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Lucas PW, Wagner M, Al-Fadhalah K, Almusallam AS, Michael S, Thai LA, Strait DS, Swain MV, van Casteren A, Renno WM, Shekeban A, Philip SM, Saji S, Atkins AG. Dental abrasion as a cutting process. Interface Focus 2016; 6:20160008. [PMID: 27274807 DOI: 10.1098/rsfs.2016.0008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A mammalian tooth is abraded when a sliding contact between a particle and the tooth surface leads to an immediate loss of tooth tissue. Over time, these contacts can lead to wear serious enough to impair the oral processing of food. Both anatomical and physiological mechanisms have evolved in mammals to try to prevent wear, indicating its evolutionary importance, but it is still an established survival threat. Here we consider that many wear marks result from a cutting action whereby the contacting tip(s) of such wear particles acts akin to a tool tip. Recent theoretical developments show that it is possible to estimate the toughness of abraded materials via cutting tests. Here, we report experiments intended to establish the wear resistance of enamel in terms of its toughness and how friction varies. Imaging via atomic force microscopy (AFM) was used to assess the damage involved. Damage ranged from pure plastic deformation to fracture with and without lateral microcracks. Grooves cut with a Berkovich diamond were the most consistent, suggesting that the toughness of enamel in cutting is 244 J m(-2), which is very high. Friction was higher in the presence of a polyphenolic compound, indicating that this could increase wear potential.
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Affiliation(s)
- Peter W Lucas
- Department of Bioclinical Sciences, Faculty of Dentistry , Kuwait University , PO Box 24923, Safat 11310 , Kuwait
| | - Mark Wagner
- Department of Mechanical Engineering, School of Engineering and Applied Science, Science and Engineering Hall, 800 22nd St NW, Washington, DC 20052 , USA
| | - Khaled Al-Fadhalah
- Department of Mechanical Engineering , Kuwait University , PO Box 5969, Safat 13060 , Kuwait
| | | | - Shaji Michael
- Department of Bioclinical Sciences, Faculty of Dentistry , Kuwait University , PO Box 24923, Safat 11310 , Kuwait
| | - Lidia A Thai
- Nanotechnology Research Facility, College of Engineering and Petroleum , Kuwait University , PO Box 5969, Safat 13060 , Kuwait
| | - David S Strait
- Department of Anthropology , Washington University in St Louis , Campus Box 1114, One Brookings Drive, St Louis, MO 63130-4899 , USA
| | - Michael V Swain
- Department of Bioclinical Sciences, Faculty of Dentistry , Kuwait University , PO Box 24923, Safat 11310 , Kuwait
| | - Adam van Casteren
- Max Planck Weizmann Center for Integrated Archaeology and Anthropology , Max Planck Institute for Evolutionary Anthropology , Deutscher Platz 6, 04103 Leipzig , Germany
| | - Waleed M Renno
- Department of Anatomy, Faculty of Medicine , Kuwait University , PO Box 24923, Safat 11310 , Kuwait
| | - Ali Shekeban
- Nanotechnology Research Facility, College of Engineering and Petroleum , Kuwait University , PO Box 5969, Safat 13060 , Kuwait
| | - Swapna M Philip
- Department of Bioclinical Sciences, Faculty of Dentistry , Kuwait University , PO Box 24923, Safat 11310 , Kuwait
| | - Sreeja Saji
- Department of Bioclinical Sciences, Faculty of Dentistry , Kuwait University , PO Box 24923, Safat 11310 , Kuwait
| | - Anthony G Atkins
- School of Construction Management and Engineering , University of Reading , Whiteknights, PO Box 219, Reading RG6 6AW , UK
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Abstract
A review is presented of the mechanical damage suffered by tooth crowns. This has been the subject of much recent research, resulting in a need to revise some of the thinking about the mechanisms involved. Damage is classified here by scale into macro-, meso- and microfracture. The focus is on the outer enamel coat because this is the contact tissue and where most fractures start. Enamel properties appear to be tailored to maximize hardness, but also to prevent fracture. The latter is achieved by the deployment of developmental flaws called enamel tufts. Macrofractures usually appear to initiate as extensions of tufts on the undersurface of the enamel adjacent to the enamel-dentine junction and extend from there into the enamel. Cracks that pass from the tooth surface tend to be deflected by an enamel region of high toughness; if they find the surface again, a chip (mesofracture) is produced. The real protection of the enamel-dentine junction here is the layer of decussating inner enamel. Finally, a novel analysis of mechanical wear (microfracture) suggests that the local toughness of the enamel is very important to its ability to resist tissue loss. Enamel and dentine have contrasting behaviours. Seen on a large scale, dentine is isotropic (behaving similarly in all directions) while enamel is anisotropic, but vice versa on a very small scale. These patterns have implications for anyone studying the fracture behaviour of teeth.
