Comparison of detachment forces of two implant overdenture attachment types: effect of detachment speed

To compare detachment (retentive) force for overdenture retainers used with conventional and "mini" implant designs over a range of different detachment (separation) speeds.

Two dental implant fixtures [Sendax MDI ("mini" dental implant) and Replace Select (conventional dental implant design)] with ball attachments were mounted in brass cylinders. Corresponding attachments were processed into acrylic denture resin blocks and connected to the ball attachments on the implants. The fixture/attachment assemblies were placed in an Instron testing system under ambient room temperature and humidity conditions (approximately 72 degrees F and 35-65% relative humidity). The assemblies were separated under tensile load at 11 speeds from 10-500 mm/minute with 10 replicates at each speed. Maximum detachment (separation) force was recorded. Mean, minimum, maximum, standard deviation and range of maximum detachment (separation) force was calculated. To test the hypothesis "the Sendax MDI and the Replace Select have the same average detachment force, at a given detachment speed", one-way ANOVA was performed. To test the hypothesis that "all detachment speeds have the same average maximum detachment force", one-way ANOVA was performed. To test the hypothesis that "the distribution of maximum detachment forces is the same for all detachment speeds", non-parametric Kruskal-Wallis analysis was performed.

For Replace Select, the mean of the maximum force varied from 6.02-3.46 N with a downward trend as detachment speed increased. For Sendax MDI, the mean of the maximum force varied from 3.43-2.86 N. One-way ANOVA and Kruskal-Wallis analyses supported rejection of the hypotheses stated above with more than 99.99% confidence. Within the limitations of this study, the retentive properties of the Sendax MDI and the Replace Select attachment properties were different. Detachment speed had an effect on separation force for the two attachments in this study. Given the range of velocities possible in masticatory function; implant overdenture attachments, optimally, should be evaluated at more than one detachment speed to evaluate clinically-relevant, strain-rate behavior.