Cracked Tooth Syndrome

Etiology

Occlusal forces are the leading cause of cracked tooth syndrome. However, various factors contribute to the tooth's susceptibility and prognosis. The mechanical properties of teeth have been extensively researched and are vital considerations when assessing the etiology of cracked teeth. The tooth tissue absorbs the forces with occlusal loading during mastication or nocturnal bruxism. Enamel, dentine, and cementum exhibit distinct structures and properties in terms of elasticity, hardness, and viscoelasticity, resulting in differential absorption of occlusal forces.[4] Notably, these mechanical properties can change with age, potentially leading to a reduction in physiological elasticity and decreased capacity to absorb occlusal forces effectively.[5] 

In addition, teeth weakened by restorations will be at an increased risk of fracture when undergoing occlusal loading. Restorations poorly placed due to contamination, poor marginal adaptation, or lack of incremental technique, resulting in a high C-factor, pose a heightened risk.[2][6] Additionally, the presence of remaining healthy tooth tissue and the size of the cavity can influence fracture risk. The interaxial dentine and the loss of one or both marginal ridges have significant roles.[7] Mondelli et al suggest that if a restoration exceeds one-quarter of the intercuspal distance, there is an elevated risk of tooth fracture.[8] 

Teeth that have undergone endodontic access display more unrestorable fracture patterns compared to those that have not been accessed.[9] Beyond restorative etiological considerations, developmental and morphological factors may also contribute to a tooth's fracture risk. Occlusal anatomy characterized by deep fissures and steep cusp angles, potentially leading to altered intercuspation, pulp chamber volume changes, rotations, and inclinations, can further influence fracture risk.[10]

Epidemiology

Cracked tooth syndrome predominantly affects adults aged 30 to 50 and is seldom reported among students.[11][12]. Roh et al's analysis of 154 cracked teeth concluded that both men and women seem to be equally affected.[13] Mandibular molars are reported to be most commonly affected, followed by maxillary premolars and molars.[14][15][16] This observation is supported by an audit conducted by Banerji et al, which determined that there may be a wedging effect of the opposing prominent maxillary mesio-palatal cusp onto the central fissure of mandibular molars.[17] 

Pathophysiology

Usually, a crack will extend from the mesial to the distal direction across the occlusal surface and then progress apically toward the cementoenamel junction. In some cases, the crack will propagate further along the root surface.[18][19] Cracks may be classified as complete or incomplete. A complete crack will propagate from the occlusal surface through to another external surface of the crown. In contrast, an incomplete fracture will propagate from the occlusal surface into the enamel, dentine, pulpal tissues, or periodontal ligament.[20][5] The trajectory of the crack will determine the tooth’s restorability and required treatment plan.

History and Physical

Diagnosing cracked teeth is notoriously challenging because of their variable presentation. Patients may describe symptoms that overlap with various diagnoses, emphasizing the importance of obtaining an accurate history and conducting diagnostic tests. The most frequently reported symptom is a sudden sharp pain upon biting down on the affected tooth.[21] Additionally, some patients experience a fleeting sharp pain upon the release of bite pressure.

Patients may also report sensitivity triggered by cold drinks and food, often struggling to identify the causative tooth.[2] If the crack extends near or into the pulp tissue, patients may report symptoms similar to irreversible pulpitis, characterized by a continuous dull ache exacerbated by hot thermal stimuli and disturbed sleep.[2] Patients with previous experiences of cracked tooth syndrome can often self-diagnose based on their symptoms.

Evaluation

In addition to obtaining a comprehensive history, several diagnostic tools can aid in elucidating the diagnosis. A thorough visual examination with magnification and illumination may reveal fracture lines and communication with existing restorations. Fibreoptic transillumination (FOTI) is particularly valuable for investigating cracked teeth. Allowing light to penetrate the tooth until deflected by a fracture produces a visible transition line from light to dark, highlighting the presence of cracks.[22] 

Bite tests are useful in eliciting the patient’s symptoms to pinpoint the affected tooth and cusp. Using a Tooth Slooth instrument, occlusal forces are directed through each individual cusp of the suspected tooth, and the patient reports which cusp triggers their symptoms.[23] Vitality testing with ethyl chloride and electronic pulp testers typically yields a positive response. However, thermal tests may elicit an exaggerated response to cold due to the proximity of the crack to the dentine.[24] 

In some cases, radiography may offer assistance, potentially revealing a thin line if the fracture runs buccolingually. However, its utility diminishes if the crack aligns mesio-distally parallel to the film.[18] Even if the radiograph fails to diagnose a crack, it remains useful in ruling out other pathologies. When radiographic assessment is inconclusive, yet a crack is strongly suspected, cone beam computed tomography (CBCT) imaging proves valuable for visualization and evaluation. 

