Retention of Mini Dental Implant Retained Overdentures

Objective: To measure the retentive capabilities of mandibular overdentures when retained by mini dental implants (MDI). The number and position of MDIs was varied.

Method: An acrylic model representing an edentulous mandibular arch and a denture were fabricated in high impact denture acrylic resin (Lucitone 199). Five mini implants were placed in the anterior region of the mandibular acrylic arch and associated housings were picked up into the mandibular denture using acrylic resin. The denture was then attached, via acrylic resin, to an aluminum plate with a perpendicular bolt for connection to the cross head of an Instron universal testing machine. The denture was pulled in a direction perpendicular to the arch at a rate of 50mm/min. The maximum load to dislodge was recorded in Newtons.  Seven combinations of position and number of implants were tested by placing and removing the O-rings.  The test was repeated twenty times to access wear of the O-rings for each of the seven combinations of  MDIs. Data was analyzed via ANOVA and Tukey-Kramer HSD tests (Jump Software).

Result: The mean force (and standard deviation) in Newtons for dislodgement for the seven combinations were as follows: 1 MDI midline = 4.13(0.15), 2 MDIs narrow = 7.84(0.24), 2 MDIs wide = 13.49(1.26), 3 MDIs narrow =18.50(0.35), 3 MDIs wide =19.54(0.21), 4 MDIs = 24.10(0.33), 5 MDIs = 26.86(1.23). Each combination was statistically significantly different from all other combinations.  Repeated testing, 20 times, did not result in a loss of retention.

Conclusion: Mini dental implant overdentures are an acceptable alternative when traditional implants are not indicated.  This study recommends four mandibular overdenture mini dental implants, as five was not a clinically significantly increase in retention.  Position affected the amount of retention only when using two mini dental implants, in which case a wide orientation was more retentive.