to many, dental caries, also known as “dental decay” or “cavities”, is better recognised from personal experience at the dentist’s office than from veterinary practice; dental caries is very common in people and has a comparatively low prevalence in dogs. One study recorded an incidence of 5.3 percent amongst a population of dogs presenting to a dental referral service (Hale, 1998). This article aims to raise awareness about this condition, its diagnosis and the main differential diagnosis. Treatment options depend on how advanced the caries lesion is and range from restorations (“fillings”) to the extraction of the affected tooth.
Anatomy of the tooth crown
The crown of a tooth consists of three principal tissues. Dentine forms the bulk of the crown; it is a hard, non-vascularised tissue. Dentine is covered by a layer of enamel, and in the centre of the crown is the pulp: a soft tissue structure consisting of blood vessels, nerves, lymphatic vessels, connective tissue and odontoblasts. Enamel is the hardest structure in the body, containing 96 percent inorganic material; dentine has a relatively lower inorganic component of 70 percent, and the added organic matter increases resilience to impact forces.
Caries is a multifactorial condition (Mount and Hume, 1998) and, if conditions are met, acids released by bacteria demineralise first the enamel and then dentine, permitting bacteria to invade deeper, until significant loss of structure of the crown is encountered. The pulp may be infected once the carious lesion has progressed sufficiently deep, and dental caries is one of the commonest indications in humans for root canal therapy. Factors promoting the development of caries lesions are regular dietary intake of sugar and erosive dietary acids, a low salivary pH, plaque presence and a reduction in salivary flow.
Dogs predisposed to dental caries
While the mean salivary pH in dogs is high (at 7.5) com-pared to humans (average pH of 6.5), and regular dietary intake of sugar tends to be lower in dogs, the combination of a number of factors may predispose a dog to the development of caries lesions.
In dogs with normal saliva production, a main factor appears to be regular sugar intake at sufficiently high concentrations. This may be refined sugar in human food, such as sweetened peanut butter, slipping the dog a daily cookie or sharing a piece of jam on toast every morning as a treat. It may also be a food item rich in natural unrefined sugar, such as honey. Dogs clearing the garden from fruit that has fallen off the tree are also at risk, despite the relatively lower sugar content, as fruit contains acids that contribute to the erosive demineralisation of the tooth surface. The most common sites of caries lesions are the occlusal pits of the molar teeth, and the developmental grooves of the maxillary fourth premolar teeth and the mandibular first molar teeth (Figure 1).
Dogs suffering from xerostomia are at an increased risk of the development of dental caries, and in these cases, caries lesions can also be found on the crown wall, close to the gingival margin.
Diagnosis of dental caries
Close inspection of the occlusal pits and developmental grooves of the molar and premolar teeth should be part of any routine dental examination under anaesthesia. The presence of dark discoloration in these areas should prompt an exploration with the sharp tip of a dental explorer. If the explorer tip sticks in the lesion, it is most likely a caries lesion, as healthy enamel should be an uninterrupted hard surface that does not let the explorer tip sink into it.
Scratching over the hard enamel surface can be both heard and felt, as the dental explorer transmits a tactile sensation to the fingertips of the operator. The index of suspicion of a dental caries lesion is further increased if a plug of plaque is noted in the centre of the discoloured groove or occlusal pit.
Dental radiography is required preoperatively to determine whether there are signs of pulp involvement such as periapical lucencies and an abnormal pulp canal width and shape. A post-operative radiograph is taken if the tooth received a restoration.
A study (Hale, 1998) found that around half of the dogs with caries lesions had bilateral and fairly symmetrically distributed lesions. It is therefore advisable to examine the entire mouth, and particularly the other molar teeth and the maxillary fourth premolar tooth, closely following the diagnosis of a caries cavity (Figure 2).
The most common cause of a brown spot in the occlusal pit of a maxillary molar tooth in the dog is food staining. The dental explorer tip will not stick in food staining, and the operator can feel that the tooth surface is still hard. Occasionally, a dark foreign body, such as small pieces of wood, may be stuck in the developmental grooves of the carnassial teeth; this should become clear on closer inspection, and the dental explorer or a dental hand scaler should be successful in the removal of the particle.
An advanced caries lesion may at first look similar to a traumatic crown fracture. A closer inspection and exploration with a dental explorer will reveal the carved-out appearance of the cavity, the softened dentine on the inside of the caries cavity and the characteristic sign of knife-sharp enamel edges created by advanced caries.
If the caries lesion has been diagnosed early enough, it can be treated with a restoration. This includes judicious removal of carious dentine with dental burs and special dental hand instruments: sharp spoon excavators. The floor of the clean cavity is inspected for any signs of pulp involvement, such as bleeding; if endodontic involvement was identified, the tooth should either be extracted or receive root canal therapy prior to proceeding with a restoration (Figure 3).
An advanced caries lesion goes along with substantial loss of tooth structure, and extraction is the only treatment option (Figure 4).
Unlike in caries prevention in humans, the regular use of fluoride-containing toothpaste in dogs is not recommended, as dogs swallow their toothpaste. The best prevention is toothbrushing with a toothpaste suitable for pets, combined with avoidance of any treats containing sugar. Many pet carers are, on initial discussion of their dogs’ caries, quite certain that their pet does not receive sugary treats. But a source is typically found after careful questioning, as the “culprit”, for example, may be a family member who gives a daily cookie without anyone else’s knowledge!
The author recommends regular use of a dental explorer during dental diagnostics, and particularly the exploration of suspected food staining in occlusal pits or developmental grooves, as a number of these will be dental caries. When diagnosed early, important large teeth, such as a carnassial tooth or maxillary first molar tooth, make good candidates for restorative treatment. Even if the tooth is extracted, early diagnosis saves the patient pain from invasion of the pulp tissue by caries bacteria. It is the author’s hypothesis that dental caries is underdiagnosed in dogs, and additional studies are required to further investigate the prevalence.