- 上一篇：java对象的介绍英文文献和中文翻译
- 下一篇：铝合金结构特性英文文献和中文翻译
1370 0.3 Barbier et al.24Overdenture 4500 0.35 Brunski et al.25Mucosa 1 0.37 Menicucci et al.26Nylon 28.3 0.4 Manufacture 3.3. Pressure on the mucosa and the contact area betweenthe denture and the mucosaTables 5 and 6 show the maximum pressure on the mucosaand the contact area between the denture and mucosarespectively. Under all three loading conditions, the maxi-mum pressure on the mucosa in model B was higher than inthe other models, especially under VI. The peak pressure inmodel B was observed under VI; it was approximately twotimes as high as in the other three models, and wasconcentrated between the labial side of the anterior alveolarridge and the denture.Under VM and IM, the contact area between the dentureand mucosa was larger than that under VI. Under VM, thecontact area between the denture and mucosa in model A wasabout 75% of the area in the other models. Under VI, thecontact between the denture and mucosa mainly took place onthe labial side of the anterior alveolar ridge for models B–D,whereas for model A it was concentrated on the left side of thewhole alveolar ridge (Fig. 6). The contact area in model A was about three times as large as in the other three models underVI. This illustrates that, when functioning with the anteriorteeth, the single-implant-retained overdenture rotated overthe implant from one side to the other.4. DiscussionThe FE models used in the present study allows representationof a more detailed and complex geometry. However, theinherent limitations of the FEA with regards to straindistribution should always be taken into consideration.22,23The models used deviated in many aspects from a clinicalsituation. The structures in the models were all assumed to behomogeneous, isotropic and linearly elastic. However, it iswell documented that the cortical bone of the jaw istransversely isotropic and inhomogeneous. In addition, a100% implant/bone interface was established, which does notmatch clinical situations. Thus, the results of FEA of a problemlike this should be interpreted with some care. The absolutevalues of the different strains obtained in this study are ofminor interest. What are of interest are the relative values ofthe different strains for the different implant overdenturedesigns. Therefore, the results we obtained should beconsidered as a reference to choose between different over-denture designs in the clinical treatment. Prospective clinicalstudies are required to verify the results.In previous studies, the interface between the denture andthe mucosa was assumed to be fixed to facilitate modellingand calculations.28,29However, our study assumed that slidingfriction existed between the denture and the mucosa. Ourmodel of overdenture could therefore rotate and slide on themucosa in various directions when functioning and so couldmore accurately simulate actual denture movement in dailyuse. In addition, we assumed in the present study that, withregard to posterior loads, the opposite side would show thesame mechanical behaviour as the loaded side.The results from our study indicated that in all models,maximum equivalent strains in peri-implant bone under allthree loading conditions were below 2500 me, and weretherefore lower than the physiological tolerance thresholdof bone.21This findings agrees with previous clinical studiesthat showed no significant difference in peri-implant boneresorption between single-, two- and four-implant-retained/supported overdentures, indicating that the strain in the bonearound implants was within the physiological threshold,having little effect on the implant survival rate.11,16,30Clinicians anticipated that with an increase in implantnumber, the maximum strain value in peri-implant bonewould decrease and the strain in the bone would be morewidely distributed. This was based on the assumption thatwhen adding more implants for anchorage and support, theforce borne by each implant would decrease, resulting in adecrease of strain in the bone. Nevertheless, according to ourresults, the peak strain value in peri-implant bone increasedwith the increase in number of implants in models A, C and Dunder three loading conditions. This can be explained by theincrease in the supporting effect of the implants. In the single-implant overdenture, most of the force was loaded on themucosal area. With increased implant numbers, more of thechewing force was shared by the implants while less wasborne by the mucosa, resulting in the increased peak strainvalues in cortical bone around the implants. This is also thereason why single- and two-implant overdentures are called‘‘implant-retained overdentures’’, while overdentures on fourimplants are called ‘‘implant-supported overdentures’’.Our study showed that under VI, which simulated theaction of cutting food with the anterior teeth, the maximumstress value in the abutments in model B was three timeshigher than in the other three models, suggesting that possibledamage to the abutments might happen more easily in two-implant overdentures than single, three and four-implantoverdentures. Kimoto et al. also reported rotational movementaround the fulcrum li