Treatment / Management

Managing cracked tooth syndrome lacks a clear, one-size-fits-all approach, as treatment depends on the extent and position of the lesion. Alleviating patient symptoms when they report pain is the initial priority before considering the long-term management of the tooth. After localizing the crack, stabilization is necessary to prevent flexing under occlusal forces, alleviating patient pain.[2] In cases without symptoms of pulpal involvement, removing the existing restoration and undermined tooth tissue/cusp to "chase out" the crack may suffice. Subsequently, placing a suitable restoration, such as a flowable composite material, is recommended.[25][26] (B3)

Placing a direct composite acts as an internal splint, preventing the crack from flexing under occlusal loading and providing immediate symptom relief.[27][25] Alternatively, using a metal orthodontic band on the affected tooth is an option for treating cracked teeth displaying signs of reversible pulpitis. The metal band acts as a bidirectional external splint, inhibiting the tooth from flexing under occlusal loading.[28] Seet et al analyzed pulp survival in 125 cracked teeth and concluded that 92.6% of teeth managed with orthodontic band placement demonstrated a healthy pulp after 2 months.[29] However, despite being minimally invasive and cost-effective, metal bands can pose challenges in maintenance due to their tendency to trap food particles. Additionally, they may be contraindicated in patients with existing periodontal disease or poor oral hygiene.[3](B3)

Indirect cuspal coverage in the form of a crown or onlay may also function extremely well as an external splint, prohibiting the flexure of the crack. Guthrie et al observed that most cracks extended into the cervical third of the crown. In their study, they concluded that 25 of the 28 tested cracked teeth became asymptomatic after receiving a full-coverage crown.[30] A full-coverage crown allows for a more equal distribution of occlusal forces across the affected tooth due to the resistant form of the crown. This prevents the crack's flexure and inhibits it from propagating further and causing more damage.[30] However, tooth preparation for full-coverage crowns is invasive and increases the risk of devitalization.[31]

Cracks that propagate into the pulp tissue are often associated with symptoms of irreversible pulpitis. In these cases, it is imperative to conduct a restorability assessment of the tooth to evaluate the extent of the crack and ascertain whether the tooth can be saved.[32] As part of the restorability assessment, the existing restorations are removed, and the tooth is accessed endodontically. This facilitates a comprehensive visual evaluation of the remaining tooth structure. Pulp chamber floor clefting typically indicates an unrestorable tooth requiring extraction. If the crack does not extend through the pulp chamber floor or reach subgingivally, attempting endodontic therapy followed by definitive cuspal coverage may stabilize the tooth. However, this approach has a poor long-term survival prognosis.[33](B2)

Differential Diagnosis

Given the significant variability in symptoms among patients, along with the potential for mimicry of alternative diagnoses, it is crucial to conduct a comprehensive investigation of symptoms alongside an accurate patient history. The depth and trajectory of the crack can evoke diverse symptoms, potentially leading to incorrect diagnosis and treatment planning.[34] For instance, short, sharp pain triggered by a cold thermal stimulus might suggest dentine hypersensitivity due to recession or caries. Pain during biting could be mistaken for parafunctional pain, especially if the patient experiences nocturnal bruxism or other parafunctional habits or has recently undergone a restoration placed slightly high in the occlusion.[2] 

A minor high spot may result in occlusal trauma when a patient has undergone recent dental treatment. In addition, it is advisable to assess static and dynamic occlusion using articulating paper and adjust the restoration if indicated. Galvanic pain should also be considered as a differential diagnosis, especially if a patient has had a recent restoration placed. In addition to the above, clinicians should consider orofacial pain as part of the differential diagnosis.

Prognosis

Early detection plays a crucial role in enhancing the prognosis of a cracked tooth. What initially appears as a minor, innocuous crack with mild symptoms can quickly develop into a complicated and extensive crack involving the pulp or root, rendering the tooth unrestorable. The extent, position, and direction of the crack determine the prognosis. Cracked teeth with normal pulp can be effectively managed with therapeutic measures such as direct composite splinting, placement of orthodontic bands, or indirect definitive cuspal coverage.

Lee et al reported a 91% pulp survival rate in cracked teeth stabilized with bidirectional splinting, while Guthrie et al reported an 11% failure rate in crowned cracked teeth necessitating endodontic therapy.[27][30] Tan et al.'s study indicated that teeth with extensive cracks reaching the pulp, necessitating endodontic therapy and definitive cuspal coverage, exhibit a diminished prognosis and are prone to eventual failure, often resulting in extraction.[33]

Complications

Cracked tooth syndrome is associated with many complications ranging from pulp necrosis to catastrophic tooth fracture requiring extraction. The condition can be further complicated in patients with extensively restored dentition and parafunctional habits such as nail biting and nocturnal bruxism.[35]