Objective: The objective of the study is to measure the in vitro retention overall pull-off force of telescopic crowns made from two different materials and with different taper angles.
Materials and methods: The telescopic crowns were digitally fabricated from two materials, Polyether-ether ketone (PEEK) disc and graphene-nano reinforced acrylic disc (GN) at three taper angles (0˚, 1˚ & 2˚). Retention force for each specimen was measured 20 times in a pull off- Test, the machine was set to a crosshead speed 50 mm/min applying tension mode of force up to crown dislodgement. Twenty cycles of insertion and removal were performed for each sample and then the retention force was computed and recorded using computer software. Statistical analysis was carried out using Two-way analysis of variance (ANOVA) to explore the effect of different materials and degree of taper on the retention load. Independent sample t-test was conducted to explore the difference between materials.
Results: The retention force of 2 ° taper showed a statistically significant lower value than 0° and 1° tapers. The specimens of the PEEK groups showed significantly higher initial retentive force values than (GN) groups.
Conclusions: Telescopic crowns fabricated from PEEK milled material showed better retention force than the GN milled material. Increasing the degree of taper angle of the telescopic crown above 1° could jeopardize the resultant retention. However, long-term clinical studies are still recommended