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ABSTRACT
Since edentate subjects have a reduced masticatory function, it can be expected that the morphology of the cancellous bone of their mandibular condyles has changed according to the altered mechanical environment. In the present study, the morphology of cylindrical cancellous bone specimens of the mandibular condyles of edentate subjects (n = 25) was compared with that of dentate subjects (n = 24) by means of micro-computed tomography and by the application of Archimedes' principle. Stiffness and strength were determined by destructive mechanical testing. Compared with dentate subjects, it appeared that, in edentate subjects, the bone was less dense and the trabecular structure was less plate-like. The regression models of stiffness and strength built from bone volume fraction and the trabecular orientation relative to the axis of the specimen were similar for both dentate and edentate subjects. This indicates that, under reduced mechanical load, the fundamental relationship between bone morphology and mechanical properties does not change.
KEY WORDS: cancellous bone, architecture, edentate, mandibular condyle.
Received July 24, 2003; Last revision December 5, 2003;
Accepted December 8, 2003
INTRODUCTION
A decreased masticatory function has been reported in relation to aging and loss of teeth (Boretti et al., 1995). The decrease in function is associated with an atrophy of masticatory muscles (Newton et al., 1993) and a reduction of bite force (Helkimo et al., 1977). This implies a reduction of forces acting on the mandibular condyle. As bone reacts to its mechanical environment (e.g., Turner, 1998; Huiskes, 2000), it is likely that the morphology of the condylar bone changes accordingly.
In previous studies, it has been shown that the cancellous bone of the mandibular condyle is adaptive, i.e., in edentate subjects, the apparent density and bone volume fraction were found to be lower than in dentate subjects (Hongo et al., 1989a; Kawashima et al., 1997; Giesen et al., 2003b). The mechanical consequence is a reduction (20-30%) in stiffness and strength (Giesen et al., 2003b). Thus far, however, there is no information available on the nature of the morphological bone changes in edentate subjects. It has been demonstrated, for example, that the apparent density of the cancellous bone in the human tibia decreases during aging (Ding et al., 1997), and that this decrease is accompanied by...