Grey or purple teeth – non-vital pulp
The veterinary surgeon needs to be aware of teeth whose damage is less dramatic than a fracture but whose need is often greater.
Grey canine following damage Transillumination of canine.
Discoloration of a tooth is normally due to trauma to the pulp and subsequent bruising leading to hemorrhage within the canal. This is usually from blunt trauma to the tooth. Common causes are catching frisbees, accidental clashes whilst playing and biting or catching hard objects like stones, bones or hard toys.
In addition the tooth may have subluxated (moved) within the socket sufficiently to cause rupture of the blood supply at the apex of the root. If blood supply to the pulp is lost the pulp will subsequently die (ischaemic necrosis).
When bleeding occurs inside the tooth, iron within the haemoglobin combines with sulphides to form iron sulphide, which then lodges within the dentin tubules to cause a purple or black colour. In addition, a pulpitis forms which studies show to be irreversible and lead to pulp death on over 92% of cases.
(Hale AF, Localisezed intrinsic staing of teeth due to pulpitis and pulp necrosis in dogs. J Vet Dent, vol 18, 1 (March 2001) pp 14-19).
This seminal reference helped us understand the best way forward with these teeth. Our normal recommendation is now to root fill or remove them. We NO LONGER WAIT to see the effect of serial radiographs over time as we feel that radiographs understate the problem. In addition, one of our dogs had this problem after a collision with another dog. Our dog was very dull and disinterested in life until we found the tooth. Once root filled we returned to normal in 3 days!
Canine undergoing root canal Files inside tooth on radiograph
Final radiograph: pulp replaced Final image - note improvement with gutta percha rubber following removal of pulp
Pulpitis and pulp death is hard to demonstrate in dogs, as it requires an accurate response from the patient to concussion and temperature tests. In general we use transillumination (see above) to assist diagnosis - along with dental radiographs. A normal tooth should evenly opalesce when backlit by a powerful light. A "dead" tooth with necrotic pulp within will block the light. Also, pulpitis cannot be seen on a radiograph but the effects can be over time once the toxins leak out of the tooth.
If the pulp dies, the odontoblasts within the canal also die. The dentine walls no longer thicken compared with the opposite normal teeth and, as necrosis ensues, the appearance of the pulp changes from a homogenous ground glass appearance to a more patchy density. An apical lucency/granuloma/abscess may also be visible. At the very least, these teeth should be radiographed to demonstrate any current pathology.