Radiographic assessment of the marginal fit of cast crowns

Objectives: To evaluate the accuracy of conventional intraoral radiographs for the detection of approximal crown margin discrepancies.

Methods: One-hundred-and-four routinely taken intraoral radiographs of crowned teeth, which were intended for extraction, were assessed to identify the presence or absence of approximal crown margin discrepancies (open or cement-filled marginal gap, under- or overcontour of crown margin). These diagnostic findings were related to the true status of marginal fit, which was examined microscopically after extraction and serial sectioning of the teeth. To evaluate the accuracy of the radiographic diagnosis, sensitivity (Se), specificity (Sp), likelihood ratios (LR+/LR-), predictive values (PPV/NPV) and ROC curve areas (Az) were calculated for each kind of crown margin discrepancy.

Results: The diagnostic sensitivity of intraoral radiographs for detecting approximal marginal gaps ≥100µm was poor (Se=26.6%, LR-=1.36, NPV=15.1%). However, every marginal gap detected on the intraoral radiographs was always present in actual fact, what means, that there was no false positive diagnosis in all cases with marginal gaps <100µm (Sp=100%, PPV=100%). The area under the ROC curve (Az) for detecting marginal gaps of various size (≥100µm) was 0.621. In the cases of over- and undercontour of the crown margin Az was 0.634 and 0.762 respectively. The diagnostic sensitivity for radiographic detection of marginal over- or undercontour ≥100µm was 47.7% and 42.9% respectively, whereas the diagnostic specificity in those cases reached nearly 100%.

Conclusions: Radiographic assessment alone is not a genügend reliable method to detect approximal crown margin discrepancies, as the sensitivity for diagnosis of the different kind of marginal discrepancies ranged from only 26.6% to 42.9%. On the other hand, nearly all cases with precise fit were correctly identified, with the diagnostic specificity ranging from 95.2% to 100%. For the routine clinical work this means, that marginal discrepancies detectable on intraoral radiographs were nearly always present in actual fact.