33: Microbiology of periodontal disease

Chapter 33 Microbiology of periodontal disease

Periodontal diseases can be defined as disorders of supporting structures of the teeth, including the gingivae, periodontal ligament and supporting alveolar bone. Everyone suffers from various degrees of periodontal disease at some point, and it is one of the major diseases afflicting humankind. However, in most people, the common chronic inflammatory diseases involving the periodontal tissues can be controlled, using mechanical cleansing techniques and good oral hygiene. A minority experience rapid progressive disease that requires assessment and management by periodontists.

Classification of periodontal disease

Periodontal disease can be broadly categorized into gingivitis and periodontitis. These are yet again subdivided into numerous categories; a recent classification of periodontal diseases is given in Table 33.1. It should be noted that there is no universally acknowledged classification of periodontal disease and the clinical descriptors used relate to:

Table 33.1 Classification of periodontal diseases

Gingival diseases

Periodontal diseases

Periodontitis usually develops from a pre-existing gingivitis; however, not every case of gingivitis develops into periodontitis.

Aetiological factors

The main aetiological agent of periodontal disease is microflora inhabiting subgingival plaque biofilms.

However, the host tissues and its specific and non-specific host defence mechanisms play crucial modulating roles (i.e. modifying factors) in the disease process. The latter will be described first.

Host tissues

The periodontium comprises the gingivae, periodontal ligament, cementum and alveolar bone (Fig. 33.1). Although the dentogingival junction is perhaps the most vulnerable site for microbial attack, it is not breached as long as oral hygiene is satisfactory. However, when plaque accumulates close to the gingival margin, the host defences are overcome, and gingival inflammation (gingivitis) and subsequent periodontal inflammation with loss of attachment ensue (periodontitis).

Host defence factors

Both the specific and non-specific immune responses of the host to subgingival plaque are considered to play critical roles in the initiation, progression and recovery from periodontal diseases. One of the most important components of the host response is the GCF, which contains both specific and non-specific defence factors (Table 33.2).

Table 33.2 Specific and non-specific defence factors in gingival crevicular fluid

Specific Non-specific
B and T lymphocytes Polymorphs
  Macrophages
Antibodies: IgG, IgA, IgM Complement system
  Proteases
  Lysozyme
  Lactoferrin

IgG, immunoglobulin G.

Specific and non-specific plaque hypotheses

Although bacteria are definitive agents of periodontal diseases, there are conflicting views as to whether a single or a limited number of species are involved in the disease process – the specific plaque hypothesis – or disease is caused by any combination of a wider range of non-specific bacteria – the non-specific plaque hypothesis.

Periodontal health and disease

Healthy gingival sulcus has a scant flora dominated by almost equal proportions of Gram-positive and facultative anaerobic organisms; spirochaetes and motile rods make up less than 5% of the organisms (Table 33.3). With increasing severity of disease, the proportions of strict anaerobic, Gram-negative and motile organisms increase significantly (Fig. 33.3).

Table 33.3 Microorganisms associated with various types of periodontal disease

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Condition Predominant microorganisms Comments
Health Streptococcus sanguinis (previously Streptococcus sanguis) Mainly Gram-positive cocci with few spirochaetes or motile rods
  Streptococcus oralis

Jan 4, 2015 | Posted by in General Dentistry | Comments Off on 33: Microbiology of periodontal disease
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