Hormone sensitive lipase ablation promotes bone regeneration.

There is an inverse relationship between the differentiation of mesenchymal stem cells (MSCs) along either an adipocyte or osteoblast lineage, with lineage differentiation known to be mediated by transcription factors PPARγ and Runx2, respectively. Endogenous ligands for PPARγ are generated during the hydrolysis of triacylglycerols to fatty acids through the actions of lipases such as hormone sensitive lipase (HSL). To examine whether reduced production of endogenous PPARγ ligands would influence bone regeneration, we examined the effects of HSL knockout on fracture repair in mice using a tibial mono-cortical defect as a model. We found an improved rate of fracture repair in HSL-ko mice documented by serial µCT and bone histomorphometry compared to wild-type (WT) mice. Similarly, accelerated rates of bone regeneration were observed with a calvarial model where implantation of bone grafts from HSL-ko mice accelerated bone regeneration at the injury site. Further analysis revealed improved MSC differentiation down osteoblast and chondrocyte lineage with inhibition of HSL. MSC recruitment to the injury site was greater in HSL-ko mice than WT. Finally, we used single cell RNAseq to understand the osteoimmunological differences between WT and HSL-ko mice and found changes in the pre-osteoclast population. Our study shows HSL-ko mice as an interesting model to study improvements to bone injury repair. Furthermore, our study highlights the potential importance of pre-osteoclasts and osteoclasts in bone repair.

Characteristics of Large Animal Models for Current Cell-Based Oral Tissue Regeneration.

The recent advances in the field of cell-based therapeutics open promising perspectives for oral tissue regeneration. The development of large animal models, which overcome the limits of the rodent models and allow to emulate clinical situations, is crucial for the validation of regenerative strategies to move toward clinical application. Currently, porcine, canine, and ovine models are mainly developed for oral regeneration and their specific characteristics have an impact on the outcomes of the studies. Thus, this systematic review investigates the application of porcine, canine, and ovine models in present cell-based oral regeneration, according to the species characteristics and the targeted tissue to regenerate. A customized search of PubMed, EMBASE, Scopus, and Web of Science databases from January 2015 to March 2020 was conducted. Relevant articles about cell-based oral tissues engineering in porcine, canine, and ovine models were evaluated. Among the evaluated articles, 58 relevant studies about cell-based oral regeneration in porcine, canine, and ovine models matched the eligibility criteria and were selected for full analysis. Porcine models, the most similar species with humans, were mostly used for bone and periodontium regeneration; tooth regeneration was reported only in pig, except for one study in dog. Canine models were the most transversal models, successfully involved for all oral tissue regeneration and notably in implantology. However, differences with humans and ethical concerns affect the use of these models. Ovine models, alternative to porcine and canine ones, were mainly used for bone and, scarcely, periodontium regeneration. The anatomy and physiology of these animals restrain their involvement. If consistency was found in defect specificities and cell trends among different species animal models of bone, dentin-pulp complex, or tooth regeneration, variability appeared in periodontium. Regeneration assessment methods were more elaborate in porcines and canines than in ovines. Risk of bias was low for selection, attrition and reporting, but unclear for performance and detection. Overall, if none of the large animal models can be considered an ideal one, they are of deemed importance for oral cell-based tissue engineering and researchers should consider their relevance to establish favorable conditions for a given preclinical cell-based therapeutics. Impact statement This systematic review investigates porcine, canine, and ovine models for current oral cell-based regeneration procedures, and researchers could refer to it for the choice of the most pertinent preclinical model for a given cell-based therapeutics.

Application of recommended preventive measures against COVID-19 could help mitigate the risk of SARS-CoV-2 infection during dental practice: Results from a follow-up survey of French dentists.

