- Tooth Morphology
- Tooth Eruption
- The Periodontium
- Saliva And Its Function
- Normal Dental Occlusion
- Abnormal Dental Occlusions
- Abnormal Numbers Of Teeth
- Abnormal Tooth Positions
- Tumors Of Dental Origin
- Craniomandibular Osteopathy
- Tight Lip Syndrome
- Cleft Palate
- Oronasal Fistulas
- Miscellaneous Dental Problems
An oral examination should be performed each time a puppy or kitten is presented. Many pathologic or potentially pathologic conditions can be detected at an early age and corrective measures taken. Introducing the pet owner to the concept of oral home care and regular professional dental prophylaxis are the two most important responsibilities of the veterinarian with regard to dental disease care and prevention.
There are three types of teeth in the deciduous dentition of puppies and kittens: incisor (I), canine (C), and premolar (P); a fourth type, molar (M), is found in the permanent dentition. Each type is designed to be self-cleaning in the non-crowded scissors occlusion, when the animal eats a natural diet, that is, catches its prey.
Each tooth type serves a specific function. Incisor teeth are for grooming and nibbling, canine teeth are for grasping and tearing, premolars are for shearing, and molars are for grinding. The cat, a true carnivore, has no occlusal surface on the mandibular molar. The maxillary molar is small and vestigial in the cat (). Each tooth is covered with enamel, the hardest body substance. The bulk of the tooth is dentin, a living tissue that continues to be deposited by the odontoblasts lining the pulp chamber in viable teeth. Cementum, modified bone, covers the tooth root.
Many factors may affect the normal development of the permanent tooth bud. Interference can produce dens-in-dente, fusion, gemination, and various other abnormalities ().
Deciduous dentition begins to erupt at 2 to 3 weeks of age in puppies and kittens. All deciduous teeth should be in place by 12 weeks in puppies and 6 weeks in kittens (). The deciduous teeth are much smaller and have relatively longer roots than the permanent teeth (). The deciduous dentition for puppies is 2 (I 3/3 C 1/1 P 3/3) = 28. If a deciduous tooth is missing developmentally, there will be no permanent tooth because both develop from the same embryonic tissues (). The last maxillary premolar has three roots; the other two premolars have two roots each. Each mandibular deciduous premolar has two roots. There are no deciduous precursors for permanent premolar 1 or the molar teeth in dogs ().
The deciduous dentition for kittens is 2 (I 3/3 C 1/1 P 3/2) = 26. The last maxillary premolar has three roots. Deciduous teeth are normally shed as the permanent counterparts erupt. There are no deciduous premolars for the permanent molar teeth in cats.
The permanent dentition in the older puppy is 2 (I 3/3 C 1/1 P 4/4 M 2/3) = 42. The permanent dentition in the older kitten is 2 (I 3/3 C 1/1 P 3/2 M 1/1) = 30. The older kitten is missing maxillary premolar 1 and mandibular premolars 1 and 2 (). The permanent toothbuds lie lingual to deciduous teeth. The maxillary canine tooth moves to a mesial location before eruption (). The crowns of the permanent teeth are formed by 11 weeks (). In the puppy, the presence or absence of a permanent tooth crown is visible radiographically at 8 to 12 weeks ().
The periodontium consists of the tissue surrounding the tooth. It is composed of the gingiva, cementum (a bone-like tissue that covers the roots), periodontal ligaments that insert into the cementum, the alveolus, periodontal tissues, and the alveolar bone that houses the teeth.
The gingival tissues are tough and nonelastic around the teeth. The gingiva protects the underlying bone and tooth structure from the trauma of chewing and gnawing. Inflammation of the gingiva occurs with the eruption of the deciduous and the permanent dentition. The gingiva probably causes an itchy sensation that causes puppies and kittens to chew excessively during the time period of tooth growth and eruption.
The attachment of the gingiva to the tooth, that is, the epithelial attachment, creates a moat around each tooth called the gingival sulcus. Im-munoglobulin A is secreted within the gingival sulcus where neutrophils, lymphocytes, and plasma cells reside. The gingival sulcus is the active zone of protection against inflammation around the teeth (). The mucogingival junction or mucogingival line marks the area where the alveolar mucosa joins the gingiva. Alveolar mucosa is mobile and forms the lining of the cheeks and sublingual tissues.
Saliva And Its Function
Saliva is released from salivary gland duct openings that are located primarily in the buccal pouch area, adjacent to the maxillary cheek teeth (P4 and M1) and sublingually. Saliva helps lubricate food for easier swallowing and keeps the oral tissues moist. Mucopolysaccharides within saliva help form the base for developing dental plaque. Dental plaque is the soft sticky material that coats the teeth if they are not brushed. It is about 80% bacteria and unless removed daily leads to halitosis and the beginning of gingivitis even in young puppies and kittens. Gingivitis is a reversible form of periodontal disease, that is, no tissue attachment is lost.
