Influence of Hydrofluoric Acid Concentration And Etching Time On Pull Off of Lithium-Disilicate Glass Anterior Crowns

Abstract

Aim: Is to evaluate the Influence of hydrofluoric acid concentration and etching time on pull off of lithium-disilicate glass anterior crowns.Material and Methods: forty-five lithium disilicate (IPS e.max cad) full coverage crowns were fabricated on prepared extracted human maxillary central incisors. The crowns (n=45) were divided into three groups (n=15) according to the hydrofluoric acid (HF) concentrations used for the cementation of these crowns to the teeth; I) HF 4.9%, 2) HF 9.6%, 3). HF 11%. Then each group was subdivided into three subgroups (A, B, C) according to etching time (20seconds ,35seconds&60seconds respectively). Each crown was cemented to the corresponding prepared tooth using an adhesive resin cement. Then, the whole crown tooth assembly were subjected to thermocycling (5°C -55°C,5000 cycles,). A universal testing machine was used to assess pull-off test. Data were collected, tabulated and statistically evaluated. Results:The results showed a statistically significant difference in the mean values of the pull off test between the groups regarding HF concentration. Group 1 (4.9% hydrofluoric acid) (206.5 ± 13.1) < group 2 (9.5% hydrofluoric acid) (244.1 ± 25.4) < group 3 (11% hydrofluoric acid) (284.4 ± 13.5). For 9.6% and 11% HF acid concentrations, etching durations used in this study do not have a significant effect on the retention of lithium disilicate glass crowns. However, for 4.9% HF the retention means significantly increased with elevating the etching duration.