Developmental Pathology and Pedodontology

Developmental Pathology and Pedodontology

Bonnie H. Shope1, Paul Q. Mitchell2, and Diane Carle3

1 Veterinary Dental Services, LLC, Boxborough, MA, USA

2 Veterinary Dental Services, North Attleboro, MA, USA

3 Animal Medical Center of Seattle, Seattle, WA, USA

4.1 Introduction

Small animal veterinary pedodontics is the branch of veterinary dentistry that provides dental care to young dogs and cats. Young dogs and cats can present with many dental conditions, including developmental abnormalities, traumatic injury, neoplasia, and oral diseases.

4.2 Dentition of Puppies and Kittens

Puppies and kittens are born with fully developed, but unerupted, deciduous dentition. Permanent dentition is present in the mandible in the bell stage, with the mandibular first molar teeth beginning to calcify [1]. The dog’s deciduous canine and incisor teeth begin erupting at three weeks and the second through third premolars erupt at 4–12 weeks, ending with a total of 28 deciduous teeth. There are no deciduous precursors to first premolar teeth in the dog or to molar teeth in the dog or the cat. Deciduous teeth begin erupting at two to three weeks in the cat, beginning with the incisor teeth, followed by the canines at three to four weeks and the premolars at three to six weeks until the cat’s full 26 deciduous teeth have erupted. Table 4.1 shows the eruption schedule of deciduous teeth. Missing deciduous teeth at six weeks of age in the cat or 12 weeks of age in the dog are significant as the associated permanent tooth is unlikely to develop [2].

Table 4.1 Eruption schedule of deciduous teeth.a

Source: From reference [56].

Deciduous teeth (weeks) Permanent teeth (months)

Dog Cat Dog Cat
Incisors 3–4 2–3 3–5 3–4
Canines 3 3–4 4–6 4–5
Premolars 4–12 3–6 4–6 4–6
Molars 5–7 4–5

a Eruption varies with breed and size of animals. Gingival eruption continues to full crown height over a period of weeks.

When identifying deciduous cheek teeth, it is important to remember that the crown of the deciduous tooth resembles the crown of the next caudal‐most permanent tooth. For example, the deciduous mandibular fourth premolar tooth has three cusps and resembles the permanent mandibular first molar tooth, rather than the single‐crowned permanent fourth premolar tooth that succeeds it (Figure 4.1). Also, the maxillary deciduous third and fourth premolar teeth closely resemble the permanent fourth premolar and first molar teeth.

Image described by caption.

Figure 4.1 Deciduous dentition in a dog. The deciduous maxillary third premolar tooth (arrow) resembles the adult maxillary fourth premolar tooth.

At about three months of age in the cat and the dog, the deciduous incisor teeth begin to shed and are replaced by their permanent counterparts. Permanent tooth eruption continues until five to seven months of age in the dog and four to six months of age in the cat. Table 4.1 shows the eruption schedule of the permanent teeth. Eruption schedules for permanent teeth can vary by weeks or even months. Teeth in large breed dogs erupt sooner than those in small breed dogs [3]. For the most part, permanent teeth erupt lingually to the deciduous teeth, except for the maxillary canine teeth, which erupt mesial to their deciduous counterparts. Occasionally, a persistent deciduous fourth premolar may be found palatal to the erupting permanent fourth premolar.

A normal dog has 42 teeth by seven months of age and cats have 30 teeth by about six months of age.

4.3 Developmental Abnormalities of the Mouth

4.3.1 Developmental Abnormalities of the Tongue

Macroglossia, or a congenitally enlarged tongue, is an uncommon condition in dogs. Brachycephalic breeds have a relatively large tongue for their oral cavity, but do not have true macroglossia. Dogs with true macroglossia will have decreased function of the tongue with reduced range of motion and increased susceptibility to lingual trauma [4]. Macroglossia has been found in seven Dachshunds with a nasopharyngeal dysgenesis resulting in abnormally thickened palatopharyngeal muscles and hypertrophic geniohyoid and genioglossus muscles. The combined effect of the enlarged tongue and thickened pharyngeal muscles resulted in coughing, retching, and progressive dysphagia. Dogs in the study appeared to have impaired ability to push a food bolus caudodorsally. Outcomes for the dogs were generally poor, even with surgery to remove excess pharyngeal tissue. No attempt was made to resect tongue tissue in any of the dogs [5]. Macroglossia was also found in a family of Giant Schnauzers with congenital hypothyroid dwarfism. Four out of five Giant Schnauzers treated with thyroid supplement had complete resolution of clinical signs [6]. In humans, macroglossia is usually treated surgically and reduction efforts aim to preserve the tip of the tongue when possible, in order to preserve aesthetic, speech, and taste capabilities [7]. Resection of the traumatized portion of the tongue has been reported to produce good clinical results in dogs [8].

