with the healthy control. The number of ICOS⁺/ICOS ligand⁺ cells was highly correlated with the periapical lesion size (r = 0.892, P < .01 and r = 0.930, P < .01, respectively).

CONCLUSIONS

The increased expression of ICOS/ICOS ligand in periapical lesions was associated with the inflammatory infiltration and alveolar bone destruction of AP.

Micro-computed tomography and histology to explore internal morphology in decapod larvae

Traditionally, the internal morphology of crustacean larvae has been studied using destructive techniques such as dissection and microscopy. The present study combines advances in micro-computed tomography (micro-CT) and histology to study the internal morphology of decapod larvae, using the common spider crab (Maja brachydactyla Balss, 1922) as a model and resolving the individual limitations of these techniques. The synergy of micro-CT and histology allows the organs to be easily identified, revealing simultaneously the gross morphology (shape, size, and location) and histological organization (tissue arrangement and cell identification). Micro-CT shows mainly the exoskeleton, musculature, digestive and nervous systems, and secondarily the circulatory and respiratory systems, while histology distinguishes several cell types and confirms the organ identity. Micro-CT resolves a discrepancy in the literature regarding the nervous system of crab larvae. The major changes occur in the metamorphosis to the megalopa stage, specifically the formation of the gastric mill, the shortening of the abdominal nerve cord, the curving of the abdomen beneath the cephalothorax, and the development of functional pereiopods, pleopods, and lamellate gills. The combination of micro-CT and histology provides better results than either one alone.

Comparison of ground sections, paraffin sections and micro-CT imaging of bone from the epiphysis of the porcine femur for morphometric evaluation

The aim of this study was to compare data on the volume fraction of bone and the thickness of the cortical compact bone acquired during microcomputed tomography (micro-CT) analysis with data acquired from identical samples using stereological analysis of either decalcified paraffin sections or ground sections. Additionally, we aimed to compare adjacent tissue samples taken from the major trochanter of the porcine femur to map the basic biological variability of trabecular bone. Fifteen pairs of adjacent tissue blocks were removed from the major trochanter of the proximal epiphyses of porcine femurs (female pigs aged 24-39 months, weight=59.16±8.15kg). In each sample, the volume of the cortical compact bone, the volume of the trabecular bone, and the thickness of the cortical compact bone was assessed using micro-CT. Afterwards, half of the samples were decalcified and processed using paraffin histological sections. Another half was processed into ground sections. The volume and thickness of bone was assessed in histological sections using stereological techniques. There were no significant differences in the bone volumes and thicknesses measured by micro-CT and the corresponding values quantified in decalcified sections. Similarly, there were no differences between the results from micro-CT and the analysis of the corresponding ground sections. Histomorphometric studies based on relatively low numbers of undecalcified ground sections or demineralized paraffin sections of bone yield data on bone volume and the thickness of cortical compact bone that is comparable with three-dimensional micro-CT examination. The pilot data on the variability of cortical compact bone and trabecular bone volumes in the porcine major trochanter provided in this study aim for planning experiments in the field of bone healing and implantology.

Activation of hypoxia-inducible factor 1 attenuates periapical inflammation and bone loss

Hypoxia (low oxygen level) is an important feature during infections and affects the host defence mechanisms. The host has evolved specific responses to address hypoxia, which are strongly dependent on the activation of hypoxia-inducible factor 1 (HIF-1). Hypoxia interferes degradation of HIF-1 alpha subunit (HIF-1α), leading to stabilisation of HIF-1α, heterodimerization with HIF-1 beta subunit (HIF-1β) and subsequent activation of HIF-1 pathway. Apical periodontitis (periapical lesion) is a consequence of endodontic infection and ultimately results in destruction of tooth-supporting tissue, including alveolar bone. Thus far, the role of HIF-1 in periapical lesions has not been systematically examined. In the present study, we determined the role of HIF-1 in a well-characterised mouse periapical lesion model using two HIF-1α-activating strategies, dimethyloxalylglycine (DMOG) and adenovirus-induced constitutively active HIF-1α (CA-HIF1A). Both DMOG and CA-HIF1A attenuated periapical inflammation and tissue destruction. The attenuation in vivo was associated with downregulation of nuclear factor-κappa B (NF-κB) and osteoclastic gene expressions. These two agents also suppressed NF-κB activation and subsequent production of proinflammatory cytokines by macrophages. Furthermore, activation of HIF-1α by DMOG specifically suppressed lipopolysaccharide-stimulated macrophage differentiation into M1 cells, increasing the ratio of M2 macrophages against M1 cells. Taken together, our data indicated that activation of HIF-1 plays a protective role in the development of apical periodontitis via downregulation of NF-κB, proinflammatory cytokines, M1 macrophages and osteoclastogenesis.

Radiographic and micro-computed tomography classification of root canal morphology and dentin thickness of mandibular incisors

Context:

Root canal anatomy is evaluated using different methodologies.

Aims:

The aim of this study is to evaluate and classify root canal morphology and dentin thicknesses (DT), comparing radiographic and micro-computed tomography (CT) analysis.

