Saving Cracked Teeth: The Current State of Evidence

Cracked teeth" are defined by unseparated surface fractures of the enamel and possibly dentin and cementum, typically extending mesially-distally from the marginal ridges. The true extension and depth of these cracks is undeterminable based on surface appearance alone.¹ In the classic presentation, patients report cold sensitivity and pain on biting. Symptoms can be exacerbated in patients with bruxism and/or clenching.¹ Historically, the term "cracked tooth syndrome" has been used, although this phrase has fallen out of favor given the variability in symptoms and patient presentation.¹

Cracked teeth are relatively common. Research indicates that 75% of adults have at least one posterior tooth with a visible crack, and 45% of these teeth are symptomatic.² Most cracks occur either in teeth without restorations or teeth with non-bonded gold or amalgam Class 1 restorations, and in patients over 50 years old.^3,4 Proximity to the temporomandibular joint, and thus, magnitude of masticatory force influences the likelihood that a tooth will be cracked. Molars, both maxillary and mandibular, and maxillary second premolars are the most commonly affected teeth.³

Cracks may be directly seen, with the use of magnification, staining, and transillumination serving as aids to their visualization. A blocked transilluminated light creates the appearance of a "light" and "dark" region of a tooth and is highly suggestive of fracture. Bite testing may be a helpful adjunct to diagnosis, but not all patients with cracked teeth are replicably symptomatic on biting. Pulp sensitivity testing, including cold testing, is diagnostically unreliable, as cracked teeth may have any pulpal diagnosis and thus exhibit a wide array of responses.^2-4 Cone-beam computed tomography (CBCT) has also been found to be unreliable in detecting cracks and fractures. According to Gao et al's 2021 literature review, various factors limit the diagnostic ability of CBCT in crack detection, including resolution of the CBCT unit, crack width, motion artifact formation, human error, and subjectivity.⁵ Per Rosen et al in 2022, "The effects of CBCT on diagnostic thinking, decision making, and treatment outcomes is limited," and clinicians should be skeptical of their own CBCT interpretations to ensure they are not "seeing" cracks where there are none.⁶

Various factors, including pulpal involvement, number of cracks, and location in the arch, can aid the clinician in assessing the prognosis of an attempt to save a cracked tooth. According to a 2019 survey of American endodontists, many such practitioners consider periodontal pocketing a prognostic factor and opt not to treat when there is crack-associated isolated periodontal pocketing (CAIPP), believing CAIPP is associated with poor prognosis.⁷ However, meta-analyses of endodontically treated cracked posterior teeth found only an 8% to 11% reduction in success for teeth with CAIPP as compared with non-cracked teeth.^8,9 These meta-analyses call into question the decision not to treat cracked teeth, which, aside from isolated pocketing, might otherwise be good candidates for endodontic and restorative therapies.

Various treatment modalities are available for cracked teeth. Some cracked teeth may be treated with resin composites. Opdam et al in 2008 found that of 40 cracked teeth treated with direct composite resins, more than 90% maintained pulp vitality after 7 years.¹⁰ However, success is influenced by a variety of prognostic factors, including bone loss and radicular extension.¹¹ For instance, while composite-treated teeth with proximal radicular fractures have a reported 5-year survival rate of 78%, the 5-year survival rate drops to 58% in deep radicular fractures.¹²

Alternatively, cracked teeth may be treated with crowns. Crowned cracked teeth may be less likely to develop pulpal pathology, thus necessitating nonsurgical root canal therapy (NSRCT). Research indicates that 65.8% of uncrowned cracked teeth developed pulpal pathology after 3 years, compared with 18.7% of crowned teeth.^13,14 Crowns, however, are less successful in maintaining pulpal health in cracked teeth with mechanical allodynia (percussion-positive teeth).¹⁵ While percussion-negative teeth had a 94% pulpal survival rate, percussion-positive teeth had 46% pulpal survival.¹⁵

In patients with cracked teeth without mechanical allodynia and that have mild pulpal symptoms, a temporary crown should be placed. If symptoms resolve, a permanent crown may then be placed and the tooth should be re-evaluated every 6 months. In teeth with temporary crowns that remain symptomatic, percussion-positive teeth, and teeth with severe symptoms such as spontaneous pain, NSRCT is the recommended initial approach. If symptoms resolve after NSRCT, a permanent crown should then be placed. However, if symptoms persist even after NSRCT, extraction is the recommended approach.^13-16