Normal Dental Occlusion
The normal dental occlusion in the dog and cat is the “scissors” occlusion (). The maxillary incisors slightly overlap the mandibular incisors, and the mandibular canine tooth lies equidistant between the maxillary third incisor and maxillary canine tooth. In the dog, the mandibular first premolar is the most rostral (mesial) cheek tooth, with the cusps of the other cheek teeth interdigitating in a pinking shear effect (). In the cat, the maxillary second premolar is the most rostral (mesial) cheek tooth. Cats have little, if any, curvature to the maxillary and mandibular incisor arches. Often cats have a level occlusion () with no detectable changes in the incisor and canine tooth relationship.
Abnormal Dental Occlusions
Abnormal dental occlusions can be part of the expected breed standard in both adult dogs and cats. Examples are the brachycephalic breeds such as the Pekingese dog and the Persian cat. Owners may be distressed to learn that the abnormal anatomy of their dog or cat is causing significant oral pathology even though it is the perfect breed standard.
Anterior crossbite, also referred to as class 1 malocclnsion, involves the incisor teeth. One or more of the maxillary incisors lies caudal to the mandibular incisors, but there is still equidis-tance between the maxillary third incisor and maxillary canine tooth with the mandibular canine tooth. Also the cusp of mandibular premolar 4 interdigitates perfectly between maxillary premolars 3 and 4. Anterior crossbite could develop into a mandibular prognathism (or maxillary brachygnathism) in the mature adult ().
Posterior crossbite occurs when the mandible is wider than the maxilla (). The mandibular molars and/or some premolars may be buccal to the maxillary cheek teeth. The abnormal anatomy causes dental calculus to accumulate on the maxillary and mandibular cheek teeth rapidly and predisposes them to periodontal disease. Home care and frequent dental prophylaxis is the treatment of choice for preventing periodontal disease.
Maxillary brachynathism is often referred to as mandibular prognathism or class 3 malocclusion. In maxillary brachynathism, the mandibular arch is longer than the maxillary arch (). This is the standard in the brachycephalic canine and feline breeds. There may be hard or soft tissue trauma and overcrowding of the maxillary cheek teeth that predisposes the adult to early periodontal disease. Extraction or reshaping of the overcrowded occlusion is recommended. Also seen with increasing frequency are dogs that should have a scissors occlusion but are “going undershot.” In the deciduous dentition, extraction of the teeth in the maxilla (the short arch) is generally recommended. Extraction of the teeth does not alter the genetic potential of the animal; it simply removes mechanical interference that may be restraining the maxillary growth (). As a result, there may be three postextraction scenarios: (1) the occlusion may remain the same, (2) the maxilla may lengthen, or (3) the mandible may grow longer faster. The pet owner should understand these possibilities before any deciduous interceptive orthodontia (extraction) is performed. Each case should be judged individually; the dental interlock may prevent the development of even more severe mandibular prognathism ().
Mandibular brachygnathism is often referred to as maxillary prognathism or class 2 mahcclusion. This occlusion is not accepted breed standard for any breed, yet it is seen with increasing frequency. It seems to occur most often in those breeds with dolichocephalic heads (). Mandibular brachygnathism has been seen in breeds as diverse as German shepherd and Chihuahua () dogs and Siamese cats. The
shortened mandible is usually more narrow and predisposes the affected dog to base-narrow mandibular canine teeth that can traumatize hard and soft tissue. Orthodontia by means of a palatally positioned incline plane appliance or mandibular expansion device is the preferred corrective procedure to crown height reduction and a pulp cap procedure. Tipping the mandibular canine teeth into an atraumatic occlusion maintains the integrity of the tooth and preserves more aesthetic function of the teeth than does crown height reduction.
Wry mouth is most commonly present when just one of the jaw quadrants grows to an inappropriate length — either too short or too long. The net result is deviation of either the mandible or the maxilla to one side or the other. Therefore, head symmetry should be evaluated in each puppy or kitten examined. Mild to severe malocclusion can develop (). Adjustment by interceptive orthodontia or active orthodontia is appropriate to relieve trauma.
