Introduction

The tissues that invest the roots of the teeth and provide their support, the alveolar process, periodontal ligament, cementum and gum, are known collectively as the periodontium (around the teeth). The term parodontium (beside the tooth) has a history at least as long and has much otherwise to recommend it; however, periodontium and its derivatives has the wider usage. Diseases of the periodontium are referred to as periodontal diseases. Nearly all are inflammatory in origin and commence as an inflammation of the gum margin, namely gingivitis. Most are chronic and persistent, and therefore in due course may involve the deeper tissues leading to loss of bone, beginning with the crests of the alveoli. There is deepening of the gingival crevices.

Some degree of chronic gingivitis is said to be almost universal in man and fully-fledged chronic periodontal disease is as common a cause of tooth loss as dental caries. Hence periodontal disease in man has been the subject of intensive study and most of our ideas of the cause and mechanism of periodontal disease in animals derive from research directed to an understanding of the human state. The following is a brief account of the mechanisms that seem to apply in general.

Bacterial plaque has already been referred to in Chapter 21 as forming on the tooth surface. However, plaque also extends to the margin of the gingiva (Fig. 24.1). This gingival plaque is formed in the same way as coronal plaque; that is, even if we assume a completely clean surface to begin with, following a meal, a layer of saliva containing food substance remains as an adsorbed layer on the surfaces of the tooth and gingiva.