In vivo horizontal forces on implants depending on the type of occlusion

Minimizing horizontal forces on implants is one of the important aims of an occlusal design. Therefore, several proposals have been made in literature, e.g. flat cuspal slopes or narrow occlusal surfaces. Our aim was to test how these occlusal designs would influence horizontal forces. Ten healthy subjects with unilateral partially edentulous arches were provided with fixed partial dentures (FPD) on two ITI‐implants. The opposing jaw was fully dentate. After an adaptation of 6 month measurement setups with a measuring FPD were put into the mouth. The sensoring device, which consisted of two abutments equipped with strain gauges, evaluated the forces in three dimensions. For each person three FPDs were made with a different design of the occlusal surface. The first FPD exhibited cusps with steep slopes (S), the second showed flat cusps (F) and the third had a narrow occlusal surface (N). The peak forces of the chewing cycles of each patient were evaluated. While chewing wine gum the average values of the vertical forces of the three different FPDs showed no significant differences and amounted to between 253·8 N (s.d. 85·7 N) and 273·9 N (s.d. 63·7 N). With the first FPD (S) mean horizontal forces of 47·9 N (s.d. 34·8 N) were found whereas with the flat surface an average force of 47·4 N (s.d. 37·1 N) was measured. The narrow occlusal surface was associated with an average reduction of the horizontal forces of about 50·9% to a mean value of 24·4 N (s.d. 10·6 N) (P < 0·005). The inclination of occlusal slopes did neither affect vertical nor horizontal forces significantly. However, narrowing of the occlusal surface in the oro‐vestibular direction by 30% showed a significant reduction of the lateral forces exerted on the implants by more than 50%. A reduced oro‐vestibular width of the occlusal surface is recommended especially for diameter‐reduced implants, in case of an unfavourable relationship between implant and crown length or for implants that are strongly inclined to the occlusal plane.