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Residual alveolar ridge resorption often occurs after tooth extraction, which causes issues requiring further prothesis rehabilitation. A treatment concept referred to as all-on-four, involving fixed dentures supported with four implants, was recently developed. The current study aimed to determine the effect of changing bone atrophy and implant length in all-on-four treatments on stress and strain in the surrounding bone of the implant. A three-dimensional finite element method was used in this research. The stress analysis was conducted with von Mises stress values. Two types of synthetic jawbone models with mild and moderate atrophy were used. Furthermore, two different implant lengths with a similar implant design and diameter were selected, and they were classified into eight models. Then, the bone model was assessed via a computed tomography (CT) scan and was transformed into a virtual model in Geomagic and SolidWorks with implant rebuilding. After modifying bone atrophy, the von Mises stresses in the surrounding bone of the implant were as follows: mild type 2 < mild type 3 < moderate type 3 < moderate type 4. The bone quantity change rate increased more than when bone conditions were limited. Compared with changes in implant lengths, the stresses in the peri-implant surrounding bone were generally higher in the 9 mm implant length group than in the 11.5 mm group. However, the results did not significantly differ. In conclusion, the von Mises stress and strain increased in the models with moderate atrophy and low-density trabecular bone. Hence, bone atrophy and its presurgical diagnosis in long-term implant prognosis are crucial. [ABSTRACT FROM AUTHOR]

Background/purpose: Impact of the implant shape on the biomechanical performance of all-on-four treatment of dental implant is still unclear. This study evaluated the all-on-four treatment with four osseointegrated implants in terms of the biomechanical effects of implant design and loading position on the implant and surrounding bone by using both in vitro strain gauge tests and three-dimensional (3D) finite element (FE) analyses.Methods: Both in vitro and 3D FE models were constructed with placing NobelSpeedy and NobelActive implants as well as a titanium framework in an edentulous jawbone based on the concept of all-on-four treatment. Three types of loads were applied: at the central incisor area (loading position 1) and at the molar regions with (loading position 2) and without (loading position 3) the denture cantilever. For the in vitro tests, the principal bone strains were recorded by rosette strain gauges and statistically evaluated using Wilcoxon's rank-sum test. The 3D FE simulations analyzed the peak von-Mises stresses in the implant and surrounding cortical bone.Results: The peak stress and strain in the surrounding bone were typically 36-62% (3D FE analysis) and 47-57% (in vitro test) (p < 0.001)higher for loading position 3 than for loading positions 1 and 2. Between those two implant designs, the bone strains and bone stresses did not differ significantly.Conclusion: For all-on-four treatment with four osseointegrated dental implants, altering the implant design does not appear to affect the biomechanical performance of the entire treatment, especially in terms of the stresses and strains in the surrounding bone. [ABSTRACT FROM AUTHOR]