Digital image ratio : a new radiographic method for quantifying changes in alveolar bone.
Part 1 : theory and methodology.

J. Periodont Res 1996 ; 31 : 161-167.

A new method, digital image ratio (DIR), has been developed for directly measuring changes in alveolar bone. The image on the computer monitor represents the relative mass change between two radiographs. A Fourier filtering is used to reduce noise artefacts. This method is validated through an experiment with a step wedge. DIR needs only a preliminary calibration of the experimental conditions of operation and avoids tedious calibrations for each measurement as in the case of Digital Image Subtraction. It is suggested to use low-voltage X-ray techniques for long-term quantitative studies of patients to minimize irradiation doses.

Digital image ratio : a new radiographic method for quantifying changes in alveolar bone.
Part 2 : clinical application.

J Periodont Res 1996 ; 31 : 533-539.

In a previous paper (part 1) we have developed a new technique, Digital Image Ratio (DIR), which theoretically avoids some of the drawbacks of quantitative digital subtraction radiography. DIR allows the direct computation and visualization of bone-mass-ratio changes. This second part describes the use of DIR analysis to examine 20 sites in 8 patients undergoing regenerative periodontal therapy. Standardized reproducible radiographs of these 20 sites were taken before and 12 months after surgery. Ten experimental sites were treated with bone graft substitutes (Natural Coral or Natural Coral + Collagen), and ten control sites by debridement alone. None of the experimental sites had a density ratio below 1, where 1 indicates no change. The error was 0.07 (0.93 - 1.07). The experimental sites showed an 18% mean increase in bone density (1.18), which increased to 23% (1.23) for sites filled with natural coral alone. All the control sites had values close to 1.00 (1.00 0.07) except for three sites, which showed a 9-15% loss of bone density. It is thus possible to compare and quantify the changes in experimental and control sites in the same patient using the percentage gain or loss of bone density. This demonstrates that DIR is suitable for clinical applications, and can be used in clinical analysis when bone changes are expected.

Example of clinical application

Scanning electron microscopic evaluation of the effects of an air-abrasive system on dental implants: A comparative in vitro study between machined and plasma-sprayed titanium surfaces.

Journal of Periodontology, Vol. 68 (1997) 12, 1215-1222

An in vitro comparative study was conducted in order to evaluate the effects of an air-abrasive system on dental implant surfaces. Eight new titanium dental implants, four standard machined implants (machined group), and four standard plasma-sprayed implants (plasma-sprayed group) were selected for investigation. Both neck and body surfaces of the implants were analyzed. Each pair of implants in each group was treated as follows: the spray of the air-abrasive unit was applied to each area for 5 seconds on the first implant and 15 seconds on the second implant. A total of 24 areas were observed: 16 test implants and 8 controls. Scanning electron photomicrographs were analyzed by 3 examiners using a category rating scale (k = 0.594). The images were also computerized for texture analysis. The results indicate that a single air-powder abrasive treatment of dental implants selected for this study modified their exposed surfaces. After treatment, the threaded neck surface of a machined group implant was least affected, whereas the body was the most altered. In the plasma-sprayed group, comparisons between implant surfaces showed little change. In the machined group, more change was observed in both neck and body areas. In all specimens, a 5-second exposure to the air-powder abrasive did not induce deep changes in the surfaces. A 15-second exposure modified all specimen surfaces. Further studies are needed to evaluate the effect of these changes on the biological osseointegration process.