BACKGROUND: During the first-wave of the COVID-19 pandemic, dentists were considered at high-risk of infection. In France, to stop the spread of SARS-CoV-2, a nationwide lockdown was enforced, during which dentists suspended their routine clinical activities, working solely on dental emergencies. This measure has had an indisputable mitigating effect on the pandemic. To continue protecting dentists after suspension of nationwide lockdown, implementation of preventive measures was recommended, including adequate personal protective equipment (PPE) and room aeration between patients. No study has explored whether implementation of such preventive measures since the end of the first-wave has had an impact on the contamination of dentists. METHODS: An online survey was conducted within a French dentist population between July and September 2020. To explore risk factors associated with COVID-19, univariate and multivariate logistic regression analyses were performed. RESULTS: The results showed that COVID-19 prevalence among the 3497 respondents was 3.6%. Wearing surgical masks during non-aerosol generating procedures was a risk factor of COVID-19, whereas reducing the number of patients was a protective factor. CONCLUSIONS: Considering the similar COVID-19 prevalence between dentists and the general population, such data suggest that dentists are not overexposed in their work environment when adequate preventive measures are applied. IMPACT: Dentists should wear specific PPE (FFP2, FFP3 or (K)N95 masks) including during non-aerosol generating procedures and reduce the number of patients to allow proper implementation of disinfection and aeration procedures. Considering the similarities between COVID-19 and other viral respiratory infections, such preventive measures may also be of interest to limit emerging variants spread as well as seasonal viral outbreaks.

Cone beam CT optimisation for detection of vertical root fracture with metal in the field of view or the exomass.

Dose optimisation has been revisited in the literature due to the frequent use of cone beam computed tomography (CBCT). Although the reduction of the field-of-view (FOV) size has shown to be an effective strategy, this indirectly increases the negative effect from the exomass. The aim of this study was to evaluate the diagnostic accuracy of an optimised CBCT protocol in the detection of simulated vertical root fracture (VRF) in the presence of metal in the exomass and/or inside the FOV. Twenty teeth were endodontically instrumented and VRF was induced in half of them. All teeth were individually placed in a human mandible covered with a soft tissue equivalent material, metallic materials were placed at different dispositions in the exomass and/or endomass, and CBCT scans were obtained at two dose protocols: standard and optimised. Five radiologists evaluated the images and indicated the presence of VRF using a 5-point scale. Area under the ROC curve (AUC), sensitivity, and specificity were calculated and compared using ANOVA (α = 0.05). Overall, AUC, sensitivity, and specificity did not differ significantly (p > 0.05) between the dose protocols. In conclusion, optimised dose protocols should be considered in the detection of simulated VRF irrespective of the occurrence of artefacts from metallic materials in the exomass and/or inside the FOV.

Protease nexin-1 deficiency increases mouse hindlimb neovascularisation following ischemia and accelerates femoral artery perfusion.

We previously identified the inhibitory serpin protease nexin-1 (PN-1) as an important player of the angiogenic balance with anti-angiogenic activity in physiological conditions. In the present study, we aimed to determine the role of PN-1 on pathological angiogenesis and particularly in response to ischemia, in the mouse model induced by femoral artery ligation. In wild-type (WT) muscle, we observed an upregulation of PN-1 mRNA and protein after ischemia. Angiography analysis showed that femoral artery perfusion was more rapidly restored in PN-1-/- mice than in WT mice. Moreover, immunohistochemistry showed that capillary density increased following ischemia to a greater extent in PN-1-/- than in WT muscles. Moreover, leukocyte recruitment and IL-6 and MCP-1 levels were also increased in PN-1-/- mice compared to WT after ischemia. This increase was accompanied by a higher overexpression of the growth factor midkine, known to promote leukocyte trafficking and to modulate expression of proinflammatory cytokines. Our results thus suggest that the higher expression of midkine observed in PN-1- deficient mice can increase leukocyte recruitment in response to higher levels of MCP-1, finally driving neoangiogenesis. Thus, PN-1 can limit neovascularisation in pathological conditions, including post-ischemic reperfusion of the lower limbs.

Radiobiological risks following dentomaxillofacial imaging: should we be concerned?

OBJECTIVES: This review aimed to present studies that prospectively investigated biological effects in patients following diagnostic dentomaxillofacial radiology (DMFR). METHODS: Literature was systematically searched to retrieve all studies assessing radiobiological effects of using X-ray imaging in the dentomaxillofacial area, with reference to radiobiological outcomes for other imaging modalities and fields. RESULTS: There is a lot of variability in the reported radiobiological assessment methods and radiation dose measures, making comparisons of radiobiological studies challenging. Most radiological DMFR studies are focusing on genotoxicity and cytotoxicity, data for 2D dentomaxillofacial radiographs, albeit with some methodological weakness biasing the results. For CBCT, available evidence is limited and few studies include comparative data on both adults and children. CONCLUSIONS: In the future, one will have to strive towards patient-specific measures by considering age, gender and other individual radiation sensitivity-related factors. Ultimately, future radioprotection strategies should build further on the concept of personalized medicine, with patient-specific optimization of the imaging protocol, based on radiobiological variables.

