英语论文网

     The marginal conical outlet. fitting the conicity of the fixture mount. the cover screw, and later the abutment cylinder, is shaped by the "high - speed" marginal countersink, which has a high peripheral velocity due to its great relative diameter. The marginal bone is well corticated incertain
regions such as the anterior mandible and. the temporal bone. In consequence, there is a theoretical risk of frictional and thermal trauma to such marginal bone in spite of good accessibility of the area for irrigation. Moreover. the marginal cortical bone is deprived of part  its superficial vascularization because of the raising of the flaps. As a result of these factors, osseointegration cannot be expected and doe not occur superiorly to the most marginal thread, cut by the slow speed and much less traumatizing tap. In addition, however, it is important that the shelf created by the counter sink always be within cortical bone (Fig 7-8). When the fixture is tightened it first hits this shelf before any fragile threads can be crashed. Consequently, thick marginal cortical bone allows deeper countersinking, and thin cortical bone allows little marginal counter sinking.
     Matching the fixture to its bone site
     Matching the fixture to the prepared bone site should be performed with the aim of avoiding
overtightening yet creating an optimal lit. Overtightening is likely to cause marginal compression
ischemia, which may result in inadverten loss of marginal bone height. On the other hand, a very close fit is mandatory for osseointegration to occur. For a study and discussion on the influence of
gaps between implant surface and bone, the reader is referred to Carlsson. Finally, very loosely textured bone may create a risky situation, because even with correctly performed surgery, only a few trabeculae touch the fixture surface to provide the initial stability.
     Penetrations to nasal cavity and maxillary sinus
     The effect of penetrations of the apical ends of fixtures into the nasal cavity or the maxillary
sinus has been the subject of only one study. The experimental animal part of it showed no adverse perifixtural tissue reactions. The clinical part showed somewhat lower survival rates for penetrating fixtures as compared to nonpenetrating fixtures. These results could not, however, be explained by the perforations only. Dehiscenses in the covering soft tissues and overloading of the
soft maxillary bone anterior to the sinus could constitute decisive factors as well.
     Adjustments of the covering soft tissues
     The surgical creation of thin, nonmobile soft tissues in the areas of future abutment penetrations should be postponed until abutment surgery. In this way, a thick and protective soft tissue cover remains during the healing period after fixture installation.
     Postoperative considerations
     Healing time
     What constitutes an adequate healing time for osseointegration to occur is influenced by most of the factor reviewed so far. Clinical healing time recommendations are a minimum of 3 months for dense bone, as in the 'mandit31e, and 6 months for cancellous type bone, as in the maxilla. These recommendations are based on long - term clinical experie本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。