Research Spotlight

Azarpazhooh, A., Diogenes, A.R., Fouad, A.F., Glickman, G.N., Kishen, A., Levin, L., Roda, R.S., Sedgley, C.M., Tay, F.R. and Hargreaves, K.M. (2021). “Insights Into the January 2021 Issue of the JOE.” J Endod 47(1): 1-2.

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Welcome to the January 2021 issue of the JOE. Here, we share some of our favorite articles that are published in this issue of the Journal. We hope you look forward to reading these and other articles in the JOE. [No abstract; excerpt from Editorial].

Piedra-Cascón, W., Fountain, J., Att, W. and Revilla-León, M. (2021). “2D and 3D patient’s representation of simulated restorative esthetic outcomes using different computer-aided design software programs: A systematic review.” J Esthet Restor Dent Jan 5. [Epub ahead of print].

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OBJECTIVE: To review the techniques and available 2D and 3D computer-aided design (CAD) software programs to perform a diagnostic waxing for restorative procedures when cone beam computed tomography is not indicated. OVERVIEW: An electronic review was performed in Medline, Embase, and Scopus search engines. A manual search was also conducted. The articles evaluating methods to obtain a 2D or 3D patient’s representation for restorative dental procedures were included. A total of 33 articles were included for full text review. CAD programs provide the capability to integrate facial features from 2D photographs or 3D facial scans and facilitate facially driven digital diagnostic waxing procedures. Diagnostic and design tools varied among the programs, and multiple technique descriptions were found. However, the literature evaluating the accuracy of virtual patients and the perception variations between the 2D and 3D dimensional representations is limited. CONCLUSIONS: The integration of digital technologies into treatment planning procedures introduce variation into the conventional interfaces; however, the concepts remain the same. Further studies are needed to evaluate the accuracy of the virtual representations and the influence of the type of dimensional representation on the esthetic perceptions among dental professionals. CLINICAL SIGNIFICANCE: The 2D and 3D CAD software programs facilitate the integration of facial features into digital diagnostic waxing procedures; however, the esthetic perception of the patient’s virtual representation might vary among the different systems.

Wang, J., Jiang, Y., Xie, X., Zhang, S., Xu, C., Zhou, Y. and Feng, J.Q. (2020). “The identification of critical time windows of postnatal root elongation in response to Wnt/β-catenin signaling.” Oral Dis Dec 12. [Epub ahead of print].

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OBJECTIVES: In this study, we attempted to define the precise window of time for molar root elongation using a gain-of-function mutation of β-catenin model. MATERIALS AND METHODS: Both the control and constitutively activated β-catenin (CA-β-cat) mice received a one-time tamoxifen administration (for activation of β-catenin at newborn, postnatal day-3, or -5, or -7, or -9), and were harvested at the same stage of P21. Multiple approaches were used to define the window of time of postnatal tooth root formation. RESULTS: In the early activation groups (tamoxifen induction at newborn, or P3 or P5) there was a lack of molar root elongation in the CA-β-cat mice. When induced at P7, the root length was slightly reduced at P21. However, the root length was essentially the same as that in the control when β-cat activated at P9. This study indicates that root elongation occurs in a narrow time of window, which is highly sensitive to a change of β-catenin levels. Molecular studies showed a drastic decrease in the levels of nuclear factor I-C (NFIC) and osterix (OSX), plus sharp reductions of odontoblast differentiation markers, including Nestin, dentin sialoprotein (DSP) and dentin matrix protein 1 (DMP1) at both mRNA and protein levels. CONCLUSIONS: Murine molar root elongation is precisely regulated by the Wnt/β-catenin signaling within a narrow window of time (newborn to day 5).

Jing, Y., Simmer, P. and Feng, J.Q. (2021). “Cell Lineage Tracing: Colocalization of Cell Lineage Markers with a Fluorescent Reporter.” Methods Mol Biol 2230: 325-335.

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Cell lineage tracing, an old technique which originated in the nineteenth century, regains popularity and relevance due to introduction of a more sensitive tomato fluorescent protein under the control of a ubiquitous promoter (Rosa 26 gene). In addition, various tissue specific CreERT2 mouse lines are widely available, making cell lineage tracing studies more specific and powerful. In this protocol, we provide a practical guide for researchers to map progeny of specific cells such as chondrocytes during development using a fluorescent reporter (tomato, red) and multiple chondrocyte Cre lines. Further, we provide valuable examples in which these tracing lines, combined with a bone reporter mouse line (2.3 Col 1a1-GFP) or costained with different immunofluorescent proteins, revealed how a chondrocyte transdifferentiates into a bone cell in vivo.

Ma, C., Jing, Y., Li, H., Wang, K., Wang, Z., Xu, C., Sun, X., Kaji, D., Han, X., Huang, A. and Feng, J.Q. (2021). “Scx(Lin) cells directly form a subset of chondrocytes in temporomandibular joint that are sharply increased in Dmp1-null mice.” Bone 142: 115687.

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It has been assumed that the secondary cartilage in the temporomandibular joint (TMJ), which is the most complex and mystery joint and expands rapidly after birth, is formed by periochondrium-derived chondrocytes. The TMJ condyle has rich attachment sites of tendon, which is thought to be solely responsible for joint movement with a distinct cell lineage. Here, we used a Scx-Cre ERT2 mouse line (the tracing line for progenitor and mature tendon cells) to track the fate of tendon cells during TMJ postnatal growth. Our data showed a progressive differentiation of Scx lineage cells started at tendon and the fibrous layer, to cells at the prechondroblasts (Sox9 -/Col I +), and then to cells at the chondrocytic layer (Sox9 +/Col I -). Importantly, the Scx + chondrocytes remained as “permanent” chondrocytes to maintain cartilage mass with no further cell trandifferentiation to bone cells. This notion was substantiated in an assessment of these cells in Dmp1 -null mice (a hypophosphatemic rickets model), where there was a significant increase in the number of Scx lineage cells in response to hypophosphatemia. In addition, we showed the origin of disc, which is derived from Scx + cells. Thus, we propose Scx lineage cells play an important role in TMJ postnatal growth by forming the disc and a new subset of Scx + chondrocytes that do not undergo osteogenesis as the Scx – chondrocytes and are sensitive to the level of phosphorous.