Fracture load and retention of milled interim implant restorations fabricated on three types of abutments and two implant diameters: An in vitro study.

Purpose: To evaluate the fracture load and retention of subtractively manufactured interim restorations for single-unit implants of two diameters, using three interim abutment types: stock abutments, titanium base (Ti-base) abutments, and pre-milled polymethyl methacrylate (PMMA) abutments.

Materials and methods: A total of 90 milled PMMA interim restorations were fabricated on three abutment types: (1) cement-retained restorations on stock abutments (stock group), (2) screw-retained restorations on Ti-base abutments (Ti-base group), and (3) screw-retained restorations fabricated on pre-milled PMMA abutments (pre-milled PMMA group). For fracture load testing, 60 restorations were allocated across implants with two diameters (Ø3.5 mm and Ø4.5 mm), forming six groups (n = 10 per group). Crown retention was evaluated by pull-out testing following cyclic loading on 30 restorations (n = 10 per abutment type), and failure modes were recorded. Statistical analyses were conducted (α = 0.05).

Results: The Ø4.5-mm implants exhibited higher fracture loads than the Ø3.5-mm implants (p < 0.001). For both implant diameters, the pre-milled PMMA group had significantly lower fracture loads than the stock and Ti-base groups (p < 0.05). Nevertheless, all groups' fracture loads were significantly higher than the reported maximum occlusal force (p < 0.001). The pre-milled PMMA group demonstrated the highest pull-out force, significantly exceeding that of the stock and Ti-base groups (p < 0.001).

Conclusions: The pre-milled PMMA group demonstrated superior retention but lower fracture load than the stock and Ti-base groups. The Ø4.5-mm implants exhibited higher fracture loads compared to the Ø3.5-mm implants. Despite the lower fracture load of the pre-milled PMMA group, all three abutment types surpassed the reported maximum occlusal force.