Materials and Methods:

Canal diameter and DT of mandibular incisors (n = 520) were evaluated using digital radiographs in buccolingual (BL) and mesiodistal (MD) directions. The diameter ratio (DR) BL/MD was classified: flattened (FL, DR >4); oval (OV, 2≤ DR ≥4); rounded (RN, 1.1< DR >2); round (RO, 0.9≤ DR ≥1.1); and with BL flatness (BL, DR <0.9). OV (n = 110) were subjected to micro-CT. DT and DR were evaluated at 3, 6, and 9 mm. ANOVA, Tukey, and paired Wilcoxon tests (P < 0.05) were used.

Results:

Radiographic classification was 23.3% FL, 41.3% OV, 27.3% RN, 4.5% RO, and 3.6% BL. DT was similar. Radiographic DT at 3 and 9 mm was greater than micro-CT (P < 0.05) and was similar at 6 mm (P > 0.05). DR differed between the analyses. Oval canals were predominant at all levels radiographically and at 9 and 6 mm in micro-CT analysis, with greater variation at 3 mm.

Conclusion:

Oval root canals are predominant in mandibular incisors at 9 mm. Radiographic DT is larger than observed in micro-CT at 3 and 9 mm, and the classification differed in each root level. The classification at 9 mm is indicated.

Decreased Expression of Semaphorin3A/Neuropilin-1 Signaling Axis in Apical Periodontitis

Apical periodontitis (AP) is a chronic infection of endodontic origin accompanied with bone destruction around the apical region. Semaphorin3A (Sema3A) and neuropilin-1 (Nrp1) are regarded as a pair of immune regulators in bone metabolism. In this study, we firstly investigated the expression pattern of Sema3A/Nrp1 in apical periodontitis and its correlation with bone destruction. Using rat animal model, we analysed the level of mandibular bone destruction and the expression of Sema3A/Nrp1 on days 0, 7, 14, 21, 28, and 35 after pulp exposure. In addition, clinical samples from apical periodontitis patients were obtained to analyse the expression of Sema3A/Nrp1. These results indicated that the bone destruction level expanded from days 7 to 35. The number of positive cells and level of mRNA expression of Sema3A/Nrp1 were significantly decreased from days 7 to 35, with a negative correlation with bone destruction. Moreover, expression of Sema3A/Nrp1 in the AP group was reduced compared to the control group of clinical samples. In conclusion, decreased expression of Sema3A/Nrp1 was observed in periapical lesions and is potentially involved in the bone resorption of the periapical area, suggesting that Sema3A/Nrp1 may contribute to the pathological development of apical periodontitis.

5-Lipoxygenase Knockout Aggravated Apical Periodontitis in a Murine Model

5-Lipoxygenase (5-LO) plays a vital role in the host innate immune response, including bacteria-induced inflammation. Apical periodontitis (AP) is due to immune disorders caused by imbalances between bacterial invasion and subsequent host defense response. In this work, we investigated the role of 5-lipoxygenase in AP by using 5- lo knockout mice (5- lo-/- mice). Results showed that 5- lo-/- mice had greater periapical bone loss and more osteoclasts positive for tartrate-resistant acid phosphatase staining than did wild-type mice, as determined by micro-computed tomography and histologic staining. The inflammation- and osteoclastogenesis-related factors IL-1β, TNF-α, RANK, and RANKL were also significantly elevated in 5- lo-/- mice, whereas osteoprotegerin was reduced. Furthermore, peritoneal macrophages from 5- lo-/- mice revealed an obviously impaired ability to phagocytose the AP pathogenic bacteria Fusobacterium nucleatum. In vivo experiments confirmed that 5- lo knockout led to decreased macrophage recruitment and increased F. nucleatum infection around the periapical area due to decreased leukotriene B₄ and LXA4 production. All these results showed that 5- lo knockout impaired the host innate immune system to promote the release of bone resorption-related factors. Therefore, 5- lo deficiency aggravated AP in an experimental murine AP model.

Capsaicin-sensitive Innervation Modulates the Development of Apical Periodontitis

INTRODUCTION

Nociceptive neurons play a critical role in the detection of stimuli evoking actual or potential tissue injury. In addition, they are involved in neurogenic inflammation by the peripheral release of neuropeptides such as calcitonin gene-related peptide (CGRP). The dental pulp and periradicular tissues are innervated by capsaicin-sensitive neurons known to release CGRP. However, the role of these capsaicin-sensitive neurons in the development of apical periodontitis is largely unknown. The aim of this study was to evaluate the contribution of peptidergic neurons to the development of apical periodontitis.

METHODS

Neonatal Sprague-Dawley rats were injected with vehicle (control group) or a single subcutaneous capsaicin dose to cause the selective ablation of peptidergic neurons (neonatal capsaicin group). Ablation of capsaicin-sensitive neurons was verified with confocal microscopy, capsaicin-induced eye-wipe nocifensive behavior test, and by measurement of immunoreactive CGRP levels in the dental pulp. Five weeks after ablation, standardized pulp exposures were made in the mandibular left first molars. Mandibles were harvested at 7, 14, 21, and 28 days after pulp exposure and imaged with micro-computed tomography (μCT) to quantify apical lesion volume. Data were analyzed by using 2-way ANOVA analysis with Bonferroni post hoc test.