Data suggests that, if managed properly, and with careful case selection, endodontically treated cracked teeth can have similar prognoses to their non-cracked counterparts. Numerous longitudinal studies have demonstrated the success of NSRCT in cracked teeth, with survival rates of 90% after 2 years and 84.1% after 5 years.^8,12,17 Placement of the definitive restoration is pivotal to survival after NSRCT, as endodontically treated teeth without crowns are four to six times less likely to survive than those restored with crowns.^18,19

Historically, if cracks were found to extend below the gingival margin, the tooth was thought to be hopeless, with extensive periodontal and/or periapical bone loss after NSRCT. Hence, extractions were recommended for cracked teeth with radicular extensions. In the absence of restorations, caries, or luxation injuries, pulpal necrosis was assumed to be the etiology of a crack extending from the occlusal to the external root surface, a presentation termed "fracture necrosis." Because a small study found that teeth presenting with fracture necrosis exhibited cracks with radicular extension, the conclusion was that teeth with fracture necrosis should similarly undergo routine extraction.¹⁹

Davis and Shariff's outcomes study argues that extractions are not always indicated for cracked teeth with radicular extensions.²⁰ The authors examined the 2- to 4-year success and survival rates of endodontically treated cracked teeth restored with full-coverage restorations with the crack extending beyond the level of the canal orifice internally up to 5 mm. Success criteria included factors such as survival of the tooth; absence of symptoms; no clinical indications of infection, swelling, or sinus tracts; functional occlusion; and patient satisfaction with the decision to undergo treatment for the cracked tooth.²¹ The success and survival rates of restored cracked teeth with radicular extensions (survival rate: 96.6%; follow-up 4 years) were similar to those of non-cracked, endodontically treated teeth (survival rate: 96%; follow-up 8 years).^20,21

Practitioners must exercise careful case selection, as certain clinical factors influence the survival of NSRCT on cracked teeth with radicular extensions. These clinical factors that have a demonstrable impact on prognosis include, but are not limited to, CAIPP, whether a single marginal ridge is fractured versus both marginal ridges being fractured, and the rapidity of post-endodontic restorative care. As previously mentioned, there is an 8% to 11% reduction in success with the presence of deeper CAIPP.^8,9 In Davis and Shariff's study, teeth with CAIPP of less than 4 mm had a 92.7% success rate, while those with CAIPP of 5 mm to 7 mm had an 83.8% success rate.²⁰ This finding closely mirrors the results from Kang et al's 2016 study on the overall prognosis of cracked teeth, showing a 96.8% survival rate for teeth with CAIPP of less than 6 mm and a 74.1% survival rate for teeth with CAIPP of more than 6 mm.³ Although CAIPP can reduce the prognosis of treatment, it is clear that these teeth are not associated with a hopeless prognosis.

When cracks were located on both mesial and distal marginal ridges, as opposed to singularly fractured teeth, the success rate was reduced to 83.9%.²⁰ Other prognostic factors include extension of the crack, quick crown placement, and location in the arch. Posterior teeth are subjected to maximum occlusal forces, and Tan et al's 2006 study revealed that cracked posterior teeth were more likely to get extracted compared to cracked anterior teeth.²² Preoperative periradicular diagnosis was not a significant predictor of success.²⁰ This conclusion contradicts the findings of Krell and Caplan, who suggested that the periradicular diagnosis of conditions such as chronic apical periodontitis, symptomatic apical periodontitis, or apical abscess is closely linked to treatment failure following endodontic treatment of cracked teeth.¹¹ Such disparities in findings may stem from variations in treatment protocols.

A summary of prognostic factors for cracked teeth with radicular extensions is provided in Figure 1.^14,20,23

The success rate of cracked teeth with radicular extensions significantly improves with proper management both during and after treatment. Davis and Shariff identified four key modifiers that play crucial roles in influencing the outcome: the preservation of internal dentin, the utilization of intraradicular orifice barriers, timely placement of crown restorations, and ensuring ideal occlusion.²⁰

Kishen and Asundi highlighted that masticatory forces predominantly exert compressive stress near the cervical region of the root, rendering this region particularly susceptible to cracks with radicular extensions.²⁴ The increased risk of crack initiation and propagation correlates with higher levels of unintended damage by medical intervention in this area.²⁴ Therefore, endodontists must prioritize conservative access and canal shaping while emphasizing thorough disinfection protocols. This entails mitigating the potential for iatrogenic errors, such as perforations and instrument separations, thereby optimizing treatment outcomes.

