The etiology of a cracked tooth is multivariable. We must consider several factors such as parafunction, excessive wear, trauma and any restorations present (their size and materials used). Even the proximity of the tooth to the TMJ is critical, as a closer proximity significantly increases the risk of tooth fractures.
Sharp pain during biting or releasing of pressure forces, pain on temperature changes, or a deep periodontal probing depth are the classic signs of a cracked tooth. The extent of the crack can be further explored with transillumination or by exploratory tooth preparation. Once the scope of the problem is clear, every clinician is faced with a dilemma – to extract the tooth or start root canal treatment. Furthermore, if root canal treatment is indicated, how long can we expect to retain the tooth?
A systematic review was done to develop a clear decision making protocol when faced with this situation. Overall, the success rate of an endodontically treated cracked tooth is favorable, similar to that of a root canal treated non-cracked tooth. We can outline the factors that can considerably affect the outcome of our treatment, in order to make our efforts as predictable as possible.
Factors Influencing Survival Of A Root Canal Treated Cracked Tooth
Age: Many studies have shown that the dentin in older patients is weaker, and cracks propagate much easier. However, in 4 studies reviewed, involving patients older than 50 years, there was no difference in the survival rate of an endodontically treated cracked tooth, compared to younger ages.
The Final Restoration Placed: The type of final restoration placed is a critical factor in the survival of the tooth. In fact, the most common reason dentists recommend and place a crown is to prevent fractures. The clamping effect of a full coverage crown can prevent potential divergence between cusps during mastication, and lower the propagation of cracks.
Placing a non-bonded restoration, such as amalgam, shows the greatest propagation of cracks following root canal treatment. This is due to sharp internal line angles and differences in thermal expansion between the material used and the tooth itself. If an incrementally cured bonded restoration is placed, the occlusal forces are distributed along the bonding layer, and the survival of the tooth is increased significantly.
Pulpal Status: A crack in combination with pulp necrosis shows a hopeless prognosis, and extraction should be considered. Pulpal necrosis is usually associated with a deeper crack, usually extending to the pulpal floor. Thus, root canal treatment of such a tooth would show unwanted post-treatment consequences, which would lead to extraction of the tooth anyways.
Periodontal Pocketing: If a tooth is shown to have a crack and a periodontal pocket, the chance of survival is significantly decreased. The presence of a periodontal pocket increases the chances for need of extraction of a tooth with a crack by 11%. Surveying 3500 endodontists in the US showed that the presence of a periodontal pocket of 6-mm was the most critical factor in deciding whether to treat the tooth or recommend extraction.
Number of Cracks: It has been hypothesized that the more cracks a tooth has, the higher the chance of propagation of those cracks. Moreover, the risk of bacterial infiltration through the cracks, compromising pulp health is thought to be higher. However, in the present review of studies, there was no difference in the survival of a tooth when showing one or more cracks.
Location of The Tooth: In first molars, the occlusal load is located slightly posteriors of the center of the tooth. Also, the palatal cusp of the upper first molar acts as “plunger” in the central fossa of the lower molars. This relationship is shown to induce structural fatigue on first molars, and therefore increases the risk of crack propagation. First molars are seen to have the highest risk of crack propagation, and failure following root canal treatment.
Taking into account the above factors can help in providing the most predictable treatments for our patients.