Marwan Abou-Rass, DDS, MDS, PhD
In his first article about cracked-tooth syndrome in 1964, Cameron wrote: “Although many dentists are aware of cracked teeth, it seldom is covered in textbooks and has not been brought to the attention of students. The most important [factor] in its diagnosis is an awareness of the problem.”1 Fifty-four years later, Cameron’s statement rings as true as ever.
Problems related to cracked teeth are the third leading cause of tooth loss after caries and periodontal disease. Yet to this day, the management of cracked teeth has not received the attention it deserves—neither in dental schools nor in continuing education. As a result, most dentists today cannot adequately identify common types of cracks. They fail to examine teeth properly, such as with transillumination, magnification, or methylene blue dye, to rule out cracks. Most notably, cracks are not managed appropriately and treatments are administered that will later be sabotaged by “hidden” cracks.
This article is intended to generate awareness of the cracked-tooth problem among dentists, to serve as a primer for a continuing education Masterclass Series I created on the subject, and to encourage our profession to cultivate awareness and education on this topic.
Cracked teeth: A clinical primer
A cracked tooth is rarely a sudden phenomenon. By the time it is visible, a crack typically has progressed through three stages: initiation, propagation, and manifestation. Once a crack is initiated, it can sometimes remain harmless and asymptomatic for years. However, this changes drastically when the crack is subjected to the stress of dental treatment—treatment that may or may not be related to the crack.
Cracks located in the marginal ridges and anatomic grooves of clinical crowns are easy to detect and diagnose. They are usually superficial and visible to the naked eye. However, other cracks are not easily detectable. They can travel deep in the crown structure and then either outward into the periodontal ligament space or inward into the pulp chamber walls and floor.
The real problem of cracked teeth diagnosis and treatment occurs with “hidden” cracks. These cracks can undermine virtually any type of procedure, including prophylactic, restorative, endodontic, orthodontic, surgical, periodontic, and orthognathic treatment. This is true even if treatment is administered responsibly. In these situations, a crack that is previously noncontributory, asymptomatic, and harmless is altered as a result of a treatment. The crack then changes to a contributory crack or fracture that causes pulpal, periapical, or periodontal pathologies.
Hidden cracks are often found in the following situations:
- on root surfaces that are next to excessively tapered, stripped, or perforated root fillings
- beneath old amalgam fillings
- beneath composite restorations that replaced old amalgam fillings
- beneath crowns of teeth treated endodontically
- on teeth in which treatment has been administered through crowns or intracoronal restorations
In 2013, a study by Hilton and Ferracane documented the prevalence of what we can safely call a cracked-tooth epidemic.2 Their work benefited from a survey of the Cracked Teeth Registry that was organized by the National Dental Practice-Based Research Network. Of the 14,346 molars and 1,962 patients evaluated, the survey showed the following:
- 31.4% of all examined molars had at least one crack
- 66.1% of patients had at least one cracked molar
- 46.2% of patients had more than one cracked molar
- 10% of patients had a symptomatic cracked molar
As the population ages in the United States, it is likely that cracked teeth will become more prevalent. “Aged dentition” not only increases the incidence of gum disease, root caries, teeth crowding, attrition, erosion, abrasion, and parafunctional occlusion, but it also exhibits an increased number of cracks.
The dental literature has identified root canal preparation and obturation as risk factors for cracks. In 1987, Gher et al. found that 71% of the teeth studied with root fractures occurred on endodontically treated teeth.3 They concluded, “Restoration of endodontic treated teeth with full crowns does not prevent root fractures.”3
Unfortunately, cracks are oftentimes initiated by improper or abusive dental treatment, including the use of improper dental materials.
In 2013, Luca De Rose noted that in studying tooth fractures, focusing on crack initiation is of more importance than studying tooth strength and resistance to fracture. He stated, “Most of the time, a fracture is a result of an ongoing crack.”4
Educating clinicians on the cracked-tooth problem
The lack of a precise definition or clinically measurable standard for the terms “crack” and “fracture” have led to confusion and incorrect diagnoses. Excellent examples of this misunderstanding can be seen in reports by Bader et al. published in 1996 and 2001.5,6 They found that 44% of dentists studied placed crowns to prevent cuspal fractures. However, this “preventive” practice is meaningless if the dentist does not remove the old restoration and examine the tooth structure underneath for cracks.
