The effect of some components on the rigidity of mandibular bilateral free end saddle dentures

One partially dentate person, his remaining teeth being 44, 43, 42, 41, 31, 32 and 33, was simultaneously provided with one maxillary complete denture and three mandibular free end saddle dentures having cobalt chromium alloy skeletons of different design. One denture was constructed with a lingual plate, another with a sublingual and a secondary bar, while on a third denture the major connector consisted of an enlarged secondary bar. On all the dentures occlusal rests were placed on teeth nos 44 and 33. Rosette strain gauges were placed in the midlines of all the major connectors. The gauges were calibrated on the master cast placed in a universal testing machine. The clinical recordings were taken from the gauges during one session under repeated loading conditions. Readings were repeated on one denture after removal of (1) the secondary bar and (2) the secondary bar and the occlusal rests. The recordings were used to calculate (1) the principal maximum and minimum strains and (2) the direction of the strains at the points of the bases beneath the centre of the gauges. The results show that studies of relevant functional deformation patterns of dentures can only be made in clinical experiments. Furthermore, they show that the base with an enlarged secondary bar exhibits more deformation than the other two types of base. Removal of the secondary bar did not significantly increase the deformation of the denture also equipped with a sublingual bar, neither did the removal of the occlusal rests. Both these changes, however, caused changes of the deformation patterns.