X-ray dark-field tomography reveals tooth cracks

Abstract

Cracked tooth syndrome (CTS) is a common clinical finding for teeth, it affects about 5% of all adults each year. The finding of CTS is favored by several risk factors such as restorations, bruxism, occlusion habits, and age. Treatment options range, depending on the severity, from no treatment at all to tooth extraction. Early diagnosis of CTS is crucial for optimal treatment and symptom reduction. There is no standard procedure for an evidence-based diagnosis up to date. The diagnosis is a challenge by the fact that the symptoms, including pain and sensitivity to temperature stimuli, cannot be clearly linked to the disease. Commonly used visual inspection does not provide in-depth information and is limited by the resolution of human eyes. This can be overcome by magnifying optics or contrast enhancers, but the diagnosis will still strongly rely on the practicians experience. Other methods are symptom reproduction with percussions, thermal pulp tests or bite tests. Dental X-ray radiography, as well as computed tomography, rarely detect cracks as they are limited in resolution. Here, we investigate X-ray dark-field tomography (XDT) for the detection of tooth microcracks. XDT simultaneously detects X-ray small-angle scattering (SAXS) in addition to the attenuation, whereas it is most sensitive to the micrometer regime. Since SAXS originates from gradients in electron density, the signal is sensitive to the sample morphology. Microcracks create manifold interfaces which lead to a strong signal. Therefore, it is possible to detect structural changes originating from subpixel-sized structures without directly resolving them. Together with complementary attenuation information, which visualizes comparatively large cracks, cracks are detected on all length-scales for a whole tooth in a non-destructive way. Hence, this proof-of principle study on three ex-vivo teeth shows the potential of X-ray scattering for evidence-based detection of cracked teeth.

Figure 1

Schematic overview of the experimental setup, including a grating interferometer. The source grating G0 provides enough spatial coherence to generate a self-interference effect after the phase-grating G1. The subsequent modulation is recorded by a phase-stepping procedure with the attenuation grating G2 and yields the attenuation as well as information about the refractive index and small-angle X-ray scattering.

Figure 2

Attenuation and mean scattering tomographic images of a molar tooth. In (a), a sagittal slice through the reconstruction depicts enamel, dentin, and pulp, which are also visible in the axial slices in (b) and (c). The dentin region is homogeneous, a crack is indicated by a white arrow. Additionally, an inlet shows the line-plot L3 with the attenuation (blue) and scattering strength (orange). The corresponding scattering signal is illustrated in (d) and (e) and shows the same crack (white arrow) as well as additional ones indicated by green arrows. Two line-plots L1 and L2 highlight the difference between both contrast modalities. The slice positions are indicated by colored lines, a scale bar indicates the approximate sample size.

Figure 3

Attenuation and mean scattering tomography images for a tooth with fillings. A sagittal slice (a) and two axial slices (b,c) illustrate the attenuation signal. The inlet in (c) depicts the line-plot L4 with the attenuation (blue) and scattering strength (orange). In (d), histograms illustrate the attenuation and mean scattering strength for different tooth regions. The composite material filling and the glass ionomer cement (GIC) are depicted as well. In (e,f), the mean scattering signal corresponding to the attenuation slices is shown. Some cracks are visible in this contrast modality and are oblique in the attenuation signal, as indicated by white arrows.

Figure 4

Attenuation and mean scattering tomography images of a carious tooth. In the first row, a sagittal slice (a) and two axial slices (b,c) show a cavity in the enamel as well as the carious region within the dentin. The scattering signal (d,e) allows to identify those regions as well and additionally detects a crack (magnified region and white arrows). In the attenuation images, however, the crack is not visible.