Microcomputed tomography (µCT) of teeth can detect demarcated radiolucencies below the enamel-dentin junction (EDJ) that are of noncarious origin, and can therefore be classified as possible developmental irregularities, show study results.
The dental images also revealed a direct pathway that exposed the dentin directly to oral micro-organisms, and could explain the phenomenon of hidden occlusal caries lesions, say the researchers.
"With respect to the possibility of such defects being misjudged as caries lesions on conventional histological images, it seems important for these findings to be taken into account when future histological studies are considered," remark Jan Kühnisch (Ludwig-Maximilians-University of Munich, Germany) and co-authors in the Journal of Dental Research.
To investigate the phenomenon of hidden caries, the team performed µCT imaging on 203 freshly extracted molar teeth with no clinical irregularities visible in visual, radiographic, or stereomicroscopic examinations.
The imaging showed that seven (3.4%) teeth had demarcated dentin radiolucencies below the EDJ, and because no gradient of demineralization was detectable, these cases were classified as noncarious defects. For four of the cases, no signs of a carious process were detected visually, says the team.
"Thus, these defects may have been due to developmental disorders and/or mineralization disturbances below the EDJ during early tooth development," write Kühnisch et al.
They conducted a 3D analysis of µCT imaging and observed a direct pathway between the bottom of the fissure and the demarcated radiolucency beyond the EDJ, indicating a lack of protective enamel over the dentin.
This finding could be due to cellular mechanisms that "failed to establish a tight alignment between the ameloblast and odontoblast cells prior to the establishment of the EDJ," they suggest.
The team also contends that the defects could explain the early onset and rapid progression of caries lesions on occlusal surfaces, which, as a consequence of direct communication between the oral cavity and outer dentin layer, make infection almost inevitable immediately after tooth eruption.
The results call into question the validity of commonly used histologic reference standards, which might overestimate the presence of caries and influence the performance of current diagnostic methods.
"Misinterpretation of such defects as caries lesions may lead to an overestimation of the patients' caries experience and will also act as a confounding factor," conclude Kühnisch and colleagues.
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