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 simultaneous force registrations in 3 dimensions. The transducers are directly mounted onto the implants, beneath the anchorage device. The force registrations were analyzed with regard to the anchorage device and retention mechanism of overdenture support. The 3 types of denture anchorage were a U-shaped bar, a round clip-bar and single telescopes. Forces were measured in the following test situations: maximum force when biting in centric occlusion, maximum bite force during biting on a bite plate, grinding and chewing bread. Multiple regression showed that the vertical component of maximum forces was dependent on the anchorage device and test situation. The transverse components reached 10 to 50% of the vertical force magnitude. With the bite plate in situ maximum forces measured in vertical direction were significantly higher on the ipsilateral implant with telescopes than with bars (p<0.01 and p<0.001). Chewing and grinding resulted in lower vertical forces compared to maximum biting. In transverse dimensions, mainly in the anterior-posterior direction, registered forces reached magnitudes that resembled the vertical component (50 to 100%). Force magnitudes of chewing and grinding were similar for all three anchorage devices. However, differences were observed between bars and telescopes with regard to the direction of transverse force components. The results of this study do not suggest the preference of one specific anchorage system or retention mechanism for overdenture support. However, rigid bars contribute to load sharing and stress distribution onto the implants.