Introduction

The incidence and severity of many oral problems (e.g. periodontal disease) increase with age; however young animals can also suffer from oral or dental disorders. The timely diagnosis and treatment of these diseases is essential and can often prevent the development of serious oral problems in later life; it is therefore important to inspect the mouth of young animals during every examination. Related to this, the question often arises as to whether an oral abnormality is hereditary or not, and in many cases this cannot be easily determined; careful history-taking (e.g. trauma, infection, similar changes in related animals) may help, and if a potentially hereditary disease is present, advice on good breeding practice should be given. Whether hereditary or not, proper treatment should always be the primary focus and this article reviews some common oral and dental problems in young dogs and cats in the period before the second dentition has fully erupted.

Developmental disorders of teeth

Number of teeth

Absence of all (anodontia) or almost all (oligodontia) teeth is rare; if present it is frequently related to a generalized disorder (e.g. ectodermal dysplasia). In contrast, one or a few missing teeth (hypodontia) is a more common finding (Figure 1). In particular, in brachycephalic, small and toy dog breeds the first premolars or last molars are often missing. Congenital aplasia of teeth is usually hereditary but trauma or infection during tooth development (< 4^th month of life) can also lead to missing teeth. Hypodontia of permanent dentition is more common than with primary dentition. When a milk tooth is missing, in most (but not all) cases its adult successor is also missing. Radiography should always be used if teeth are absent in order to exclude the possibility of retained or impacted teeth. Hypodontia is mainly a cosmetic problem and requires no therapy, but depending on the breed standard some animals may be excluded from breeding 1 2. An excess of teeth (hyperdontia) can occur in both primary and adult dentition, and again this can be inherited or be related to problems during tooth development. Most frequently the incisors or premolars are involved (Figure 2). Again radiographs must be taken in order to differentiate supernumerary teeth from incompletely separated teeth (see below) and retained milk teeth. Supernumerary teeth can cause problems with eruption, crowding or deviation of adjacent teeth. Moreover, teeth that are crowded together accumulate more plaque, predisposing to periodontal disease. When this happens, the tooth which is most abnormal in terms of size, shape or position should be extracted. However if the hyperdontia causes no clinical problem, no therapy is needed 1 2.

Alteration in shape

• Gemination, fusion and concrescence
  Gemination, or twinning, is the partial or complete splitting of a dental germ. The most frequent result is a tooth with a root and 2 crowns that are separate to a greater or lesser extent. Gemination is often seen in the incisors and can occur in both milk and adult teeth (Figure 3a and b). 

Fusion is where two dental germs fuse together, and can involve the entire length of the tooth or just the root area, depending on the timepoint at which it occurs during tooth development. The pulp of both teeth can also be fused (Figure 4a and b). Both etiologies are unknown, although trauma and/or a genetic component have been suggested 1. 

Concrescence is the fusion of two adjacent teeth by the root cementum; crowding of the roots or trauma are considered to be possible causes. 

All three conditions typically require no treatment, unless changes lead to clinical problems such as periodontal or endodontic disease. Where treatment is advisable, pre-operative radiographs are essential to plan treatment, as roots are often abnormal in number or shape, and abnormal pulp conditions may be present 1.

• Dilaceration 
  This is defined as a kinking of the root or crown of a tooth and is usually caused by trauma during tooth development (Figure 5a-c). Dilacerations of the crown may be a purely esthetic problem but the surface is often rough and irregular, leading to increased plaque retention and subsequent periodontal disease. Dilacerations in the root area lead to problems with extraction or endodontic treatment. Pre-operative radiographs are again a prerequisite in these cases. Serious dilacerations can occasionally affect the eruption of affected teeth 1 3.
  
   

 

• Dens invaginatus
  Dens invaginatus (or dens in dente) is a rare condition of unknown etiology where the enamel and dentine invaginate into the pulp chamber during development; the invagination can be limited to the crown or may extend into the roots. Clinically this can lead to exposure of the pulp, predisposing to infection and subsequent pulp necrosis and periapical inflammation. Periodontal disease may also occur due to increased plaque retention 1 3.
  
  

• Supernumerary roots
  Accessory tooth roots are most frequently found in the dog at upper P3 and the maxillary second and third premolar in the cat, but are occasionally found in other teeth (Figure 6). Radiological evaluation is important when planning extraction or endodontic treatment of the teeth concerned 1.
  
   

 

Structural defects of hard dental tissues

Various developmental problems, with many different causes, can lead to structural defects (dysplasias) of the hard tissues (enamel and dentine) of the teeth. Typically these dysplasias are acquired (e.g. via trauma, infection) and may affect either the enamel or dentine in isolation, or the entire tooth (odontodysplasia) may be involved.

