Correlation of mandibular impacted tooth and bone morphology determined by cone beam computed topography on a premise of third molar operation.

PURPOSE: To determine the width and morphology of the mandible in the impacted third molar region, and to identify the location of the mandibular canal prior to planning impacted third molar operations. METHODS: Cone beam computed tomography (CBCT) data of 87 mandibular third molars from 62 Japanese patients were analyzed in this study. The width of the lingual cortical bone and apex-canal distance were measured from cross-sectional images in which the cortical bone was thinnest at the lingual side in the third molar region. Images were used for measuring the space (distance between the inner border of the lingual cortical bone and outer surface of the third molar root), apex-canal distance (distance from the root of the third molar tooth to the superior border of the inferior alveolar canal) and the cortical bone (width between the inner and outer borders of the lingual cortical bone). RESULTS: The means of the space, apex-canal distance and lingual cortical width were 0.31, 1.99, and 0.68 mm, respectively. Impacted third molar teeth (types A-C) were observed at the following frequencies: type A (angular) 37 %; type B (horizontal), 42 %; type C (vertical), 21 %. The morphology of the mandible at the third molar region (types D-F) was observed as: type D (round), 49 %; type E (lingual extended), 18 %; and type F (lingual concave), 32 %. CONCLUSIONS: The width and morphology of the mandible with impacted teeth and the location of the mandibular canal at the third molar region could be clearly determined using cross-sectional CBCT images.

Analyzing the eye movement of dentists during their reading of CT images.

In order to evaluate the eye movements of dentists when they were interpreting radiographs, ten normal computed tomography (CT) images and ten images with pathologic lesions were shown to eight dentists, and the pattern of their eye movement was qualitatively analyzed. Six fixation point parameters were calculated, including the time required to discriminate between normal and pathologic images (X(1)), the total fixation point count (X(2)), the total travel distance between fixation points (X(3)), the average time spent on each fixation point (X(4)), the total gaze fixation time (X(5)), and the maximum gaze fixation time spent on each image (X(6)). When the subjects were interpreting pathologic images, X(2) and X(4) were shorter; however, when they were viewing normal images, time was spent on observing multiple fixation points before the completion of the interpretive process. While pathologic images were recognized through top-down processing, there was a tendency for normal images to be recognized through bottom-up processing. The results of discriminant analysis, using a linear discriminant function, indicated that the independent variables X(2) and X(4) and the dependent variable X(5) were the only variables that contributed significantly to differentiating between normal and pathologic images. The linear discriminant function was Z = 9.0 x 10(-2) x X(2) + 3.0 x X(4) - 2.1 (discriminant score: Z < 0, pathologic image; Z > or = 0, normal image). When the mean value of each individual's gaze fixation data was substituted into the discriminant formula, the hit rate for normal and pathologic images was discriminated at 94% (15 of 16).

Osseointegration in implant-embedded mandible in rats fed calcium-deficient diet: a radiological study.

OBJECTIVE: The purpose of the present study was to investigate osseointegration using radiographs of titanium (Ti) implants into the osteoporotic mandible of rats. MATERIALS AND METHODS: Rats were divided into three groups: first group, which were fed a standard diet throughout (control group), second group which were fed a Ca-deficient diet for only 1 week before implantation (group A), and those which were fed the Ca-deficient diet before and after implantation (group B). On the 7th and 42nd days after implantation, bone changes in those rats were examined by microradiographs and autoradiographs. RESULTS: On the 7th day after implantation, calcification of newly formed bones was lower in groups A and B than in the control group, 45Ca uptake was seen in surrounding bones adjacent to the implant, as well as throughout the mandible. On the 42nd day after implantation, trabecular bone in group A showed radiopacity as seen in the control group. In the alveolar crest and peri-implanted bones in group B, thin bone formation with active 45Ca incorporation was found. CONCLUSIONS: It is suggested that irrespective of the calcium deficiency status in rats, trabecular bones around the implant are restored to a healthy state to some extent by resuming an intake of a necessary amount of dietary calcium. In continued calcium deficiency, osseointegration with the implant and alveolar bone was still observed as in the healthy rats suggesting calcium deficiency is not always a factor to regulate osseointegration of mandibular endosseous implants.

[Analysis of carbapenem resistant plasmid isolated from Serratia marcescens].

Four nontransferable plasmids of about 28-32 kbp were isolated in 120 Serratia marcescens strains isolated from patients with urinary tract infection. All of these plasmids were tranformable in Escherichia coli, and showed a high frequency of mobilization by R9-5 plasmid of incompatibility group F II. The MICs of carbapenems were significantly lower than those of cephalosporins. This trend was more marked when MICs were determined at 10(6)cfu/ml. Based on the substrate profiles and on the effect of inhibitors of the beta-lactamase, the enzyme was classified as a class B beta-lactamase, so called carbapenemase. The carbapenem resistance genes of these 4 plasmids were cloned into vector plasmid pHSG398 using Bam H1 digestion and the size of the DNA was found to be 4.9 kb.

[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)

The appearance of mental foramina on panoramic and periapical radiographs. II. Experimental evaluation.

The image of the mental foramen was studied on panoramic and periapical radiographs taken on four dry skulls with a variety of vertical and horizontal angulations, skull positions, and exposure times. It was found that any change in exposure conditions affected both the type of appearance (continuous, separated, diffuse, or unidentified) and the relative vertical position of the foramen. The radiographic position agreed with the actual position less than half the time regardless of technique, although the apparent diameter of the foramen was close to the true diameter.

The appearance of mental foramina on panoramic radiographs. I. Evaluation of patients.

The appearance of the mental foramen on panoramic radiographs can be classified as a continuous, separated, diffuse, or unidentified type. In a sample of 297 patients, the most frequent appearance was separated (43%), followed by diffuse (24%), continuous (21%), and unidentified (12%). There were no significant differences in foramen diameter or relative vertical position within foramen types or developmental stages of the dentition. It is strongly suspected that sometimes the radiographic landmark presumed to be the mental foramen may actually be the reappearance of the mental canal.