There have been many reports showing the usefulness of CT examinations for preoperative dental implant treatment, and some reports on clinical statistics using CT examinations. However, there have been few reports on alveolar bone height and width of over 1,000 Japanese cases.
The purpose of this study was to evaluate alveolar bone height and width of 4,123 sites in 1,056 Japanese cases using preoperative CT examinations.
The subjects consisted of 4,123 regions in 1,056 cases (370 males and 686 females, mean age 56.1 years old, range 15-87) of preoperative CT examinations conducted from January 2008 to March 2009. The CT examinations were performed using the Aquilion^TM64 (Toshiba Medical Systems Corporation) as the MDCT unit, and ZIOSTATION (ZIOSOFT) as the workstation. The CT images were displayed on the workstation, and the alveolar bone height and width were measured to one decimal place (rounded off to two decimal places).
The average alveolar bone height was 14.8 mm (SD ± 3.8) in the upper anterior area, 11.2 mm (SD ± 5.5) in the upper premolar area, 6.8 mm (SD ± 5.4) in the upper molar area, 19.5 mm (SD ± 5.4) in the lower anterior area, 14.2 mm (SD ± 3.9) in the lower premolar area, and 13.4 mm (SD ± 3.4) in the lower molar area.
The average alveolar bone width was 4.3 mm (SD ± 1.9) in the anterior area, 5.7 mm (SD ± 2.3) in the upper premolar area, 7.9 mm (SD ± 3.1) in the upper molar area, 4.8 mm (SD ± 2.1) in the lower anterior area, 5.9 mm (SD ± 2.2) in the lower premolar area, and 6.9 mm (SD ± 2.5) in the lower molar area.
Our results using preoperative CT examinations indicated that many of the Japanese cases had insufficient alveolar bone height and width for dental implants.

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Objectives: Proper amount of stress produced by mastication around dental implants is an important factor to ensure their long-term stability. 3D-finite element analysis (FEA) is an effective tool for analyzing the distribution of stress in and around dental implants. Recent advances in CT technology have made it possible to create 3D-FEA models directly from CT data, but these models do not precisely reproduce the implant-bone interface contact. This study compared the displacement of implants under pressure in experimental models with those of a 3D-FEA model created using only CT data and 3D-FEA models which reflected implant-bone interface contact.
Methods: Five experimental models were manufactured, consisting of dummy jaw bones with inserted implants. These models were scanned using a micro CT, and three types of FEA model were created using an FEA software program (Mechanical Finder^®): FEA model A with the implant in full contact with the dummy jaw bone; FEA model B with a hollow under the tip of the implant; and FEA model C with the implant in partial contact with the dummy jaw bone. The displacement of implants under pressure in the experimental models was measured by applying a vertical pressure of 200 N. Three FEA models were also analyzed under the same conditions, comparing the experimental models and the FEA models for the displacement of implants under pressure.
Results:
1. A significant difference (p<0.01) was observed between the experimental model (35.7 ± 2.0 μm) and FEA model A (27.4 ± 2.4 μm), but not with FEA models B (34.9 ± 3.4 μm) and C (38.5 ± 3.8 μm).
2. The stress was concentrated in the cancellous bone of the implant bottom in FEA model A, but was concentrated in the cortical bone of the implant in FEA models B and C.
Discussion and Conclusions: It seems possible to create a 3D-FEA model that precisely reproduces the displacement of an implant under pressure, if the implant-bone interface contact is correctly reflected.

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Purpose: Long-term implant patients often experience loose or fractured prosthetic screws. Our previous study using geometric analysis clarified the effects of occlusal load on prosthetic screws. However, the values obtained from geometric analysis are theoretical. For this study, implant superstructures were manufactured and the maximum loading at which the prosthetic screw actually fractured was measured to examine the correlation with the geometric analyses made in our previous study.
Method: The theoretical maximum loading was obtained using the formula and fracture resistance (1,104 ±10 N) of the prosthetic screws obtained in our previous study. To obtain the actual maximum loading, five superstructures were manufactured on an abutment replica using a CAD/CAM system, and tested with a universal testing machine at a crosshead speed of 1.0 mm/sec. The theoretical value was compared with the actual values from those tests.
Results: The actual maximum loading (236±10 N on average) was significantly lower (p＜0.01) than the theoretical maximum loading (271±4 N on average) obtained by geometric analysis. While each specimen is under load, the platform's outermost part, which serves as the pivot point of rotation, undergoes a displacement of 0.15 mm due to the deformed edge of the superstructure. The theoretical value (250±3 N) obtained by taking into account the displacement of the pivot point was not significantly different from the actual value (p＞0.01) .
Conclusion: It is suggested that when determining the maximum loading of prosthetic screws using geometric analysis, it is necessary to consider the displacement of the pivot point of rotation, which will also make the geometric analysis more relevant.

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