figure 1

© Mykyta Dolmatov/iStock/Getty Images Plus

Tooth infractions, cracks and fractures (ICF) represent mechanically induced discontinuities within the dental hard tissues. Such findings are commonly observed in clinical practice, and whilst often asymptomatic, may be associated with a range of symptoms and/or aesthetic issues. In part 1 of this two-part series, we offer top tips for assessment and diagnosis of these problems.

  1. 1.

    Terminology

    1. a.

      Key definitions are shown in Table 1 and Figures 1 and 2. Definitions are adapted from Abbot and Leow.1

      Table 1 Definitions of tooth infractions, cracks and fractures
      Full size table
      Fig. 1
      figure 2

      Enamel infractions in anterior teeth

      Full size image
      Fig. 2
      figure 3

      Lower right 6 with vertical crack-line in mid-lingual aspect, and fracture of the disto-lingual cusp

      Full size image
    2. b.

      Patients with cracked and fractured teeth may present with a range of symptoms including: no symptoms, pain on biting (or release), temperature sensitivity, or (if pulpitis) spontaneous pain. Such symptoms in cracked teeth are often collectively referred to as 'cracked tooth syndrome'. However, this terminology is erroneous because the word 'syndrome' relates to a 'disease', whereas a crack is a clinical finding not a disease.1

  1. 2.

    Aetiology

    1. a.

      The high inorganic content of enamel makes it hard but inflexible, with a flexural modulus variously reported to be within the range 10-130 GPa.2 However, the relative flexibility of dentine (flexural modulus within the range 10-20 GPa),3 periodontal (suspensory) ligament, (and to a much lesser extent) alveolar bone, combined with neuromuscular occlusal force feedback mechanisms, reduces the risk of overloading of teeth. However, where the flexural strength of tooth tissue is exceeded, crack initiation may occur and, if the crack propagates, fracture with separation of the fragments may ultimately occur.

    2. b.

      ICFs may be caused by acute dental trauma related to events such as accidents, physical assault and sporting mishaps. Such incidents should be screened for within the history taking.

    3. c.

      The muscles of mastication can generate large occlusal forces. One study reported a patient who could generate a biting force of 575N within the molar/premolar region.4 Frequent or sustained occlusal forces (associated with parafunctional activity) can be problematic, and a correlation between bruxism and cracks and fractures in teeth has been reported.5 Parafunction can take several forms, and it is useful to screen for the following habits: clenching/holding teeth together, tapping teeth together, grinding, fingernail chewing, and cheek chewing.

    4. d.

      Hard diets (eg nuts/bone/ice) may cause ICFs.

    5. e.

      Unfavourable inter-occlusal relationships (eg non-working side interferences, edge to-edge incisors/canine relationship, and cusps that occlude with the opposing marginal ridges) can predispose to ICFs. In addition to clinical examination to identify these features, a history of repeated failure of restoration(s) should signal that unfavourable occlusal relationships/forces may be at play.

    6. f.

      ICFs may unfortunately also be induced iatrogenically. Awareness of the potential for this to occur, and undertaking mitigating action, should reduce the incidence of this. Areas for consideration include: ultrasonics (use lowest power suitable to the task), rubber dam clamp selection (plastic vs metal, or alternatively use of elastic rubber dam stabilising cord), avoidance of excessive wedging forces during compaction of root canal fillings and amalgam, and avoiding use of dentine pins and threaded posts.

  1. 3.

    Pathophysiology

    1. a.

      Dentinal pain, characterised by 'sharp'/intense/short-lasting pain upon application of suitable stimulus (eg thermal/sweet/drying/mechanical), may arise in vital teeth with exposed dentine (+/- porosities in enamel) +/- cracks or fractures. The hydrodynamic theory of dentine sensitivity postulates that dentinal pain is related to the induction of transient fluid movement within dentinal tubules (caused by application of a suitable stimulus, which in turn stimulates Aδ nociceptors within the pulp/dentine complex6). If upon removal of the stimulus, the symptoms cease immediately, this suggests that at that time the problem is confined to dentine, and that significant pulpal inflammation has not yet occurred.

    2. b.

      Coronal cracks/fractures may act as a portal for bacteria and their by-products to infiltrate the dentine and pulpal complex, with complications including: tertiary dentine formation/calcific metamorphosis (causing yellow discolouration of the crown) (Figures 3 and 4), and pulpitis (reversible or irreversible) that may ultimately lead to pulpal necrosis and apical disease.

      Fig. 3
      figure 4

      a, b) Labial and palatal views of an upper right 3 (13) with yellow discolouration. The tooth had been traumatised five years previously. There was a crack-line in the palatal aspect. The tooth was asymptomatic and tested positive with electric pulp test (but negative with cold testing)

      Full size image
      Fig. 4
      figure 5

      A long cone peri-apical radiograph demonstrated calcific metamorphosis and an intact periodontal ligament space. No treatment was deemed necessary and the tooth placed under long-term clinical and radiographic review

      Full size image
    3. c.

      Cracks extending into the root may initiate additional complications within the periodontal ligament complex. For example, periodontal tissues adjacent to an infected crack or fracture will undergo inflammatory events, which classically result in periodontal attachment loss that vertically aligns with the crack forming a deep narrow periodontal pocket. With further crack propagation to the apex (especially in the case of root fractures), more extensive periodontal destruction may ensue resulting in the radiographic appearance of crater or (classically) 'J-shaped' bone loss. A further (unusual) presentation of note is an apico-coronal root fracture in a tooth testing 'vital', which can present with a peri-apical radiolucency +/- symptoms of apical periodontitis (typically presenting in maxillary second molars with 'spindly' roots).

  1. 4.

    Top tips for assessment

    1. a.

