Reduction of surface treatment time by combination of citric acid and ascorbic acid while restoring shear bond strength of metal brackets bonded to bleached enamel: a pilot study

Abstract

Background: To investigate the effect of a 50% ascorbic acid with 50% citric acid solution on the immediate shear bond strength (SBS) of metallic brackets after tooth bleaching. The enamel etching pattern and the required quantity of these combined acids as antioxidants following 35% hydrogen peroxide (HP) bleaching were also determined.

Methods: The stability of the solution at room temperature was assessed at various time intervals. Fifty teeth were randomly divided into five groups: non-bleached (G1), bleached then acid etched (G2), bleached followed by a 10-minute treatment with 10% sodium ascorbate and acid etched (G3), 5-minute treatment with 50% ascorbic acid (G4), and 5-minute treatment with a combination of 50% ascorbic acid and 50% citric acid (G5). Groups G2, G3, G4 and G5 were bleached by 35% HP gel for a total of 32 min. Acid etching in groups G1, G2, and G3 was performed using 37% phosphoric acid (Ormco®, Orange, CA, USA) for 15 s. In all groups, metal brackets were immediately bonded using Transbond™ XT primer and Transbond™ PLUS adhesive, with light curing for 40 s. The SBS was tested with a universal testing machine, and statistical analysis was conducted using one-way ANOVA followed by Tukey's HSD test. The level of significance was set at p < 0.05 for all statistical tests.

Results: Stability tests demonstrated that the combined acids remained effective for up to 21 days. Group G5 significantly increased the SBS of bleached teeth to the level of G1 (p < 0.05), while G3 did not achieve the same increase in SBS (p > 0.05). SEM analysis revealed enamel etching patterns similar to those of both control groups (G1 and G2). Kinetic studies at 6 min indicated that the antioxidation in G5 reacted 0.2 mmole lower than in G3 and G4.

Conclusion: 5-minute application of the combined acids enhanced the SBS of bleached teeth comparable to unbleached teeth. The combined acids remain stable over two weeks, presenting a time-efficient, single-step solution for antioxidant application and enamel etching in orthodontic bracket bonding.

Keywords: Antioxidant; Ascorbic acid; Bleaching; Citric acid; Combined of citric acid and ascorbic acid; Shear bond strength and brackets.

Fig. 1

The illustration of Bonding index. (A) the prepared crown was ligated to the guiding index with an elastomeric o-ring at the center of the guiding wire. (B) the prepared crown attached to the guiding index was placed on a PVC pipe which contained self-cured acrylic. The palatal half of the tooth was embedded in self-cured acrylic at the established position

Fig. 2

The experimental diagram of (A) stability test, (B) reaction kinetics and (C) HPLC chromatogram of AACA and calculation of antioxidant loss

Fig. 3

Stability test results; 50%AA: 50% ascorbic acid; 50%CA: 50% citric acid.; 10%SA: 10%Sodium Ascorbate; 50AA/ 50CA: 50% ascorbic acid and 50% citric acid

Fig. 4

The scanning electron micrograph of the enamel surface after the bleaching agent and antioxidant treatment were applied. A = 37% phosphoric acid on unbleached teeth for 15 s; B = 37% phosphoric acid on bleached teeth 15 s; C = 10% sodium ascorbate treatment 10 min on bleached teeth and follow by 37% phosphoric acid 15 s; D = 50% ascorbic acid on bleached teeth 5 min; E = 50% ascorbic acid plus 50% citric acid formulation on bleached teeth 5 min

Fig. 5

The reaction kinetics between hydrogen peroxide and 50% ascorbic acid, and 50% ascorbic acid in the mixed solution and 10% sodium ascorbate, with p < 0.05