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Cracked Tooth Syndrome Aetiology, Diagnosis, Management, and Prevention
Cracked Tooth Syndrome (CTS) is a condition caused by cracks in the teeth that can result in a series of symptoms that can be challenging to diagnose and manage.
The symptoms of CTS include spontaneous pain, bite pain, and cold irritation pain. Bite pain typically worsens when the bite force increases. Unfortunately, there is no obvious correlation between these symptoms and the appearance of cracked teeth, making it essential to comprehensively diagnose CTS using auxiliary tools. Failure to diagnose and manage CTS reasonably may result in irreversible severity in symptoms.

Aetiology of Cracked Tooth Syndrome (CTS)
The aetiology of CTS can be multifactorial and may vary from individual to individual. Understanding the aetiology of CTS is essential for its prevention, diagnosis, and management. Factors that increase the force acting on the teeth or those that weaken the resistance of the teeth to the chewing forces are predisposing factors for CTS. The aetiology of CTS is related to non-iatrogenic and iatrogenic factors.
Non-iatrogenic Factors
Ageing: CTS is more common in people over 40 due to the increased fragility of hard tissues and loss of dentin elasticity.
Oral Habit: Bad habits such as chewing hard objects or unilateral chewing can promote CTS, as they subject teeth to forces beyond their normal range.
Dental Structure: Structural defects such as large grooves, bifurcations, and incomplete fusion during tooth development can cause CTS. High and steep cusp inclinations also increase the risk.
Odontiatrogenic Factors
Head and Neck Radiotherapy (HNRT): HNRT alters tooth structure and contributes to a dry environment, tooth demineralisation, and decreased saliva flow, all of which increase the risk of enamel craze line (ECL).
Root Canal Therapy: The stress of the procedure on root dentine can cause CTS, especially when performed in a dry environment. The placement of intra-canal posts, the use of higher concentrations of sodium hypochlorite, and the excessive widening of the root canal can also increase the risk of vertical root fractures (VRFs).
Restorative Procedures: Intracoronal restorations, friction locks, and self-threaded dentin pins can cause stress on the tooth structure and lead to cracks. Excessive removal of tooth tissue during preparation can also reduce the hardness of the tooth and increase the risk of CTS.
Material Performance: Metallic materials and materials with different thermal expansion coefficients than the tooth can cause abnormal bite force distribution and increase the risk of CTS.

Diagnosis of Cracked Tooth Syndrome (CTS)
The diagnosis of CTS can be challenging as the symptoms can be variable and can be similar to other dental problems. Diagnosing cracked teeth in the early stages can be challenging due to blurred symptoms and signs. Various techniques can be used for diagnosis, including clinical examination, radiography, and new technologies.
• Clinical examination: Clinical examination techniques, such as percussion, point load, and cold stimulation tests, along with the use of plastic bite blocks and methylene blue dye staining, can aid dentists in diagnosing cracked teeth. Fibre Optic transillumination (FOTI) and operating microscopes are also valuable tools for diagnosing enamel cracks.
• Radiography: Cone-beam computed tomography (CBCT) can detect loss of periapical bone during vertical root fractures (VRFs), but its resolution is not suitable for the clinical diagnosis of cracked teeth and detection of early VRFs.
• Swept-Source Optical Coherence Tomography (SS-OCT): SS-OCT is a non-destructive imaging technique that emits different wavelengths of light using a laser source with variable wavelengths. It can detect and analyse incipient enamel caries and early CTS, but its main application is restricted to early diagnosis due to its confined penetration depth.
• Near-Infrared Imaging: Near-infrared imaging, such as indocyanine green-assisted near-infrared fluorescence (ICG-NIRF) imaging, can detect enamel-dentin and enamel cracks in vitro, but it cannot distinguish crack types and obtain accurate crack depth information.
• Ultrasonic: Ultrasonic system detection has promising potential for detecting CTS because it can penetrate hard tissue and lacks the hazards associated with ionising radiation.
• Infrared Thermography: Infrared thermography technology is effective in detecting small cracks in dentin, especially when other diagnostic techniques fail. The technique works by vibrating the smaller cracks with ultrasonic power. However, this method is not effective in detecting wider cracks.
• Near-Infrared 810nm Diode Laser: This technology can help manage symptomatic CTS by irradiating teeth with suspicious symptoms. Most patients experience sharp pain when the laser energy is applied, which may be due to irritation caused by the energy reaching the pulp.
Management of Cracked Tooth Syndrome (CTS)
The management of CTS depends on the severity of the crack and the symptoms experienced by the patient.

1. Immediate Management
• Occlusal adjustment: Occlusal adjustment is recommended to minimise loading on the CTS tooth and to alleviate symptoms. After adjustment, restoration should be placed on the affected cusp to avoid further fractures in the tooth.
• Copper rings and stainless steel bands: Copper rings and stainless steel bands can be used for the diagnosis and management of early CTS cases. Stainless steel bands are preferred over copper ones as they result in low gingival irritation.
• Direct Composite Splint (DCS): Direct Composite Splint (DCS) is a marginally invasive method that can be used for short-term management. Careful inclusion criteria, selection of a suitable composite resin, proper bonding systems, and application methods should be considered.
• Temporary crowns: Temporary crowns are recommended for full-coverage crowns to fix a crack. However, temporary crown fabrication can be time-consuming and intrusive, and it may delay fracture fixation.
2. Direct Restoration
Direct restorations are usually performed when patients visit a dentist for dental caries and other oral diseases. Direct restorations using composite resin are preferred over bonded silver amalgam restorations. Indirect and direct composite resin restorations fully protect cracked teeth. Amalgam restorations show a significant increase in fracture resistance, while composite resin restorations are more resistant to fracture than amalgam restorations. The coronal approach damages the adhesive interface between the tooth and restoration under periodic functional loads, making bonded silver amalgam restorations less favourable than resin-covered restorations.