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Affiliation(s)
- Peter W. Lucas
- Department of Bioclinical Sciences, Faculty of Dentistry, Kuwait University, Jabriya, Kuwait
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McGuire JD, Walker MP, Mousa A, Wang Y, Gorski JP. Type VII collagen is enriched in the enamel organic matrix associated with the dentin-enamel junction of mature human teeth. Bone 2014; 63:29-35. [PMID: 24594343 PMCID: PMC4012641 DOI: 10.1016/j.bone.2014.02.012] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Revised: 02/20/2014] [Accepted: 02/21/2014] [Indexed: 11/23/2022]
Abstract
The inner enamel region of erupted teeth is known to exhibit higher fracture toughness and crack growth resistance than bulk phase enamel. However, an explanation for this behavior has been hampered by the lack of compositional information for the residual enamel organic matrix. Since enamel-forming ameloblasts are known to express type VII collagen and type VII collagen null mice display abnormal amelogenesis, the aim of this study was to determine whether type VII collagen is a component of the enamel organic matrix at the dentin-enamel junction (DEJ) of mature human teeth. Immunofluorescent confocal microscopy of demineralized tooth sections localized type VII collagen to the organic matrix surrounding individual enamel rods near the DEJ. Morphologically, immunoreactive type VII collagen helical-bundles resembled the gnarled-pattern of enamel rods detected by Coomassie Blue staining. Western blotting of whole crown or enamel matrix extracts also identified characteristic Mr=280 and 230 kDa type VII dimeric forms, which resolved into 75 and 25 kDa bands upon reduction. As expected, the collagenous domain of type VII collagen was resistant to pepsin digestion, but was susceptible to purified bacterial collagenase. These results demonstrate the inner enamel organic matrix in mature teeth contains macromolecular type VII collagen. Based on its physical association with the DEJ and its well-appreciated capacity to complex with other collagens, we hypothesize that enamel embedded type VII collagen fibrils may contribute not only to the structural resilience of enamel, but may also play a role in bonding enamel to dentin.
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Affiliation(s)
- Jacob D McGuire
- Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri - Kansas City, Kansas City, MO 64108, USA.
| | - Mary P Walker
- Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri - Kansas City, Kansas City, MO 64108, USA; Center of Excellence in Musculoskeletal and Dental Tissues, University of Missouri - Kansas City, Kansas City, MO 64108, USA
| | - Ahmad Mousa
- Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri - Kansas City, Kansas City, MO 64108, USA
| | - Yong Wang
- Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri - Kansas City, Kansas City, MO 64108, USA; Center of Excellence in Musculoskeletal and Dental Tissues, University of Missouri - Kansas City, Kansas City, MO 64108, USA
| | - Jeff P Gorski
- Department of Oral and Craniofacial Sciences, School of Dentistry, University of Missouri - Kansas City, Kansas City, MO 64108, USA; Center of Excellence in Musculoskeletal and Dental Tissues, University of Missouri - Kansas City, Kansas City, MO 64108, USA
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A comparative study on component volumes from outer to inner dental enamel in relation to enamel tufts. Arch Oral Biol 2014; 59:568-77. [DOI: 10.1016/j.archoralbio.2014.03.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2013] [Revised: 02/27/2014] [Accepted: 03/05/2014] [Indexed: 11/18/2022]
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McGuire JD, Mousa AA, Zhang BJ, Todoki LS, Huffman NT, Chandrababu KB, Moradian-Oldak J, Keightley A, Wang Y, Walker MP, Gorski JP. Extracts of irradiated mature human tooth crowns contain MMP-20 protein and activity. J Dent 2014; 42:626-35. [PMID: 24607847 DOI: 10.1016/j.jdent.2014.02.013] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2013] [Revised: 01/17/2014] [Accepted: 02/18/2014] [Indexed: 10/25/2022] Open
