2 Examining the Head and Oral Cavity

2.1 Anatomy and Morphology of the Oral Cavity

Even after the crown of a tooth has erupted, the development of the tooth is far from complete. A mature root takes several months to develop. Initially, development is dominated by a large pulp cavity and an open apical foramen ( ? Fig. 2.1). During this period, dental injuries with subsequent pulpitis usually cannot be treated, which is why stress on the teeth should be minimized in the animal's first year of life. The development of an individual tooth is not complete until the root apex has formed and the tooth has reached its full height ( ? Fig. 2.2). The development periods vary due to the differences in eruption patterns.

Fig. 2.1 Diagram of a young tooth. The pulp of the crown and root occupies a great deal of space, while the tooth walls are still very thin. The Hertwig epithelial root sheath is soft and the apical foramen provides a wide point of entry to the dental pulp.

Fig. 2.2 Diagram of a mature tooth. The "adult" tooth has a closed pulp chamber that narrows and shrinks inward as the animal ages, forming normal dentin.

The junctional gingival epithelium ( ? Fig. 2.3, ? Fig. 2.4) creates the epithelial attachment, the first barrier in the gingival sulcus. Attached via hemidesmosomes, this barrier prevents bacteria and their toxins from entering the fibrous, desmodontal attachment. However, the epithelial attachment is susceptible to trauma, which is why dental health requires good dental care to preserve this structure. The bacteria in the soft plaque and the development of a biofilm impair the epithelial attachment and destroy the desmodontal attachment. The next step is the deterioration of the periodontal ligament and resorption of the alveolar bone ( ? Fig. 2.5).

Fig. 2.3 Junctional gingival epithelium. In a medium-sized dog, the normal gingival sulcus is approximately 2 mm deep and in cats, it is approximately 1 mm deep. Near the sulcus floor, special non-keratinized cells attach the gingiva to the tooth at the cementoenamel junction.

Fig. 2.4 Cells of the junctional gingival epithelium. The cells of the junctional gingival epithelium employ hemidesmosomes for attachment to the tooth surface. The epithelial cells are connected via desmosomes. Because they are non-keratinized, these cell layers are permeable and permit the host's immune factors and cells to penetrate the gingiva at the sulcus.

Fig. 2.5 Comparison of healthy and diseased periodontium. The periodontium on the left is healthy. The inner lining of the gingival sulcus, along with the junctional gingival epithelium, seals off the periodontium on the oral cavity side, forming a gingival cuff. The periodontium on the right is diseased. The junctional gingival epithelium (orange) has migrated apically. Normal gingival mucosal cells have shifted into the sulcus, but are unable to provide a barrier. The gingival sulcus has deepened due to the damaged epithelium and desmodontal attachment and the loss of the fibrous and bony support of the alveolar bone.

The maxilla ( ? Fig. 2.6) consists of the maxillary, premaxillary and palatine bones, all of them paired, which are connected by sutures.

Fig. 2.6 Maxilla. The incisors are located in the premaxillary bone, and the canine teeth and cheek teeth are embedded in the maxillary bone. The palatine bone does not contain any teeth. The two large rostral openings between the maxillary and premaxillary bones are the palatine fissures, through which the vomeronasal organ communicates with the oral cavity.

The mandible ( ? Fig. 2.7) consists of the paired mandibular bones, which are connected rostrally in the band-like symphysis. Unlike in humans, no solid bony structure is formed at the symphysis.

Fig. 2.7 Mandible. The mandible consists of the horizontal body of the mandible and the vertical ramus of mandible. While the maxilla increases in size appositionally and along the sutures, the mandible widens caudally. Each mandibular condyle articulates with the base of the skull at the mandibular fossa of the temporal bone.

The teeth can be classified by function ( ? Fig. 2.8). The mandibular teeth are all embedded in the alveolar part of the mandible while the maxillary incisors are embedded in the alveolar part of the premaxillary bone, and the canine teeth and cheek teeth are embedded in the alveolar part of the maxillary bone.

Fig. 2.8 Tooth classification. The different groups of teeth are color-coded as follows: incisors: blue; canine teeth: green; premolars: orange; molars: yellow.

In dogs and cats, the salivary glands are grouped caudally to the angle of the mandible. Only the zygomatic gland is located separately behind the zygomatic arch ( ? Fig. 2.9, ? Fig. 2.10).

Fig. 2.9 Lateral view of the salivary glands. The parotid gland (green) is situated directly below the base of the ear with one rostral and one caudal part. Directly below the parotid glands, in the area of Viborg's triangle, is the mandibular gland (red), which is covered by a capsule that includes the caudal part of the sublingual gland (blue). The zygomatic gland (magenta), is located separately, behind the zygomatic arch.

Fig. 2.10 Ventral view of the salivary glands. The ducts of the mandibular and sublingual glands open at the frenulum of the tongue. The duct of the parotid gland opens on the buccal mucosa at the level of the buccal surface of the maxillary carnassial teeth. The short duct of the zygomatic gland opens just caudally to this.

Dental charts ( ? Fig. 2.11, ? Fig. 2.12) are used for diagnostics and follow-up. They are for recording information on the animal and findings from examination of the mouth. Calculus and the degree of gingivitis are recorded and a legend is used to record other changes such as fractures, oral masses, etc. Changes to the jaw or planned orthodontic appliances can also be outlined in the overview section. The cut-out ( ? Fig. 2.13) shows how periodontal pocket depth is assigned for each tooth.

Fig. 2.11 Canine dental chart, dentition. Dogs have a total of 42 permanent teeth. The only teeth with cusps for grinding are the molars. The chart has a separate box for each tooth.

Fig. 2.12 Feline dental chart, dentition. Cats have 30 teeth, all of which have only a cutting function.

Fig. 2.13 Canine dental chart, detail. The boxes containing an "x" are used to record the individual pocket depths of each area. The veterinarian can also record planned and past treatments here.

In dogs and cats, normal occlusion involves close interdigitation of the upper and lower teeth, so even small anomalies in an individual tooth or minimal changes in position can alter the jaw's closure. The powerful coronoid process of the caudal ramus of the mandible, which attaches to the powerful mouth-closing muscles, controls movement. The close anatomical proximity of the dental roots to the adjacent structures of the head is illustrated in ? Fig. 2.14, ? Fig. 2.15 and ? Fig. 2.16.

Fig. 2.14 Canine skull, frontal view. The frontal view of the canine skull shows the close anatomical proximity of the maxillary canine roots to the nasal cavity. The mesial surface of the maxillary canine root is separated from the nasal cavity by only a paper-thin bony cover.

Fig. 2.15 Canine maxilla, lateral view. The lateral view shows the proximity of the caudal maxillary cheek teeth and the orbital cavity. The orbital floor is not protected by a bony structure, but consists of soft tissue. Firmness of the orbital floor thus may indicate inflammatory changes in the caudal maxilla or in the space caudal to the molars....