How To Recognize the 5 Types of Tooth Cracks

Cracks! The term conjures up a feeling of uneasiness or concern. Rightfully so!

For instance, consider a crack in a wooden chair: will it break when someone sits in it?

A crack in the floor: Is someone going to trip and fall?

Or a crack in a tree branch: Is the branch going to break off?

All are possibilities and valid questions regarding the cracks described. They are all concerning questions, but all manageable situations. The chair may be glued and repaired. The floor may be sealed and smoothed. And the branch may be trimmed. Disasters avoided!

What about a cracked tooth? Again, a very uneasy feeling. But this situation raises much greater concern. Depending upon the crack position and degree, the result may be catastrophic — a tooth may be lost! This can represent a complete disaster, encompassing emotional, financial, and functional considerations.

The question is: Could the cracked tooth have been recognized, and could the outcome from the crack have been predicted to avoid a dental catastrophe? Having an understanding of crack origin, etiology, symptomology, and prognosis can provide better diagnosis and patient communication and may save a catastrophe from happening to our patients.

A cracked tooth is a common occurrence in dentistry; we see them each day in our patient treatment. Diagnosing cracks and treatment planning for tooth longevity are critical factors for helping patients maintain their teeth.

One of the primary considerations in an observed cracked tooth is when to intervene. Should the tooth be restored, crowned, or extracted? All are possible treatments. Identifying and classifying cracks will guide treatment planning and treatment outcomes. Many cracked teeth can be saved! The keys are identification, understanding signs and symptoms, and early detection.

The American Association of Endodontists has identified five types of tooth cracks. These types are:

• Craze lines
• Fractured cusp
• Cracked tooth
• Split root
• Vertical root fracture

Craze lines 

Craze lines, also called “enamel infractions,” are microfractures that are contained within the enamel only and do not penetrate the dentin layer. All teeth have craze lines, which are more often seen in anterior teeth as vertical striations within the enamel and on marginal ridges. Transillumination provides clear observation of craze lines.

Tooth trauma can contribute to craze lines. This trauma can be the result of blunt force or more recurrent functional forces, such as bruxism and parafunction. 

Treatment

There are typically no symptoms with craze lines. Treatment can be for esthetic reasons only, and the prognosis is very good. Prevention of bruxism, parafunction, and excessive trauma from occlusal forces is recommended.

Fractured cusp 

A fractured cusp is a complete or incomplete fracture of the tooth’s crown that extends subgingivally. The extent and degree of the fractured cusp are variable. The most common cuspal areas to fracture are the lingual cusps of the lower molars and the buccal cusps of the upper molars.

The fracture originates on the occlusal surface and extends gingivally along a buccal or lingual groove and the mesial or distal marginal ridge. Occlusal trauma/force plays an integral role in the propagation of the fracture line. Undermined cusps from existing restorations are also a contributing factor.

The fractured cusp may break and separate at the time of a traumatic event. The resultant tooth segment may be attached to the gingival tissues and needs to be removed. The remaining exposed tooth area may be sensitive to temperature until it’s restored. Alternatively, the patient may have complaints of biting or temperature sensitivity before the complete cuspal fracture. Biting complaints are typically pain on compression and/or on release of biting pressure. Once the fractured cusp is removed, the biting pain is relieved.

Transillumination can be helpful for identifying fractured cusps. The transilluminated light will not penetrate beyond the fractured segment into the rest of the tooth.

Treatment

Depending on the degree of the fracture, there is a good prognosis for retaining the tooth. Root canal therapy or crown lengthening may be needed if the extent of the fractured cusp is significant. Cuspal coverage is recommended for teeth that exhibit early fractured cusp symptoms.

Maintaining tooth integrity using crowns or onlays may prevent crack propagation and fracture. Continued, long-term patient observation is recommended.

Cracked tooth

A cracked tooth is defined as an incomplete fracture initiated from the crown and extending subgingivally. The crack is usually in a mesial–distal direction. The crack may extend through one marginal ridge or through both proximal surfaces. The vertical depth of the crack is also variable.  

The crack may be entirely contained within the crown of the tooth, or it may extend vertically into the root portion of the tooth. A cracked tooth is more centered, occlusally, than a fractured cusp. Also, because a cracked tooth may progress apically, rather than laterally, there is a greater chance of pulpal and periapical pathosis.