Abstract
OBJECTIVES We recently demonstrated a significant correlation between enamel delamination and tooth-level radiation dose in oral cancer patients. Since radiation can induce the synthesis and activation of matrix metalloproteinases, we hypothesized that irradiated teeth may contain active matrix metalloproteinases. MATERIALS AND METHODS Extracted teeth from oral cancer patients treated with radiotherapy and from healthy subjects were compared. Extracted mature third molars from healthy subjects were irradiated in vitro and/or incubated for 0-6 months at 37°C. All teeth were then pulverized, extracted, and extracts subjected to proteomic and enzymatic analyses. RESULTS Screening of irradiated crown extracts using mass spectrometry identified MMP-20 (enamelysin) which is expressed developmentally in dentine and enamel but believed to be removed prior to tooth eruption. MMP-20 was composed of catalytically active forms at Mr=43, 41, 24 and 22kDa and was immunolocalized predominantly to the morphological dentine enamel junction. The proportion of different sized MMP-20 forms changed with incubation and irradiation. While the pattern was not altered directly by irradiation of healthy teeth with 70Gy, subsequent incubation at 37°C for 3-6 months with or without prior irradiation caused the proportion of Mr=24-22kDa MMP-20 bands to increase dramatically. Extracts of teeth from oral cancer patients who received >70Gy radiation also contained relatively more 24 and 22kDa MMP-20 than those of healthy age-related teeth. CONCLUSION MMP-20 is a radiation-resistant component of mature tooth crowns enriched in the dentine-enamel. We speculate that MMP-20 catalyzed degradation of organic matrix at this site could lead to enamel delamination associated with oral cancer radiotherapy.
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Affiliation(s)
- J D McGuire
- Department of Oral and Craniofacial Science, Center of Excellence in Dental and Musculoskeletal Tissues, School of Dentistry, University of Missouri-Kansas City, Kansas City, MO, United States
| | - A A Mousa
- Department of Oral and Craniofacial Science, Center of Excellence in Dental and Musculoskeletal Tissues, School of Dentistry, University of Missouri-Kansas City, Kansas City, MO, United States
| | - Bo J Zhang
- Department of Oral and Craniofacial Science, Center of Excellence in Dental and Musculoskeletal Tissues, School of Dentistry, University of Missouri-Kansas City, Kansas City, MO, United States
| | - L S Todoki
- Department of Oral and Craniofacial Science, Center of Excellence in Dental and Musculoskeletal Tissues, School of Dentistry, University of Missouri-Kansas City, Kansas City, MO, United States
| | - N T Huffman
- Department of Oral and Craniofacial Science, Center of Excellence in Dental and Musculoskeletal Tissues, School of Dentistry, University of Missouri-Kansas City, Kansas City, MO, United States
| | - K B Chandrababu
- Center for Craniofacial Molecular Biology, Ostrow School of Dentistry, University of Southern California, Los Angeles, CA, United States
| | - J Moradian-Oldak
- Center for Craniofacial Molecular Biology, Ostrow School of Dentistry, University of Southern California, Los Angeles, CA, United States
| | - A Keightley
- Biological Mass Spectrometry and Proteomics Facility, School of Biological Sciences, University of Missouri-Kansas City, MO, United States
| | - Y Wang
- Department of Oral and Craniofacial Science, Center of Excellence in Dental and Musculoskeletal Tissues, School of Dentistry, University of Missouri-Kansas City, Kansas City, MO, United States
| | - M P Walker
- Department of Oral and Craniofacial Science, Center of Excellence in Dental and Musculoskeletal Tissues, School of Dentistry, University of Missouri-Kansas City, Kansas City, MO, United States
| | - J P Gorski
- Department of Oral and Craniofacial Science, Center of Excellence in Dental and Musculoskeletal Tissues, School of Dentistry, University of Missouri-Kansas City, Kansas City, MO, United States.
