Direct digital imaging with and without niobium filtration for detection of density differences beneath steel orthodontic bands

Tissue radiation dosages using the RVG-S with and without niobium filtration

Tissue doses for a modified Rando head- and-neck phantom were measured for imaging with speed group E film with standardized aluminium filtration and the RVG-S both with and without added niobium filtration. Cylindrical holes drilled into the phantom's tissue-equivalent material permitted the placement of a small ionization chamber into anatomically correct sites representing the thyroid, parotid, submandibular and sublingual glands. To establish the necessary cone positions, angulations and time settings for each exposure, diagnostically acceptable images of six teeth, representative of different intraoral regions, were made for a DXXTR mannequin. Entrance and exit points were marked and transferred to the phantom to allow reproducible repeat exposures. The RVG-S provided reductions in average skin entrance dose of 31 per cent to 39 per cent with standard aluminium filtration and 51 per cent to 60 per cent with the addition of niobium filtration to attenuate the beam. While dose reductions relative to E-speed film usage were found for deep tissue sites, these were site and projection specific. The cumulative reduction from use of the RVG-S without niobium filtration was 32 per cent. It was 42 per cent with additional niobium filtration. It should be noted, however, that adding niobium filtration resulted in increased dosages to the deeper soft tissues such as the thyroid gland.

Observer differentiation of proximal enamel mechanical defects versus natural proximal dental caries with computed dental radiography

OBJECTIVES

Various models have been used to study the accuracy of imaging systems for detection of dental caries. This study compares the ability of dentists to detect mechanically created defects versus natural dental caries cavitations on the proximal surfaces of extracted teeth with Computed Dental Radiography (Schick Industries, Long Island City, N.Y.). Detection rates are investigated according to lesion depth to permit comparisons to be made between studies in the literature with other mechanical defects or natural caries models. Discrimination of natural caries versus artificial defects with Computed Dental Radiography is also compared with a previous report that used standard dental film.

STUDY DESIGN

Fifty-two extracted molar and premolar teeth were mounted into representative sets of maxillary and mandibular posterior arches for bite-wing radiography. There were 16 proximal surfaces with natural caries and 28 proximal surfaces with mechanical defects. An optical bench was used to ensure constant beam geometry. A 1.8 cm acrylic soft tissue equivalent attenuator was placed in front of the receptor. Thirty dentists acted independently as observers to differentiate between sound proximal tooth surfaces, natural dental caries, and mechanical defects. Evaluation of intra- and interobserver variability was made with use of the kappa statistic. The Zelen test of odds ratios was used to test for homogeneity, and the Mantel-Haenszel analysis plus stratified logistic regression were used for inference about the common odds ratio. Significance was set at p < 0.05.

RESULTS AND CONCLUSIONS

Ignoring stipulation of cavity type, detection was 74% for mechanical defects and 67% for natural caries. The odds of detecting a mechanical defect were 1.40 times the odds of finding natural dental caries cavitation of the same depth. Lesion depth did influence the probability of correctly identifying the presence of a lesion; the odds of identifying cavitation increased 1.41 times with every 0.1 mm increase in lesion depth. Correct designation of lesion type was 1.42 times more likely with mechanical defects than with natural caries (p = 0.003). Intraobserver (kappa = 0.65) and interobserver (kappa = 0.43) agreements were fair to good. Discrimination between natural and artificial lesions was less with the Computed Dental Radiography than that found in our previous study with standard direct emulsion x-ray film.