28

In the case of a Kennedy Class II Mod. I, correct planning results in dental rests which form a support-triangle. Occlusal forces on the entirely tooth-supported saddle create no problems. However, the free-end saddle acts as a lever. When the saddle is depressed, the denture rotates around an axis formed by connecting the two most distal support points, or rests, one on each side of the arch. Lifting forces occur perpendicularly on the opposite side of the axis of rotation. The law of leverage applies here: Load x Load arm = Effort x Effort arm (L • I = K • k) (Fig. 28).

29

This lever effect of the free-end saddle must be very carefully controlled. Upon detailed observation the desirability of keeping the product K* k larger than L*l becomes apparent. Since K and L are to a certain extent fixed, one must attempt to keep k large and I small.

If the distal abutment on the entirely tooth- supported side is designed only to support a mesial rest, a portion of the effort arm is sacrificed. The addition of a distal rest is virtually obligatory. On the side with the posterior edentulous space, in addition to the mesial rest required to prevent tipping, the terminal tooth should also be equipped with a distal rest. In this manner, the statics can be greatly improved (Fig. 29).

30

After analyzing all the possible difficulties we might encounter with a unilateral free-end saddle, it is no wonder that many consider doing without a denture and attempting to solve the case in another manner altogether. With the situation illustrated in Fig. 29, it is quite practical for one to consider closing the space on the tooth-supported side with a bridge from 24-27 and leaving the side with the posterior edentulous space untreated. Naturally, this is only possible if the case in point has met certain necessary criteria.

The criteria are: function, esthetics, muscular- joint diseases, antagonists (Fig. 30).