In vitro Assessment of the DNA Damage Response in Dental Mesenchymal Stromal Cells Following Low Dose X-ray Exposure.

Stem cells contained within the dental mesenchymal stromal cell (MSC) population are crucial for tissue homeostasis. Assuring their genomic stability is therefore essential. Exposure of stem cells to ionizing radiation (IR) is potentially detrimental for normal tissue homeostasis. Although it has been established that exposure to high doses of ionizing radiation (IR) has severe adverse effects on MSCs, knowledge about the impact of low doses of IR is lacking. Here we investigated the effect of low doses of X-irradiation with medical imaging beam settings (<0.1 Gray; 900 mGray per hour), in vitro, on pediatric dental mesenchymal stromal cells containing dental pulp stem cells from deciduous teeth, dental follicle progenitor cells and stem cells from the apical papilla. DNA double strand break (DSB) formation and repair kinetics were monitored by immunocytochemistry of γH2AX and 53BP1 as well as cell cycle progression by flow cytometry and cellular senescence by senescence-associated ß-galactosidase assay and ELISA. Increased DNA DSB repair foci, after exposure to low doses of X-rays, were measured as early as 30 min post-irradiation. The number of DSBs returned to baseline levels 24 h after irradiation. Cell cycle analysis revealed marginal effects of IR on cell cycle progression, although a slight G2/M phase arrest was seen in dental pulp stromal cells from deciduous teeth 72 h after irradiation. Despite this cell cycle arrest, no radiation-induced senescence was observed. In conclusion, low X-ray IR doses (< 0.1 Gray; 900 mGray per hour), were able to induce significant increases in the number of DNA DSBs repair foci, but cell cycle progression seems to be minimally affected. This highlights the need for more detailed and extensive studies on the effects of exposure to low IR doses on different mesenchymal stromal cells.

Prevalence and risk indicators of first-wave COVID-19 among oral health-care workers: A French epidemiological survey.

BACKGROUND: Previous studies have highlighted the increased risk of contracting the COVID-19 for health-care workers and suggest that oral health-care workers may carry the greatest risk. Considering the transmission route of the SARS-CoV-2 infection, a similar increased risk can be hypothesized for other respiratory infections. However, no study has specifically assessed the risk of contracting COVID-19 within the dental profession. METHODS: An online survey was conducted within a population of French dental professionals between April 1 and April 29, 2020. Univariable and multivariable logistic regression analyses were performed to explore risk indicators associated with laboratory-confirmed COVID-19 and COVID-19-related clinical phenotypes (i.e. phenotypes present in 15% or more of SARS-CoV-2-positive cases). RESULTS: 4172 dentists and 1868 dental assistants responded to the survey, representing approximately 10% of French oral health-care workers. The prevalence of laboratory-confirmed COVID-19 was 1.9% for dentists and 0.8% for dental assistants. Higher prevalence was found for COVID-19-related clinical phenotypes both in dentists (15.0%) and dental assistants (11.8%). Chronic kidney disease and obesity were associated with increased odds of laboratory-confirmed COVID-19, whereas working in a practice limited to endodontics was associated with decreased odds. Chronic obstructive pulmonary disease, use of public transportation and having a practice limited to periodontology were associated with increased odds of presenting a COVID-19-related clinical phenotype. Moreover, changes in work rhythm or clinical practice were associated with decreased odds of both outcomes. CONCLUSIONS: Although oral health-care professionals were surprisingly not at higher risk of COVID-19 than the general population, specific risk indicators could exist, notably among high aerosol-generating dental subspecialties such as periodontology. Considering the similarities between COVID-19-related clinical phenotypes other viral respiratory infections, lessons can be learned from the COVID-19 pandemic regarding the usefulness of equipping and protecting oral health-care workers, notably during seasonal viral outbreaks, to limit infection spread. IMPACT: Results from this study may provide important insights for relevant health authorities regarding the overall infection status of oral health-care workers in the current pandemic and draw attention to particular at-risk groups, as illustrated in the present study. Protecting oral health-care workers could be an interesting public health strategy to prevent the resurgence of COVID-19 and/or the emergence of new pandemics.

