into a full-scale defense against pathogens, are vital to uncover.
Review Questions
1. What causes the extraction of molar teeth to be more difficult than incisor teeth?
2. Does the periodontal ligament support the tooth like a hammock (under tension) or like a cushion (under compression)?
3. What are the functions of the periodontium?
4. Why is it important to place an avulsed tooth back in its socket as soon as possible?
5. What similarities and differences are there between cementum, dentin, and bone?
6. What features of the junctional epithelium provide a barrier to the progress of plaque microorganism into the periodontal ligament?
7. What is the nerve and blood supply of the periodontium?
8. How is the periodontium affected by changes in the level of female hormones?
9. What evidence suggests that cementum formation may be induced by cells of epithelial origin?
10. What are the functions of cementum?
11. What role do epithelial cell rests have in preventing ankylosis?
12. Why is the formation of new cementum essential during healing of the periodontal ligament?
References
[1] Lindskog S, Blomlöf L, Hammarström L. Evidence for a role of odontogenic epithelium in maintaining the periodontal space. J Clin Periodontol 1988; 15(6):371–373
[2] Fujiyama K, Yamashiro T, Fukunaga T, Balam TA, Zheng L, Takano-Yamamoto T. Denervation resulting in dento-alveolar ankylosis associated with decreased Malassez epithelium. J Dent Res 2004; 83(8):625–629
[3] Xiong J, Mrozik K, Gronthos S, Bartold P. Epithelial cell rests of Malassez contain unique stem cell populations capable of undergoing epithelial mesenchymal transition. Stem Cells Dev. 2012; 21 (11):2012–25
[4] Luan X, Ito Y, Diekwisch T. Evolution and development of Hertwig’s epithelial root sheath. Dev Dyn 2006 May; 235(5): 1167–1180
[5] Harahashi H, Odajima T, Yamamoto T, Kawanami M. Immunohistochemical analysis of periodontal reattachment on denuded root dentin after periodontal surgery. Biomed Res 2010; 31(5):319–328
Suggested Readings
Amar S, Chung KM. Influence of hormonal variation on the periodontium in women. Periodontol 2000 1994; 6(6):79–87
Berkovitz BK. Periodontal ligament: structural and clinical correlates. Dent Update 2004; 31(1):46–50, 52, 54
Lovegrove JM. Dental plaque revisited: bacteria associated with periodontal disease. J N Z Soc Periodontol 2004; 87(87):7–21
Lyngstadaas SP, Wohlfahrt JC, Brookes SJ, Paine ML, Snead ML, Reseland JE. Enamel matrix proteins; old molecules for new applications. Orthod Craniofac Res 2009; 12(3):243–253
Marsh PD, Martin MV, Lewis MAO, Williams DW. Oral microbiology. London: Churchill Livingstone; 2009
Mineoka T, Awano S, Rikimaru T, et al. Site-specific development of periodontal disease is associated with increased levels of Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia in subgingival plaque. J Periodontol 2008; 79(4):670–676
Scott DA, Krauss J. Neutrophils in periodontal inflammation. Front Oral Biol. 2012; 15:56–83
Wesselink PR, Beertsen W. The prevalence and distribution of rests of Malassez in the mouse molar and their possible role in repair and maintenance of the periodontal ligament. Arch Oral Biol 1993; 38(5):399–403
Xiong J, Mrozik K, Gronthos S, Bartold PM. Epithelial cell rests of Malassez contain unique stem cell populations capable of undergoing epithelial-mesenchymal transition. Stem Cells Dev 2012; 21(11):2012–2025
4 The Ecology of the Oral Cavity
The Biofilms of the Oral Environment
Oral Ecology and Dental Caries
The Influence of Fluorides on the Oral Ecosystem
Mucosal Immunity and Oral Ecology
Abstract
The oral cavity provides a variety of niche habitats for hundreds of species of oral bacteria. There are potential habitats on the teeth, tongue, or gingival sulcus and a constant supply of nutrients from food residues, saliva, and the products of other bacteria. The human host and its bacterial partners in the oral cavity and gut have a cooperative relationship which goes back millions of years. Cooperation between different bacterial species is just as important as competition in conserving this relationship; their interdependence holds together several different species in a consortium, a sort of mutual benefit community. If dental caries or periodontal disease occurs, it is always due to a disturbance in the dominance or hierarchy of bacteria within the consortium, often caused by something as simple as an increase of sugar in the diet, or at the other extreme, malnutrition. All the members of the consortium are well-established residents, so dental caries and periodontal disease are not the result of foreign pathogens but may be classified as noncommunicable diseases. The balance between the efforts of organisms to maintain growth on the oral surfaces, by both competitive and cooperative tactics, and the host’s factors which tend to support and tolerate certain commensals, but inhibit potential pathogens, is the theme of this chapter. Oral health strategies, which work best, are those based on an understanding of the principal factors which regulate and maintain a stable oral microbiome.
Keywords: oral environment, oral ecology, salivary pellicle, oral fluids, gingival fluid, dental plaque, calculus, dental caries, diet and caries, nutrition and oral health, fluorides, mucosal immunity, oral tolerance
4.1 Introduction
Ecology is the study of the relationship between living organisms and their environment. An ecosystem is a specific environment in which plant and animal species live in an interconnected web of cooperation and competition. For example, a forest is an ecosystem in which trees, bushes, and smaller plants interact with insects, soil bacteria, birds, small mammals, and reptiles, in fact, a large spectrum of most major classes of living organisms. Within the forest, each tree could be seen as a small ecosystem on its own, as it supports a characteristic collection of interactive bacteria and insects. The complexity and stability of an ecosystem take a long time to develop. If a temperate forest were to be cleared to the ground, it is estimated that it would take 200 years to regain its original rich and varied number of species.
The oral cavity is an ecosystem on a smaller scale, which also requires time to acquire a mature ecological balance of organisms. The time is much shorter than that needed for a