31 Pulp and periapical disease – an introduction
Trauma to a tooth (mechanical, chemical, thermal, infective) often results in pulpal inflammation (pulpitis). Depending on the type of trauma, its severity or duration, the pulpitis may be reversible, but often this is not the case and the inflammation becomes irreversible. The result of untreated irreversible pulpitis is pulp necrosis, followed by the spread of inflammation to affect the apical periodontium (apical periodontitis) and the periapical bone, resulting in bone destruction around the apex of the root (periapical disease).
A tooth affected by pulp and periapical diseases should always be treated, it cannot just be ignored. There are two available treatment options, namely to extract the tooth or to perform endodontic treatment and retain the tooth. Endodontic therapy is a specialist procedure and should not be undertaken without adequate training and supervised experience. The principles of endodontic therapy, which allows a tooth to be maintained, are outlined in Appendix 4.
The immature tooth has a wide pulp cavity. As the tooth matures, secondary dentine is laid down and the pulp cavity becomes narrower. Note that the contours of the pulp chamber mimic the shape of the crown, so the pulpal horns are always relatively close to the surface. Consequently, crown fracture very often involves exposure of the pulp in the older animal as well as the young.
As the animal gets older there is normally a reduction in the size of the pulp cavity, which is associated with continued deposition of secondary dentine. There are conditions that accelerate the rate of deposition of secondary dentine, thus prematurely reducing the size of the pulp cavity. Attrition and abrasion are two common conditions resulting in a narrow pulp cavity. Injury, orthodontic force and disease can all alter and decrease the pulp chamber and canals. In extreme cases, injury to a tooth will result in the complete obliteration of the pulp chamber and root canals. More unusually, the obliteration is partial, with the pulp chamber retaining the size and shape it had at the time of the injury, and the root canals becoming completely obliterated. On the other hand, injuries that cause inflammation and degeneration/necrosis of the pulp also account for many abnormally large pulp cavities, as dentine production ceases when the pulp is chronically inflamed or necrotic.
Pathology in the area surrounding the apex of a root, i.e. periapical pathology, is most commonly a sequel to chronic pulpitis or pulp necrosis. The source of the infection may be blood borne, but such cases are rare. The earliest radiographic evidence of periapical pathology is widening of the periodontal ligament space in the apical region. This widening is due to inflammation of the apical periodontal ligament. If untreated, the apical periodontitis progresses to involve the surrounding bone, resulting in destruction of the bone, which is replaced by soft tissue. This is evident as an apical rarefaction on a radiograph. The soft tissue may be granulation tissue (periapical granuloma), cyst (periapical or radicular cyst) or abscess (periapical abscess). Definitive differentiation between these three possibilities requires histopathology of the tissue. In veterinary dentistry, histopathology of periapical lesions is rarely performed. Treatment for all three entities is the same, i.e. endodontic therapy or if there are complicating factors, e.g. advanced periodontitis, then extraction. It is important to remember that not all apical rarefaction is pathological in dogs and cats. The periapical bone of normal canines often appears radiolucent in the dog. Comparison should always be made with other teeth of the same type in the same animal. A distinctly round radiolucent area, however, is usually pathological. Periapical sclerosis, instead of radio-lucency, as a result of a chronically inflamed/necrotic pulp can sometimes be seen.
The periapical cyst usually occurs as a sequel to the periapical granuloma. It is a true cyst, since the lesion consists of a pathological, often fluid-filled, cavity that is lined by epithelium. Periapical cysts enlarge due to the osmotic gradient set up between the lumen of the cyst and tissue fluids in the surrounding connective tissue. These lesions can become very large at the expense of the adjacent bone tissue, which is resorbed due to pressure from the cyst.
An untreated periapical abscess can lead to complications such as osteomyelitis and cellulitis through spread of the infection. A fistulous tract opening on the skin or oral mucosa may develop.
Periapical lesions may be entirely asymptomatic or excruciatingly painful. The periapical granuloma and periapical cyst rarely cause severe discomfort, but they may undergo exacerbation and develop into a periodontal abscess, which usually is an extremely painful condition. The clinical signs indicative of periapical pathology are often insidious and not noticed by the owner. It is often only after completion of treatment that the owner reports a dramatic improvement in the animal’s general demeanour. Consequently, periapical lesions confirmed by radiography should be treated even if the animal is not showing obvious signs of pain or discomfort. Similarly, discoloured teeth with a necrotic pulp need to be treated before periapical pathology develops. Once diagnosed, patients with necrotic pulps and periapical pathology should receive endodontic treatment (referral) or extraction of the affected tooth as soon as possible.