Abnormal Numbers Of Teeth
Oligodontia, or hypodontia, refers to too few teeth (). Anodontia, the total absence of teeth, is rare in dogs and cats (). Missing teeth occur most commonly in small breed and in certain large-breed dogs (). Large breeds such as the Doberman pinscher, Rottweiler, and German shepherd are often affected. These large breeds must have a full dentition, that is, 42 teeth, to be exhibited (). There is a familial tendency in Tibetan and wheaten terriers for delayed eruption (). Dental radiographs can determine the presence or absence of nonerupted permanent teeth at 8 to 12 weeks of age (). Operculectomy (removal of the gingiva covering the tooth) may be necessary for complete eruption to occur ().
Polyodontia (extra teeth) occurs occasionally in young dogs and cats (). Extra teeth may not need to be extracted unless oral trauma or overcrowding results. Extraction of teeth in the overcrowded area helps deter the development of early periodontal disease. The extra teeth are usually in the incisor or premolar area (), although an occasional extra canine tooth is found ().
Retained Deciduous Teeth
Retained deciduous teeth usually remain in place with the corresponding permanent teeth positioned lingually. The exception to this rule is the maxillary permanent canine tooth that is mesial (rostral) to the retained deciduous canine tooth (). A retained deciduous tooth may remain in the dentition for several years when there is no permanent tooth to replace it (). Retained deciduous teeth occur most commonly in small dog breeds but are seen occasionally in large-breed dogs and cats. Occasionally, a permanent maxillary fourth premolar erupts buccal to a retained deciduous maxillary premolar in small breeds such as the Pomeranian.
Extraction of retained deciduous teeth is best accomplished using a very small root tip elevator () such as the Henry Schein HI, H2, or H3. The long, slender deciduous roots fracture easily. If the retained deciduous tooth is preventing a permanent tooth from moving
into normal position, the root, if it fractures, should be carefully removed. The crown of an extracted retained deciduous tooth can be trimmed to a wedge shape and forced into the alveolar space on the lingual aspect of its respective permanent tooth. This temporary wedge will help lever the permanent tooth into the space vacated by the retained deciduous tooth. The wedge will fall out in 2 to 3 days ().
Abnormal Tooth Positions
Undescended Maxillary Canine Teeth
Nondescended maxillary canine teeth that are rostrally deviated are seen in small dogs such as Shetland sheepdogs and less frequently in cats (). These teeth usually respond well to orthodontic movement once the roots have developed. Changing the anchor tooth from maxillary premolar 4 to mandibular molar 1 every 3 to 5 days decreases the possibility of movement of the anchor tooth. Orthodontic treatment is not instituted until the roots of the anchor tooth develop at 9 to 10 months of age.
Narrow-Base Mandibular Canine Teeth
Narrow-base mandibular canine teeth refer to the lingually displaced mandibular canine teeth (). The positioning of the mandibular canine teeth lingually usually occurs in conjunction with retained deciduous teeth or with mandibular brachygnathism (). The condition can occur when there is insufficient space between the maxillary third incisor and the maxillary canine tooth for the mandibular canine tooth to interdigitate. Significant oral trauma such as oronasal fistula and attrition of opposing teeth may occur ().
Orthodontic treatment with an acrylic incline plane appliance or mandibular expansion device can be used to reposition the mandibular canine teeth. Extraction of the maxillary third incisor and alveoloplasty is satisfactory when the cause is insufficient interdental space. An acrylic bite opener is usually positioned around the maxillary incisor teeth until the soft tissue heals. Crown height reduction is a last choice because it decreases the functionality of the canine tooth. A pulp cap is not always 100% successful, that is, the tooth may need endodontic treatment or extraction secondary to abscessation from a failed pulp cap procedure. If the mandibular canine teeth are only slightly base-narrow and there is sufficient space for the mandibular canine tooth in the maxilla, a gingivoplasty of the interdental space between maxillary canine tooth and maxillary third incisor may be the only treatment needed to correct the problem.
Tumors Of Dental Origin
Fibromatous epulis has been reported in a 4-month-old German shepherd puppy (). Other tumors of dental origin occur with abnormal tooth development. For instance, if the tooth germ becomes cystic before enamel and dentin formation, a primordial cyst develops; a cystic enamel organ forms a dentigerous cyst, which usually surrounds the nonerupted crown; and teeth that form in an irregular mass constitute an odontoma (). When a permanent tooth does not erupt, especially if a swelling develops in the area, dental radiographs can help identify the problem. Tumors of dental origin should be removed surgically.
Craniomandibular osteopathy is likely to be a genetic condition in West Highland white, Scottish, cairn, and bull terriers and affects young dogs. The jaw may appear swollen due to the bilateral mandibular enlargement from periosteal proliferation of the horizontal ramus, with extension into the temporomandibular joint region at times. Oral discomfort and reluctance to eat may affect some individuals, and symptomatic treatment may make them more comfortable. The condition typically regresses by around 11 to 13 months of age as bone maturation and ossification are completed ().
