A modal analysis of a splinted and a NO-splinted superstructure on the three-ranged dental implants placed in a mandibular free end model

1HOK3 ePOSTER BASIC RESEARCH

Background: Prosthetic design of the superstructures, splinted or NO-splinted, are not an easy step because success of dental implant treatments and their prognosis may in part be associated to prosthetic vibration which affects the implant surrounding tissues. In this study, the vibration characteristics of implant superstructures on the mandible are clarified by modal analysis, it may be possible to select the design of the implant superstructure according to each patient.

Aim/Hypothesis: The aim of this study is to evaluate the effect of two types of superstructures (splinted crowns or NO-splinted crowns) fabricated on three-ranged implants placed in a mandibular free end distal extension missing tooth model on four vibration parameters by modal analysis.

Materials and Methods: Three implants were placed in a mandibular distal extension missing tooth model, splinted or NO-splinted crowns were designed on CAD software, and a zirconia disc was milled with a milling maCHINA to produce the superstructures (n = 5). After setting four measurement points on each crown of the prostheses, vibration was applied to center of the mandibular right central incisor with an impact hammer, and the transfer function of each measurement point was detected. Using modal analysis software, natural frequency and damping ratio (DAR) were calculated from the transfer function, the number of vectors in antiphase was counted from the observed mode shape, and the maximum displacement (MDP) assuming the lateral force during mastication was simulated. T-test was performed for the averaged values of natural frequency, MDP and DAR (P < 0.05). Mann-Whitney U test was performed on the average of the number of vectors in antiphase (P < 0.05).

Results: Eight or more natural frequencies were obtained in both the splinted crowns and the NO-splinted crowns between the frequencies of 0 and 2 kHz. Natural frequency was significantly higher in the splinted crowns (758.2 Hz) than in the NO-splinted crowns (752.8 Hz) (P = 0.047). DAR in the splinted crowns (3.32%) was not significantly different from that in the NO-splinted crowns (3.19%) (P = 0.535). The number of vectors in antiphase was significantly smaller in the NO-splinted crown (4.4) than in the splinted crown (10) (P = 0.008). MDP was significantly smaller in the splinted crowns (6.68 micro meter) than in the NO-splinted crown (7.25 micro meter) (P = 0.048).

Conclusions and Clinical Implications: The vibration characteristics of the superstructures differed between designs with splinted and NO-splinted crowns. The splinted crowns increased their rigidity and natural frequency, and decreased the MDP. However, increase in the number of vectors in antiphase twists the superstructures in general. Therefore, our results suggest that splinting crowns has less effect on deformation of the superstructure, the implants and the surrounding tissues than no splinting.

Acknowledgements: The authors express many thanks to Mr. Satoru Fujikawa, a dental technician of E-joint laboratory for fabrication of implant superstructures, and Dr. Tamaki Hada, RDT, MS for statistical analysis.

Keywords: Modal analysis, Implant prostheses, Vibrational characteristics, Natural frequency, mandibular free end