Navigating clinical oral anatomy imperative to successful oral care
Practical knowledge of veterinary dental anatomy and physiology is essential to the veterinarian and veterinary technician involved in providing quality oral care to their patients. Quality surgical skills are only attainable with a thorough understanding of these concepts.
The following discussion provides a basic guide to the veterinary oral anatomy and physiology commonly encountered in practice.
During tooth formation, enamel is derived embryologically from the ameloblasts that lay down matrix that eventually mineralizes into a series of microscopic rods. These rods are arranged in a perpendicular fashion to the dentino-enamel junction and the crown of the tooth. This arrangement becomes important because tooth fractures and defects may leave rods unsupported, predisposing to further fracture and enamel compromise. Any disruption of the production of enamel during the developmental stage can result in defects on the tooth such as enamel hypocalcification (Photo 1). As enamel surrounds the crown of the tooth, cementum covers the root.Dentin’s role
Dentin is formed from the odontoblast. These cells have processes that run the entire width of the dentin from the pulp to the DEJ within the tubules of dentin that they themselves create. Acute enamel damage can lead to exposure of dentin with resultant death of the odontoblasts creating a direct route of migration for oral microbes to infect the pulp (Photo 2). Restorative treatment is needed to seal the tubules to prevent microbial insult (Photo 3). Chronic enamel wear that extends into dentin may result in gradual repair with the deposition of tertiary or reparative dentin (Photo 4). Many of these chronic lesions need no treatment. It should be mentioned that the tubules within dentin become larger as they get closer to the pulp, therefore the deeper the lesion into dentin, the more likely that pulp changes will ensue.
Pulp consists of primarily blood vessels, nerves, fibroblasts, odontoblasts and undifferentiated mesenchymal cells. Pulp can be compromised from trauma or systemic infection (Photo 5).
Pulp necrosis results from irreparable pulp insult from infection and/or trauma. Characteristic changes associated with pulp necrosis radiographically are an enlarged pulp chamber compared to the fellow tooth on the contralateral mandible or maxilla and/or an area of increased lucency surrounding the root apex (Photo 6).
Anatomy and physiology of the periodontal tissue is extremely important to the veterinary dental clinician. Periodontal disease is ubiquitous in our patients and represents the majority of cases we see in general practice. The periodontal ligament is a collection of miniscule collagen fibers that attach the cementum to the alveolar bone. Radiographically, the space between the cementum and bone coincides with the region where these fibers reside. A change in the width of this periodontal ligament space around the tooth indicates pathology (Photo 7).
The bone that surrounds the periodontal ligament space and the tooth is known as the alveolar process. Collectively, it is the cribriform plate (bone lining the tooth socket) known radiographically as the lamina dura, the alveolar margin and the trabecular bone. Radiographic density changes in the various portions of the alveolar process indicate pathology. Periodontal disease, neoplasia, cysts and fractures are examples that may result in changes in alveolar process radiographic density.
The alveolar process is covered by periosteum. A region of attached gingiva is tightly adhered to the periosteum and is separated from vestibular mucosa (unattached gingiva) by the mucogingival line or junction. The edge or free margin of the gingiva is termed marginal gingiva (Photo 8). Mobilization of tissue for closure at extraction sites often requires periosteal elevation of the attached gingiva beyond the mucogingival line (Photo 9). The tissue that attaches the gingiva to the tooth is called the junctional epithelium. It rests at the base of the gingival sulcus. A periodontal probe properly placed within the sulcus will come to rest on the junctional epithelium (Photo 10).
Periodontal disease compromises the junctional epithelium and increased probing depths and bleeding upon probing are encountered.
Radiographic or gross pathology is generally described by the location of the pathology in relation to various structures within the oral cavity. Directional terms commonly used to describe pathology in relation to the dental arcades are defined as follows (Photos 11, 12 and 13) :
- Mesial = toward the midline of the dental arch in either mandible or the maxilla,
- Distal = away from the midline of the dental arch,
- Vestibular = (formerly buccal) toward the cheek,
- Lingual = toward the tongue,
- Palatal = toward the palate,
- Labial = toward the lip. This pertains to the canine and incisor region.
- Facial = general term used to indicate either vestibular or labial direction.
Note: Caudal, rostral, lateral, medial, dorsal and ventral are used to describe direction when not associated with the arcades. For example, the “inflammation of caudal buccal mucosa” or a lesion described as “rostral to the lingual frenulum” are proper uses of these terms.
Palatal bone and soft tissue, known collectively as the palate, comprise the majority of the maxillary portion of the oral cavity separating it from the nasal cavity and nasopharynx. The hard palate is comprised of the maxillary, incisive and palatine bones.
