Methodology for measuring the in vitro seating and unseating forces of prefabricated attachment systems used to retain implant overdentures

J Prosthodont. 2010 Feb;19(2):87-94. doi: 10.1111/j.1532-849X.2009.00525.x. Epub 2009 Nov 4.


Purpose: The purpose of this in vitro investigation was to measure the forces generated during the continuous seating and unseating of prefabricated attachment systems used to retain implant overdentures.

Materials and methods: An experimental design consisting of interchangeable fixture mounts, a radially indexable fixture holder, and a materials testing systems (MTS) machine was used to measure forces generated during the insertion and removal of spherical stud attachments (Straumann, Inc, Waltham, WA). Three separate experiments were conducted measuring the seating and unseating forces of a vertically aligned patrix/matrix assembly, a 20 degrees angled patrix opposing a vertically positioned matrix, and a vertically positioned patrix opposing a 20 degrees angled matrix. For each patrix/matrix combination, three specimens were tested. Measurements were continuously recorded under reproducible conditions in the presence of artificial saliva. All specimens were subjected to 10,000 seating/unseating cycles. Statistical analysis was performed with rank analysis of variance (ANOVA) for a group comparison (alpha= 0.05).

Results: Results showed variability in the initial insertion and removal forces among experimental groups and among specimens within each experiment. A marked increase in the seating and unseating forces was recorded for all specimens during the first 300 cycles, followed by a gradual decrease in these forces. The exact p-values for the Kruskal-Wallis test showed no significant difference between the initial and final seating/unseating forces (p > 0.1) nor in the maximum seating/unseating forces (p > 0.6) among the three experimental groups.

Conclusions: Spherical stud attachments exhibited consistent seating and unseating forces over 10,000 cycles. A 20 degrees angle between the patrix and matrix had no effect on the overall seating and unseating force values.

Publication types

  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Analysis of Variance
  • Dental Prosthesis, Implant-Supported*
  • Dental Stress Analysis / instrumentation
  • Dental Stress Analysis / methods*
  • Denture Design
  • Denture Precision Attachment*
  • Denture Retention / instrumentation*
  • Denture, Overlay*
  • Saliva, Artificial
  • Statistics, Nonparametric


  • Saliva, Artificial