RESULTS

Rats in the control group displayed a robust capsaicin-induced nocifensive behavior, which was nearly abolished in the neonatal capsaicin group. In addition, the neonatal capsaicin group showed a significant depletion of susceptible neurons and CGRP in the dental pulp compared with control. Importantly, micro-computed tomography analysis showed larger periradicular lesions at 7 and 14 days after pulp exposure in the neonatal capsaicin group when compared with control.

CONCLUSIONS

Results identify a protective role for capsaicin-sensitive neurons in the initial phase of apical periodontitis. Thus, interventions or disorders that alter activity of capsaicin-sensitive fibers are likely to alter the development of apical periodontitis.

Micro-CT evaluation of several glide path techniques and ProTaper Next shaping outcomes in maxillary first molar curved canals

AIM

To evaluate the ability of ProGlider instruments, PathFiles and K-files to maintain canal anatomy during glide path preparation using X-ray computed micro-tomography (micro-CT).

METHODOLOGY

Forty-five extracted maxillary first permanent molars were selected. Mesio-buccal canals were randomly assigned (n = 15) to manual K-file, PathFile or ProGlider groups for glide path preparation. Irrigation was achieved with 5% NaOCl and 10% EDTA. After glide path preparation, each canal was shaped with ProTaper Next X1 and X2 to working length. Specimens were scanned (isotropic voxel size 9.1 μm) for matching volumes and surface areas and post-treatment analyses. Canal volume, surface area, centroid shift, canal geometry variation through ratio of diameter ratios and ratio of cross-sectional areas were assessed in the apical and coronal levels and at the point of maximum canal curvature. One-way factorial anovas were used to evaluate the significance of instrument in the various canal regions.

RESULTS

Post-glide path analysis revealed that instrument factor was significant at the apical level for both the ratio of diameter ratios and the ratio of cross-sectional areas (P < 0.001), with an improved maintenance of root canal geometry by ProGlider and PathFile. At the coronal level and point of maximum canal curvature, ProGlider demonstrated a tendency to pre-flare the root canal compared with K-file and PathFile. PathFile and ProGlider demonstrated a significantly lower centroid shift compared with K-file at the apical level (P = 0.023). Post-shaping analysis demonstrated a more centred preparation of ProGlider, compared with PathFile and K-files, with no significant differences for other parameters.

CONCLUSIONS

Use of ProGlider instruments led to less canal transportation than PathFiles and K-files.

Use of micro-computed tomography for the assessment of periapical lesions in small rodents: a systematic review

This systematic review aimed to evaluate the literature on the acquisition-, reconstruction- and analysis parameters of micro-computed tomography (micro-CT) for the assessment of periapical lesions in rats and mice, and to illustrate the effect of variation in these parameters. The PubMed database was searched from 2000 to January 2015 (English-language publications) for reports on the use of micro-CT to evaluate periapical lesions in rats and mice. QUADAS criteria were used to rate the quality of the studies. To illustrate the effect of variations in acquisition-, reconstruction-, and analysis parameters on images of periapical lesions, micro-CT examination of two hemi-mandibles of mice, with periapical lesions around the first molar was undertaken. Twenty-one studies were identified, which analysed periapical lesions in rats or mice using micro-CT. According to the QUADAS, no study was classified as high-, seven were classified as moderate-, and 14 as low quality. The effect of variation in parameters was that voxel size may interfere with image sharpness, reconstruction may interfere with image sharpness and contrast, and inadequate plane orientation may alter the size of the periapical lesion. Nonpersonalized ROIs resulted in areas that were not part of the periapical lesion. Changing the limits of the threshold for bone-tissue visualization increased lesion size. There is no defined protocol for acquiring and analysing micro-CT images of periapical lesions in rats and mice. Furthermore, acquisition-, reconstruction- and analysis parameters are not adequately explained, which may compromise the scientific impact of the studies.

Genistein suppresses Prevotella intermedia lipopolysaccharide-induced inflammatory response in macrophages and attenuates alveolar bone loss in ligature-induced periodontitis

OBJECTIVE

Genistein is a major isoflavone subclass of flavonoids found in soybean and a potent tyrosine kinase inhibitor. The present study aimed to assess the effect of genistein on the production of proinflammatory mediators in murine macrophages stimulated with lipopolysaccharide (LPS) isolated from Prevotella intermedia, a pathogen associated with different forms of periodontal disease, and to evaluate its possible influence on alveolar bone loss in ligature-induced periodontitis using micro-computed tomography (micro-CT) analysis as well.

