In elderly edentulous patients, the treatment with two interforaminal implants provides evidence of neuromuscular adaptation towards values of healthy dentate. Thus, the known benefits of implant placement such as tissue perseverance and improved function are complemented by improved neuromuscular adaptation.
This study introduces a modified dynamic testing mode with gradual load increase and examines whether this could be an alternative to customary methods of static loading or chewing simulation. Seventy-two extracted human maxillary root-canal-treated central incisors were randomly divided into six groups with 12 teeth each. Three groups were restored with titanium posts cemented with chemically curing resin cement. The other three groups were restored with glass-fiber posts cemented with dual-curing composite cement. All teeth were capped with full ceramic crowns. Both kinds of restoration were tested by linear compressive (static) loading, a modified gradual (cycling) dynamic loading, and by chewing simulation followed by static loading until failure occurred. The maximum load capacity was recorded. Statistical comparison showed that maximum load capacities of the same post material obtained from gradual dynamic loading did not differ significantly from that of linear compressive loading or of chewing simulation. In contrast, comparisons of different post materials under static loading resulted in significantly different load capacities. Dynamic testing with gradual load increase can be considered an economic alternative for chewing simulation, because it provides equivalent results. Both procedures, however, imply different conclusions than static loading with respect to post materials.
When a certain bite force is applied during unilateral chewing, the combination of jaw elevator muscle activities is different than when a comparable force is applied in unilateral isometric biting, e.g. on a force transducer. Masticatory peak force is generated in a nearly isometric phase of the chewing cycle, with a jaw gape of about 1 mm. In contrast, peak force in isometric biting on force measuring equipment usually induces jaw gapes of 6 mm or even more. Therefore, we tested the hypothesis that the jaw gape influences relative activation of elevator muscles in unilateral isometric biting. We further examined whether such influence could explain the different activity combinations of chewing and isometric biting. In thirty asymptomatic males, masseter and temporalis activities were recorded during intermittent isometric biting with jaw gapes of 6, 5, 3, 2 and 1 mm and during unilateral chewing. Activity combinations were described by working/balancing ratios and by temporalis/masseter ratios. With decreasing jaw gape the working/balancing ratio of the posterior temporalis decreased (P < 0.002) while that of the masseter increased (P < 0.001). Likewise, the temporalis/masseter ratio on the balancing side increased (P < 0.001). With decreasing jaw gape, activity ratios of isometric biting approached ratios of chewing. We conclude that: (i) relative jaw muscle activation in isometric biting depends on the jaw gape, (ii) relative muscle activation in chewing resembles relative activation of isometric biting with a small 'chewing-like' gape. This suggests that characteristic activity combinations in chewing are mainly a result of the approximately isometric contraction during the slow closing phase of the chewing cycle.
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