Dental disease and malocclusion in Octodon degus

Dental pathologies/disease in Octodon degus are one of the most common causes of veterinary appointments. To date, more than 60% of the consultations for a degu concern a dental disease. The best known is malocclusion, although it is not the only one, as they can develop other dental pathologies. From the age of 2 years onwards, 76% of these rodents have tooth problems ⁰¹. Veterinary researchers have found that degus have a high requirement for calcium in their diet ⁰². However, most mixtures offered in pet shops are not adapted to the needs of these rodents ⁰³. In addition, it is essential for the degu to have good tooth wear. This requires chewing, and therefore a healthy diet, with fresh plants and hay available at all times ⁰⁴.

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The dentition of the Octodon degus

Tooth development

If the degu is born with functional incisors, it acquires its premolars and molars within a few days. The maxillary jaw is the first to develop teeth, with the premolars and molars erupting within 2-5 days after birth. It is only after 10 days that these crowns are fully effective. Thus, young degus will be able to feed by 8 days of age⁰⁵. However, it is only around the first 30 to 40 days that the premolars and molars really emerge, to be fully functional by 72 days after birth. This also corresponds with the age of weaning. Finally, contrary to a persistent rumour, it is very likely that Octodon degus has no milk teeth at all⁰⁶ or loses them during the management of their mother. At present, it is not possible to say whether the degu has deciduous teeth.

 

Anatomy

The teeth of the Octodon degus are rootless, with high crowns, called hypsodonts. Their growth is continuous⁰⁷, hence the importance of good chewing in degus⁰⁸. They have 20 teeth, whose dental formula is: I1, C0, P1, M3. This means that they have two pairs of incisors, two pairs of premolars and three pairs of molars. These dental characteristics are also shared by all rodents of the suborder Hystricomorpha, such as chinchillas and guinea pigs.

Degus have two pairs of incisors, which are visible and naturally coloured yellow/orange on the outside. They are separated from the premolars and molars by a large empty cavity, the diastema. The enamel of the incisors is only present on the orange side and on the edges, and their physiology makes these teeth very resistant to wear. The crowns are the part of the tooth below the gum line and in the alveolus, it is the “attachment” of the tooth. The part above the gum line, and therefore visible, is called the clinical crown. Finally, there are the premolars and molars at the back of the mouth, which are used for thorough chewing and, in case of problems, can create malocclusions. 

Abrasion and mastication

Because of its natural diet, the Octodon degus eats plants that are relatively low in energy. It therefore needs to eat a large quantity of plants to meet its needs. This involves a long and meticulous chewing process, which allows the teeth to wear well. The incisors and the other teeth play a separate role during meals. To chew properly, the incisors work from top to bottom, while chewing with the premolars and molars is done from left to right. These two “isolated” chews make double malocclusion rare in the wild. However, in captivity, double malocclusions are quite common. Rodents of the suborder Hystricomorpha have a specific muscular and articular anatomy in the mandibles, allowing them to chew and gnaw quite powerfully.

Mechanisms of dental disease

Dental disease, and in particular dental malocclusion, is one of the most common conditions in degus. Up to 76% of all degus seen in veterinary practices will be diagnosed with a dental problem⁰⁹⁰⁷. Moreover, they are sometimes “masked” by other diseases, such as respiratory diseases, which are in reality consequences of malocclusion. But if the degu is so inclined to this kind of pathologies, it is because its diet is often not adapted. The degu is mainly subject to dental malocclusion, but these are not the only dental pathologies that it can develop. Cavities or other infections are common and rarely detected⁰⁸. These can degenerate into an odontoma¹⁰, non-cancerous mass, but which may prevent the degu from eating or breathing, due to repeated rubbing.

Dental diseases are often very painful for the rodent, and can lead to many other health problems, such as the cessation of intestinal transit¹¹. In the degu, as in many small mammals, it is essential that the transit remains stable, because the degu eats all day long. But transit is far from being the only thing affected. Sight, hearing and smell can be affected, in various ways, to a greater or lesser degree. This also causes pain and stress, which can lead to other pathologies. It is a never-ending cycle, which will lead to chronic pain and stress.