DESIGN

LPS was isolated from P. intermedia ATCC 25611 by using the standard hot phenol-water method. Culture supernatants were analyzed for nitric oxide (NO) and interleukin-6 (IL-6). Inducible NO synthase (iNOS) protein expression was evaluated by immunoblot analysis. Real-time PCR was carried out to measure iNOS and IL-6 mRNA expression. In addition, effect of genistein on alveolar bone loss was evaluated in a rat model of experimental periodontitis using micro-CT analysis.

RESULTS

Genistein significantly attenuated P. intermedia LPS-induced production of iNOS-derived NO and IL-6 with attendant decrease in their mRNA expression in RAW264.7 cells. In addition, when genistein was administered to rats, decreases in alveolar bone height and bone volume fraction induced by ligature placement were significantly inhibited. Genistein administration also prevented ligature-induced alterations in the microstructural parameters of trabecular bone, including trabecular thickness, trabecular separation, bone mineral density and structure model index.

CONCLUSIONS

While additional studies are required, we suggest that genistein could be utilized for the therapy of human periodontitis in the future.

Quantitative analysis of bone and soft tissue by micro-computed tomography: applications to ex vivo and in vivo studies

Micro-computed tomography (micro-CT) is a high-resolution imaging modality that is capable of analysing bone structure with a voxel size on the order of 10 μm. With the development of in vivo micro-CT, where disease progression and treatment can be monitored in a living animal over a period of time, this modality has become a standard tool for preclinical assessment of bone architecture during disease progression and treatment. For meaningful comparison between micro-CT studies, it is essential that the same parameters for data acquisition and analysis methods be used. This protocol outlines the common procedures that are currently used for sample preparation, scanning, reconstruction and analysis in micro-CT studies. Scan and analysis methods for trabecular and cortical bone are covered for the femur, tibia, vertebra and the full neonate body of small rodents. The analysis procedures using the software provided by ScancoMedical and Bruker are discussed, and the routinely used bone architectural parameters are outlined. This protocol also provides a section dedicated to in vivo scanning and analysis, which covers the topics of anaesthesia, radiation dose and image registration. Because of the expanding research using micro-CT to study other skeletal sites, as well as soft tissues, we also provide a review of current techniques to examine the skull and mandible, adipose tissue, vasculature, tumour severity and cartilage. Lists of recommended further reading and literature references are included to provide the reader with more detail on the methods described.

Histochemical localization of Dickkopf-1 in induced rat periapical lesions

INTRODUCTION

The purpose of this study was to evaluate the expression of Dickkopf-1 (DKK-1), a secreted antagonist of the Wnt (wingless)/beta-catenin signaling pathway, during the development of periapical lesions in rats.

METHODS

Periapical lesions were induced in Wistar rats by occlusal exposure of the pulp of their mandibular first molars. The animals were sacrificed randomly at 0, 7, 14, 21, and 28 day after pulpal exposure. Jaws containing the first molar were obtained and routinely prepared for histologic, immunohistochemical, and enzyme histochemical double immunofluorescence analyses. Data were analyzed using 1-way analysis of variance and Pearson correlation test.

RESULTS

The expansion of the area of periapical lesions was visible from days 7-21 and slowed down thereafter. A few DKK-1- and receptor activator of nuclear factor kappa B ligand (RANKL)-positive cells and osteoclasts were observed on day 7. All positive samples peaked in number on day 14. The expression levels of DKK-1 and RANKL and the number of osteoclasts decreased on days 21 and 28. DKK-1 expression was positively correlated with RANKL expression and osteoclast number from days 7-28.

CONCLUSIONS

DKK-1 expression was up-regulated during periapical lesion development. DKK-1 may be associated with the inflammatory response and bone resorption in periapical lesions.

Kinetics of glycogen synthase kinase (GSK)3β and phosphorylated GSK3β (Ser 9) expression in experimentally induced periapical lesions

AIM

To investigate the kinetics of GSK3β and p-GSK3β (Ser 9) expression in experimentally induced rat periapical lesions and to explore their possible functions in the pathogenesis of periapical lesions.

METHODOLOGY

Periapical lesions were established in Wistar rats by occlusal pulp exposure in mandibular first molar teeth. The animals were killed on days 0, 7, 14, 21 and 28. Micro-computed tomographic, histological and enzyme histochemical analyses were performed to detect the progression of periapical lesions. Immunohistochemistry, double-dye immunofluorescence and Western blot were performed to determine the expression of GSK3β and p-GSK3β (Ser 9) in periapical tissues.

RESULTS

From day 0 to day 28, the lesion volume and area gradually expanded, and the GSK3β-positive cells gradually ascended. A few p-GSK3β (Ser 9)-positive cells and osteoclasts appeared on day 7 and then climaxed on day 14. The numbers then simultaneously decreased from day 21 to day 28. Western blot analysis revealed that p-GSK3β (Ser 9) and GSK3β proteins were expressed at all time-points. The positive cells and protein expression ratio of p-GSK3β (Ser 9) against GSK3β increased from day 0 to day 14 and then decreased from day 14 to day 28. Finally, double-dye immunofluorescence assay revealed that p-GSK3β (Ser 9)-positive and RANKL-positive cells were co-localized around periapical lesions on days 14 and 28.

