Maximum dislodging forces of mandibular implant-assisted removable partial dentures: in vitro assessment.

PURPOSE: The initial retention of implant-assisted removable partial dentures (IARPDs) is unknown. The purpose of this in vitro study was to compare maximum dislodging forces of distal extension mandibular IARPD with two different attachments and three clasp designs. MATERIALS AND METHODS: A simulated class I partially edentulous mandible was prepared with two screw-type 3.75 x 12 mm implants in the first molar regions and 2 metal-ceramic crowns on distal abutments. Fifteen bilateral distal extension frameworks were conventionally fabricated in three clasp designs (suprabulge, infrabulge, no clasp). Locator attachments were connected to the 15 denture bases with autopolymerized resin. Each specimen was subject to four types of retention pulls (main, anterior, posterior, unilateral pull) five times with a universal testing machine. Locator attachments were replaced with O-ring attachments, and the same procedure was performed. Therefore, the study groups included: IRPD with Locator attachment and suprabulge clasp (group 1), IRPD with Locator attachment and infrabulge clasp (group 2), IRPD with Locator attachment and no clasp (group 3), IRPD with O-ring attachment and suprabulge clasp (group 4), IRPD with O-ring attachment and infrabulge clasp (group 5), IRPD with O-ring attachment and no clasp (group 6). Data were analyzed using one-way ANOVA, two-way ANOVA, and Tukey tests. RESULTS: The highest mean value was 22.99 lb for prostheses with a Locator attachment and suprabulge clasp. The lowest retentive values were recorded for IARPDs with O-ring attachments. CONCLUSION: The results of this in vitro study suggest that the precise selection of attachments with or without clasp assemblies may affect the clinical success of mandibular IARPDs.