Contrast-enhanced intraoral digital subtraction radiography and its application to caries diagnosis.

Project Details


Despite the significant decline in the incidence of dental caries that is observed in the last two decades, clinical diagnosis by visual examination has become more problematic. These findings are also indicative of the difficulties that exist among present populations in detecting slowly progressing dentinal lesions, obscured by apparently intact enamel. In recent years, bitewing radiography has become an approved clinical method in the diagnosis of posterior approximal lesions, and currently is considered as a significant adjunct to clinical examination. The effectiveness of the conventional radiographic method in detecting caries, nevertheless, has been seriously questioned. Gratt et al. and Douglas et al. concluded from their studies that the sensitivity of bitewing radiographs in detecting incipient dental caries is only a disappointing 60% or less, while the actual depth of a carious lesion is consistently underestimated. The reason that small density changes evade detection by direct assessment of conventional radiographs probably may be the radiographic appearance of a demineralized area corresponding to a carious lesion, which is not a well-defined radiolucency but instead shows a distinctive gradient of decreasing optical density from the outer enamel surface towards the dentinoenamel junction. In view of the treatment ramifications of advanced caries, sensitive diagnostic methods that allow for a minimal invasive therapy remain of crucial importance.
In a number of in vitro caries studies, digital subtraction radiography (DSR), however, has been demonstrated to be capable of revealing minute changes in mineralization not perceptible by direct visual comparison of radiographs. That DSR still did not yet gain acceptance as a clinical caries diagnosis tool may appear strange, certainly when judged against the rapid proliferation of DSR procedures in general medicine. However, a combination of theoretical as well as practical problems unique to the application of DSR for the longitudinal assessment of caries progression makes that the expected advantages are not always fully realized. The greatest challenge arises from the difficulty in securing a reproducible exposure geometry between consecutive radiographs. This aspect is especially important for the assessment of caries progression, due to the location of the caries initiation sites on the outer surface of the enamel layer. Because of the sharp density contrasts between air and enamel, even the slightest misalignment may lead to extremely large artifacts that can obfuscate or even mimic true changes in radiolucency.
Traditionally, mechanical stabilization, based on intra- and extraoral devices, has been used to ensure a consistent exposure geometry. Sophisticated extraoral stabilization systems, however, are too cumbersome for routine clinical application. Intra-oral stabilization devices, instead, crucially depends on the use of occlusal stents that must be custom made for each patient. Stents have been found to ensure accurate relocation only over periods no longer than a year. This is due to the distortion of the stent itself during occlusion, or by subsequent restoration, migration, or extraction of the supporting teeth in the time span between consecutive exposures. The use of individualized stents also poses significant logistical problems, caused by the need for storage and sterilization between successive examinations. Moreover, it has been demonstrated that even with a meticulous mechanical stabilization, small variations in exposure geometry persist.
More recently, focus has been largely on the use of retrospective geometrical standardization algorithms. Such algorithms can to some degree correct for differences in exposure geometry after the actual acquisition of the radiographs, relying on numerical transformations to bring radiographic pairs into spatial correspondence. Originally conceived to replace mechanical stabilization, retrospective geometrical stabilization currently is regarded as an important adjunct, capable of correcting for residual alignment errors. A significant theoretical limitation of these algorithms is that they can only account for so called reversible geometrical errors, introduced by changes in the relative position of imaging sensor and dentition. Another more practical limitation as to the use of retrospective geometrical stabilization arises from the very nature of the commonly used algorithms. To reconstruct the exposure geometry these algorithms depend on the manual assignment of corresponding anatomical landmarks in pairs of radiographs. However, anatomical landmarks are not always easy to identify on radiographs acquired with an inconsistent exposure geometry, which can introduce considerable operator variability. The impact of the operator variability on the precision of retrospective geometrical standardization algorithms has been well recognized in previous publications. Manual retrospective standardization algorithms are time consuming, and require considerable dexterity on the part of the operator. Moreover, it is highly unlikely, that a method requiring such an extensive operator involvement will ever find acceptance as part of a clinical diagnostic tool.
In the light of the clinical limitations of DSR for the longitudinal monitoring of caries progression, we wish to pioneer a new and completely automatic method of contrast-enhanced DSR, enabling the instantaneous diagnosis of incipient caries lesions. Such a method will depend on the topical application of a specifically developed contrasting solution, in combination with the use of a CCD-based direct digital intra-oral radiography system, a reusable commercial sensor holder modified to index the dentition by means of a disposable silicone imprint material, a previously developed method for completely automatic retrospective geometrical standardization of radiographs, and a simplified software interface that integrates all previous listed components in an intuitive and quickly to operate computer environment.
Effective start/end date1/01/0631/12/07


  • radiography
  • contrast
  • intraoral
  • caries diagnosis
  • dental
  • subtraction

Flemish discipline codes

  • Electrical and electronic engineering
  • Mathematical sciences
  • Basic sciences
  • (Bio)medical engineering