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 Table of Contents  
REVIEW ARTICLE
Year : 2019  |  Volume : 11  |  Issue : 6  |  Page : 329-333

In vivo and in vitro diagnosis of cracked teeth: A review


1 King Abdulaziz Dental Center, Riyadh, Kingdom of Saudi Arabia
2 College of Dentistry, King Saud Bin Abdulaziz University for Health Sciences, Riyadh, Kingdom of Saudi Arabia
3 Al Yamamah Hospital, Ministry of Health, Riyadh, Kingdom of Saudi Arabia

Date of Web Publication26-Nov-2019

Correspondence Address:
Dr. Abdulrahman N Alsolaihim
King Abdulaziz Dental Center, King Abdulaziz Medical City, Ministry of National Guard Health affairs, Mail Code: 1243, P. O. Box 22490, Riyadh 11426.
Kingdom of Saudi Arabia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jioh.jioh_92_19

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  Abstract 

Dentinal microcracks are a diagnostic challenge, which determines the longevity of the tooth structure. A few etiological factors of dentinal microcracks are traumatic occlusion in aging teeth and also the effect of rotary files, heavy spreader pressure during condensation, and post-placement during root canal treatment. This article describes the various in vivo and in vitro diagnostic aids and describes in detail various recent methods used for the detection of microcracks in vitro with special emphasis on micro-computed tomography (micro-CT). Micro-CT has wide applications in medical imaging. Micro-tomography scanners offer isotropic resolution, and therefore three-dimensional images can be displayed. Also, micro-CT is very precise, has remarkable space resolution, and requires a shorter capture time than cone beam computed tomography.

Keywords: Dentinal microcracks, detection, Micro-CT


How to cite this article:
Alsolaihim AN, Alsolaihim AA, Alowais LO. In vivo and in vitro diagnosis of cracked teeth: A review. J Int Oral Health 2019;11:329-33

How to cite this URL:
Alsolaihim AN, Alsolaihim AA, Alowais LO. In vivo and in vitro diagnosis of cracked teeth: A review. J Int Oral Health [serial online] 2019 [cited 2019 Dec 12];11:329-33. Available from: http://www.jioh.org/text.asp?2019/11/6/329/271785


  Introduction Top


Cracks in teeth are one of the major causes of devastating and hopeless tooth prognosis leading to extraction after dental caries and periodontal diseases. Early enamel cracks are often neglected as they are asymptomatic. However, when the cracks are in the deeper layers of enamel or superficial dentin, the teeth tend to show hypersensitivity, but once the crack reaches the deep dentin layers or pulp, it will lead to more serious complications such as pulpitis and apical periodontitis.[1] Early intervention for cracked teeth is more likely to produce a better long-term prognosis, it can also avoid drastic consequences such as pain, periapical pathoses, or the need for tooth extraction. However, if cracked teeth have advanced to developing pulpitis or periapical periodontitis, the prognosis is poor. The early diagnosis of a cracked tooth is the key factor in determining whether the treatment plan is successful and prognosis is positive.[2] Diagnosis and treatment require precise information regarding the location and depth of the crack. There are many methods for the diagnosis of cracked teeth. When the crack extends to the mesial and/or distal marginal ridges, it can be easily diagnosed through macroscopic observation, iodine staining, transillumination methods, microscopic observation, and other methods in combination with clinical manifestations.[3] Micro-computed tomography (micro-CT) is one of the foremost methods of detecting microcracks in vitro, which makes it an indispensable tool for research and analysis. Micro-CT system uses micro focal spot X-ray sources and high-resolution detectors that allow for projections rotated through multiple viewing directions to produce three-dimensional (3D) reconstructed images of samples. As the imaging process is nondestructive, the internal features of the same sample may be examined many times and the samples remain available after scanning for additional biological and mechanical testing.[4],[5] High-resolution micro-CT systems are commercially available for both in vivo imaging of small animals and in vitro imaging of tissue specimens. This article outlines the various types of fractures occurring in the tooth and the various tools for their detection with special emphasis on micro-CT.

According to the American Association of Endodontists (AAE), longitudinal fractures are classified as craze lines, fractured cusps, cracked tooth, split tooth, and vertical root fracture (VRF).[6]


  Craze Lines Top


Craze lines are faults located only in the enamel portion of the tooth structure. They can occur either on buccal and/or lingual surfaces. Differential diagnosis of craze lines is performed using transillumination to distinguish it from a crack. If light is blocked, it is diagnosed as a crack, and if it illuminates the entire crown, it is called as craze line.


  Fractured Cusp Top


Fractured cusps are identified by a separated cusp from the rest of the tooth by complete or incomplete fracture. These fracture lines generally extend from occlusal surface and continue toward the cervical region of the tooth structure.

These fractures are typically seen in the buccal cusp of maxillary bicuspids, mesiobuccal, and distobuccal cusp of maxillary molars. Bader et al.[7] also found lingual cusp fractured more commonly than buccal cusp in mandibular molars.

Diagnosis: They are mostly related with large restorations with inadequately supported cuspal enamel.

  • Subjective findings include sharp pain on mastication, which is more distinct on biting pressure release and sensitive to cold.


