Radiographic and Digital Methods in Dental ID

Periapical radiographs are the foundation of forensic dental comparison because they provide the greatest anatomical detail for individual teeth and because they match the format most commonly found in clinical antemortem records. A periapical series covering all quadrants, produced with consistent parallel technique, gives the examiner a set of images that can be overlaid directly against AM films or digital images taken years earlier.

The features a periapical radiograph shows that are relevant to identification include: the number, shape, and position of roots; the width and taper of the root canal; the shape and density of restoration materials; the marginal bone height and pattern; periapical pathology (cysts, granulomas) that may be visible in both AM and PM records; and the internal morphology of the pulp chamber, which changes predictably with age through secondary dentine deposition.

Bitewing radiographs complement periapical images by showing interproximal contacts and the height and density of the interproximal crest bone. A restoration visible in bitewing view may not appear clearly in the periapical image if its margins are at the contact point. Including bitewing views in the PM series increases the information available for comparison with AM bitewing records, which are among the most common radiographs taken in routine dental care.

The orthopantomogram is the most common dental radiograph in clinical practice. Many patients have one as part of their dental record, which makes it a frequent source of AM data, particularly for patients who received their primary care at practices where panoramic rather than full-mouth periapical series were the routine. For the forensic odontologist, a panoramic image in the AM record is valuable but requires careful interpretation.

• Panoramic strengths: captures all teeth and both jaws in one image; shows third molar development useful for age estimation; visible features include root morphology, alveolar bone height, and major pathology.
• Panoramic limitations: magnification varies across the arch; the focal trough concept means teeth positioned outside the focal zone are blurred; ghost images of contralateral structures cause artefacts; fine restoration detail is less reliable than on periapical images.
• Comparison with PM panoramic: when both AM and PM images are panoramic from the same type of equipment, direct comparison is straightforward for broad features. Software tools that normalise for magnification differences between different machines improve precision.

Cone beam computed tomography produces a three-dimensional volumetric dataset of the jaws from which images can be reconstructed in any plane: axial, coronal, sagittal, and oblique. It is not a routine postmortem tool in most forensic settings, but it has a defined role in specific circumstances.

CBCT is most useful for burned or fragmented remains where conventional radiographic positioning is difficult or impossible, for cases where the AM record includes a clinical CBCT scan from the person's dental treatment, and for assessment of complex root morphology where multi-rooted teeth have overlapping root structures that are obscured on two-dimensional images. The three-dimensional dataset allows surface rendering that can be compared with AM CBCT data using software registration algorithms.

Research groups in Europe and North America have developed software pipelines that register postmortem CBCT data against antemortem CBCT or medical CT datasets using surface matching algorithms. These automated methods show promise for mass casualty work where large numbers of comparisons must be made efficiently, but they remain research tools in most jurisdictions rather than validated operational methods.

The practical problem with visual overlay comparison is the difficulty of accounting for size differences, orientation differences, and contrast differences between two images taken years apart on different equipment. Digital superimposition software addresses these problems by allowing the examiner to scale, rotate, and adjust the transparency of one image overlaid on another, then to assess correspondence systematically.

Software tools used in forensic dental identification include WinID (widely used in the United States for data management and comparison), DVI System International (used by INTERPOL and many national DVI teams), and general-purpose image analysis tools that include layer-based overlay functionality. None of these tools makes the identification decision; they present the comparison in a form that the odontologist can assess and document.

• Landmark alignment: the examiner identifies corresponding anatomical landmarks in both images (e.g., the root apex of a specific tooth, the crest of the alveolar bone) and aligns the images on these points. The overlay then reveals how well the non-landmark features correspond.
• Subtraction radiography: a technique in which the registered PM image is subtracted from the AM image digitally. In a perfect match, the subtraction image shows no residual features. Areas of genuine change (new restorations, bone loss, root resorption) appear as positive or negative densities.
• Limitations: software comparison requires both images to be in digital form. Film AM radiographs must be digitised, which introduces an additional quality step. Geometric differences between AM and PM images limit the reliability of automated comparison and must be acknowledged in the case report.

The frontal sinuses are paired air spaces within the frontal bone of the skull, above the eye sockets. They vary enormously between individuals in size, shape, septation, and extension into the frontal bone. They are asymmetric in approximately 54 to 65 percent of people, with rates varying by population. Their outline is stable from late adolescence and does not change with age, dental treatment, or disease unless the sinus itself is directly injured or surgically altered.

For identification purposes, the frontal sinus outline on a posteroanterior skull radiograph, a CT coronal section, or an anterior skull CT reconstruction is compared between the AM and PM images. Correspondence of the outline, including all the major projections, scallops, and septal positions, constitutes strong evidence for identification. Frontal sinus comparison has been used as the primary identification method in cases where dental records were unavailable and has been accepted as evidence in courts in several countries.

The trabecular bone pattern of the mandible and maxilla, the fine meshwork of cancellous bone visible on dental radiographs, has been investigated as an individualising marker since the 1990s. The rationale is straightforward: trabecular patterns are formed during bone development and are influenced by local mechanical loading, vascular supply, and genetics. They are highly individual, stable over decades, and visible on periapical radiographs taken at routine dental appointments.

Qualitative comparison of trabecular patterns is performed by experienced observers who assess the general architecture, trabecular density, and trabecular orientation in a defined region of interest. Computer-assisted quantitative methods using fractal dimension analysis and image texture metrics have been developed and validated in research settings. Studies have reported high accuracy in distinguishing matched from unmatched pairs, and the method has been proposed as an additional line of evidence in cases with limited direct dental feature comparison.