      The aspiration is to either directly visualise the ICF, or in symptomatic cases, achieve ICF localisation by precise replication of the patient-reported symptoms.

    2. b.

      Teeth should be dried (with a 3:1 syringe) and examined under good lighting conditions with magnification (loupes or microscope).

    3. c.

      Pulp testing with both cold (eg Endo-Frost, Coltène/Whaledent, Langenau, Germany) and Electric Pulp Test (EPT) provides a surrogate measure for pulp vitality.

    4. d.

      Rubber dam held in place with fingers (or rubber dam clamp) can be readily used to individually isolate suspect and 'control' teeth, prior to application of stimuli relevant to the patient's pain history. For example:

      1. i.

        Cold or warm water can be syringed into the dam to form a pool around the tooth and left for several seconds before being aspirated out

      2. ii.

        Air may be blown over the tooth using a 3:1 syringe.

  1. e.

    The character of pain (eg sharp/aching/throbbing etc), intensity of pain (using a visual analogue scale 1-10), and duration (fleeting or lingering) should be determined. Taken together, these findings can help localise the source of pain, and the structure(s) involved (eg specific tooth/cusp, and whether dentine/pulp +/- peri-apical tissues). It should be noted that pulpless teeth with vertical root fractures may sometimes give a false positive test with a hot/cold stimulus due to fluid percolation through the fracture line to the periodontal ligament.

  2. f.

    Transillumination of teeth may demonstrate cracks/fractures by virtue of refraction phenomenon at the crack/fracture boundary (Fig. 5). However, the effectiveness of transillumination is reduced in teeth with restorations, and not possible in teeth with full-coverage restorations. Where (direct/indirect) restorations are removed as part of a restorability assessment, it is useful to carry out transillumination (again) once the tooth structure is revealed.

    Fig. 5
    figure 6

    Same case as shown in Figure 1, with transillumination of the upper left central incisor tooth highlighting enamel infractions

    Full size image
  3. g.

    A Tooth Slooth (Professional Results, Laguna Niguel, USA) is a plastic device for identifying teeth/specific cusps eliciting pain on biting (or, following biting, upon release). The device should be used methodically, placing it on one specific cusp at a time, and asking the patient to bite onto it. The patient's reported pain experience (if any) should be recorded for each tooth/ cusp of interest.

  4. h.

    Deep narrow periodontal defects associated with cracks or fractures may be subtle and can easily be missed. A UNC15 probe is well suited for periodontal assessment and should be carefully 'walked around' the tooth/teeth of interest - noting the pocketing profile. Where inflammation is present, the patient may signal particular discomfort on periodontal probing, and an under-estimation of pocket depth may be made. In such cases, we would advise the administration of infiltrations of local anaesthesia prior to re-probing. It should also be noted that whereas the buccal and palatal/lingual aspects are usually readily accessible for periodontal probing, where a proximal tooth contact exists, access to probing in that area will be compromised. In such cases, where a Class II restoration is present which requires removal, the gingival sulcus at the proximal surface(s) should be re-probed after removal of the restoration.

  5. i.

    Dyes, such as methylene blue, may also be used in the detection of cracks in teeth.

  6. j.

    Two-dimensional radiographs will not directly demonstrate fractures unless the x-ray beam is within four degrees of the plane of fracture.7 However, appropriate intra-oral radiographs may be indicated if there is no previous or recent imaging available in order to screen for caries/defective restorative margins/crestal bone levels/peri-radicular pathology.

  7. k.

    Three-dimensional radiographic imaging (eg cone beam computerised tomography [CBCT]) has been shown to be able to predictably detect root fractures in the lab-based setting.8 However, in the clinical situation, the reliability of CBCT for detection of root fractures is limited by voxel size (linked to the need to keep radiation dose as low as reasonably practicable), and degree of separation of the fractured portions potentially being below the limit of resolution. Additionally, where the tooth has been previously root-filled, imaging artefacts caused by gutta percha can frustrate attempts to screen for root fractures.9 However, as previously mentioned, the finding of deep localised or 'J-shaped' radiolucency (on either 2D or 3D radiographs) is characteristic of the pattern of bone loss associated with cracked or fractured roots (Figures 6 and 7).

    Fig. 6
    figure 7

    Localised infrabony defect distal to a root-filled upper left 5 tooth

    Full size image
    Fig. 7
    figure 8

    A restorability assessment of the upper left 5 tooth (shown in Fig. 6) revealed that the root was cracked, deemed not predictably restorable, and to be extracted. Crack-line is arrowed

    Full size image
  1. 5.

    Top tips for diagnosis

    1. a.

      Following assessment, relevant provisional or (ideally) definitive diagnoses are made based on triangulation of findings.

    2. b.

      Causes of signs and symptoms other than cracks/fractures must be identified (and managed) including: dentine sensitivity secondary to gingival recession, caries, non-carious tooth surface loss, or defective restorations.

    3. c.

      The following diagnoses may be appropriate within the context of cracked or fractured vital teeth:

      1. i.

        Enamel infraction

      2. ii.

        Enamel or enamel-dentine fracture +/- pulp exposure (eg complicated or uncomplicated)

      3. iii.

        (Apico-coronal) root fracture +/- (clinical symptoms of) pulpitis

      4. iv.

        Dentine sensitivity secondary to crack/fracture

      5. v.

        Reversible pulpitis secondary to crack/fracture

      6. vi.

        Irreversible pulpitis secondary to crack/fracture.

    4. d.

      The following diagnoses may be appropriate within the context of cracked or fractured non-vital teeth:

      1. i.

        Apical periodontitis (acute or chronic) secondary to crack/fracture

      2. ii.

        Perio-endo lesion secondary to crack/fracture of root.

We hope you have found these hints and tips helpful. Top tips for managing enamel infractions, cracks and fractures will be discussed in part 2 of this series.