In vivo force measurements on maxillary implants supporting a fixed prosthesis or an overdenture: A pilot study

Statement of problem. In this preliminary study an attempt was made to meas ure in vivo forces simultaneously on 5 maxillary implants with different ty pes of superstructure. Material and methods. Force measurements were carried out on 1 test patient with 5 ITI implants in the edentulous maxilla. A screw-retained fixed comp lete denture and an overdenture were fabricated for comparative measurement s of forces. The overdenture could be mounted to 2 different types of bars. The measuring method was used with piezo-electric force transducers that w ere directly mounted onto the implants. This allowed for simultaneous measu rements of forces in 3 dimensions, ie, in axial and transverse directions. Static and functional forces such as maximum biting (clenching), biting on a bite plate, and chewing food were registered. All measurements were repea ted in the same way 2 years later. Results. The registered forces exhibited similar force patterns with both t ypes of superstructure and both types of bars for overdenture connection. T he force magnitudes were significantly different for the 3 dimensions (P<.0 5) with highest forces along the implant axis. On the posterior implants, f orce magnitudes were significantly higher (P<.05) than on the anterior impl ants in all 3 dimensions. On the anterior implants, under some test conditi ons, the transverse force components reached up to 100% of the axial force or even exceeded it during the chewing of food. During maximum biting, no u pward force (tensile force) was found on any implant with the fixed complet e denture, but upward force was found on one anterior implant with the over denture. When chewing food, small force magnitudes in upward directions wer e regularly found with both superstructures. The force patterns between the first and second registrations showed similar trends, and no obvious diffe rences were found. Conclusion. From these results it was concluded that similar patterns of fo rce transmission onto the implants are observed with a fixed complete dentu re and an overdenture connected to maxillary implants. The bar design did n ot significantly influence the force pattern.