[Effect of ball attachments with different materials on retention of mandibular implant supported overdenture].

PURPOSE: To investigate the effect of ball attachments with different materials on retention of mandibular implant supported overdenture. METHODS: The experimental groups were divided into group A (titanium ball / titanium cap group) and group B (titanium ball / golden cap group), each group had 3 samples. A standard mandibular edentulous model was made, and the implants (4.8*10 RN SP) were embedded in the bilateral canine region. Mandibular complete dentures were made routinely and the attachments were attached. Five thousand times of insertion-separation cycles were carried out. After 200 times of cycles, the retention force was tested. The difference between 2 groups was compared by using SPSS 13.0 software package. The change of positive structure surface morphology was observed under scanning electron microscope at the beginning and the end of the experiment. RESULTS: The retention force of group A decreased from （27.00+/-0.16） N to （4.18+/-0.03） N, and the retention force of group B decreased from （21.58+/-0.06） N to （19.15+/-0.06）N. Decay of retention of group A was significantly greater than that of group B. At the end of the experiment, the globular structure of group A was severely broken, while a smooth and clear spherical structure was displayed in group B. CONCLUSIONS: The retention of mandibular implant supported overdenture decreases with the increase of insertion-separation times. The decay of retention force is related to destruction of positive structure surface. The fatigue resistance of the precious metal material is better.