| Objective：To analyse the stress distribution of porcelain laminate veneers based ondifferent incisal and cervical preparation design of maxillary central incisor by3D finite element method under different loading conditions. To discuss theinfluence of stress distribution of porcelain laminate veneers based on differentpreparation design and to provide theory basis for the clinical design andapplication of porcelain laminate veneers.Methods：3D finite element models of porcelain laminate veneers based on differentpreparation design of maxillary central incisor are respectively established byCT scanning and MSC/NATRAN finite element software:1.Based on chamfer cervical preparation design,there are four incisalpreparation design types including window preparations, feathered incisal,incisal bevel and incisal overlapping.2. Based on incisal bevel preparation design,there are three cervicalpreparation design types including knife edge, chamfer and round shoulder.Simulating the loading condition of100newton in the incisal edge parallelor at60degree angle to the long axis of tooth by the finite element analysissoftware--MSC/PATRAN,the stress distribution,Von Mises value anddisplacement change of porcelain laminate veneers based on differentpreparation designs of maxillary central incisor are analysed and compared. Results：1〠The Von Mises values of loading at60degree angle to the long axis oftooth from palate to labial surface are all more than parallel to the longaxis of tooth.2〠In two loading conditions, high stress areas of porcelain laminate veneersbased on different preparation design concentrate on the areas nearby theloading point and cervical margin mostly.3〠Cervical design is chamfer and incisal design is different under moredestructive inclining loading:(1) In any loading condition the destructive Von Mises stress of every layerof window preparations is larger.(2) The stress of layer of porcelain laminate veneer of feathered incisal isthe least, and the layer of bonding is more.(3) The stress of layer of porcelain laminate veneer of incisal bevel whichlowers incisal height is more, but the stress of the layers of bonding andabutment is uniform.(4) The stress of layer of porcelain laminate veneer of incisal overlapping ismore, but the stress of the layers of bonding and abutment is least, whichcontributes to protect the layers of bonding and abutment.(5) The cervical porcelain laminate veneer and lingual areas of incisaloverlapping are areas of stress concentration.4〠In inclining loading condition, when incisal design is bevel type and cervical design is different:(1) In inclining loading condition, the Von Mises value of the layer ofporcelain laminate veneer of chamfer cervical design is minimum, butthe layer of bonding is maximum.(2) The round shoulder design easily leads to stress concentration of thelayer of porcelain laminate veneer, and destructive stress value is morethan knife edge and chamfer design.Conclusion：1〠The3D finite element method is an effective way of analog computationof stress distribution of porcelain laminate veneers based on differentdesign in different loading condition.2〠The stress distribution of porcelain laminate veneer is closely relatedwith the loading direction. The destructive stress values of every layer ofporcelain laminate veneer in inclining loading condition is far more thanparallel to the long axis of tooth.3〠Cervical design is chamfer and incisal design is different:（1） The destructive Von Mises stress of window preparations ofporcelain laminate veneer is larger, which is easily damaged than others.（2） Feathered incisal design contributes to protect the layer of porcelainlaminate veneer, but the layer of bonding is easily damaged.（3） The destructive stress of layer of porcelain laminate veneer ofincisal bevel and incisal overlapping is more, but the stress of the layers of bonding and abutment is more uniform than window preparationsand feathered incisal, which contributes to protect the layers of bondingand abutment.（4） The cervical porcelain laminate veneer and lingual areas of incisaloverlapping are areas of vulnerable spot.4〠The chamfer cervical design type contributes to lower the destructivestress of the layer of porcelain laminate veneer, but the destructive stressof the layer of bonding is more. The round shoulder design easily leadsto stress concentration of the layer of porcelain laminate veneer, whicheasily leads to rupture of porcelain compared with knife edge andchamfer design in the same condition.5〠The experiment offers reference for clinical optimal design of porcelainlaminate veneer.The choice should combine with the oral practicalsituation. |
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