Occlusal force pattern during chewing and biting in dentitions restored with fixed bridges of cross-arch extension. I. Bilateral end abutments.

The pattern of axially directed occlusal forces, i.e. magnitude, distribution, duration and frequency of occlusal forces perpendicular to the occlusal plane, was studied during chewing, swallowing and biting in twelve subjects whose dentitions were periodontally treated and prosthetically restored with fixed, cross-arch bridges whose periodontal support included bilateral end abutments. The measuring devices consisted of four strain gauge transducers bilaterally mounted into pontics of maxillary bridges to represent the posterior and anterior regions. The forces could thus be studied in various parts of as well as over the entire dentition simultaneously. All subjects exhibited a rhythmic chewing pattern with preference of one side as chewing side. Local chewing and biting forces were always larger in the posterior than in the anterior regions and largest in the posterior region of the preferred chewing side. The total chewing and swallowing forces were about 100 Newtons (N) whereas the total maximal bite force in habitual occlusion amounted to 320 N. On average 37% of the total maximal bite force in habitual occlusion was utilized during chewing (and swallowing). The capacity of the periodontal tissues on the preferred chewing side to withstand transient occlusal forces was utilized to an average of 25% during chewing and swallowing and to an average of 57% during biting with maximal strength in habitual occlusion. The mean duration of that part of the chewing cycle during which the teeth were subjected to occlusal forces was 240 ms. The duration of the occlusal forces during swallowing was about three times longer. It is concluded that the periodontal tissues can withstand transient occlusal forces which are much larger than those generally operating during chewing, swallowing and biting with maximal strength in habitual occlusion. However, when the bite force is concentrated to a limited area of the tooth-arch, its magnitude seems to be limited by feedback mechanisms evoked in the periodontal tissues of that region.