Non uniformity in the PDL: structure and function of the dense collar

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ABSTRACT: Teeth function under high repetitive masticatory loads throughout lifetime. They need to quickly adapt to food in different sizes and consistencies in order to enable an efficient masticatory process. This quick adaptation capability is provided by a unique soft tissue that connects the tooth to the alveolar bone, the periodontal ligament (PDL). The PDL, therefore, is critical for proper tooth function and survival. At present, there are different solutions for restoring teeth and alveolar bone structure to different extents but no predictable methods exist for restoring the PDL. This proposal will establish a platform for a regeneration therapy for the PDL. The PDL is a non-uniform tissue, we recently identify a unique structure of dense collagen network at the most coronal part of the PDL and coined the term dense collar. This region is consists of dense, short horizontal fibers with a directionality preference that corresponds to natural drift direction of the tooth. Our recent studies show higher stiffness of the dense collar when compared to the furcation region in the PDL as well as unique composition. We therefore hypothesize that the dense collar is a central contributor to the overall tooth stability and therefore any impairment to the dense collar structure will affect the entire PDL function. To test this hypothesis we will take a multidisciplinary approach investigating the structure and function of this tissue and its role in the entire PDL function and tooth stability. We will generate a base line of the ECM and cellular profile of this region in comparison to other regions in the PDL using localized proteomics and mass cytometry. We will measure the mechanical properties of the dense collar using high frequency AFM and tooth mobility using an in-situ loading device and we will unravel the collagen structure using a novel in-situ Raman spectroscopy and our microCT based method for soft tissue imaging. We will combine theses cutting edge methodologies utilizing unfixed samples with minimal sectioning to enable sample collection with their 3D structural context. We will then test the effect of different interventions to the structural integrity of the dense collar on tooth mobility. We will use a modified pre-periodontitis model and orthodontic tooth movement in mice model and compare the structural and mechanical properties of the dense collar to the base line. In the last stage we will identify a method to strengthen the dense collar to increase tooth stability. This proposal will determine the role of the dense collar in tooth stability and the association between structural changes in the dense collar and overall PDL function. Most importantly, unraveling the structure and function of a specific region within the PDL will generate a platform for structural interventions to reinforce this region and control the entire PDL function and tooth stability. This proposal will lay the ground to a paradigm shift in different dental fields such as orthodontics, dental trauma, and periodontics.