Causes

Diet

In the wild, the degu spends most of its days outdoors, searching for food. Its diet consists mainly of plants (stems, leaves) and during the dry seasons, of grain¹². By chewing these plants, the degu wears out its premolars and molars spontaneously throughout the day. By eating seeds, pods or bark, it also wears out its incisors. Through its diet, but also its exposure to the sun, the degu will produce enough vitamin D, which is essential for the good growth of the teeth¹³.

These two types of chewing are complementary and should be offered in captivity. While the degu has a natural tendency to gnaw in its cage, often out of boredom, it is chewing that is most often the problem. Hay plays a very important role in this, but the degu often refuses to eat sufficient hay. This is often due to the fact that the octodon is fed too much food all the time¹⁴.

Food is the primary trigger for dental disease in degus¹⁵. The degu should therefore be fed a healthy diet with a maximum of 20% seeds¹¹which corresponds to its average consumption over a year in the wild, and 80% of plants¹⁶. This diet provides a high Calcium:Phosphorus ratio of at least 1.6:2¹⁷ for good tooth growth, but also provides a healthier chewing action. Pellets, because of their shape and compression, do not allow the animal to eat all day. In addition, the composition of the pellets is often not adapted to the degu’s needs, as they are too rich. The degu will then select its food and refuse to eat food that is lower in sugar or fat. The high calcium intake is essential for the degu, unlike other rodents, for a healthy dentition. Finally, thanks to the low energy intake, the degu will have an optimal weight. A veterinary team has developed a diet adapted to the Octodon degus, the SAB degu Mix. A regular supply of vitamin D is also essential for the good health of degus¹⁸.

Other causes

While diet plays a major role in dental disease, there may be other causes¹⁸ :

• Housing condition: lack of exposure to light or lack of UV intake induces a deficiency of vitamin D3, leading to several pathologies, including dental problems.
• Metabolic bone disease: this is a brittleness of bones and teeth, which is found in many rodents and may exist in the Octodon degus.
• Chronic tooth wear: usually induced by a diet consisting only of pellets, not allowing long chewing¹⁵.
• Genetic predisposition: Many other rodents may show genetic predisposition to dental disease in certain lines. These are numerous, and can include malformations of the skull or teeth.
• Traumatic damage: It is possible that by accident, teeth are dislodged or deflected by traumatic damage, which interferes with natural wear. This may be due to bites, falls or simply because the degu gnaws on its bars out of boredom.
• Stress: The Octodon degus is sensitive to loud noises or smells, or being too hot or too cold depending on the environment it is in. These conditions cause psychological and physiological stress. Stress reduces the strength of the periodontal ligaments, which hold the teeth in their sockets. The quality of the ligaments and gums is also affected, with injuries occurring more easily in stressed individuals¹¹. 

Symptoms

Symptoms of dental problems in the degu can go unnoticed quite easily. Indeed, it is possible that the degu presents a small weight loss over a long period, or presents symptoms which lead to other tracks, in particular respiratory. It is therefore essential to monitor the condition of the degu in order to detect dental problems early.

Among the most common symptoms, we find⁰⁷ : 

• Weight loss: One of the first symptoms of many health problems is weight loss, which is quite pronounced and long lasting. It is recommended that these degus be weighed on a weekly basis, so that their weight curve can be monitored.
• Excessive growth of the incisors: if the growth of the incisors is in itself a dental pathology, it can result from other health problems, not allowing the degu to wear the teeth correctly. Teeth may be too long, of different sizes or growing crooked.
• Massing around and under the jaw: this may be a sign of a dental problem. The degu may develop an odontoma or cancerous mass due to repeated rubbing of the tissue.
• Difficulty with chewing: If the degu has a lot of difficulty chewing, or “chokes” during feeding, it is possible that something is bothering its teeth.
• Drooling/hypersalivation: an animal that starts drooling may have dental problems, but also many other health problems.
• Feeding difficulties: the degu may have many feeding difficulties, and may stand near food, or pick it up and drop it.
• Nasal / eye discharge:  a degu that “cries” may be the result of an infection or perforation of the jaw related to a dental problem¹⁹.
• Difficulty breathing: it is possible that too much tooth growth is preventing the animal from breathing properly, or is causing discomfort, which can lead to lung infections.
• Dirty or unkempt coat: this may be a sign of pain or difficulty in using the tongue to properly maintain the coat¹⁵.
• Stopped transit: whether complete or partial, stopped transit may be related to problems.
• White or pale yellow teeth: white teeth in degu are a sign of dental imbalance and may also be related to other conditions.

