The presence of a malignant lesion in the maxillo-facial region can now be easily detected now using X-ray CT or MR imaging. However, patients with such lesions usually first visit a medical or dental clinic, and it is therefore still important for dental clinicians to be able to detect such a lesion on a panoramic tomograph (PT), especially in cases in which the lesion is present in the maxillary bone or its adjacent structures, regions that are not easy to observe directly. However, in the previous study, we found that the presence of such a lesion was overlooked in some of the patients and that a correct diagnosis could be established even in those patients in whom lesion had been overlooked by checking certain structures depicted on routine PTs.
In this study, the abilities of trainee dentists (graduate students of dental universities) to detect abnormal findings on PTs were investigated PT films of eight patients with malignant lesions of the maxillary sinus and adjacent tissue were given to trainee dentists who volunteered to participate in this study. The trainee dentists were requested to read the films within 2.5 minutes and to record their findings. The trainee dentists were randomly divided into three groups: one group in which films were read using the schema of PT from a textbook on oral radiology (group A), one group in which films were read using an original schema showing significant lines on a PT (group B), and one group in which films were read using the same shema as that given to group B conbined with a tabular checklist for significant structures.
After reading the films, the dentists were given a lecture on the principles and normal anatomy of PTs and on detailed findings of the films. Furthermore, 18 dentists were randomly selected from the trainee dentists who volunteered to participate in this study, and this group of trainee dentists read another film series before and after the lecture. After that, improvement in their reading ability was analyzed.
Trainee dentists in group A could detect almost no abnormal findings. Trainee dentists in group B showed higher scores than trainee dentists in group A, but could detect less than half the total number of destroyed structures. Trainee dentists in group C showed significantly greater ability to detect abnormalities than trainee dentists in the other two groups. Trainee dentists in group S misread the films and could detect almost no abnormalities before the lecture but showed significant improvement after the lecture.
From these results, we concluded that the most important factor in detecting abnormalities on PTs is checking the important lines on PT, including unfamiliar structures for dental clinicians, and comparing these lines on both sides.

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Purpose: To evaluate the effect of parameters of spiral CT scanning on the image quality required for the planning of dental implants operations.
Materials and method: A semi-anthropomorphic mandible phantom which has artificial mandibular canals and teeth roots was used as a standard object for imaging. Spiral CT scans for the phantom settled in water phantom with diameters of 20 and 16cm were performed. Visibility of the artificial mandibular canal made of a Teflon tube and gaps between tooth apex and canal in the mandibular phantom was evaluated for various combinations of the slice thickness, table speeds, angles to the canal. and x-ray tube currents. Teeth roots were made of PVC (noly vinyl chloride).
Results: The artificial mandibular canal was clearly observed on the images of 1mm slice thickness. At the same table speed of 2mm/rotation, the images of thin slice (1mm) were superior to that of thick slice (2mm). The gap between teeth apex and canal was erroneously diagnosed on the images with table speeds of 3mm/rotation. Horizontal scanning in parallel to the canal result in poor image quality for observation of mandibular canals because of the partial volume effect. A relatively high x-ray tube current (125mA) at thin slice (1mm) scanning was required for scanning the mandibular phantom in 20cm water vessel.
Conclusion: Spiral scanning with slice thickness of 1mm and table speeds of 1 to 2mm/rotation seemed to be suitable for dental implants. The result of this study suggested that diagnosis from two independent spiral scans with a different angle to the object was more accurate and more efficient than single spiral scanning.

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Purpose: To develop a procedure for quantitative analysis using intraoral radiographs of alveolar bone after placement of dental implants and to consider the validity of the method.
Materials and methods: We evaluated the ten patients (2 males and 8 females, average age: 48.4years-old), who were treated with dental implant operation in the site of mandibular molar region, since October of 1999 until September of 2000 in Kimura Dental Clinic (Kumamoto, Japan). We evaluated the intraoral radiographs taken pre- and post- operatively and at follow-up examination. To detect alveolar bone change on radiograph, we adopted the digital subtraction method. Although the radiographs were taken under an ordinary technique with cone indicator, we did not apply the standardized technique with fixing material customized for each patient. Therefore, we used geometric correction and density compensation before subtraction. We assessed the basic statistical values (mean, variance, kurtosis and skewness) of the ROI of the subtracted images. Also, we noted PPD (probing pocket depth) and BOP (bleeding on probing) at each site as indicators of clinical findings and all implanted sites were classified according to the PPD or BOP, i. e. PPD increased group “PPD (+) ” and PPD stable group “PPD (-) ”, likewise BOP positive group “BOP (+)” and negative group “BOP (-)”. We considered the statistical values of ROT in each group and compared these findings.
Result: Mean and variance values of PPD (+) were higher than those of PPD (-) and there was a significant difference in mean value (p=0.031). Similarly, mean and variance values of BOP (+) were statistically higher than those of BOP (-)(p=0.041 and p=0.0087, respectively). Concerning kurtosis and skewness, there was no difference between PPD (+) and PPD (-), or between BOP (+) and BOP (-).
Conclusion: Using our method, the radiographs taken for follow-up examination could be assessed quantitatively. It is suggested that geometric correction and density compensation could abbreviate the standardized intraoral radiographic technique prepared for subtraction.

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