Torque loss under mechanical cycling of long-span zirconia and titanium-cemented and screw-retained implant-supported CAD/CAM frameworks

Authors

  • Érica Alves Gomes,

    1. Department of Dental Materials and Prosthodontics, Dental School of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Brazil
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  • Rodrigo Tiossi,

    1. Department of Dental Materials and Prosthodontics, Dental School of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Brazil
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  • Adriana Cláudia Lapria Faria,

    1. Department of Dental Materials and Prosthodontics, Dental School of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Brazil
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  • Renata C. S. Rodrigues,

    1. Department of Dental Materials and Prosthodontics, Dental School of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Brazil
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  • Ricardo Faria Ribeiro

    Corresponding author
    1. Department of Dental Materials and Prosthodontics, Dental School of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Brazil
    • Corresponding author:

      Ricardo Faria Ribeiro

      Department of Dental Materials and Prosthodontics, Dental School of Ribeirão Preto

      Av. do Cafe, sn - Monte Alegre

      14040-904 - Ribeirao Preto - SP Brazil

      Tel.: +55 16 3602 4046

      Fax: +55 16 3602 0547

      e-mail: rribeiro@forp.usp.br

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Abstract

Objectives

This study evaluated the screw joint stability after cyclic loading of implant-supported titanium and zirconia CAD/CAM frameworks for fixed dental prostheses (FDPs) with different retention methods.

Material and methods

Twenty four one-piece frameworks supported by six threaded implants placed in the maxilla were fabricated using a CAD/CAM technique (NeoShape). Dry-pressed porcelain crowns were luted to the frameworks to standardize the specimens. The specimens were then divided into four groups (n = 6) according to framework material (titanium or zirconia) and retention method for the prosthesis (cement- or screw-retained): G1, Ti-cemented; G2, Ti-screw-retained; G3, Zr-cemented; and G4, Zr-screw-retained. A digital torque ratchet was used to assess the initial preload removal torque. Torque was then reapplied and the specimens were submitted to a 200 N cyclic load, at a frequency of 2 Hz, underwater in controlled temperature of 37°, and for 1 × 106 cycles. An opposing lower dental arch was fabricated using bis-acrylic resin to simulate occlusal contacts in centric. After cyclic loading, postload removal torque was measured. Preload and postload torque loss was expressed as a percentage of the initial load. Data were submitted to a linear mixed-effects model for statistical significance (α = 0.05) to evaluate the effect of cyclic loading in the screw torque loss used with frameworks of different materials and retention methods.

Results

Significant screw torque loss (%) was found for the tested groups (before/after cyclic loading, respectively): G1 (39.77/61.83), G2 (37.57/50.96), G3 (34.87/54.10), and G4 (47.56/73.50) (P < 0.05).

Conclusions

The screw removal torque was significantly reduced for all groups in this study after cyclic loading the specimens. Screw-retained zirconia specimens presented the highest torque loss before and after the cyclic loadings compared with the other specimens that were tested.

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