Method for Measuring Dynamic Extraction Force of Test-Mandrel from Dental-Handpiece

Objective: The objective of this work is to report a novel method for measuring the dynamic extraction-force of a test-mandrel from a dental handpiece and use this method to collect dynamic extraction-force data on a dental air-turbine handpiece for comparison with static extraction-force data.

Methods: Six disposable-dental-handpieces from one manufacturer (Azenic Inc.) were tested using an Instron-Universal-Testing-Machine. Three handpieces were used for static-testing(S1,S2,S3) and three for dynamic-testing(D1,D2,D3) respectively. Custom-made components include an extra-long test mandrel fitted with a bushing inserted into a dental-bearing placed inside a cylindrical fixture which pulls the handpiece against a stationary fixture plate(Fig1). For each handpiece in the respective groups, five extraction tests were performed. The maximum-force was recorded as the extraction-force. For the static extraction-force tests, the test-mandrels were extracted at 5mm/min without the handpieces running. For the dynamic extraction-force tests, the test-mandrels were extracted at 20mm/min with the handpiece operating at the manufacturer's recommended operating pressure of 40psi. The faster rate for the dynamic-testing was for heating concerns. Pilot testing determined that the maximum-force during extraction was unaffected by these different extraction rates.

Results: See Table1. The average force required to extract a test-mandrel during operation was found to be significantly less than that required for extraction under a non-operational state by approximately 18.7N (one-wayANOVA, p<0.05). Note that ISO7785-1 “Dental-handpieces-Part1:High-speed air-turbine handpieces” specifies the force required to extract a test-mandrel from a dental-handpiece should be at least 22N.        

Conclusions:   A novel test method for measuring the dynamic extraction force of a test-mandrel from a dental handpiece is reported along with the results of using this method to collect dynamic extraction force data for a disposable dental air-turbine handpiece for comparison with static extraction force data.