Comparing the Retentive Force of O-ring and Several Retained Systems for One-piece Root-form Implant-retained Overdentures

  • Kobayashi Mariko
    Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine

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Purpose: Little is known about the connection between the Nobel Direct (ND; Nobel Biocare, Sweden) abutment head and the denture base when ND is used for an overdenture. This study evaluated the retentive force of several retainers for ND-retained overdentures.<BR>Methods: The bodies of two sizes of ND [3.0-mm dia. (ND3.0); 4.3-mm dia. (ND4.3)] were embedded in a brass patrix frame (10×10×25 mm) by using autopolymerized polymethyl methacrylate (PMMA; Unifast II, GC Corp.). Four sizes of O-rings [O3 (1.6-mm dia.), O4 (1.9-mm dia.), O5 (2.8-mm dia.), O6 (3.8-mm dia.)], ND healing caps (HC; Nobel Biocare), and protection caps (PC; Straumann) were prepared for attachment matrixs. O3 to O6, ND, and PC were placed at the ND3.0 and ND4.3 abutment heads, respectively. As a control, the PMMA resin (RE) was directly used to connect the abutment head to the denture base resin without retainers. For ND4.3, the entire and upper-half of the abutment head was covered with the above materials to compare the different contact areas between the patrix and matrix. The connected patrix and matrix frames were mounted on a screw-driven mechanical testing machine (Model UTM II, Toyo Boldwin, Japan). The retention of double retainers (20-mm apart) were also measured with the angles of two ND4.3 abutment heads of 0, 6, and 12 degrees. The retentive force (n=5, N) obtained at a crosshead speed of 40 mm/min was analyzed by analysis of variance (ANOVA)/Scheffé’s test (α=0.05).<BR>Results: The retentive force of ND3.0 and ND4.3 was significantly the greatest when O3 and PC, respectively, (P<0.05) were used. For ND3.0, the retentive force of O4, RE, and HC was one-third of that of O3. For ND4.3, the retentive force of RE and O5 was two-thirds of that of PC and that of O6 was one-third of the retentive force of PC. The retentive force of full contact was approximately two times greater than that of the upper-half contact. The angle of the two NDs did not affect the retentive force (P>0.05).<BR>Conclusion: When the medium-sized O-ring, PMMA, and HC were used, an appropriate retentive force was obtained for the ND implant-retained overdentures.

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