Objectives： A limited cone-beam X-ray CT (3DX multi-image micro CT；3DX-FPD) is widely used in dentistry because it provides a lower cost, smaller size, and higher spatial resolution than a CT for medicine. Our recent research suggested that the patient dose of 3DX-FPD was less than 7/10 of that of CT, and it was several to 10 times more than that of dental or panoramic radiography.
The purpose of this study was to evaluate the spatial dose distribution from 3DX-FPD and to estimate the influence of dose by positioning of the region of interest.
Methods： Dosimetry of the organs and the tissues was performed using an anthropomorphic Alderson Rando phantom and X-ray films for measurement of radiotherapeutic dose. Measurements of dose distribution were performed using a cylinder-type tank of water made of acrylic resin imitating the head and X-ray films.
Results： The results are summarized as follows：
1. The dose was higher as the ratio of the air region included in the region of interest increased.
2. The dose distribution was not homogeneous and the dose was highest in the skin region.
3. The dose was higher for several seconds after the beginning of exposure.
Conclusions： It was concluded that patient positioning, as well as exposure conditions including the size of the exposure field and tube current, could greatly influence the patient dose in 3DX-FPD. In addition, it is necessary to consider the influence of image quality for the treatment of dental implants.
To investigate the effects on bone formation of differences in surface topography of titanium plates, circular titanium plates (diameter of 6.0 mm) were manufactured with a groove of 30 μm or 120 μm depth semilaterally on the machined surface, or with no groove as the control machined surface. We then embedded the plates in parietal bone defects of rats, and compared the histology of the central and peripheral areas of neonatal bone growth formed on the plate surfaces. Quantitative analysis was performed using a stereoscopic microscope, using Alizarin Red S to digitize the concentrations of unstained and stained portions. The comparative results of the surface area of neonatal bone per unit area of each measurement region led to the following conclusions.
1. The grooved surfaces showed a significantly higher amount of neonatal bone formation than the control surface.
2. There was no significant difference in neonatal bone formation between the 30 μm and 120 μm grooved surfaces.
3. There was no significant difference in neonatal bone formation between the peripheral areas of the grooved surface and control surface.
4. There was a highly significant difference in neonatal bone formation between the central areas of the grooved surface and control surface.
5. In the peripheral and central areas of the grooved surface, neonatal bone formation showed a high, positive correlation of R2=0.62
These conclusions indicate that a titanium plate with a groove on one side can act as a beneficial scaffold for neonatal bone formation.
It is important to know whether the generated bone from guided bone regeneration (GBR) treatment can be stabilized and keep its shape or whether it will change after it is made to function for the implant treatment, because it can affect the prognosis after the implant treatment.
The purpose of this study was to periodically analyze and assess the change in the shape of bone that was generated by GBR treatment.
In our method, we produced study models with the same patient, which were immediately before and after the GBR and also after three years had passed. The elapsed time for the study models after the GBR was about four months on average. We analyzed the study models for each period. When given the GBR treatment, the bones are enlarged horizontally. Therefore, the forms of the parts to which the GBR treatments were given in the study models expand horizontally. By applying trigonometric functions to these dilated forms, we represented them as GBR angles, and compared and examined them statistically by the increase or decrease in GBR angles.
The results were as follows:
(1) Four months after the GBR, the average increase of GBR angles was 80.3% in the upper jaw,49.8% in the lower jaw, and 57.8% in the upper and lower jaws. Three years after the root form implant was installed, decrease of GBR angles or absorption of the bones was observed, compared with four months after the GBR treatment.
On the other hand, compared with the condition before the GBR treatment, the increase of GBR angles was 31.7% in the upper jaw, 32.2% in the lower jaw, and 32.0% in the upper and lower jaws.
With this measuring method some conditions are modified by the thickness of mucous membranes, etc., because the form of the inner bones is predicted from the gum surfaces; however, it is suggested that by setting up exception criteria, this analytical method can be adjusted and is an effective assessment method after GBR treatment.