Microglossia is a recessive autosomal defect that results in a short, narrow, pointed, upward curled tongue. This condition is also known as “bird tongue” and has been reported in a litter of Miniature Schnauzers [9]. The condition was also reported in one or more puppies in 12 different related Basset Hound litters [10]. The condition initially presents as an inability to suckle properly. Dogs affected with this defect may initially be diagnosed with “fading puppy” syndrome until the malformed tongue is identified [9]. The condition in the Schnauzer dogs was associated with other serious congenital syndromes and euthanasia was recommended as the puppies failed to thrive even with intensive nursing care [9]. The condition in the Basset Hound litter was not associated with any other abnormalities [10]. There is no known treatment for microglossia in dogs [4, 9, 10].

Ankyloglossia, or “tongue‐tie” is characterized by a congenitally short and thick lingual frenulum. This abnormality is often accompanied by a notched or “W” shaped tip of the tongue [11]. In most cases, there are no other craniofacial abnormalities, although a single case of concurrent lingual bifida has been reported [11, 12]. Individuals affected by ankyloglossia often have difficulty suckling, licking, swallowing, and vocalizing. Dogs can also have difficulty with thermoregulation due to a reduced ability to cool themselves through the tongue. Difficulty with prehension of food and excessive drooling have also been reported [13]. The condition is very rare in dogs and has only been reported in Anatolian Shepherd dogs (Kangal dog). Ankyloglossia is believed to arise from failure of breakdown of the cranial 2/3 of the membrane that adheres the tongue to the floor of the mouth in early development [11]. Successful treatment has been achieved by freeing the abnormally attached portion of the tongue with frenuloplasty [13, 14].

Heterotrophic hair shafts, also known as “hairy tongue,” is a condition where hairs are found along the median sulcus of the tongue (Figure 4.2). This condition has been attributed to hair becoming embedded in the tongue’s dorsal surface as a result of grooming. However, post mortem histology has shown that hairs found on tongues of at least some dogs were actually heterotrophic hair shafts and this has been attributed to normal surface ectoderm‐neural crest mesenchyme interaction, which normally results in hair formation, occurring in an inappropriate location [15, 16]. This condition is usually not treated unless the hairs cause glossitis. Treatment is removal of the hairs and flushing with an antibacterial solution; however, the hairs frequently grow back [4].

Image described by caption.

Figure 4.2 Heterotrophic hair shafts along the median raphe of a Labrador Retriever’s tongue.

4.3.2 Abnormalities in Teeth Variations in Number of Teeth

Variations in the number of teeth that develop are common in animals. Hyperdontia (HYP) is the development of extra, or supernumerary, teeth in the mouth. Supernumerary teeth (T/SN) are thought to develop from continued proliferation of the permanent or deciduous dental lamina to form a third tooth germ, or from disturbances during tooth development. They can be found in either primary or permanent dentition, but are most commonly found in permanent dentition [17, 18]. Supernumerary teeth are common in the Greyhound, Boxer, Bulldog, and Rottweiler dogs but are rarely found in cats [17, 19]. Supernumerary teeth are more commonly found in the maxilla than the mandible. One study found more than one‐third of Greyhounds had supernumerary teeth, most frequently the first premolar tooth. Supernumerary incisor teeth have been noted in Boxers and Bulldogs [18, 20]. Extra teeth can cause crowding and increased risk of periodontal disease, although in dolichocephalic breeds they do not commonly cause crowding [18]. If supernumerary teeth cause crowding or a malocclusion, they should be extracted to prevent periodontal or occlusal complications. A supernumerary maxillary fourth premolar tooth is shown in Figure 4.3. This has been associated with facial swelling in a dog and was attributed to food impaction and occlusal trauma resulting in periodontitis [21].

