Dental Anatomy, Pathophysiology, and the Triadan Tooth-Numbering System

Dental anatomy is the foundation of every clinical dentistry task the VTNE tests — charting, radiographic positioning, extraction, and periodontal staging all require you to name a tooth precisely and reason about its structure. Teeth are classified by crown type: brachydont teeth (dogs, cats, humans) have a short crown covered in enamel, a constricted neck at the cementoenamel junction (CEJ), and a single root seated in a socket by the periodontal ligament; hypsodont teeth (horses, rabbits, guinea pigs) have long crowns that erupt continuously through life to offset abrasive wear; sectoral teeth (carnassials) have blade-like crowns for shearing. Each tooth has a crown (above the gingiva, covered in enamel), a root (below the gingiva, covered in cementum), and a pulp cavity running through both — pulp contains odontoblasts, blood vessels, and nerves and communicates with the periapical space through the root apex.

The periodontium is the attachment apparatus that holds the tooth in the alveolus: gingiva (oral mucosa), periodontal ligament (collagen fiber sling between cementum and alveolar bone), cementum (root surface, where PDL fibers insert), and alveolar bone (jaw bone forming the socket). Periodontal disease is the most common disease in companion animals — by age three, roughly 70 to 80 percent of dogs and cats show some periodontal pathology. The disease process is:

1. Plaque biofilm forms within hours of cleaning — a structured bacterial matrix adherent to the tooth surface; it is invisible and cannot be rinsed off. Plaque, not calculus, drives inflammation.
2. Gingivitis — reversible inflammation of the gingiva only; no loss of attachment. Plaque bacteria (Gram-positive aerobes initially, shifting to Gram-negative anaerobes like Porphyromonas and Prevotella as disease progresses) trigger cytokines, neutrophil infiltration, and edema.
3. Calculus (tartar) — mineralized plaque; it is inert but rough, creating a surface for further plaque retention. Removing calculus without disrupting subgingival plaque does not treat disease.
4. Periodontitis — irreversible destruction of PDL and alveolar bone; pocket formation, mobility, furcation exposure, recession. Once bone is lost, it does not regenerate without guided tissue regeneration or bone grafting.

The Modified Triadan System

The Triadan system gives every tooth a unique three-digit number and is the international standard for veterinary dental charting (analogous to FDI in human dentistry). The first digit identifies the quadrant, the last two digits identify the tooth position within that quadrant, counting from the midline (01 = central incisor) caudally.

Permanent teeth use the 100-series base for dogs (the quadrants are 100s, 200s, 300s, 400s) and the 110-series base for cats (since cats have fewer teeth, the numbering shifts). The trick for remembering the quadrant numbering is the clockwise rule viewed from the front: start at the upper right, move to upper left, then lower left, then lower right.

Worked examples — permanent dentition

• 104 — upper right, position 04 = the upper right canine (maxillary canine) of the dog. (Cats use the same numbering: 104 is also the upper right canine.)
• 108 — upper right, position 08 = upper right fourth premolar (maxillary P4) — the upper carnassial in the dog.
• 204 — upper left canine.
• 304 — lower left canine.
• 404 — lower right canine.
• 309 — lower left, position 09 = the lower left first molar (mandibular M1) — the lower carnassial. The 108/409 pair forms the shearing carnassial unit in dogs.
• 406 — lower right third premolar; this is a tooth commonly affected by mesioversion (the rostral crossbite) in small-breed dogs.

Deciduous (primary) dentition

Deciduous teeth in Triadan use the 500-series base: upper right 500s, upper left 600s, lower left 700s, lower right 800s. Dogs have 28 deciduous teeth (no molars); cats have 26. Deciduous dentition is present from roughly 3 to 6 weeks of age and exfoliates by 6 to 7 months. Persistent deciduous teeth (failure to exfoliate) are most common at the canine teeth (504, 604, 704, 804) — the rule is to extract the retained deciduous tooth as soon as the permanent counterpart is erupting, because the deciduous root lies lingual/palatal to the permanent crown and diverts the permanent tooth into malocclusion.

Tooth counts to memorize

• Dog — 42 permanent teeth: 12 incisors (3 per quadrant), 4 canines (1 per quadrant), 16 premolars (P1-P4 upper, P1-P4 lower; the dog has four upper premolars but the first is often absent), 10 molars (2 upper, 3 lower per side). The maxillary arcade: I3-C1-P4-M2; mandibular arcade: I3-C1-P4-M3.
• Cat — 30 permanent teeth: 12 incisors, 4 canines, 10 premolars (P2, P3, P4 upper; P2, P3, P4 lower — cats have lost P1), 4 molars (1 upper M1, 1 lower M1 per side). The cat's maxillary arcade: I3-C1-P3-M1; mandibular arcade: I3-C1-P2-M1.

A high-yield VTNE trap: the upper fourth premolar (108 in dogs) and lower first molar (409 in dogs) are the carnassial teeth — the carnassial root system is complex (the 108 has three roots: mesial, distal, and palatal), so extraction of the 108 requires sectioning into three single-rooted segments. A second trap: cats do not have a maxillary first premolar (105 is absent) or a mandibular first or second molar (there is only M1) — a cat tooth chart that shows a 105 or 410 is wrong.