There are three types of enamel dysplasia: enamel hypoplasia, enamel hypomaturation and enamel hypomineralization. Enamel hypoplasia is characterized by an insufficient quantity of enamel. The defects can be focal or multifocal, and the crowns of affected teeth can show both dysplastic enamel and areas with normal enamel formation. In enamel hypomaturation and hypomineralization the enamel matrix development is disturbed, leading to the formation of soft enamel which is quickly eroded.

Congenital (genetically related) dysplasias are very rare and include amelogenesis imperfecta (enamel dysplasia) and dentinogenesis imperfecta (dentine dysplasia). Acquired enamel dysplasias are common in dogs but rather rare in cats. The defects are due to external influences during enamel formation (up to about the 4^th month of life) and the extent of enamel damage depends on the intensity of the insult, the duration of its effect and the stage of enamel formation at the time of the damage. In principle, any systemic disease, such as distemper virus, as well as severe nutritional deficits at an early age, can lead to enamel dysplasia during tooth development in many or all teeth. Areas of normal enamel may be present as some enamel may have developed before the insult occurs (Figure 7). 

Note that local effects such as trauma or inflammation (e.g. bite injuries, milk tooth fractures with pulp exposure and subsequent periapical inflammation, incorrect extraction of milk teeth) can also lead to enamel dysplasia, but these typically affect individual teeth (Figure 8). 

Clinically, enamel dysplastic teeth show variable but extensive defects of the enamel. When the teeth erupt the defects are usually white in colour, although sometimes the enamel can be transparent. The defects quickly become yellow or brown due to deposition of food pigments, and the brittle enamel can easily flake off with chewing. Freshly exposed dentine is painful as the dentine tubules become exposed, but the pain subsides over time as a result of reparative dentine laid down by the odontoblasts of the dental pulp. However, in severe cases the irritation can lead to pulpitis or pulp necrosis, and teeth showing enamel dysplasia should be evaluated by radiography in order to rule out complications such as periapical lesions. 

Affected teeth can have a very rough surface, leading to increased accumulation of plaque and tartar and thus a higher risk of periodontal disease. Treatment aims to seal the exposed dentine tubules; localized defects should be filled with composite, but for very extensive enamel defects the tooth can be crowned. These measures also restore a smooth surface to the tooth, reducing the risk of periodontal disease. Despite this, such teeth need good oral home care (daily tooth brushing) and the use of dental diets can be helpful to reduce the accumulation of plaque and the formation of tartar. Teeth that already show periapical lesions require endodontic therapy or should be extracted 1 2 4 5.

Dental fractures

Fracture of immature permanent teeth

Whereas extraction is the treatment of choice for a broken milk tooth, the preferred treatment for a fractured permanent tooth is to preserve it, especially if the tooth is functionally important. Immature permanent teeth are characterized on radiography by thin dentine and an absence of root closure; conventional root canal treatment is not possible here. Uncomplicated fractures (where pulp is not exposed) should be treated by composite restoration; where a fracture is very near to the pulp, the site of the near-pulpal exposure is first sealed by indirect pulp capping (to preserve the pulp vitality) and then a composite restoration is applied to the entire fracture area (to seal any remaining exposed dentine tubules and mechanically protect the indirect pulp cap). If there is a complicated fracture (exposed pulp), the vitality of the pulp must be assessed. Where the pulp is vital, a partial pulpectomy performed under sterile conditions, followed by direct pulp capping and fracture site restoration, is necessary (Table 1). The prognosis for this sort of treatment depends primarily on the duration of pulp exposure, as the pulp starts to deteriorate after 48 hours (Figure 10).

In immature fractured teeth with a necrotic pulp, apexification (to obtain a hard tissue root closure) can be attempted (Table 2). The prognosis for this, however, is guarded. For all the treatment options described for fractured immature permanent teeth, periodic radiological follow-up is required for timely identification and treatment of any periapical pathological changes that may occur 2 3 46 7 8.

 

Pre-operative radiography usually facilitates identification of the correct tooth and also shows to what extent the milk tooth root has been resorbed. The milk teeth must be extracted carefully as they have long, thin roots that break easily; damage to the permanent dentition must be avoided. In difficult cases, and to remove fractured root remnants, an open (surgical) extraction technique is recommended 1 2 3 4 9.

Impacted and embedded teeth

Embedded and impacted teeth are teeth that have not erupted. With impacted teeth there is a physical barrier in the eruption path which prevents the tooth from erupting (e.g. other teeth, milk tooth remnants, very tough gums), whilst no such obstacle can be found with embedded teeth. Embedded and impacted teeth must be differentiated from missing teeth, and therefore radiography is mandatory whenever a tooth is clinically absent. Teeth that remain in the jaw can lead to formation of a dentigerous cyst, which can result in wide-spread bone absorption and damage to neighboring teeth (Figure 12).