CONCLUSIONS

GSK3β and p-GSK3β (Ser 9) can be observed and may be involved in alveolar bone resorption and inflammatory response in periapical lesions, as well as associated with periapical lesion pathogenesis.

Limitations of global morphometry in predicting trabecular bone failure

Efforts in finding independent measures for accurate and reliable prediction of trabecular bone failure have led to the development of a number of morphometric indices characterizing trabecular bone microstructure. Generally, these indices assume a high homogeneity within the bone specimen. However, in the present study we found that the variance in bone volume fraction (BV/TV) in a single bone specimen can be relatively large (CV = 9.07% to 28.23%). To assess the limitations of morphometric indices in the prediction of bone failure for specimens in which the assumption of homogeneity is not met, we harvested 13 cadaveric samples from a single human spine. We tested these cylindrical samples using image-guided failure assessment (IGFA), a technique combining stepwise microcompression and time-lapsed micro-computed tomography (µCT). Additionally, we computed morphometric indices for the entire sample as well as for 10 equal subregions along the anatomical axis. We found that ultimate strength was equally well predicted by BV/TV of the entire sample (R(2)  = 0.55) and BV/TV of the weakest subregion (R(2)  = 0.57). Investigating three-dimensional animations of structural bone failure, we showed that two main failure mechanisms determine the competence of trabecular bone samples; in homogeneous, isotropic trabecular bone samples, competence is determined by a whole set of trabecular elements, whereas in inhomogeneous, anisotropic bone samples a single or a missing trabeculae may induce catastrophic failure. The latter failure mechanism cannot be described by conventional morphometry, indicating the need for novel morphometric indices also applicable to the prediction of failure in inhomogeneous bone samples.

Performance of RaCe Instrumentation System in Curved Root Canals: A Comprehensive Analysis by Three Study Methods

In this study, curved maxillary molar root canals were instrumented with RaCe rotary system to evaluate: 1. the occurrence of canal transportation using a radiographic platform; 2. the action of the instruments on the dentin walls, centering ability and canal enlargement by analysis of digital images; and the percentage of regular dentin surfaces and debris within the canal by histological analysis. Ten mesiobuccal roots of extracted human maxillary molars were embedded in acrylic resin and sectioned at the middle and apical thirds. Root canal shaping was performed using the RaCe rotary system at 250 rpm and 1 Ncm torque. Each instrument set was used five times according to a crown-down technique in the following sequence: 40/0.10, 35/0.08, 25/0.06, 25/0.04, 25/0.02 (working length - WL), 30/0.02 (WL) and 35/0.02 (WL). Each instrument was inserted until resistance was felt and then pulled back, followed by brushing movements towards all canal walls. Each specimen was assessed by three study methods: radiographic platform, digitized image assessment and histological analysis. The radiographic platform showed lack of apical transportation. No statistically significant difference (Wilcoxon test, p>0.05) was found between the middle and apical thirds regarding instrument action on dentin walls, centering ability, area of root canal enlargement, percentage of regular dentin surfaces and debris within the root canal. It may be concluded that RaCe system is a suitable method for the preparation of curved root canals, regarding the maintenance of root canal original path, action on dentin walls, canal enlargement and removal of debris from the root canal lumen.

RNA interference-mediated silencing of Atp6i prevents both periapical bone erosion and inflammation in the mouse model of endodontic disease

Dental caries is one of the most prevalent infectious diseases in the United States, affecting approximately 80% of children and the majority of adults. Dental caries may lead to endodontic disease, where the bacterial infection progresses to the root canal system of the tooth, leading to periapical inflammation, bone erosion, severe pain, and tooth loss. Periapical inflammation may also exacerbate inflammation in other parts of the body. Although conventional clinical therapies for this disease are successful in approximately 80% of cases, there is still an urgent need for increased efficacy of treatment. In this study, we applied a novel gene-therapeutic approach using recombinant adeno-associated virus (AAV)-mediated Atp6i RNA interference (RNAi) knockdown of Atp6i/TIRC7 gene expression to simultaneously target periapical bone resorption and periapical inflammation. We found that Atp6i inhibition impaired osteoclast function in vitro and in vivo and decreased the number of T cells in the periapical lesion. Notably, AAV-mediated Atp6i/TIRC7 knockdown gene therapy reduced bacterial infection-stimulated bone resorption by 80% in the mouse model of endodontic disease. Importantly, Atp6i(+/-) mice with haploinsufficiency of Atp6i exhibited protection similar to that in mice with bacterial infection-stimulated bone erosion and periapical inflammation, which confirms the potential therapeutic effect of AAV-small hairpin RNA (shRNA)-Atp6i/TIRC7. Our results demonstrate that AAV-mediated Atp6i/TIRC7 knockdown in periapical tissues can inhibit endodontic disease development, bone resorption, and inflammation, indicating for the first time that this potential gene therapy may significantly improve the health of those who suffer from endodontic disease.

