The Effect of Hydrofluoric Acid Concentration and Heat on the Bonding to Lithium Disilicate Glass Ceramic

Abstract

The aim of this study was to evaluate the effects of hydrofluoric acid (HF) concentration and previous heat treatment (PHT) on the surface morphology and micro-shear bond strength (mSBS) of a lithium disilicate glass ceramic (EMX) to resin cement. One hundred four EMX specimens were randomly assigned to two groups (n=52) according to the HF concentration: 5% and 10%. A new random distribution was made according to the PHTs (n=13): control (no PHT); previously heated HF (70 °C); previously heated EMX surface (85 °C); the combination of heated HF + heated EMX surface. The etching time was set at 20 s. All EMX blocks were silanated and received a thin layer of an unfilled resin. Five resin cement cylinders were made on each EMX surface using Tygon tubes as matrices, and then stored for 24 h at 37 °C. One random etched EMX sample from each group was analyzed using field-emission scanning electron microscopy (FE-SEM). The data were subjected to two-way ANOVA and multiple comparisons were performed using the Tukey post hoc test (a=0.05). For the control groups, 5% HF showed statistically lower mSBS values when compared to 10% HF (p<0.05). PHT increased the mSBS values for 5% HF, yielding statistically similar results to non-PHT 10% HF (p<0.05). FE-SEM images showed increased glassy matrix removal when PHT was applied to HF 5%, but not to the same degree as for 10% HF. PHT has the potential to improve the bond strength of 5% HF concentration on lithium disilicate glass ceramic.

Effect of hydrofluoric acid concentration and etching time on resin-bond strength to different glass ceramics

“…The authors state that the 10% HF removes a larger amount of the glass matrix and exposes more lithium disilicate crystals compared to the 5% HF because it has a higher amount of ionized HF available. By containing half of the ionized HF, the 5% HF did not remove enough glass matrix to produce a suitable micromechanical bond between the ceramic and the resin cement, 30 which may explain the results of our study. Sundfeld Neto et al 31 also investigated different HF concentrations and observed that higher concentrations provided higher bond strengths between disilicate ceramic and resin cement, but for leucite-reinforced ceramics the variation did not yield significant differences, corroborating our findings.…”

“…29 The second hypothesis that different concentrations of HF effect the bond strength was partially accepted, as only the pressed disilicate (LDHP) had a significant increase in bond resistance with the use of 10% HF for 60s. Sundfeld et al 30 who also evaluated 5 and 10% HF in pressed disilicate, observed that 5% HF promoted a lower bond strength compared to the 10% conditioning. The authors state that the 10% HF removes a larger amount of the glass matrix and exposes more lithium disilicate crystals compared to the 5% HF because it has a higher amount of ionized HF available.…”

Influence of different treatments of the ceramic surface and thermal cycling on the bond strength of brackets to ceramic

“…Although, HF acid is well accepted by dental professionals because the solution is easy and quick to apply, effective and cheap 14 . However, it may be harmful for patients and dental personnel 10 because it is corrosive, highly toxic and reactive 15 .…”

Lithium disilicate glass-ceramic surface analysis by atomic force microscopy and optical microscopy

“…The producer of IPS e.max CAD 36 suggests hydrofluoridric acid 5% etching during 20 seconds, but a new study shows that no difference between HF acid 10% and 5% in the same time 37 and, for micro-shear bond, HF 10% is higher when compared with the HF 5% 34 . Furthermore, hydrofluoridric acid 5% etching does not remove enough glassy matrix of lithium disilicate to increase the micromechanical retention of the resin cement in the ceramic surface; in contrast, the HF 10% removes 35 . Hydrofluoridric acid 10% removes the glass-matrix and exposes only lithium disilicate crystals, creating an irregular surface 33 .…”

“…HF acid 5% and 10% are the most usual acids used to change the surface ceramics 35 . The producer of IPS e.max CAD 36 suggests hydrofluoridric acid 5% etching during 20 seconds, but a new study shows that no difference between HF acid 10% and 5% in the same time 37 and, for micro-shear bond, HF 10% is higher when compared with the HF 5% 34 .…”