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Effects of in vitro cyclic dislodging on retentive force and removal torque of three overdenture attachment systems

Authors

  • Mariko Kobayashi,

    1. Division of Fixed Prosthodontics and Occlusion, School of Dental Medicine, University of Geneva, Geneva, Switzerland
    2. Department of Removable Prosthodontics, School of Dental Medicine, Tsurumi University, Yokohama, Japan
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    • These authors equally contributed to this work.
  • Murali Srinivasan,

    1. Division of Gerodontology and Removable Prosthodontics, School of Dental Medicine, University of Geneva, Geneva, Switzerland
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    • These authors equally contributed to this work.
  • Patrick Ammann,

    1. Division of Bone Diseases, Department of Rehabilitation and Geriatrics, Geneva University Hospital, Geneva, Switzerland
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  • Jean Perriard,

    1. Division of Fixed Prosthodontics and Occlusion, School of Dental Medicine, University of Geneva, Geneva, Switzerland
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  • Chikahiro Ohkubo,

    1. Department of Removable Prosthodontics, School of Dental Medicine, Tsurumi University, Yokohama, Japan
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  • Frauke Müller,

    1. Division of Gerodontology and Removable Prosthodontics, School of Dental Medicine, University of Geneva, Geneva, Switzerland
    2. Department of Internal Medicine, Rehabilitation and Geriatrics, University Hospitals of Geneva, Geneva, Switzerland
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  • Urs C. Belser,

    1. Division of Fixed Prosthodontics and Occlusion, School of Dental Medicine, University of Geneva, Geneva, Switzerland
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  • Martin Schimmel

    Corresponding author
    1. Division of Gerodontology and Removable Prosthodontics, School of Dental Medicine, University of Geneva, Geneva, Switzerland
    • Corresponding author:

      Martin Schimmel, PD, Dr med dent, MAS Oral Biol

      Department of Gerodontology and Removable Prosthodontics

      University of Geneva, School of Dental Medicine

      19, rue Barthélemy-Menn

      1205 Geneva, Switzerland

      Tel.: +41 22 379 40 60

      Fax: +41 22 379 40 52

      e-mail: martin.schimmel@unige.ch

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Abstract

Background

Mandibular two-implant-retained overdentures were suggested as first choice of treatment for edentulous mandibles. However, wear of the attachments may reduce their retention and compromise long-term clinical success.

Aim

The aim of this in vitro study was to compare the change in the retentive force and removal torque of three attachment systems during simulation of insertion-removal cycles.

Materials and Methods

Thirty custom-manufactured polyvinyl chloride blocks mimicking an implant-retained overdenture using Locator®-, spherical Dalbo®-PLUS - and SFI®-Bar-attachments on Straumann® RN Implants were fabricated. The samples were distributed equally into three groups which were subdivided into two sets of five blocks, one set with implants parallel to one another and the other with angulated implants (12°). All attachments were tightened to 35Ncm, while the fixation screws of the SFI®-Bar were tightened to 15Ncm. Testing was carried out with an Instron® universal testing machine for a total of 14,600 insertion-removal cycles in 0.9% sodium chloride solution. Retentive forces from cycles 10, 100, 1000, 5000, 10,000 and 14,600 were used for the analysis. The removal torque of the attachments was measured before and at the end of the study. Statistical analysis comprised three-way ANOVA and multiple linear regression models.

Results

Initially, all three attachment systems demonstrated increasing retentive forces. From cycle 5000 on, Locator®-attachments showed lower mean retentive forces than the Dalbo®-PLUS and SFI®-Bar-groups. The Dalbo®-PLUS and SFI®-Bar-attachments showed a steady yet not significant increase during the whole observation period. Implant-angulation had no significant influence on the retention forces. The final mean removal torques were significantly reduced. No complete failure was observed.

Conclusions and clinical implications

Within the limits of this in vitro study, it can be concluded that the investigated overdenture attachment systems are sufficiently resistant to wear. However, the Dalbo®-Plus- and SFI®-Bar- exhibit higher retentive capacities than the Locator®-attachment over time. The fixation screw of the SFI®-Bar may loosen during long-term use, but these observations might be less important if 1-year recall intervals are respected. An angulation of up to 12° between implants does not seem to have a significant effect on attachment wear.

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