STRESS ANALYSIS EVALUATION OF COMBINING RESILIENT ATTACHMENTS WITH DIFFERENT CANTILEVER BAR LENGTH ON SUPPORTING STRUCTURES OF IMPLANT SUPPORTED OVERDENTURE IN-VITRO STUDY

Four screw type implants(Pitt-easy Implant System, SIS, Germany) were placed in the interforaminal region of mandibular acrylic model then the abutments(Titanium sleeve abutment,Pitt –easy, Germany) intimately fitted over the hex of the implant. Two bar-ball designs were constructed on single model; Design I: Bar with yellow colored clips(Vario- Soft bar- Pattern VSP) connecting four implants with 8 mm distal cantilever bar extension with distally placed ball attachment (Patrix VKS - SG,Bredent,Germany) Design II: Bar with yellow clips connecting four implants with 16 mm distal cantilever with distally placed ball attachment. Two bar-ball designs were constructed on single model as follow: The bar connecting the abutments were held with mandrel, so that it’s rounded surface facing occlusally and its flat surface facing to the ridge. The wires of the strain gauges(Kaywan, Electronic Instrument, Tokyo, Japan) were embedded in specially prepared channels in the base of the model. The straight load applicator bar of the universal testing machine(LLyod Instruments, Japan) was allowed to touch the denture teeth. Vertical unilateral loading was applied unilaterally at the central fossae of the left second premolar.All data of the study were collected and statistically analyzed. Using student T test to compare between two designs, it is found that there is statistically significant difference between design I and design II. The result obtained from this study showed that there is increase in the stresses applied to the nearby abutment this was due to the distal extension that act as hidden cantilever which add to bending moment and the fact that in design II the bending moment will decrease, thus decreasing the amount of force on the abutment.