Image described by caption.

Figure 4.3 A supernumerary maxillary left fourth premolar tooth at the palatal aspect of the fourth premolar tooth.

Tooth agenesis is failure of one or more teeth to develop. Hypodontia (HYP) describes the absence of one to six teeth, while oligodontia is used to refer to the absence of more than six teeth. Anodontia is the complete lack of tooth development [2]. Hypodontia and oligodontia are more commonly seen in humans in the permanent dentition than in the deciduous dentition [22]. When a deciduous tooth is missing, the permanent successor is more likely to be missing as well [2]. Tooth agenesis is believed to result from a failure of the dental lamina and neural crest mesenchyme to interact. Hypodontia, oligodontia, and anodontia have been reported in dogs and cats and are associated with hairless breeds as well as a variety of syndromes including ectodermal dysplasia [17]. Oligodontia of the deciduous teeth and anodontia of permanent dentition has been reported in an otherwise normal cat and anodontia has been reported in an adult cat whose dentition as a kitten was unknown [23, 24]. Complete anodontia has also been reported in a dog [3]. In cats, the maxillary second premolar is frequently absent, and the prevalence of this varies widely with location, ranging from 3 to 28% [19]. Tooth agenesis has been associated with the Affenpinscher, the Kerry Blue Terrier, hairless breed dogs, large dolichocephalic breed dogs, and small breed dogs including the Miniature Poodle, [17, 20, 25]. In humans, non‐syndromic tooth agenesis has been demonstrated to be inherited as an autosomal dominant, autosomal recessive, or sex‐linked trait, but this has not been researched in dogs and cats [2]. Variation in Size of Teeth

Variations of normal tooth size can occur in animals. These disorders can be generalized or localized in the mouth. Microdontia (T/MIC) and macrodontia (T/MAC) refer to teeth that are smaller than normal or larger than normal, respectively. In humans, macrodontia is a rare dental anomaly where a tooth is larger than average [26]. In veterinary medicine this has been reported to occur with tooth germination [17]. Microdontia describes teeth with crowns, roots, and nerves that are normal in shape yet smaller than usual. This commonly occurs in the third incisors in the dog. One form of microdontia is a “peg tooth” where the crown of the tooth has an abnormal conical shape in a tooth that normally has a more complex crown shape [27].

4.3.3 Variation in Structure of the Tooth

Teeth can vary greatly in shape, and often this can be attributed to morphological anomalies of developmental origin. The term “double teeth” refers to two teeth that are partially joined by dentin or even pulp. These abnormal looking teeth are either the result of gemination (T/GEM) or fusion (T/FUS). Gemination is thought to result from the failed attempt of one tooth germ to divide into two and should be suspected when there is a large tooth and a normal tooth count. Fusion is believed to arise from the union of two normally separated tooth germs. Double teeth are most likely the result of fusion when the adjacent tooth is missing. Fusion may involve the entire length of the tooth or only the roots. Both gemination and fusion are seen in primary and permanent dentition [17].

A condition known as dens invaginatus (T/DENS) or dens‐en‐dente is found in dogs and humans [28, 29] (Figure 4.4). This condition develops during tooth development from an in‐folding of the dental papilla prior to calcification of the dental tissues [30]. It has been reported in dogs in the maxillary canine tooth and in the mandibular first and second molar teeth [29, 31, 32]. The etiology of this condition is unknown, but there is some evidence in humans that it may be genetic in origin [33]. These teeth may be incompletely lined by enamel [31]. Teeth with suspected dens invaginatus should be radiographed. If no periapical pathology is noted and no obvious opening in the invagination is seen, the teeth can be treated conservatively with periodic radiographs. However, invaginations can predispose the tooth to endodontic disease as well as periodontal disease and these teeth frequently require extraction. There are numerous reports of successful endodontic treatment of these teeth in humans [34]. A report of a dog treated successfully with endodontic treatment recommends extensive irrigation and chemical debridement, but standard obturation techniques were used [29].

Image described by caption.

Figure 4.4 Mandibular right first molar tooth in a dog with dens invaginatus. The dark linear defect between the mesial and central cusps is an infolding of the enamel. The radiograph shows marked periapical bone loss at both roots, the result of endodontic disease from the infolded enamel.