Diagnostic

Whenever a dental problem is suspected, the degu should be taken to a competent veterinarian for diagnosis¹⁵.In order to do this, it will often be necessary to carry out one or more clinical examinations. First, the condition of the incisors can be checked and the skull palpated for any suspicious mass. It is necessary for the veterinarian to carry out a complete imaging of the head, in order to avoid missing early pathologies.

One of the most common ways of detecting malocclusions is by X-ray. The animal is anaesthetised and x-rays of the skull are taken from different angles to check the growth of premolars and molars. Computed tomography is also a good way to detect any problems, especially for molar crowns. However, it is also worthwhile for the veterinarian to carry out an intraoral examination, so that other lesions, such as periodontal disease, caries or dental resorption, are not missed. It is possible to perform these examinations via endoscopy⁰⁸, in order to be able to detect these dental pathologies, which are not always visible by radiography. Finally, a “manual” examination must also be carried out by the veterinarian, through observation and palpation of the degu’s skull, in order to detect possible pathologies and to check the state of the incisors and the mouth.

Treatments

There are several methods to treat your degu. They almost all require a surgical act, under general anaesthesia. According to the diagnosis, the veterinarian will have to treat the degu in the most adapted way. It is possible to simply file the teeth in the simplest cases of malocclusions, but also to remove cancerous masses… Only a veterinarian is able to make the diagnosis and choose the appropriate treatment. In addition to the procedure under anaesthesia, the veterinarian may provide antibiotic treatment, analgesia or nutritional support. Unfortunately, it is not possible to permanently fix dental disease, so regular monitoring is necessary to avoid relapse, as well as good feeding management.

Dental diseases and disorders in Octodon degus

Incisor disorder

Malocclusion

Malocclusion of the incisors is the excessive growth of the incisors, or irregular growth, which no longer allows natural wear movement.

It is the easiest dental malocclusion to understand because it is directly visible. This pathology comes from the elongation of the incisors, or an irregular, “twisted” growth of the latter. Incisor-related diseases and especially coronal elongation can be related to poor nutrition and malocclusion of molars and premolars in the mouth. 

Other pathologies

The degu can also develop other incisor pathologies than malocclusion. Indeed, it is possible to encounter pathologies such as depigmentation, enamel hypoplasia (the degu has white teeth), ridges on the enamel, or demineralisation of the cementum or dentine. These pathologies are due to disorders of the germinal tissue, linked to metabolic imbalances. The latter are often due to a poor diet, systemic diseases or trauma (accidents, bites, ….). It is therefore important to regularly check the condition of your degu’s incisors.

Tooth whitening is also a sign of an important dietary imbalance and requires a revision of the overall diet. In general, the degu should have orange teeth, if they become pale or yellow, this is a sign of incipient bleaching. If the degu has had white teeth for some time, it is very important to check the overall condition of the jaw to avoid missing another related dental condition.

Premolar or molar disorders

Malocclusion

Dental malocclusions of the premolars or molars are the excessive growth of these teeth, which may result in the choking of the animal or the perforation of jaw bones.

Dental malocclusions, particularly those affecting premolars and molars, are very common in rodents, and are most common in the Octodon degus. In chinchillas, malocclusions appear to be related to nutritional and genetic causes, which are the dominant factors in dental pathologies. In captivity, degus tend to have longer teeth than in the wild. This is related to reduced chewing, especially due to the unsuitable and less abrasive industrial food. In degu, dietary imbalances and lack of calcium, with a Ca:P ratio of 1:1, leads to malocclusion of all teeth in just 6 months!¹⁷In addition, it also reduces the bone density in some parts of their body. It is the excessive growth of premolars and molars that causes most of the clinical signs associated with dental disease in degus. The elongation of these teeth can lead to pain in particular, due to the pressure of the teeth on the nerve endings. In addition, it is possible for the tooth to grow through tissue and damage the oral area, or puncture bony areas, such as the nasal or frontal bone.¹⁹. It is then possible to feel irregularities during palpation of the external areas of the jaw.

