Comparative Evaluation of the Effect of Location and Number of Implants on the Retention and Stability of Magnetically Retained Implant Supported Mandibular Overdenture: An In Vitro Study

The present in vitro study was conducted to comparatively evaluate the effect of location and number of implants on the retention and stability of magnetically retained implant supported mandibular overdenture. A mandibular reference denture was fabricated on a mandibular edentulous model. It was used to position the implant replicas in the three wax models obtained from a lower edentulous model former. The wax models were processed to obtain three acrylic test models with the implant replicas incorporated in them. All the three acrylic models were duplicated to obtain stone casts on each of which a mandibular test denture was fabricated respectively. The components of the magnetic attachments were incorporated into the acrylic test models and the test dentures. Each acrylic model with the test denture represented one test specimen. Specimen A comprised of a mandibular test denture with the magnetic attachment system connected to the implant replicas placed in the B and D position in the mandibular edentulous acrylic model. Specimen B comprised of a mandibular test denture with the magnetic attachment system connected to the implant replicas placed in the A and E position in the mandibular edentulous acrylic model. Specimen C comprised of a mandibular test denture with the magnetic attachment system connected to the implant replica placed in the C position in the mandibular edentulous acrylic model. The three test models with the test dentures were subjected to the tests for retention and stability in an universal testing machine by application of a pulling force with a cross head speed of 50mm/min. The load at which the denture detached from the model was considered as the dislodging force and it was recorded in Newtons. Each test denture was subjected to three different tests. Test No.1 was conducted to evaluate the effect of vertically directed dislodging forces. Test No.2 was conducted to evaluate the effect of oblique rotational dislodging forces. Test No.3 was conducted to evaluate the effect of posterior rotational dislodging forces. The results of the study showed that for the Test No.1 the specimen B had the highest values followed by specimen A and specimen C. On comparison between the specimens it was shown that there was no statistically significant difference between specimen A and specimen B and a statistically significant difference between specimen B and specimen C and also between specimen A and specimen C. For Test No.2 the specimen A had the highest values followed by specimen B and specimen C. On comparison between the specimens it was shown that there was statistically significant difference between all the three specimens. For Test No.3 the specimen B had the highest values followed by specimen A and specimen C. On comparison between the specimens it was shown that there was no statistically significant difference between specimen A and specimen B and a statistically significant difference between specimen A and specimen C and also between specimen B and specimen C. Specimen A samples had highest values for Test No.1 followed by Test No.2 and Test No.3. Specimen B samples had highest values for Test No.1 followed by Test No.3 and Test No.2. Specimen C samples had highest values for Test No.1 followed by Test No.3 and Test No.2. On comparison within Specimens it was seen that there was a statistical significance difference between the results of all three tests in all the three specimen except between Test No.2 and Test No.3 of Specimen B. The present study concluded that the change of location of implants from B and D to A and E position did not significantly affect the retention and stability of the overdenture, with respect to the vertically directed dislodging forces and posterior rotational dislodging forces. Whereas the retention and stability significantly decreases with respect to oblique rotational forces. The mandibular overdenture with magnetic attachment over a single implant has the least retention and stability. Even though the retention and stability of the mandibular overdenture with a single implant in the midline was the least, it can still be considered as an amenable option for edentulous patients of lower socio-economic status. It can also be considered as an option in elderly patients with atrophic mandible in whom extensive surgery is not feasible. This option can also improve satisfaction with complete dentures in patients with adaptive disorders