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Retention forces of spherical attachments as a function of implant and matrix angulation in mandibular overdentures:
Sergio M Ortegón1, Geoffrey A Thompson, John R Agar
1Prosthodontics Department, University of Texas Dental Branch at Houston, TX 77030, USA. Sergio.Ortegon@uth.tmc.edu
Statement Of Problem:
Nonparallel implants, when used to retain overdentures, may present a restorative challenge, particularly when using attachments. Premature wear of the components and loss of retention may be observed, resulting in increased maintenance.
Purpose:
The purpose of this study was to compare the retentive behavior, over time, of spherical attachments when used in nonparallel and parallel implant scenarios in a cyclic testing mode.
Material And Methods:
Thirty sets of 2-implant-supported overdenture models were evaluated: 4.0 x 13-mm implants (Astra-Tech Osseospeed) with 1.5-mm ball abutments (Astra-Tech) were used as the intraoral analog to the implants, and spherical attachments (Preci Clix) were used as the overdenture analog. Five different attachment and implant-abutment complex angulations were evaluated. Angulation was determined by deviation from the vertical reference plane. The groups consisted of the following: Group 0-0, 0-degree implants/0-degree attachments; Group 10-0, 10-degree implants/0-degree attachments; Group 15-0, 15-degree implants/0-degree attachments; Group 10-10, 10-degree implants/10-degree attachments; and Group 15-15, 15-degree implants/15-degree attachments. The specimens were subjected to cyclic loading (3500 cycles). Peak and valley retention loads were recorded at the first pull and then after every 100 cycles; therefore, 36 data points per specimen were recorded. Nonparametric analyses followed by post hoc analyses were conducted to test for differences in median peak load among groups (alpha=.05).
Results:
Peak load to dislodgment values for all groups ranged from 11.43 N to 23.56 N. Group 0-0 had the highest median retention value overall, 21.3 N, and Group 15-15 had the lowest median value, 17.3 N. Nonparametric analyses showed significant differences between Groups 0-0 and 15-15 (P=.014); and 10-0 and 15-15 (P=.002).
Conclusions:
Within the limitations of this study, it was observed that there was a decrease in retention in the groups with 30-degree divergent implants and divergent attachments compared to the groups with parallel implants and parallel attachments. In general, retention varied from 11 N to 23 N, and attachment retention stabilized after initial loss in most groups.
