Laser Holographic Interferometric Analysis Of The Effect Of Proximal Contact Area On The Displacement Of Cantilever Fixed Partial Denture

With the development of material science, porcelain-fused-to-metal(PFM) prosthesis has been widely used in practice. But because of unfavorable leverages during mastication, the use of cantilever fixed partial denture(GFPD) may lead to the loss of contact area, food impaction and finally the failure of restoration.In normal dentitions, natural teeth are integrated by contact areas which may remain them in balance, avoid their abnormal movement, and are helpful for the self cleaning of gingival papilla. Although contact areas are so important for the dentition, clinicians usually restored them depending on patients' feelings and their own experience, and there has been no report about the effect of proximal contact area on the movement of CFPD.Laser holography interferometry(LHI) is a method to measure the micro displacement of a subject, which is achieved by analyzing the figure and distribution of stripes produced by interferometric principles. It has been agreed that when the mandible second molar is lost, the edentulous distal extension area can be restored with a posterior CFPD using the mandible first molar and second premolar as free-end abutments. Based on that, this study establishes a CFPD model in vitro, and investigates the effect of proximal contact area on the displacement of prosthesis and alveolar bone by double-exposure holography interferometry(DHI).The results showed as following:1.When a concentrated load is exerted on the pontic, abutments move distally, lingually and gingivally. With increasing load, the movement increases. The direction of load only affects the value of displacement, but not the changing trend of it.2. When loaded on the pontic, stress is concentrated at the cervical area of abutments. The displacement of pontic is larger than abutments, alveolar bone and the adjacent tooth, and the displacement of distal abutment is greater than that of medial abutment.3.After the proximal contact area is restored, the displacement of pontic, abutments and alveolar bone decreases. With the increase of contact force, the displacement of pontic, abutments and alveolar bone around abutments decreases; the displacement of adjacent tooth and alveolar bone around it decreases firstly, and then increases.4. With the increase of contact force, the stress of abutments' alveolar bone decreases, and that of the adjacent tooth's bone increases. A contact force of 1.0N is recommended.5.Under oblique loading, the displacement is smallest when the proximal contact is located at buccal area. Under vertical loading, the displacement is smallest when the contact area is located at the middle of the proximal area, and this location is also recommended to decrease the displacement of cantilever bridge and alveolar bone.