The Finite Element Analysis Of Deformation Of Maxillary Sinus Membrane After Lifted By Closed Maxillary Sinus Floor Elevation

Background1, The reason for bone absence of maxillary teeth implantationMaxillary sinus cover from the maxillary second premolar to third molar, whose bottom wall is apart from the teeth roots only by a thinner bone plate or membrane. Once maxillary posterior tooth missing, the alveolar ridge was absorpted and the residual bone was shortage to make implant operation. The implant survival rate of this area is also lower than the other areas.2, Maxillary sinus surgeryMaxillary sinus floor elevating operation is the main method to solve the bone deficiency in the posterior maxilla area. Through lifting the maxillary sinus membrane, the maxillary sinus floor implant bone wall can be effectively increased with or without autogenous bone and bone substitute. Tatum first reported this technology in1977. He used the maxillary sinus radical operation approach (Caldwell-Luc), namely the side wall fenestration of maxillary sinus floor elevation. In1994, Summers reported the minimally invasive technology about the maxillary sinus floor lifting from alveolar ridge to maxillary sinus membrane (transalveolar osteotome technique). Because it is not necessary to open the lateral wall of the maxillary sinus, they are also called Closed maxillary sinus floor elevation operation.3, Complications of Closed maxillary sinus membrane operationPerforation of maxillary sinus membrane is the most common clinical complications for anatomical structure complexity of the maxillary sinus, especially in the region of bone crest. The incidence of membrane perforation was2.2%-21%. Maxillary sinus membrane is consist of pseudostratified ciliated columnar epithelium, which plays a key role in protecting the normal structure of the maxillary sinus. Perforation of the maxillary sinus membrane make the implants and bone grafting materials direct contact with maxillary sinus cavity, which can lead to chronic sinus inflammation and bone absorption. On the other hand, maxillary sinus membrane cells induced expression of cell factor such as alkaline phosphatase, osteocalcin, osteopontin, bone morphogenetic protein adhesion and so on for osteogenesis. Therefore, the integrity of the maxillary sinus membrane plays an important role in implant operation. Clinical studies showed that more than half of the maxillary sinus lifting operation failed when the maxillary sinus membrane perforation had happened.Purpose of the experimentIn order to reduce the occurrence of maxillary sinus membrane perforation, scholars have done a lot of research, including how to protect the maxillary sinus membrane during operation and how to mend the perforation of maxillary sinus membrane. But these methods aren’t suitable for Closed maxillary sinus lifting operation. It is not easy to judge maxillary sinus membrane intergrity during Closed maxillary sinus lifting operation. Therefore, the prevention the perforation of maxillary sinus membrane has important significance.Biomechanical method becomes the most popular way to research the mechanism features of human tissue. For example, Koca, Fanuscu and other scholars studied biomechanical of the bone tissue and the implant in the Closed maxillary sinus floor lifting operation. But it has not been reported biomechanical study about modeling and stress analysis in maxillary sinus membrane. Bernhard Pommer obtained Maxillary sinus membrane samples from the20cases of fresh cadavers in2009and tested the mechanical parameters of the maxillary sinus membrane. Based on Bernhard Pommers’ result, In ours experiment, we applied finite element analysis method to simulate Closed maxillary sinus lifting operation to prevent the perforation of maxillary sinus membrane.Research MethodsBiomechanics research methods include holographic photomechanical stress testing and stress testing and finite element analysis and so on. Finite element analysis(FEA) method originated in Aeronautical Engineering in twentieth Century. It divided object into limited mechanical unit to obtain the properties of the elastomer. Due to the high precision of the computational finite element model, it has been widely used for soft tissue simulation. In our experiment, we built the three-dimensional geometric model and finite element model of maxillary sinus membrane with implant and simulated Closed maxillary sinus floor lifting operation by setting the implant and maxillary sinus membrane contacted.Research content 1Generation of Closed maxillary sinus floor lifting modelPreprocessor module in ANSYS finite element analysis software was used to generate the shell model of the maxillary sinus membrane and implant model to complete their geometric modeling. Then, the maxillary sinus membrane shell model was given corresponding mechanical parameters and meshed in SHELL63shell element to generate the finite element analysis model. In order to achieve a similar effect with clinical operation, implant and maxillary sinus membrane were definited to surface contact relationship and the implant model was moved to contact circle of maxillary sinus membrane.2Influence on operation of Closed maxillary sinus membrane elevating by local anatomical factors.2.1Influence of maxillary sinus membrane thickness in Closed maxillary sinus membrane elevating operation.The membrane thickness is seen from0.3mm to0.8mm at clinical work. Therefore, we set the three-dimensional