A novel 'stop-hole' strategy to extend the fatigue life of orthodontic thermoformed retainers: an in vitro study.

Objectives: This study aimed to investigate the potential to limit crack propagation in thermoformed retainers (TRs) and extend their fatigue life by placing a 'stop-hole'.

Methods: Thirty-two TRs, fabricated from 1 mm thick, round polyethylene terephthalate glycol (PETG) blanks of ICONIC®, underwent testing within a custom-built fatigue tester. After initial crack growth of 3 mm, the TRs were divided into three groups: a control group (C) and two experimental groups based on the stop-hole placement method. In the first experimental group, stop-holes were placed using a 1 mm round carbide bur on a slow-speed handpiece (ES), while the second group utilized a heated 1-mm-width ball-ended CPITN probe (EH). Following the placement of a stop-hole at the crack-tip, all 32 TRs resumed testing until the final crack length of 10 mm was reached.

Results: Stop-hole placement significantly prolonged the delay in crack re-initiation in both experimental groups compared to the control group (P < .001 for both). The mean re-initiation times for the ES and EH groups were 104.50 and 129.50 min, respectively, whereas the control group was 28.94 min. Consequently, this discrepancy was reflected in the total testing times, with both experimental groups requiring significantly longer time to reach the final crack length (P < .001). There was no significant difference in the testing times between the two experimental groups.

Limitations: This is an in vitro study.

Conclusions: The stop-hole methodology significantly extended the fatigue life of a TR in a controlled laboratory environment.