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Yuan X, Liu B, Cuevas P, Brunski J, Aellos F, Petersen J, Koehne T, Bröer S, Grüber R, LeBlanc A, Zhang X, Xu Q, Helms J. Linking the Mechanics of Chewing to Biology of the Junctional Epithelium. J Dent Res 2023; 102:1252-1260. [PMID: 37555395 PMCID: PMC10626588 DOI: 10.1177/00220345231185288] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/10/2023] Open
Abstract
The capacity of a tissue to continuously alter its phenotype lies at the heart of how an animal is able to quickly adapt to changes in environmental stimuli. Within tissues, differentiated cells are rigid and play a limited role in adapting to new environments; however, differentiated cells are replenished by stem cells that are defined by their phenotypic plasticity. Here we demonstrate that a Wnt-responsive stem cell niche in the junctional epithelium is responsible for the capability of this tissue to quickly adapt to changes in the physical consistency of a diet. Mechanical input from chewing is required to both establish and maintain this niche. Since the junctional epithelium directly attaches to the tooth surface via hemidesmosomes, a soft diet requires minimal mastication, and consequently, lower distortional strains are produced in the tissue. This reduced strain state is accompanied by reduced mitotic activity in both stem cells and their progeny, leading to tissue atrophy. The atrophied junctional epithelium exhibits suboptimal barrier functions, allowing the ingression of bacteria into the underlying connective tissues, which in turn trigger inflammation and mild alveolar bone loss. These data link the mechanics of chewing to the biology of tooth-supporting tissues, revealing how a stem cell niche is responsible for the remarkable adaptability of the junctional epithelium to different diets.
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Affiliation(s)
- X. Yuan
- Department of Surgery, Stanford University School of Medicine, Stanford, CA, USA
- Department of Otolaryngology-Head & Neck Surgery, School of Medicine, Indiana University, Indianapolis, IN, USA
| | - B. Liu
- Department of Surgery, Stanford University School of Medicine, Stanford, CA, USA
| | - P. Cuevas
- Department of Surgery, Stanford University School of Medicine, Stanford, CA, USA
| | - J. Brunski
- Department of Surgery, Stanford University School of Medicine, Stanford, CA, USA
| | - F. Aellos
- Department of Surgery, Stanford University School of Medicine, Stanford, CA, USA
| | - J. Petersen
- Department of Orthodontics, University of Leipzig Medical Center, Saxony, Germany
| | - T. Koehne
- Department of Orthodontics, University of Leipzig Medical Center, Saxony, Germany
| | - S. Bröer
- Institute of Pharmacology and Toxicology, School of Veterinary Medicine, Freie Universität Berlin, Berlin, Germany
| | - R. Grüber
- Department of Oral Biology, University Clinic of Dentistry, Medical University of Vienna, Vienna, Austria
| | - A. LeBlanc
- Centre for Oral, Clinical & Translational Sciences, Faculty of Dentistry, Oral & Craniofacial Sciences, King’s College London, London, UK
| | - X. Zhang
- Department of Surgery, Stanford University School of Medicine, Stanford, CA, USA
- State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Disease, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - Q. Xu
- Department of Surgery, Stanford University School of Medicine, Stanford, CA, USA
- The Affiliated Hospital of Qingdao University, College of Stomatology, Qingdao University, Qingdao, China
| | - J.A. Helms
- Department of Surgery, Stanford University School of Medicine, Stanford, CA, USA
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Wang B, Nguyen N, Kang M, Srirangapatanam S, Connelly S, Souza R, Ho SP. Contact ratio and adaptations in the maxillary and mandibular dentoalveolar joints in rats and human clinical analogs. J Mech Behav Biomed Mater 2022; 136:105485. [PMID: 36209587 DOI: 10.1016/j.jmbbm.2022.105485] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2022] [Revised: 09/19/2022] [Accepted: 09/21/2022] [Indexed: 11/19/2022]
Abstract
