Mechanical behavior of major connectors--part 2: influence of denture teeth height and loading direction.

Statement of the problem: When force is applied on a denture the moments may develop at the denture major connector (MC) interface and thus enabling more framework deformation. PURPOSE: To determine the influence of crown height and loading directions on the stiffness of different MC designs when supported by an oral cavity simulating model. MATERIAL AND METHODS: Oral cavity models were used as support for different major connector's designs. A set of metal tooth casted crowns, 8, 10, and 12 mm in height, was prepared from molar plastic phantom teeth. The crowns were connected to premolar or molar regions of the major connectors and loaded vertically or in 45 to the occlusal plane. The stiffness of the system was measured. RESULTS: Changing tooth-crown height resulted in small changes in stiffness values when loaded vertically to the occlusal plane. Loading in oblique to the occlusal plane, the mean stiffness value decreased 30% when crown height increased from 8 mm to 12 mm. A reduction in stiffness values of 80-90% compared to vertical loading was found. CONCLUSION: Long denture crowns reduce the rigidity of the removable partial dentures. Clinical implications: The removable partial denture should be supported by the maximal oral tissues. This stresses the importance of periodical examinations for any need of denture-base relining to maintain good support.