John W. Preece

Radiobiologic risk estimation from dental radiology: Part I. Absorbed doses to critical organs

The aim of the present study was to generate one consistent set of data for evaluating and comparing radiobiologic risks from different dental radiographic techniques. To accomplish this goal, absorbed doses were measured in fourteen anatomic sites from (1) five different panoramic machines with the use of rare-earth screens, (2) a twenty-film complete-mouth survey with E-speed film, long round cone, (3) a twenty-film complete-mouth survey with E-speed film, long rectangular cone, (4) a four-film interproximal survey with E-speed film, long round cone, and (5) a four-film interproximal survey with E-speed film, long rectangular cone. The dose to the thyroid gland, the active bone marrow, the brain, and the salivary glands was evaluated by means of exposure of a tissue-equivalent phantom, fitted with lithium fluoride thermoluminescent dosimeters (TLDs) at the relevant locations.

Radiobiologic risk estimation from dental radiology. Part II. Cancer incidence and fatality.

With the use of the measured absorbed doses from part I of this article, the specific radiobiologic risk to the patient from (1) five different panoramic machines with rare-earth screens, (2) a 20-film complete-mouth survey with E-speed film, long round cone, (3) a 20-film complete-mouth survey with E-speed film, long rectangular cone, (4) a 4-film interproximal survey with E-speed film, long round cone, and (5) a 4-film interproximal survey with E-speed film, long rectangular cone, was calculated. The estimated risks are expressed in two ways: the probability of radiation-induced cancer in specific organs per million examinations and the probability of expression of a fatal cancer per million examinations. The highest risks calculated were from the complete-mouth survey with the use of round collimation. The lowest risks calculated were from panoramic radiography and four interproximal radiographs with rectangular collimation.

Craniofacial polyostotic fibrous dysplasia: a case report and review of the literature

Craniofacial fibrous dysplasia is 1 of 3 types of fibrous dysplasia that can affect the bones of the craniofacial complex, including the mandible and maxilla. A 49-year-old white male presented with an extensive previous medical history. Initial radiographic assessment comprised panoramic and PA cephalometric radiographs and provided a working diagnosis of fibrous dysplasia. Advanced imaging included conventional CT, cone beam CT, and MRI. Three areas in the craniofacial complex were diagnosed as FD. The patient also presented with severe degenerative joint disease of the left TMJ. In this case, all FD lesions were radiopaque and presented with ground glass appearance. The relative importance of each imaging modality in the diagnosis and assessment of FD is discussed.

Digital subtraction temporomandibular joint tomography

Receiver operating characteristics analysis was performed to demonstrate differences in diagnostic performance among conventional tomograms, digitized tomograms, and subtraction tomograms. Digital subtraction tomography was found to be the best imaging modality for detecting artificially created lesions in the two selected temporomandibular joint locations. There was a statistically significant difference in diagnostic performance between conventional tomograms and subtraction tomograms for the detection of temporomandibular joint bony lesions. There was also a statistically significant difference in diagnostic performance between digitized tomograms and subtraction tomograms in the detection of these bony lesions. There was no statistically significant difference in diagnostic performance between conventional tomograms and digitized tomograms for the detection of temporomandibular joint bony lesions. The significance level was set at p = 0.05. Results of the analyses of variance showed that with digital subtraction tomograms, observer reliabilities were higher than with conventional and digitized tomograms.

The posterior wall of the maxillary sinus as seen in panoramic radiography

The dental and sinus projection programs of the PM 2002cc panoramic x-ray unit were compared with regard to the visualization of the maxillary sinus posterior wall of a dried skull. The posterior wall of the maxillary sinus appeared different on each program. In the sinus projection program the posterior wall appeared narrower than that in the dental projection program. The main cause for the difference of the maxillary sinus posterior wall image was the projection angle. In the sinus projection x-rays entered more tangentially to the posterior wall of the sinus than in the dental projection, but in the dental projection x-rays entered more tangentially to the mediosuperior and medioinferior region of the maxillary sinus posterior wall. Thus a large, widely destructive lesion in the posterior wall of the maxillary sinus would be more easily detected with the sinus projection. On the other hand, lesions confined to the mediosuperior and medioinferior regions of the posterior wall will be depicted more clearly with the dental projection program.

Comparison of x-radiation doses between conventional and rare earth panoramic radiographic techniques

The radiation dose to radiobiologically critical organs at various anatomic sites in a phantom was compared with the use of rare earth screen/film combinations and calcium tungstate screen/film combinations. Rare earth screens and films produced a reduction in dose up to 40% to 50% depending on the anatomic site.