Quality of root fillings performed with two root filling techniques. An in vitro study using micro-CT

Objective.

The aim of this study was to compare the presence of voids in root fillings performed in oval and ribbon-shaped canals with two root filling techniques, lateral compaction technique (LCT) or hybrid technique (HT), a combination of a gutta-percha masterpoint and thermoplastic gutta-percha. Furthermore, the obturation time for the two techniques was evaluated.

Materials and methods.

Sixty-seven roots with oval and ribbon-shaped canals were prepared using Profile Ni-Ti rotary files. After preparation, the roots were randomly allocated to two groups according to root filling technique. All roots were filled with AH plus and gutta-percha. Group 1 was filled using LCT (n = 34) and group 2 was filled using HT (n = 33). The obturation time was measured in 30 cases evenly distributed between the two techniques. Voids in relation to the root canal fillings were assessed using cross-section images from Micro-computed Tomography scans.

Results.

All root canal fillings had voids. Permutation test showed no statistically significant difference between the two root filling techniques in relation to presence of voids (p = 0.092). A statistically significant difference in obturation time between the two techniques was found (p < 0.001).

Conclusion.

The present study found no statistically significant difference in percentage of voids between two root filling techniques. A 40% reduction in obturation time was found for the HT compared to the LCT.

In vivo degradation performance of micro-arc-oxidized magnesium implants: a micro-CT study in rats

Biodegradable Mg alloys are of great interest for osteosynthetic applications because they do not require surgical removal after they have served their purpose. In this study, fast-degrading ZX50 Mg-based implants were surface-treated by micro-arc oxidation (MAO), to alter the initial degradation, and implanted along with untreated ZX50 controls in the femoral legs of 20 male Sprague-Dawley rats. Their degradation was monitored by microfocus computed tomography (μCT) over a total observation period of 24weeks, and histological analysis was performed after 4, 12 and 24weeks. While the MAO-treated samples showed almost no corrosion in the first week, they revealed an accelerated degradation rate after the third week, even faster than that of the untreated ZX50 implants. This increase in degradation rate can be explained by an increase in the surface-area-to-volume ratio of MAO-treated implants, which degrade inhomogeneously via localized corrosion attacks. The histological analyses show that the initially improved corrosion resistance of the MAO implants has a positive effect on bone and tissue response: The reduced hydrogen evolution (due to reduced corrosion) makes possible increased osteoblast apposition from the very beginning, thus generating a stable bone-implant interface. As such, MAO treatment appears to be very interesting for osteosynthetic implant applications, as it delays implant degradation immediately after implantation, enhances fracture stabilization, minimizes the burden on the postoperatively irritated surrounding tissue and generates good bone-implant connections, followed by accelerated degradation in the later stage of bone healing.

Quantifying mineralization using bone mineral density distribution in the mandible

BACKGROUND

Micro-computed tomography is an efficient method for quantifying the density and mineralization of mandibular microarchitecture. Conventional radiomorphometrics such as bone and tissue mineral density are useful in determining the average overall mineral content of a scanned specimen; however, relying solely on these metrics has limitations. Using bone mineral density distribution (BMDD), the complex array of mineralization densities within a bone sample can be portrayed. This information is particularly useful as a computational feature reflective of the rate of bone turnover. We demonstrate the utility of BMDD analyses in the rat mandible and generate a platform for further exploration of mandibular pathology and treatment.

METHODS

Male Sprague-Dawley rats (n = 8) underwent micro-computed tomography, and histogram data were generated from a selected volume of interest. A standard curve was derived for each animal, and reference criteria were defined. An average histogram was produced for the group, and descriptive analyses including the means and SDs are reported for each of the normative metrics.

RESULTS

M(peak) (3444 Hounsfield units [SD, 138]) and M(width) (2221 Hounsfield units [SD, 628]) are 2 metrics demonstrating reproducible parameters of BMDD with minimal variance. A total of 8 valuable metrics quantifying biologically significant events concerning mineralization are reported.

CONCLUSIONS

We quantify the vast wealth of information depicted in the complete spectrum of mineralization established by the BMDD analysis. We demonstrate its potential in delivering mineralization data that encompass and enhance conventional reporting of radiomorphometrics. Moreover, we explore its role and translational potential in craniofacial experimentation.

Pathogenicity of Treponema denticola Wild-Type and Mutant Strain Tested by an Active Mode of Periodontal Infection Using Microinjection

The available passive mode of periodontal infections in mice requires high efficiency of bacterial attachment and invasiveness and is not always suitable to test the pathogenicity of genetically engineered mutant strains. We developed an active mode of oral infection, using microinjection in the marginal gingiva of mice, to test the pathogenicity of a genetically engineered Treponema denticola mutant strain deficient in intermediate-like filaments, compared to the wild-type strain. This targeted mode of infection inoculates the bacterial strain to be tested directly at a lesion site (needle entry point) located at the future periodontal lesion site. The efficiency of T. denticola wild-type strain to elicit bone loss contrasted with the lack of pathogenicity of the intermediate-like filament deficient mutant strain in comparison to the sham infection. The periodontal microinjection oral model in mice can be used for a variety of applications complementary to the passive mode of periodontal infection in context of pathogenicity testing.

