How to Recognize the 5 Types of Tooth Cracks

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How to Recognize the 5 Types of Tooth Cracks

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Cracks! The term conjures up a feeling of uneasiness or concern. Rightfully so! For instance, a crack in a wood chair: Is the chair going to break when someone sits in it? A crack in a 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 tooth cracks? Again, a very uneasy feeling. But this situation carries a much greater amount of concern. Depending upon the crack position and degree, the result may be catastrophic. A tooth may be lost! This can represent a complete disaster that can include emotional, financial, and functional considerations.

The question is: could the tooth crack be recognized, and could the outcome from the crack have been predicted to avoid a dental catastrophe? This article is written to help dentists recognize and categorize tooth cracks. Having an understanding of the crack origin, etiology, symptomology, and prognosis can provide better diagnosis and patient communication and may save a catastrophe from happening to our patients.

Tooth cracks are a common occurrence in dentistry. Diagnosing cracks and treatment planning for tooth longevity are critical factors for helping patients maintain their teeth.

One of the main considerations regarding an observed tooth crack is the question of when to intervene. Should the tooth be restored, crowned, or extracted? All are possible treatments. Identifying and classifying cracks will provide some guidance as to treatment planning and treatment outcome. Many teeth with cracks 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

Understanding and identifying these five types can guide treating cracked teeth. The vertical order of these cracks, from top to bottom, signifies the general prognosis for a particular crack. That is, craze lines have a good prognosis, whereas a vertical root fracture has a very poor prognosis.

Craze lines 

Craze lines are micro-fractures of the enamel only. They may also be termed enamel infractions.  The micro-fractures are contained within the enamel only. They do not penetrate the dentin layer.

All teeth have craze lines. They are more often seen in anterior teeth as vertical striations within the enamel. They are also seen on marginal ridges. Trans-illumination 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. 

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 defined as a complete or incomplete fracture of the crown of the tooth extending 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 be required to be removed.

The remaining exposed tooth area may be sensitive to temperature until it is restored. Alternatively, the patient may have complaints of biting or temperature sensitivity before the complete cuspal fracture. The biting complaints are typically pain upon compression and/or pain upon release of biting pressure. Once the fractured cusp is removed, the biting pain is relieved.

Transillumination can be helpful in fractured cusp identification. The transilluminated light will not penetrate beyond the fractured segment into the rest of the tooth. Depending on the degree of the fracture, there is a good prognosis for retaining the tooth. Root canal therapy or crown lengthening procedures may be needed if the extent of the fractured cusp is significant. Cuspal coverage is recommended for those teeth that exhibit early fractured cusp symptoms.

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

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 may extend 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 the crack may be difficult to determine. Some cracks are easily seen with magnification, or because they are stained from 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 crack on the surface enamel does not correlate directly to the extent of the crack apically. Patient symptoms are variable, as well. Some patients will exhibit temperature and/or biting pain. Others will not exhibit any symptoms.

Excessive occlusal forces are a contributing factor to creating tooth cracks. Weakened tooth structure from existing restorations also contributes to tooth cracks. Undermined cusps and marginal ridges create an environment for cracks to occur. Removal of old restorations is recommended for evaluation of 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 aiding in the evaluation of 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 period probe may be utilized to evaluate for a narrow/ 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 are highly variable in extent and symptoms.

Cracked tooth treatment is variable and is dependent on the 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.

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 upon the crack extent and depth and structural integrity of the remaining tooth, the restoring dentist must decide what mode of treatment is appropriate. The dentist’s experience will play a role as to whether or not and to what extent the cracked tooth is maintained and restored.

A cracked tooth prognosis is always questionable. There is always the possibility that the crack will progress, even if cuspal coverage is performed. Limiting the amount of tooth flexure is the goal with bite adjustment and cuspal protection.

But the micro-movement of tooth function can contribute to crack propagation over the long term. Not all cracked teeth are destined to fail. But depending on patient circumstances, occlusal stability, and patient cooperation, a cracked tooth may eventually fail. Removing damaging habits (for example, by providing a night guard 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 

“Split tooth” is defined as the complete fracture initiated from the crown extending 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)! The tooth segments are entirely separated. The split may occur suddenly, but is typically the result of the long-term growth from an incomplete crack.

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

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 where only a single root may be 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. Many times they are 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. The prognosis of vertical root fracture is virtually hopeless in all cases.

Prevention of vertical root fracture is important. Minimizing dentin removal during root canal therapy will provide better structural integrity for tooth longevity. Avoid posts and post-build-ups if possible. Reduce condensation forces during root canal obliteration. Cuspal coverage following root canal treatment is always advised.

Tooth cracks represent a day-to-day finding in our dental practices. It is our goal to save teeth for a lifetime for all of our patients. Proper diagnosis and crack treatment will provide longevity and predictability of care. 


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