Study of deflections in maxillary major connectors: a finite element analysis.

The Major connector is the major component of the cast partial denture to which all other parts are directly or indirectly attached. It also provides cross arch stability to help resist displacement by functional stresses. The major connector should be rigid. A flexible major connector causes an unequal distribution of forces with changes in their intensity and may cause damage to the supporting structures. Thus rigidity is of paramount to resist flexing and torquing forces. The commonly used major connectors for the maxillary arch are Anteroposterior strap, palatal strap and complete palatal plate. Application of load on the prosthesis will result in deflection. The magnitude and direction of the deflection that the prosthesis undergoes depends on the rigidity of the major connector. (1) To determine the deflection seen in maxillary removable partial denture frameworks under simulated occlusal load. (2) To compare the rigidity and deflection characteristics of different maxillary major connectors used in maxillary Kennedy's class I, class II, class III and class IV situations. A CT scan of human edentulous maxilla was taken and each section from the incisive foramen to the hamular notch was projected on the graph paper and three dimensional volumes were created from the connected successive profiles to define the final solid geometry of bone. Six framework models with different Maxillary major connectors such as Anteroposterior straps and complete palatal plate for Kennedy's class I, class II, class III and class IV situations were created. Three Dimensional Finite Element Models corresponding to the geometric model were created using ANSYS 9.0 version. The model was assigned the material properties. A vertical biting force of 20 N was applied. The results showed maximum displacements were observed at the posterior edge of the saddle for all the frameworks. Anteroposterior palatal strap in class III and class IV situation showed the least deflection when compared to class I and class II (distal extension situation) Anteroposterior palatal strap is more rigid connector than the full palatal plate, single palatal strap, and U-shaped palatal strap and can be used in all situations.