Properties of a custom-made hinge clasp compared with a conventional circumferential clasp

The use of the hinge clasp in removable partial denture design, together with the design of a custom-made hinge unit, is discussed in this article. Tests of the retention provided by these custom-made hinge clasps were made, together with conventional clasps, and the results were compared. Six custom-made hinge clasps were constructed and attached to blocks of acrylic resin. The forces required to open these clasps and the effect of wear on the clasps were measured. Six conventional cast clasping units were also constructed and tested. The results indicated that the average force required to open the hinge clasps was 8.13 N (SD 1.99). After a period of simulated wear, the mean value of force required was 7.70 N (SD 2.33) and there was no statistically significant deterioration caused by wear. The mean forces required to withdraw these clasps vertically from a tooth were 30.25 N (SD 6.51) for the conventional clasps and 49.67 N (SD 18.69) for the hinge clasps. It was also found that the hinge clasps had to be withdrawn further from their seated position than the conventional clasps before retention was finally lost. However, neither of these differences were statistically significant.