Influence of voxel size on cone beam computed tomography artifacts arising from the exomass.

OBJECTIVES: The objective of this study was to evaluate the influence of voxel size on artifacts arising from the exomass in cone beam computed tomography (CBCT). STUDY DESIGN: An imaging phantom was scanned using 2 CBCT units, each adjusted to 2 voxel sizes: 0.2 and 0.3 mm. From 1 to 3 metal inserts of titanium, cobalt-chromium, or amalgam were placed in the exomass and additional CBCT scans were acquired. Mean voxel gray values were obtained from 16 homogeneous areas of the phantom and averaged, and the standard deviation was calculated to obtain voxel gray value variability. The data were analyzed using 2-way analysis of variance, Tukey, and Dunnett tests (α =.05). RESULTS: Overall, mean voxel gray values and voxel gray value variability did not differ significantly between CBCT scans obtained with voxel sizes of 0.2 and 0.3 mm for either CBCT model tested (P > .05). Despite some exceptions in which significant differences were observed between the 2 voxel sizes (P < .05), the mean voxel gray values and voxel gray value variability resulting from different metal compositions and, in most situations, for different numbers of metal inserts in the exomass were not affected. CONCLUSION: Voxel size has little influence on exomass-related CBCT artifacts.

Does the administration of meloxicam before head and neck radiotherapy reduce the risk of mandibular osteoradionecrosis? An animal model study.

OBJECTIVE: To assess whether the administration of meloxicam before head and neck radiotherapy reduces the risk of mandibular osteoradionecrosis in rats. MATERIAL AND METHODS: Sixty male Wistar rats were randomly divided into 6 groups (n = 10) according to the meloxicam administration and radiation therapy: control (C), irradiated (I), single dose of meloxicam (M1), single dose of meloxicam and irradiated (M1I), triple dose of meloxicam (M3), triple dose of meloxicam and irradiated (M3I). Meloxicam was administrated (20 mg/kg per dose) 1 h before the radiation therapy (single dose of 20 Gy) and 24 h and 48 h after the radiation therapy for groups with two additional doses. Ten days after the radiation therapy, the three right mandibular molars were extracted from all rats, who were euthanatized after 21 or 35 days (n = 5 per group). The mandibles were assessed by macroscopic evaluation and micro-CT analysis. RESULTS: The right hemimandibles of the irradiated groups revealed macroscopic signs of osteoradionecrosis, and those of the non-irradiated groups revealed complete gingival healing. A significant delay in alveolar socket healing in all irradiated groups was observed in the micro-CT assessment regardless meloxicam treatment. CONCLUSION: The administration of meloxicam before head and neck radiotherapy does not reduce the risk of mandibular osteoradionecrosis when associated to dental extractions. CLINICAL RELEVANCE: Since meloxicam has been shown to be a potential radiation-protective agent, and osteoradionecrosis physiopathology is believed to be related to an inflammatory process, possible interactions are relevant to be investigated.

A novel system exploits bone debris for implant osseointegration.

BACKGROUND: Bone debris generated during site preparation is generally evacuated with irrigation; here, we evaluated whether retention of this autologous material improved the rate of peri-implant bone formation. METHODS: In 25 rats, a miniature implant system composed of an osseo-shaping tool and a tri-oval-shaped implant was compared against a conventional drill and round implant system. A split-mouth design was used, and fresh extraction sockets served as implant sites. Histology/histomorphometry, immunohistochemistry, and microcomputed tomography (µCT) imaging were performed immediately after implant placement, and on post-surgery days 3, 7, 14, and 28. RESULTS: Compared with a conventional drill design, the osseo-shaping tool produced a textured osteotomy surface and viable bone debris that was retained in the peri-implant environment. Proliferating osteoprogenitor cells, identified by PCNA and Runx2 expression, contributed to faster peri-implant bone formation. Although all implants osseointegrated, sites prepared with the osseo-shaping tool showed evidence of new peri-implant bone sooner than controls. CONCLUSION: Bone debris produced by an osseo-shaping tool directly contributed to faster peri-implant bone formation and implant osseointegration.

