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Periodontal disease is a collective term for a number of plaque-induced inflammatory lesions that affect the periodontium. It is a unique infection in that it is not associated with a massive bacterial invasion of the tissues. '''Gingivitis''' is inflammation of the gingiva and is the earliest sign of disease. Individuals with untreated gingivitis may develop '''periodontitis'''. The inflammatory reactions in periodontitis result in destruction of the periodontal ligament and alveolar bone. The result of untreated periodontitis is ultimately exfoliation of the affected tooth. Thus, gingivitis is inflammation that is not associated with destruction (loss) of supporting tissue – it is reversible. In contrast, periodontitis is inflammation where the tooth has lost a variable degree of its support (attachment) – it is irreversible. Infection of the periodontium may cause discomfort to the affected animal. There is also strong evidence that a focus of infection in the [[Oral Cavity Overview - Anatomy & Physiology|oral cavity]] has been associated with disease of distant organs. Consequently, prevention and treatment of periodontal diseases is, contrary to common belief, not a cosmetic issue, but a general health and welfare issue.

Periodontal disease is a collective term for a number of plaque-induced inflammatory lesions that affect the periodontium. It is a unique infection in that it is not associated with a massive bacterial invasion of the tissues. '''Gingivitis''' is inflammation of the gingiva and is the earliest sign of disease. Individuals with untreated gingivitis may develop '''periodontitis'''. The inflammatory reactions in periodontitis result in destruction of the periodontal ligament and alveolar bone. The result of untreated periodontitis is ultimately exfoliation of the affected tooth. Thus, gingivitis is inflammation that is not associated with destruction (loss) of supporting tissue – it is reversible. In contrast, periodontitis is inflammation where the tooth has lost a variable degree of its support (attachment) – it is irreversible. Infection of the periodontium may cause discomfort to the affected animal. There is also strong evidence that a focus of infection in the [[Oral Cavity Overview - Anatomy & Physiology|oral cavity]] has been associated with disease of distant organs. Consequently, prevention and treatment of periodontal diseases is, contrary to common belief, not a cosmetic issue, but a general health and welfare issue.

Initially, the bacterial flora tend to be non-motile aerobes or facultative anaerobes. However, as the supply of oxygen is reduced by supragingival plaque accumulation and pocket formation, the bacterial flora become more motile and anaerobic. Important bacterial flora responsible include ''Porphyromonas gingivalis, Bacteroides asaccharolyticus, Fusobacterium nucleatum, Actinomyces viscosus'' and ''Actinomyces odontolyticus''.  

Recent research into dog periodontitis has shown that the bacteria present in healthy canine mouths differ significantly from those found in healthy human mouths. Dogs lack significant numbers of streptococcal species which helps to explain why the incidence of [[Dental Caries]] is so much lower in dogs than humans. Instead, healthy canine plaque is dominated by aerobic gram negative bacteria including several ''Neisseria'' species along with ''Bergeyella zoohelcum'' and a canine ''Moraxella'' species. These differences between dog and human oral microbiology are important as they indicate that products or treatments developed for human oral care may not automatically be suitable for dog oral care. Treatments targeted at ''Streptococcus mutans'' are a case in point as we now know that dogs do not have this bacterium in their mouths. As periodontal disease progresses, the oral bacterial population shifts towards a more gram positive distribution with anaerobic species becoming more prevalent as the supply of oxygen is depleted, especially in periodontal pockets. Members of the genus Peptostreptococcae become much more prevalent, although the role of these bacteria is not yet known. Whether specific bacteria cause the onset of periodontitis has not yet been proven in either dog or human and it may be that the transition to the disease state might be facilitated by multiple different combinations of bacteria working together.

Gingival inflammation starts because of dental calculus (tartar) from diets high in minerals and diets consisting of soft rather than hard crunchy food. Dental plaque becomes calcified and the whole [[Enamel Organ#Crown|crown]] may become covered in brown chalky material. Calculus forms a brittle dirty brown covering to the tooth which may not affect the [[Enamel Organ#Enamel|enamel]] at all but may produce mild gingivitis around the edge and the gum may start to recede. This exposes more of the crown, and may subsequently reach the level of the [[Enamel Organ#Dentine|dentine]] and infection may enter the alveolus and loosen the ligaments holding tooth in and ultimately the tooth will become loose and fall out.

Dental calculus (tartar) forms when plaque is left undisturbed for a number of days. Calcium salts from saliva start to become deposited in the plaque causing it to harden and become resistant to removal. Diets high in minerals and diets consisting of soft rather than hard crunchy food exacerbate the problem. As dental plaque becomes calcified and the whole crown may become covered in brown chalky material. Calculus forms a brittle dirty brown covering to the tooth which may not affect the enamel at all but may produce mild gingivitis around the edge and the gum may start to recede. This exposes more of the crown, and may subsequently reach the level of the dentine and infection may enter the alveolus and loosen the ligaments holding tooth in and ultimately the tooth will become loose and fall out.

'''Gingivitis''' - Reversible inflammation of the marginal gingival tissues that does not affect the [[Enamel Organ|periodontal ligament or the alveolar bone]].

'''Gingivitis''' - Reversible inflammation of the marginal gingival tissues that does not affect the [[Enamel Organ|periodontal ligament or the alveolar bone]].