STRESS ANALYSIS OF IMPLANTS RETAINED MANDIBULAR OVER DENTURE WITH BAR ATTACHMENT: COMPARATIVE STUDY WITH DIFFERENT CANTILEVER LENGTH (AN IN VITRO STUDY)

Abstract: This study was performed to compare between the stress distribution pattern of three implant retained bar attachment with different cantilever length.
Materials & Methods: Acrylic model was constructed as a test model . Three root-form implants were placed two bilaterally in the canine region and one at the mid line of an edentulous acrylic mandibular model and connected with a resilient bar/clip attachment and attached to the over denture. The strain gauges made a tight contact with implant surfaces. A universal testing machine was used to exert a vertical pressure on the three implants and the strain rate of the implants was measured .The experiment was conducted in two phases: The first phase :(group I) the cantilever bar length was 5mm. The second phase: (group II) the cantilever bar length was 10mm. Micro strains recorded by vertical load applied to the cantilever bar framework were taken for both groups (group I as 5 mm bar and group II as 10 mm bar)..
Results: The mean and standard deviation were calculated and tabulated for further statistical study labio-lingual and Mesio-Distal to the three implants in which the bar with clip was supported the over denture, for (group I) and (group II) there was significant increase of peripheral implants in micro strains than the central implant ,and( group II) revealed that there was significant increase of peripheral implants in micro strains when compare with (group I) , while there was insignificant increase in micro strains of the peripheral implants for both groups.
Conclusion: The 5 mm cantilevered bar with clip was recommended when 3 implants were used to support mandibular over dentures as it demonstrated the lowest magnitude of strains on the central implant ,and regarding the peripheral implants of both groups there was no significant differences between peri -implant sites.