THE HEALTHY COLLIE: DENTITION
The Basics of Teeth and the Oral Cavity in the Dog

by Dr. David Hansen
Camloch Collies

The purpose of this article is to acquaint the reader with the basic anatomy and terminology of the oral cavity in the dog. There are many abnormalities that can occur in the oral cavity or with the dentition at different ages. It is important for breeders to know what normal looks like, so that at key ages they can recognize a potential problem. Many abnormalities are very easy to treat inexpensively, if they are recognized early. A mild abnormality may develop into a major problem if not promptly treated. Most can still be corrected to give the dog a comfortable and functional mouth, but it can be more difficult and expensive. I will present a series of case reports of abnormalities in a future article.

Dental Formulas
It is important to know the number of teeth of both the puppy and adult dog along with the eruption times of the teeth. Puppies have a total of 28 "deciduous" (baby or immature) teeth. Looking only at the right side of the mouth, there are 3 upper and 3 lower incisors, 1 upper and 1 lower canine, and 3 upper and 3 lower premolars. The numbers are added together and multiplied by 2 (right and left sides) to total 28. The formula is written as follows:

2X (3/3 i, 1/1c, 3/3pm) = 28

All of these teeth should eventually be replaced with the mature (adult, permanent) counterpart along with another upper and lower premolar and 2 upper and 3 lower molars on each side (Figure 1). This results in a total of 42 teeth as indicated by the following formula:

2X (3/3I, 1/1C, 4/4PM, 2/3M) = 42

Figure: 1 Adult Teeth

The times that the deciduous and mature teeth erupt are critical, as failure to erupt can cause major problems. The following chart is the normal eruption times:

As the mature tooth bud develops, the deciduous tooth begins to have its root resorbed, resulting in exfoliation (falling off) of its crown. The exfoliation occurs as the mature tooth crown is erupting through the gingiva.

Directional terminology
Before discussion of dental anatomy, a general understanding of directional and surface terminology is required (Figure: 2). The surface of the incisor and canine teeth directed toward the lip is referred to as the "labial" surface. The surface of the premolar and molar teeth directed toward the cheek is the "buccal" surface. The surface of all of the lower (mandibular) teeth directed toward the tongue is referred to as the "lingual" surface. The surface of all of the upper (maxillary) teeth directed toward the palate is referred to as the "palatal" surface. The surface of the premolars and molars facing the teeth of the opposite jaw during closing of the mouth is called the "occlusal" surface. The term "distal" (caudal, posterior) is referring to the surface of the tooth furthest away from the middle (1st) incisor or median line. The opposite direction or surface is called "mesial" (anterior, cranial).

Figure: 2 Lower Jaw

The Tooth
The tooth can be broken down into the crown (above the gingival or gums) and the root (below the gingiva)(Figure: 3). The incisor, canine, and first premolars have 1 root. The upper fourth premolars and upper first and second molars have 3 roots. The rest of the teeth have 2 roots. The "cusp" is the point or tip of the crown. The opposite end from the cusp is the "apex" or tip of the root. The term "coronal" is used to indicate the direction toward the crown tip or occlusal surface. The term "apical" is used to indicate the direction toward the root tip and away from the crown tip.

Figure: 3 Upper Jaw

Anatomy of the Tooth
The tooth is covered by enamel on the crown and cementum on the root (Figure 4). Enamel is the hardest substance in the body. Dentin is the substance underneath the enamel and cementum. The pulp tissue is located in the pulp cavity in the central portion of the tooth. The pulp contains cells, blood vessels, lymphatics, nerves and connective tissue. The pulp functions include forming the dentin, responding to noxious stimuli, nutritional support and perception of stimuli (pain). The space where the pulp is located in the crown is called the pulp chamber and in the root is called the root canal. The apex of the tooth has multiple small openings, which allow for communication between the contents of the root canal and periapical tissues. The periodontium generally refers to the supporting apparatus of the tooth and includes the gingiva, periodontal ligament, cementum and alveolar bone. The periodontal ligament has fibers embedded in the cementum and alveolar bone, which hold the tooth in the alveolus (socket). The junction of the cementum and enamel is referred to as the cementoenamel junction (CEJ). The attachment of the gingiva to the tooth is at the level of the CEJ. In the normal healthy mouth the shallow gingival sulcus created between the tooth and the unattached gingival tissue is considered to have a normal depth of 1-3 mm in the dog.

Figure: 4 Upper jaw

Oral Cavity
The other structures in the oral cavity include the hard and soft palate, tongue and floor of the mouth. The hard and soft palate serves to separate the oral cavity from the nasal cavity. The hard palate is the anterior portion of the roof of the mouth between the right and left side that has soft tissue overlying bone. The soft palate extends caudally after the bone ends. The teeth are in sockets in the incisive, mandible and maxillary bones.

Conclusion
I'm sure that this is enough of the "boring" facts. Keep this information handy for the future case reports. The first one will have to deal with problems that can develop when there is a "missing" tooth.

David E. Hansen, DVM, FAVD, graduated from Kansas State College of Veterinary Medicine in 1987. In 1989 he and his wife, Krista, formed Camloch Collies. He developed an interest in advanced veterinary dentistry in 1990 and in 2001 became one of only 69 Fellows of the elite worldwide organization, Academy of Veterinary Dentistry.