Spatial maps of function-based contact areas and resulting mechanical strains in bones of intact fibrous joints in preclinical small-scale animal models are limited. Functional imaging in situ on intact dentoalveolar fibrous joints (DAJs) in hemimandibles and hemimaxillae harvested from 10 male Sprague-Dawley rats (N = 5 at 12 weeks, N = 5 at 20 weeks) was performed in this study. Physical features including bone volume fraction (BVF), bone pore diameter and pore density, and cementum fraction (CF) of the molars in the maxillary and mandibular joints were evaluated. Biomechanical testing in situ provided estimates of joint stiffness, changes in periodontal ligament spaces (PDL-space) between the molar and bony socket, and thereby localization of contact area in the respective joints. Contact area localization revealed mechanically stressed interradicular and apical regions in the joints. These anatomy-specific contact stresses in maxillary and mandibular joints were correlated with the physical features and resulting strains in interradicular and bony socket compartments. The mandibular joint spaces, in general, were higher than maxillary, and this trend was consistent with age (younger loaded: Mn - 134 ± 55 μm, Mx - 110 ± 47 μm; older loaded: Mn - 122 ± 49 μm, Mx - 105 ± 48 μm). However, a significant decrease (P < 0.05) in mandibular and maxillary joint spaces with age (younger unloaded: Mn - 147 ± 51 μm; Mx - 125 ± 42 μm; older unloaded: Mn - 134 ± 46 μm; Mx - 116 ± 44 μm) was observed. The bone volume fraction (BVF) of mandibular interradicular bone (IR bone) increased significantly with age (P < 0.05) with the percent porosity of coronal mandibular bone lower than its maxillary counterpart. The contact ratio (contact area to total surface area) of maxillary teeth was significantly greater (P < 0.05) than mandibular teeth; both maxillary interradicular and apical contact ratios (IR bone: 41%, 56%; Apical bone: 4%, 12%) increased with age, and were higher than the mandibular (IR bone: 19%, 44%; Apical bone: 1%, 4%) counterpart. Resulting higher but uniform strains in maxillary bone contrasted with lower but higher variance in mandibular strains at a younger age. Anatomy-specific colocalization of physical properties and functional strains in bone provided insights into form-guided adaptive dominance of the maxilla compared to material property-guided adaptive dominance of the mandible. These age-related trends from the preclinical animal model paralleled with age- and tooth position-specific variabilities in mandibular craniofacial bones of adolescent and adult patients following orthodontic treatment.
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Affiliation(s)
- Bo Wang
- State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Dalian University of Technology, Dalian, 116023, PR China; International Research Center for Computational Mechanics, Dalian University of Technology, Dalian, 116023, PR China; Ningbo Institute of Dalian University of Technology, Ningbo, 315016, PR China; DUT-BSU Joint Institute, Dalian University of Technology, 116023, PR China; Division of Preclinical Education, Biomaterials & Engineering, Department of Preventive and Restorative Dental Sciences, School of Dentistry, University of California San Francisco, CA 94143, USA
| | - Nam Nguyen
- Division of Preclinical Education, Biomaterials & Engineering, Department of Preventive and Restorative Dental Sciences, School of Dentistry, University of California San Francisco, CA 94143, USA
| | - Misun Kang
- Division of Preclinical Education, Biomaterials & Engineering, Department of Preventive and Restorative Dental Sciences, School of Dentistry, University of California San Francisco, CA 94143, USA
| | | | - Stephen Connelly
- Division of Oral Surgery, Department of Orofacial Sciences, School of Dentistry, University of California San Francisco, CA, 94143, USA
| | - Richard Souza
- Departments of Physical Therapy and Rehabilitation Science, Radiology and Biomedical Orthopaedic Surgery, School of Medicine, University of California San Francisco, CA, 94143, USA
| | - Sunita P Ho
- Division of Preclinical Education, Biomaterials & Engineering, Department of Preventive and Restorative Dental Sciences, School of Dentistry, University of California San Francisco, CA 94143, USA.
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