Root hypoplasia, also called dentin hypoplasia, has been found in dogs, and often accompanies other disorders such as enamel hypoplasia (Figure 4.5). The root begins developing after the crown shape has formed, but before calcification, so developmental insults affecting enamel can also affect the developing root. Root hypoplasia has been documented in dogs with histories of distemper as well as a dog with unknown history, but the condition appears to be often accompanied by enamel dysplasia [3537]. In humans, root hypoplasia is attributed to disruption in the development of Hertwig’s root sheath [38]. Nutritional factors such as deficiency in vitamin D or phosphorus, infectious factors, and traumatic factors have been implicated in root hypoplasia. Hypoplastic roots often are not mobile and are functional for several years [35]. These teeth can be left in place unless they have radiographic signs of disease or are mobile.

Image described by caption.

Figure 4.5 Root hypoplasia in a 10‐month‐old hound dog mix.

Dilaceration refers to an abnormal bend in the root or crown of a tooth. It occurs most frequently in the root of the tooth, but can appear anywhere along the length of the tooth. The condition is thought to occur due to trauma or infection during tooth formation [17]. In humans, dilacerated teeth have been associated with non‐eruption, prolonged retention of the deciduous predecessor teeth, and apical fenestration of the labial cortical plate [39]. In dogs and cats, these teeth are usually asymptomatic, although they can be more difficult to extract and more difficult to treat with endodontic therapy.

Supernumerary roots are common in dogs in the upper second and third premolar teeth, and in cats in the upper third premolar tooth [19, 40, 41]. Convergent roots, where two normally shaped roots are fused, can be found in dogs and cats [27]. Concrescence is a form of fusion when two neighboring teeth are joined by cementum. This process, which is thought to be related to trauma or crowding, can take place before or after eruption [17]. Teeth with these types of variations in root structures are not usually clinically significant, but are important to recognize when extracting teeth.

4.3.4 Regional Odontodysplasia

Regional odontodysplasia, or odontoblastic dysplasia, is a condition where all the components of the tooth that derive from the dental organ in the affected teeth are abnormal. This includes the enamel, dentin, and cementum. However, unlike other similar conditions, only one or a few teeth are affected, as opposed to conditions such as amelogenesis imperfecta, where all the teeth are involved. Patients with regional odontodysplasia often present for delayed eruption or failure of eruption of teeth. Teeth can have non‐inflammatory gingival swellings near the affected teeth due to caries, or bacterial infection of the pulp through defective enamel or dentin [42]. Histologically, the pulp chamber and canals of a tooth are filled with abnormal dentin and collagenous stroma [43]. This condition has been reported in a maxillary canine tooth in a Beagle and in multiple teeth in a Boerboel dog [42, 43].

4.3.5 Enamel Defects

During enamel development, several abnormalities may occur. These are sometimes found on clinical, radiological, or histological examination. Enamel formation starts before the eruption of the first teeth and involves many different genes. Defects in any one of these genes can result in defects in the formation of deciduous and permanent teeth. Amelogenesis imperfecta is the general term that includes any genetic and/or developmental enamel formation and maturation abnormalities [44]. This condition results from a disturbance in the ectodermal layers of developing teeth. It is often a hereditary abnormality that includes genetic and/or developmental enamel formation and maturation abnormalities such as enamel hypoplasia (E/H) and enamel hypomineralization (E/M). This condition is inherited in the Standard Poodle, Italian Greyhound, and the Samoyed [4547]. In the Italian Greyhound and the Samoyed, this disease is known to have an autosomal recessive inheritance pattern, although different genetic mutations are involved. Normal enamel functions to seal the tooth from bacteria, protect and insulate the tooth, provide strength to the tooth, and create a smooth surface, which helps prevent plaque from accumulating on the surface of the tooth. The crowns of affected teeth are pitted, rough, and are chalky or discolored brown. The teeth readily stain and attract plaque. Dogs affected with enamel defects, regardless of the cause, are prone to abrasion and fracture of teeth, periodontal disease, dentin sensitivity, and possibly pulpitis and pulp death. Restoration of teeth can be performed to protect the pulp from thermal and mechanical stress and from bacterial infection, to decrease sensitivity, plaque adhesion, susceptibility to abrasion and fracture, and to improve cosmetic appearance [4850]. Fastidious oral hygiene is also important to keep the periodontium healthy.

