Abutment-to-fixture load transfer and peri-implant bone stress.

PURPOSE: To uncover design principles for the abutment-fixture complex that reduce the stress concentration on the bone. METHODS: A 3-dimensional finite element model was used to vary shape, elasticity, and connectivity of the abutment-fixture complex. We compared peri-implant bone stress of these designs. RESULTS: Peri-implant bone stress was increased when the abutment could slide frictionless along the rim of the fixture, allowing the abutment to "lean into" the fixture rim and transfer loads near the bone crest. Conversely, bone stress was reduced when no motion was allowed (or no contact was made at all) between the abutment and the fixture rim. Bone stress was also reduced when the fixture was stiffer and thus more resistant to deformation, or when the fixture was wider.

Osteocyte morphology and orientation in relation to strain in the jaw bone.

Bone mass is important for dental implant success and is regulated by mechanoresponsive osteocytes. We aimed to investigate the relationship between the levels and orientation of tensile strain and morphology and orientation of osteocytes at different dental implant positions in the maxillary bone. Bone biopsies were retrieved from eight patients who underwent maxillary sinus-floor elevation with ß-tricalcium phosphate prior to implant placement. Gap versus free-ending locations were compared using 1) a three-dimensional finite-element model of the maxilla to predict the tensile strain magnitude and direction and 2) histology and histomorphometric analyses. The finite-element model predicted larger, differently directed tensile strains in the gap versus free-ending locations. The mean percentage of mineralised residual native-tissue volume, osteocyte number (mean ± standard deviations: 97 ± 40/region-of-interest), and osteocyte shape (~90% elongated, ~10% round) were similar for both locations. However, the osteocyte surface area was 1.5-times larger in the gap than in the free-ending locations, and the elongated osteocytes in these locations were more cranially caudally oriented. In conclusion, significant differences in the osteocyte surface area and orientation seem to exist locally in the maxillary bone, which may be related to the tensile strain magnitude and orientation. This might reflect local differences in the osteocyte mechanosensitivity and bone quality, suggesting differences in dental implant success based on the location in the maxilla.