Other diseases

With impaired chewing, the octodon may have swallowing problems or develop pronounced dysphagia. The crowns of the molars also tend to elongate in the degu, often towards the tongue. It is then possible for the teeth to “jam” the tongue in severe cases, with the formation of a dental “bridge”.

Periodontal disease

Periodontal disease attacks and destroys the tissues that support the teeth, such as the gums and bones²⁰. It is a bacterial disease that develops slowly, sometimes over several years.

Little studied in the degu, it is a very common disease in the chinchilla, which is a closely related species. It is therefore possible that this disease, which affects 63% of chinchillas, is also present in the degu²¹. This disease is related to various factors such as: other dental pathology, genetic factors, age, oral microflora and nutrition. Untreated periodontal disease will progress and lead to bone and tooth resorption.

Dental resorption

Dental resorption is the progressive disappearance, physiological or pathological, of the crown and/or root of a tooth.

In the degu, this leads to the loss of the clinical crowns of the premolars and molars. This greatly impairs chewing and feeding. The loss of the tooth creates a void where food remains can lodge, thus creating other pathologies (caries, periodontal disease). Tooth resorption can also create a malocclusion due to the lack of wear of the opposing tooth. This condition is a source of chronic intraoral pain, leading to reduced and insufficient food intake followed by weight loss and potential metabolic complications such as ketoacidosis (a complication of diabetes) and hepatic lipidosis (a kind of jaundice). Therefore, patients with clinical signs and symptoms suggestive of periodontal disease should be assessed and treated appropriately.

Dental caries

Dental caries is the demineralisation and destruction of the tooth after a bacterial infection. This occurs through the production of lactic acid by cariogenic bacteria²². Present in many chinchillas, more than 50% of rodents in captivity, decay can also affect the degu. Again, the diet is to blame. High sucrose levels, as well as a lack of long chewing, lead to the formation of cavities. Indeed, poor chewing can lead to increased plaque formation on the teeth and reduced salivation. In addition, dental malocclusions of molars and premolars also lead to the accumulation of bacterial plaque, which is linked to caries²¹.

Néoplasie et lésions cancéreuses

The most common oral tumours in degus are elodontomas²³. They are defined as a continuously developing hamartoma of odontogenic tissue and alveolar bone at the periapical bud of elodont teeth²⁴²⁵. In simple terms, a large mass of tissue that develops in the area of the skull. These lesions are related to trauma, inflammation, age or other dental diseases, especially malocclusions. The life expectancy of a degu with this type of pathology varies greatly, with an average of 6 months, with palliative treatment and assisted feeding. 

Other tumours found in the oral cavity of degus include melanoma and fibrosarcoma²⁶. Finally, the degu may develop “pseudodontomas”, (pseudoneoplastic lesions) as a result of the continuous deposition of dental structures, creating a mass. Unfortunately, this mass can obstruct the nasal cavity, causing intermittent or chronic mild to severe respiratory distress.²⁴.

Dental abscesses

Abscesses are lumps of pus in a body cavity. In degus, these can be related to primary (bacterial) or secondary infections. The latter can have several causes, such as trauma (bites, splinters, …) or other dental diseases. They can develop around the teeth and in the soft tissues for the most important ones. It is not uncommon for dental abscesses to be related to malocclusions. In this case, it is necessary to differentiate between²⁷ if they form at the base of the tooth and are then related to the penetration of the root in tissues or if they form in the soft tissues, due to an elongation of the dental crowns. These different abscesses need to be managed appropriately in order to treat the degu correctly. 

Conclusion

In order to avoid as much as possible the dental pathologies so common in degu, it is advisable to control its diet. On the one hand by proposing an adapted diet, with a rate of Calcium:Phosphorus of at least 1,6:1, up to 20% ²¹, but also of many plants, dry or fresh, in order to allow an optimal chewing, up to 80% of the diet. In order to maintain the health of the chinchilla, a regular supply of vitamin D is essential.

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