STRESS ANALYSIS OF TWO DIFFERENT ATTACHMENTS FOR A TWO IMPLANT RETAINED MANDIBULAR OVERDENTURE

Background: Implant overdenture retained by two implants installed in the interforaminal area of the completely edentulous mandible has become the standard of care for completely edentulous patients. Various attachments have been used to retain a mandibular implant retained over denture, the ball attachment has been the most commonly used un-splinted attachment to retain a mandibular overdenture owing to its low cost and simplicity. A newly introduced attachment made from polyetherketoneketone (PEKK) which have reported to have high chemical and mechanical resistance to wear and high tensile, fatigue and flexural strengths. The aim of this in vitro study is to analyze the distribution of stresses around the two installed implants in the inter-foraminal area of a completely edentulous mandible using strain gauges utilizing an implant retained overdenture with two different types of attachments one with a nylon cap and the other with a PEKK cap.Materials and Methods: A clear heat cured acrylic completely edentulous mandibular model has been used in this in vitro study to fabricate a lower conventional acrylic denture following conventional steps. In the canine region bilaterally two dummy implants were installed and attached to the model using self-cure acrylic resin. The acrylic resin was prepared around each implant into a box shape with a thickness of 1mm into four surfaces; buccal, lingual, mesial and distal. Strain gauges of length 5mm, resistance of 120.4±0.4 Ω and a gauge factor of 2.09 ± 1 %, were attached to each surface. The same lower acrylic denture was used for pickup of the two attachments; the ball and CMLOC attachment. The implant retained overdenture retained by the each attachments was subjected to unilateral and bilateral vertical static load of 100N using a universal testing machine. The wires of the strain gauges were connected to the strain meter to record the micro-strain using a special software, 10 readings were recorded for each attachment. Results: when the implant retained overdenture have been subjected to unilateral loading, the loading side have recorded a higher statistically significant mean micro-strain than the unloaded side retained by both attachments, The overdenture retained with ball attachment have shown a significant increase in micro-strain on the loaded side than that with the CM LOC attachment, while for the unloaded side the overdenture retained with CMLOC attachment induced more micro strain than the ball attachment. While during bilateral loading, a statistically significant higher mean micro strain was recorded in the left implant than the right implant, and the CM lOC have shown a higher statistically significant mean micro strain than the ball attachment for the left implant , while the ball attachment have shown a statistically significant increase in micro strain for the right implant. Conclusion: The newly introduced attachment the CM LOC tends to show a better performance with regards to the micro-strains induced around the implants and also regarding improving the stability of the denture, On the other hand the ball attachments despite having induced more micro-strain around the implants, it could have a higher retention than the CM LOC attachment. Further studies comparing the retention of the new attachment CM LOC and the ball attachment has to be carried out to confirm the conclusion of the present study.