  • Objective test: bite test (Burlew wheel/tooth slooth).


  • Pulp test: usually normal until there is pulp exposure.[7]


  • Radiograph: normal


  • Surgical microscopes can be used for identification



  •   Cracked Tooth Top


    A cracked tooth is defined by the AAE[6] as a crack extending from the occlusal surface of the tooth apically without separation of the two segments. The cracks are usually present mesiodistally. According to Seo et al.[8] and Roh and Lee,[9] most common direction is mesiodistal but it can also occur buccolingually.

    Diagnosis of cracks: They can be identified by staining and transillumination. However, Seo et al.[8] stated that bite test is the most reliable test for identifying cracked tooth. It is usually associated with a deep narrow pocket and pain on mastication. After staining the tooth with dyes, magnification using loupes or dental operating microscope can also be used for the detection of cracks. Methylene blue is one of the dyes commonly used for diagnosis. Dye penetrated inside the crack indicates crack location.[10]

    Transillumination using fiber-optic scope is also a useful adjunct for diagnosis.[11] Bite tests using Burlew wheel will be positive when the lesion has reached the periapical region causing apical periodontitis. Pain on release of pressure is also a common symptom of cracked tooth. In certain cases, when there is unexplained sinus tract, it is indicated to perform diagnostic surgery for root surface for cracks. Radiographs are not particularly useful in the diagnosis of fractures occurring in the crown portion of the teeth. However, in later stages when there is separation of fragments, radiograph is a useful tool. Vitality testing is not a significant diagnostic test for cracks as they can occur irrespective of the vitality status of the tooth.


      Split Tooth Top


    Split tooth occurs when crack in the dentin deepens and this incomplete crack separates, resulting into multiple fragments. These teeth have poor prognosis and should be extracted.

    Diagnosis:

  • Occurs commonly in root canal (RC)-treated tooth


  • Frequently involves pulp


  • Fragments may be mobile


  • Easy to diagnose


  • Periodontal abscess may be present


  • Patient has marked pain on mastication


  • Horizontal bone loss present


  • Microscopes and cone beam computed tomography (CBCT) are useful



  •   Vertical Root Fracture Top


    According to the AAE, VRF has been defined as complete or incomplete fracture initiated from the root and is usually in buccolingual direction. It may lead to extraction of the affected root or tooth and can be associated with a history of root canal treatment (RCT).[6]

    VRFs can occur in endodontically treated teeth as well as non-endodontically treated teeth. Tang et al.[12] reported that VRF mainly occurs in endodontically treated teeth.

    Early diagnosis of VRF is crucial to conserve remaining bone in that region, which may optimize further restoration of that area.[13] VRF can occur during intracanal procedures such as obturation and post-placement.

    Diagnosis: The presence of a deep narrow periodontal pocket and a halo radiolucency can be indicative of a VRF. Periodontal tissue breakdown can happen due to necrotic debris and bacteria in the fracture, which can form a deep periodontal pocket.[14] J-shaped/halo-shaped/hanging drop appears in radiographs. CBCT is a useful tool for detecting the extent of VRF in vivo.[15]


      Advanced In Vivo Diagnostic Tools Top


    Microscopes

    Higher resolution (×6–8 magnification or higher) microscopes are more accurate for the detection of cracked teeth as opposed to the use of lower resolution loupes.

    Optical coherence tomography

    Optical coherence tomography (OCT) is an emerging technology for performing high-resolution (1–15 μm) cross-sectional imaging, using the echo time delay and intensity of backscattered or back reflected light.[16] OCT displays high-resolution image, allowing the visualization of microscopic details and some cellular features. However, most samples examined under this microscope show scattering of light and hence it is not widely recommended.

    Transillumination

    The AAE[17] states that transillumination is the most appropriate tool in the armamentarium for the diagnosis of fracture. It is the shining of a light through an area or organ to check for abnormalities. This beam of light will travel through a substrate until it reaches a gap, after which the light beam is reflected. This results in a light and dark area separated by the fracture line. According to Wilcox et al.,[18] transillumination is one of the frequently used diagnostic tools for traditional crack diagnosis in clinics; a major limitation is present in its use. It magnifies all faults causing even the most minute craze lines to be visualized as deep microcracks leading to misdiagnosis and overtreatment. Thus, methylene blue dye has been widely used along with transillumination to highlight cracks. Methylene blue dye is helpful because of its pooling tendency.[19] However, some limitations have also been pointed out,[11] such as dyes cannot flow into the cracks unless there is a discontinuity extending to the enamel. Also, these dyes stain plaque, which may further mask the cracks.


      In Vitro Diagnostic Tools Top


    Micro-computed tomography as methodological tool

    The pixel sizes of the images in micro-CT are in the micrometer levels. This device visualizes and creates a 3D model without damaging the object. The attributes of the micro-CT device are superior to the conventional CT machine, which are as follows:[20]

    1. The X-rays used in micro-CT are in the high-energy range, thus they can pass through thicker layers of tissue samples.


    2. Micro-CT device needs more time for exposure, thereby increasing the signal-to-noise ratio, which in turn will offset the loss in signal.