The major palatine arteries and the major branch of the maxillary division of the trigeminal nerve supply and innervate the oral portion of the palate.
These structures enter the oral cavity though the major palatine foramina generally present at the level of the central portion of maxillary fourth premolar close to halfway to the palatal midline (Photo 14, p. 7). The major palatine arteries are of great importance when performing palatal surgery from the standpoint of vascular preservation and ligation. Palatine nerve blocks are paramount to intraoperative safety and post-operative patient comfort. The minor palatine foramina lies directly caudal to the major foramina and through them pass the nerve and blood supply to the soft palate.
The paired incisive foramina are present in the rostral hard palate adjacent to the canine teeth. The branches of the major palatine nerve and artery enters the nasal cavity through the incisive foramina.
Palatal mucosa is keratinized and contains numerous rugae or transverse ridges. The line in the mucosa at the midline is called the median raphe (Photo 15). The raised region at the rostral extent of the mucosa at the midline, caudal to the incisors is the incisive papilla. Paired incisive ducts exist lateral to the papilla and communicate directly with the vomeronasal organ. Inflammation of the mucosa of these structures can become a clinical concern when food and debris accumulate abnormally.
The soft palate is the caudal extension of the hard palatal mucosa, contains no rugae and should terminate at the tip of the epiglottis close to the level of the middle of the tonsils. Extension of the soft palate beyond the tip of the epiglottis is an important contributor to respiratory compromise, especially in brachycephalic dogs.
The fauces compose the lateral walls of the oropharynx (Photo 16). Commonly, but incorrectly, referred to as the fauces, the caudal buccal mucosa is the tissue lateral to the soft palate. The tissue lateral to the fauces is correctly referred to as the palatoglossal fold.
Additional oral-cavity structures of clinical interest are the zygomatic and parotid salivary papillae and their associated ducts. Palatal repositioning of the papillae is necessary in most cases to achieve closure of the mucoperiosteal flap following extraction of the maxillary first molar in the dog (Photo 17).
Lateral and ventral to the tongue are the lingual folds. These folds, when excessive, become traumatized during mastication producing sublingual traumatic granulomas otherwise known as “gum chewer’s syndrome” (Photo 18). The tongue is secured to the floor of the oral cavity rostrally by the lingual frenulum.
The lingual frenulum should not be confused with the mandibular labial frenulum (Photo 19), an extension of unattached mucosa vestibular to the mandibular first premolar. This structure may require surgical alteration in cases where its presence is a contributing factor to periodontal disease associated with the mandibular canine teeth.
Maxillary, mandibular landmarks
Several anatomical structures of clinical importance exist in the maxillary and the mandibular bone. Landmarks for the regional nerve blocks of the oral cavity are as follows (Photos 20, 21 and 22):
- Infraorbital block = infraorbital foramen,
- Maxillary block = distal to the maxillary second molar,
- Inferior alveolar block = mandibular foramen,
- Mental block = middle mental foramen.
The infraorbital neurovascular bundle courses in a rostral direction as it exits the infraorbital canal. It can be palpated as a large band beneath the vestibular mucosa. Divisions of the arteries and nerves are found throughout the deeper tissue of the upper lip and must be avoided when preparing mucoperiosteal flaps for extractions and oronasal fistula repair.
Although not as prominent as the infraorbital structures, the nerves and arteries emanating from the caudal, middle and rostral mental foramina should be avoided or ligated if surgical exposure is required in the soft-tissue region of the rostral mandible.
As a note of clarity, the proper nomenclature describing the horizontal portion of the mandible is the mandibular body. There is no horizontal ramus. The vertical portion of the mandible is the ramus. There is no vertical ramus.
The temporomandibular joint (TMJ) is formed by the condylar process of the mandible and the mandibular fossa of the temporal bone (Photo 23). Abnormalities in this area can result in pain, crepitance and the inability to close or open the mouth. Traumatic dislocations are common, especially in the cat. Radiographic positioning is tedious for this region, and CT imaging is becoming the technique of choice for more involved cases (Photo 24).
The muscles of mastication include the muscles that open and close the mouth. Those that close the mouth are the strongest and most numerous for obvious reasons and include the temporalis, masseter and lateral and medial pterygoid. The digasticus muscle is the muscle that acts to open the mouth. A commonly recognized problem associated with the muscles of mastication is masticatory muscle myositis that results in acute pain and eventual inability to open the mouth due to chronic inflammation and fibrosis.Recognition of the major anatomical structures within the oral cavity gives the veterinarian and technician a comfortable base for making medical and surgical decisions that benefit the patient. The veterinary dental knowledge base has expanded dramatically in the recent past. This review has provided updates with current and accepted nomenclature and has provided some clinical syndromes commonly associated with that anatomy.