| The severely resorbed posterior maxilla after tooth missing often causes the absence of bone quantity and the decrease of the height from the crest of alveolar ridge to maxillary sinus floor, which results in the absence of the implant stability and the sinus infection because the implant penetrates the mucosa of maxillary sinus, then the implant fails. So the severely resorbed posterior maxilla presents a challenge for the maxillofacial surgeon and the restorative dentist planning implant restorations. Summers brought osteotome sinus floor elevation (OSFE) that the adjacent bone layer wound be compressed and the mucosa of maxillary floor wound be elevated when the crest of alveolar ridge was impelled and knocked on slightly in the posterior maxilla by use of tapered osteotome whose diameter ranged from 1mm to 4mm. Compared with the sinus window, OSFE has some advantages: 1.Minor damage that can protect the vessels in maxilla and less the postoperative complication 2.Shortens the healing and waiting period. 3.Preserves bone tissue and improves bone density. 4.Expands the alveolar ridge by use of larger osteotome and bone substitute. OSFE has wide employ foregound as a kind of new and developing, low damage technique of maxillary sinus elevation. But it has some limitation, such as minor indication range, needing higher residual bone, minor elevation of maxillary sinus and the absence of systemic biomechanical theoretic foundation now, et al. So it needs further systemic study so as to be applied clinically. This study utilized 3-D finite element method to establish the finite element model. Two-dimensional images of maxilla was scanned by CT. The boundary of these images was transacted into data and the data were input into computer. Then three-dimensional digital model was developed by MSC/PATRAN software. Seven sorts of models were developed according to the shape of the top of osteotome, the shape of maxillary sinus floor and the distance between the top of osteotome and maxillary sinus floor. Then these models were classified into three groups as follows: Group I: the shape of the top of osteotome and of maxillary sinus floor are convex, but the distance between the top of osteotome and maxillary sinus floor is 1mm,2.5mm and 4mm respectively. Group II: the shape of the top of osteotome is convex, and the distance between the top of osteotome and maxillary sinus floor is 1mm, but the shape of maxillary sinus floor is convex, flat and concave respectively. Group III: the shape of maxillary sinus floor is convex, and the distance between the top of osteotome and maxillary sinus floor is 1mm, but the shape of the top of osteotome is convex, flat and concave respectively.Stress and displacement on osteotome-bone interface and maxillary sinus floor were compared within each group. The load was vertically acted on maxillary sinus floor by osteotome, the speed of osteotome was 10 meters per sec. and the weight of osteotome was 240g. These models were analyzed by ABAQUS analyzing software, and then the data of stress peak and maximal displacement were obtained. Analytic result:1,In the first group of models, when osteotomes is 1 mm from maxillary sinus floor, displacement,tensile stress and compressive stress are most at maxillary sinus floor. So the rate of maxillary sinus mucosa perforation may be the highest, and the venture is also the most. And the displacement is the least on osteotomes-bone interface, which illuminates that advance rate is the lowest, so this method is not good.The most displacement on osteotomes-bone interface when osteotomes is 2.5 mm from the maxillary sinus floor,is larger than that when osteotomes is 4 mm from the maxillary sinus floor. So the elevation efficiency is higher in 2.5mm group than in 4mm group. But displacement,tensile stress and compressive stress are in 4mm group less than in 2.5mm group, and the rate of maxillary sinus mucosa perforation is also low in 4mm group. Consequently in clinic the distance may be 2.5mm or 4mm according to operational time and patient condition. 2,In the second group of models, the largest displacement among three models is almost same on osteotomes-bone interface. If the maxillary sinus floor is flat, tensile stress is maximum at the maxillary sinus floor. If themaxillary sinus floor is concave, tensile stress is in the middle. So flat maxillary sinus floor mucosa perforation is deformed easiest, next when the maxillary sinus floor is concave. So in clinal we should pay more attention to flat and concave the maxillary sinus floor. 3,In the third group of models, when the top shape of osteotomes is concave, displacement,tensile stress are maximum at the maxillary sinus floor and maxillary sinus mucosa perforation takes place most easily. But when the top shape of osteotomes is flat, displacement,tensile stress and compressive stress are minimum and sinus floor mucosa is not perforation usually, but whitch may cut down the efficiency and extend operatal time and increase suffering on patient. And if the top shape of osteotomes is convex, the displacement on osteotomes-bone interface is larger than the top shape of osteotomes is flat and concave. If this way can not lead to maxillary sinus mucosa perforation, that can high-performancely compress bone cliff and lift mucosa at the maxillary sinus floor. So it is better choice that the top shape of osteotomes is convex. Conclusion is followed: 1.Stress and displacement are different if the distance between osteotomes and the maxillary sinus floor is differet, elevation efficiency is lowest and the rate of maxillary sinus mucosa perforation is highest when the distance is 1mm. So this way must be adoped cautiously. 2.Elevation efficiency of the maxillary sinus floor is almost same whatever the shape of maxillary sinus floor is. |