Interconnectivity analysis of supercritical CO₂-foamed scaffolds

This paper describes a computer algorithm for the determination of the interconnectivity of the pore space inside scaffolds used for tissue engineering. To validate the algorithm and its computer implementation, the algorithm was applied to a computer-generated scaffold consisting of a set of overlapping spherical pores, for which the interconnectivity was calculated exactly. The algorithm was then applied to micro-computed X-ray tomography images of supercritical CO(2)-foamed scaffolds made from poly(lactic-co-glycolic acid) (PLGA), whereby the effect of using different weight average molecular weight polymer on the interconnectivity was investigated.

Protective effect of metformin on periapical lesions in rats by decreasing the ratio of receptor activator of nuclear factor kappa B ligand/osteoprotegerin

INTRODUCTION

Metformin, one of the antihyperglycemic agents commonly used for the treatment of type 2 diabetes, was shown to inhibit osteoclast formation. The current study aimed to investigate the effects of systemically administered metformin on alveolar bone resorption and on the ratio of receptor activator of nuclear factor kappa B ligand/osteoprotegerin (RANKL/OPG) in rats subjected to experimental periapical lesions.

METHODS

Forty adult male Wistar rats were divided equally into control and experimental groups, and the pulp chambers of their mandibular first molars were exposed to the oral environment to induce periapical lesions. The experimental group received daily intramuscular injections of metformin at 40 mg/kg doses, whereas the control group received only the saline vehicle. The injections were initiated 1 day before the periapical lesion induction and then were continued daily throughout the entire experimental period. Two or 4 weeks after pulp exposure, the rats were killed, and the mandibles were prepared for histologic analysis, enzyme histochemistry, immunohistochemistry, and immunofluorescence.

RESULTS

The number of RANKL-positive and tartrate-resistant acid phosphatase (TRAP)-positive cells in the metformin-treated groups decreased on day 14, whereas the number of OPG-positive cells increased on day 28. The periapical bone loss area in the metformin-treated group significantly decreased on day 28 compared with the control group.

CONCLUSIONS

Metformin inhibits the periapical lesions possibly by lowering the RANKL/OPG ratio, subsequently reducing the number of osteoclasts and bone resorption areas.

Magnesium alloys for temporary implants in osteosynthesis: in vivo studies of their degradation and interaction with bone

This study investigates the bone and tissue response to degrading magnesium pin implants in the growing rat skeleton by continuous in vivo microfocus computed tomography (μCT) monitoring over the entire pin degradation period, with special focus on bone remodeling after implant dissolution. The influence of gas release on tissue performance upon degradation of the magnesium implant is also addressed. Two different magnesium alloys - one fast degrading (ZX50) and one slowly degrading (WZ21) - were used for evaluating the bone response in 32 male Sprague-Dawley rats. After femoral pin implantation μCTs were performed every 4 weeks over the 24 weeks of the study period. ZX50 pins exhibited early degradation and released large hydrogen gas volumes. While considerable callus formation occurred, the bone function was not permanently harmed and the bone recovered unexpectedly quickly after complete pin degradation. WZ21 pins kept their integrity for more than 4 weeks and showed good osteoconductive properties by enhancing bone accumulation at the pin surface. Despite excessive gas formation, the magnesium pins did not harm bone regeneration. At smaller degradation rates, gas evolution remained unproblematic and the magnesium implants showed good biocompatibility. Online μCT monitoring is shown to be suitable for evaluating materials degradation and bone response in vivo, providing continuous information on the implant and tissue performance in the same living animal.

Bone Remodeling in Onlay Beta-Tricalcium Phosphate and Coral Grafts to Rat Calvaria: Microcomputerized Tomography Analysis

This study was conducted to establish the efficiency of microcomputerized tomography (micro-CT) in detection of trabecular bone remodeling of onlay grafts in a rodent calvaria model, and to compare bone remodeling after onlay grafts with beta-tricalcium phosphate (TCP) or coral calcium carbonate. Ten rats received calvarial onlay blocks—5 with TCP and 5 with coral calcium carbonate. The grafts were fixed with a titanium miniplate screw and were covered with a collagen resorbable membrane. Three months after surgery, the calvaria were segmented, and a serial 3-dimensional micro-CT scan of the calvarium and grafted bone block at 16-micrometer resolution was performed. Image analysis software was used to calculate the percentage of newly formed bone from the total block size. Newly formed bone was present adjacent to the calvarium and screw in all specimens. The mean area of newly formed bone of the total block size ranged from 34.67%–38.34% in the TCP blocks, and from 32.41%–34.72% in the coral blocks. In the TCP blocks, bone remodeling was found to be slightly higher than in the coral blocks. Micro-CT appears to be a precise, reproducible, specimen-nondestructive method of analysis of bone formation in onlay block grafts to rat calvaria.

