| The restoration of dentition meant not only to fill the missing teeth and increase the efficiency of mastication, but also to maintain the integrity of dentition and the health of residual teeth, especially loosen teeth that could be reserved. Bone resorption might lead to teeth mobility and the change of occlusal pattern and proximal relationship. Also, the endurant threshold to bite force decreased. Occlusal loads within the normal range to loosen teeth would lead to broken down of periodontal tissues. But by appropriate treatments, loosen teeth of low-grade could be used for a long term, and even took the part of abutments of dentures. This was very important, because of more teeth and bone tissues remained, less dental tissues cut, concise denture designs, more comfortable and convenience to denture wearers. The treatments and denture designs of patients with loosen teeth were a hot potato. So, precisely estimating the functional states of loosen teeth, dentures of suitably designed, decreasing the stress of periodontal tissues during functional movements were the crux of perennial curative effects of restoration. At present, there was no method reported to test the dynamic chewing forces of a single natural tooth in its physiological movements, and there were a limited number of studies about the maximal bite forces and influencing factors.The aims of this study were to determine the rules of bite force changes andsome factors, including proximal contact, bone support level, crown to root ratio, occlusal relationship of anterior teeth and tooth wear of loosen teeth. For further studying of dynamic chewing forces, we developed a new system of PVDF-based, which could be used in natural teeth as well as dentures. The biological security, including thrill, cell toxicity, hypersusceptibility and hemolysis characteristics, were also examined. Then, we evaluated the chewing forces during three basal functional movements-tapping, biting and laterotrusion, using the new instrument. The following results were obtained:1. The values of maximum bite force were various according to individuals and the sites of teeth in dental arches. Alveolar bone resorption resulted in decreasing of maximal bite force. There was an exponential relationship between maximal bite force and crown to root ratio.2. There was a close relationship between tooth wear index and tooth mobility. The tooth wear indices of mobile teeth mainly ranged from 1 ~2. Stable teeth had different tooth wear indices to mobile teeth of II III degree, while tooth wear indices were similar between mobile teeth of II III degree. The locations of tooth wear facets of mobile anterior teeth were the same as health teeth; while those of posterior teeth were anomaly distributing.3. Patients with loosen teeth inclined to have abnormal overbite and overjet relationships of anterior teeth. The proximal contacts lost if the mobilities of the neighboring two teeth were both I degree or one of them exceeded II degree.4. The results of biological security evaluation indicated that the PVDF piezoelectricity film had good biocompatibility, which meant it was a secure and reliable material for clinical application. The size and bending shape had little effect on capability of PVDF-based transducer. The new system was stable andsensitive to dynamic forces, and could be used in clinical examination.5. The peak values during rhythmic tapping movements of natural first lower molars were 24 to 27 kg, to which 100 to 110 ms needed; in the movements of opening-closing with maximal forces, the peak values were 27 to 30 kg, 800 ms needed; in laterotrusions, the peak values were 26 to 28 kg, the courses of chewing forces patterns might be divided into 5 phases. The peak values of chewing forces in the working sides were higher than the other sides.6. The peak values during rhythmic tapping movements, opening-closing movements, laterotrusions of loosen teeth were smaller than healthy teeth, and the times needed were longer.In teeth...
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