Enamel hypoplasia refers to inadequate deposition of enamel matrix (Figure 4.6). This results in normal density or mineralization but enamel that is thinner than normal. This can affect one or several teeth and may be focal or multifocal. The crowns of affected teeth can have areas of normal enamel next to areas of hypoplastic or missing enamel [44]. The thin enamel often gives view to the yellowish‐brown dentin underneath. Enamel hypoplasia can be found in dogs that have a history of distemper while in utero or during formation of permanent dentition. Enamel hypomineralization refers to inadequate mineralization of enamel matrix, resulting in white, yellow, or brown spots in the enamel. This often affects several or all teeth. The crowns of affected teeth may be soft and wear faster than normal teeth. The enamel can be difficult to distinguish from dentin radiographically in these teeth, as it has the same radiopacity as the dentin.

Image described by caption.

Figure 4.6 Enamel dysplasia in the Samoyed dog.

Dentinogenesis imperfecta is a hereditary abnormality in the formation of dentin. The clinical appearance of affected teeth varies from gray to brownish violet to a yellowish‐brown color, but the teeth can also exhibit a characteristic unusual translucent or opalescent hue. The enamel frequently can be separated from the dentin quite easily, and the exposed dentin demonstrates rapid attrition. Radiographically, the teeth exhibit thin roots, cervical constrictions, and pulp chambers and root canals may be partially or completely obliterated [51]. Dental hypomineralization has also been documented as a recessive genetic condition in related Border Collies, causing abnormal abrasion and exposure of teeth [52].

4.3.6 Congenital Porphyria

Congenital porphyria is a rare hereditary defect of hemoglobin formation resulting in anemia and discolored teeth and bones. It is an autosomal recessive trait. The congenital form has not been reported in dogs, but has been seen in cats. Affected teeth emit a red fluorescence, which can distinguish the condition from tetracycline‐associated staining that emits a more orange or yellow green color and teeth stained by fluoride toxicosis that will not fluoresce at all. Urine of affected cats will contain porphyrin. There are no published reports of treatment outcomes or prognosis for affected cats, but milder forms may permit reasonable quality of life for more than 10 years [53].

4.4 Abnormalities in Tooth Eruption

4.4.1 Persistent Deciduous Teeth (DT/P)

In human dentistry, a deciduous premolar tooth is considered persistent if the tooth remains when more than three‐fourths of the replacing tooth has erupted [54]. In veterinary dentistry, there is no precise definition of when a tooth is considered persistent, but deciduous teeth that persist (DT/P) for more than a few days after eruption of the permanent teeth should be removed to prevent displacement of the adult teeth (Figure 4.7). Deciduous teeth that persist without a corresponding permanent tooth must be radiographed to rule out an unerupted permanent tooth. If no permanent tooth is present and the deciduous tooth is clinically and radiographically healthy, the tooth can be left in place. However, the tooth should be monitored, because deciduous teeth are smaller and more delicate than permanent teeth and may be more prone to fracture. Furthermore, the roots of these teeth can eventually resorb and become mobile and must be extracted at that point. Studies in persistent deciduous human teeth with no permanent successor have found that the deciduous teeth can remain healthy for prolonged periods of time, although ankylosis of the root is an occasional complication [54].

Image described by caption.

Figure 4.7 Photograph of a persistent left maxillary deciduous canine tooth.

Persistent deciduous teeth (DT/P) are rare in the cat, but have been noted in the maxillary canine teeth and maxillary third premolar teeth. Persistent deciduous canine teeth in cats are found distal to the permanent canines [55, 56].

Extraction is often necessary to treat persistent deciduous teeth, but may also be helpful in treating traumatic fractures to deciduous teeth and in treating various malocclusions of puppies and kittens. Whenever performing extractions of these delicate teeth, extreme care and finesse should be exercised to avoid fracturing their roots and to avoid damage to the surrounding permanent teeth. The adjacent permanent tooth may be in vulnerable stages of development and can be damaged as a result of the extraction process, even with the greatest of care. Pet owners should always be informed of the possibility of adult tooth damage during deciduous tooth extraction.

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Aug 15, 2020 | Posted by in GENERAL | Comments Off on Developmental Pathology and Pedodontology

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