With training, it is possible to eliminate common misunderstandings and gaps in knowledge regarding cracked teeth. There are clinical, anatomic, and pathologic classifications of harmless (noncontributory) and harmful (contributory) cracks, which I discuss in the Masterclass Series referred to at the start of this article. Harmful cracks include ones that cause pulp calcification and pulpal, periapical, and periradicular pathologies.
One can also use the “4 Rs” operational diagnosis protocol for the differential diagnosis of line cracks, fissure cracks, and fracture cracks. Clinicians should be cognizant of these characterizations in daily practice and be able to manage each type of problem.
In order to understand the cracked-tooth problem, it is also important to expand one’s knowledge about treatment. For example, in one study, it was found that contributory line cracks may cause symptomatic reversible pulpitis that is treated successfully (without endodontics) in 80% of cases.7 In another study, 20% of symptomatic reversible pulpitis cases needed root canal treatment following conservative therapy and crown placement.8,9 This study also showed that the survival of endodontically treated cracked teeth is 92% after five years.
Inadequate endodontics is another consideration. It is important to investigate poor endodontic treatments regardless of the patient’s symptoms to provide an in-depth understanding of the cause of treatment failure and to rule out the presence of cracks. The treatment may need to be modified accordingly to prevent further breakdown of the alveolar bone and worsening of the crack. In developing training in this area, I have found it useful to introduce the concept of interim endodontic therapy for hopeless teeth. This is to eliminate infection and regenerate native bone in the site before extraction and immediate dental implant placement.
For more information on this topic, I encourage clinicians to view the references at the end of this article and also consider taking the Masterclass Series. Through awareness and education, the cracked-tooth syndrome Cameron described in 1964 can finally be managed by dental professionals.
Part I—Introducing the “4 Rs” Operational Diagnosis Protocol
Part II—How Tooth Structure Cracks Complicate and Affect Dental Treatments
Part III—Definitions, Classification, Etiology, and Initiation Mechanism of Tooth Structure Cracks
Part IV—Symptomatic Cracked Teeth with Pulpal, Periradicular, and Periapical Involvements
Part V—How and Why Substandard Endodontic Treatments Fail
1. Cameron CE. Cracked-tooth syndrome. The Journal of the American Dental Association. 1964;68(3):405-411.
2. Hilton T, Ferracan J. Cracked Teeth Registry. National Dental PBRN Western Regional Meeting. September 28, 2013.
3. Gher ME, Dunlap RM, Anderson MH, Kuhl LV. Clinical survey of fractured teeth. JADA. 1987;114:174-177.
4. De Rose L. Les facteurs influencant la formation de fissure et de fracture des dents traitees endodontiquement: une revue. 2013. Universite de Geneve.
5. Bader JD, Shugars DA, Roberson TM. Using crowns to prevent tooth fracture. Community Dentistry and Oral Epidemiology. 1996;24:47-51.
6. Bader JD, Martin JA, Shugars DA. Incidence rates for complete cusp fracture. Community Dentistry and Oral Epidemiology. 2001;29:346-53.
7. Abbott P. Predictable management of cracked teeth with reversible pulpitis. Australian Dental Journal. Dec 2009;54(4):306-315.
8. Krell KV, Rivera EM. A six-year evaluation of cracked teeth diagnosed with reversible pulpitis: treatment and prognosis. Journal of Endodontics. 2007;33(12):1405.
9. Sim IG, Lim TS, Krishnaswamy G, Chenn NN. Decision making for retention of endodontically treated posterior cracked teeth: a 5-year follow-up study. Journal of Endodontics. 2016;42(2):225-229.
1. Abou-Rass M. Interim endodontic therapy for alveolar socket bone regeneration of infected hopeless teeth prior to implant therapy. Journal of Oral Implantology. 2010;36(1): 37-59.
2. Abou-Rass M. Crack lines: the precursors of tooth fractures—their diagnosis and treatment. Quintessence International. 1983;4:437-448.
Marwan Abou-Rass, DDS, MDS, PhD, is a professor emeritus at the University of Southern California. He holds a master’s degree in dental science in prosthodontics, a certificate in endodontics, and a doctorate in higher education. Dr. Abou-Rass served as endodontic department chairman and director of the Advanced Endodontic Program at the University of Southern California School of Dentistry from 1971 to 2000. Dr. Abou-Rass moved to Riyadh, Saudi Arabia, in 2000, where he directed the AEGD program at PAADI from 2000 to 2012. He is currently the publisher of Dental Economics MENA Journal and CEMENAOnline.com.