The location and extent of a cracked tooth may be difficult to determine. Some cracks are easily seen with magnification or are stained by bacterial migration. Additionally, some cracks are identified with a dental explorer because they have caused a true separation of the enamel. However, the extent of the surface enamel crack does not directly correlate with the extent of the apical crack. Patient symptoms are variable as well: some patients exhibit temperature or biting pain, while others don’t.

Excessive occlusal forces are a contributing factor in the development of a cracked tooth. Weakened tooth structure from existing restorations also contributes to tooth cracks. Undermined cusps and marginal ridges create an environment conducive to crack formation. Removal of old restorations is recommended to evaluate crack extent and depth.

There are numerous diagnostic tests available for cracked tooth situations. Removing old restorations in the presence of a crack is a starting point. Magnification is paramount for evaluating the extent of the crack.

The crack may be visualized extending along the pulpal floor from mesial to distal. Extending the pulpal floor to “follow” the crack apically can provide information on depth and nerve proximity.

If the crack extends apically into the interproximal area, a perio probe may be used to evaluate for a narrow or isolated band of bone loss vertically down the root. This is a pathognomonic sign of root fracture (to be discussed next). Tooth staining, transillumination, or wedging are techniques for assessing the extent of the crack. Pulp vitality and patient symptoms will aid in determining the extent of the crack. Tooth cracks vary widely in extent and symptoms.

Treatment

Cracked tooth treatment is variable and is dependent on crack extent, operator experience, judgment, and patient symptoms. There are no definitive restorative recommendations in the literature about the treatment of cracked teeth. Proper diagnosis and preventive strategies are recommended for the treatment of cracked teeth.

Obviously, root canal treatment is possible if pulpal and periapical symptoms dictate need, but cracked tooth treatment may be as limited as replacement of a direct restoration to full- or partial-cuspal coverage. Depending on the extent and depth of the crack and the remaining tooth’s structural integrity, the restorative dentist must decide which treatment modality is appropriate. The dentist’s experience will play a role in determining whether and to what extent the cracked tooth is maintained and restored.

Cracked tooth prognosis is always questionable. There’s always the possibility that the crack will progress, even with cuspal coverage. Limiting tooth flexure is the goal of bite adjustment and cuspal protection, but micromovement during tooth function can contribute to long-term crack propagation.

Not all cracked teeth are destined to fail, but depending on patient circumstances, occlusal stability, and patient cooperation, it might eventually happen. Removing damaging habits (for example, by providing a nightguard and controlling bruxism), covering cusps, and counseling patients on the variability of cracked tooth treatment are recommended preventive strategies. In cases of cracked teeth, the patient should be informed of the questionable prognosis associated with this condition.

Split tooth 

A “split tooth” is defined as a complete fracture initiated in the crown that extends subgingivally. It typically extends through both marginal ridges and the proximal surfaces to the proximal root. A split tooth is the result of a cracked tooth (evolution!), but the tooth segments are now entirely separated. The split may occur suddenly, but it’s typically the result of the long-term growth from an incomplete crack.

Again, damaging habits such as bruxism, parafunction, and chewing ice can contribute to crack propagation and, ultimately, a split tooth. There may be preexisting pain with mastication, but not always.

Treatment

The split segments may be visualized or “by wedging” the segments apart, but the tooth prognosis is hopeless in most cases. Sometimes a split may occur in which only a single root is affected (e.g., an upper molar root). In those cases, it may be possible to remove the “split root” and salvage the remaining tooth. Once the tooth is removed, tooth replacement may be discussed and initiated.

Vertical root fracture 

A vertical root fracture is a complete or incomplete fracture of the root in a buccal–lingual direction. The fracture may extend the length of the root or as a shorter segment along any portion of the root. There may or may not be patient symptoms associated with the fracture. They are often discovered on routine periapical X-rays.

Virtually all vertical root fractures are associated with a history of root canal treatment. The existence of a sinus tract or a narrow, vertical periodontal pocket along the root surface is consistent with vertical root fracture.

Treatment

The prognosis of a vertical root fracture is virtually hopeless in all cases, so prevention is essential:

• Minimizing dentin removal during root canal therapy will improve tooth structural integrity and longevity.
• Avoid posts and post build-ups, if possible.
• Reduce condensation forces during root canal obliteration.
• Cuspal coverage after root canal treatment is always advised.

A cracked tooth represents a day-to-day finding in our dental practices. It’s our goal to save teeth for a lifetime for all our patients. Proper diagnosis and cracked tooth treatment provide longevity and predictability of care.