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Rivera C, Arola D, Ossa A. Indentation damage and crack repair in human enamel. J Mech Behav Biomed Mater 2013; 21:178-84. [PMID: 23541701 DOI: 10.1016/j.jmbbm.2013.02.020] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Revised: 02/18/2013] [Accepted: 02/23/2013] [Indexed: 10/27/2022]
Abstract
Tooth enamel is the hardest and most highly mineralized tissue in the human body. While there have been a number of studies aimed at understanding the hardness and crack growth resistance behavior of this tissue, no study has evaluated if cracks in this tissue undergo repair. In this investigation the crack repair characteristics of young human enamel were evaluated as a function of patient gender and as a function of the distance from the Dentin Enamel Junction (DEJ). Cracks were introduced via microindentation along the prism direction and evaluated as a function of time after the indentation. Microscopic observations indicated that the repair of cracks began immediately after crack initiation and reaches saturation after approximately 48 h. During this process he crack length decreased up to 10% of the initial length, and the largest degree of reduction occurred in the deep enamel, nearest the DEJ. In addition, it was found that the degree of repair was significantly greater in the enamel of female patients.
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Affiliation(s)
- C Rivera
- School of Engineering, Eafit University, Cra 49 No 7 Sur 50, Medellín, Colombia
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Yahyazadehfar M, Bajaj D, Arola DD. Hidden contributions of the enamel rods on the fracture resistance of human teeth. Acta Biomater 2013; 9:4806-14. [PMID: 23022547 DOI: 10.1016/j.actbio.2012.09.020] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Revised: 09/17/2012] [Accepted: 09/18/2012] [Indexed: 11/19/2022]
Abstract
The enamel of human teeth is generally regarded as a brittle material with low fracture toughness. Consequently, the contributions of this tissue in resisting tooth fracture and the importance of its complex microstructure have been largely overlooked. In this study an experimental evaluation of the crack growth resistance of human enamel was conducted to characterize the role of rod (i.e. prism) orientation and degree of decussation on the fracture behavior of this tissue. Incremental crack growth was achieved in-plane, with the rods in directions longitudinal or transverse to their axes. Results showed that the fracture resistance of enamel is both inhomogeneous and spatially anisotropic. Cracks extending transverse to the rods in the outer enamel undergo a lower rise in toughness with extension, and achieve significantly lower fracture resistance than in the longitudinal direction. Though cracks initiating at the surface of teeth may begin extension towards the dentin-enamel junction, they are deflected by the decussated rods and continue growth about the tooth's periphery, transverse to the rods in the outer enamel. This process facilitates dissipation of fracture energy and averts cracks from extending towards the dentin and vital pulp.
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Affiliation(s)
- M Yahyazadehfar
- Department of Mechanical Engineering, University of Maryland Baltimore County, Baltimore, MD 21250, USA
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Constantino PJ, Lee JJW, Morris D, Lucas PW, Hartstone-Rose A, Lee WK, Dominy NJ, Cunningham A, Wagner M, Lawn BR. Adaptation to hard-object feeding in sea otters and hominins. J Hum Evol 2011; 61:89-96. [DOI: 10.1016/j.jhevol.2011.02.009] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Revised: 02/03/2011] [Accepted: 02/08/2011] [Indexed: 10/18/2022]
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Lee JJW, Constantino PJ, Lucas PW, Lawn BR. Fracture in teeth: a diagnostic for inferring bite force and tooth function. Biol Rev Camb Philos Soc 2011; 86:959-74. [PMID: 21507194 DOI: 10.1111/j.1469-185x.2011.00181.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Teeth are brittle and highly susceptible to cracking. We propose that observations of such cracking can be used as a diagnostic tool for predicting bite force and inferring tooth function in living and fossil mammals. Laboratory tests on model tooth structures and extracted human teeth in simulated biting identify the principal fracture modes in enamel. Examination of museum specimens reveals the presence of similar fractures in a wide range of vertebrates, suggesting that cracks extended during ingestion or mastication. The use of 'fracture mechanics' from materials engineering provides elegant relations for quantifying critical bite forces in terms of characteristic tooth size and enamel thickness. The role of enamel microstructure in determining how cracks initiate and propagate within the enamel (and beyond) is discussed. The picture emerges of teeth as damage-tolerant structures, full of internal weaknesses and defects and yet able to contain the expansion of seemingly precarious cracks and fissures within the enamel shell. How the findings impact on dietary pressures forms an undercurrent of the study.
