INVESTIGATION OF A PRACTICAL PATIENT DOSE INDEX FOR ASSESSMENT OF PATIENT ORGAN DOSE FROM CONE-BEAM COMPUTED TOMOGRAPHY IN RADIATION THERAPY USING A MONTE CARLO SIMULATION.

The purpose of this study was to investigate a practical patient dose index for assessing the patient organ dose from a cone-beam computed tomography (CBCT) scan by comparing eight dose indices, i.e. CTDI100, CTDIIEC, CTDI∞, midpoint doses f(0)PMMA for a cylindrical polymethyl methacrylate (PMMA) phantom, f(0)Ap for an anthropomorphic phantom and f(0)Pat for a prostate cancer patient, as well as the conventional size specific dose estimations (SSDEconv) and modified SSDE (SSDEmod), with organ dose for the prostate (ODprost) obtained via Monte Carlo (MC) simulation. The ODprost was the reference dose used to find the practical dose index at the center of the pelvic region of a prostate cancer patient. The smallest error rate with respect to the ODprost of 19.3 mGy (reference) among eight dose indices was 5% for f(0)Pat. The practical patient dose index was the f(0)Pat, which showed the smallest error with respect to the reference dose.

[Intraoperative indirect monitoring of electrocardiogram].

The electrocardiogram (ECG) is used as a standard monitoring method during anesthesia and operation. But during the operation of severely burnt patients, the electrodes for ECG cannot be placed on the ideal points for the standard limb leads. We tried the indirect monitoring of the ECG. We placed the electrodes on the sheet over the operating table, and connected the patient and the electrodes with water. By this way the ECG similar to the standard limb leads could be recorded. This method is useful for the patients, with such diseases as severe burn, severe atopic dermatitis and epidermolysis bullosa hereditaria.

[Clinical applications of Brånemark system implant in the Nippon Dental University Hospital. A 5-year report].

A clinical review was performed on patients who requested implantation and visited the Nippon Dental University Hospital during the five years from April 1985 to June 1990. This report describes patient characteristics and treatment results. 1. The total number of new patients was 127 (68 males and 59 females). Their ages ranged from 20 to 80 years. 2. The number of patients who were diagnosed with an indication for implantation and completed the 1st stage operation was 39 (30.7%). An additional 23 patients (18.1%) entered preoperative treatment and are waiting for their operation. Overall, implantation was indicated in 48.8% of all new patients. 3. The ages of patients at fixture installation ranged from 20 to 79 years (mean 60.54, S.D. 11.21) among the 39 patients (20 males and 19 females) who completed the 1st stage operation. As for the number of jaws, implantation was indicated in 40 jaws (21 in male patients and 19 in females). Maxillary implants were indicated in 8 jaws and mandibular implants were indicated in 32 jaws (1 male patient had indications in both jaws). 4. The total number of implanted fixtures was 198, of which 39 were installed in the maxilla, and 159 in the mandible (1 female patient was 5 mandibular fixtures installed at the University of British Columbia, Canada). 5. Of the fixtures implanted in 40 jaws, 94.9% of maxillary fixtures and 98.1% of mandibular fixtures remained stable after the 1st stage operation.(ABSTRACT TRUNCATED AT 250 WORDS)

[Stress analysis at the metal-enamel junction of the anterior adhesive bridge on non-prepared teeth with three dimensional photoelastic experiment].

To study the dynamic action at the metal-enamel junction of an adhesive bridge, the author calculated the values of principal stress and maximum shearing stress, and determine the stress distribution at the junction of the adhesive bridge, for which an unprepared central incisor and a canine were used as abutments for a defect of the maxillary lateral incisor, using a three-dimensional photoelastic experiment. Two models were produced for the experiment on the basis of assumed intercuspal position: Model 1 with a loading point set around the incisal edge and model 2 with a loading point at the lingual cingulum. The results were as follows. (1) In both Models, tensile stress was distributed as the principal stress at the metal-enamel junction, except for the loading point, in the adhesive bridge of the non-prepared type. (2) The maximum principal stress was observed in compressive stress at the loading point in the central incisor of Model 2, being 720 kgf/cm2. Model 2 tended to show a higher concentration of stress at the loading point than Model 1. (3) Values of compressive stress at the loading point of the central incisor and canine were compared in Models 1 and 2. The central incisor showed higher stress values than the canine in both models; the canine had 50-60% of the stress values in the central incisor. (4) Investigation of distribution of the maximum shearing stress revealed a value of 360 kgf/cm2 on the surface directly under the loading point of the central incisor and 240 kgf/cm2 at the loading point of the canine in Model 2, and 215 kgf/cm2 at the loading point of the central incisor and 120 kgf/cm2 at the loading point of the canine in model 1. These values were all above the shearing stress of adhesive resin cement.

[Photoelastic stress analysis at the metal-enamel junction of the anterior adhesive bridge on non-prepared teeth in eccentric jaw position].

To study the stress involved at the metal-enamel junction of an adhesive bridge during the eccentric movement of the mandible, the author calculated the values of principal stress and maximum shearing stress, and determined the stress distribution at the adhesive surface which exists between retainer and enamel, for which an unprepared canine and a centaral incisor, using a three-dimensional photoelastic experiment. Based on the assumed eccentric movement of the mandible, three models with loading at different parts of the adhesive bridge were used for the experiment: Model 1 with loading only on the central incisor, Model 2 with loading on the pontic of the lateral incisor and Model 3 with loading only on the canine. The results were as follows. (1) Models 1 and 3 showed stress concentration directly under the loading point, where the compressive stress was 610 kgf/cm2 in Model 1 and 610 kgf/cm2 in Model 3. (2) Model 1 showed distribution of stress of 30-80 kgf/cm2 at the metal-enamel junction of the canine, while in Model 3 the stress of 80-150 kgf/cm2 was distributed at the metal-enamel junction of the central incisor. Loading only on the canine produced higher levels and broader distribution of stress than loading only on the central incisor. (3) Model 2 showed distribution of stress of about 60 kgf/cm2 at the metal-enamel junction of the central incisor and canine. Extremely intense stress, 250 kgf/cm2, was noted in the canine slice contiguous to the pontic. Stress as high as 70 kgf/cm2 was also observed in the central incisor slice contiguous to the pontic. (4) The maximum shearing stress values were 305 kgf/cm2 in Model 1 and 325 kgf/cm2 in Model 3 at the sites directly under the loading point, showing similarly high levels. (5) A comparative investigation of the maximum shearing stress appearing at the metal-enamel junction among the models showed that the distributed maximum shearing stress in Model 3 was about twice that in Model 1. (6) Model 2 had the maximum shearing stress, which was located toward the pontic in the canine, with an intensity closed to the shearing strength of currently available adhesive resin cement, suggesting a high risk of desquamation at this site.