With timely diagnosis of retained or impacted teeth before completion of root development, the obstacle in the eruption path can be removed and the crown can be freed to allow the tooth to erupt. If removal of the obstacle is not possible, the affected tooth should either be extracted or undergo regular radiological monitoring. If a cyst is present, the tooth and the entire cyst lining must be removed in order for the cyst to heal. With very widespread cysts, the defect can be filled with a bone graft 1 2 3.

Dental and skeletal malocclusions 

Malocclusions are more common in the dog than in the cat. Treatment is indicated wherever the animal’s health is impaired, but is not required for purely cosmetic reasons. Abnormal tooth position with normal jaw length is known as dento-alveolar malocclusion; malocclusions due to a discrepancy in jaw length are known as baso-skeletal malocclusions. If there is no clear cause, or there are jaw abnormalities that cannot be explained by development or trauma, hereditary influences should be assumed. The malocclusion may already exist in the primary dentition or only occur in permanent dentition. Treatment options for malocclusions include extraction or crown reduction of the affected tooth, or orthodontic corrections.

Linguoversion, or lingual displacement of the lower canine teeth in dogs, is a common malocclusion that always requires treatment. Full details are outwith the scope of this article but some brief notes are appropriate. If the lower deciduous canine teeth are lingually displaced and impinge on the palate, this may lead to interlocking of the maxilla and mandible which can affect jaw growth. Frequently, dogs with this problem already have a retrognathic mandible (Figure 13) and here the lower canines should be extracted as early as possible; this immediately eliminates pain caused by the teeth impinging on the palate and allows the proper genetic development of the lower jaw.

The approach to the problem in the adult patient should, on the contrary, involve retention of the affected teeth; options include orthodontic correction of the malocclusion or shortening of the lower canine teeth. Orthodontic correction involves the use of expansion screws or inclined planes which move the teeth into a position that avoids trauma to the palate (Figure 14a and b). Shortening the lower canine teeth immediately eliminates the pain experienced when the teeth impinge on the maxilla; however, endodontic treatment is required with this option as in almost all cases the pulp is opened when the tooth is shortened. In addition a partial pulpotomy and direct pulp capping should be carried out, as the roots of the teeth concerned are generally not yet mature (Table 1). For full details on orthodontic correction, the clinician is referred to the relevant literature 1 2 3 10 11.

 

Cleft palates

A cleft palate is formed by missing or incomplete fusion of the palatine shelves during fetal development, and presents clinically as a longitudinal defect of the primary (incisive bone) and/or secondary palate (maxillary and palatine bone and soft palate) (Figure 15). This results in the affected animal being unable to suckle; food is frequently inhaled into the respiratory tract, leading to pneumonia. Clinically an affected animal demonstrates coughing and sneezing, with milk noted at the nostrils when suckling. Such animals are often retarded in their physical development and are frequently euthanized. Should a surgical closure of the defect be planned, the animal must be fed several times a day by tube until attaining a reasonable size; surgery can usually be attempted at 2-4 months of age when the animal is big enough to allow the extensive mobilization of the oral tissues necessary to permit closure of the cleft palate. The surgical intervention must be carefully planned as the first attempt offers the best chance of success; despite this, in many cases follow-up operations are needed to completely close the defect.

The two methods most often employed to close the cleft palate are the bi-pedicle advancement technique and the overlapping flap technique. For the first, the medial edges of the palate in the area of the cleft palate are incised and the mucosa of the palate undermined. Lateral releasing incisions ensure the necessary mobility of the resulting mucoperiosteal flaps (Figure 15). Blood supply to the area from the major palatine artery must be preserved and the flaps must be mobilized as much as possible to allow tension-free closure of the defect; the lateral release incisions heal by secondary granulation. The disadvantage of this method is that sutures are positioned over the defect and have no bony support. For the overlapping flap technique, a flap from the palatine mucosa is prepared on one side of the cleft palate, with the incision made parallel to the teeth and the base of the flap located at the cleft. The flap is folded over the defect, drawn to the opposite side of the cleft and sutured in position, so that the former oral epithelium forms the floor of the nose and the connective tissue side faces the oral cavity. Here too preservation of the blood supply from the major palatine artery is vital. The advantage of this method is that the sutures are supported by bone on one side of the defect; the disadvantage is that the technique is more difficult, requiring extensive preparation and leaving a large area of exposed bone to granulate 1 2 3 4 12 13. 

Conclusion

The clinician that dismisses dental disease or defects in young animals on the erroneous assumption that the development of adult dentition will remedy most problems does no service to the animal. Good knowledge of the various dental conditions that can exist in young animals, along with an awareness of the pathology and a conscientious approach to treatment, will ensure that a puppy or kitten that develops a problem will receive appropriate care and thus deliver long-term benefits for the animal concerned.