Resistance of an enamel-bonding agent to saliva and acid exposure in vitro assessed by liquid scintillation

Abstract

Objectives: To determine the leakage and resistance of a bonding agent and a light-curing fine hybrid composite when exposed to saliva or lactic acid (pH 4) in vitro. Methods: Twenty discs in each of four groups of selected irradiated bovine lower central incisors were treated with one of three sealing options: an enamel bond (Heliobond, Vivadent, Schaan, Liechenstein) in a single-step application; Heliobond in a two-step application; and Tetric Flow (Vivadent) as the negative control. One group served as the positive control and remained unsealed. Loss of apatite was determined using the radiochemical method of liquid scintillation. The Cherenkov radiation was assessed in order to evaluate the acid resistance and leakage of smooth surface enamel bonding after exposure to saliva and lactic acid. In addition, replicas were made for SEM analysis of micromorphologic surface changes. Results: A mean loss of 416.5 μg (s.d. 57.0) apatite was observed over the unsealed sites following 14 days of exposure to lactic acid. The application of Heliobond in a one- and two-step application still revealed a remarkable degree of leakage, and substance losses of 196.5 μg (s.d. 38.9) and 161.8 μg (s.d. 39.7), but a protective potential was evident. In saliva, untreated, as well as sealed teeth, showed a modest leakage that was less than 20 μg. When Tetric Flow was used (negative control) leakage was reduced to a minimum of 2.4 μg (s.d. 1.0) in saliva and 12.8 μg (s.d. 19.6) in lactic acid. These results were confirmed by SEM analysis. Significance: The method of liquid scintillation was revealed to be of considerable value in evaluating leakage and acid resistance of potential smooth enamel sealing options. Sealing with an unfilled resin still demonstrated remarkable levels of acid dissolution, although a protection tendency could be observed. This leads to the conclusion that there is a need for further investigation to establish more acid-resistant enamel sealing agents.