IADR Abstract Archives
Over-etching of Silica-based Ceramics
Objectives: To investigate the effect of over-etching on silane priming efficacy and to explore methods to remove the white solid generated by over-etching.
Methods: Porcelain discs (GC-Initial) were used as received, or etched by Porcelain Etchant (4%HF/5min-appropriately etching, or 9.5%HF/10min-overetching; Bisco). The etched porcelain discs were subjected to tap water or pressurized water rinse (1min), ultrasonication cleaning in water bath (2min), or phosphoric acid etchant cleaning (37%-1min) with or without agitation. One sample from each group was then examined by microscope and scanning electron microscope (SEM). The remaining samples in each group were applied with a silane primer (Bisco Porcelain Primer) for 5 minutes, followed by ethanol rinse to dissolve/remove non-chemically bonded primer and then contact angles were measured with a contact angle meter (NRL CA Goniometer, NJ) (n=5).
Results:
Etching | Cleaning | SEM/microscope | Contact Angle1, degree (SD) | |
Priming | No Priming | |||
As received | A)Pressurized water | Smear layer | 71.8(3.4)c | 18.6(1.1)b |
4%HF/5min | B)Tap water | Clean/rough surface | 77.3(3.9)d | / |
C)Pressurized water | 80.2(6.5)d | |||
9.5%HF/10min (over-etching) | D)Tap water
| White solid
| 10.4(3.2)a, 78.6(5.2)d* | |
E)Pressurized water | Clean/rough surface
| 80.0(3.9)d | ||
F)Ultrasonication | 79.8(6.3)d | |||
G)Phosphoric acid with agitation – tab water rinse | 74.2(6.2)cd | |||
H) Phosphoric acid no agitation – tab water rinse | Partially Covered with white solid | 11.3(1.1)a, 82.2(5.4)d* | ||
1Values with the same letter (a,b,c,d) are not significantly different (p>0.05). Values with * were subjected to additional ultrasonic cleaning in de-ionized water after tab water rinse following priming and ethanol rinse.
Conclusion: Over-etching produced white solid on the porcelain surface. The white solid can be removed by ultrasonication cleaning, pressurized water rinse, or phosphoric acid agitation. The white solid was probably an un-soluble hexaflurosilicate salt which was trapped inside the etched ceramic surface. Phosphoric acid probably converted it into a soluble hexaflurosilicic acid. Surprisingly, even over-etched surface can still be efficiently primed by a silane primer.