Cracked Tooth

Definition and Classification
A cracked tooth is a type of longitudinal fracture classified as an incomplete fracture.

Nature and Extent of the Fracture

Definition: A cracked tooth refers to a fracture that originates from the crown and extends further, but remains incomplete, meaning it does not reach a surface in all directions.
Orientation: The fracture is typically mesiodistal in direction, extending subgingivally and progressing cervically/apically.
Tissues involved: Unlike craze lines, which affect only enamel, cracked teeth involve additional hard and soft tissues. Extension into dentin may produce symptoms or structural damage.
Bacterial penetration: Deeper fractures such as cracked teeth provide a pathway for bacterial invasion, potentially leading to pulpal, periapical, and periodontal pathology.
Differentiation from fractured cusp: Cracked teeth are more centrally located than fractured cusps and have a higher likelihood of pulpal exposure.
Differentiation from split tooth: Over time, a cracked tooth may progress into a split tooth, the terminal stage of the condition, in which the fracture extends through all surfaces and divides the tooth into two distinct segments.

Clinical Features and Diagnosis

Diagnosis of cracked teeth is challenging due to subtle and variable clinical presentations.

Pain: Patients often report pain during chewing or upon release of biting pressure.
Biting test: Diagnostic tools such as the Tooth Slooth applied to specific cusps can elicit sharp pain on pressure or release, indicating a cracked tooth.
Periodontal involvement: If the fracture extends into the root, localized deep periodontal pockets may develop.
Transillumination: Fiber-optic light is used as an adjunctive diagnostic method. Unlike craze lines (which transmit light through enamel), fractures extending into dentin block light transmission. The fracture line reflects light, producing a sudden change in brightness.
Staining: Dyes such as methylene blue, iodine, or caries-detecting solutions can highlight fracture lines and help determine their extent. Visualization is enhanced with magnification (e.g., surgical microscope).
Direct examination: Existing restorations may need to be removed to allow direct inspection of the fracture.
Wedging test: Application of wedge devices can reveal the degree of separation between tooth segments. Minimal or absent separation indicates an incomplete fracture (cracked tooth).
Differential diagnosis: If the fracture extends to the pulp, clinical signs of pulpal and periapical pathology may appear, necessitating careful differential diagnosis.

Management and Prognosis

Management of cracked teeth is complex and depends on the location and extent of the fracture.

Vital pulp: If the pulp remains vital, prognosis is significantly improved.
Root canal treatment (RCT): RCT may be indicated based on clinical findings and symptoms, and is often successful. Access preparation is typically required for improved visualization. Cracked teeth are a common cause of symptomatic irreversible pulpitis, for which RCT or extraction is recommended.
Extraction: If the fracture extends to the pulp chamber floor or into the root canal system, accompanied by deep periodontal probing defects, prognosis is poor and extraction is indicated.
Prognostic considerations: Even under optimal conditions, prognosis remains questionable, as fractures may continue to propagate.
Restorative protection: Protection of weakened cusps (e.g., with full cast crowns) is essential to minimize excessive flexure and prevent progression of incomplete fractures.

Summary

A cracked tooth represents an incomplete but clinically significant fracture originating from the crown. Unlike superficial craze lines, it provides a pathway for bacterial invasion into deeper dental structures, potentially leading to pulpal and periodontal disease. Early diagnosis and appropriate management—whether removal of fractured segments, root canal therapy, or extraction—are critical to prevent progression into a split tooth.