THE American Veterinary Dental College (AVDC) has recently revised its classification of dental fractures. The aim of this article is to try and help veterinary surgeons standardise their use of the new terminology and to discuss some clinical features.
The typical passive biting force of dogs is of the order of 300-800 psi (2,000-5,500 Kpa) and the abrupt snapping biting force can be 100 times this value – so dogs’ teeth are designed to be highly resilient.
An outer coating of enamel (the hardest substance in the body) covers a lining of dentine, which in turn protects the sensitive pulpal tissues. The tooth itself is then suspended in a complex shock absorber, the periodontal ligament, which helps diffuse much of the biting forces. It is a testament to this normal strength and design that tooth fractures are not more common.
Enamel infraction
Figures 1A and 1B show infraction: these are typically old teeth in dogs that have been active chewers. The enamel has a series of fine lines or cracks running across its surface. There does not seem to be any increased sensitivity in the teeth and whilst there is a theoretical weakening of the tooth, this does not appear to have any clinical relevance.
The good news is that these teeth usually require no treatment; however, as an indicator that the teeth may have been subject to repeated and strong forces, it makes sense to closely examine the rest of the mouth for any other more severe fractures.
Enamel fracture
Enamel fracture is where the fracture has actually removed a small fragment of the enamel, exposing a deeper layer of enamel or the underlying dentine. These little fractures are commonly seen along the cusps of the teeth (Figures 2A and 2B).
These fractures will frequently go undiagnosed and will often cause little or no problems. Occasionally there may be heightened sensitivity, especially in younger dogs where the pulp chamber is wider and closer to the exposed fracture site. A small “patch repair” of light-cured composite can be applied at the time of another procedure.
Uncomplicated crown fracture
A deeper fracture line exposes the tooth’s dentine – but does not impinge on the pulp chamber itself. It is important to remember that dentine’s structure is a series of small tubes (like a stack of straws) that run towards the pulp chamber.
These are formed by the odontoblasts which lay down the dentine and continue to do so during the life of the tooth. If the odontoblast dies, then a direct channel is opened up to the pulp chamber itself. This intimate relationship between the dentine and the pulp chamber (which contains the tooth’s blood vessels, nerves, lymphatics, etc.) explains why uncomplicated tooth fractures (Figures 3A and 3B) are frequently associated with some sensitivity of the teeth. Dogs may be reluctant to drink very cold water, or may preferentially use one side of their mouths.
Although, as can be seen from the radiograph (Figure 3C), the pulp chamber itself is not compromised by the fracture, these fractures can occasionally lead to tooth death. Radiographic assessment and follow-up is desirable.
Wherever possible I like to place a protective “cap” over these fractures. After the tooth is prepared it is carefully acid etched. It is important to remember that the exposed dentine can provide a pathway for irritants to affect the pulp – therefore etching is never as prolonged as it would be for uncompromised enamel.
A light-cured adhesive is then applied and a “white filling” of lightcured composite is placed over the exposed fracture site. After curing, the filling is carefully shaped and polished to try and limit plaque accumulation post-operatively.
Clients frequently report an improvement in the dog’s behaviour post-operatively.
Figures 4A and 4B show an uncomplicated fracture and its repair.
Complicated crown fracture
With a complicated fracture, the fracture line extends into the pulp chamber (Figure 5).
Whilst not recognised in the AVDC classification, clinically these fractures can be divided into “fresh” and “old”. Fresh fractures may present with acute pain and bleeding from the exposed pulp, or for a few days they will still show a pink or reddish pulp. For these very acute fractures, it can be possible to preserve the vitality of the tooth by performing a vital partial pulpotomy.
Here the tooth is prepared in a sterile fashion, a small portion of the pulp is removed – hopefully retaining healthy vital pulp. A “bandage” of calcium hydroxide (I initially use a powder preparation, then a solid version) is followed by a white filling material.
The sooner a fractured tooth is presented, the better the chances of a successful vital partial pulpotomy (Figures 6A to 6F); if left more than 24-48 hours, success rates decrease. Additionally, the older the tooth, the narrower the pulp chamber and the poorer the blood supply – this can also decrease the chances of success.
If this procedure is performed, it is vital that the owner “buys into” the fact that follow-up radiographic assessment will be required for a minimum of three years – as “late failures” have been known. If the fracture is older, the tooth more mature, or if a more certain result is required, then a full root canal treatment (or extraction) should be performed.
Older fractures tend to present with a darkly coloured or black pit at the entrance to the exposed pulp cavity. These teeth require either extraction or full root canal treatment; if left, tooth root granulomae or root abscesses will develop.
Certainly they are associated with on-going pain and malaise – however, this may only be recognised by the owner (or veterinary surgeon) after treatment has resolved the problem.
Abrasion
Abrasion is not a fracture of the tooth, merely an abnormal excessive wearing process (as opposed to attrition, which is the normal wear from mastication). With excessive wear, the crown of the tooth is reduced in height, bringing the pulp chamber closer to the active surface of the tooth.
The odontoblasts lining the pulp chamber respond to this by laying down reparative (Figure 7A) or tertiary dentine to allow the pulp chamber to retreat away from the active surface. This tertiary dentine is often more disorganised and tends to take up staining from the oral cavity, resulting in a brown pigmentation.
This can be difficult to differentiate from an exposed pulp chamber (Figure 7B) unless a dental explorer is run over its surface. The probe will drop into the pit of an exposed pulp chamber, whereas it will glide over the surface of reparative dentine.
One of the worst causes of dental abrasion is tennis balls (Figure 8). These trap dirt and grit in their fabric and effectively act as sandpaper on the teeth. Sometimes the wear patterns are quite characteristic. Kong toys and similar pose fewer problems.
Uncomplicated crown root fracture
Figures 9A to 9C show uncomplicated crown root fractures and 9D with a crown in place.
Because of the gingival attachment, the fractured tooth fragment may remain in place, which can hinder diagnosis. However, because the “enamel bulge” of the tooth is lost, food materials tend to pack into the periodontal space, inevitably leading to periodontal disease.
Whilst crowns in a situation where they will be closely adjacent to the gingival margin are not ideal, they do allow protection of the sensitive periodontal areas. Therefore, with compliant clients providing good oral hygiene, they can be considered.
Complicated crown root fracture
Figure 10 shows a complicated crown root fracture. If the fracture line extends just below the gingival margin, then the tooth can sometimes be salvaged by using a procedure to “crown lengthen the tooth (effectively moving the gingival attachments down onto the root of the tooth) and then performing a root canal treatment. However, many cases are similar to those in Figures 11A and B which are impossible to treat and require extraction.
Root fractures
The clinical signs of a root fracture (Figure 12) will vary with the level of the fracture. If the fracture is within the first third (the most apical portion) of the root, then the tooth is likely to be quite stable.
The tooth may also survive and the tooth root may heal if the trauma has not been too severe and there is minimal displacement. However, if the blood supply is compromised then the tooth may die and colour changes can be seen on the tooth crown.
If the fracture is within the coronal third (the portion nearest to the crown), then the crown itself may be unstable and be identified for extraction.
Without a pre-operative radiograph, the veterinary surgeon may be faced with an unpleasant surprise when only extracting a portion of the tooth root and faced with a more complicated extraction than expected.
Conclusion
Using the internationally agreed terminology will assist both in accurate record-keeping and also in providing the practitioner with assistance in decision making.
