materials Article 3D Printed In Vitro Dentin Model to Investigate Occlusive Agents against Tooth Sensitivity Shiva Naseri 1,† , Megan E. Cooke 2,† , Derek H. Rosenzweig 2 and Maryam Tabrizian 1, *   Citation: Naseri, S.; Cooke, M.E.; Rosenzweig, D.H.; Tabrizian, M. 3D Printed In Vitro Dentin Model to Investigate Occlusive Agents against Tooth Sensitivity. Materials 2021, 14, 7255. https://doi.org/10.3390/ ma14237255 Academic Editors: Mutlu Özcan and Ludwig Cardon Received: 5 October 2021 Accepted: 24 November 2021 Published: 27 November 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Biomedical Engineering, McGill University, Montreal, QC H3A 2B4, Canada; shiva.naseri@mail.mcgill.ca 2 Department of Surgery, McGill University, Montreal, QC H3G 1A4, Canada; megan.cooke@mail.mcgill.ca (M.E.C.); derek.rosenzweig@mcgill.ca (D.H.R.) * Correspondence: maryam.tabrizian@mcgill.ca † Shiva Naseri and Megan E. Cook contributed equally to this work. Abstract: Tooth sensitivity is a painful and very common problem. Often stimulated by consuming hot, cold, sweet, or acidic foods, it is associated with exposed dentin microtubules that are open to dental pulp. One common treatment for tooth hypersensitivity is the application of occlusive particles to block dentin microtubules. The primary methodology currently used to test the penetration and occlusion of particles into dentin pores relies upon dentin discs cut from extracted bovine/human teeth. However, this method is limited due to low accessibility to the raw material. Thus, there is a need for an in vitro dentin model to characterize the effectiveness of occlusive agents. Three- dimensional printing technologies have emerged that make the printing of dentin-like structures possible. This study sought to develop and print a biomaterial ink that mimicked the natural composition and structure of dentin tubules. A formulation of type I collagen (Col), nanocrystalline hydroxyapatite (HAp), and alginate (Alg) was found to be suitable for the 3D printing of scaffolds. The performance of the 3D printed dentin model was compared to the natural dentin disk by image analysis via scanning electron microscopy (SEM), both pre- and post-treatment with occlusive microparticles, to evaluate the degree of dentinal tubule occlusion. The cytocompatibility of printed scaffolds was also confirmed in vitro. This is a promising biomaterial system for the 3D printing of dentin mimics. Keywords: 3D printing; dentin; occlusive particles; tooth sensitivity 1. Introduction Dentin contains thousands of open-ended microtubules to ensure its permeability. This permeability is essential to support the physiology and reaction patterns of the pulp– dentin organ. Nutrients and impulses are transported from the pulp via the odontoblast process, while the contents of its tubules maintain the dentin as a vital tissue. When dentin microtubules are exposed to the oral environment [1] through receding gums, loss of the cementum, and smear layers and tooth wear [2], it results in hypersensitivity [3,4]. Dentin hypersensitivity is a very common dental problem characterized by short and sharp pain. It arises in response to stimuli, typically thermal (hot or cold), evaporative, tactile, osmotic (sweet or salty), chemical (acidic or basic), or electrical, with no effective remedy [5,6]. Common short-term treatments include applying fluoride gels, rinses, or varnishes that can be applied to sensitive areas of the teeth at regular intervals to help strengthen the tooth, or tooth surface treatment with occluding agents [7,8]. A current area of interest to reduce dentin sensitivity is decreasing tubule permeability through occlusion [9]. A number of studies have shown that dentin sensitivity is reduced when the dentinal tubules are occluded [10–12]. The current gold standard to determine the penetration and adhesion of occlusive particles into dentin pores is to use dentin discs cut from extracted bovine/human teeth Materials 2021, 14, 7255. https://doi.org/10.3390/ma14237255 https://www.mdpi.com/journal/materials