Modal analysis of two different types of fixed implant-supported prostheses embedded in edentulous maxillae.

PURPOSE: Modal analysis has been used to monitor and quantify the vibration of each component of a prosthesis at its natural frequency. An understanding of the vibrational characteristics of a prosthesis can guide selection of the appropriate prosthesis configuration to prevent excessive stress. In this study, modal analysis of fixed implant-supported prostheses with 4 or 6 abutments in edentulous maxillae was performed. METHODS: Sixteen patients underwent maxillary dental implant treatment and received screw-fixed implant-supported prostheses (9 patients received 4-abutment prostheses and 7 patients received 6-abutment prostheses) in edentulous maxillae. An impact hammer was used for excitation of the prostheses, and vibration was detected on every crown of the prostheses. The modal parameters were determined in each subject. Furthermore, the modal shapes were compared at each natural frequency. RESULTS: The median natural frequencies of subjects with 4- and 6-abutment prostheses were 697 and 781Hz, respectively. The mean damping ratios did not differ significantly between 4- (8.2±1.7%) and 6-abutment (6.6±1.7%) prostheses (p=0.125). The mean maximum displacements of fixed prostheses were significantly lower for 6-abutment (10.3±3.3µm) than for 4- (20.3±9.1µm) prostheses (p=0.004). The median number of vectors in antiphase was significantly lower for 6- (4) than for 4-abutment prostheses (14) (p=0.001). CONCLUSIONS: The current study demonstrated less adverse vibration in the 6-abutment prostheses than in the 4-abutment prostheses, suggesting that modal analysis can contribute to novel future developments in the designs of dental implant prostheses.

Vibratory properties of maxillary dentition in maxillectomy patients wearing metal framework obturator prostheses with three different metal materials.

PURPOSE: The purpose of this study was to evaluate the vibratory properties of maxillary dentition in maxillectomy patients wearing metal framework obturator prostheses with three different material types of metal frameworks and to determine the optimal type by applying in vivo modal analysis. METHODS: The three metal framework obturator prostheses using gold alloy, cobalt-chromium alloy and titanium alloy were fabricated for four maxillectomy patients, whose shapes were almost the same for each patient. All patients were classified into Aramany's Class II. The transfer functions of the maxillary dentition with and without obturator prostheses were measured to obtain the natural frequency, modal shape and damping ratio. A forced response simulation was carried out, in which an impact assuming occlusal force was applied to the lateral segment teeth on the non-defect side, and the maximum displacements of the measurement points were calculated. RESULTS: As for the natural frequency, wearing the obturator prostheses caused reduction of the natural frequency of the maxillary dentition. The modal shapes of titanium alloy obturator prostheses showed the strongest splint-like effect and were concluded to be the most preferable. The damping ratio of titanium alloy obturator prostheses was significantly higher than cobalt-chromium obturator prostheses. The maximum displacement of gold alloy obturator prostheses was significantly the highest of all. CONCLUSION: From the viewpoint of preserving abutments and remaining teeth, we conclude that titanium alloy is a more preferable material than gold alloy and cobalt-chromium alloy for the metal frameworks of metal framework obturator prostheses.