Radiological and histopathological evaluation of experimentally-induced periapical lesion in rats

Objective

This study evaluated experimentally-induced periapical bone loss sites using digital radiographic and histopathologic parameters.

Material and Methods

Twenty-seven Wistar rats were submitted to coronal opening of their mandibular right first molars. They were radiographed at 2, 15 and 30 days after the operative procedure by two digital radiographic storage phosphor plates (Digora^®). The images were analyzed by creating a region of interest at the periapical region of each tooth (ImageJ) and registering the corresponding pixel values. After the sacrifice, the specimens were submitted to microscopic analysis in order to confirm the pulpal and periapical status of the tooth.

Results

There was significant statistically difference between the control and test sides in all the experimental periods regarding the pixel values (two-way ANOVA; p<0.05).

Conclusions

The microscopic analysis proved that a periapical disease development occurred during the experimental periods with an evolution from pulpal necrosis to periapical bone resorption.

Extracting 3D information on bone remodeling in the proximity of titanium implants in SRμCT image volumes

Bone-implant integration is measured in several ways. Traditionally and routinely, 2D histological sections of samples, containing bone and the biomaterial, are stained and analyzed using a light microscope. Such histological section provides detailed cellular information about the bone regeneration in the proximity of the implant. However, this information reflects the integration in only a very small fraction, a 10 μm thick slice, of the sample. In this study, we show that feature values quantified on 2D sections are highly dependent on the orientation and the placement of the section, suggesting that a 3D analysis of the whole sample is of importance for a more complete judgment of the bone structure in the proximity of the implant. We propose features describing the 3D data by extending the features traditionally used for 2D-analysis. We present a method for extracting these features from 3D image data and we measure them on five 3D SRμCT image volumes. We also simulate cuts through the image volume positioned at all possible section positions. These simulations show that the measurement variations due to the orientation of the section around the center line of the implant are about 30%.

Micro-computerized tomography analysis of alveolar bone loss in ligature- and nicotine-induced experimental periodontitis in rats

BACKGROUND AND OBJECTIVE

Nicotine reportedly is a risk factor for periodontitis, but accurate data regarding nicotine-induced alveolar bone loss is lacking. The aim of this study was to quantitatively assess alveolar bone loss in ligature- and nicotine-induced periodontitis in rats using micro-computerized tomography (micro-CT).

MATERIAL AND METHODS

Thirty-six adult male rats were treated by placing silk ligatures around the cervixes of the right second maxillary molar; the contralateral tooth was untreated. After ligation, the animals were randomly divided into three groups: group A received intraperitoneal injections of saline solution, group B received 0.83 mg of nicotine/kg/d, and group C received 1.67 mg of nicotine/kg/d. Six animals in each group were killed on days 14 and 28 after ligature placement, and then micro-CT examinations were conducted.

RESULTS

  In all groups, bone mineral density (BMD), bone volume fraction (BVF), trabecular number (Tb.N) and trabecular thickness (Tb.Th) values of the ligated sides were significantly lower than those of the unligated sides (p < 0.001), whereas alveolar bone height loss (ABHL) and trabecular separation (Tb.Sp) of the ligated sides were significantly higher than those of the unligated sides (p < 0.001). Compared with the control group, nicotine administration increased the ABHL value and decreased the BMD, BVF and Tb.Th values of both sides in a dose-dependent manner (p < 0.05).

CONCLUSION

  Our results confirmed that ligature could cause significant loss in the trabecula of alveolar bone, and daily administration of nicotine resulted in further bone loss and microstructure deterioration.

Effect of alendronate on alveolar bone resorption and angiogenesis in rats with experimental periapical lesions

AIM

To investigate the effects of systemically administered alendronate, one of the most potent bisphosphonates (BPs), on alveolar bone resorption and angiogenesis in rats subjected to experimental periapical lesions over two time periods.

METHODOLOGY

Forty adult Sprague-Dawley (SD) rats were divided equally into control and experimental groups, and the pulp chambers of mandibular first molars of all rats were exposed to the oral environment to induce periapical lesions. The experimental group received daily subcutaneous injections of alendronate at a dose of 0.25 mg kg(-1), whereas the control group received only the saline vehicle. These injections were initiated 1 week before the periapical lesion induction and then continued daily throughout the entire experimental period. After 2 or 4 weeks following pulp exposure, the rats were killed, and the mandibles were examined histologically for periapical bone loss area, number of microvascular vessels (NMV) and tartrate-resistant acid phosphatase (TRAP) activity.

RESULTS

Overall, periapical bone loss area and the number of TRAP-positive cells (osteoclasts) were significantly decreased at 2 and 4 weeks, respectively, after daily subcutaneous injection of alendronate compared with the control group (P < 0.05). There was no significant decrease change in NMV (P > 0.05).

CONCLUSIONS

Administration of alendronate to rats might inhibit alveolar bone resorption associated with periapical disease, which might not lead to impairment of angiogenesis. However, because of the differences between rats and humans, one has to consider the possible consequences of this treatment in the clinic.