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Treating the discoloured tooth

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01 May 2010, at 1:00am

BOB PARTRIDGE explains why a discoloured tooth needs treatment.

“BUT my previous vet said, ‘Just keep an eye on it…’” Of all of the comments I hear in my practice, this is the one that most commonly fills me with dread. Let’s have a look at one of the dental conditions that clients are commonly recommended to “monitor”.

Cause of discolouration 

Discolouration of teeth (Figure 1) can occur from cigarette or caffeine staining – fortunately, few of our pets indulge in these vices. The commonest single cause of generalised staining is from haemorrhage within the pulp. 

Going back to dental anatomy, the pulp chamber at the centre of the tooth contains the blood vessels, nerves and lymphatics that supply the tooth. Typically haemorrhage results from blunt trauma to the tooth – biting on a stone or a bone, catching a hard ball or fighting with another dog
would be common examples. 

The structure of dentine is a mass of tiny tubules radiating out from the pulp towards the enamel at the outside of the tooth. The freed blood leaks down into the tubules and then undergoes haemolysis and releases haemoglobin. This further degrades (into haematoidin, haematoporphyrin and haemosiderin), effectively releasing iron which combines with hydrogen sulphide to produce the black compound, iron sulphide. 

This same process occurs in the development of a bruise with the characteristic colour changes from red or pink, to a bluish colour and finally to a darker grey-brown. As cat and dog enamel is relatively thin, its translucent nature allows the discolouration of the dentine to be clearly seen. 

In 2001, a retrospective study of 84 discoloured teeth concluded that 92% of these teeth were suffering from irreversible pulp necrosis. In man this is an acutely painful condition and there is no reason to suppose that it is any different for our species. 

Initially, the pain stems from increased pressure affecting the nerve endings within the tooth. Once the pulp contents become necrotic, the nerve endings within the tooth die. However, the chemical inflammatory mediators can still leak out of the apical delta and stimulate healthy nerve endings in the periodontal area of root apex. In other words, the tooth is dead – but the pain carries on. 

The area of inflammation at the root apex is also a fertile incubation site for blood-borne bacteria (a process called anachoresis) and so a tooth root abscess can develop without an obvious tooth fracture.

Trained observers 

As veterinary surgeons, we are trained observers. The trouble is that often the mouth and dentition does not get the attention it deserves. Twirl your Hercule Poirot moustache and observe Figures 2 and 3. 

It is clear that 404 (the lower right canine) is discoloured. This is a more recent injury than Figure 1 as the colour is fairly pink rather than grey. Comparison with the upper canine 104, or its opposite number on the lef

However, how many general practitioners would recommend treatment? Unfortunately, for many dogs this means that they are condemned to on-going low grade discomfort, with occasional episodes of acute pain. How many of the “bad tempered” GSD’s actually relate to this sort of dental problem?
All too often it is only when anachoresis leads to the tooth root abscess (seen as the pustule arising from the canine root – located dorsal to the 1st premolar in Figure 4) that treatment is advocated. 

Fortunately, many of my referring practitioners are aware of this problem and spot trouble early. 

Unfortunately, irreversible pulpitis has only two treatments: extraction or endodontic (root canal) therapy. 

On preparing a discoloured tooth for treatment, it is easy to see how the discolouration arises. The central pulp (Figure 5) is clearly visible (it is also worth noting that it is not bleeding, indicating the non-vital nature of the pulp) with the discolouration radiating out towards the unaffected white enamel. 

Using a barbed broach, the necrotic pulp contents can be removed (Figure 6). If these teeth are treated fairly early (as in this case) then the classic “rotting flesh” smell which characterises many root canal treatments will not be detected.