3-D IN-VIVO FORCE MEASUREMENTS ON MANDIBULAR IMPLANTS SUPPORTING OVERDENTURES - A COMPARATIVE-STUDY

Force transmission onto implants supporting overdentures was measured in vivo by means of piezoelectric transducers that allow for simultane ous force registrations in 3 dimensions. The transducers are directly mounted onto the implants, beneath the anchorage device. The force reg istrations were analyzed with regard to the anchorage device and reten tion mechanism of overdenture support. The 3 types of denture anchorag e were a U-shaped bar, a round clip-bar and single telescopes. Forces were measured in the following test situations: maximum force when bit ing in centric occlusion, maximum bite force during biting on a bite p late, grinding and chewing bread. Multiple regression showed that the vertical component of maximum forces was dependent on the anchorage de vice and test situation. The transverse components reached 10 to 50% o f the vertical force magnitude. With the bite plate in situ maximum fo rces measured in vertical direction were significantly higher on the i psilateral implant with telescopes than with bars (p<0.01 and p<0.001) . Chewing and grinding resulted in lower vertical forces compared to m aximum biting. In transverse dimensions, mainly in the anterior-poster ior direction, registered forces reached magnitudes that resembled the vertical component (50 to 100%). Force magnitudes of chewing and grin ding were similar for all three anchorage devices. However, difference s were observed between bars and telescopes with regard to the directi on of transverse force components. The results of this study do not su ggest the preference of one specific anchorage system or retention mec hanism for overdenture support. However, rigid bars contribute to load sharing and stress distribution onto the implants.