| Background:Previously, the choice of prosthetic implant retained overdenture has depended on data from previous studies about the retention fatigue strengthof the attachment system selected and stress distribution and flexing occurred at the bone surrounding the overdenturesupport foundations. Little or no data have been available on the correlation between the attachment system selected and the overdenture support configuration in relation to the previously mentioned parameters.Aims of the study:Is to evaluate the retention fatigue strength, stress distributions and alveolar bone flexing of different attachment systems and support designs of overdenture prosthesis.Materials and Methods:Twelve models were included in the study; six main models (A,B,C,D,E and F)were selected according to the support designs of overdenture prosthesis, each model was further divided according to the attachment combinations into model1; Dalbo elliptic and/or O-ring attachments only and model2; with flexible acrylic attachments. Model A contained three overdenture supports:two free standing mini dental implants in the canine region and at the midline, and one simulated tooth root with dalborotex screwed in. Model B contained four overdenture support foundations:two free standing mini dental implants in the right canine region and the first premolar region, and two simulated tooth roots with dalborotex screwed in, at the same mini dental implant position, but on the left side of the model. Model C contained three overdenturesupport foundations:two free standing mini dental implants in the canine region and at the midline, and one simulated tooth root with mini dental implant screwed in. Model D contained four overdenture support foundations: two free standing mini dental implants in the right canine region and the first premolar region, and two simulated tooth roots with mini dental implants screwed in, at the same mini dental implant position, but on the left side of the model. Model E contained three free standing mini dental implants one at the midline and two bilaterally located at the canine regions. Model F contained four free standing mini dental implants bilaterally located at the canine and first premolar regions. Retention force measured only for models A,B,C and D, five samples were prepared for each model and retention force values (N) were recorded initially (0cycles) and after360,720,1440and2880insertion and removal cycles. Stress distributions and flexing were evaluated after applying35N vertical load and17.5N lateral load under static conditions to simulate the occlusal forces following the concept of lingualized occlusion, all conditions were set using the finite element program ANSYS v13.0, maximum von-Mises stressand flexing at the level of the attachments and at the bone support foundation interfaces were compared in all models. Values of absolute force and relative force were statistically analyzed by two-way ANOVA and multiple comparisons Tukey’s tests between models and cycles periods.Results:Retention fatigue strength tests show a50%reduction in retention force in the models with flexible acrylic attachments. A triangular design of overdenture support foundations with O-ring attachments revealed the lowest value of absolute force and a relatively high reduction in relative force. Stress and flexing on all models was analyzed after loading condition; free standing triangular design of mini dental implants and flexible acrylic attachments model revealed the lowest von-Mises stressand flexing in relative comparison to other models.Conclusions:Four overdenture support designs with flexible acrylic attachments improved the retention force and reduced the fatigue retention and flexible acrylic attachments offer a wide range of retention forces. Furthermore, free standing mini dental implants with flexible acrylic attachment systems supporting overdenture reduced stresses and flexing in the supporting alveolar bone. |
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