3. Indirect Restoration
A. Inlay Restorations
Traditional inlay restorations can undermine the residual tooth structure when preparing the tooth, leading to tooth fractures. Additionally, they use a “wedge retention” concept, which can cause occlusal pressure on the tooth before and during use. Thus, conventional inlays are not effective in managing CTS cases. However, indirect resin-bonded composite inlays and bonded mesial-occlusal-distal (MOD) ceramic inlays can improve the fracture strength of prepared teeth to a level similar to healthy teeth. Ceramic inlays are more efficient than resin composite inlays in restoring CTS.
CAD/CAM-fabricated resin inlays have better-accelerated fatigue resistance and reduced propensity for cracking in large MOD restorations than direct resin restorations.

B. Onlay Restorations
Gold onlays cemented with resin-modified glass ionomer luting cement are the most conservative restoration approach. They have a satisfactory survival rate of 89% after 60 months. Ceramic onlays have excellent properties such as resistance to wear and friction, outstanding appearance, and biocompatibility. Indirect composite resin onlay restorations are effective in treating painful, cryptically fractured teeth, and have a higher fracture resistance than ceramic onlays.

C. Full Crown
Full crowns are the first choice of treatment for CTS. They have a higher survival rate and lower incidence of complications compared to acrylic resin crowns. Metal-ceramic crowns are frequently used as fixed restorations to meet the aesthetic requirements of patients. The estimated 10-year survival rate of pulpal activity for metal-ceramic crowns is 84.4%. However, pulpal injuries may arise at the time of crown placement, which may require consequential root canal therapy. Regular radiological follow-up is necessary.

Prevention of Cracked Tooth Syndrome (CTS)
Preventing CTS is essential in stopping its development caused by medical, environmental, or genetic factors. This can be achieved through good oral hygiene practices, healthy chewing habits, and a proper diet, as well as increasing the frequency of oral examinations. Dental appliances such as hard acrylic and soft splints can also be effective in preventing CTS by dividing the force throughout the masticatory system. In cases where symptoms of CTS occur, occlusal adjustments or bonded restorations can be performed to prevent further extension of the cracked tooth.

Conclusion
Cracked Tooth Syndrome (CTS) is a common dental problem that can be difficult to diagnose and manage. The aetiology of CTS can be multifactorial, and the diagnosis requires a thorough clinical examination and diagnostic tools. The management of CTS depends on the severity of the crack and the symptoms experienced by the patient, and prevention can be achieved through good oral hygiene, regular dental check-ups, and avoiding habits that can lead to tooth damage.
Vitality tests in cracked tooth syndrome
The typical tooth with cracked tooth syndrome would be hypersensitive to hot and cold and therefore you would expect it to be vital. Of course, vitality testing in itself does not confirm a diagnosis of cracked tooth syndrome.
Periapical radiography
A periapical radiograph would not demonstrate a crack. However, it would be helpful in eliminating other causes of dental pain, which can be confused with cracked tooth syndrome. For example, an acute periapical periodontitis may be tender to percussion in the same way as cracked tooth syndrome. However, a widened periodontal ligament space apically would suggest the former diagnosis.
Bitewing radiography
A bitewing radiograph would not demonstrate a crack. However, it would be helpful in eliminating other causes of dental pain which can be confused with cracked tooth syndrome. For example, dental caries may produce sensitivity to hot and cold, in a similar way to cracked tooth syndrome.
Stimulation with ethyl chloride
Application of cold would help to identify the tooth causing dental pain. A tooth with cracked tooth syndrome would typically be hypersensitive to cold. Other methods of application of hot and cold would include ice sticks and hot gutta percha sticks. Other reasons for teeth to be hypersensitive to hot and cold should be borne in mind.
Applying pressure to an individual cusp
A number of methods have been used for this. The intention is to open and close the crack. A bite stick will precisely apply pressure to an individual tooth. Often the patient will feel pain on release of the pressure as the crack closes again. If only one tooth is found to respond, then this is a good indication that cracked tooth syndrome is the correct diagnosis. Less precise methods of applying pressure in this way are pieces of rubber dam or cotton wool roll.
Transillumination
Transillumination may be applied by using a dental mirror to reflect the operating light, by using a composite curing light or with a special fibre optic transillumination unit. It may be possible to directly visualise a crack with these methods.
Staining
It has been suggested that sealing in iodine into a cavity will demonstrate a crack. Equally, in the case of more obvious cracks, it may be possible to directly visualise a crack without staining.
Tenderness to percussion
Teeth with cracked tooth syndrome are often tender to percussion, especially if the cracked tooth is tested. However, other causes of tenderness to percussion should be borne in mind.
Placement of a copper band
Placement of a copper band would be an attempt to ‘tie the tooth together’ and thus prevent opening and closing of a crack. Temporary crowns can also be used for this, if crown preparation is a sensible option for the longer term anyway.