    3. It has better clarity as the focal spots are smaller.


    A micro-CT device includes an X-ray source, rotating sample platform, detection array, and 3D reconstruction software. The device irradiates the object and records attenuated intensities of the X-ray beam, whereas the object rotates on its own axis, thus allowing the device to collect projection data of the object from all angles.[21]

    The first incidence of 3D imaging of dentinal cracks without damaging the tooth was carried out using contrast BaSO4 stain precipitation in elephant dentin and extracted human molars.[22] Other authors[23] also used contrast media (BaSO4) and micro-CT to show microcracks occurring because of cleaning and shaping procedures of rotary instruments.

    Another study[24] conducted the evaluation without the use of any contrast agents and determined the presence of dentinal microcracks after biomechanical preparation of the tooth. However, they found that, surprisingly, all the cracks seen in the postoperative scans were already present in the teeth before the treatment itself.

    Thus, the following can be concluded:[20],[24]

    • - The accurate location and reconstruction of microcracks can be carried out using micro-CT.


    • - As it is a nondestructive method, the tissue can be examined in all stages of the RCT, and it also allows determination of the presence of dentinal microcracks in preoperative samples.


    The disadvantage of this method is that the micro-CT device cannot be used in in vivo conditions. Also, the cost and time taken for analysis are quite high.

    Scanning electron microscopy

    The scanning electron microscope (SEM) uses a focused beam of high-energy electrons to determine the external morphology, chemical composition, and crystalline structure of the sample.[16]

    SEM technique has the advantages of the possibility to view the 3D external shape of an object, also of being a nondestructive and a highly sensitive technique.[25] The images produced by it can visualize cracks less than 1nm in size.[26] The major drawback of this method is that this imaging technique cannot visualize the extent of the crack into the dentin. Also, the tissue assembly in the microscope requires vacuum-causing surface defects.

    Sectioning methods

    Sectioning method is an inherently destructive method, which requires preparation of the tissue into thin slices. This cross-sectioning technique causes further damage to the fragile and thin sections of the tooth, thus leading to incorrect results. However, sectioning methods have been used in a large number of endodontic research, and the methods of accomplishing the sectioning also are numerous. This causes a wide disparity of data reported. But it still remains one of the more popular methods used as the control group is easy to manipulate and is cost-effective.

    Stereomicroscope

    The aforementioned sample preparation method of sectioning requires visualization of cracks using primarily stereomicroscope systems.[27] This device offers a wide range of magnification, but for the dental purpose of observing microcracks, a ×16 magnification level is ideal. Magnification and illumination have become the norm for standard dental care as they provide additional information that can be easily missed by naked eye. Also, in endodontic research, one of the most often used adjuncts for visualization has been stereomicroscope. However, it also has its share of drawbacks. The high false-positive interpretation of defects is a common problem.[27] This could be due to erratic light reflection.

    Synchrotron radiation-based micro-computed tomography

    This device is an upgraded modification of conventional micro-CT. Conventional micro-CT uses X-ray radiation of lower energy, thus leading to lower transmission capabilities. Conversely, synchrotron radiation-based micro-CT (SRCT) produces high-energy ray called “hard” X-rays, which have wavelengths of 0.10–0.01nm or energy in the range of 10–120keV. Therefore, these high-energy rays are able to enter deeply into the tissues, thus giving a more vivid picture of the subsurface details. The synchrotron X-ray beam also emits a coherent and polarized beam. SRCT scans use this coherent beam, which performs a 3D visualization of the teeth at a high-spatial resolution.[28] Also, SRCT can detect very small discrepancies in densities in a sample.[18] However, very few researchers have used SRCT for endodontic purposes. The reasons for this could be the prohibitive cost and the apparent rarity of the device.

    Transmission electron microscopy

    A transmission electron microscope (TEM) uses a beam of electrons, which are of higher energy than SEM and provides high-resolution (below 1nm) and high-magnification imaging. The image is produced by illuminating the sample with the electron beam within a high vacuum and detecting the electrons that are transmitted through the sample onto a phosphorescent screen or through a camera.[21] Studies[29] using TEM to examine dentinal microcracks have been performed and have shown that cracks can be visualized deep inside the sample without destroying it. High-resolution images with propagation patterns of dentinal defects have been obtained using TEM. Disadvantages of this method include false-positive result interpretation of dentinal defects.


      Conclusion Top


    Dentinal microcracks have always presented a diagnostic dilemma to the clinician as well as the in vitro researcher. However, several refinements have been made in the field of diagnostics and associated devices and have led to an improved detection of these dentinal cracks. However, although a perfect foolproof method of detection of microcracks is yet to be developed, the micro-CT, offering a nondestructive 3D volumetric reconstruction of the microcrack lines, is the best in vivo tool currently available.

    Financial support and sponsorship

    Nil.

    Conflicts of interest

    There are no conflicts of interest.

     
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      In this article
    Abstract
    Introduction
    Craze Lines
    Fractured Cusp
    Cracked Tooth
    Split Tooth
    Vertical Root Fr...
    Advanced I
    In...
    Conclusion
    References

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