Introduction

Cracked tooth syndrome, as the name suggests, is defined as a posterior tooth fracture involving enamel and dentin may or may not extend to pulp. Ellis later defined it as a fracture plane of unknown depth and direction passing through the tooth structure that, if not already involved, may progress to communicate with the pulp and/or periodontal ligament. 

American Association of Endodontists classified cracked tooth into 5 categories: 

• Craze line

• Fractured cusp

• Cracked tooth

• Split tooth

• Vertical root fracture 

Etiology

• Age - as age increases, the tooth fatigue increases, dentin loses its elasticity - when the force is imposed on the tooth, it cracks.

• Oral habits - unilateral chewing, bruxism, etc causes excessive force on the tooth beyond normal range, leading CTS

• Structural defects like deep radicular grooves, cuspal inclinations, bifurcation, large pulp spaces

• Head and neck radiotherapy - structural changes in tooth

• Root canal treatment - Dentin is stressed due to the contact between the instrument and the canal wall

• Restorative procedures - decrease the structural strength and increase risk of CTS

• Restorative materials - difference in coefficient of thermal expansion may risk CTS

Symptoms

• Acute pain on chewing

• Sharp pain on cold food

• Spontaneous pain

• Patient identifies the offending tooth

Diagnosis

Clinical examination: 

• Percussion test

• Bite test using tooth sloth etc

• Methylene blue staining to visualise the crack lines

• Fiber optic transillumination - a crack in a tooth stops the transmission of line.

Radiographs:

• Traditional IOPA radiographs

• CBCT can also be used

Newer techniques:

• Swept source - optical coherence tomography - emits different wavelengths of light using a laser source with variable wavelengths to detect cracks.

• Indocyanine green-assisted near-infrared fluorescence (ICG-NIRF) imaging to detect enamel-dentin and enamel cracks

• Infrared thermography

Management

As a rule, if the crack involves pulp or nearing pulp, root canal treatment is done.

Immediate relief:

Occlusal adjustment - to minimise the load, alleviate the symptoms and delay the cracking process. But it weakens the tooth.

Direct composite splints

Temporary crowns

Direct restorations:

It is more minimally invasive than indirect restoration. Direct composite restorations with cuspal coverage can be done. It avoids provisional restoration. It is cost effective.

Indirect restorations:

Inlays, onlays, full coverage crowns can be done to restore the teeth.

Inlays improve fracture resistance but the preparation undermines the remaining structure.

Onlays are more conservative than full coverage crowns but has lower fatigue resistance.

Full coverage crowns has lower risk of complications but may have pulpal injuries.