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Affiliation(s)
- James J-W Lee
- Ceramics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
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Ford C, Bush MB, Lawn B. Effect of wear on stress distributions and potential fracture in teeth. JOURNAL OF MATERIALS SCIENCE. MATERIALS IN MEDICINE 2009; 20:2243-2247. [PMID: 19536639 DOI: 10.1007/s10856-009-3802-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2009] [Accepted: 06/05/2009] [Indexed: 05/27/2023]
Abstract
Finite element analysis is conducted on a tooth model with different degrees of wear. The model is taken as a hemispherical shell (enamel) on a compliant interior (dentin). Occlusal loading is simulated by contact with a flat or curved, hard or soft, indenter. Stress redistributions indicate that development of a wear facet may enhance some near-contact fracture modes (cone-ring cracks, radial-median cracks, edge-chipping), but have little effect on far-field modes (margin cracks). Contacts on worn surfaces with small, hard food objects are likely to be most deleterious, generating local stress concentrations and thereby accelerating the wear process. More typical contacts with larger-scale soft foods are unlikely to have such adverse effects. Implications concerning dietary habits of animals is an adjunct consideration in this work.
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Affiliation(s)
- Chris Ford
- School of Mechanical Engineering, The University of Western Australia, Crawley, WA, Australia
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Myoung S, Lee J, Constantino P, Lucas P, Chai H, Lawn B. Morphology and fracture of enamel. J Biomech 2009; 42:1947-51. [PMID: 19559438 DOI: 10.1016/j.jbiomech.2009.05.013] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2009] [Revised: 03/27/2009] [Accepted: 05/08/2009] [Indexed: 10/20/2022]
Abstract
This study examines the inter-relation between enamel morphology and crack resistance by sectioning extracted human molars after loading to fracture. Cracks appear to initiate from tufts, hypocalcified defects at the enamel-dentin junction, and grow longitudinally around the enamel coat to produce failure. Microindentation corner cracks placed next to the tufts in the sections deflect along the tuft interfaces and occasionally penetrate into the adjacent enamel. Although they constitute weak interfaces, the tufts are nevertheless filled with organic matter, and appear to be stabilized against easy extension by self-healing, as well as by mutual stress-shielding and decussation, accounting at least in part for the capacity of tooth enamel to survive high functional forces.
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Affiliation(s)
- Sangwon Myoung
- Ceramics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
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Chai H, Lee JJW, Kwon JY, Lucas PW, Lawn BR. A simple model for enamel fracture from margin cracks. Acta Biomater 2009; 5:1663-7. [PMID: 19269906 DOI: 10.1016/j.actbio.2008.11.007] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2008] [Revised: 10/10/2008] [Accepted: 11/13/2008] [Indexed: 10/21/2022]
Abstract
We present results of in situ fracture tests on extracted human molar teeth showing failure by margin cracking. The teeth are mounted into an epoxy base and loaded with a rod indenter capped with a Teflon insert, as representative of food modulus. In situ observations of cracks extending longitudinally upward from the cervical margins are recorded in real time with a video camera. The cracks appear above some threshold and grow steadily within the enamel coat toward the occlusal surface in a configuration reminiscent of channel-like cracks in brittle films. Substantially higher loading is required to delaminate the enamel from the dentin, attesting to the resilience of the tooth structure. A simplistic fracture mechanics analysis is applied to determine the critical load relation for traversal of the margin crack along the full length of the side wall. The capacity of any given tooth to resist failure by margin cracking is predicted to increase with greater enamel thickness and cuspal radius. Implications in relation to dentistry and evolutionary biology are briefly considered.
