| Objective In this study,three-dimensional finite element method was used to analyze the effect of the relationship between the implant apex and the cortical bone at the sinus floor on the stress distribution.Through a comprehensive study of the stress distribution at the implant bone interface of different lengths and diameters of the implant apices far away from the sinus floor cortical bone,penetrating into the sinus floor cortical bone and penetrating out of the sinus floor cortical bone(the implant apices are located in the maxillary sinus),the effects of the changes of implant length and diameter on the implant bone interface were compared under certain load conditions It can provide reference for the selection of clinical implant scheme.Methods ABAQUS 6.14 was used to draw a simplified model of alveolar bone block in maxillary posterior area.The distance between proximal and distal bone block was set as 15mm according to the research needs.The height of residual bone from alveolar crest top to maxillary sinus floor was set as 10mm.The thickness of cortical bone at alveolar crest top and maxillary sinus floor was set as 1mm,and the height of cancellous bone was set as 8mm.Three different lengths(8mm,10mm,12mm),two different diameters(4.1mm,4.8mm)implant and abutment combination models and the first molar crown models were drawn and assembled according to the research needs.According to the average daily chewing force of Chinese people,loads of 150N in vertical direction and 30N in horizontal direction were loaded into different models to simulate the situation of unilateral chewing with implant fixed denture.Results 1.When the height of residual bone from alveolar crest to maxillary sinus floor is fixed(RBH=10mm),under the condition of 150N vertical load,the stress is different with the different relationship between the implant apex and the cortical bone at the sinus floor.The maximum Von Mises force(MVMS)of the implant neck cortical bone was larger when the implant apical part penetrated into the cortical bone of the maxillary sinus floor,that is,when the implant length was 10mm,than when the implant apical part penetrated out of the cortical bone of the maxillary sinus floor,that is,when the implant length was 12mm.In addition,the experimental results showed that MVMS of cortical bone in the maxillary sinus floor increased significantly when the implant penetrated into the maxillary sinus floor,while MVMS of cortical bone in the maxillary sinus floor did not change significantly when the implant penetrated out of the cortical bone in the maxillary sinus floor.With the change of the relationship between the apex and the sinus floor,the stress distribution of cancellous bone did not change significantly.The maximum stress of implant neck also changed,but there was no obvious rule.2.When the remaining bone height is certain(RBH=10mm),when the implant root tip penetrates into the upper sinus cortical bone under the condition of horizontal load of 30N,the MVMS value of the implant neck is larger than that of the implant root tip far from the base of the maxillary sinus,while the MVMS value of the implant neck is smaller than that of the former two.In addition,the MVMS value of the periosteal bone of the maxillary sinus increased with the increase of the length of the implant,and the change of the implant tip penetrating the bone of the sinus floor was more obvious than that of the bone penetrating the inferior cortex of the maxillary sinus.The stress distribution of cancellous bone was not obvious with the change of the relationship between the tip of the implant and the sinus bottom.When the implant tip penetrated into the sinus cortical bone,the stress of the implant decreased,but there was no obvious rule.3.When the relationship between the tip of the implant and the cortical bone of the sinus floor is different,the stress of the surrounding bone changes with the diameter of the implant.Under the vertical stress,with the increase of implant diameter,MVMS of the bone of the crest of the alveolar crest or the inferior maxillary sinus cortex decreased,and the MVMS of the bone of the sinus bottom cortex was significantly higher than that of the crest of the alveolar.The stress distribution of cancellous bone was not obvious with the increase of diameter.When the root tip of the implant is far away from the base of the maxillary sinus,penetrated into the cortex bone of the maxillary sinus and the bone penetrating the sinus bottom cortex,the stress of the implant decreases with the increase of the diameter of the implant.4.When the relationship between the tip of the implant and the sinus cortical bone is different,the MVMS of the implant neck crest crest is decreased with the increase of the implant diameter under horizontal stress,and the MVMS of the bone of the maxillary sinus bottom cortex is not obvious.The stress distribution of cancellous bone was not obvious with the increase of diameter.When the root tip of the implant is far away from the base of the maxillary sinus,the stress of the implant decreases with the increase of the diameter of the implant.5.With the difference between the root tip and the sinus bottom,that is,with the tip of the implant far away from the sinus cortical bone,penetrating into the upper sinus cortical bone and penetrating the sinus cortical bone,the neck movement of the implant decreases gradually under horizontal load,but the change of the root tip is not obvious.With the increase of diameter,the neck movement of implant decreased more obviously.Conclusions The results show that bicortical bone fixation can effectively improve the stress distribution of the bone around the implant:1.When the height of the remaining bone is constant,MVMs of the cortical bone around the implant neck that penetrates the cortical bone at the root apex of the implant is smaller than that of the cortical bone around the implant neck that penetrates the cortical bone at the root apex of the implant and is far away from the cortical bone at the bottom of the maxillary sinus,and it is obvious when the implant is stressed horizontally,but the other stress values do not change significantly.2.When the relationship between the apical part of the implant and the cortical bone of the maxillary sinus floor is different,the stress of each part of the implant decreases with the increase of the diameter.With the change of various factors,the stress distribution of the cancellous bone does not change significantly.3.In conclusion,when the height of residual bone is constant,the implant with the length of cortical bone passing through the bottom of maxillary sinus is the best choice for stress distribution;The larger diameter of the implant is more conducive to the stress distribution of the implant bone interface. |
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