IADR Abstract Archives
Evaluation of Various Neutralizing Agents for Hydrofluoric Acid
Objectives: When using hydrofluoric acid intraorally to condition silicate ceramic for resin bonding, it may be advantageous to neutralize the acid before rinsing it off with water spray. The purpose of this laboratory study was to evaluate the effectiveness of various potential neutralization agents for hydrofluoric acid (HF) on lithium disilicate ceramic.
Methods: Four potential neutralizing agents (NA) were tested (n=8): NA1: calcium carbonate + chlorhexidine gel; NA2: calcium hydroxide; NA3: calcium D-gluconate monohydrate + chlorhexidine gel; NA4: IPS neutralizing powder + water. Each agent was mixed in excess with 9 % HF, according to the calculated ratio, for 30 s followed by determining the pH value. Forty lithium disilicate ceramic specimens were randomly divided into 5 groups (n=8), followed by HF etching (20 s), neutralizing (30 s) and water-rinsing (30 s), according to the surface pretreatment protocol: HF; HF+NA1; HF+NA2; HF+NA3; HF+NA4. Then, the surface of all lithium disilicate ceramic specimens was examined for precipitates by scanning electron microscope (SEM) and energy-dispersive X-ray (EDX) analysis.
Results: When determining the pH value after neutralization, the pH indicator paper showed a lower pH value in the peripheral area than in the center of the applied mixture of NA and HF due to diffusion or evaporation of the not completely neutralized HF. Mean central pH values ranged from a minimum of 6 (HF+NA3) to a maximum of 11 (HF+NA2, HF+NA4). Visual assessment with SEM showed precipitates on some surfaces of lithium disilicate ceramic specimens in group HF+NA2 only. EDX analysis confirmed residues of calcium fluoride among others.
Conclusions: HF could be neutralized with the tested neutralizing agents used in the calculated concentrations under laboratory conditions. When using NA2 for the neutralization of HF on a lithium disilicate ceramic, precipitates could remain on the surface, that might influence the resin bond strength.
Methods: Four potential neutralizing agents (NA) were tested (n=8): NA1: calcium carbonate + chlorhexidine gel; NA2: calcium hydroxide; NA3: calcium D-gluconate monohydrate + chlorhexidine gel; NA4: IPS neutralizing powder + water. Each agent was mixed in excess with 9 % HF, according to the calculated ratio, for 30 s followed by determining the pH value. Forty lithium disilicate ceramic specimens were randomly divided into 5 groups (n=8), followed by HF etching (20 s), neutralizing (30 s) and water-rinsing (30 s), according to the surface pretreatment protocol: HF; HF+NA1; HF+NA2; HF+NA3; HF+NA4. Then, the surface of all lithium disilicate ceramic specimens was examined for precipitates by scanning electron microscope (SEM) and energy-dispersive X-ray (EDX) analysis.
Results: When determining the pH value after neutralization, the pH indicator paper showed a lower pH value in the peripheral area than in the center of the applied mixture of NA and HF due to diffusion or evaporation of the not completely neutralized HF. Mean central pH values ranged from a minimum of 6 (HF+NA3) to a maximum of 11 (HF+NA2, HF+NA4). Visual assessment with SEM showed precipitates on some surfaces of lithium disilicate ceramic specimens in group HF+NA2 only. EDX analysis confirmed residues of calcium fluoride among others.
Conclusions: HF could be neutralized with the tested neutralizing agents used in the calculated concentrations under laboratory conditions. When using NA2 for the neutralization of HF on a lithium disilicate ceramic, precipitates could remain on the surface, that might influence the resin bond strength.