Influence of the exomass on the detection of simulated root fracture in cone-beam CT - an ex-vivo study.

OBJECTIVES: To evaluate the influence of exomass-related metal artefacts on the detection of simulated vertical root fracture (VRF) in cone-beam computed tomography (CBCT). METHODS: 20 teeth were endodontically instrumented and VRF was induced in half of them. All teeth were individually placed in an empty socket of a human mandible. Metallic materials were differently arranged in the exomass [zone outside of the field of view (FOV) but between the X-ray source and the receptor] and/or endomass (zone inside of the FOV), and CBCT scans were obtained. Four radiologists evaluated the presence of VRF using a 5-point scale. Sensitivity, specificity, and area under the receiver operating curve (AUC) were compared using ANOVA. Also, the tooth of interest was replaced with a tube filled with a radiopaque solution and all CBCT scans were repeated to analyse the data objectively. Mean grey and noise values were obtained from the tube and compared using ANOVA followed by Tukey's test (α = 0.05). RESULTS: Mean grey values were significantly lower and noise was significantly higher when metallic materials were present in the endomass or both the exomass and endomass. Sensitivity, specificity, and AUC were not influenced by the artefacts from the metallic materials irrespective of the arrangement condition. CONCLUSIONS: Exomass-related metal artefacts did not influence the diagnosis of simulated VRF in CBCT.

Development of Enthesopathies and Joint Structural Damage in a Murine Model of X-Linked Hypophosphatemia.

X-linked hypophosphatemia (XLH) is characterized by rickets and osteomalacia, caused by inactivating mutations in the Phosphate-regulating endopeptidase homolog X-linked (PHEX) gene. With aging, adult patients develop paradoxical heterotopic calcifications of tendons and ligaments at their insertion sites (enthesophytes), and joint alterations. Understanding the progression of this structural damage that severely affects patients' quality of life will help to improve the management of XLH. Here, we characterized the occurrence of enthesophytes and joint alterations through a 12 month in vivo micro-CT follow-up in the Hyp mouse, a murine model of XLH (n = 5 mice per group). Similar to adult patients with XLH, Hyp mice developed calcaneal enthesophytes, hip joint alterations, erosions of the sacroiliac joints and periarticular calcifications. These lesions were already present at month 3 and gradually worsened over time. In sharp contrast, no abnormalities were observed in control mice at early time points. Histological analyses confirmed the presence of bone erosions, calcifications and expansion of mineralizing enthesis fibrocartilage in Hyp mice and their absence in controls and suggested that new bone formation is driven by altered mechanical strain. Interestingly, despite a strong deformation of the curvature, none of the Hyp mice displayed enthesophyte at the spine. Peripheral enthesophytes and joint alterations develop at the early stages of the disease and gradually worsen overtime. Overall, our findings highlight the relevance of this preclinical model to test new therapies aiming to prevent bone and joint complications in XLH.

Voxel-based superimposition of Cone Beam CT scans for orthodontic and craniofacial follow-up: Overview and clinical implementation.

INTRODUCTION: The increasing use of three-dimensional (3D) imaging in orthodontics has led to the development of 3D superimposition techniques. These techniques use stable anatomic structures as references in order to compare Cone Beam CT (CBCT) scans of the same subject at different time-points. Three methods have been described in the literature: landmark-based, surface-based and voxel-based 3D superimpositions. OBJECTIVE: This article focuses on the voxel-based approach, which is the most described and the only one that can be fully automatized. The aim of this paper is to offer clinicians a practical tutorial on craniofacial voxel-based 3D superimposition. MATERIAL AND METHODS: We provide an updated overview of the available implementation methods, describing their methodology, validations, main steps, advantages and drawbacks. The historical open-source method is the most widespread for research purposes, but takes around three hours to achieve for an experienced operator. Several commercially-available software perform superimpositions in a few minutes. RESULTS: We used two of the available methods to conduct the superimposition process with three representative clinical cases in order to illustrate the different types of results that can be obtained. CONCLUSIONS: Commercially-available software provide user-friendly and fully automatized superimposition methods, allowing clinicians to perform it easily and helping to reduce human error in image analysis. Still, quantitative evaluation of the results remains the main challenge of this technique.

