Effect of application technique and coping design on the retention of cemented implant-supported crowns.

Statement of problem: Cement-retained implant crowns are susceptible to biological complications from excess cement extrusion and unpredictable retention because of variations in cementation technique and coping design. However, the biomechanical and hydrodynamic effects of cement volume, application method, and venting features on retention and marginal seal integrity remain inadequately characterized.

Purpose: The purpose of this in vitro study was to investigate how cement volume, application method, and coping design affect crown retention and cement extrusion.

Material and methods: Fifty computer numerical control (CNC)-milled stainless-steel copings were machined with an average +133 µm tolerance fit on 3-mm hexagonal abutments and were divided equally into 5 groups consisting of closed-end coping with measured cement, no aging (CE-MC-NA); closed-end coping with filled cement, no aging (CE-FC-NA); closed-end coping with measured cement, aged (CE-MC-AG); closed-end coping with filled cement, aged (CE-FC-AG); and open-vented coping with filled cement, aged (OV-FC-AG). Assemblies were weighed before cementation (W₁), after cementation (W₂), and after excess cement removal (W₃). Cement extrusion=(W₂ - W₃) - W₁ and net retained cement =W₃ - W₁. For measured-coated copings, a controlled volume of cement (not exceeding the internal void volume) was applied using a brush, and the net cement delivered was calculated based on weight differences before and after cementation. Aging consisted of 500 thermocycles (5 °C to 55 °C, 30-second dwell). Marginal integrity was evaluated using dye penetration and microscopic inspection, and retention strength (N) was measured using a dislodgement test. Analyses used Mann‑Whitney U, Kruskal‑Wallis with Bonferroni‑adjusted planned contrasts, and a 2×2 factorial ANOVA.

Results: Group CE-MC-NA had significantly lower retained cement weight than group CE-FC-NA (P<.001), with comparable retention strength (P>.05). After aging, group CE-MC-AG showed significantly less retained cement than group CE-FC-AG (P<.001), and both retained less cement than group OV-FC-AG (P<.001). Retention strengths were similar for groups CE-MC-AG and CE-FC-AG (P>.05), while OV-FC-AG exhibited superior retention (P<.001). No marginal leakage was detected in any group.

Conclusions: Under the experimental conditions, measured thin-film cementation combined with vented or geometrically optimized copings provided a biomechanically effective and biologically safer alternative to traditional bulk-filling techniques. By standardizing application and leveraging interface design, this protocol should redefine luting cement as a precise sealing interface rather than a bulk retentive material.