Tight Lip Syndrome
Chinese shar-pei dogs are predisposed to the condition of tight lip syndrome, which is caused by a band of collagenous fibers in the mandibular lip that extends between the mandibular frenula. This fibrous band prevents forward growth of the mandible, and soft tissue trauma occurs when the lip rolls over the mandibular incisor and canine teeth. Surgical intervention to transect the fibrous band at multiple sites releases the pressure and eliminates the soft tissue trauma. Evaluation of the occlusion is necessary after complete surgical healing has occurred. In very young puppies, surgical intervention is usually successful.
Primary cleft palate occurs early embryonically () and involves the incisive bone and/or the lip (). Secondary cleft palate occurs later in development and involves the hard palate and/ or soft palate (). Surgical treatment is possible, but most affected puppies and kittens die from aspiration pneumonia or are euthanized.
Damage secondary to chewing on electric cords is considered hard palate or arch defects. The tissue necrosis can affect soft tissue, bone, and developing tooth structures. Mild to severe oronasal fistulas as well as scar tissue in the tongue and lips can result.
Miscellaneous Dental Problems
Canine distemper teeth was the term used for years to describe the discolored chalky irregular crown surface that was observed in the permanent dentition of dogs surviving canine distemper. Ameloblasts, which form tooth enamel, require perfect physiologic conditions for effective enamel formation. Because of this, enamel may not be laid down evenly in young dogs and cats during abnormal health periods, such as high fever, heavy parasitism, extreme nutritional deficiency, or even multiple surgeries in young puppies or kittens. The result is a weakened tooth with less organized matrix than normal (). Management of these teeth may include smoothing of the tooth surface, application of dentinal sealer, weekly stannous fluoride applications, or placement of composite restorations for cosmetic purposes.
Enamel hypoplasia is thinning of enamel over all or part of the tooth crown. It often occurs in conjunction with enamel hypocalcification ().
Malformed Permanent Teeth
Malformed erupted or nonerupted permanent teeth can be the result of trauma to the face or iatrogenic damage secondary to the extraction of a deciduous tooth. In the early stage of crown development, the calcified crown tip can be moved slightly off the developing permanent tooth bud. The result can be a tooth with a short, angulated crown that has a self-induced trauma related pulp cap on the remaining root and crown.
Tetracycline discoloration occurs in deciduous teeth (or other calcium-forming tissues) if the mother is given tetracycline or its derivatives during the formation of the deciduous teeth in utero. If puppies or kittens are given tetracycline or its derivative during formation of the permanent tooth buds, tetracycline can be incorporated into the enamel and dentin, resulting in yellow discoloration. Enamel hypoplasia has been reported in these dogs (). Discoloration may, however, be the only adverse effect in tetracycline-treated teeth ().
Deciduous teeth that are fractured should be extracted (). The open endodontic system can shuttle bacteria to the area of the developing permanent tooth bud. Infection of the permanent tooth bud may then result in malformation and/or destruction of the remaining crown or root (). Fractured immature permanent teeth should be treated endodontically with calcium hydroxide to encourage the closure of the apex if patent and to thicken the dental walls (). Conventional root canal therapy should follow when further development of the dentinal walls has ended ().
Avulsed teeth should be gently lavaged with sterile saline solution before reimplantation. The tooth (or teeth) is stabilized with a figure-of-eight wire that can then be overlaid with orthodontic acrylic powder and liquid (cooled with water during the exothermic polymerization). Root canal therapy is necessary after healing occurs ().
Periodontal Disease and Home Care
Periodontal disease is caused by the accumulation of plaque on the teeth (). Periodontal disease is the most common disease found in young dogs and cats (). The daily removal of plaque by brushing from the teeth of puppies and kittens begins a life-long prevention of periodontal disease. There are many good home care products available for dogs and cats. Some contain enzymatic compounds, and others have calculus complexing ingredients or are antiseptic. A dry toothbrush will, however, work well in removing accumulation of plaque. The most important aspect of home care is that it be performed on a daily basis.
Annual dental prophylaxis usually begins at 2 years of age for most dogs and cats. The first dental prophylaxis may need to be performed at about 9 to 12 months of age. A brief dental prophylaxis, that is, brushing the teeth with chlorhexidine, charting the teeth, polishing the teeth, and giving a fluoride treatment, can be performed in the healthy puppy or kitten at the time of the standard neutering procedure. This early exposure to proper dental prophylaxis gives owners an indication of the importance of dental care for their pets.
Selections from the book: “Veterinary pediatrics: dogs and cats from birth to six months”. Johnny D. Hoskins. (2001)
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