Root resorption and ensuing cementum repair by Wnt/ß-catenin dependent mechanism.

INTRODUCTION: Physiological root resorption is a common occurrence in mammalian teeth, which suggests that there must be a corollary consisting of physiological cementum repair. The mechanism(s) responsible for this physiological repair process is unknown and was the focus of this study. METHODS: Using a rat model, we explored first the prevalence of physiological root resorption and then asked whether this prevalence changed as a result of an osteoporotic phenotype. The cellular mechanisms of resorption were characterized using a combination of finite element modeling coupled with in-vivo histologic, molecular, and cellular analyses in rats. A potential molecular mechanism for cementum repair was uncovered using a strain of transgenic mice in which Wnt-responsive cells could be labeled and followed over time. RESULTS: In rats, most resorption lacunae were concentrated on the distal surfaces of the roots. Rat molars undergo a physiological tooth drift distally, and using finite element modeling, we calculated the magnitude of the compressive strains that accumulated on these surfaces in response to mastication. Although the overall strain magnitudes were low, they were constant and coincided with the presence of resorption lacunae. Where resorption lacunae were present, progeny from a Wnt-responsive population of stem cells, embedded in the periodontal ligament, directly contributed to the repair of the lacunae. CONCLUSIONS: Despite the fact that both are clastic conditions, an osteoporotic phenotype in rats was not associated with an increase in the prevalence of physiological root resorption. The location of the resorption lacunae corresponded to sites of low but constant compressive strains produced by physiological distal drift. At least 1 mechanism responsible for physiological cementum repair involved the contribution of Wnt-responsive stem or progenitor cells originating in the periodontal ligament. These data point toward a potential Wnt-based strategy to regenerate cementum in subjects with disease or damage.

Distribution of metal artifacts arising from the exomass in small field-of-view cone beam computed tomography scans.

OBJECTIVES: To evaluate the distribution of metal artifacts from the exomass in small field-of-view (FOV) cone beam computed tomography (CBCT) scans. STUDY DESIGN: An image phantom was scanned by using 3 CBCT units. Metal objects were positioned in the exomass, and additional CBCT scans were obtained. Mean gray values were obtained from 16 homogeneous areas and the standard deviation was calculated to quantify gray level inhomogeneity according to distinct zones of the FOV: total area and outer, inner, right, left, and mid-zones. The discrepancy between each zone and the total area was calculated to compare different CBCT units. Mean gray, gray level inhomogeneity, and discrepancy values were separately assessed by using analysis of variance (ANOVA) and Tukey's test (α = 0.05). RESULTS: Overall, the mean gray values were significantly lower in the inner zone, and the gray level inhomogeneity values were significantly higher in the inner and mid-zones irrespective of the presence of metal objects in the exomass. The 3 CBCT units presented significantly different discrepancy values in most conditions. CONCLUSIONS: The distribution of metal artifacts from the exomass follows the inherent gray value dispersion of CBCT images, with greater inhomogeneity in the inner zone of the FOV. This is exacerbated when metal objects are in the exomass.

Quantification of DNA Double Strand Breaks and Oxidation Response in Children and Adults Undergoing Dental CBCT Scan.

Assessing the possible biological effects of exposure to low doses of ionizing radiation (IR) is one of the prime challenges in radiation protection, especially in medical imaging. Today, radiobiological data on cone beam CT (CBCT) related biological effects are scarce. In children and adults, the induction of DNA double strand breaks (DSBs) in buccal mucosa cells and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) and antioxidant capacity in saliva samples after CBCT examination were examined. No DNA DSBs induction was observed in children nor adults. In children only, an increase in 8-oxo-dG levels was observed 30 minutes after CBCT. At the same time an increase in antioxidant capacity was observed in children, whereas a decrease was observed in adults. Our data indicate that children and adults react differently to IR doses associated with CBCT. Fully understanding these differences could lead to an optimal use of CBCT in different age categories as well as improved radiation protection guidelines.

Publisher Correction: Halve the dose while maintaining image quality in paediatric Cone Beam CT.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.