Overview of Dentitions and Tooth Anatomy

When identifying a tooth, clinicians often use the D-A-Q-T naming order to ensure no information is missed:

• D (Dentition): Is it primary or permanent?
• A (Arch): Is it maxillary (upper) or mandibular (lower)?
• Q (Quadrant): Is it the right or left side?
• T (Tooth): What is the specific tooth type or number?

For more detailed periodontal charting, an arch can be further divided into three sextants (e.g., maxillary right posterior, maxillary anterior, and maxillary left posterior).

Tooth Anatomy: Tissues and Structures

A tooth is composed of several distinct tissues and structures that work together to facilitate function and resist forces.

Crown and Root Anatomy

The tooth is divided into the crown and the root. However, clinicians must distinguish between the anatomic and clinical definitions:

• Anatomic Crown/Root: The portion of the tooth covered by specific tissues—enamel covers the anatomic crown, while cementum covers the anatomic root.
• Clinical Crown/Root: The portion of the tooth that is actually visible in the mouth. The clinical crown can change due to gingival recession or enlargement, whereas the anatomic crown remains constant.

The junction where the enamel of the crown meets the cementum of the root is known as the cementoenamel junction (CEJ), also referred to as the cervix or "neck" of the tooth.

Internal and Supporting Tissues

Beneath the hard outer layers lies the pulp, the soft tissue containing blood vessels and nerves. The tooth is held in place within the alveolus (socket) by the periodontium, which includes the supporting structures of the jaw.

Root Morphology and Clinical Implications

The shape and orientation of the root are vital for periodontal health and restorative success. Roots are generally widest at the CEJ and taper toward the apex (the tip).

Clinicians must be aware of several specific root features:

• Root Axis Line: The long axis of the root. Teeth are rarely perfectly vertical, and their angulation affects how a clinician must approach them during scaling or instrumentation.
• Concavities: Depressions on the root surface that can trap biofilm and calculus.
• Furcations: The area where roots divide in multirooted teeth.
• Crown-to-Root Ratio: This is the relationship between the portion of the tooth above the alveolar bone and the portion below it. A low ratio (a very large clinical crown with little root support) can negatively impact the prognosis of the tooth.

Clinical Alert: When performing periodontal probing, always visualize the long axis of the tooth and be prepared to adapt your instrument to root concavities to ensure thorough cleaning.