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Simmer JP, Hu Y, Lertlam R, Yamakoshi Y, Hu JCC. Hypomaturation enamel defects in Klk4 knockout/LacZ knockin mice. J Biol Chem 2009; 284:19110-21. [PMID: 19578120 DOI: 10.1074/jbc.m109.013623] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Kallikrein 4 (Klk4) is believed to play an essential role in enamel biomineralization, because defects in KLK4 cause hypomaturation amelogenesis imperfecta. We used gene targeting to generate a knockin mouse that replaces the Klk4 gene sequence, starting at the translation initiation site, with a lacZ reporter gene. Correct targeting of the transgene was confirmed by Southern blot and PCR analyses. Histochemical X-gal (5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside) staining demonstrated expression of beta-galactosidase in maturation stage ameloblasts. No X-gal staining was observed in secretory stage ameloblasts or in odontoblasts. Retained enamel proteins were observed in the maturation stage enamel of the Klk4 null mouse, but not in the Klk4 heterozygous or wild-type mice. The enamel layer in the Klk4 null mouse was normal in thickness and contained decussating enamel rods but was rapidly abraded following weaning, despite the mice being maintained on soft chow. In function the enamel readily fractured within the initial rod and interrod enamel above the parallel enamel covering the dentino-enamel junction. Despite the lack of Klk4 and the retention of enamel proteins, significant levels of crystal maturation occurred (although delayed), and the enamel achieved a mineral density in some places greater than that detected in bone and dentin. An important finding was that individual enamel crystallites of erupted teeth failed to grow together, interlock, and function as a unit. Instead, individual crystallites seemed to spill out of the enamel when fractured. These results demonstrate that Klk4 is essential for the removal of enamel proteins and the proper maturation of enamel crystals.
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Affiliation(s)
- James P Simmer
- Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, Michigan 48108, USA.
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Abstract
Tooth enamel is inherently weak, with fracture toughness comparable with glass, yet it is remarkably resilient, surviving millions of functional contacts over a lifetime. We propose a microstructural mechanism of damage resistance, based on observations from ex situ loading of human and sea otter molars (teeth with strikingly similar structural features). Section views of the enamel implicate tufts, hypomineralized crack-like defects at the enamel-dentin junction, as primary fracture sources. We report a stabilization in the evolution of these defects, by "stress shielding" from neighbors, by inhibition of ensuing crack extension from prism interweaving (decussation), and by self-healing. These factors, coupled with the capacity of the tooth configuration to limit the generation of tensile stresses in largely compressive biting, explain how teeth may absorb considerable damage over time without catastrophic failure, an outcome with strong implications concerning the adaptation of animal species to diet.
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Lee J.W, Kwon JY, Chai H, Lucas P, Thompson V, Lawn B. Fracture Modes in Human Teeth. J Dent Res 2009; 88:224-8. [DOI: 10.1177/0022034508330055] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The structural integrity of teeth under stress is vital to functional longevity. We tested the hypothesis that this integrity is limited by fracture of the enamel. Experiments were conducted on molar teeth, with a metal rod loaded onto individual cusps. Fracture during testing was tracked with a video camera. Two longitudinal modes of cracking were observed: median cracking from the contact zone, and margin cracking along side walls. Median cracks initiated from plastic damage at the contact site, at first growing slowly and then accelerating to the tooth margin. Margin cracks appeared to originate from the cemento-enamel junction, and traversed the tooth wall adjacent to the loaded cusp from the gingival to the occlusal surface. All cracks remained confined within the enamel shell up to about 550 N. At higher loads, additional crack modes—such as enamel chipping and delamination—began to manifest themselves, leading to more comprehensive failure of the tooth structure.
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Affiliation(s)
- J.J.-.W. Lee
- Ceramics Division, National Institute of Standards and Technology,
Gaithersburg, MD 20899-8520, USA
- School of Nano and Advanced Materials Engineering, Changwon National
University, Changwon, Kyung-Nam, Korea
- School of Mechanical Engineering, Faculty of Engineering, Tel Aviv
University, Tel Aviv, Israel
- Department of Anthropology, George Washington University, Washington,
DC 20052, USA; and
- New York University College of Dentistry, New York, NY 10010,
USA
| | - J.-Y. Kwon
- Ceramics Division, National Institute of Standards and Technology,
Gaithersburg, MD 20899-8520, USA
