The influence of two different cements on remaining cement excess in cement-retained implant-supported zirconia crowns.

Implant-supported restorations can be screw- or cement-retained. A key drawback of cement-retained restorations is biological complications associated with undetected residual cement, which can irritate peri-implant tissues, promote bacterial adhesion, and contribute to peri-implant disease. Prior clinical observations report higher rates of biological complications and greater bone loss with cement-retained restorations compared with screw-retained ones, and a strong association between residual cement and peri-implant inflammation. Removing excess cement is challenging, especially with submucosal finish lines and in interproximal areas. Material properties may influence ease of cement excess removal. A hybrid calcium aluminate glass ionomer cement (CAGIC) exhibits a rubber-like consistency during setting, thin film thickness, relatively short setting time, and higher hardness/strength, potentially enabling easier removal versus conventional zinc phosphate (ZNPH). Research question/hypothesis: Does the cement type affect the amount of remaining cement excess after cementation of implant-supported zirconia crowns? Hypothesis: CAGIC will leave less remaining cement excess than ZNPH due to its handling and mechanical properties.

The paper summarizes prior evidence indicating that residual cement around implant restorations is common and is linked to peri-implant disease; biological complications are more frequent in cement- versus screw-retained restorations, with reports of increased bone loss around cement-retained implants. Studies show removal of cement is difficult, particularly with submucosal margins, undercuts, low viscosity, and larger implant diameters. The timing of removal differs by cement type; early removal is advised for resin and glass ionomer to prevent adhesion. CAGIC has favorable properties (rubber-like set, thin film, higher hardness and compressive strength) that may facilitate removal compared with ZNPH, traditionally considered a standard water-based cement but brittle and prone to fragment during removal.

Design: In vitro experimental study. Specimens: 22 identical casts with implant analogs in the position of the maxillary right central incisor and gingival masks were fabricated; after pilot testing on 2 models, 20 zirconia crowns were included and allocated to two groups: CAGIC (Ceramir Crown & Bridge) n=10 and ZNPH (Harvard Cement) n=10. Abutments: Titanium abutments with a guide chute; finish line approximately 1.5 mm below the gingival margin. Crowns: Zirconia (DD cube ONE HT+), designed and milled with a cement gap of 0.35 µm; venting holes sealed with a composite lid to allow later disassembly and prevent cement leakage. Screw access protected with PTFE tape and silicone. Surfaces cleaned with ethanol and water. Cementation protocol: Capsules activated per manufacturers’ instructions and mixed (CAGIC 8 s; ZNPH 10 s) at 4500 rpm. Cement applied to crown intaglio; crowns weighed pre- and post-cement application to standardize cement amount and document cement weight per specimen. After 1 min, crowns were seated with maximal finger pressure (~55 N) for 3 min (CAGIC) or 10 min (ZNPH). Excess cement removal timing followed manufacturer guidance but doubled for the ex vivo setting: CAGIC excess removed at ~4 min at a rubber-like set; ZNPH excess removed after 10 min. Removal tools: Stainless steel probe and dental floss to simulate clinical removal. After initial seating, an axial load of 52 N was applied for 5 min for both groups. After 24 h, the specimen (crown+abutment) was removed from the cast via abutment screw access. Measurements of remaining cement: Two methods were used. 1) Pixel area calculation: Each specimen was positioned in six custom putty/silicone molds corresponding to the six hex sides of the abutment. Images were captured under a stereomicroscope at 12× zoom and analyzed with Leica Suite and Adobe Photoshop. A standardized measurement window was defined (bounded by the hex side edges and 1 mm coronally beyond the finish line). Cement remnants were manually selected; particles smaller than 8 pixels were excluded. Total cement pixels per side were recorded; six measurements per specimen yielded n=120 areas. 2) Weighing: After imaging, cement remnants on specimens and in gingival masks were removed and weighed on a 0.0001 g precision scale to obtain total remaining cement mass. Statistics: Independent Samples t-test compared groups for mean total pixels and mean total mass per specimen. Significance level p=0.05. Single operator performed all steps to avoid inter-operator variability.

- Zinc phosphate cement (ZNPH) left significantly more remaining cement than calcium aluminate glass ionomer cement (CAGIC) by both metrics: pixel area (p=0.002) and mass in grams (p=0.005). - Distribution: For ZNPH, the greatest amount of remaining cement was mesial (putty mold P6). For CAGIC, the greatest amount was distal (P2).

Findings support the hypothesis that cement type influences the ease and completeness of excess cement removal. CAGIC’s shorter setting time to a rubber-like phase and higher hardness likely facilitated removal in larger, more coherent pieces, reducing remnants. In contrast, ZNPH’s brittle nature led to fragmentation into multiple small pieces, increasing residual cement. Timing of removal aligned with manufacturer recommendations but occurred at different set stages for the two materials, which may have influenced outcomes; however, this reflects real-world handling differences. Submucosal finish lines (~1.5 mm) and interproximal constraints increased difficulty of removal for both groups, with more remnants mesially/distally than buccal/palatal, consistent with prior literature. Measurement methods complemented each other: pixel analysis localized remnants but excluded cement retained in gingival masks; weighing captured total remnants from both specimen and mask but lacked spatial detail. Despite these methodological nuances, both methods consistently showed higher remnants with ZNPH.

Within the limitations of this in vitro study, calcium aluminate glass ionomer cement (CAGIC) resulted in less remaining cement excess than zinc phosphate (ZNPH) when cementing implant-supported zirconia crowns. CAGIC may be a more suitable cement for cement-retained implant restorations and could potentially reduce peri-implant biological complications related to cement remnants. Confirmation in future clinical studies is needed.

- In vitro model may not fully replicate clinical conditions. - Finish line positioned ~1.5 mm submucosal increases difficulty of removal and may influence generalizability. - Interproximal areas were partially represented by gingival mask and dental stone (only half papilla in mask), potentially affecting access and cement retention; mesial fit of the gingival mask was tighter than distal. - Pixel-based measurement excluded cement left within the gingival mask and omitted very small particles (<8 pixels); straight-line measurement windows on a conical abutment may have left small areas unmeasured or risked overlap. - Different removal timing stages between cements (per manufacturer guidance) could influence outcomes. - Single operator; while reducing inter-operator variability, limits assessment of technique variability. - Sample size modest (n=10 per group) and only two cement types evaluated; no clinical outcomes assessed.