Photoelastie Stress Analysis Ofvariousretention Meehanisms On Implanted Complete Overdentures

Edentulous is a common disease in oral cavity,caused by dental caries, periodontal disease, trauma, developmental abnormalities, cancer and other factors. Complete dentures is the conventional repair treatment method for edentulous patients, but retention stability of the complete dentures is not satisfactory and less effective.With the development of science and technology, implanted technology plays a important role in the improvement of the denture retention stability.Restoration of edentulous with the implant supported overdentures is a ideal repair method for the edentulous patients, which cost less and has high retention force and simple productive process, the number of the used implants is also fewer.How to properly designs the different attachment structures so that the stress in the supporting tissues around the implants low enough to achieve long-term stable retention is an important clinical problem. Therefore the photoelastic stress analysis was introduced into the present study to compare the stress condition in the supporting tissues around the implants on two-implant supported mandibular complete overdenture applied with ball attachment, magnetic attachment, resilient attachment and bar attachment, with the load force of 100,200,300,400 N was exerted on different parts, to provide experimental evidence for the rational design of the clinical overdenture.The study consisted 4 parts,the first part was the establishment of photoelastic edentulous mandibular model of implanted complete overdentures applied with various attachments; the second part was the photoelastic analysis of the implanted complete overdentures applied with different attachments applied on the unilateral posterior teeth load; the third part was the photoelastic analysis of the implanted complete overdentures applied with different attachments when centric occlusion was occured; the fourth part was the photoelastic analysis of the implanted complete overdentures applied with different attachments When. the anterior teeth were borne load.The results were as followed:1. The epoxy resin mandibular photoelastic models with implants were made, the two-plant-supported mandibular complete overdentures were established according to the procedures of clinical practice. Geometric and mechanical similarity which was between model and clinical practice denture were ensured. Photoelastic model has high transparency and no initial stress, provided a good experimental basis for the stress experiment.2. As shown in the stress fringe pattern, the stress mostly concentrated in the apical part in the implant, no matter which part bore load.3. Under the same attachment condition, as the load increased stress in the supporting structure around the implants increased as well.4. When applied on the unilateral posterior teeth load, under the same load force, ball attachment showed the least stress in the supporting structure around the implants compared with others, by contrast the bar attachment showed the highest stress,while the magnetic attachment showed less stress than resilient attachment.5. when the middle of the whole dentition bore load, under the same load force, ball attachment showed the lowest stress in the supporting structure around the implants compared with others, by contrast the bar attachment showed the highest while the resilient attachment showed less stress than magnetic attachment.6. when the little forces was loaded on the anterior teeth, under the same load force, ball attachment showed the lowest stress in the supporting structure around the implants compared with others, by contrast the bar attachment showed the highest while the resilient attachment showed less stress than magnetic attachment.; when the load force was greater than 200N, ball attachment showed the least stress in the supporting structure around the implants compared with others, by contrast the bar attachment showed the highest stress,while the magnetic attachment showed less stress than resilient attachment.The results indicated that:stress in supporting structure around implants of 4 attachments was different when occlusion was occurred on centric teeth, unilateral posterior teeth and anterior teeth in implanted overdentures, ball attachment which transmited the lowest stress was conducive to the health of tissue around the implanted alveolar bone. Ball attachment is a advisable clinical choice which had the features such as small volume, simple structure, low cost, easy oral hygiene maintaining, good retention and fine stress dispersion and so on.