The use of orifice barriers significantly enhances the prognosis for cracked teeth with radicular extensions.²⁰ These barriers should be positioned apically to the extent of the crack, often with the assistance of a surgical microscope, and serve as coronal seals over the gutta-percha. Unlike crowns, orifice barriers extend fully along the crack's trajectory, thereby strengthening fracture resistance and mitigating bacterial biofilm formation within the crevices. Boonrawd et al's 2022 study examined the effect of composite resin core level on crack propagation in endodontically treated teeth using extended finite element method analysis.²⁵ The study revealed that when intraorifice barriers are placed beneath the crack's level and crestal bone, teeth exhibit markedly enhanced resistance to both fracture initiation and crack propagation.²⁵

After treatment, it is crucial to promptly place a full-coverage restoration to optimize the success rate. Chen et al demonstrated that the 2-year success rate for endodontically treated cracked teeth with a crown was 94%, contrasting starkly with the 20% success rate observed without a crown.²³ This underscores the pivotal role of timely crown placement as the foremost determinant of cracked teeth prognosis. Prolonged provisional restoration significantly elevates the failure rate, and delayed placement of the full-coverage crown correlates with lower survival rates for cracked teeth. Regarding crown materials, zirconia exhibits superior fracture resistance compared to leucite-reinforced all-ceramic and composite crowns, which are more prone to failure.²⁶ In general, crowns composed of materials possessing a higher elastic modulus than enamel serve to fortify the dental structures of posterior teeth.²⁶

Finally, it is important to ensure atraumatic occlusion following restoration of cracked teeth. Teeth with excursive interference are 2.3 times more likely to experience cracking than teeth without excursive interferences.²⁷ According to Ratcliff et al, when parafunction and excursive interference were present, the odds of fracture propagation following treatment were 5.8.²⁷

Davis and Shariff recommend an optimal post-endodontic protocol for cracked teeth with three key steps (Figure 2).²⁰ First, immediately following NSRCT with the use of intraorifice barrier placement, the tooth should be completely relieved from occlusal forces. Secondly, a crown should be placed promptly and proper occlusion should be achieved; the importance of this step should effectively be communicated to general dentists. Finally, patients should be scheduled for follow-up appointments at 6 weeks, 6 months, and 1 year postoperatively to thoroughly monitor the healing process.

A case of a cracked tooth undergoing treatment according to Davis and Shariff's protocol is illustrated in Figure 3 through Figure 8. In the case, a first molar showed visible fracture lines along both the mesial marginal ridge and palatal wall, was tender to percussion and biting, and exhibited a heightened and lingering response to cold. A CAIPP of 5 mm was found on the mesial aspect. The patient had extreme thermal intolerance, with pain radiating to the jaw and the face. CBCT scanning revealed apical periodontal ligament (PDL) widening and a mesial crestal bony defect. NSRCT was performed with immediate placement of a bonded intraorifice barrier and occlusal reduction. The patient was referred back to his general dentist for expedient crown placement with careful attention given to occlusion, including an occlusal follow-up.

Saving cracked teeth, with appropriate case selection, represents a less invasive alternative to extraction and implant placement. Both implant treatment and NSRCT have similar success rates, but being able to save a tooth circumvents potential postoperative sequelae, such as peri-implantitis and peri-implant mucositis. Thus, in light of the aforementioned evidence, clinicians should carefully consider the feasibility of saving cracked teeth before deciding on extraction.

The historical apprehension among dentists regarding the treatment of cracked teeth is increasingly unfounded in the light of recent research. By implementing proper management strategies, such as the preservation of internal dentin, the use of intraradicular orifice barriers, and the timely placement of a crown restoration with proper occlusion, the success rate of saving cracked teeth, even those with radicular extensions, can be significantly enhanced. While acknowledging the relevance of prognostic factors, it is incumbent upon dental providers to thoroughly consider the possibility of saving a tooth before proceeding with extraction. Through evidence-based practices, confidence in treating cracked teeth can be fostered, leading to improved patient outcomes.

Min Son, DMD Candidate
Harvard School of Dental Medicine, Boston, Massachusetts

Lauren Quintela, DMD Candidate
Harvard School of Dental Medicine, Boston, Massachusetts.

Rebekah Lucier Pryles, DMD, Certificate in Endodontics
Assistant Clinical Professor, Department of Endodontics, Tufts University School of Dental Medicine, Boston, Massachusetts; Lecturer, Department of Restorative Dentistry and Biomaterials Science, Harvard School of Dental Medicine, Boston, Massachusetts; Private Practice limited to Endodontics, White River Junction, Vermont

Brooke Blicher, DMD, Certificate in Endodontics
Assistant Clinical Professor, Department of Endodontics, Tufts University School of Dental Medicine, Boston, Massachusetts; Lecturer, Department of Restorative Dentistry and Biomaterials Science, Harvard School of Dental Medicine, Boston, Massachusetts; Private Practice limited to Endodontics, White River Junction, Vermont