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es.
     A partial loss of osseointegration (ie, loss of marginal bone support) is difficult to handle if it also entails exposure of threads to ward mobile oral mucosa. Grinding or filling the threads is of limited or no value. There is always difficulty in keeping the depth of the thread closest to the bone margin free from bacterial plaque. In fact, this situation may be the only one that could ultimately require removal of a stable fixture by means of a trephine bur. Guided tissue regeneration has not been tested for this indication and may not work well when the titanium surface has already been contaminated. The same applies to recovering the fixture with a fresh periosteal flap with or without an interposed bone graft.
     The recommendations by Lekhom et al on how to manage mobile fixtures and other clinical
surgical complications still hold true.
     Maintaining osseointegration
     Two factors influencing the fixture-supporting bone must be controlled for the lifespan of the fixture, namely, loading and the periabutment conditions.
     Loading
     As emphasized earlier in this chapter, the perifixtural bone adapts to the load applied.  Its full strength is seldom reached until after a year of adequate load. Overloading even after several years (eg, by bruxism, change of the opposing bite to porcelain crowns, or by a change of extension or fit of the suprastructure) could cause perifixtural microfractures, which then may heal with non-mineralized connective scar tissue. As a result, the fixtures will become mobile. On the other hand, if adequately loaded, fixtures may contribute to the preservation of mandibular bone height.
     Periabutment and perifixtural conditions
     Any inflammation in the periabutment soft tissues caused by trauma and/or microbiological agents could cause marginal bone resorption and should consequently be avoided. When the marginal oral soft tissue are healthy, there is only minute marginal bone resorption of approximately l mm through the first year, and then only 0.l mm annually for the following years. Individual variations could, however, be considerable and their reasons are not well known. The preoperative host factor could influence the marginal bone support and well as the postoperative conditions. For example, whether basal jawbone for fixture support has a greater resistance to loss of marginal bone height than the alveolar process proper has not been investigated.
     Summary
     When due attention is paid to the individual preoperative host conditions, when treatment is carried out with precision according to recommended guidelines, and when the above factors for maintenance are controlled, a number of long-term studies on large materials indicate that osseointegration of fixtures, once established, will be maintained for many years with a predictable, high degree of load-bearing capacity.

VOCABULARY

l. osseointegration 骨结合
2. Haversion bone 哈佛氏骨
3. instant 直接的，立刻的
4. tibia 腔骨
5. granuloma 肉芽肿
6. interfere with 干扰
7. inclination 倾斜
8. postmenopausal 绝经后的
9. osteoporosis 骨质疏松症
10. colitis 结肠炎
11. osteomalacia 骨软化
12. Paget' s disease 变形性骨炎
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