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This paper presents a method that uses the threaded dental implant as a reference object for the inter-image alignment necessary for digital subtraction radiography. The implant is furthermore used to define a measurement coordinate system and to automate the placement of reference areas used for contrast correction. The method is intended for studies of diffuse bone density changes in the vicinity of the implant. The method is shown to be insensitive to large variations in exposure time and geometry, and is together with the contrast correction method of Ruttimann et al., able to detect clinically invisible simulated bone density changes.

The controversy over combining teeth and implants for support of fixed partial dentures still remains after almost three decades of debate. The aim of this review was to evaluate what support that could be found in the literature for extracting teeth in favour of implants, and to elucidate whether tooth-implant prostheses were inferior to solely implant supported constructions in terms of survival and complications. The methods for gathering relevant information entailed electronic searches on PubMed using relevant key words, as well as complementary manual searches in the retrieved publications. The results showed that there was no support for extracting teeth in favour of placing implants. On the contrary, the healthy tooth had a survival that was life-long, which is yet to be shown for the dental implant. Also the use of teeth as abutments in combination with dental implants for support of fixed dental prostheses could be endorsed in certain situations with solid albeit limited scientific support. in a wider sense, such prostheses could be used as a reliable therapy in all regions of the jaws. However the status of the abutment teeth in terms of periodontal support, pulpal status and risk for carious lesions and biomechanical complications should always be considered in relation to the long-term prognosis of the prosthesis. The conclusion was that teeth should not be extracted in favour of placing dental implants without a specific indication, and that tooth-implant supported prostheses should be considered as a viable prosthetic option.

Periodontitis involves bacterial infection, inflammation of the periodontium, degradation of gum tissue, and alveolar bone resorption, which eventually leads to loss of teeth. To study the role of the broad-spectrum protease plasmin in periodontitis, we examined the oral health of plasminogen (Plg)-deficient mice. In wild-type mice, the periodontium was unaffected at all time points studied; in Plg-deficient mice, periodontitis progressed rapidly, within 20 weeks. Morphological study results of Plg-deficient mice revealed detachment of gingival tissue, resorption of the cementum layer, formation of necrotic tissue, and severe alveolar bone degradation. IHC staining showed massive infiltration of neutrophils in the periodontal tissues. Interestingly, doubly deficient mice, lacking both tissue- and urokinase-type plasminogen activators, developed periodontal disease similar to that in Pig-deficient mice; however, mice lacking only tissue- or urokinase-type plasminogen activator remained healthy. Supplementation by injection of Pig-deficient mice with human plasminogen for 10 days led to necrotic tissue absorption, inflammation subsidence, and full regeneration of gum tissues. Notably, there was also partial regrowth of degraded alveolar bone. Taken together, our results show that plasminogen is essential for the maintenance of a healthy periodontium and plays an important role in combating the spontaneous development of chronic periodontitis. Moreover, reversal to healthy status after supplementation of Pig-deficient mice with plasminogen suggests the possibility of using plasminogen for therapy of periodontal diseases. (Am J Pathol 2011, 179:819-828; DOI: 10.1016/j.ajpath.2011.05.003)