- School of Nano and Advanced Materials Engineering, Changwon National
University, Changwon, Kyung-Nam, Korea
- School of Mechanical Engineering, Faculty of Engineering, Tel Aviv
University, Tel Aviv, Israel
- Department of Anthropology, George Washington University, Washington,
DC 20052, USA; and
- New York University College of Dentistry, New York, NY 10010,
USA
| | - H. Chai
- Ceramics Division, National Institute of Standards and Technology,
Gaithersburg, MD 20899-8520, USA
- School of Nano and Advanced Materials Engineering, Changwon National
University, Changwon, Kyung-Nam, Korea
- School of Mechanical Engineering, Faculty of Engineering, Tel Aviv
University, Tel Aviv, Israel
- Department of Anthropology, George Washington University, Washington,
DC 20052, USA; and
- New York University College of Dentistry, New York, NY 10010,
USA
| | - P.W. Lucas
- Ceramics Division, National Institute of Standards and Technology,
Gaithersburg, MD 20899-8520, USA
- School of Nano and Advanced Materials Engineering, Changwon National
University, Changwon, Kyung-Nam, Korea
- School of Mechanical Engineering, Faculty of Engineering, Tel Aviv
University, Tel Aviv, Israel
- Department of Anthropology, George Washington University, Washington,
DC 20052, USA; and
- New York University College of Dentistry, New York, NY 10010,
USA
| | - V.P. Thompson
- Ceramics Division, National Institute of Standards and Technology,
Gaithersburg, MD 20899-8520, USA
- School of Nano and Advanced Materials Engineering, Changwon National
University, Changwon, Kyung-Nam, Korea
- School of Mechanical Engineering, Faculty of Engineering, Tel Aviv
University, Tel Aviv, Israel
- Department of Anthropology, George Washington University, Washington,
DC 20052, USA; and
- New York University College of Dentistry, New York, NY 10010,
USA
| | - B.R. Lawn
- Ceramics Division, National Institute of Standards and Technology,
Gaithersburg, MD 20899-8520, USA
- School of Nano and Advanced Materials Engineering, Changwon National
University, Changwon, Kyung-Nam, Korea
- School of Mechanical Engineering, Faculty of Engineering, Tel Aviv
University, Tel Aviv, Israel
- Department of Anthropology, George Washington University, Washington,
DC 20052, USA; and
- New York University College of Dentistry, New York, NY 10010,
USA
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Lucas P, Constantino P, Wood B, Lawn B. Dental enamel as a dietary indicator in mammals. Bioessays 2008; 30:374-85. [DOI: 10.1002/bies.20729] [Citation(s) in RCA: 232] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Paulson RB. Scanning electron microscopy of enamel tuft development in human deciduous teeth. Arch Oral Biol 1981; 26:103-9. [PMID: 6944022 DOI: 10.1016/0003-9969(81)90078-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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Thylstrup A. A scanning electron microscopical study of normal and fluorotic enamel demineralized by EDTA. Acta Odontol Scand 1979; 37:127-35. [PMID: 108914 DOI: 10.3109/00016357909027579] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Normal and fluorotic primary and permanent teeth were demineralized in 10% EDTA at pH 7 for varying periods of time up to 4 weeks. The fluorotic teeth initially dissolved at a much slower rate than non-fluorotic specimens and appeared to contain more organic material. After almost complete removal of the outer enamel a soft organic layer remained on the dentin surface. This consisted of a fine fibrillar mesh and some more dense material. After four weeks much of the organic material had disappeared leaving only a thin membrane on the dentin surface.
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Thylstrup A. A scanning electron microscopical study of normal and fluorotic enamel demineralized by EDTA. Acta Odontol Scand 1979; 37:127-35. [PMID: 113977 DOI: 10.3109/00016357909004687] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Normal and fluorotic primary and permanent teeth were demineralized in 10% EDTA at pH 7 for varying periods of time up to 4 weeks. The fluorotic teeth initially dissolved at a much slower rate than non-fluorotic specimens and appeared to contain more organic material. After almost complete removal of the outer enamel a soft organic layer remained on the dentin surface. This consisted of a fine fibrillar mesh and some more dense material. After four weeks much of the organic material had disappeared leaving only a thin membrane on the dentin surface.
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TAKUMA S, KURAHASHI Y, YOSHIOKA N, YAMAGUCHI A. Some considerations of the microstructure of dental tissues revealed by the electron microscope. ORAL SURGERY, ORAL MEDICINE, AND ORAL PATHOLOGY 1956; 9:328-43. [PMID: 13297394 DOI: 10.1016/0030-4220(56)90011-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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SOGNNAES RF, SHAW JH. Salivary and Pulpal Contributions to the Radiophosphorus Uptake in Enamel and Dentin. J Am Dent Assoc 1952; 44:489-505. [PMID: 14917513 DOI: 10.14219/jada.archive.1952.0103] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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