finite element models of three thickness maxillary sinus membrane with0.3,0.5and0.8mm. The surface stress distribution of maxillary sinus membrane was calculated and statistical analyzed.2.2Influence of membrane lifting height in Closed maxillary sinus membrane elevating operation.Maxillary posterior alveolar bone height often refers to the distance from alveolar bone crest to maxillary sinus floor. The residual bone height of alveolar bone and membrane lifting height have the relevant with the selection of implant. Therefore, the three-dimensional finite element model of maxillary sinus membrane and implant were generated. The equivalent stress values of the membrane surface were calculated and statistical analyzed when it was lift from1mm to5mm.3Influence on the operation of Closed maxillary sinus membrane lifting by implant factorsImplant diameter has been considered to be the related factor about implant primary stability and the stress distribution surrounding bone tissue in Closed maxillary sinus membrane elevating operation. In this experiment, four diameters implants with four maxillary sinus membranes were generated to study membrane tensile deformation when they were lift from lmm to5mm. Then the stress distribution of maxillary sinus membrane surface was calculated and statistical analyzed.4Influence on membrane deformation by different operation mode.According to whether the autogenous bone and allogenic bone were used, Closed maxillary sinus lifting operation have different operation mode. Through this experiment, the models of maxillary sinus membrane contacting by pure titanium implant, autogenous cancellous bone and hydroxyapatite bone were made and the stress distribution of maxillary sinus membrane surfaces from lmm to5mm were calculated separately and compared.Main results1The thin shell model of maxillary sinus membrane and Cylinder model of implant were generated by Preprocessor module in ANSYS finite element analysis software. Then, they were given corresponding mechanical parameters and meshed in SHELL63shell element. So we got the finite element analysis model of maxillary sinus membrane which has930nodes,1758units and implant model which has1113nodes,2172units. Cylinder implant model was set to contact and move the circle maxillary sinus membrane model to simulate Closed maxillary sinus lifting operation.2Through the stress analysis of three thickness of maxillary sinus membrane when they were lift from lmm to5mm, we found the tensile gradually transition from the top to the edge of maxillary sinus membrane accompanying with the lift height increasing. High deformation zone occurs at the top center of maxillary sinus membrane. At the same height, the thicker of maxillary sinus membrane, the smaller of the high deformation area. When the maxillary sinus membrane was lift to5mm, the maximum Von Mises stress value at the top center of maxillary sinus membrane is not significant difference compared0.3mm,0.5mm and0.8mm three thickness membrane (P>0.05).3Through analysis equivalent stress values of0.3mm thickness of maxillary sinus membrane surface when it was lift from lmm to5mm, we found mild membrane stress changes when the membrane was lift1-3mm and the average stress values showed no significant difference (P>0.05). When maxillary sinus membrane was lift4mm, membrane stress increases and the average stress has a statistically significant difference compared with lmm,2mm,3mm (P<0.05). When maxillary sinus membrane was lift5mm, membrane stress values were significant difference compared with lmm,2mm,3mm and4mm (P<0.05).4With the increasing of implant diameter, the district range of maxillary sinus membrane maximum stress value enlarges moderately. According to the result of statistical analysis, the equivalent stress values of four diameter implants show significant difference with others when they were elevated from1mm to5mm (P<0.05). 5This experimental results show that almost no difference on the effect of the maxillary sinus membrane deformation comparing with elevating by implant, grafting autogenous cancellous bone and hydroxyapatite bone substitute materials.Main conclusions1The membrane perforation risk is no different when maxillary sinus membrane thickness range from0.3mm to0.8mm in Closed maxillary sinus lifting operation.2When maxillary sinus membrane is lift to4mm, the Von Mises stress values of membrane surface increases substantially and faces more probability to perforate. Therefore, the lift height of maxillary sinus membrane should be controlled within3mm in Closed maxillary sinus lifting operation.3With the diameter growing, the maximum stress value range in the center area of maxillary sinus membrane was abroad moderately.The wider diameter implants can reduce the chance of maxillary sinus membrane perforation and are more suitable to be used in Closed maxillary sinus lifting operation.4The effect on membrane deformation by implant, grafting autogenous cancellous bone and hydroxyapatite bone substitute materials has no difference within5mm height. Closed maxillary sinus floor lifting operation with implant elevating the maxillary sinus membrane directly is the most simple and minimally invasive way in clinical work.However, our research has limitation for anatomical structure complexity of the maxillary sinus and the error of FEM model. We believe that biomechanical study of maxillary sinus area implant will provide more theoretical basis for clinical application in the future.