Stress Analysis Of The Bi-layered All-ceramic Crown With A Numerical Approach

Objective: Using finite element method analysis of two-tier structure decorated with porcelain occlusal thickness and the thickness of the core porcelain occlusal zirconia all-ceramic crowns internal stress distribution, and provide a theoretical basis for clinical production of all-ceramic crowns, thereby enhancing the use of prosthesislife expectancy.Methods:Maxillary first molar zirconia all-ceramic crowns dimensional finite element model, set the double-layer crown decorated with porcelain occlusal thickness (V) and core porcelain occlusal surface thickness (C), divided into the following seven groups (in mm):V=1.7C=0.3;V=1.5, C=0.5;V=1.3, C=0.7;V=1.1, C=0.9;V=0.9;C=1.1; V=0.7;C=1.3;V=0, C=2. Set the all-ceramic crowns, the maximum principal stress (S1) peak stress observed. Five kinds of loading mode on the all-ceramic crowns. Observed two factors that change the size of the all-ceramic crown ceramic layer and the interface stress.Results:1. With the increase of the thickness of the veneered veneered stress decreases first and then rose decorated porcelain thickness of0.7mm, S173.20MPa. Rose to0.9mm, S1decreased to54.56MPa. Thickness to1.7mm, S1, up to60.16MPa. The stress of the core porcelain, with the increase in the thickness of the core porcelain, the stress decreases the core porcelain thickness of0.3mm, S1116.40MPa. Thickness rose to1.3mm, the S1is decreased to4.17MPa, the peak stress decrease of96.75%.2. When the core porcelain thickness of2mm (single crown), five loading mode S1values were more than double the highest stress values3. Uniform occlusion, group A to group F, decorated with porcelain occlusal S1varied in the same. However, with decreasing thickness of the veneered and veneered neck at the edge tensile stress gradually increased. The maximum principal stress of the core porcelain peak loading point corresponds to the surface and the load side of the neck at the edge of nuclear porcelain. Core porcelain thickness of0.3mm, core porcelain near the tongue side of the shoulder, the stress concentration zone S1values up to3.29MPa when the thickness of0.5-1.3mm, core porcelain neck shoulder stress distribution significant stress concentration.4. The chewing load of the tongue side of20°upward trend with the increase of the thickness of the veneered veneered stress that the thickness of the veneered0.9mm, S1is7.36MPa. Rose to1.7mm, S1increased to8.85MPa. With the increase in the thickness of the core porcelain, stress still decreases its peak stress decrease of82.79%. Core porcelain thickness is0.3mm,0.5mm,0.7mm inner surface near the tongue side of the neck, shoulder pull stress concentration, and other locations evenly distributed stress.Conclusion:1. Comprehensive five loading methods of stress analysis for all-ceramic crowns, you can draw the double-layer all-ceramic crowns decorated with porcelain occlusal thickness and core porcelain occlusal thickness range:0.9mm≤V≤1.5mm, C≥0.5mm. This requirement must leave enough space for all-ceramic crowns the abutments prepare, at least for both minimum and1.4mm.2. The existence of core porcelain can reduce the the veneered stress, thereby reducing the possibility of damage decorated porcelain.3. Concentrated loads, the inner surface of the nuclear porcelain tensile stress is much larger than the cusp staggered stress the value of the corresponding position in the occlusal state. Should be avoided in clinical practice, produced a sharp cusp blunt cusp form of increased occlusal contact area, replace the point contact, surface contact and dispersion stress; should avoid premature contact and occlusal interference, try to spread the occlusal to prevent the prosthesis rupture, and to extend the life of the all-ceramic crowns.4. In clinical practice, should avoid the production of a sharp cusp, occlusal contact area should be increased in order to blunt cusp form, replace the points of contact, surface contact and dispersion stress; should be avoided early contact and Last10interference, as far as possible scattered Scots force to the anti-prosthesis rupture, to extend the life of the all-ceramic crowns.5. Masticatory forces can cause relatively large all-ceramic crowns and neck shoulder stress. Shoulder and neck edge part of the design of clinical tooth preparation and crown production process should be strengthened to prevent all-ceramic crowns fractured.