Influence of abutment height and thermocycling on retrievability of cemented implant-supported crowns.

Abstract To evaluate the influence of abutment height and thermocycling on the retrievability of cemented implant crowns. Ninety tapered titanium abutments (6 degree taper, 4.3 mm diameter, 8.5 mm height) were shortened to 2, 3, or 4 mm, respectively. Ninety crowns were designed and manufactured using CAD/CAM techniques and laser sintering a CoCr alloy. The crowns were cemented either with a glass-ionomer, a polycarboxylate, or a composite resin cement followed by 3-day storage in demineralized water without thermocycling or 150-day storage with 37,500 thermal cycles. The force (in N) and the number of attempts needed to remove the crowns using a universal testing machine (UTM) or a clinically used removal device (Coronaflex) were recorded. Statistical analysis at a level of significance of P ≤ .05 was conducted using the Kruskal-Wallis and Mann-Whitney U tests (Coronaflex) and three-way and two-way ANOVA, Tukey's HSD post hoc tests, and t tests (UTM). Regardless of whether the crowns were retrieved with Coronaflex or UTM, the crowns cemented with the glass-ionomer cement were significantly easier to retrieve followed by the polycarboxylate and the resin cement, both of which differed significantly from each other (P ≤ .001). With both retrieval methods, the cement, abutment height, and thermocycling were significantly influential (P ≤ .0001). Significant interactions could be found for retrieval with UTM between the abutment height and thermocycling, between the cement and thermocycling, and between all three factors (P ≤ .05). Glass-ionomer cement may be used for retrievable cementation of implant restorations, whereas polycarboxylate cement and especially composite resin cement should be used for a nonretrievable permanent cementation.